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Impact of flexor digitorum superficialis on gliding function of the flexor digitorum profundus according to regions in zone II1
Impact of Flexor Digitorum Superficialis on Gliding Function of the Flexor Digitorum Profundus According to Regions in Zone II Jin Bo Tang, MD, Yan Xu, MD, Feng Chen, PhD, Nantong, China
Purpose: Structures and gliding characteristics of the flexor tendons vary remarkably according to regions of zone II in the hand. We studied the impact of the flexor digitorum superficialis (FDS) on the work of flexion and excursion efficiency of the flexor digitorum profundus (FDP) tendon in different regions of zone II. Methods: Twenty-one fresh-frozen human fingers were used as an experimental model. The FDP was pulled to flex the finger with a tensile machine. The work of flexion of the finger and gliding excursion of the tendon were recorded in the fingers with the FDS intact, after excision of the FDS proximal to, under, or distal to the A2 pulley. Results: The FDS tendon exerts notably different effects on the work of flexion and excursion efficiency of the FDP in subregions of zone II. Removal of the FDS under the A2 pulley affected the FDP most manifestly, causing a 12% decrease in the work of flexion and a loss of the excursion efficiency at the metacarpophalangeal joint. Removal of the FDS proximal to the A2 pulley had a less notable effect on the work of flexion. Removal of the FDS distal to the pulley did not markedly alter the biomechanics of the FDP. Conclusions: Removal of the FDS tendon in the area of the A2 pulley reduces the work of flexion most notably and causes a loss of excursion efficiency. Removal of the FDS tendon distal to the A2 pulley does not change the work of flexion, and removal of the FDS tendon proximal to the A2 pulley has a notable but less pronounced effect on the FDP tendon. (J Hand Surg 2003;28A: 838-844. Copyright © 2003 by the American Society for Surgery of the Hand.) Key words: Flexor tendon, gliding function, pulley and sheath, subregions, biomechanics.
A prominent feature of the flexor tendons of zone II in the hand is the existence of both flexor digitoFrom the Department of Hand Surgery, Hand Surgery Research Center, Affiliated Hospital of Nantong Medical College, Nantong, Jiangsu, China. Received for publication October 3, 2002; accepted in revised form June 4, 2003. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Jin Bo Tang, MD, Department of Hand Surgery, Affiliated Hospital of Nantong Medical College, 20 West Temple Rd, Nantong 226001, Jiangsu, China. Copyright © 2003 by the American Society for Surgery of the Hand 0363-5023/03/28A05-0020$30.00/0 doi:10.1053/S0363-5023(03)00300-9
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rum superficialis (FDS) and flexor digitorum profundus (FDP) tendons and a narrow constricting fibroosseous pulley system.1–5 A major challenge for hand surgeons is reducing adhesion formation between repaired tendons and the surrounding sheath during tendon repair. Excision of the FDS tendon was proposed in the past as a way of eliminating the possibility of adhesions between the FDS and the FDP tendons and of leaving room for gliding of the FDP tendon.6 – 8 This concept, however, was challenged because the blood supply to the FDP tendon is via vincula that attach to the FDS tendon.9,10 In addition, excision of the FDS tendon may weaken the force of finger flexion and result in the loss of an
Tang, Xu, and Chen / Gliding Function of Flexor Tendons
important constraint preventing hyperextension of the proximal interphalangeal (PIP) joint.10 –12 Although the majority of hand surgeons prefer to repair the FDS tendon when both tendons are lacerated, the impact of preservation or excision of the FDS tendon on function of the hand has not been determined in many aspects. Ferlic and Clayton13 resected one slip of the FDS tendon to decompress the digital theca in trigger fingers. Zhao et al14 found that resection of the FDS tendon reduces gliding resistance after FDP tendon repair under the A2 pulley. Recent work on tendon function after preservation or excision of the FDS tendon was primarily in the region of the major flexor pulley—the A2 pulley, the area designated as zone IIc by Tang and Shi,15 who consider this area the most constricting part of the digital sheath and thus vital to function of repaired tendons.4,13,14,16 –19 The sheath components and tendon anatomy in the area of the A2 pulley are remarkably different from those in the other regions of zone II (Fig. 1); thus it is likely that the FDS tendon has differential effects on the gliding of the FDP in these regions. Clinically, surgical repair of the FDS tendon within the sheath is under question because of the risk for adhesions and the mechanical impact of 2 healing tendons within a tight space.15–17 We studied the effect of FDS excision within zone II on the work of flexion and tendon excursion to obtain insights into interactions of the FDS and FDP. In human cadaver fingers we measured the work of flexion and excursion efficiency of the FDP tendon before and after excision of the FDS in subregions of zone II.
Figure 1. Human pulleys in digits showing marked variations in sheath diameters in zone II and the narrowest portion at the middle of the A2 pulley—zone IIc. The sheath in both zones IIb and IId apparently has greater transverse diameters. The tendons within zones IIb and IId are covered segmentally by a synovial sheath with narrow pulleys. In contrast, the tendons in zone IIc are covered entirely by a lengthy A2 pulley over the phalangeal shaft.
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Because the work of flexion is the energy required to flex the fingers against resistance,19 –21 its changes resulting from removal of the FDS should indicate the impact of the FDS tendon on the gliding function of the FDP. We hypothesized that removal of the FDS tendon exerted different effects on the gliding function of the FDP tendon in different regions of zone II.
Materials and Methods Twenty-one fresh-frozen cadaveric fingers were used. We used the index, middle, and ring fingers from adult cadaveric hands. The ages of the adults were 46 to 70 years old at the time of death. The hands had been transected at the distal part of the forearm and had no detectable trauma or deformities.
Preparation and Test Setup After being thawed completely each hand was mounted firmly on a board with 2 Steinman pins passed through the radius and ulna. The board was secured to the lower clamp of a tensile testing machine with a load cell of 500 N (Instron Model 4411; Instron Corp., Canton, MA). The motion of the distal interphalangeal, PIP, and metacarpophalangeal (MCP) joints were not restricted, but motion of the carpal bones and radiocarpal and distal radial ulnar joint was prevented by firmly immobilizing them with multiple K-wires. Through a rectangular skin excision at the middle of the palm, the FDS and FDP tendons were identified and transected sharply with a surgical blade. The level of tendon transection was about 2 cm proximal to the reflection of the digital synovial sheath. The tendons were cut when the fingers were held in a position of full extension. The proximal stump of the FDP tendon was then sutured with 3-0 sutures (Ethilon 663G; Ethicon Inc., Somerville, NJ). The line sutured to the FDP tendon was connected to the upper clamp of the testing machine. Parts of the skin and subcutaneous tissue in the palm were removed to facilitate exposure and allow gliding of the FDP tendon without interference by surrounding tissues. Before the test the fingers were pulled passively over full range of flexion for 4 or 5 consecutive runs. Preconditioning the fingers was intended to minimize changes in viscoelasticity of the sheath and tendon elongation during subsequent tests and to ensure that joint stiffness would not interfere with tendon gliding.22
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Experimental Stages The group of 21 fingers was divided into 2 parts: 15 fingers were assigned randomly to the test of work of flexion, and 6 fingers were assigned to the test of excursion efficiency. In each finger tendon gliding was tested in the following experimental stages (Fig. 2): (1) Intact FDS: work of flexion of the FDP tendons was tested with the FDS tendon intact in the entire zone II. The proximal end of the FDS was tensioned through a suture (Ethilon 663G; Ethicon Inc.) connected to a 5 N longitudinal load. (2) Removal of the FDS tendon proximal to the A2 pulley– zone IId: the FDS tendon proximal to the proximal margin of the A2 pulley was removed completely. (3) Removal of the FDS tendon beneath the A2 pulley–zone IIc: the FDS under the A2 pulley, including its bifurcated FDS slips, was removed but the FDS slips distal to the A2 pulley were kept intact. (4) Removal of the FDS tendon distal to the A2 pulley– zone IIb: the FDS tendon distal to the FDP tendon was excised up to the insertion of the tendon on the middle phalanx. In each stage of the test, the FDS tendon segment was excised with a sharp surgical blade through transverse incisions in the sheath at the
proximal or distal borders of the A2 pulley and at the insertion of the FDS tendon. Excision of the FDS segments in all stages was at full extension of the fingers. Pulleys were not disturbed. The sheath incision was closed with 6-0 sutures (Ethilon 689; Ethicon Inc.) to ensure a smooth gliding floor for the FDP tendon. In the fingers for the test of the work of flexion, the distal interphalangeal, PIP, and MCP joints of the fingers were placed at 0° at the beginning of the test, and the FDP tendons were loaded with 1.0 N preload. With the FDS intact (stage 1), the force and work of the FDP tendon excursion required to flex the fingers completely were determined. In the test the overhead cross-bar secured to the upper clamp was advanced at a constant speed of 25 mm/min. As the proximal stump of the tendon was pulled the finger joints were flexed continuously. Pulling was terminated when the finger pulp entirely touched the palm. During the testing, displacement of the tendons and the force of tendon pulling were measured continuously by the testing machine with a software program (Series IX; Instron Corp.) and the data were stored in computer files. The tendon displacement during finger flexion
Figure 2. Areas of FDS excision in experimental stages. Regions with FDS excision are marked with dark grey.
Tang, Xu, and Chen / Gliding Function of Flexor Tendons
was recorded as the tendon excursion. In the subsequent stages the excursions with the FDS tendon intact were used as the excursion value in tests. The fingers for the test of excursion efficiency were mounted on the board and connected to the testing machine as described earlier. The distal interphalangeal and PIP joints were immobilized in extension by a K-wire along the longitudinal axis of the distal 2 phalanges through the fingertip. In each stage of the FDS excision the MCP joints of the fingers were placed at 0° at the beginning of the test, and the FDP tendons were preloaded and pulled proximally with the method identical to that in the tests described earlier. A large clear plastic goniometer was fixed securely beside the fingers to the board, with the rotation center of the goniometer at the MCP joint motion axis. Pulling on the tendon was terminated when the K-wire through the phalanges overlapped the 90° maker on the goniometer at the stage with FDS tendon intact. During the testing the excursions of the FDP tendons were recorded by the testing machine. With an identical tendon excursion, the joint flexion range was recorded after removal of the FDS tendon in each region.
Data Analysis Work of flexion. The work needed to flex the fingers completely was obtained by calculating the area under the load-displacement curve.19,20 Work of flexion represents the energy consumption during the finger flexion caused by resistance to the FDP excursion, mostly frictional resistance, and viscoelasticity of the sheath and FDS tendon, and joint stiffness. On each data file, the peak force on the load-displacement curve also was recorded as measures of the force resisting tendon gliding.
Excursion efficiency. Excursion efficiency represents the relationship between angular rotation and a fixed tendon excursion for each experimental condition. It indicates ranges of joint angulation produced by a given excursion of a tendon moving the joint. Excursion efficiency can be expressed in another way: as changes in tendon excursions over a fixed range of joint angulation.19 Bowstringing of the tendon after loss of pulleys across the joint decreases the efficiency of tendon excursion.17–20 Removal of the FDS tendon segment palmar to the FDP tendon allows the FDP to move farther away from the joint rotation centers, and theoretically decreases its efficiency. In this study the excursion efficiency was recorded as a percent of the range of joint flexion
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compared with that with intact FDS (90°) with an identical excursion.
Statistical Analysis Data are summarized as means ⫾ SD and were analyzed statistically by one-way analysis of variance for repeated measurements of the same variable. When significant differences were found the 2-tailed paired Student’s t-test was applied to determine the levels of significance between pairs of data with a significant level at p ⬍ .05. In this study the paired t-test was used because variables were measured in the same fingers with or without FDS in the different regions, and the data from the test stages were paired naturally. Individual fingers presented substantial natural variation in the work of flexion and excursion efficiency. To present changes in the variables in results they were normalized by dividing measured values by those before FDS excision in the same fingers to obtain percent changes.
Results Work of Flexion The work of flexion decreased by 6% after excision of the FDS proximal to the A2 pulley and 12% after excision of the FDS under the A2 pulley when compared with the work of flexion with the FDS intact in respective regions (Table 1). The work of flexion decreased significantly after excision of the FDS in the areas proximal to or beneath the A2 pulley (p ⫽ .0002, p ⫽ .001, respectively). The work of flexion of the FDP tendon, however, was almost identical before and after removal of the FDS distal to the A2 pulley. In other words the FDS tendon caused the greatest increase in the work of flexion in the area of the A2 pulley, which was more than twice the increase in that of the FDP tendon proximal to the A2 pulley. The existence of the FDS distal to the pulley did not increase the work (Fig. 3). Further analysis of the peak force during finger flexion revealed the impact of the FDS on the FDP identical to that indicated by the work of flexion (Table 1).
Excursion Efficiency The excursion efficiency of the FDP tendon was 97% after excision of the FDS proximal to the A2 pulley, 91% after excision of the FDS under the A2 pulley, and 90% after FDS excision distally, when compared with that with the FDS intact (Table 1). Excursion efficiency changes significantly after excision of the
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Table 1. Changes in the Work of Flexion, Peak Force, and Excursion Efficiency of the Flexor Digitorum Profundus Tendon After Flexor Digitorum Superficialis Excision in Different Regions of Zone II FDS Tendon
Work of Flexion (%)
Peak Force (%)
Excursion Efficiency (%)
Intact Excision, proximal to A2 pulley Excision, under A2 pulley Excision, distal to A2 pulley
94.1 ⫾ 7.0* 81.9 ⫾ 10.0† 80.0 ⫾ 10.1
95.5 ⫾ 4.2* 84.3 ⫾ 6.1† 82.6 ⫾ 6.3
96.7 ⫾ 4.5 90.5 ⫾ 5.3† 90.1 ⫾ 5.2
Values are means ⫾ SD. Data are percent changes obtained by dividing values of the variables measured after FDS excision by those with intact FDS in the same fingers. Percent changes of these variables in the stage of intact FDS are 100%. *Significantly different from those of the fingers with intact FDS. †Significantly different from those after FDS excision proximal to the pulley.
FDS beneath the A2 pulley (p ⫽ .001), but not after excision of the FDS distal to the A2 pulley.
Discussion The structures of flexor tendons in zone II of the hand are extremely complicated; the presence of rigid, narrow, and segmental pulleys and manifested changes in relative locations of the FDS and FDP are the unique features. Differential strategies and outcomes of the repair among regions of zone II have been explored during recent years,15–17,23,24 which should relate to the anatomy and biomechanics of the tendons in each area of zone II. The work of flexion reflects the ease with which the tendon may glide in the confined fibroosseous tunnel.19 –21 Determination of this variable helps understand tendon interactions in each region of zone II, highlighting the points to be considered in planning surgical treatment. Remarkable differences in the impact of the FDS on the work of flexion were noted between different regions. The FDS tendon under the A2 pulley had the greatest effect on the gliding of the FDP, its removal causing the most pronounced decrease in the work of flexion. The removal of the FDS proximal to the A2 pulley had a smaller effect on the FDP and removal
Figure 3. Changes in the work of flexion of the FDP tendon after excision of the FDS in different regions of zone II.
of the FDS distally had no such effects. The FDS tendon overlapping the A2 pulley apparently is the segment most constricting to the gliding of the FDP tendon and its presence within an intact A2 pulley increases the gliding resistance of the FDP tendon. Removal of the FDS tendon distal to the A2 pulley had no notable effects on the work of flexion, indicating that preservation of the FDS tendon distal to the A2 pulley does not increase the likelihood of constriction of the gliding of the FDP. Vascular supplies from the long vincula of the FDP tendon penetrate the fan-shaped membrane vincula (short vincula) of the FDS tendon.9,25 The fan-shaped vincula insert to a lengthy segment of the FDS tendon distal to the A2 pulley.4 Therefore preservation of the FDS distal to the A2 pulley can favor the nutrition of the FDP but, as revealed by this study, does not increase the gliding resistance. The FDS tendon runs entirely parallel to the FDP in the region proximal to the A2 pulley. The magnitude of the impact of the presence of the FDS tendon proximal to the A2 pulley on gliding resistance was less than half that of the FDS under the pulley. Unlike the FDS tendon in the area of the A2 pulley, which takes the form of a finger trap to constrict or lock the FDP during powerful grip,4,5 the FDS proximal to the A2 pulley provides a smooth gliding surface for the FDP. Considering remarkably lower resistance of this FDS segment on the FDP, we believe that its removal does not add much to reducing the gliding resistance of the FDP in the region proximal to the A2 pulley. Changes in excursion efficiency were limited but were significant after removal of the FDS tendon beneath the A2 pulley (p ⫽ .001). In contrast, removal of the FDS other parts did not alter the efficiency. These findings indicate that the FDS in area IIc—a tendon segment with bifurcation that the FDP tendon glides against—functions as a pulley. This
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Table 2. Summary of Anatomic, Biomechanical, In Vivo Studies, and Clinical Observations Related to Tendons in the Subregions of Zone II Investigations Anatomic* FDS tendon Pulleys Biomechanical FDS tendon† Pulleys
In vivo studies FDS tendon Pulleys
Area of FDS Insertion (Zone IIa) Insertion A4, C2
2 slips dorsal to FDP, with vincula A3, C1
No gliding
Not constrict FDP
Beneath A2 Pulley (Zone IIc)
-
-
Repair (Tang and Shi,15 Britto et al24)
A4 venting (Kwai Ben and Elliot17)
-
Proximal to A2 Pulley (Zone IId)
Bifurcation
Flattened, palmar to FDP
A2, most narrow
A1, PA
Constrict FDP, as a moving pulley A4 release is feasible May incise one pulley Partial release is feasible (Savage27, Tomaino (Tang and Xie,28 Lin (Tang,4 Tomaino et al18) 18 3 et al ) et al )
Clinical options FDS tendon
Pulleys
Distal to A2 Pulley (Zone IIb)
Release favors FDP gliding (Tang et al19)
Little constriction -‡
-
Resection or repair (Tang and Repair both tendons (Tang and Shi15) Shi,15,16 Kwai Ben and 17 29 Elliot, Elliot ) Resection of one slip (Zhao et al14) Partial release (Tang,4 Kwai Ben and Elliot,17 Elliot29) Pulley shortening (partial excision) or plasty (Paillard et al30)
*Anatomic features of the FDS and pulleys are list according to the work by Tang and Shi15,16 †Summarized based on results of the current study. ‡Subjects were not studied or had not been well determined.
tendon segment glides from beneath the A2 pulley and moves across the MCP joint as the finger flexes. We hypothesize that the FDS in zone IIc serves as a moving pulley to fine-tune moment arms and motion arcs of the FDP tendon during finger flexion. The FDS of zone IId locates proximal to the MCP joint and that of zone IIb dorsal to the FDP, thereby having no effect on the excursion efficiency. The most notable FDS and FDP interaction in the A2 pulley area, in contrast to that in the regions distal or proximal to the pulley, coincides with the complexity of the anatomy of the tendon system in this area. The area of the A2 pulley is considered special because of (1) the presence of the longest and most rigid pulley of the finger; (2) the bifurcation of the FDS tendon; (3) the lack of vincula insertion on the tendons and the poorest in vascular perfusion, indicative of bearing a greater compression force4,25; (4) the surrounding of the FDP tendon by the FDS rather than the FDS overlying on the tendon; and (5) its being the narrowest part in zone II.4,16 Several surgical procedures have been proposed to
reduce the constriction of the tendon gliding for zone II flexor tendons. Tang4 proposed either incision of a part of the major pulleys or excision of a part of the FDS under the pulleys. Kwai Ben and Elliot17 released a part of the A2 pulley to allow tendon gliding without compression during the surgery. Strickland26 proposed the release of a part of the sheath or pulleys to place a suture and to eliminate compression to the tendon. Zhao et al14 advocated the excision of a slip of the FDS tendon based on the study of gliding resisting force under the A2 pulley. A decade ago, Tang and Shi15 advocated a clinical treatment– oriented subdivision system of zone II, which divides zone II into 4 regions with characteristics of the FDS and the location of the major pulley (the A2 pulley) as landmarks. This subdivision system takes into consideration the functional impacts of major pulleys and variances of the FDS structures, which were proven in recent studies vital to understanding the tendon function and exploring treatment of zone II flexor tendons.14,18,30 Our study supplemented the previous work on this aspect with clear
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pictures of differential interaction of the FDS with the FDP tendons in subregions of zone II (Table 2). The presence of the FDS leads to only mild increases in resistance to tendon gliding—resulting in less than 18% changes in the force and less than 20% changes in the work—which reflects elegance of nature’s design for smooth movement of both tendons in the narrow tunnel. In the in vitro testing we were unable to evaluate adhesions or healing of the tendons or include tissue edema or reparative reactions in the study. Tissue reactions and adhesions of a traumatized and repaired tendon would potentially add to the other factors, increasing the force and work of tendon gliding. In vivo studies in models of tendon injuries should be performed to elucidate these additional factors. This study provides fundamental insights into the impact of the FDS on function of the FDP in different regions of the complex sheath area and may serve as a basis toward a rationale for treatment of the FDS and the pulley.
References 1. Doyle JR. Anatomy of the finger flexor tendon sheath and pulley system. J Hand Surg 1988;13A:473– 484. 2. Strickland JW. Flexor tendon surgery. Part I: primary flexor tendon repair. J Hand Surg 1989;14B:261–272. 3. Lin G-T, Amadio PC, An K-N, Cooney WP. Functional anatomy of the human digital flexor pulley system. J Hand Surg 1989;14A:949 –956. 4. Tang JB. The double sheath system and tendon gliding in zone 2C. J Hand Surg 1995;20B:281–285. 5. Walbeehm ET, McGrouther DA. An anatomical study of the mechanical interactions of flexor digitorum superficialis and profundus and the flexor tendon sheath in zone 2. J Hand Surg 1995;20B:269 –280. 6. Green WL, Niebauer JJ. Results of primary and secondary flexor-tendon repairs in no man’s land. J Bone Joint Surg 1974;56A:1216 –1222. 7. Tsuge K, Ikuta Y, Matsuishi Y. Repair of flexor tendons by intratendinous tendon suture. J Hand Surg 1977;2:436 – 440. 8. Nielsen AB, Jensen PO. Primary flexor tendon repair in ‘no man’s land.’ J Hand Surg 1984;9B:279 –281. 9. Lundborg G, Myrhage R, Rydevik B. The vascularization of human flexor tendons within the digital synovial sheath region—structural and functional aspects. J Hand Surg 1977; 2:417– 427. 10. Amadio PC, Hunter JM, Jaeger SH, Wehbe MA, Schneider LH. The effect of vincular injury on the results of flexor tendon surgery in zone 2. J Hand Surg 1985;10A:626 – 632. 11. Lister GD, Kleinert HE, Kutz JE, Atasoy E. primary flexor tendon repair followed by immediate controlled mobilization. J Hand Surg 1977;2:441– 451. 12. Kleinert HE, Schepel S, Gill T. Flexor tendon injuries. Surg Clin North Am 1981;61:267–286.
13. Ferlic DC, Clayton ML. Flexor tenosynovectomy in the rheumatoid finger. J Hand Surg 1978;3:364 –367. 14. Zhao C, Amadio PC, Zobitz ME, An K-N. Resection of the flexor digitorum superficialis reduces gliding resistance after zone II flexor digitorum profundus repair in vitro. J Hand Surg 2002;27A:316 –321. 15. Tang JB, Shi D. Subdivision of flexor tendon “no man’s land” and different treatment methods in each sub-zone. Chin Med J 1992;105:60 – 68. 16. Tang JB. Flexor tendon repair in zone 2C. J Hand Surg 1994;19B:72–75. 17. Kwai Ben I, Elliot D. “Venting” or partial lateral release of the A2 and A4 pulleys after repair of zone 2 flexor tendon injuries. J Hand Surg 1998;23B:649 – 654. 18. Tomaino M, Mitsionis G, Basitidas J, Grewal R, Pfaeffle J. The effect of partial excision of the A2 and A4 pulleys on the biomechanics of finger flexion. J Hand Surg 1998;23B:50 – 52. 19. Tang JB, Wang YH, Gu YT, Chen F. Effect of pulley integrity on excursions and work of flexion in healing flexor tendons. J Hand Surg 2001;26A:347–353. 20. Peterson WW, Manske PR, Bollinger BA, Lesker PA, McCarthy JA. Effect of pulley excision on flexor tendon biomechanics. J Orthop Res 1986;4:96 –101. 21. Peterson WW, Manske PR, Dunlap J, Horwitz DS, Kahn B. Effect of various methods of restoring flexor sheath integrity on the formation of adhesions after tendon injury. J Hand Surg 1990;15A:48 –56. 22. Lane JM, Black J, Bora FW Jr. Gliding function following flexor-tendon injury. A biomechanical study of rat tendon function. J Bone Joint Surg 1976;58A:985–989. 23. Harris SB, Harris D, Foster AJ, Elliot D. The aetiology of acute rupture of flexor tendon repair in zones 1 and 2 of the fingers during early mobilization. J Hand Surg 1999;24B: 275–280. 24. Britto JA, Ragoowansi R, Flemming AFS. A novel method for repair of flexor digitorum superficialis lacerations in zone 2. Plast Reconstr Surg 2001;18:456 – 459. 25. Ochiai N, Matsui T, Miyaji N, Merklin RJ, Hunter JM. Vascular anatomy of flexor tendons. I. Vincular system and blood supply of the profundus tendon in the digital sheath. J Hand Surg 1979;4:321–330. 26. Strickland JW. Flexor tendon injuries. Part 2. Flexor tendon repair. Orthop Rev 1986;15:701–721. 27. Savage R. The mechanical effect of partial resection of the digital fibrous flexor sheath. J Hand Surg 1990;15B:435– 442. 28. Tang JB, Xie RG. Effect of A3 pulley and adjacent sheath integrity on tendon excursion and bowstringing. J Hand Surg 2001;26A:855– 861. 29. Elliot D. Primary flexor tendon repair— operative repair, pulley management and rehabilitation. J Hand Surg 2002; 27B:507–513. 30. Paillard PJ, Amadio PC, Zhao C, Zobitz ME, An KN. Pulley plasty versus resection of one slip of the flexor digitorum superficialis after repair of both flexor tendons in zone II. A biomechanical study. J Bone Joint Surg 2002;84A:2039 – 2045.
Purpose: Structures and gliding characteristics of the flexor tendons vary remarkably according to regions of zone II in the hand. We studied the impact of the flexor digitorum superficialis (FDS) on the work of flexion and excursion efficiency of the flexor digitorum profundus (FDP) tendon in different regions of zone II. Methods: Twenty-one fresh-frozen human fingers were used as an experimental model. The FDP was pulled to flex the finger with a tensile machine. The work of flexion of the finger and gliding excursion of the tendon were recorded in the fingers with the FDS intact, after excision of the FDS proximal to, under, or distal to the A2 pulley. Results: The FDS tendon exerts notably different effects on the work of flexion and excursion efficiency of the FDP in subregions of zone II. Removal of the FDS under the A2 pulley affected the FDP most manifestly, causing a 12% decrease in the work of flexion and a loss of the excursion efficiency at the metacarpophalangeal joint. Removal of the FDS proximal to the A2 pulley had a less notable effect on the work of flexion. Removal of the FDS distal to the pulley did not markedly alter the biomechanics of the FDP. Conclusions: Removal of the FDS tendon in the area of the A2 pulley reduces the work of flexion most notably and causes a loss of excursion efficiency. Removal of the FDS tendon distal to the A2 pulley does not change the work of flexion, and removal of the FDS tendon proximal to the A2 pulley has a notable but less pronounced effect on the FDP tendon. (J Hand Surg 2003;28A: 838-844. Copyright © 2003 by the American Society for Surgery of the Hand.) Key words: Flexor tendon, gliding function, pulley and sheath, subregions, biomechanics.
A prominent feature of the flexor tendons of zone II in the hand is the existence of both flexor digitoFrom the Department of Hand Surgery, Hand Surgery Research Center, Affiliated Hospital of Nantong Medical College, Nantong, Jiangsu, China. Received for publication October 3, 2002; accepted in revised form June 4, 2003. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Jin Bo Tang, MD, Department of Hand Surgery, Affiliated Hospital of Nantong Medical College, 20 West Temple Rd, Nantong 226001, Jiangsu, China. Copyright © 2003 by the American Society for Surgery of the Hand 0363-5023/03/28A05-0020$30.00/0 doi:10.1053/S0363-5023(03)00300-9
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rum superficialis (FDS) and flexor digitorum profundus (FDP) tendons and a narrow constricting fibroosseous pulley system.1–5 A major challenge for hand surgeons is reducing adhesion formation between repaired tendons and the surrounding sheath during tendon repair. Excision of the FDS tendon was proposed in the past as a way of eliminating the possibility of adhesions between the FDS and the FDP tendons and of leaving room for gliding of the FDP tendon.6 – 8 This concept, however, was challenged because the blood supply to the FDP tendon is via vincula that attach to the FDS tendon.9,10 In addition, excision of the FDS tendon may weaken the force of finger flexion and result in the loss of an
Tang, Xu, and Chen / Gliding Function of Flexor Tendons
important constraint preventing hyperextension of the proximal interphalangeal (PIP) joint.10 –12 Although the majority of hand surgeons prefer to repair the FDS tendon when both tendons are lacerated, the impact of preservation or excision of the FDS tendon on function of the hand has not been determined in many aspects. Ferlic and Clayton13 resected one slip of the FDS tendon to decompress the digital theca in trigger fingers. Zhao et al14 found that resection of the FDS tendon reduces gliding resistance after FDP tendon repair under the A2 pulley. Recent work on tendon function after preservation or excision of the FDS tendon was primarily in the region of the major flexor pulley—the A2 pulley, the area designated as zone IIc by Tang and Shi,15 who consider this area the most constricting part of the digital sheath and thus vital to function of repaired tendons.4,13,14,16 –19 The sheath components and tendon anatomy in the area of the A2 pulley are remarkably different from those in the other regions of zone II (Fig. 1); thus it is likely that the FDS tendon has differential effects on the gliding of the FDP in these regions. Clinically, surgical repair of the FDS tendon within the sheath is under question because of the risk for adhesions and the mechanical impact of 2 healing tendons within a tight space.15–17 We studied the effect of FDS excision within zone II on the work of flexion and tendon excursion to obtain insights into interactions of the FDS and FDP. In human cadaver fingers we measured the work of flexion and excursion efficiency of the FDP tendon before and after excision of the FDS in subregions of zone II.
Figure 1. Human pulleys in digits showing marked variations in sheath diameters in zone II and the narrowest portion at the middle of the A2 pulley—zone IIc. The sheath in both zones IIb and IId apparently has greater transverse diameters. The tendons within zones IIb and IId are covered segmentally by a synovial sheath with narrow pulleys. In contrast, the tendons in zone IIc are covered entirely by a lengthy A2 pulley over the phalangeal shaft.
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Because the work of flexion is the energy required to flex the fingers against resistance,19 –21 its changes resulting from removal of the FDS should indicate the impact of the FDS tendon on the gliding function of the FDP. We hypothesized that removal of the FDS tendon exerted different effects on the gliding function of the FDP tendon in different regions of zone II.
Materials and Methods Twenty-one fresh-frozen cadaveric fingers were used. We used the index, middle, and ring fingers from adult cadaveric hands. The ages of the adults were 46 to 70 years old at the time of death. The hands had been transected at the distal part of the forearm and had no detectable trauma or deformities.
Preparation and Test Setup After being thawed completely each hand was mounted firmly on a board with 2 Steinman pins passed through the radius and ulna. The board was secured to the lower clamp of a tensile testing machine with a load cell of 500 N (Instron Model 4411; Instron Corp., Canton, MA). The motion of the distal interphalangeal, PIP, and metacarpophalangeal (MCP) joints were not restricted, but motion of the carpal bones and radiocarpal and distal radial ulnar joint was prevented by firmly immobilizing them with multiple K-wires. Through a rectangular skin excision at the middle of the palm, the FDS and FDP tendons were identified and transected sharply with a surgical blade. The level of tendon transection was about 2 cm proximal to the reflection of the digital synovial sheath. The tendons were cut when the fingers were held in a position of full extension. The proximal stump of the FDP tendon was then sutured with 3-0 sutures (Ethilon 663G; Ethicon Inc., Somerville, NJ). The line sutured to the FDP tendon was connected to the upper clamp of the testing machine. Parts of the skin and subcutaneous tissue in the palm were removed to facilitate exposure and allow gliding of the FDP tendon without interference by surrounding tissues. Before the test the fingers were pulled passively over full range of flexion for 4 or 5 consecutive runs. Preconditioning the fingers was intended to minimize changes in viscoelasticity of the sheath and tendon elongation during subsequent tests and to ensure that joint stiffness would not interfere with tendon gliding.22
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Experimental Stages The group of 21 fingers was divided into 2 parts: 15 fingers were assigned randomly to the test of work of flexion, and 6 fingers were assigned to the test of excursion efficiency. In each finger tendon gliding was tested in the following experimental stages (Fig. 2): (1) Intact FDS: work of flexion of the FDP tendons was tested with the FDS tendon intact in the entire zone II. The proximal end of the FDS was tensioned through a suture (Ethilon 663G; Ethicon Inc.) connected to a 5 N longitudinal load. (2) Removal of the FDS tendon proximal to the A2 pulley– zone IId: the FDS tendon proximal to the proximal margin of the A2 pulley was removed completely. (3) Removal of the FDS tendon beneath the A2 pulley–zone IIc: the FDS under the A2 pulley, including its bifurcated FDS slips, was removed but the FDS slips distal to the A2 pulley were kept intact. (4) Removal of the FDS tendon distal to the A2 pulley– zone IIb: the FDS tendon distal to the FDP tendon was excised up to the insertion of the tendon on the middle phalanx. In each stage of the test, the FDS tendon segment was excised with a sharp surgical blade through transverse incisions in the sheath at the
proximal or distal borders of the A2 pulley and at the insertion of the FDS tendon. Excision of the FDS segments in all stages was at full extension of the fingers. Pulleys were not disturbed. The sheath incision was closed with 6-0 sutures (Ethilon 689; Ethicon Inc.) to ensure a smooth gliding floor for the FDP tendon. In the fingers for the test of the work of flexion, the distal interphalangeal, PIP, and MCP joints of the fingers were placed at 0° at the beginning of the test, and the FDP tendons were loaded with 1.0 N preload. With the FDS intact (stage 1), the force and work of the FDP tendon excursion required to flex the fingers completely were determined. In the test the overhead cross-bar secured to the upper clamp was advanced at a constant speed of 25 mm/min. As the proximal stump of the tendon was pulled the finger joints were flexed continuously. Pulling was terminated when the finger pulp entirely touched the palm. During the testing, displacement of the tendons and the force of tendon pulling were measured continuously by the testing machine with a software program (Series IX; Instron Corp.) and the data were stored in computer files. The tendon displacement during finger flexion
Figure 2. Areas of FDS excision in experimental stages. Regions with FDS excision are marked with dark grey.
Tang, Xu, and Chen / Gliding Function of Flexor Tendons
was recorded as the tendon excursion. In the subsequent stages the excursions with the FDS tendon intact were used as the excursion value in tests. The fingers for the test of excursion efficiency were mounted on the board and connected to the testing machine as described earlier. The distal interphalangeal and PIP joints were immobilized in extension by a K-wire along the longitudinal axis of the distal 2 phalanges through the fingertip. In each stage of the FDS excision the MCP joints of the fingers were placed at 0° at the beginning of the test, and the FDP tendons were preloaded and pulled proximally with the method identical to that in the tests described earlier. A large clear plastic goniometer was fixed securely beside the fingers to the board, with the rotation center of the goniometer at the MCP joint motion axis. Pulling on the tendon was terminated when the K-wire through the phalanges overlapped the 90° maker on the goniometer at the stage with FDS tendon intact. During the testing the excursions of the FDP tendons were recorded by the testing machine. With an identical tendon excursion, the joint flexion range was recorded after removal of the FDS tendon in each region.
Data Analysis Work of flexion. The work needed to flex the fingers completely was obtained by calculating the area under the load-displacement curve.19,20 Work of flexion represents the energy consumption during the finger flexion caused by resistance to the FDP excursion, mostly frictional resistance, and viscoelasticity of the sheath and FDS tendon, and joint stiffness. On each data file, the peak force on the load-displacement curve also was recorded as measures of the force resisting tendon gliding.
Excursion efficiency. Excursion efficiency represents the relationship between angular rotation and a fixed tendon excursion for each experimental condition. It indicates ranges of joint angulation produced by a given excursion of a tendon moving the joint. Excursion efficiency can be expressed in another way: as changes in tendon excursions over a fixed range of joint angulation.19 Bowstringing of the tendon after loss of pulleys across the joint decreases the efficiency of tendon excursion.17–20 Removal of the FDS tendon segment palmar to the FDP tendon allows the FDP to move farther away from the joint rotation centers, and theoretically decreases its efficiency. In this study the excursion efficiency was recorded as a percent of the range of joint flexion
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compared with that with intact FDS (90°) with an identical excursion.
Statistical Analysis Data are summarized as means ⫾ SD and were analyzed statistically by one-way analysis of variance for repeated measurements of the same variable. When significant differences were found the 2-tailed paired Student’s t-test was applied to determine the levels of significance between pairs of data with a significant level at p ⬍ .05. In this study the paired t-test was used because variables were measured in the same fingers with or without FDS in the different regions, and the data from the test stages were paired naturally. Individual fingers presented substantial natural variation in the work of flexion and excursion efficiency. To present changes in the variables in results they were normalized by dividing measured values by those before FDS excision in the same fingers to obtain percent changes.
Results Work of Flexion The work of flexion decreased by 6% after excision of the FDS proximal to the A2 pulley and 12% after excision of the FDS under the A2 pulley when compared with the work of flexion with the FDS intact in respective regions (Table 1). The work of flexion decreased significantly after excision of the FDS in the areas proximal to or beneath the A2 pulley (p ⫽ .0002, p ⫽ .001, respectively). The work of flexion of the FDP tendon, however, was almost identical before and after removal of the FDS distal to the A2 pulley. In other words the FDS tendon caused the greatest increase in the work of flexion in the area of the A2 pulley, which was more than twice the increase in that of the FDP tendon proximal to the A2 pulley. The existence of the FDS distal to the pulley did not increase the work (Fig. 3). Further analysis of the peak force during finger flexion revealed the impact of the FDS on the FDP identical to that indicated by the work of flexion (Table 1).
Excursion Efficiency The excursion efficiency of the FDP tendon was 97% after excision of the FDS proximal to the A2 pulley, 91% after excision of the FDS under the A2 pulley, and 90% after FDS excision distally, when compared with that with the FDS intact (Table 1). Excursion efficiency changes significantly after excision of the
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Table 1. Changes in the Work of Flexion, Peak Force, and Excursion Efficiency of the Flexor Digitorum Profundus Tendon After Flexor Digitorum Superficialis Excision in Different Regions of Zone II FDS Tendon
Work of Flexion (%)
Peak Force (%)
Excursion Efficiency (%)
Intact Excision, proximal to A2 pulley Excision, under A2 pulley Excision, distal to A2 pulley
94.1 ⫾ 7.0* 81.9 ⫾ 10.0† 80.0 ⫾ 10.1
95.5 ⫾ 4.2* 84.3 ⫾ 6.1† 82.6 ⫾ 6.3
96.7 ⫾ 4.5 90.5 ⫾ 5.3† 90.1 ⫾ 5.2
Values are means ⫾ SD. Data are percent changes obtained by dividing values of the variables measured after FDS excision by those with intact FDS in the same fingers. Percent changes of these variables in the stage of intact FDS are 100%. *Significantly different from those of the fingers with intact FDS. †Significantly different from those after FDS excision proximal to the pulley.
FDS beneath the A2 pulley (p ⫽ .001), but not after excision of the FDS distal to the A2 pulley.
Discussion The structures of flexor tendons in zone II of the hand are extremely complicated; the presence of rigid, narrow, and segmental pulleys and manifested changes in relative locations of the FDS and FDP are the unique features. Differential strategies and outcomes of the repair among regions of zone II have been explored during recent years,15–17,23,24 which should relate to the anatomy and biomechanics of the tendons in each area of zone II. The work of flexion reflects the ease with which the tendon may glide in the confined fibroosseous tunnel.19 –21 Determination of this variable helps understand tendon interactions in each region of zone II, highlighting the points to be considered in planning surgical treatment. Remarkable differences in the impact of the FDS on the work of flexion were noted between different regions. The FDS tendon under the A2 pulley had the greatest effect on the gliding of the FDP, its removal causing the most pronounced decrease in the work of flexion. The removal of the FDS proximal to the A2 pulley had a smaller effect on the FDP and removal
Figure 3. Changes in the work of flexion of the FDP tendon after excision of the FDS in different regions of zone II.
of the FDS distally had no such effects. The FDS tendon overlapping the A2 pulley apparently is the segment most constricting to the gliding of the FDP tendon and its presence within an intact A2 pulley increases the gliding resistance of the FDP tendon. Removal of the FDS tendon distal to the A2 pulley had no notable effects on the work of flexion, indicating that preservation of the FDS tendon distal to the A2 pulley does not increase the likelihood of constriction of the gliding of the FDP. Vascular supplies from the long vincula of the FDP tendon penetrate the fan-shaped membrane vincula (short vincula) of the FDS tendon.9,25 The fan-shaped vincula insert to a lengthy segment of the FDS tendon distal to the A2 pulley.4 Therefore preservation of the FDS distal to the A2 pulley can favor the nutrition of the FDP but, as revealed by this study, does not increase the gliding resistance. The FDS tendon runs entirely parallel to the FDP in the region proximal to the A2 pulley. The magnitude of the impact of the presence of the FDS tendon proximal to the A2 pulley on gliding resistance was less than half that of the FDS under the pulley. Unlike the FDS tendon in the area of the A2 pulley, which takes the form of a finger trap to constrict or lock the FDP during powerful grip,4,5 the FDS proximal to the A2 pulley provides a smooth gliding surface for the FDP. Considering remarkably lower resistance of this FDS segment on the FDP, we believe that its removal does not add much to reducing the gliding resistance of the FDP in the region proximal to the A2 pulley. Changes in excursion efficiency were limited but were significant after removal of the FDS tendon beneath the A2 pulley (p ⫽ .001). In contrast, removal of the FDS other parts did not alter the efficiency. These findings indicate that the FDS in area IIc—a tendon segment with bifurcation that the FDP tendon glides against—functions as a pulley. This
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Table 2. Summary of Anatomic, Biomechanical, In Vivo Studies, and Clinical Observations Related to Tendons in the Subregions of Zone II Investigations Anatomic* FDS tendon Pulleys Biomechanical FDS tendon† Pulleys
In vivo studies FDS tendon Pulleys
Area of FDS Insertion (Zone IIa) Insertion A4, C2
2 slips dorsal to FDP, with vincula A3, C1
No gliding
Not constrict FDP
Beneath A2 Pulley (Zone IIc)
-
-
Repair (Tang and Shi,15 Britto et al24)
A4 venting (Kwai Ben and Elliot17)
-
Proximal to A2 Pulley (Zone IId)
Bifurcation
Flattened, palmar to FDP
A2, most narrow
A1, PA
Constrict FDP, as a moving pulley A4 release is feasible May incise one pulley Partial release is feasible (Savage27, Tomaino (Tang and Xie,28 Lin (Tang,4 Tomaino et al18) 18 3 et al ) et al )
Clinical options FDS tendon
Pulleys
Distal to A2 Pulley (Zone IIb)
Release favors FDP gliding (Tang et al19)
Little constriction -‡
-
Resection or repair (Tang and Repair both tendons (Tang and Shi15) Shi,15,16 Kwai Ben and 17 29 Elliot, Elliot ) Resection of one slip (Zhao et al14) Partial release (Tang,4 Kwai Ben and Elliot,17 Elliot29) Pulley shortening (partial excision) or plasty (Paillard et al30)
*Anatomic features of the FDS and pulleys are list according to the work by Tang and Shi15,16 †Summarized based on results of the current study. ‡Subjects were not studied or had not been well determined.
tendon segment glides from beneath the A2 pulley and moves across the MCP joint as the finger flexes. We hypothesize that the FDS in zone IIc serves as a moving pulley to fine-tune moment arms and motion arcs of the FDP tendon during finger flexion. The FDS of zone IId locates proximal to the MCP joint and that of zone IIb dorsal to the FDP, thereby having no effect on the excursion efficiency. The most notable FDS and FDP interaction in the A2 pulley area, in contrast to that in the regions distal or proximal to the pulley, coincides with the complexity of the anatomy of the tendon system in this area. The area of the A2 pulley is considered special because of (1) the presence of the longest and most rigid pulley of the finger; (2) the bifurcation of the FDS tendon; (3) the lack of vincula insertion on the tendons and the poorest in vascular perfusion, indicative of bearing a greater compression force4,25; (4) the surrounding of the FDP tendon by the FDS rather than the FDS overlying on the tendon; and (5) its being the narrowest part in zone II.4,16 Several surgical procedures have been proposed to
reduce the constriction of the tendon gliding for zone II flexor tendons. Tang4 proposed either incision of a part of the major pulleys or excision of a part of the FDS under the pulleys. Kwai Ben and Elliot17 released a part of the A2 pulley to allow tendon gliding without compression during the surgery. Strickland26 proposed the release of a part of the sheath or pulleys to place a suture and to eliminate compression to the tendon. Zhao et al14 advocated the excision of a slip of the FDS tendon based on the study of gliding resisting force under the A2 pulley. A decade ago, Tang and Shi15 advocated a clinical treatment– oriented subdivision system of zone II, which divides zone II into 4 regions with characteristics of the FDS and the location of the major pulley (the A2 pulley) as landmarks. This subdivision system takes into consideration the functional impacts of major pulleys and variances of the FDS structures, which were proven in recent studies vital to understanding the tendon function and exploring treatment of zone II flexor tendons.14,18,30 Our study supplemented the previous work on this aspect with clear
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pictures of differential interaction of the FDS with the FDP tendons in subregions of zone II (Table 2). The presence of the FDS leads to only mild increases in resistance to tendon gliding—resulting in less than 18% changes in the force and less than 20% changes in the work—which reflects elegance of nature’s design for smooth movement of both tendons in the narrow tunnel. In the in vitro testing we were unable to evaluate adhesions or healing of the tendons or include tissue edema or reparative reactions in the study. Tissue reactions and adhesions of a traumatized and repaired tendon would potentially add to the other factors, increasing the force and work of tendon gliding. In vivo studies in models of tendon injuries should be performed to elucidate these additional factors. This study provides fundamental insights into the impact of the FDS on function of the FDP in different regions of the complex sheath area and may serve as a basis toward a rationale for treatment of the FDS and the pulley.
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13. Ferlic DC, Clayton ML. Flexor tenosynovectomy in the rheumatoid finger. J Hand Surg 1978;3:364 –367. 14. Zhao C, Amadio PC, Zobitz ME, An K-N. Resection of the flexor digitorum superficialis reduces gliding resistance after zone II flexor digitorum profundus repair in vitro. J Hand Surg 2002;27A:316 –321. 15. Tang JB, Shi D. Subdivision of flexor tendon “no man’s land” and different treatment methods in each sub-zone. Chin Med J 1992;105:60 – 68. 16. Tang JB. Flexor tendon repair in zone 2C. J Hand Surg 1994;19B:72–75. 17. Kwai Ben I, Elliot D. “Venting” or partial lateral release of the A2 and A4 pulleys after repair of zone 2 flexor tendon injuries. J Hand Surg 1998;23B:649 – 654. 18. Tomaino M, Mitsionis G, Basitidas J, Grewal R, Pfaeffle J. The effect of partial excision of the A2 and A4 pulleys on the biomechanics of finger flexion. J Hand Surg 1998;23B:50 – 52. 19. Tang JB, Wang YH, Gu YT, Chen F. Effect of pulley integrity on excursions and work of flexion in healing flexor tendons. J Hand Surg 2001;26A:347–353. 20. Peterson WW, Manske PR, Bollinger BA, Lesker PA, McCarthy JA. Effect of pulley excision on flexor tendon biomechanics. J Orthop Res 1986;4:96 –101. 21. Peterson WW, Manske PR, Dunlap J, Horwitz DS, Kahn B. Effect of various methods of restoring flexor sheath integrity on the formation of adhesions after tendon injury. J Hand Surg 1990;15A:48 –56. 22. Lane JM, Black J, Bora FW Jr. Gliding function following flexor-tendon injury. A biomechanical study of rat tendon function. J Bone Joint Surg 1976;58A:985–989. 23. Harris SB, Harris D, Foster AJ, Elliot D. The aetiology of acute rupture of flexor tendon repair in zones 1 and 2 of the fingers during early mobilization. J Hand Surg 1999;24B: 275–280. 24. Britto JA, Ragoowansi R, Flemming AFS. A novel method for repair of flexor digitorum superficialis lacerations in zone 2. Plast Reconstr Surg 2001;18:456 – 459. 25. Ochiai N, Matsui T, Miyaji N, Merklin RJ, Hunter JM. Vascular anatomy of flexor tendons. I. Vincular system and blood supply of the profundus tendon in the digital sheath. J Hand Surg 1979;4:321–330. 26. Strickland JW. Flexor tendon injuries. Part 2. Flexor tendon repair. Orthop Rev 1986;15:701–721. 27. Savage R. The mechanical effect of partial resection of the digital fibrous flexor sheath. J Hand Surg 1990;15B:435– 442. 28. Tang JB, Xie RG. Effect of A3 pulley and adjacent sheath integrity on tendon excursion and bowstringing. J Hand Surg 2001;26A:855– 861. 29. Elliot D. Primary flexor tendon repair— operative repair, pulley management and rehabilitation. J Hand Surg 2002; 27B:507–513. 30. Paillard PJ, Amadio PC, Zhao C, Zobitz ME, An KN. Pulley plasty versus resection of one slip of the flexor digitorum superficialis after repair of both flexor tendons in zone II. A biomechanical study. J Bone Joint Surg 2002;84A:2039 – 2045.