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Repair of Partial-Thickness Rotator Cuff Tears: A Biomechanical Analysis of Footprint Contact Pressure and Strength in an Ovine Model
Repair of Partial-Thickness Rotator Cuff Tears: A Biomechanical Analysis of Footprint Contact Pressure and Strength in an Ovine Model Karin S. Peters, M.D., Patrick H. Lam, M.Eng.Sc., and George A. C. Murrell, M.D., D.Phil.
Purpose: The purpose of this study was to determine whether transtendon repair by use of a novel small-diameter knotless anchor showed enhanced mechanical properties compared with tear completion and repair. Methods: Articular-sided partial-thickness tears were created ex vivo in the infraspinatus of 24 ovine shoulders. The specimens were randomized into 4 groups of 6 each: (1) no repair, (2) transtendon repair, (3) completion of tear with tension-band single-row repair, and (4) completion of tear with double-row repair. Footprint contact pressure and ultimate load to failure were measured in each specimen. Results: Technical failure of the transtendon anchors occurred in 3 of 15 shoulders. Transtendon repair (mean ⫾ SEM, 0.8 ⫾ 0.1 MPa) and double-row repair (1 ⫾ 0.09 MPa) showed 3-fold (P ⬍ .001) greater footprint contact pressures than tension-band single-row repair (0.3 ⫾ 0.03 MPa) and no repair (0.3 ⫾ 0.02 MPa). The ultimate load to failure for transtendon repair (544 ⫾ 22 N) was more than 3 times greater than that for the double-row repair (157 ⫾ 23 N) (P ⬍ .001) and the single-row repair (116 ⫾ 11 N) (P ⬍ .001). Conclusions: Transtendon repair of partial-thickness tears by use of specifically designed anchors biomechanically outperformed tear completion and repair in an ovine model. Transtendon repair showed the best combination of high footprint contact pressure and high ultimate failure load. However, the high insertion failure rate of these transtendon anchors is of concern. Clinical Relevance: On the basis of the biomechanical data, transtendon repair of partial-thickness rotator cuff tears may be used as an alternative to tear completion and repair, but the specific transtendon anchors used in this study need further evaluation before their clinical use can be recommended.
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artial-thickness tears of the rotator cuff are an important part of the spectrum of rotator cuff pathology and are often symptomatic.1,2 The overall incidence of these tears has been reported to be 13% to 37%.3,4 The pathogenesis of partial-thickness tears is multifactorial, with intrinsic degeneration, extrinsic
From the Orthopaedic Research Institute, St. George Hospital Campus, University of New South Wales, Sydney, Australia. The Orthopaedic Research Institute has received institutional support from ArthroCare, Austin, Texas. The authors report no conflict of interest. Received October 9, 2009; accepted April 6, 2010. Address correspondence and reprint requests to George A. C. Murrell, M.D., D.Phil., Orthopaedic Research Institute, St. George Hospital, 4-10 South Street, Kogarah, NSW 2217, Australia. E-mail: [email protected] © 2010 by the Arthroscopy Association of North America 0749-8063/9604/$36.00 doi:10.1016/j.arthro.2010.04.007
impingement, and trauma/microtrauma thought to play important roles.5-11 Partial-thickness tears can be divided into 3 categories: bursal sided, articular sided, and intratendinous. Articular-sided tears occur most commonly and predominantly affect the supraspinatus tendon.12 Debridement of partial-thickness tears, with or without acromioplasty, has led to satisfactory results in tears extending to less than 50% of the tendon’s thickness.13-16 Results after debridement of tears extending to greater than 50% of the tendon’s thickness are less favorable, and rotator cuff repair has been frequently advocated.1,15,17-19 Traditionally, this would involve completion of the tear to a full-thickness tear and subsequent repair. A drawback of this technique is that intact tendon tissue is sacrificed, whereas if this tissue is left intact, it could add to the strength of repair.20,21 Several authors have addressed this issue,
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describing an arthroscopic transtendon technique for repairing articular-sided tears by which the lateral footprint is kept intact and the medial footprint is repaired.22-25 Recently, new anchors have been developed to facilitate transtendon repair of articular-sided partialthickness tears. The purpose of this study was to determine whether transtendon repair with the use of these anchors had enhanced mechanical properties compared with tear completion and single- or doublerow repair. We hypothesized that transtendon repair would have better footprint contact pressure and a higher failure load than both single- and double-row repairs. METHODS Twenty-four fresh-frozen ovine shoulders were thawed at room temperature and dissected free of soft tissue, with only the humerus, scapula, and infraspinatus tendon and muscle being retained. The infraspinatus tendon was used because of its similarity to the human supraspinatus tendon26 and its reproducible biomechanical properties.27,28 No pre-existing rotator cuff abnormalities were found in any of the specimens. The specimens were divided into 4 groups of 6 shoulders: (1) no repair, (2) transtendon repair, (3) completion of tear with tension-band single-row repair, and (4) completion of tear with double-row repair (Fig 1). With a digital caliper, the medial-lateral and anterior-posterior dimensions of the infraspinatus footprint were measured. The mean anterior-posterior length of the footprint of the specimens used was 18.3 mm (SEM, 0.22 mm), and the mean medial-lateral length was 11.9 mm (SEM, 0.17 mm). By use of these values, articular-sided partial-thickness tears were cre-
ated by sharply excising the entire anterior-posterior width of the tendon off the footprint to 75% of the medial-lateral width of the footprint. We chose 75% to represent a high-grade (⬎50%) partial-thickness tear for which repair is commonly advocated.17,18 The tear size was confirmed by measurement with a digital caliper. The mean medial-lateral length of the tendon tears was 8.9 mm (SEM, 0.15). The center of the created bare medial footprint was determined with a caliper. An 8-mm hole was drilled through the humeral head (bare of soft tissues), perpendicular to and through the center of the footprint, to accommodate a 4.5-mm-diameter metal probe connected to an Instron load cell (Instron, Norwood, MA) (as described in the “Biomechanical Testing” section). An 8-mm hole was chosen to facilitate placement of the 4.5-mm probe without it touching the sides of the hole, causing false readings. The shoulders were then randomized to either no repair or repair (based on a previously generated randomization list) using 1 of the 3 techniques with equal distribution between right and left shoulders. Transtendon Repair Traversing the tendon with the drill bit, we drilled 1.5-mm holes in the anterior and posterior medial footprint, at equal distances from the previously drilled central hole. The TwinLock system (ArthroCare, Austin, TX) was used (Fig 1). This is a knotless anchor system containing two 1.8-mm anchors with a suture connecting them. The anchors were inserted through the tendon into the predrilled holes in the medial footprint. After the bone locks of the anchors were deployed, the suture between the anchors was tensioned with a knotless ratchet system compressing the tendon onto the footprint. The suture was then locked in the anchor and the remaining loose suture tail was trimmed (Fig 2A). Completion of Tear and Tension-Band Single-Row Repair
FIGURE 1. TwinLock anchor system used in transtendon repair and double-row repair. The inset shows the 2 anchors with the bone lock (wings) deployed and the suture in between, which can be tensioned with the ratchet system on the handle.
The tear was completed to a full-thickness tear by releasing the rest of the tendon off the lateral footprint. Two sutures were passed in a horizontal mattress configuration through the tendon with a suture passer (SmartStitch PerfectPasser; ArthroCare). Two 3-mm holes were drilled in the lateral footprint, each 5 mm from and at a 40° angle to the previously drilled central hole in the footprint. One of the sutures was passed through an anchor (OPUS Magnum-2 knotless anchor; ArthroCare), and the anchor was inserted in
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FIGURE 2. Three repair techniques used: (A) in situ transtendon repair, (B) completion of tear with single-row tensionband repair, and (C) completion of tear with double-row repair.
the predrilled hole. The bone lock was engaged, and the suture was then tensioned with a ratchet system, after which the suture lock was deployed. This was repeated for the second suture and anchor (Fig 2B). Completion of Tear and Double-Row Repair After completion of the tear, 2 anchors with tension-band sutures were used for the lateral row, and TwinLock anchors were used for the medial row by the same techniques as described previously (Fig 2C). Biomechanical Testing Footprint Contact Pressure: We used a technique developed at our institution to quantitatively measure the compressive force at the footprint insertion site.29 A 4.5-mm-diameter metal probe connected to an Instron load cell was passed through the previously drilled 8-mm hole in the footprint and positioned 1.7 mm proud to the footprint (Fig 3). The load cell was then calibrated and zeroed. The infraspinatus tendons were repaired over the probe by use of 1 of the 3 techniques described previously. A multidirectional vice clamp with tilting function and its supporting column were used to position and secure the humerus. A counterbalance hook connected to the humerus was used to neutralize the load experienced by the humerus while loading the tendon. A column with a pulley and markings was used for testing at varying abduction angles. Each specimen was preloaded for 1 minute with 10 N after repair. Footprint contact pressures were measured at 0°, 15°, and 30° of abduction in each group. At each abduction angle, 3 different loads (10, 20, and 30 N) were used to distract the tendon.
Pull to Failure: Upon completion of contact pressure tests, each specimen was labeled and stored at ⫺20°C before pull-to-failure testing. The specimens were thawed at room temperature and kept moist in gauze soaked in normal saline solution. Pull-to-failure testing was performed with a mechanical tensile testing machine (Instron 8874). The humerus was secured to the baseplate with an 8-mm bolt. The baseplate was mounted to the tensile tester with an industrial vice. The repaired infraspinatus tendon was secured in a tendon-grasping clamp. The repair was tested in tension with the direction of pull 90° to the shaft of the humerus, simulating the position of the patient’s arm at the side. The specimens were preloaded with 10 N for 30 seconds; the tendon was then pulled at 1.25
FIGURE 3. Diagram of experimental setup for measurement of footprint contact pressures.
0.66 ⫾ 0.10 0.78 ⫾ 0.10 0.87 ⫾ 0.10 0.53 ⫾ 0.10 0.57 ⫾ 0.09 0.60 ⫾ 0.08 0.47 ⫾ 0.10 0.48 ⫾ 0.08 0.46 ⫾ 0.08 0.2 ⫾ 0.01 0.30 ⫾ 0.02 0.40 ⫾ 0.03 0.08 ⫾ 0.01 0.13 ⫾ 0.01 0.17 ⫾ 0.02 0.05 ⫾ 0.00 0.06 ⫾ 0.01 0.07 ⫾ 0.01 30°
15°
10 N 20 N 30 N 10 N 20 N 30 N 10 N 20 N 30 N 0°
NOTE. Values are expressed as mean ⫾ SEM; comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method. Abbreviation: NS, no significance.
P P P P P P P P P NS NS NS NS NS NS NS NS NS ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P NS NS NS NS NS NS NS P ⬍ .05 P ⬍ .05 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P 0.80 ⫾ 0.08 1.00 ⫾ 0.09 1.13 ⫾ 0.09 0.68 ⫾ 0.08 0.76 ⫾ 0.08 0.81 ⫾ 0.09 0.61 ⫾ 0.08 0.63 ⫾ 0.08 0.61 ⫾ 0.09
No Repair v Double Row No Repair v Single Row No Repair v Transtendon Repair Double-Row Repair (MPa) Single-Row Repair (MPa) No Repair (MPa)
Transtendon repair (mean ⫾ SEM at a 20-N load, 0.8 ⫾ 0.1 MPa) and double-row repair (1 ⫾ 0.09 MPa) showed significantly (P ⬍ .001) higher footprint contact pressures than single-row repair (0.3 ⫾ 0.03 MPa) and no repair (0.3 ⫾ 0.02 MPa) at all abduction angles (Table 1, Fig 4). There were no significant differences in footprint contact pressure between transtendon repair and double-row repair, except at 0° and 15° of abduction with 30 N of tension across the tendon, in favor of double-row repair (P ⬍ .05) (Table 1, Fig 5). There were no significant differences in footprint contact pressures between singlerow repair and no repair (Table 1).
Abduction Angle
Footprint Contact Pressure
Transtendon Repair (MPa)
Technical failure of the TwinLock transtendon anchors occurred in 3 of the initial 12 shoulders that were repaired with TwinLock anchors. In 2 instances an anchor pulled out while the suture was being tightened, and in 1 instance the suture lock failed to fire. These 3 shoulders were excluded, and 3 extra shoulders were repaired and included in the study. There were 6 shoulders in each of the 4 groups.
Comparison of Footprint Contact Pressures
RESULTS
TABLE 1.
A sample size calculation was performed by use of the SD (0.02 MPa) from data collected previously for the single-row tension-band repair at 0° of abduction and a 20-N load at our institution.29 A difference in contact pressure of 0.06 MPa between the transtendon repair and single- and double-row repair was considered relevant33; this would indicate a 2-fold increase in footprint contact pressure from single-row repair29 to transtendon repair. With ␣ equaling 0.05 and power equaling 0.80, at least 4 specimens per group were needed based on a 1-way analysis of variance sample size calculation. Differences in footprint contact pressures and load to failure were analyzed by 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method. The level of statistical significance was defined as P ⬍ .05.
Transtendon v Single Row
Statistical Analysis
0.19 ⫾ 0.02 0.30 ⫾ 0.03 0.41 ⫾ 0.04 0.11 ⫾ 0.01 0.16 ⫾ 0.02 0.23 ⫾ 0.02 0.06 ⫾ 0.01 0.09 ⫾ 0.01 0.12 ⫾ 0.02
Transtendon v Double Row
Single Row v Double Row
mm/s to failure with the data captured at 100 Hz on a computer. The velocity of 1.25 mm/s was chosen based on previously used rates in the literature.30-32 The mode of failure was recorded for each shoulder with a charge-coupled device camera.
⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001
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Load Across Tendon
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FIGURE 4. Footprint contact pressures (mean and SEM) with 20-N load placed across tendon at varying abduction angles. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
Footprint contact pressures decreased in all groups with increasing abduction angle. With a 20-N load across the tendon, the mean footprint contact pressure decreased from 0.8 MPa (0° of abduction) to 0.5 MPa (30° of abduction) for transtendon repair, from 0.3 MPa to 0.1 MPa for single-row repair, from 1.0 MPa to 0.6 MPa for double-row repair, and from 0.3 MPa to 0.1 MPa for no repair (Fig 4). In all repairs the footprint contact pressure increased with increasing load placed on the tendon at 0° and 15° of abduction (Fig 5). At 30° of abduction,
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FIGURE 6. Footprint contact pressures (mean and SEM) at 30° of abduction with various loads placed across tendon. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair at all loads (P ⬍ .001). Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
footprint contact pressures continued to increase in the single-row group with increasing loads placed across the tendon but not in the transtendon and double-row groups (Fig 6). Ultimate Failure The ultimate loads to failure for transtendon repair (544 ⫾ 22 N) and no repair (532 ⫾ 24 N) were significantly higher than those for double-row repair (157 ⫾ 23 N) (P ⬍ .001) and single-row repair (116 ⫾ 11 N) (P ⬍ .001) (Fig 7). In the single- and double-row repair groups, the mode of failure was the sutures pulling through the tendon in all cases. In the transtendon repair group and no-repair group, the mode of failure was midsubstance tendon failure in all cases (the footprint remained intact). DISCUSSION
FIGURE 5. Footprint contact pressures (mean and SEM) at 0° of abduction with various loads placed across tendon. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair at all loads and between double-row repair and transtendon repair (P ⬍ .05) at 30 N. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
The purpose of this study was to compare the biomechanical properties of transtendon repair of articular-sided partial-thickness tears by use of specifically designed anchors with tear completion and repair. Our first hypothesis was that transtendon repair would have a higher footprint contact pressure than tear completion and repair. This was true when compared with single-row repair. However, we found no difference compared with double-row repair. Our second hypothesis was that ultimate failure load would be higher with transtendon repair compared with tear
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FIGURE 7. Ultimate load to failure (mean and SEM). Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
completion and repair. We found this hypothesis to be true with a significantly higher ultimate failure load for transtendon repair compared with both single- and double-row repairs. Two other biomechanical studies have evaluated transtendon fixation. Mazzocca et al.34 looked at strain patterns of the supraspinatus tendon with the creation of articular-sided partial-thickness tears and the effect of the repair in cadaveric shoulders. They found a significant difference in rotator cuff strain between the intact rotator cuff tendon and partial-thickness tears comprising 50% and 75% of the tendon thickness. The cuff strain returned to the intact state with in situ transtendon repair by use of a parachute or metal corkscrew anchor. Gonzalez-Lomas et al.35 studied gap formation and ultimate failure strength of transtendon repair compared with tear completion and double-row repair in articular-sided partial-thickness tears comprising 50% of the tendon thickness in cadaveric shoulders. The transtendon repair had significantly less gapping and higher mean ultimate failure load than the double-row repair. The ultimate failure loads they found in cadaveric shoulders were comparable to the ultimate failure loads we found in ovine shoulders (485 ⫾ 160 N for transtendon repair and 246 ⫾ 29 N for double-row repair). Both these studies support an in situ transtendon repair with high ultimate failure load, little gapping, and small strain. We focused on footprint contact pressure, because it is likely another important factor for the healing potential of rotator cuff repairs. A number of studies have shown that pressure between tendon and bone can be beneficial for healing.36-39 To our knowledge, this is the first study looking at footprint contact
pressures for transtendon repair. There have, however, been other studies assessing footprint contact pressures for full-thickness tear repair techniques.33,40-42 In a recent study, Park et al.42 found a decrease in footprint contact pressure with increasing abduction angles. We also found this decrease in contact pressure with increasing abduction. In addition, we found increasing footprint contact pressures with increasing loads placed across the tendon. These findings may be of interest when deciding whether to give a patient an abduction pillow postoperatively. In our study failure of the transtendon anchors occurred in 3 of 15 cases. In 2 cases an anchor pulled out while the suture was being tensioned. A possible explanation for this might be the use of ovine shoulders. Ovine bone is typically denser than human bone, which might prevent the wings of the anchor from expanding fully when the bone lock is being deployed, thus leading to a decrease in fixation strength. Studies in human shoulders are needed to evaluate this further before we can recommend the transtendon anchors for clinical use. Several limitations of this study must be considered. First, ovine shoulders were used because of the similarity of the infraspinatus tendon to the human supraspinatus tendon,26 as well as their easy access and reproducible biomechanical properties.27,28 Human cadaveric shoulders would better represent the clinical population. Our load-to-failure test data show that having remaining cuff tissue at the footprint leads to a significantly higher ultimate failure load than conversion to a full-thickness tear and repair. However, this ultimate failure load may be overestimated in an ovine model with a non-tendinopathic infraspinatus. The
PARTIAL-THICKNESS ROTATOR CUFF TEAR REPAIR tendon fibers of the ovine infraspinatus are, however, more parallel compared with the human supraspinatus and thus may fail at a lower load than the human supraspinatus tendon. Second, this is an ex vivo study, which does not give information on healing biology and only measures initial contact pressure. The pressure characteristics may change after motion at the repair site. Although we did preload the specimens, cyclical loading may have been better able to evaluate this. Third, repairs done in a laboratory after softtissue stripping are generally easier to perform than arthroscopic repairs. The transtendon anchors were relatively easy to use in this setting but may not necessarily be so in vivo. Lastly, we evaluated both transtendon repair and a new anchor system. This reduces the ability to determine the effect that each variable (repair type and anchor system) has on the result. To dynamically measure footprint contact pressure, we used a metal probe inserted through the footprint and connected to a load cell. Other studies have used pressure-sensitive film or Tekscan pressure sensors to measure contact pressure in rotator cuff repairs.33,40-42 Pressure-sensitive film can only be used once to measure maximum applied pressure. An advantage of our setup is that footprint contact pressure can be measured dynamically with different loads and angle variations. Tekscan pressure sensors (Tekscan, Boston, MA) can also measure dynamic pressure changes on the footprint, but the rigid surface of the sensor mesh may create uneven loading conditions on the convex footprint. A disadvantage of our setup is that pressure is measured over only a small area of the footprint, and the total footprint contact area cannot be calculated. Transtendon repair avoids the need to complete the tear, leaving the lateral footprint intact. This has the potential advantages of increased repair strength and a better chance of re-creating the original footprint without length-tension mismatch. A potential drawback of transtendon repair is that the intact tendon at the lateral footprint is likely to be tendinopathic, which might compromise strength and make the repair more susceptible to retear. Furthermore, passage of a drill or bone punch and insertion of the anchors through the cuff might damage the intact cuff. The transtendon anchors we tested in this study have a diameter of only 1.8 mm, compared with the 4.5- to 5.5-mm anchors previously described for transtendon techniques. Damage to the tendon did not seem to be an important factor in our study, with ultimate failure occurring at the midsubstance and not at the footprint. Another
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potential drawback of transtendon repair is that the pressure created by the tensioned suture on top of the tendon may strangulate the tendon, compromising vascularity, which could hinder the healing process. On the other hand, most of the blood supply to the supraspinatus comes from the bursal side of the tendon43; thus, by keeping the bursal side intact, the vascularity may be preserved. In vivo studies are needed to evaluate these and other potential factors to optimize the healing environment. CONCLUSIONS Transtendon repair of partial-thickness tears using specifically designed anchors biomechanically outperformed tear completion and repair in an ovine model. Transtendon repair showed the best combination of high footprint contact pressure and high ultimate failure load. However, the high insertion failure rate of these transtendon anchors is of concern. REFERENCES 1. Ellman H. Diagnosis and treatment of incomplete rotator cuff tears. Clin Orthop Relat Res 1990:64-74. 2. Matava MJ, Purcell DB, Rudzki JR. Partial-thickness rotator cuff tears. Am J Sports Med 2005;33:1405-1417. 3. Fukuda H, Mikasa M, Yamanaka K. Incomplete thickness rotator cuff tears diagnosed by subacromial bursography. Clin Orthop Relat Res 1987:51-58. 4. Uhthoff HK, Sano H. Pathology of failure of the rotator cuff tendon. Orthop Clin North Am 1997;28:31-41. 5. Gotoh M, Hamada K, Yamakawa H, Tomonaga A, Inoue A, Fukuda H. Significance of granulation tissue in torn supraspinatus insertions: An immunohistochemical study with antibodies against interleukin-1 beta, cathepsin D, and matrix metalloprotease-1. J Orthop Res 1997;15:33-39. 6. Ogata S, Uhthoff HK. Acromial enthesopathy and rotator cuff tear. A radiologic and histologic postmortem investigation of the coracoacromial arch. Clin Orthop Relat Res 1990:39-48. 7. Ozaki J, Fujimoto S, Nakagawa Y, Masuhara K, Tamai S. Tears of the rotator cuff of the shoulder associated with pathological changes in the acromion. A study in cadavera. J Bone Joint Surg Am 1988;70:1224-1230. 8. Neer CS II. Impingement lesions. Clin Orthop Relat Res 1983:70-77. 9. Neer CS II. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: A preliminary report. J Bone Joint Surg Am 1972;54:41-50. 10. Sano H, Ishii H, Yeadon A, Backman DS, Brunet JA, Uhthoff HK. Degeneration at the insertion weakens the tensile strength of the supraspinatus tendon: A comparative mechanical and histologic study of the bone-tendon complex. J Orthop Res 1997;15:719-726. 11. Uhthoff HK, Hammond DI, Sarkar K, Hooper GJ, Papoff WJ. The role of the coracoacromial ligament in the impingement syndrome. A clinical, radiological and histological study. Int Orthop 1988;12:97-104. 12. Fukuda H. The management of partial-thickness tears of the rotator cuff. J Bone Joint Surg Br 2003;85:3-11.
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repair in comparison to double-row repair with consideration of the suture configuration and suture material. Knee Surg Sports Traumatol Arthrosc 2008;16:1052-1060. Golish SR, Caldwell III PE, Miller MD, et al. Interference screw versus suture anchor fixation for subpectoral tenodesis of the proximal biceps tendon. Arthroscopy 2008;24:11031108. Hepp P, Osterhoff G, Engel T, Marquass B, Klink T, Josten C. Biomechanical evaluation of knotless anatomical double-layer double-row rotator cuff repair: A comparative ex vivo study. Am J Sports Med 2009;37:1363-1369. Park MC, ElAttrache NS, Tibone JE, Ahmad CS, Jun BJ, Lee TQ. Part I: Footprint contact characteristics for a transosseousequivalent rotator cuff repair technique compared with a double-row repair technique. J Shoulder Elbow Surg 2007;16: 461-468. Mazzocca AD, Rincon LM, O’Connor RW, et al. Intra-articular partial-thickness rotator cuff tears: Analysis of injured and repaired strain behavior. Am J Sports Med 2008;36:110-116. Gonzalez-Lomas G, Kippe MA, Brown GD, et al. In situ transtendon repair outperforms tear completion and repair for partial articular-sided supraspinatus tendon tears. J Shoulder Elbow Surg 2008;17:722-728. Goradia VK, Rochat MC, Kida M, Grana WA. Natural history of a hamstring tendon autograft used for anterior cruciate ligament reconstruction in a sheep model. Am J Sports Med 2000;28:40-46. Pinczewski LA, Clingeleffer AJ, Otto DD, Bonar SF, Corry IS. Integration of hamstring tendon graft with bone in reconstruction of the anterior cruciate ligament. Arthroscopy 1997;13: 641-643. Rodeo SA, Arnoczky SP, Torzilli PA, Hidaka C, Warren RF. Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog. J Bone Joint Surg Am 1993;75:17951803. Weiler A, Peine R, Pashmineh-Azar A, Abel C, Sudkamp NP, Hoffmann RF. Tendon healing in a bone tunnel. Part I: Biomechanical results after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep. Arthroscopy 2002;18:113-123. Baums MH, Spahn G, Steckel H, Fischer A, Schultz W, Klinger HM. Comparative evaluation of the tendon-bone interface contact pressure in different single- versus double-row suture anchor repair techniques. Knee Surg Sports Traumatol Arthrosc 2009;17:1466-1472. Park MC, Cadet ER, Levine WN, Bigliani LU, Ahmad CS. Tendon-to-bone pressure distributions at a repaired rotator cuff footprint using transosseous suture and suture anchor fixation techniques. Am J Sports Med 2005;33:1154-1159. Park MC, Pirolo JM, Park CJ, Tibone JE, McGarry MH, Lee TQ. The effect of abduction and rotation on footprint contact for single-row, double-row, and modified double-row rotator cuff repair techniques. Am J Sports Med 2009;37:1599-1608. Lohr JF, Uhthoff HK. The microvascular pattern of the supraspinatus tendon. Clin Orthop Relat Res 1990:35-38.
Purpose: The purpose of this study was to determine whether transtendon repair by use of a novel small-diameter knotless anchor showed enhanced mechanical properties compared with tear completion and repair. Methods: Articular-sided partial-thickness tears were created ex vivo in the infraspinatus of 24 ovine shoulders. The specimens were randomized into 4 groups of 6 each: (1) no repair, (2) transtendon repair, (3) completion of tear with tension-band single-row repair, and (4) completion of tear with double-row repair. Footprint contact pressure and ultimate load to failure were measured in each specimen. Results: Technical failure of the transtendon anchors occurred in 3 of 15 shoulders. Transtendon repair (mean ⫾ SEM, 0.8 ⫾ 0.1 MPa) and double-row repair (1 ⫾ 0.09 MPa) showed 3-fold (P ⬍ .001) greater footprint contact pressures than tension-band single-row repair (0.3 ⫾ 0.03 MPa) and no repair (0.3 ⫾ 0.02 MPa). The ultimate load to failure for transtendon repair (544 ⫾ 22 N) was more than 3 times greater than that for the double-row repair (157 ⫾ 23 N) (P ⬍ .001) and the single-row repair (116 ⫾ 11 N) (P ⬍ .001). Conclusions: Transtendon repair of partial-thickness tears by use of specifically designed anchors biomechanically outperformed tear completion and repair in an ovine model. Transtendon repair showed the best combination of high footprint contact pressure and high ultimate failure load. However, the high insertion failure rate of these transtendon anchors is of concern. Clinical Relevance: On the basis of the biomechanical data, transtendon repair of partial-thickness rotator cuff tears may be used as an alternative to tear completion and repair, but the specific transtendon anchors used in this study need further evaluation before their clinical use can be recommended.
P
artial-thickness tears of the rotator cuff are an important part of the spectrum of rotator cuff pathology and are often symptomatic.1,2 The overall incidence of these tears has been reported to be 13% to 37%.3,4 The pathogenesis of partial-thickness tears is multifactorial, with intrinsic degeneration, extrinsic
From the Orthopaedic Research Institute, St. George Hospital Campus, University of New South Wales, Sydney, Australia. The Orthopaedic Research Institute has received institutional support from ArthroCare, Austin, Texas. The authors report no conflict of interest. Received October 9, 2009; accepted April 6, 2010. Address correspondence and reprint requests to George A. C. Murrell, M.D., D.Phil., Orthopaedic Research Institute, St. George Hospital, 4-10 South Street, Kogarah, NSW 2217, Australia. E-mail: [email protected] © 2010 by the Arthroscopy Association of North America 0749-8063/9604/$36.00 doi:10.1016/j.arthro.2010.04.007
impingement, and trauma/microtrauma thought to play important roles.5-11 Partial-thickness tears can be divided into 3 categories: bursal sided, articular sided, and intratendinous. Articular-sided tears occur most commonly and predominantly affect the supraspinatus tendon.12 Debridement of partial-thickness tears, with or without acromioplasty, has led to satisfactory results in tears extending to less than 50% of the tendon’s thickness.13-16 Results after debridement of tears extending to greater than 50% of the tendon’s thickness are less favorable, and rotator cuff repair has been frequently advocated.1,15,17-19 Traditionally, this would involve completion of the tear to a full-thickness tear and subsequent repair. A drawback of this technique is that intact tendon tissue is sacrificed, whereas if this tissue is left intact, it could add to the strength of repair.20,21 Several authors have addressed this issue,
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describing an arthroscopic transtendon technique for repairing articular-sided tears by which the lateral footprint is kept intact and the medial footprint is repaired.22-25 Recently, new anchors have been developed to facilitate transtendon repair of articular-sided partialthickness tears. The purpose of this study was to determine whether transtendon repair with the use of these anchors had enhanced mechanical properties compared with tear completion and single- or doublerow repair. We hypothesized that transtendon repair would have better footprint contact pressure and a higher failure load than both single- and double-row repairs. METHODS Twenty-four fresh-frozen ovine shoulders were thawed at room temperature and dissected free of soft tissue, with only the humerus, scapula, and infraspinatus tendon and muscle being retained. The infraspinatus tendon was used because of its similarity to the human supraspinatus tendon26 and its reproducible biomechanical properties.27,28 No pre-existing rotator cuff abnormalities were found in any of the specimens. The specimens were divided into 4 groups of 6 shoulders: (1) no repair, (2) transtendon repair, (3) completion of tear with tension-band single-row repair, and (4) completion of tear with double-row repair (Fig 1). With a digital caliper, the medial-lateral and anterior-posterior dimensions of the infraspinatus footprint were measured. The mean anterior-posterior length of the footprint of the specimens used was 18.3 mm (SEM, 0.22 mm), and the mean medial-lateral length was 11.9 mm (SEM, 0.17 mm). By use of these values, articular-sided partial-thickness tears were cre-
ated by sharply excising the entire anterior-posterior width of the tendon off the footprint to 75% of the medial-lateral width of the footprint. We chose 75% to represent a high-grade (⬎50%) partial-thickness tear for which repair is commonly advocated.17,18 The tear size was confirmed by measurement with a digital caliper. The mean medial-lateral length of the tendon tears was 8.9 mm (SEM, 0.15). The center of the created bare medial footprint was determined with a caliper. An 8-mm hole was drilled through the humeral head (bare of soft tissues), perpendicular to and through the center of the footprint, to accommodate a 4.5-mm-diameter metal probe connected to an Instron load cell (Instron, Norwood, MA) (as described in the “Biomechanical Testing” section). An 8-mm hole was chosen to facilitate placement of the 4.5-mm probe without it touching the sides of the hole, causing false readings. The shoulders were then randomized to either no repair or repair (based on a previously generated randomization list) using 1 of the 3 techniques with equal distribution between right and left shoulders. Transtendon Repair Traversing the tendon with the drill bit, we drilled 1.5-mm holes in the anterior and posterior medial footprint, at equal distances from the previously drilled central hole. The TwinLock system (ArthroCare, Austin, TX) was used (Fig 1). This is a knotless anchor system containing two 1.8-mm anchors with a suture connecting them. The anchors were inserted through the tendon into the predrilled holes in the medial footprint. After the bone locks of the anchors were deployed, the suture between the anchors was tensioned with a knotless ratchet system compressing the tendon onto the footprint. The suture was then locked in the anchor and the remaining loose suture tail was trimmed (Fig 2A). Completion of Tear and Tension-Band Single-Row Repair
FIGURE 1. TwinLock anchor system used in transtendon repair and double-row repair. The inset shows the 2 anchors with the bone lock (wings) deployed and the suture in between, which can be tensioned with the ratchet system on the handle.
The tear was completed to a full-thickness tear by releasing the rest of the tendon off the lateral footprint. Two sutures were passed in a horizontal mattress configuration through the tendon with a suture passer (SmartStitch PerfectPasser; ArthroCare). Two 3-mm holes were drilled in the lateral footprint, each 5 mm from and at a 40° angle to the previously drilled central hole in the footprint. One of the sutures was passed through an anchor (OPUS Magnum-2 knotless anchor; ArthroCare), and the anchor was inserted in
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FIGURE 2. Three repair techniques used: (A) in situ transtendon repair, (B) completion of tear with single-row tensionband repair, and (C) completion of tear with double-row repair.
the predrilled hole. The bone lock was engaged, and the suture was then tensioned with a ratchet system, after which the suture lock was deployed. This was repeated for the second suture and anchor (Fig 2B). Completion of Tear and Double-Row Repair After completion of the tear, 2 anchors with tension-band sutures were used for the lateral row, and TwinLock anchors were used for the medial row by the same techniques as described previously (Fig 2C). Biomechanical Testing Footprint Contact Pressure: We used a technique developed at our institution to quantitatively measure the compressive force at the footprint insertion site.29 A 4.5-mm-diameter metal probe connected to an Instron load cell was passed through the previously drilled 8-mm hole in the footprint and positioned 1.7 mm proud to the footprint (Fig 3). The load cell was then calibrated and zeroed. The infraspinatus tendons were repaired over the probe by use of 1 of the 3 techniques described previously. A multidirectional vice clamp with tilting function and its supporting column were used to position and secure the humerus. A counterbalance hook connected to the humerus was used to neutralize the load experienced by the humerus while loading the tendon. A column with a pulley and markings was used for testing at varying abduction angles. Each specimen was preloaded for 1 minute with 10 N after repair. Footprint contact pressures were measured at 0°, 15°, and 30° of abduction in each group. At each abduction angle, 3 different loads (10, 20, and 30 N) were used to distract the tendon.
Pull to Failure: Upon completion of contact pressure tests, each specimen was labeled and stored at ⫺20°C before pull-to-failure testing. The specimens were thawed at room temperature and kept moist in gauze soaked in normal saline solution. Pull-to-failure testing was performed with a mechanical tensile testing machine (Instron 8874). The humerus was secured to the baseplate with an 8-mm bolt. The baseplate was mounted to the tensile tester with an industrial vice. The repaired infraspinatus tendon was secured in a tendon-grasping clamp. The repair was tested in tension with the direction of pull 90° to the shaft of the humerus, simulating the position of the patient’s arm at the side. The specimens were preloaded with 10 N for 30 seconds; the tendon was then pulled at 1.25
FIGURE 3. Diagram of experimental setup for measurement of footprint contact pressures.
0.66 ⫾ 0.10 0.78 ⫾ 0.10 0.87 ⫾ 0.10 0.53 ⫾ 0.10 0.57 ⫾ 0.09 0.60 ⫾ 0.08 0.47 ⫾ 0.10 0.48 ⫾ 0.08 0.46 ⫾ 0.08 0.2 ⫾ 0.01 0.30 ⫾ 0.02 0.40 ⫾ 0.03 0.08 ⫾ 0.01 0.13 ⫾ 0.01 0.17 ⫾ 0.02 0.05 ⫾ 0.00 0.06 ⫾ 0.01 0.07 ⫾ 0.01 30°
15°
10 N 20 N 30 N 10 N 20 N 30 N 10 N 20 N 30 N 0°
NOTE. Values are expressed as mean ⫾ SEM; comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method. Abbreviation: NS, no significance.
P P P P P P P P P NS NS NS NS NS NS NS NS NS ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P NS NS NS NS NS NS NS P ⬍ .05 P ⬍ .05 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 P P P P P P P P P 0.80 ⫾ 0.08 1.00 ⫾ 0.09 1.13 ⫾ 0.09 0.68 ⫾ 0.08 0.76 ⫾ 0.08 0.81 ⫾ 0.09 0.61 ⫾ 0.08 0.63 ⫾ 0.08 0.61 ⫾ 0.09
No Repair v Double Row No Repair v Single Row No Repair v Transtendon Repair Double-Row Repair (MPa) Single-Row Repair (MPa) No Repair (MPa)
Transtendon repair (mean ⫾ SEM at a 20-N load, 0.8 ⫾ 0.1 MPa) and double-row repair (1 ⫾ 0.09 MPa) showed significantly (P ⬍ .001) higher footprint contact pressures than single-row repair (0.3 ⫾ 0.03 MPa) and no repair (0.3 ⫾ 0.02 MPa) at all abduction angles (Table 1, Fig 4). There were no significant differences in footprint contact pressure between transtendon repair and double-row repair, except at 0° and 15° of abduction with 30 N of tension across the tendon, in favor of double-row repair (P ⬍ .05) (Table 1, Fig 5). There were no significant differences in footprint contact pressures between singlerow repair and no repair (Table 1).
Abduction Angle
Footprint Contact Pressure
Transtendon Repair (MPa)
Technical failure of the TwinLock transtendon anchors occurred in 3 of the initial 12 shoulders that were repaired with TwinLock anchors. In 2 instances an anchor pulled out while the suture was being tightened, and in 1 instance the suture lock failed to fire. These 3 shoulders were excluded, and 3 extra shoulders were repaired and included in the study. There were 6 shoulders in each of the 4 groups.
Comparison of Footprint Contact Pressures
RESULTS
TABLE 1.
A sample size calculation was performed by use of the SD (0.02 MPa) from data collected previously for the single-row tension-band repair at 0° of abduction and a 20-N load at our institution.29 A difference in contact pressure of 0.06 MPa between the transtendon repair and single- and double-row repair was considered relevant33; this would indicate a 2-fold increase in footprint contact pressure from single-row repair29 to transtendon repair. With ␣ equaling 0.05 and power equaling 0.80, at least 4 specimens per group were needed based on a 1-way analysis of variance sample size calculation. Differences in footprint contact pressures and load to failure were analyzed by 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method. The level of statistical significance was defined as P ⬍ .05.
Transtendon v Single Row
Statistical Analysis
0.19 ⫾ 0.02 0.30 ⫾ 0.03 0.41 ⫾ 0.04 0.11 ⫾ 0.01 0.16 ⫾ 0.02 0.23 ⫾ 0.02 0.06 ⫾ 0.01 0.09 ⫾ 0.01 0.12 ⫾ 0.02
Transtendon v Double Row
Single Row v Double Row
mm/s to failure with the data captured at 100 Hz on a computer. The velocity of 1.25 mm/s was chosen based on previously used rates in the literature.30-32 The mode of failure was recorded for each shoulder with a charge-coupled device camera.
⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001 ⬍ .001
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FIGURE 4. Footprint contact pressures (mean and SEM) with 20-N load placed across tendon at varying abduction angles. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
Footprint contact pressures decreased in all groups with increasing abduction angle. With a 20-N load across the tendon, the mean footprint contact pressure decreased from 0.8 MPa (0° of abduction) to 0.5 MPa (30° of abduction) for transtendon repair, from 0.3 MPa to 0.1 MPa for single-row repair, from 1.0 MPa to 0.6 MPa for double-row repair, and from 0.3 MPa to 0.1 MPa for no repair (Fig 4). In all repairs the footprint contact pressure increased with increasing load placed on the tendon at 0° and 15° of abduction (Fig 5). At 30° of abduction,
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FIGURE 6. Footprint contact pressures (mean and SEM) at 30° of abduction with various loads placed across tendon. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair at all loads (P ⬍ .001). Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
footprint contact pressures continued to increase in the single-row group with increasing loads placed across the tendon but not in the transtendon and double-row groups (Fig 6). Ultimate Failure The ultimate loads to failure for transtendon repair (544 ⫾ 22 N) and no repair (532 ⫾ 24 N) were significantly higher than those for double-row repair (157 ⫾ 23 N) (P ⬍ .001) and single-row repair (116 ⫾ 11 N) (P ⬍ .001) (Fig 7). In the single- and double-row repair groups, the mode of failure was the sutures pulling through the tendon in all cases. In the transtendon repair group and no-repair group, the mode of failure was midsubstance tendon failure in all cases (the footprint remained intact). DISCUSSION
FIGURE 5. Footprint contact pressures (mean and SEM) at 0° of abduction with various loads placed across tendon. Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair at all loads and between double-row repair and transtendon repair (P ⬍ .05) at 30 N. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
The purpose of this study was to compare the biomechanical properties of transtendon repair of articular-sided partial-thickness tears by use of specifically designed anchors with tear completion and repair. Our first hypothesis was that transtendon repair would have a higher footprint contact pressure than tear completion and repair. This was true when compared with single-row repair. However, we found no difference compared with double-row repair. Our second hypothesis was that ultimate failure load would be higher with transtendon repair compared with tear
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FIGURE 7. Ultimate load to failure (mean and SEM). Significant differences are shown between no repair and single-row repair versus transtendon repair and double-row repair. Comparisons between groups were performed with 1-way analysis of variance with correction for multiple comparisons by the Holm-Sidak method.
completion and repair. We found this hypothesis to be true with a significantly higher ultimate failure load for transtendon repair compared with both single- and double-row repairs. Two other biomechanical studies have evaluated transtendon fixation. Mazzocca et al.34 looked at strain patterns of the supraspinatus tendon with the creation of articular-sided partial-thickness tears and the effect of the repair in cadaveric shoulders. They found a significant difference in rotator cuff strain between the intact rotator cuff tendon and partial-thickness tears comprising 50% and 75% of the tendon thickness. The cuff strain returned to the intact state with in situ transtendon repair by use of a parachute or metal corkscrew anchor. Gonzalez-Lomas et al.35 studied gap formation and ultimate failure strength of transtendon repair compared with tear completion and double-row repair in articular-sided partial-thickness tears comprising 50% of the tendon thickness in cadaveric shoulders. The transtendon repair had significantly less gapping and higher mean ultimate failure load than the double-row repair. The ultimate failure loads they found in cadaveric shoulders were comparable to the ultimate failure loads we found in ovine shoulders (485 ⫾ 160 N for transtendon repair and 246 ⫾ 29 N for double-row repair). Both these studies support an in situ transtendon repair with high ultimate failure load, little gapping, and small strain. We focused on footprint contact pressure, because it is likely another important factor for the healing potential of rotator cuff repairs. A number of studies have shown that pressure between tendon and bone can be beneficial for healing.36-39 To our knowledge, this is the first study looking at footprint contact
pressures for transtendon repair. There have, however, been other studies assessing footprint contact pressures for full-thickness tear repair techniques.33,40-42 In a recent study, Park et al.42 found a decrease in footprint contact pressure with increasing abduction angles. We also found this decrease in contact pressure with increasing abduction. In addition, we found increasing footprint contact pressures with increasing loads placed across the tendon. These findings may be of interest when deciding whether to give a patient an abduction pillow postoperatively. In our study failure of the transtendon anchors occurred in 3 of 15 cases. In 2 cases an anchor pulled out while the suture was being tensioned. A possible explanation for this might be the use of ovine shoulders. Ovine bone is typically denser than human bone, which might prevent the wings of the anchor from expanding fully when the bone lock is being deployed, thus leading to a decrease in fixation strength. Studies in human shoulders are needed to evaluate this further before we can recommend the transtendon anchors for clinical use. Several limitations of this study must be considered. First, ovine shoulders were used because of the similarity of the infraspinatus tendon to the human supraspinatus tendon,26 as well as their easy access and reproducible biomechanical properties.27,28 Human cadaveric shoulders would better represent the clinical population. Our load-to-failure test data show that having remaining cuff tissue at the footprint leads to a significantly higher ultimate failure load than conversion to a full-thickness tear and repair. However, this ultimate failure load may be overestimated in an ovine model with a non-tendinopathic infraspinatus. The
PARTIAL-THICKNESS ROTATOR CUFF TEAR REPAIR tendon fibers of the ovine infraspinatus are, however, more parallel compared with the human supraspinatus and thus may fail at a lower load than the human supraspinatus tendon. Second, this is an ex vivo study, which does not give information on healing biology and only measures initial contact pressure. The pressure characteristics may change after motion at the repair site. Although we did preload the specimens, cyclical loading may have been better able to evaluate this. Third, repairs done in a laboratory after softtissue stripping are generally easier to perform than arthroscopic repairs. The transtendon anchors were relatively easy to use in this setting but may not necessarily be so in vivo. Lastly, we evaluated both transtendon repair and a new anchor system. This reduces the ability to determine the effect that each variable (repair type and anchor system) has on the result. To dynamically measure footprint contact pressure, we used a metal probe inserted through the footprint and connected to a load cell. Other studies have used pressure-sensitive film or Tekscan pressure sensors to measure contact pressure in rotator cuff repairs.33,40-42 Pressure-sensitive film can only be used once to measure maximum applied pressure. An advantage of our setup is that footprint contact pressure can be measured dynamically with different loads and angle variations. Tekscan pressure sensors (Tekscan, Boston, MA) can also measure dynamic pressure changes on the footprint, but the rigid surface of the sensor mesh may create uneven loading conditions on the convex footprint. A disadvantage of our setup is that pressure is measured over only a small area of the footprint, and the total footprint contact area cannot be calculated. Transtendon repair avoids the need to complete the tear, leaving the lateral footprint intact. This has the potential advantages of increased repair strength and a better chance of re-creating the original footprint without length-tension mismatch. A potential drawback of transtendon repair is that the intact tendon at the lateral footprint is likely to be tendinopathic, which might compromise strength and make the repair more susceptible to retear. Furthermore, passage of a drill or bone punch and insertion of the anchors through the cuff might damage the intact cuff. The transtendon anchors we tested in this study have a diameter of only 1.8 mm, compared with the 4.5- to 5.5-mm anchors previously described for transtendon techniques. Damage to the tendon did not seem to be an important factor in our study, with ultimate failure occurring at the midsubstance and not at the footprint. Another
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potential drawback of transtendon repair is that the pressure created by the tensioned suture on top of the tendon may strangulate the tendon, compromising vascularity, which could hinder the healing process. On the other hand, most of the blood supply to the supraspinatus comes from the bursal side of the tendon43; thus, by keeping the bursal side intact, the vascularity may be preserved. In vivo studies are needed to evaluate these and other potential factors to optimize the healing environment. CONCLUSIONS Transtendon repair of partial-thickness tears using specifically designed anchors biomechanically outperformed tear completion and repair in an ovine model. Transtendon repair showed the best combination of high footprint contact pressure and high ultimate failure load. However, the high insertion failure rate of these transtendon anchors is of concern. REFERENCES 1. Ellman H. Diagnosis and treatment of incomplete rotator cuff tears. Clin Orthop Relat Res 1990:64-74. 2. Matava MJ, Purcell DB, Rudzki JR. Partial-thickness rotator cuff tears. Am J Sports Med 2005;33:1405-1417. 3. Fukuda H, Mikasa M, Yamanaka K. Incomplete thickness rotator cuff tears diagnosed by subacromial bursography. Clin Orthop Relat Res 1987:51-58. 4. Uhthoff HK, Sano H. Pathology of failure of the rotator cuff tendon. Orthop Clin North Am 1997;28:31-41. 5. Gotoh M, Hamada K, Yamakawa H, Tomonaga A, Inoue A, Fukuda H. Significance of granulation tissue in torn supraspinatus insertions: An immunohistochemical study with antibodies against interleukin-1 beta, cathepsin D, and matrix metalloprotease-1. J Orthop Res 1997;15:33-39. 6. Ogata S, Uhthoff HK. Acromial enthesopathy and rotator cuff tear. A radiologic and histologic postmortem investigation of the coracoacromial arch. Clin Orthop Relat Res 1990:39-48. 7. Ozaki J, Fujimoto S, Nakagawa Y, Masuhara K, Tamai S. Tears of the rotator cuff of the shoulder associated with pathological changes in the acromion. A study in cadavera. J Bone Joint Surg Am 1988;70:1224-1230. 8. Neer CS II. Impingement lesions. Clin Orthop Relat Res 1983:70-77. 9. Neer CS II. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: A preliminary report. J Bone Joint Surg Am 1972;54:41-50. 10. Sano H, Ishii H, Yeadon A, Backman DS, Brunet JA, Uhthoff HK. Degeneration at the insertion weakens the tensile strength of the supraspinatus tendon: A comparative mechanical and histologic study of the bone-tendon complex. J Orthop Res 1997;15:719-726. 11. Uhthoff HK, Hammond DI, Sarkar K, Hooper GJ, Papoff WJ. The role of the coracoacromial ligament in the impingement syndrome. A clinical, radiological and histological study. Int Orthop 1988;12:97-104. 12. Fukuda H. The management of partial-thickness tears of the rotator cuff. J Bone Joint Surg Br 2003;85:3-11.
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