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Flexor tendon repair
FLEXOR TENDON REPAIR BY JOHN GRAY SEILER III, MD
During the last 20 years there have been significant innovations in injury repair and aftercare for patients who sustain zone 2 flexor tendon injuries. Improvements in our understanding of the mechanisms of repair and the variables that impact the function of the repair site have resulted in outcome improvements. The purpose of this article is to review advances in flexor tendon surgery and to discuss current trends in the repair of zone 2 flexor tendon injuries. Copyright © 2001 by the American Society for Surgery of the Hand efore 1966, flexor tendon lacerations in the area of the digit were treated with delayed methods of tendon reconstruction. In 1977, Lister and colleagues reported their experience with flexor tendon repair for complete transections in “no– man’s–land” of the hand. Since that report, considerable work has been done that has added to the understanding of the basic science events that characterize the process of intrasynovial flexor tendon repair (Table 1). Clinical investigators have reported improvements in treatment methods that have significantly improved the outcome for patients who have sustained flexor tendon injuries. Significant improvements in treatment methods have been derived both from careful reporting of individual experience with certain methods and from scientific evaluation of various aspects of tendon repair. Although improvements have occurred for patients who have sustained flexor tendon injuries, not all patients obtain a satisfactory outcome. The goal of tendon healing without significant adhesion formation (differential incorporation of the soft tissues) is not always achievable.
B
From Georgia Hand and Microsurgery. Address reprint requests to John Gray Seiler III, MD, 1938 Peachtree St, Ste 603, Atlanta, GA 30303. E-mail: [email protected] Copyright © 2001 by the American Society for Surgery of the Hand 1531-0914/01/0103-0005$35.00/0 doi:10.1053/jssh.2001.26283
The purpose of this report is to review the molecular and mechanical events that characterize flexor tendon repair and to report the results of clinical series that describe the outcome of patients who have sustained flexor tendon injuries.1
CHARACTERIZING
THE
REPAIR RESPONSE
In 1978, Lundborg and Rank2 reported that intrasynovial flexor tendons could initiate an intrinsic repair response after tendon transection. This observation stimulated subsequent investigators to characterize various aspects of the repair process. With improvements in histology, biochemistry, biomechanics, and animal modeling, investigators have reported various important aspects of flexor tendon repair.2-4 In the early 1980s, Gelberman and colleagues5 developed a clinically relevant experimental model to study various aspects of flexor tendon repair in zone 2. Early studies on flexor tendon repair focused on the effect of early digital mobilization. Researchers compared total, delayed, and early mobilization. Biomechanical testing performed 12 weeks after tendon repair showed a significant improvement in angular digital rotation and ultimate load to failure for the immediate mobilization group. Linear tendon excursion was very limited (19% of contralateral control digit) in the immobilization group, suggesting that
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TABLE 1 Stages of Intrinsic Repair for Intrasynovial Flexor Tendons Inflammatory phase (0 to 14 d) Fibrin clot forms at the repair site Macrophage migration and leukocyte migration to the repair site Phagocytosis of the repair site Fibronectin production peaks (chemotaxis) bFGF production peaks Upregulation of integrins Cells from the epitenon proliferate and migrate to the repair site Gliding surface is restored Fibrin strands identified in fibroblasts surrounding the repair site Immediately after repair, the strength of the repair is related to the strength of the suture and the suture method Reparative phase (2 to 6 wk) Intense collagen production, mostly type I Fibers of collagen are laid down randomly and gradually orient themselves along the axis of tensile forces Cellular ingrowth from the epitenon fills the repair site gap Neovascularization of the repair site occurs TGF production peaks Fibrinous strands of collagen bridge the repair site DNA content is increased At 2 weeks after repair, the repair site strength may decrease, but it increases during this period as collagen deposition occurs at the repair site. Repair site strength is still principally related to the strength of the suture and the suture material Remodeling phase (⬎6 weeks) Collagen fibers are smooth and uniform in the repair site Collagen fibers are remodeling to be oriented parallal to the longitudinal axis of the tendon The surface of the tendon is smooth and nonadherent DNA content remains increased Decreased rates of cell division Increase in repair site strength
the formation of peritendinous adhesions (extrinsic tendon repair) dominated the repair process. In contrast, immediate mobilization resulted in significantly better linear tendon excursion, suggesting that intrinsic tendon repair dominated the repair process for these animals.5 Further evaluation showed that immediate mobilization improved the biologic response of the tendon for repair. In a dog study, Gelberman et al6 showed that restoration of the gliding surface was superior in animals treated with immediate digital mobilization.
Tendons treated with early passive digital mobilization were characterized by early epitenon proliferation and migration to the repair site. Collagen production was primarily from the cells of the epitenon. The formation of peritendinous adhesions was limited. Careful ultrastructural examination found that the gliding surface had been restored by a flattened layer of epitenon cells at 10 days after repair. In contrast, tendons treated with immobilization showed a repair response that was dominated by extrinsic mechanisms of repair. By 10 days after repair, the ingrowth of peripheral adhesions dominated the repair site. Ultrastructural examination of the repair site suggested that collagen synthesis was limited. The clinical significance of these studies was to confirm that precise tendon suture and early digital mobilization could alter the primary mechanism of tendon repair in favor of the desired mechanism, intrinsic tendon repair.6 Basic science studies focused on the nutrition of the repair site have concluded that in experimental animals, the repair site is revascularized by approximately 17 days after repair. Vessels form along the surface of the tendon and migrate to the repair site through normally avascular areas. The channel created by passage of the suture material for repair was also characterized by dense neovascularization. Before the time of repair site neovascularization, cellular nutrition is likely supplied from synovial sources of tendon nutrition.7 More recently, researchers have begun to focus on the cellular signals, which influence tendon repair. In 1992, Duffy and colleagues8,9 identified flexor tendons as composite tissues that had significant mitogenic potential. The results of their study suggested that the mitogenic potential of intrasynovial flexor tendons is highest early in the repair process because of the presence of growth factors within the tendon. Because of the pattern of early mitogenic activity, the researchers proposed that one growth factor that was active in flexor tendon repair was basic fibroblast growth factor (bFGF). bFGF is bound to the extracellular matrix glycosaminoglycans and may be released by the stimulus of injury. bFGF is also strongly angiogenic. Early in the repair process, there is an increase in biologically active compounds that are known to facilitate angiogenesis and that promote cellular signals from the extracellular matrix to the cell interior (integrins).10
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MECHANICAL EVENTS The effect of multistrand, multigrasp core suture methods was reported by Noguchi and colleagues11 in an in vitro study that compared the strength of 5 different suture methods in canine and human tendons. This study compared the surgical methods described by Kessler et al for the purpose of zone 2 flexor tendon repair. In addition to establishing valid control data, this study confirms that there is no significant difference between the repair methods when they are compared at time zero. The Savage and Tajima methods produced the best gliding function. The multistrand, multigrasp Savage method produced the strongest initial repair site strength. Schuind et al12 have reported that the mean force in the flexor digitorum profundus tendon during active flexion was 19 N. Based on this in vitro study, the strength of the Savage repair would be predicted to consistently withstand the force of light active motion postoperatively. The low profile suture methods proposed by Savage and Tajima (suture methods with the suture knots within the repair site) provided superior tendon gliding characteristics at time zero. The researchers proposed that suture methods that require external knots may exhibit less tendon gliding and joint rotation because of knot trapping in the tight confines of the fibro-osseous tunnel.11,12 Researchers have concluded that the method of flexor tendon repair has the greatest influence on the strength of the repair site during the first 6 weeks after repair. A seminal study on the strength of the immobilized flexor tendon repair site found that the repair site softened significantly during the early postoperative period. In this study, a significant decrease in repair site strength was observed by 5 days after surgery.13,14 More recently, several basic science investigators have reported that increasing the loads applied to the flexor tendon repair site may stimulate the repair process and significantly shorten or eliminate the period of early repair site softening that was identified by earlier investigators.15 In a study designed to determine the effect of multistrand, multigrasp suture methods on the strength and gliding function of intrasynovial tendons after repair, Winters and colleagues16 report a significant improvement in repair site strength for multistrand, multigrasp methods. They compared com-
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monly used 2-strand suture methods with newer multistrand, multigrasp suture methods (Savage and 8-strand repair) using a clinically relevant animal model over the first 6 weeks after repair. They report that the Savage and 8-strand methods had significantly greater strength than did the Tajima method at each time interval. The 8-strand suture method had significantly greater load values than the Savage method at both 3 and 6 weeks after repair. On intergroup comparison, normalized data did not show any significant effect for suture method on joint rotation or gliding function of the repaired tendons.
GAP FORMATION
AT THE
REPAIR SITE
Lindsay and Thomson17 credited Mason and Shearon18 with first identifying the problem of gap formation after tendon repair. In an experimental study, Lindsay and Thomson subsequently concluded that gap formation was a problem that could be associated with decreased gliding function of the tendon, increased adhesion formation, and a poor clinical outcome. They identified at least 4 factors that could increase the probability of repair site gap formation: (1) breakage of the suture material, (2) inadequate suture methods, (3) poor immobilization, and (4) excessive proximal muscle pull. In their study, the precise amount of gap formation and outcome from repair were not specifically discussed.17-19 To determine if newer multistrand, multigrasp suture methods were associated with less gap site formation than traditional 2-strand suture methods, investigators have evaluated these new methods using
TABLE 2 Commonly Used Flexor Tendon Core Suture Methods
Method
Strands
Knot No.
Knot Location
Kessler Bunnell Tajima Tsuge Lateral trap Strickland Savage Lee Winters
2 2 2 2 4 4 6 8 8
2 1 2 1 2 2 1 2 1
External External Internal Internal External Internal Internal Internal Internal
Additional
Loop suture
Loop suture
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biomechanical testing (Table 2). Gliding resistance, gap formation, and ultimate strength of flexor digitorum profundus tendons were studied in 12 cadaveric hands after repair with either 2-, 4-, or 6-strand techniques. Each of the techniques exhibited similar increases in gliding resistance. In this study, the 2-strand method showed more gap formation under cyclic loading than the other repairs. The 6-strand suture method provided significantly higher tensile strength than the other repairs.20 More recently, basic science studies have focused on the precise size of the repair site gap that is likely to be associated with a poor outcome. These basic science studies have concluded that increasing the size of the gap at the repair site significantly decreases the tensile properties of the repair site. Tendon repairs with gaps greater than 3 mm had significantly less ultimate force and lower rigidity than tendon repairs that healed without gap formation. The repair method also has a significant effect on gap formation. Tendons repaired with multistrand, multigrasp suture methods heal with less gap formation than tendons repaired with 2-strand methods. Among multistrand methods, 8-strand methods are associated with less gap formation than 4-strand methods.21
THE EFFECT OF SUTURE TYPE AND SUTURE GAUGE In one of the first studies of materials used for flexor tendon repair, Ketchum22 examined 6 suture materials: monofilament stainless steel, braided stainless steel, caprolactan, monofilament nylon, monofilament propylene, and braided polyester fiber (Tables 3 and 4). Three weeks after repair, Ketchum reported that
TABLE 4 Materials Used for Flexor Tendon Repair
Material
Tissue Reaction
Ease of Handling
High local reaction Minimal local reaction Limited reaction Mild local reaction Mild reaction Limited reaction Limited reaction
Very easy Very difficult Difficult
Monofilament
Silk
No
Stainless steel
Yes
Nylon
Yes
Tevdek
No
Mersilene Polypropylene
No Yes
Supramid
Yes*
Easy Easy Difficult Easy
*A multifilament suture covered in a sheath of caprolactan so that it looks and handles like a monofilament suture.
monofilament stainless steel suture and caprolactan sutures had the best ability to withstand gap formation and had withstood the highest force to rupture. Supramid suture is composed of nylon strands encased in a caprolactan tube, which gives it the appearance of being a monofilament suture and gives it improved handling and strength characteristics. In this study the researchers observed some deterioration in strength for both Prolene and monofilament nylon sutures. Ketchum concluded that small kinks in the monofilament suture would diminish the diameter, concentrate force application, and increase the likelihood of material rupture22 (Table 5). Urbaniak13 reported the effect of knot tying on the tensile strength of suture material. In his study, knot tying remarkably altered the strength of the suture. Nylon showed a 22% reduction in tensile strength when knotted, Mersilene showed a 36% reduction, and Tevdek showed a 46% reduction. Although both
TABLE 3 Suture Properties That Influence the Strength of Repair
TABLE 5 Ideal Core Suture
Material strength Number of strands Method of suture placement Configuration Grasps Initial interaction between the material and the tendon Time-dependent interaction between the material and the tendon
Material suture properties of sufficient strength to allow early mobilization Easy material handling when placed into soft tissue Material durable through the process of tendon repair Surgical method that is easy to perform and accurately coapts the tendon ends Surgical method should not interfere with tendon repair
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stainless steel and polyester sutures were strong enough to allow for early digital mobilization, Urbaniak concluded that polyester suture was a superior material because of its flexibility and ease of handling and because it caused minimal mechanical trauma to the tendon. Further, Ketchum23 has observed that nylon suture has a significant amount of memory and must be knotted 4 times to resist untying.
THE EFFECT
OF THE
PERIPHERAL SUTURE
METHOD The peripheral tendon suture was initially introduced as a method of smoothing the repair site and improving the gliding function of the tendon within the narrow synovial sheath. Lister24 recommended that a circumferential, peripheral suture be placed for the primary purpose of smoothing the epitenon layer and suggested methods to invert the tendon edges if necessary to prevent exposure of the epitenon layer. Since that time, basic science investigators have examined the improvement in strength that is associated with the placement of various types of peripheral sutures. Reporting on the mechanical limitations of the Kessler suture method, Wade and colleagues25 concluded that the peripheral suture was an important component of the tendon repair and prevented early gap formation. Lin and colleagues26 reported that the placement of a locked peripheral suture significantly augments the strength of tendon repair. In Lin’s study, a core suture method was not performed, and the strength of the locked peripheral suture alone was found to average 24.3 N. The locked suture method was also found to absorb significantly more energy at failure than the simple suture. Interestingly, Lin and colleagues found that the failure strength of the locking suture was approximately 50% of the suture material alone. They opined that the tensile forces are unevenly distributed after suture placement and may be concentrated in certain areas of an individual loop or grasp. Diao and colleagues27 examined the effect of the depth of the suture placement on the strength of the peripheral repair and found that the deeper placement of the peripheral suture within the tendon substance significantly increased the strength of the tendon repair site.
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THE AMOUNT OF SUTURE WITHIN THE REPAIR SITE Norris and colleagues28 reported a quantitative analysis of the suture material within the repair site. In their in vitro study, they calculated the volume and cross-sectional area that was occupied by commonly used suture methods. The 2 internal knots that are placed in the repair site by the Tajima method occupy 27% of the cross-sectional area available for repair. The suture material used for the Savage method occupied 18% of the repair site. The suture material used for the Kessler method occupied 2% of the repair site. Although the Tajima method has been used successfully for a number of years, this suture method occupies significantly more area available for repair than do the other suture methods evaluated in this study. Pruitt and Manske29 reported on the effect of suture knot location on the tensile strength after flexor tendon repair. Pruitt examined the Savage method of repair with the knot inside the repair site and the knot outside the repair site. After following up animals in this in vivo survival study for 6 weeks, they found that the placement of the knot suture material within the repair site did not have any deleterious effect on the tensile strength of the repair site.
STRATEGIES
TO
MODIFY
THE
REPAIR RESPONSE
Prevention of adhesions after flexor tendon surgery continues to be a significant focus for basic science research. Peritendinous flexor tendon adhesions formed after injury and repair may be in part related to fibroblast upregulation in the synovial sheath that is due to increased local levels of cytokines (such as tumor growth factor [TGF]–1). Repaired rabbit flexor tendons that were infiltrated with TGF-1 antibodies showed twice as much range of motion as control specimens. The introduction of TGF-I antibodies to the local flexor tendon environment was associated with a diminished fibroblast response in the synovial sheath and decreased peritendinous adhesion formation. 5-fluorouracil has also been investigated as an agent to diminish peritendinous adhesions after tendon repair. In 2 recently reported studies, tendon healing was not adversely affected when 5-fluorouracil was
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applied at the time of tendon repair. Interestingly, the application of 5-fluorouracil was associated with fewer peritendinous adhesions but was not associated with an increase in the rate of tendon rupture. Externally applied devices have also been investigated as a tool to control adhesion formation. Expanded polytetrafluoroethylene (e-PTFE) has been used to reconstruct the synovial sheath in the zone of the repair. In a rabbit model, a decrease in adhesion formation was reported at 2, 3, and 6 weeks after repair. Although e-PTFE has been shown to decrease protein and collagen synthesis in the tendon matrix, the tensile strength of tendons repaired with e-PTFE was similar to that in controls.
THE EFFECT
OF THE
INTERVAL
TO
REPAIR
To identify the optimal period for primary flexor tendon repair, Gelberman and colleagues30 reported a canine study that examined biomechanical, biochemical, and morphologic observations. In their study, they found a significant benefit to early repair. Animals that underwent immediate repair had significantly improved functional characteristics (digital angular rotation) when compared with animals that underwent delayed repair. Significant differences in repair site strength and total concentration of collagen at the repair site were not found. Because of the benefit of improvement in functional characteristics seen with early repair, tendon repair is ideally performed in the first week after injury.
METHODS
OF
TENDON REPAIR
In general, the surgical method of tendon repair should restore tendon continuity and allow for smooth tendon gliding within the synovial sheath of the digit. The repair method should be strong enough to maintain precise tendon coaptation until the tendon is strong enough to withstand the force required for flexion of the finger. Since Bunnell’s initial description of a suture method for tendon repair,31 a significant amount of research effort has been devoted to optimizing the method of tendon suture. In 1975, Urbaniak et al13 reported an excellent study that compared the tensile strength of a number of different methods of tendon repair. For the specific case of end-to-end tendon repair, they identified improvement in repair
site strength for suture methods that were able to grasp the tendon during the repair. Because of the improvement observed with grasping methods of tendon repair, the Kessler method and other 2-strand grasping methods became the methods used most commonly by clinicians for the purpose of flexor tendon repair.32 More recently, investigators have focused on the development of stronger suture methods for aftercare regimens that feature early active digital flexion. These methods have in common the use of larger suture, multiple strands, and multiple grasps to increase the initial repair strength above that predicted to be necessary for active flexion. Repair methods are distinguished by the strength of the repair site on mechanical testing. In general, the strength of the repair site is related to the gauge of the suture material, the nature of the material, the method of suture placement, the number of strands and grasps, and the interaction of the suture materials with the tendon during the period of tendon repair.33-38
SURGICAL PRINCIPLES Whenever possible, flexor tendon repairs in zone 2 should be completed within 7 days of the time of injury. At the time of preoperative consultation, the surgeon should review with the patient the nature of this injury and the aftercare regimen. The tendon repair should be performed in the operating room using optical magnification by an experienced hand surgeon. Careful inspection of the injury wound will allow the surgeon to plan a skin incision that allows adequate exposure of the flexor apparatus. In general, the incision is extended using a zigzag or midlateral incision (Fig 1). After the superficial dissection is completed, a complete assessment of the injury is performed. Tendon retrieval may require a second transverse incision in the palm to locate the retracted proximal tendon stump (Fig 2). Because handling of the tendon is often correlated with subsequent adhesion formation, great care should be taken to minimize any handling of the tendon surface. When possible, the tendon is grasped with fine forceps at the site of laceration. Often, additional openings in the synovial sheath are necessary to allow tendon retrieval. When necessary, the openings should be made through areas of the sheath that are not crucial to tendon position (Fig 3). The tendon should be passed
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flexion and the metacarpophalangeal joints in 50° to 70° of flexion. The interphalangeal joints should be positioned in 0° to 10° of flexion.
OUTCOMES AFTER TENDON REPAIR
FIGURE 1. A Bruner-type incision incorporating the laceration allows both complete exposure of the flexor apparatus in the digit and identification of the digital nerves and arteries.
into the distal wound in its anatomic position and stabilized with a thin hypodermic needle (Fig 4). The specific tendon suture method should be selected based on the nature of the tendon injury and the anticipated form of aftercare (Figs 5 and 6). If both tendons are lacerated, the flexor digitorum superficialis slips should be repaired first. Often these small slips require mattress-type sutures for accurate coaptation of the tendon ends. More proximally, as the caliber of the tendon increases, a standard core suture can be used. If the transection of the flexor digitorum profundus tendon is significantly oblique, then it is often helpful to repair the back wall of the tendon with a 6-0 epitendinous suture to aid in smoothing the tendon repair site. After the core suture (3-0 or 4-0 braided suture) has been inserted and secured, the palmar surface of the epitendinous repair can be completed. Next, any additional nerve or arterial repairs that may be necessary should be completed. Finally, stabilizing needles are removed, and the finger is passively flexed and extended to ensure that there is smooth gliding of the digit through the digital sheath and to assess for significant repair site gap formation. Postoperatively, the patient is placed in a dorsal blocking splint with the wrist positioned in 40° of
A number of systems have been suggested to report the function of the finger after flexor tendon repair. Most systems used for grading outcome rely on calculating or estimating range of motion. Boyes39 recommended that the function of the finger be estimated by measurement of the distance between the pulp of the fingertip and the distal palmar crease. This distance relates to the amount of composite flexion and gives an estimation of digit function. Although this is a quick and easy method for estimating digital function, it must be performed in a standardized manner to avoid errors in measurement. In 1976, the American Society for Surgery of the Hand endorsed a measurement of digital function that calculates total active motion and total passive motion. Motion is calculated as the number of degrees of flexion minus the extension deficit. For the purpose of this system of measurement, the end point of extension was considered to be 0°, and all flexion measurements were made with the hand in a fist position. This system is useful for comparing the preoperative and postoperative function of a single digit but is less valuable in critically assessing the results of flexor tendon repair. Because this measurement includes the range of motion of the metacarpophalangeal joint, which is uncommonly affected by flexor tendon laceration, the results are often better than would be anticipated (Fig 7). To effectively standardize the method of reporting outcomes after flexor tendon repair, Strickland developed a formula for reporting results.32 Strickland’s method of calculation is the most stringent system currently available for measuring results and accurately reflects the differential functions of the tendon repair. His method does not take into account the range of motion at the metacarpophalangeal joint, because neither the flexor digitorum superficialis nor the flexor digitorum profundus is solely responsible for flexion at this joint. To calculate digital performance using Strickland’s method, this equation is used:
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FIGURE 2. A small, flexible Silastic tube can be passed proximally to allow atraumatic retrieval into the site of digital laceration.
关共PIP⫹DIP flexion兲⫺共extensor lag兲兴/175° ⫻100 ⫽% of normal PIP and DIP motion (DIP, distal interphalangeal; PIP, proximal interphalangeal). Because his method is based on data that would be collected in a similar manner by different observers, Strickland’s methods are probably most accurate for cross-comparing studies (Table 6). More recently, investigators have begun to use other standardized outcomes as assessment tools in the reporting of results after flexor tendon repair. Evaluations such as the SF 36, disabilities of the arm, shoulder and hand questionnaire (DASH), Hand Jebsen-Taylor test, and Purdue pegboard test give additional information about the general hand use ability and patient satisfaction after tendon repair (Table 7).
During the last 20 years, there have been significant advances in the care of patients, which have resulted in improved outcomes. The larger comparative series clearly show improvement in digital range of motion. Although these larger series have often focused on the method of aftercare as influencing results, the clinical principles used for tendon suture were also changing and contributing to improvements in outcome. General surgical methods, the methods of surgical exposure, methods of tendon retrieval, atraumatic methods of tendon manipulation, and the method of tendon suturing have all improved during this time and contribute to the improvement in reported outcomes. In 1980, Strickland and Glogovac40 reported their results of treatment for patients who sustained transection of the flexor tendons in zone 2. This clinical
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sive range of motion. After establishing that early passive range of motion had a positive influence on the restoration of the tendon gliding surface, Gelberman proposed that increasing the frequency of digital range of motion would improve ultimate digital performance. After undergoing zone 2 tendon repair using a 2-strand method, patients were randomized to an early passive range of motion program or to a high-frequency passive range of motion program. Patients in the high-frequency group used a continuous passive motion device to obtain a mean 12,000 cycles. Patients in the standard passive motion group averaged 1,000 cycles. Based on Strickland’s method of analysis, patients who completed the high-frequency range of motion program had a significantly improved outcome when compared with patients in the standard passive range of motion group. Tendon ruptures were similar between the groups. In 1992, Silfverskiold et al42,43 reported on the use of a new epitendinous suture method in combination with a 2-strand core suture method with a new after-
FIGURE 3. Tendon retrieval and identification are facilitated by opening the tendon sheath over the membranous areas of the tendon sheath.
trial was one of the first to critically compare variables that might impact the outcome after flexor tendon repair. They reported on 50 consecutive digits with flexor tendon lacerations, with 25 digits treated by 3.5 weeks of immobilization and 25 digits treated by a rehabilitation protocol of early passive digital range of motion. They reported 4 ruptures (16%) in the immobilization group and 1 rupture (4%) in the early passive mobilization group. In his report, Strickland showed a statistically significant improvement in outcome for patients who had early postoperative passive digital mobilization after tendon repair. Using standard assessment criteria, Strickland established a baseline data set that could be used to benchmark future research efforts. In 1991, Gelberman and coworkers41 reported the results of a prospective multicenter trial that evaluated passive range of motion and high-frequency pas-
FIGURE 4. 20-gauge hypodermic needles passed transversely through sheath and tendons stabilize the tendon ends for repair.
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FIGURE 5. Several popular techniques for core sutures.
care regimen for the treatment of patients with zone 2 flexor tendon injuries. With this method, the researchers sought to maximize interphalangeal joint flexion and increase tendon excursion within the digital sheath. In general, they reported a poor outcome with increasing repair site gap size. Often, however, significant repair site gaps were associated with a good clinical outcome. In 1994, Silfverskiold reported on a group of patients treated with early active digital mobilization. In
this cohort, he showed an improvement in outcome when compared with the group that was treated with the 4-finger method of tendon rehabilitation. Both methods were associated with a low complication rate. With his suture method, the amount of late repair site gap formation was similar when comparing the active group and the 4-finger group. Although not a true comparative trial, Silfverskiold was able to use his own data set from previous publications to allow for comparison between the active and improved passive
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FIGURE 6. Several popular techniques for the epitendinous suture.
methods of aftercare. In this study, the authors conclude that early active digital mobilization may be correlated with improved digital performance after tendon repair.
Most recently, Trumble et al44 reported the results of a prospective, randomized, multicenter trial that focused on the optimal method of aftercare for patients treated with a 4-strand core suture method. The
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FIGURE 7. Assessment of postoperative tendon function: (A) Independent FDP function. (B) Excellent total active range of motion. (C) FDS function. (D) Full extension without postoperative extensor lag.
researchers reported a significant improvement in the DASH scores for both cohorts of patients. However, a significant difference between the groups could not be determined. Patients who sustained a nerve injury had increased contractures of the interphalangeal joints
and less overall motion than patients without nerve injuries. Overall, patients with crushing injuries had less range of motion than patients with sharp injuries. In this series, there were not enough patients to allow TABLE 7
TABLE 6 Classification of Results After Flexor Tendon Repair Excellent Good Fair Poor
75-100 50-74 25-49 0-24
NOTE. Using Strickland’s method with the International Federation for Hand Surgeons System classification of outcome.
Factors That Influence the Outcome After Flexor Tendon Repair Age Mechanism of injury Comorbid conditions Level of tendon injury Individual patient considerations Compliance Psychology Physiology
FLEXOR TENDON REPAIR 䡠 SEILER
for meaningful intergroup comparison to determine if early active range of motion could overcome the effect of mechanism of injury. An effect from workman’s compensation status could not be determined when comparing final range of motion values. The rate of tenolysis was higher in the passive group than in the active group. There was one tendon rupture in each group. Interestingly, this study also identified smoking as a covariable that adversely affected outcome. Patients who smoked had less overall active motion and greater overall flexion contractures. In the report, a significant improvement in outcome was seen in patients who were treated with an aftercare program that used early active digital mobilization.44
FLEXOR TENDON REPAIR
IN
CHILDREN
Fitoussi and colleagues45 reported a retrospective review of their experience with pediatric flexor tendon injuries. In their series, patients who sustained zone 2 injuries had a worse outcome than patients with injuries in other areas of the hand. In their series, a positive effect for early mobilization could not be determined. They recommended postoperative immobilization in an above-elbow cast for 4 weeks. Patients with zone 2 injuries had a total active motion of 76° at an average follow-up of 3 years. Outcomes were worse if the age was less than 5 years, the injury was in zone 2, if both tendons were lacerated, and if a below-elbow splint was used after surgery. The overall repair rupture rate in their series was 9%. In a multicenter clinical study of children with flexor tendon injuries, O’Connell et al46 reported the results of treatment for 78 patients less than 16 years of age. Children with isolated zone 1 flexor digitorum profundus injuries that were treated with prompt repair had an excellent outcome. The researchers also concluded that children who were immobilized for up to 4 weeks had outcomes similar to those treated with an early passive range of motion program. When stratifying outcomes by age, the researchers found similar outcomes for all ages of children with combined flexor digitorum superficialis and flexor digitorum profundus injuries that were treated with an early passive range of motion program (72% total active motion). Similar to other studies on flexor tendon
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injury, O’Connell reported poorer results in patients with more complex injuries.46
PARTIAL TENDON INJURIES Using a clinically relevant canine model, Boardman and colleagues47 reported that transverse lacerations of up to 70% could be treated with protection and early mobilization. Further, they reported that tendon repair may have an adverse effect on the mechanical properties of the repair site after the repair of smaller partial transverse lacerations (30%). These basic science findings confirm the work of previous research, which suggests that the tendon structure is quite strong and that not all partial lacerations require tendon repair. Other investigators focusing on clinical complications from partial tendon laceration have recommended tendon repair of partial injuries to limit the likelihood of tendon entrapment, triggering, or late rupture.48 Summarizing the issue of partial tendon injuries, Strickland concluded that partial tendon injuries of 50% or greater should be repaired. All injured tendons should be treated with protection and early mobilization. Currently, there is no consensus regarding the optimal method of aftercare for partial tendon injuries.1,48
AFTERCARE PROGRAMS Most postoperative programs for adults use a dorsal protective hand splint and either passive or early active digital range of motion exercises. Careful coordination of aftercare with a skilled occupational therapist and patient cooperation are important variables in the final outcome. Programs That Use Passive Digital Mobilization In 1975, Duran49 reported on a method of rehabilitation that used passive flexion of the fingers and was designed to cause 3 to 5 mm of tendon excursion and limit the formation of peritendinous adhesions. When compared with immobilization of the hand, tendon rehabilitation programs that used passive digital mobilization have shown significant improvements in patient outcome. Further, tendon rehabilitation programs, which use a high frequency of digital motions, have shown an improved outcome when compared with lower-frequency programs.25,49
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FLEXOR TENDON REPAIR 䡠 SEILER
Programs That Feature Active Digital Mobilization Recently, researchers have studied the effect of rehabilitation programs that use early digital motion after tendon repair. By applying proximal load to the tendon, these rehabilitation programs seek to increase the amount of tendon excursion within the sheath. In an effort to increase tendon excursion after repair, Cooney et al50 have developed a dynamic splint that has a hinge at the wrist. Use of this splint was reported to increase the differential excursion between flexor tendons. Significant effort has been devoted to determining the force at the repair site for various levels of physical activity. Based on these studies, it can be predicted that passive digital flexion applies 2 to 4 N of force to the repair site, light active digital flexion applies approximately 10 N, moderate digital flexion applies approximately 17 N, and strong composite grip applies 70 N to the repair site. Schuind et al11 have concluded that the forces in the flexor digitorum profundus are consistently higher than the forces pro-
duced in the flexor digitorum superficialis. These studies provide excellent guidelines for predicting the strength of repair necessary to withstand early active digital mobilization after flexor tendon repair.1,11,51,52 Basic science studies that have examined the effects of low- versus high-force rehabilitation methods have reported that increases in force may be associated with improved tendon excursion and improved outcomes but do no accelerate the tendon repair process per se.53
CONCLUSION Transection of the flexor tendons in zone 2 continues to be one of the more challenging problems in hand surgery. By using recent advances in the basic science of tendon repair, surgical methods of repair, and rehabilitation, satisfactory outcomes can be obtained in most of patients with zone 2 flexor tendon injuries. Successful results require both precise surgical technique and strict adherence to a rehabilitation program.
REFERENCES 1. Strickland JW. Development of flexor tendon surgery: twenty-five years of progress. J Hand Surg [Am] 2001;25A: 214-235. 2. Lundborg G, Rank F. Experimental intrinsic healing of flexor tendons based on synovial fluid nutrition. J Hand Surg [Am] 1978;3:21-31. 3. Manske PR, Lesker PA, Gelberman RH, Rucinsky TE. Intrinsic restoration of the flexor tendon surface in the nonhuman primate. J Hand Surg [Am] 1985;5:632-637. 4. Graham MF, Becker H, Cohen K, Merritt W, Diegelmann RF. Intrinsic tendon fibroplasias, documentation by in vitro studies. J Orthop Res 1984;1:251-256. 5. Gelberman RH, Manske PR, Akeson WH, Woo SL-Y, Lundborg G, Amiel D. Flexor tendon repair. J Orthop Res 1986; 4:119-128. 6. Gelberman RH, VandeBerg JS, Lundborg GN, Akeson WH. Flexor tendon healing and restoration of the gliding surface. J Bone Joint Surg Am 1983;65A:70-80. 7. Gelberman RH, Khabie V, Cahill CJ. The revascularization of healing flexor tendons in the digital sheath. J Bone Joint Surg Am 1991;73A:868-880. 8. Duffy FJ, Seiler JG, Hergrueter CA, Kandel J, Gelberman RH. Intrinsic mitogenic potential of canine flexor tendons. J Hand Surg [Br] 1992;17B:275-277. 9. Duffy FJ, Seiler JG, Hergrueter CA, Gelberman RH. Isolation and characterization of a heparin-binding growth factor from canine flexor tendons. Surgical Forum 1993;590-591. 10. Bidder M, Towler DA, Gelberman RH, Boyer MI. Expression of messenger RNA for vascular endothelial growth factor
11.
12.
13.
14.
15.
16.
17. 18.
during the early phase of flexor tendon healing. J Orthop Res 2000;18:247-252. Noguchi M, Seiler JG, Gelberman RH, Sofranko RA, Woo SL-Y. In vitro biomechanical analysis of suture methods for flexor tendon repair. J Orthop Res 1993;11:603-611. Schuind F, Garcia-Elias M, Cooney WP III, An K-N. Flexor tendon forces: in vivo measurements. J Hand Surg [Am] 1992;17:291-298. Urbaniak JR, Cahill JD, Mortenson RA. Tendon suture methods. Analysis of tensile strengths. AAOS symposium on tendon surgery in the hand. 1975:70-80. Gelberman RH, Woo SL-Y, Lothringer R, et al. Effects of early intermittent passive mobilization on healing of canine flexor tendons. J Hand Surg [Am] 1982;7A:170-175. Aoki M, Kubota H, Pruitt D, Manske P. Early active motion following flexor tendon repair. An experimental study in dogs. Presented at the 50th annual meeting of the American Society for Surgery of the Hand. San Francisco, September 12-16, 1995. Winters SC, Gelberman RH, Woo SL-Y, Chan SS, Grewal R, Seiler JG. The effects of multiple-strand suture methods on the strength and excursion of repaired intrasynovial flexor tendons: a biomechanical study in dogs. J Hand Surg [Am] 1998;23A:97-104. Lindsay WK, Thomson HG. Digital flexor tendons: an experimental study. Br J Plast Surg 1960;12:260-267. Mason ML, Shearon CG. Process of tendon repair: an experimental study of tendon suture and tendon graft. Arch Surg 1932;25:616-691.
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19. Seradge H. Elongation of the repair configuration following flexor tendon repair. J Hand Surg [Am] 1983;8:182-185. 20. Thurman RT, Trumble TE, Hanel DP, et al. Two-, four-, and six-strand zone 2 flexor tendon repairs: an in situ biomechanical comparison using a cadaver model. J Hand Surg [Am] 1998;23A: 261-265. 21. Boyer MI, Gelberman RH, Burns ME, Dinopoulos H, Hofem R, Silva MI. Intrasynovial flexor tendon repair. An experimental study of low versus high levels of in vivo force rehabilitation in canines. Submitted for publication. 22. Ketchum LD, Martin NL, Kappel DA. Experimental evaluation of factors affecting the strength of tendon repairs. Plast Reconstr Surg 1977;59:708-719. 23. Ketchum LD. Suture materials and suture techniques used in tendon repair. Symposium on flexor tendon surgery. Hand Clin 1985;1(1):43-53. 24. Lister GD, Kleinert HE, Kutz JE, Atasoy E. Primary flexor tendon repair followed by immediate controlled mobilization. J Hand Surg 1977;2:441-451. 25. Wade PJF, Muir IK, Hutcheon LL. Primary flexor tendon repair: the mechanical limitations of the modified Kessler technique. J Hand Surg [Br] 1986;11B:71-76. 26. Lin GT, An KN, Amadio PC, Cooney WP III. Biomechanical studies of running suture for flexor tendon repair in dogs. J Hand Surg [Am] 1998;13:553-558. 27. Diao E, Hariharan JS, Soehima O, Lotz JC. Effect of peripheral suture depth on strength of tendon repairs. J Hand Surg 1996;21:234-239. 28. Norris SR, Ellis FD, Chen MI, Seiler JG III. Flexor tendon suture methods: a quantitative analysis of suture material within the repair site. Orthopaedics 1999;22(4):1-4. 29. Pruitt DL, Manske PR. The effect of suture knot location on tensile strength after flexor tendon repair. J Hand Surg 1966; 21:969-973. 30. Gelberman RH, Siegel DB, Woo SL-Y, Amiel D, Takai S, Lee D. Healing of digital flexor tendons: importance of the interval from injury to repair. J Bone Joint Surg Am 1991; 73A:66-75. 31. Bunnell S. Repair of tendons in the fingers and description of two new instruments. Surg Gynecol Obstet 1918;26:103110. 32. Strickland JW. Panel on Flexor tendon surgery. Annual meeting of the American Society for Surgery of the Hand. San Antonio, September 9-12, 1987. 33. Savage R, Risitano G. Flexor tendon repair using a six-strand method of repair and early active digital mobilization. J Hand Surg [Br] 1989;14B:396-399. 34. Tsuge K, Ikuta Y, Matsuishi Y. Intratendinous tendon suture in the hand: a new technique. Hand 1975;7:250-255. 35. Tajima T. History, current status and aspects of hand surgery in Japan. Clin Orthop Rel Res 1984;184:41-49. 36. Becker H. Primary repair of flexor tendons in the hand without immobilization: preliminary report. Hand 1978;10: 37-47. 37. Kessler I, Nissim F. Primary repair without immobilization of flexor tendon division within the digital sheath: an experimental and clinical study. Acta Orthop Scand 1969;40:587601.
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38. Lee H. Double loop locking suture: a technique of tendon repair for early active mobilization. Part I. Evolution of technique and experimental study. J Hand Surg [Am] 1990; 15:945-952. 39. Boyes JH. Flexor tendon grafts in the fingers and thumb. An evaluation of end results. J Bone Joint Surg Am 1950;32A: 489-499. 40. Strickland JW, Glogovac SV. Digital function following flexor tendon repair in zone II: a comparison of immobilization and controlled passive motion techniques. J Hand Surg 1980;5:537-543. 41. Gelberman RH, Nunley JA, Osterman AL, Breen TF, Dimick MP, Woo SL-Y. Influences of the protected passive mobilization interval on flexor tendon healing: a prospective, randomized clinical study. Clin Orthop Rel Res 1991;264: 189-196. 42. Silfverskiold KL, May EJ, Tornvall AH. Flexor digitorum profundus tendon excursions during controlled motion after flexor tendon repair in zone II: a prospective clinical study. J Hand Surg [Am] 1992;17A:122-131. 43. Silfverskiold KL, May EJ, Tornvall AH. Gap formation during controlled motion after flexor tendon repair in zone II. A prospective clinical study. J Hand Surg [Am] 1992;17A:539546. 44. Trumble TE, Idler RS, Strickland JW, Stern PJ, Gilbert MM. Randomized prospective trial of active versus passive motion after zone II flexor tendon repair. Submitted for publication. 45. Fitoussi F, Yebellec Y, Frajman JM, Pennecot GF. Flexor tendon injuries in children: Factors influencing prognosis. J Ped Orthop 1999;19:818-821. 46. O’Connell SJ, Moore MM, Strickland JW, Frazier GT, Dell PC. Results of zone I and zone II flexor tendon repair in children. J Hand Surg [Am] 1994;19A:48-52. 47. Boardman ND, Morifusa S, Chan Saw SS, et al. Effects of tenorrhaphy on the gliding function and tensile properties of partially lacerated canine digital flexor tendons. J Hand Surg [Am] 1999;24A:302-309. 48. Schlenker JD, Lister GD, Kleinert HE. Three complications of untreated partial lacerations of flexor tendon. Entrapment, rupture and triggering. J Hand Surg 1981;6:392-396. 49. Duran RE. Controlled passive motion following tendon repair in zone II and III. In: The American Academy of Orthopaedic Surgeons. Symposium on tendon surgery in the hand. St. Louis: Mosby, 1975:105-114. 50. Cooney WP, Lin Gt, An KN. Improved tendon excursions follow flexor tendon repair. J Hand Ther 1989;2:102-113. 51. Greenwald D, Shumway S, Allen C, Mass D. Dynamic analysis of profundus tendon function. J Hand Surg [Am] 1994; 19A:626-635. 52. Aoki M, Kubota H, Pruitt DL, Manske PR. Biomechanical and histological characteristics of canine flexor repair using early postoperative mobilization. J Hand Surg [Am] 1997; 22A:107-114. 53. Boyer MI, Gelberman RH, Burns ME, Dinopoulos H, Hofem R, Silva MJ. High levels of in vivo force rehabilitation in canines. Submitted for publication.
During the last 20 years there have been significant innovations in injury repair and aftercare for patients who sustain zone 2 flexor tendon injuries. Improvements in our understanding of the mechanisms of repair and the variables that impact the function of the repair site have resulted in outcome improvements. The purpose of this article is to review advances in flexor tendon surgery and to discuss current trends in the repair of zone 2 flexor tendon injuries. Copyright © 2001 by the American Society for Surgery of the Hand efore 1966, flexor tendon lacerations in the area of the digit were treated with delayed methods of tendon reconstruction. In 1977, Lister and colleagues reported their experience with flexor tendon repair for complete transections in “no– man’s–land” of the hand. Since that report, considerable work has been done that has added to the understanding of the basic science events that characterize the process of intrasynovial flexor tendon repair (Table 1). Clinical investigators have reported improvements in treatment methods that have significantly improved the outcome for patients who have sustained flexor tendon injuries. Significant improvements in treatment methods have been derived both from careful reporting of individual experience with certain methods and from scientific evaluation of various aspects of tendon repair. Although improvements have occurred for patients who have sustained flexor tendon injuries, not all patients obtain a satisfactory outcome. The goal of tendon healing without significant adhesion formation (differential incorporation of the soft tissues) is not always achievable.
B
From Georgia Hand and Microsurgery. Address reprint requests to John Gray Seiler III, MD, 1938 Peachtree St, Ste 603, Atlanta, GA 30303. E-mail: [email protected] Copyright © 2001 by the American Society for Surgery of the Hand 1531-0914/01/0103-0005$35.00/0 doi:10.1053/jssh.2001.26283
The purpose of this report is to review the molecular and mechanical events that characterize flexor tendon repair and to report the results of clinical series that describe the outcome of patients who have sustained flexor tendon injuries.1
CHARACTERIZING
THE
REPAIR RESPONSE
In 1978, Lundborg and Rank2 reported that intrasynovial flexor tendons could initiate an intrinsic repair response after tendon transection. This observation stimulated subsequent investigators to characterize various aspects of the repair process. With improvements in histology, biochemistry, biomechanics, and animal modeling, investigators have reported various important aspects of flexor tendon repair.2-4 In the early 1980s, Gelberman and colleagues5 developed a clinically relevant experimental model to study various aspects of flexor tendon repair in zone 2. Early studies on flexor tendon repair focused on the effect of early digital mobilization. Researchers compared total, delayed, and early mobilization. Biomechanical testing performed 12 weeks after tendon repair showed a significant improvement in angular digital rotation and ultimate load to failure for the immediate mobilization group. Linear tendon excursion was very limited (19% of contralateral control digit) in the immobilization group, suggesting that
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FLEXOR TENDON REPAIR 䡠 SEILER
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TABLE 1 Stages of Intrinsic Repair for Intrasynovial Flexor Tendons Inflammatory phase (0 to 14 d) Fibrin clot forms at the repair site Macrophage migration and leukocyte migration to the repair site Phagocytosis of the repair site Fibronectin production peaks (chemotaxis) bFGF production peaks Upregulation of integrins Cells from the epitenon proliferate and migrate to the repair site Gliding surface is restored Fibrin strands identified in fibroblasts surrounding the repair site Immediately after repair, the strength of the repair is related to the strength of the suture and the suture method Reparative phase (2 to 6 wk) Intense collagen production, mostly type I Fibers of collagen are laid down randomly and gradually orient themselves along the axis of tensile forces Cellular ingrowth from the epitenon fills the repair site gap Neovascularization of the repair site occurs TGF production peaks Fibrinous strands of collagen bridge the repair site DNA content is increased At 2 weeks after repair, the repair site strength may decrease, but it increases during this period as collagen deposition occurs at the repair site. Repair site strength is still principally related to the strength of the suture and the suture material Remodeling phase (⬎6 weeks) Collagen fibers are smooth and uniform in the repair site Collagen fibers are remodeling to be oriented parallal to the longitudinal axis of the tendon The surface of the tendon is smooth and nonadherent DNA content remains increased Decreased rates of cell division Increase in repair site strength
the formation of peritendinous adhesions (extrinsic tendon repair) dominated the repair process. In contrast, immediate mobilization resulted in significantly better linear tendon excursion, suggesting that intrinsic tendon repair dominated the repair process for these animals.5 Further evaluation showed that immediate mobilization improved the biologic response of the tendon for repair. In a dog study, Gelberman et al6 showed that restoration of the gliding surface was superior in animals treated with immediate digital mobilization.
Tendons treated with early passive digital mobilization were characterized by early epitenon proliferation and migration to the repair site. Collagen production was primarily from the cells of the epitenon. The formation of peritendinous adhesions was limited. Careful ultrastructural examination found that the gliding surface had been restored by a flattened layer of epitenon cells at 10 days after repair. In contrast, tendons treated with immobilization showed a repair response that was dominated by extrinsic mechanisms of repair. By 10 days after repair, the ingrowth of peripheral adhesions dominated the repair site. Ultrastructural examination of the repair site suggested that collagen synthesis was limited. The clinical significance of these studies was to confirm that precise tendon suture and early digital mobilization could alter the primary mechanism of tendon repair in favor of the desired mechanism, intrinsic tendon repair.6 Basic science studies focused on the nutrition of the repair site have concluded that in experimental animals, the repair site is revascularized by approximately 17 days after repair. Vessels form along the surface of the tendon and migrate to the repair site through normally avascular areas. The channel created by passage of the suture material for repair was also characterized by dense neovascularization. Before the time of repair site neovascularization, cellular nutrition is likely supplied from synovial sources of tendon nutrition.7 More recently, researchers have begun to focus on the cellular signals, which influence tendon repair. In 1992, Duffy and colleagues8,9 identified flexor tendons as composite tissues that had significant mitogenic potential. The results of their study suggested that the mitogenic potential of intrasynovial flexor tendons is highest early in the repair process because of the presence of growth factors within the tendon. Because of the pattern of early mitogenic activity, the researchers proposed that one growth factor that was active in flexor tendon repair was basic fibroblast growth factor (bFGF). bFGF is bound to the extracellular matrix glycosaminoglycans and may be released by the stimulus of injury. bFGF is also strongly angiogenic. Early in the repair process, there is an increase in biologically active compounds that are known to facilitate angiogenesis and that promote cellular signals from the extracellular matrix to the cell interior (integrins).10
FLEXOR TENDON REPAIR 䡠 SEILER
MECHANICAL EVENTS The effect of multistrand, multigrasp core suture methods was reported by Noguchi and colleagues11 in an in vitro study that compared the strength of 5 different suture methods in canine and human tendons. This study compared the surgical methods described by Kessler et al for the purpose of zone 2 flexor tendon repair. In addition to establishing valid control data, this study confirms that there is no significant difference between the repair methods when they are compared at time zero. The Savage and Tajima methods produced the best gliding function. The multistrand, multigrasp Savage method produced the strongest initial repair site strength. Schuind et al12 have reported that the mean force in the flexor digitorum profundus tendon during active flexion was 19 N. Based on this in vitro study, the strength of the Savage repair would be predicted to consistently withstand the force of light active motion postoperatively. The low profile suture methods proposed by Savage and Tajima (suture methods with the suture knots within the repair site) provided superior tendon gliding characteristics at time zero. The researchers proposed that suture methods that require external knots may exhibit less tendon gliding and joint rotation because of knot trapping in the tight confines of the fibro-osseous tunnel.11,12 Researchers have concluded that the method of flexor tendon repair has the greatest influence on the strength of the repair site during the first 6 weeks after repair. A seminal study on the strength of the immobilized flexor tendon repair site found that the repair site softened significantly during the early postoperative period. In this study, a significant decrease in repair site strength was observed by 5 days after surgery.13,14 More recently, several basic science investigators have reported that increasing the loads applied to the flexor tendon repair site may stimulate the repair process and significantly shorten or eliminate the period of early repair site softening that was identified by earlier investigators.15 In a study designed to determine the effect of multistrand, multigrasp suture methods on the strength and gliding function of intrasynovial tendons after repair, Winters and colleagues16 report a significant improvement in repair site strength for multistrand, multigrasp methods. They compared com-
179
monly used 2-strand suture methods with newer multistrand, multigrasp suture methods (Savage and 8-strand repair) using a clinically relevant animal model over the first 6 weeks after repair. They report that the Savage and 8-strand methods had significantly greater strength than did the Tajima method at each time interval. The 8-strand suture method had significantly greater load values than the Savage method at both 3 and 6 weeks after repair. On intergroup comparison, normalized data did not show any significant effect for suture method on joint rotation or gliding function of the repaired tendons.
GAP FORMATION
AT THE
REPAIR SITE
Lindsay and Thomson17 credited Mason and Shearon18 with first identifying the problem of gap formation after tendon repair. In an experimental study, Lindsay and Thomson subsequently concluded that gap formation was a problem that could be associated with decreased gliding function of the tendon, increased adhesion formation, and a poor clinical outcome. They identified at least 4 factors that could increase the probability of repair site gap formation: (1) breakage of the suture material, (2) inadequate suture methods, (3) poor immobilization, and (4) excessive proximal muscle pull. In their study, the precise amount of gap formation and outcome from repair were not specifically discussed.17-19 To determine if newer multistrand, multigrasp suture methods were associated with less gap site formation than traditional 2-strand suture methods, investigators have evaluated these new methods using
TABLE 2 Commonly Used Flexor Tendon Core Suture Methods
Method
Strands
Knot No.
Knot Location
Kessler Bunnell Tajima Tsuge Lateral trap Strickland Savage Lee Winters
2 2 2 2 4 4 6 8 8
2 1 2 1 2 2 1 2 1
External External Internal Internal External Internal Internal Internal Internal
Additional
Loop suture
Loop suture
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180
biomechanical testing (Table 2). Gliding resistance, gap formation, and ultimate strength of flexor digitorum profundus tendons were studied in 12 cadaveric hands after repair with either 2-, 4-, or 6-strand techniques. Each of the techniques exhibited similar increases in gliding resistance. In this study, the 2-strand method showed more gap formation under cyclic loading than the other repairs. The 6-strand suture method provided significantly higher tensile strength than the other repairs.20 More recently, basic science studies have focused on the precise size of the repair site gap that is likely to be associated with a poor outcome. These basic science studies have concluded that increasing the size of the gap at the repair site significantly decreases the tensile properties of the repair site. Tendon repairs with gaps greater than 3 mm had significantly less ultimate force and lower rigidity than tendon repairs that healed without gap formation. The repair method also has a significant effect on gap formation. Tendons repaired with multistrand, multigrasp suture methods heal with less gap formation than tendons repaired with 2-strand methods. Among multistrand methods, 8-strand methods are associated with less gap formation than 4-strand methods.21
THE EFFECT OF SUTURE TYPE AND SUTURE GAUGE In one of the first studies of materials used for flexor tendon repair, Ketchum22 examined 6 suture materials: monofilament stainless steel, braided stainless steel, caprolactan, monofilament nylon, monofilament propylene, and braided polyester fiber (Tables 3 and 4). Three weeks after repair, Ketchum reported that
TABLE 4 Materials Used for Flexor Tendon Repair
Material
Tissue Reaction
Ease of Handling
High local reaction Minimal local reaction Limited reaction Mild local reaction Mild reaction Limited reaction Limited reaction
Very easy Very difficult Difficult
Monofilament
Silk
No
Stainless steel
Yes
Nylon
Yes
Tevdek
No
Mersilene Polypropylene
No Yes
Supramid
Yes*
Easy Easy Difficult Easy
*A multifilament suture covered in a sheath of caprolactan so that it looks and handles like a monofilament suture.
monofilament stainless steel suture and caprolactan sutures had the best ability to withstand gap formation and had withstood the highest force to rupture. Supramid suture is composed of nylon strands encased in a caprolactan tube, which gives it the appearance of being a monofilament suture and gives it improved handling and strength characteristics. In this study the researchers observed some deterioration in strength for both Prolene and monofilament nylon sutures. Ketchum concluded that small kinks in the monofilament suture would diminish the diameter, concentrate force application, and increase the likelihood of material rupture22 (Table 5). Urbaniak13 reported the effect of knot tying on the tensile strength of suture material. In his study, knot tying remarkably altered the strength of the suture. Nylon showed a 22% reduction in tensile strength when knotted, Mersilene showed a 36% reduction, and Tevdek showed a 46% reduction. Although both
TABLE 3 Suture Properties That Influence the Strength of Repair
TABLE 5 Ideal Core Suture
Material strength Number of strands Method of suture placement Configuration Grasps Initial interaction between the material and the tendon Time-dependent interaction between the material and the tendon
Material suture properties of sufficient strength to allow early mobilization Easy material handling when placed into soft tissue Material durable through the process of tendon repair Surgical method that is easy to perform and accurately coapts the tendon ends Surgical method should not interfere with tendon repair
FLEXOR TENDON REPAIR 䡠 SEILER
stainless steel and polyester sutures were strong enough to allow for early digital mobilization, Urbaniak concluded that polyester suture was a superior material because of its flexibility and ease of handling and because it caused minimal mechanical trauma to the tendon. Further, Ketchum23 has observed that nylon suture has a significant amount of memory and must be knotted 4 times to resist untying.
THE EFFECT
OF THE
PERIPHERAL SUTURE
METHOD The peripheral tendon suture was initially introduced as a method of smoothing the repair site and improving the gliding function of the tendon within the narrow synovial sheath. Lister24 recommended that a circumferential, peripheral suture be placed for the primary purpose of smoothing the epitenon layer and suggested methods to invert the tendon edges if necessary to prevent exposure of the epitenon layer. Since that time, basic science investigators have examined the improvement in strength that is associated with the placement of various types of peripheral sutures. Reporting on the mechanical limitations of the Kessler suture method, Wade and colleagues25 concluded that the peripheral suture was an important component of the tendon repair and prevented early gap formation. Lin and colleagues26 reported that the placement of a locked peripheral suture significantly augments the strength of tendon repair. In Lin’s study, a core suture method was not performed, and the strength of the locked peripheral suture alone was found to average 24.3 N. The locked suture method was also found to absorb significantly more energy at failure than the simple suture. Interestingly, Lin and colleagues found that the failure strength of the locking suture was approximately 50% of the suture material alone. They opined that the tensile forces are unevenly distributed after suture placement and may be concentrated in certain areas of an individual loop or grasp. Diao and colleagues27 examined the effect of the depth of the suture placement on the strength of the peripheral repair and found that the deeper placement of the peripheral suture within the tendon substance significantly increased the strength of the tendon repair site.
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THE AMOUNT OF SUTURE WITHIN THE REPAIR SITE Norris and colleagues28 reported a quantitative analysis of the suture material within the repair site. In their in vitro study, they calculated the volume and cross-sectional area that was occupied by commonly used suture methods. The 2 internal knots that are placed in the repair site by the Tajima method occupy 27% of the cross-sectional area available for repair. The suture material used for the Savage method occupied 18% of the repair site. The suture material used for the Kessler method occupied 2% of the repair site. Although the Tajima method has been used successfully for a number of years, this suture method occupies significantly more area available for repair than do the other suture methods evaluated in this study. Pruitt and Manske29 reported on the effect of suture knot location on the tensile strength after flexor tendon repair. Pruitt examined the Savage method of repair with the knot inside the repair site and the knot outside the repair site. After following up animals in this in vivo survival study for 6 weeks, they found that the placement of the knot suture material within the repair site did not have any deleterious effect on the tensile strength of the repair site.
STRATEGIES
TO
MODIFY
THE
REPAIR RESPONSE
Prevention of adhesions after flexor tendon surgery continues to be a significant focus for basic science research. Peritendinous flexor tendon adhesions formed after injury and repair may be in part related to fibroblast upregulation in the synovial sheath that is due to increased local levels of cytokines (such as tumor growth factor [TGF]–1). Repaired rabbit flexor tendons that were infiltrated with TGF-1 antibodies showed twice as much range of motion as control specimens. The introduction of TGF-I antibodies to the local flexor tendon environment was associated with a diminished fibroblast response in the synovial sheath and decreased peritendinous adhesion formation. 5-fluorouracil has also been investigated as an agent to diminish peritendinous adhesions after tendon repair. In 2 recently reported studies, tendon healing was not adversely affected when 5-fluorouracil was
182
FLEXOR TENDON REPAIR 䡠 SEILER
applied at the time of tendon repair. Interestingly, the application of 5-fluorouracil was associated with fewer peritendinous adhesions but was not associated with an increase in the rate of tendon rupture. Externally applied devices have also been investigated as a tool to control adhesion formation. Expanded polytetrafluoroethylene (e-PTFE) has been used to reconstruct the synovial sheath in the zone of the repair. In a rabbit model, a decrease in adhesion formation was reported at 2, 3, and 6 weeks after repair. Although e-PTFE has been shown to decrease protein and collagen synthesis in the tendon matrix, the tensile strength of tendons repaired with e-PTFE was similar to that in controls.
THE EFFECT
OF THE
INTERVAL
TO
REPAIR
To identify the optimal period for primary flexor tendon repair, Gelberman and colleagues30 reported a canine study that examined biomechanical, biochemical, and morphologic observations. In their study, they found a significant benefit to early repair. Animals that underwent immediate repair had significantly improved functional characteristics (digital angular rotation) when compared with animals that underwent delayed repair. Significant differences in repair site strength and total concentration of collagen at the repair site were not found. Because of the benefit of improvement in functional characteristics seen with early repair, tendon repair is ideally performed in the first week after injury.
METHODS
OF
TENDON REPAIR
In general, the surgical method of tendon repair should restore tendon continuity and allow for smooth tendon gliding within the synovial sheath of the digit. The repair method should be strong enough to maintain precise tendon coaptation until the tendon is strong enough to withstand the force required for flexion of the finger. Since Bunnell’s initial description of a suture method for tendon repair,31 a significant amount of research effort has been devoted to optimizing the method of tendon suture. In 1975, Urbaniak et al13 reported an excellent study that compared the tensile strength of a number of different methods of tendon repair. For the specific case of end-to-end tendon repair, they identified improvement in repair
site strength for suture methods that were able to grasp the tendon during the repair. Because of the improvement observed with grasping methods of tendon repair, the Kessler method and other 2-strand grasping methods became the methods used most commonly by clinicians for the purpose of flexor tendon repair.32 More recently, investigators have focused on the development of stronger suture methods for aftercare regimens that feature early active digital flexion. These methods have in common the use of larger suture, multiple strands, and multiple grasps to increase the initial repair strength above that predicted to be necessary for active flexion. Repair methods are distinguished by the strength of the repair site on mechanical testing. In general, the strength of the repair site is related to the gauge of the suture material, the nature of the material, the method of suture placement, the number of strands and grasps, and the interaction of the suture materials with the tendon during the period of tendon repair.33-38
SURGICAL PRINCIPLES Whenever possible, flexor tendon repairs in zone 2 should be completed within 7 days of the time of injury. At the time of preoperative consultation, the surgeon should review with the patient the nature of this injury and the aftercare regimen. The tendon repair should be performed in the operating room using optical magnification by an experienced hand surgeon. Careful inspection of the injury wound will allow the surgeon to plan a skin incision that allows adequate exposure of the flexor apparatus. In general, the incision is extended using a zigzag or midlateral incision (Fig 1). After the superficial dissection is completed, a complete assessment of the injury is performed. Tendon retrieval may require a second transverse incision in the palm to locate the retracted proximal tendon stump (Fig 2). Because handling of the tendon is often correlated with subsequent adhesion formation, great care should be taken to minimize any handling of the tendon surface. When possible, the tendon is grasped with fine forceps at the site of laceration. Often, additional openings in the synovial sheath are necessary to allow tendon retrieval. When necessary, the openings should be made through areas of the sheath that are not crucial to tendon position (Fig 3). The tendon should be passed
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flexion and the metacarpophalangeal joints in 50° to 70° of flexion. The interphalangeal joints should be positioned in 0° to 10° of flexion.
OUTCOMES AFTER TENDON REPAIR
FIGURE 1. A Bruner-type incision incorporating the laceration allows both complete exposure of the flexor apparatus in the digit and identification of the digital nerves and arteries.
into the distal wound in its anatomic position and stabilized with a thin hypodermic needle (Fig 4). The specific tendon suture method should be selected based on the nature of the tendon injury and the anticipated form of aftercare (Figs 5 and 6). If both tendons are lacerated, the flexor digitorum superficialis slips should be repaired first. Often these small slips require mattress-type sutures for accurate coaptation of the tendon ends. More proximally, as the caliber of the tendon increases, a standard core suture can be used. If the transection of the flexor digitorum profundus tendon is significantly oblique, then it is often helpful to repair the back wall of the tendon with a 6-0 epitendinous suture to aid in smoothing the tendon repair site. After the core suture (3-0 or 4-0 braided suture) has been inserted and secured, the palmar surface of the epitendinous repair can be completed. Next, any additional nerve or arterial repairs that may be necessary should be completed. Finally, stabilizing needles are removed, and the finger is passively flexed and extended to ensure that there is smooth gliding of the digit through the digital sheath and to assess for significant repair site gap formation. Postoperatively, the patient is placed in a dorsal blocking splint with the wrist positioned in 40° of
A number of systems have been suggested to report the function of the finger after flexor tendon repair. Most systems used for grading outcome rely on calculating or estimating range of motion. Boyes39 recommended that the function of the finger be estimated by measurement of the distance between the pulp of the fingertip and the distal palmar crease. This distance relates to the amount of composite flexion and gives an estimation of digit function. Although this is a quick and easy method for estimating digital function, it must be performed in a standardized manner to avoid errors in measurement. In 1976, the American Society for Surgery of the Hand endorsed a measurement of digital function that calculates total active motion and total passive motion. Motion is calculated as the number of degrees of flexion minus the extension deficit. For the purpose of this system of measurement, the end point of extension was considered to be 0°, and all flexion measurements were made with the hand in a fist position. This system is useful for comparing the preoperative and postoperative function of a single digit but is less valuable in critically assessing the results of flexor tendon repair. Because this measurement includes the range of motion of the metacarpophalangeal joint, which is uncommonly affected by flexor tendon laceration, the results are often better than would be anticipated (Fig 7). To effectively standardize the method of reporting outcomes after flexor tendon repair, Strickland developed a formula for reporting results.32 Strickland’s method of calculation is the most stringent system currently available for measuring results and accurately reflects the differential functions of the tendon repair. His method does not take into account the range of motion at the metacarpophalangeal joint, because neither the flexor digitorum superficialis nor the flexor digitorum profundus is solely responsible for flexion at this joint. To calculate digital performance using Strickland’s method, this equation is used:
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FIGURE 2. A small, flexible Silastic tube can be passed proximally to allow atraumatic retrieval into the site of digital laceration.
关共PIP⫹DIP flexion兲⫺共extensor lag兲兴/175° ⫻100 ⫽% of normal PIP and DIP motion (DIP, distal interphalangeal; PIP, proximal interphalangeal). Because his method is based on data that would be collected in a similar manner by different observers, Strickland’s methods are probably most accurate for cross-comparing studies (Table 6). More recently, investigators have begun to use other standardized outcomes as assessment tools in the reporting of results after flexor tendon repair. Evaluations such as the SF 36, disabilities of the arm, shoulder and hand questionnaire (DASH), Hand Jebsen-Taylor test, and Purdue pegboard test give additional information about the general hand use ability and patient satisfaction after tendon repair (Table 7).
During the last 20 years, there have been significant advances in the care of patients, which have resulted in improved outcomes. The larger comparative series clearly show improvement in digital range of motion. Although these larger series have often focused on the method of aftercare as influencing results, the clinical principles used for tendon suture were also changing and contributing to improvements in outcome. General surgical methods, the methods of surgical exposure, methods of tendon retrieval, atraumatic methods of tendon manipulation, and the method of tendon suturing have all improved during this time and contribute to the improvement in reported outcomes. In 1980, Strickland and Glogovac40 reported their results of treatment for patients who sustained transection of the flexor tendons in zone 2. This clinical
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sive range of motion. After establishing that early passive range of motion had a positive influence on the restoration of the tendon gliding surface, Gelberman proposed that increasing the frequency of digital range of motion would improve ultimate digital performance. After undergoing zone 2 tendon repair using a 2-strand method, patients were randomized to an early passive range of motion program or to a high-frequency passive range of motion program. Patients in the high-frequency group used a continuous passive motion device to obtain a mean 12,000 cycles. Patients in the standard passive motion group averaged 1,000 cycles. Based on Strickland’s method of analysis, patients who completed the high-frequency range of motion program had a significantly improved outcome when compared with patients in the standard passive range of motion group. Tendon ruptures were similar between the groups. In 1992, Silfverskiold et al42,43 reported on the use of a new epitendinous suture method in combination with a 2-strand core suture method with a new after-
FIGURE 3. Tendon retrieval and identification are facilitated by opening the tendon sheath over the membranous areas of the tendon sheath.
trial was one of the first to critically compare variables that might impact the outcome after flexor tendon repair. They reported on 50 consecutive digits with flexor tendon lacerations, with 25 digits treated by 3.5 weeks of immobilization and 25 digits treated by a rehabilitation protocol of early passive digital range of motion. They reported 4 ruptures (16%) in the immobilization group and 1 rupture (4%) in the early passive mobilization group. In his report, Strickland showed a statistically significant improvement in outcome for patients who had early postoperative passive digital mobilization after tendon repair. Using standard assessment criteria, Strickland established a baseline data set that could be used to benchmark future research efforts. In 1991, Gelberman and coworkers41 reported the results of a prospective multicenter trial that evaluated passive range of motion and high-frequency pas-
FIGURE 4. 20-gauge hypodermic needles passed transversely through sheath and tendons stabilize the tendon ends for repair.
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FIGURE 5. Several popular techniques for core sutures.
care regimen for the treatment of patients with zone 2 flexor tendon injuries. With this method, the researchers sought to maximize interphalangeal joint flexion and increase tendon excursion within the digital sheath. In general, they reported a poor outcome with increasing repair site gap size. Often, however, significant repair site gaps were associated with a good clinical outcome. In 1994, Silfverskiold reported on a group of patients treated with early active digital mobilization. In
this cohort, he showed an improvement in outcome when compared with the group that was treated with the 4-finger method of tendon rehabilitation. Both methods were associated with a low complication rate. With his suture method, the amount of late repair site gap formation was similar when comparing the active group and the 4-finger group. Although not a true comparative trial, Silfverskiold was able to use his own data set from previous publications to allow for comparison between the active and improved passive
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FIGURE 6. Several popular techniques for the epitendinous suture.
methods of aftercare. In this study, the authors conclude that early active digital mobilization may be correlated with improved digital performance after tendon repair.
Most recently, Trumble et al44 reported the results of a prospective, randomized, multicenter trial that focused on the optimal method of aftercare for patients treated with a 4-strand core suture method. The
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FIGURE 7. Assessment of postoperative tendon function: (A) Independent FDP function. (B) Excellent total active range of motion. (C) FDS function. (D) Full extension without postoperative extensor lag.
researchers reported a significant improvement in the DASH scores for both cohorts of patients. However, a significant difference between the groups could not be determined. Patients who sustained a nerve injury had increased contractures of the interphalangeal joints
and less overall motion than patients without nerve injuries. Overall, patients with crushing injuries had less range of motion than patients with sharp injuries. In this series, there were not enough patients to allow TABLE 7
TABLE 6 Classification of Results After Flexor Tendon Repair Excellent Good Fair Poor
75-100 50-74 25-49 0-24
NOTE. Using Strickland’s method with the International Federation for Hand Surgeons System classification of outcome.
Factors That Influence the Outcome After Flexor Tendon Repair Age Mechanism of injury Comorbid conditions Level of tendon injury Individual patient considerations Compliance Psychology Physiology
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for meaningful intergroup comparison to determine if early active range of motion could overcome the effect of mechanism of injury. An effect from workman’s compensation status could not be determined when comparing final range of motion values. The rate of tenolysis was higher in the passive group than in the active group. There was one tendon rupture in each group. Interestingly, this study also identified smoking as a covariable that adversely affected outcome. Patients who smoked had less overall active motion and greater overall flexion contractures. In the report, a significant improvement in outcome was seen in patients who were treated with an aftercare program that used early active digital mobilization.44
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CHILDREN
Fitoussi and colleagues45 reported a retrospective review of their experience with pediatric flexor tendon injuries. In their series, patients who sustained zone 2 injuries had a worse outcome than patients with injuries in other areas of the hand. In their series, a positive effect for early mobilization could not be determined. They recommended postoperative immobilization in an above-elbow cast for 4 weeks. Patients with zone 2 injuries had a total active motion of 76° at an average follow-up of 3 years. Outcomes were worse if the age was less than 5 years, the injury was in zone 2, if both tendons were lacerated, and if a below-elbow splint was used after surgery. The overall repair rupture rate in their series was 9%. In a multicenter clinical study of children with flexor tendon injuries, O’Connell et al46 reported the results of treatment for 78 patients less than 16 years of age. Children with isolated zone 1 flexor digitorum profundus injuries that were treated with prompt repair had an excellent outcome. The researchers also concluded that children who were immobilized for up to 4 weeks had outcomes similar to those treated with an early passive range of motion program. When stratifying outcomes by age, the researchers found similar outcomes for all ages of children with combined flexor digitorum superficialis and flexor digitorum profundus injuries that were treated with an early passive range of motion program (72% total active motion). Similar to other studies on flexor tendon
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injury, O’Connell reported poorer results in patients with more complex injuries.46
PARTIAL TENDON INJURIES Using a clinically relevant canine model, Boardman and colleagues47 reported that transverse lacerations of up to 70% could be treated with protection and early mobilization. Further, they reported that tendon repair may have an adverse effect on the mechanical properties of the repair site after the repair of smaller partial transverse lacerations (30%). These basic science findings confirm the work of previous research, which suggests that the tendon structure is quite strong and that not all partial lacerations require tendon repair. Other investigators focusing on clinical complications from partial tendon laceration have recommended tendon repair of partial injuries to limit the likelihood of tendon entrapment, triggering, or late rupture.48 Summarizing the issue of partial tendon injuries, Strickland concluded that partial tendon injuries of 50% or greater should be repaired. All injured tendons should be treated with protection and early mobilization. Currently, there is no consensus regarding the optimal method of aftercare for partial tendon injuries.1,48
AFTERCARE PROGRAMS Most postoperative programs for adults use a dorsal protective hand splint and either passive or early active digital range of motion exercises. Careful coordination of aftercare with a skilled occupational therapist and patient cooperation are important variables in the final outcome. Programs That Use Passive Digital Mobilization In 1975, Duran49 reported on a method of rehabilitation that used passive flexion of the fingers and was designed to cause 3 to 5 mm of tendon excursion and limit the formation of peritendinous adhesions. When compared with immobilization of the hand, tendon rehabilitation programs that used passive digital mobilization have shown significant improvements in patient outcome. Further, tendon rehabilitation programs, which use a high frequency of digital motions, have shown an improved outcome when compared with lower-frequency programs.25,49
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Programs That Feature Active Digital Mobilization Recently, researchers have studied the effect of rehabilitation programs that use early digital motion after tendon repair. By applying proximal load to the tendon, these rehabilitation programs seek to increase the amount of tendon excursion within the sheath. In an effort to increase tendon excursion after repair, Cooney et al50 have developed a dynamic splint that has a hinge at the wrist. Use of this splint was reported to increase the differential excursion between flexor tendons. Significant effort has been devoted to determining the force at the repair site for various levels of physical activity. Based on these studies, it can be predicted that passive digital flexion applies 2 to 4 N of force to the repair site, light active digital flexion applies approximately 10 N, moderate digital flexion applies approximately 17 N, and strong composite grip applies 70 N to the repair site. Schuind et al11 have concluded that the forces in the flexor digitorum profundus are consistently higher than the forces pro-
duced in the flexor digitorum superficialis. These studies provide excellent guidelines for predicting the strength of repair necessary to withstand early active digital mobilization after flexor tendon repair.1,11,51,52 Basic science studies that have examined the effects of low- versus high-force rehabilitation methods have reported that increases in force may be associated with improved tendon excursion and improved outcomes but do no accelerate the tendon repair process per se.53
CONCLUSION Transection of the flexor tendons in zone 2 continues to be one of the more challenging problems in hand surgery. By using recent advances in the basic science of tendon repair, surgical methods of repair, and rehabilitation, satisfactory outcomes can be obtained in most of patients with zone 2 flexor tendon injuries. Successful results require both precise surgical technique and strict adherence to a rehabilitation program.
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38. Lee H. Double loop locking suture: a technique of tendon repair for early active mobilization. Part I. Evolution of technique and experimental study. J Hand Surg [Am] 1990; 15:945-952. 39. Boyes JH. Flexor tendon grafts in the fingers and thumb. An evaluation of end results. J Bone Joint Surg Am 1950;32A: 489-499. 40. Strickland JW, Glogovac SV. Digital function following flexor tendon repair in zone II: a comparison of immobilization and controlled passive motion techniques. J Hand Surg 1980;5:537-543. 41. Gelberman RH, Nunley JA, Osterman AL, Breen TF, Dimick MP, Woo SL-Y. Influences of the protected passive mobilization interval on flexor tendon healing: a prospective, randomized clinical study. Clin Orthop Rel Res 1991;264: 189-196. 42. Silfverskiold KL, May EJ, Tornvall AH. Flexor digitorum profundus tendon excursions during controlled motion after flexor tendon repair in zone II: a prospective clinical study. J Hand Surg [Am] 1992;17A:122-131. 43. Silfverskiold KL, May EJ, Tornvall AH. Gap formation during controlled motion after flexor tendon repair in zone II. A prospective clinical study. J Hand Surg [Am] 1992;17A:539546. 44. Trumble TE, Idler RS, Strickland JW, Stern PJ, Gilbert MM. Randomized prospective trial of active versus passive motion after zone II flexor tendon repair. Submitted for publication. 45. Fitoussi F, Yebellec Y, Frajman JM, Pennecot GF. Flexor tendon injuries in children: Factors influencing prognosis. J Ped Orthop 1999;19:818-821. 46. O’Connell SJ, Moore MM, Strickland JW, Frazier GT, Dell PC. Results of zone I and zone II flexor tendon repair in children. J Hand Surg [Am] 1994;19A:48-52. 47. Boardman ND, Morifusa S, Chan Saw SS, et al. Effects of tenorrhaphy on the gliding function and tensile properties of partially lacerated canine digital flexor tendons. J Hand Surg [Am] 1999;24A:302-309. 48. Schlenker JD, Lister GD, Kleinert HE. Three complications of untreated partial lacerations of flexor tendon. Entrapment, rupture and triggering. J Hand Surg 1981;6:392-396. 49. Duran RE. Controlled passive motion following tendon repair in zone II and III. In: The American Academy of Orthopaedic Surgeons. Symposium on tendon surgery in the hand. St. Louis: Mosby, 1975:105-114. 50. Cooney WP, Lin Gt, An KN. Improved tendon excursions follow flexor tendon repair. J Hand Ther 1989;2:102-113. 51. Greenwald D, Shumway S, Allen C, Mass D. Dynamic analysis of profundus tendon function. J Hand Surg [Am] 1994; 19A:626-635. 52. Aoki M, Kubota H, Pruitt DL, Manske PR. Biomechanical and histological characteristics of canine flexor repair using early postoperative mobilization. J Hand Surg [Am] 1997; 22A:107-114. 53. Boyer MI, Gelberman RH, Burns ME, Dinopoulos H, Hofem R, Silva MJ. High levels of in vivo force rehabilitation in canines. Submitted for publication.