Arthroscopic Suprapectoral and Open Subpectoral Biceps Tenodesis: A Comparison of Restoration of Length-Tension and Mechanical Strength Between Techniques Brian C. Werner, M.D., Matthew L. Lyons, M.D., Cody L. Evans, M.D., Justin W. Griffin, M.D., Joseph M. Hart, Ph.D., Mark D. Miller, M.D., and Stephen F. Brockmeier, M.D.
Purpose: This study aimed to (1) evaluate the ex vivo restoration of the long head biceps length-tension for both arthroscopic suprapectoral biceps tenodesis (ASPBT) and open subpectoral biceps tenodesis (OSPBT) techniques and (2) assess how location in the proximal humerus affects pullout strength for tenodesis using an interference screw implant. Methods: Eighteen matched cadaveric shoulders were randomized to OSPBT or ASPBT groups (9 each). Tenodesis was performed using clinical techniques. Preoperatively, a metallic bead was placed in the biceps tendon and a fluoroscopic image was obtained. Postoperatively, an image was obtained to evaluate the location of the tenodesis and the metallic bead and determine tensioning. Biomechanical load-to-failure testing was then performed. Results: The ASPBT technique resulted in an average of 2.15 0.62 cm of biceps overtensioning compared with 0.78 0.35 cm (P < .001) in the OSPBT group. The average load to failure in the ASPBT group was 138.8 29.1 N compared with 197 38.6 N (P ¼ .002) in the OSPBT group. Failure caused by implant pullout was significantly more frequent in the ASPBT group (7 of 9) than in the OSPBT group (1 of 9). Conclusions: The described ASPBT technique using an interference screw implant has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaveric specimens. Clinical Relevance: This study shows differences in the biomechanical properties of OSPBT and ASPBT. Modification of currently published ASPBT techniques may be necessary to improve restoration of the physiological length-tension relationship of the biceps. Clinical studies may need to clarify if the lower ultimate load to failure for the ASPBT technique is clinically significant.
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ong head biceps tenodesis has gained considerable popularity in the surgical management of a spectrum of disorders including biceps instability, biceps tendinopathy, biceps tears, superior glenoid labrum/ biceps anchor pathologic processes, massive rotator cuff tears, and associated subscapularis tears.1 Tenodesis is promoted as preferable to biceps tenotomy in young
From Department of Orthopaedic Surgery, University of Virginia Health System, Charlottesville, Virginia, U.S.A. The authors report the following potential conflict of interest or source of funding: S.F.B. receives support from Arthrex, MicroAire Surgical Instruments, Tornier, and Springer. Received May 20, 2014; accepted October 23, 2014. Address correspondence to Stephen F. Brockmeier, M.D., Department of Orthopaedic Surgery, Sports Medicine and Shoulder Surgery, University of Virginia Health System, 400 Ray C Hunt Dr, Ste 330, Charlottesville, VA 22908, U.S.A. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14426/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.10.012
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and active patients, thin patients, and patients concerned with cosmetic deformity; it is also used to reduce the possibility of cramping with repetitive use.2 Numerous options for surgical approach, location, and method of fixation have been investigated for biceps tenodesis in both cadaveric and clinical studies. Long head biceps tenodesis can be performed with an open3-18 or arthroscopic technique9,18-33 and can be positioned high at the entrance of the bicipital groove, in the suprapectoral location just proximal to the pectoralis major tendon,9,16,22,30,31,34 in a subpectoral location at or distal to the pectoralis major tendon,6,10,12,15,16,34 or in other positions, including the conjoint tendon or soft tissue tenodesis sites.27,32,33,35 Arthroscopic suprapectoral and open subpectoral techniques are 2 common distal techniques for biceps tenodesis.9 Although numerous cadaveric and biomechanical studies have assessed these methods in isolation,4,7,17,36-41 few studies are available that directly compare the 2 techniques.9,39 Additionally, there has
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been increasing recognition that restoration of the anatomic length-tension relationship of the long head biceps is a critical aspect of the tenodesis procedure.22,42,43 These data are valuable to orthopaedic surgeons using these techniques, because little data exist guiding practitioners regarding the differences in these commonly used methods. The purposes of this study were to (1) evaluate the ex vivo restoration of the long head biceps lengthtension for both ASPBT and OSPBT techniques and (2) assess how location in the proximal humerus (suprapectoral or subpectoral) and surgical technique affect pullout strength for biceps tenodesis using an interference screw implant. Our null hypothesis was that no difference existed between ASPBT and OSPBT regarding restoration of the length-tension relationship and pullout strength.
Methods Specimens Nine matched pairs (n ¼ 18) of fresh-frozen cadaveric arms (including shoulder and forearm) without evidence of significant previous trauma were obtained for this study. Right and left shoulders were randomized to either the arthroscopic suprapectoral biceps tenodesis (ASPBT) group or the open subpectoral biceps tenodesis (OSPBT) group, such that within each pair, one shoulder underwent an ASPBT and the other underwent an OSPBT. Before any study procedures, dualenergy x-ray absorptiometry (DEXA) scanning was completed on all specimens, and T scores were calculated. The specimens were thawed for 24 hours before testing. Preoperative Preparation Before each tenodesis procedure, a spherical metallic marker was placed 1 cm distal to the long head biceps musculotendinous junction using a nonabsorbable suture. A small incision was made in the area of the musculotendinous junction, and the soft tissues were dissected until the location was confirmed. After the metallic marker was stitched in place, the skin was closed with nonabsorbable suture. This procedure was repeated for all cadaveric specimens in both the ASPBT and OSPBT groups. After placement of the metallic marker, a fluoroscopic image of each shoulder was obtained and saved for later measurement. Operative Technique Cadaveric shoulders were secured to a mounted fixture to approximate a beach-chair position to maintain a consistent orientation among procedures. Two senior sports fellowship-trained orthopaedic surgeons (M.D.M., S.F.B.) performed the procedures. Each surgeon was randomly assigned to the procedure
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(ASPBT or OSPBT) to be performed on each cadaveric shoulder pair. For each tenodesis technique, standard arthroscopic portals were established. A spinal needle was placed percutaneously through the long head biceps tendon between 1 and 2 cm distal to its superior labral attachment. A polydioxanone suture was passed through the tendon using a needle to facilitate retrieval (for OSPBT) or for control of the tendon (for ASPBT). The biceps was then released from its superior labral attachment. Arthroscopic Suprapectoral Tenodesis. For the arthroscopic technique, the arthroscope was redirected into the subacromial space. Using a direct lateral portal, a bursectomy was performed to facilitate visualization of the biceps tendon in the subdeltoid space. The camera was then repositioned in the lateral portal, and the biceps tendon was identified in its sheath within the intertubercular groove. Cautery was used to release the biceps from its sheath, and an appropriate site for tenodesis was localized just proximal to the pectoralis major tendon, which was easily visible using this approach. A spinal needle was used to localize an appropriate position and angle through which tenodesis fixation could be performed. A portal was established at this location, and a sharp-tipped 7.5-mm reamer was drilled to a depth of 20 mm. The proximal tendon was held to native tension using the previously placed polydioxanone suture. A 7 mm 19.5 mm forked Arthrex SwiveLock PEEK anchor (Arthrex, Naples, FL) was then used to affix the tendon to the reamed tenodesis site. The tendon was pushed into the tunnel using the fork of the implant, typically from a superior and inferior direction. Care was taken to avoid wrapping the tendon with the implant as the implant was tightened. Open Subpectoral Tenodesis. For the open subpectoral technique, the long head biceps was tenotomized arthroscopically as described for the arthroscopic technique. After this, a 3-cm vertical incision was made near the axillary fold. The overlying fascia and fatty tissue were incised. A pointed Hohmann retractor was placed under the pectoralis major and a Chandler retractor was placed over the medial aspect of the humerus to assist in visualization. The soft tissues were dissected, and the long head biceps was isolated just posterior to the pectoralis major insertion. A right-angle clamp was used to pull the biceps tendon from underneath the pectoralis major and deliver it through the incision. The bicipital groove was palpated, and the periosteum was reflected using an elevator at a point just proximal to the inferior edge of the pectoralis major. The musculotendinous transition site was identified, and the distal 20 mm of the tendinous portion of the biceps was whip-stitched. The remaining biceps tendon was
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Assessment of Tenodesis Location A standard anteroposterior fluoroscopic image was obtained after the procedure to determine the location of the tenodesis site (observed as a translucent circle in the humerus). The location was measured as the distance from the top of the humeral head to the center of the circular tenodesis site (tenodesis distance on the humerus). A line was drawn from the most proximal aspect of the humeral head to a horizontal line drawn through the center of the tenodesis site perpendicular to the vertical line drawn from the most superior aspect of the humerus (Fig 1).
Fig 1. Postoperative cadaveric anteroposterior fluoroscopic image showing the method for determining the location of the biceps tenodesis site in relation to the humeral head. This was repeated for all cadaveric specimens.
then amputated. A guidewire was placed, and a 7.5-mm cannulated reamer was drilled to a depth of 20 mm. A 7 mm 15 mm Arthrex PEEK Bio-Tenodesis Screw (Arthrex, Naples, FL) was then used to affix the tendon to the reamed tenodesis site after docking the tendon stump in the prepared tunnel. Again, care was taken to avoid tendon wrapping during final fixation.
Assessment of Length-Tension Relationship The ex vivo restoration of the long head biceps length-tension relationship was assessed using the preoperatively placed spherical metallic marker. The preoperative and postoperative digital fluoroscopic images were evaluated for the location of the metallic marker. For consistency, the location of the marker was measured as the distance from the top of the humeral head to the location of the metallic marker (Fig 2). Fluoroscopic images were obtained at a standard distance from the radiographic source. To further reduce the chance for error based on imaging technique, all measurements were normalized to the known diameter of the metallic marker, which was 5 mm. The difference in location of the metallic marker from preoperatively to postoperatively was considered to reflect the underor overtensioning of the biceps tendon during tenodesis. Each fluoroscopic image was digitized and processed using Adobe Photoshop CS6 (Adobe Systems, San Jose, CA). Two evaluators (B.C.W., M.L.L.) independently performed all measurements; these were averaged to yield the final measurement for each preoperative and postoperative specimen.
Fig 2. Anteroposterior preoperative (left) and postoperative (right) fluoroscopic images showing the change in position of the metallic marker during the tenodesis procedure. The location of the metallic marker was measured on both images, and the absolute difference between the preoperative and postoperative measurements indicated the change in length/tension on the biceps resulting from the tenodesis procedure.
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Fig 3. Setup for biomechanical testing. The humerus was potted and then mounted in an inverted position into an MTS machine. The biceps tendon was whip-stitched and then placed in the tendon clamp for the MTS machine.
Biomechanical Technique and Measurements After completion of the preceding in vivo measurements, the humeri were dissected to remove all tissue other than that of the biceps tendon and tenodesis site and were frozen until testing. Each specimen was thawed to room temperature for at least 24 hours before testing. The shaft of each humerus was amputated just proximal to the epicondyles of the distal humerus, and the distal end was potted in a fast-setting resin in a custom-fashioned polyvinyl chloride cylinder. Each humerus was then mounted in an MTS 858 Mini Bionix materials testing machine (MTS, Eden Prairie, MN). The humerus was mounted in an inverted manner so that the cyclic and load-to-failure forces were close to parallel to the longitudinal axis of the humerus to approximate the in vivo loading of the long head biceps tendon at an angle of about 30 to the humeral shaft, which was the same between groups (Fig 3). A low-force (2.5 kN) load cell was used. An MTS tendon clamp was used to attach the distal end of the biceps tendon to the MTS machine (Fig 3). All testing was performed at room temperature. Care was taken to keep the specimens moist to avoid degradation. The tendons were first cycled from 0 to 10 N of load at a frequency of 1.0 Hz for 100 cycles. After the cyclic loading, a load-to-failure test was conducted on the same specimens at a rate of 1.0 mm/s until a peak load was observed. Data recorded for the load-tofailure testing included the ultimate failure load and the mode of failure.
Dual-energy x-ray absorptiometry of the proximal humerus revealed no significant differences between the ASPBT and OSPBT groups. The average T score in the ASPBT group was 2.7 1.0; the average T score in the OSPBT group was 2.7 0.8 (P ¼ 1.000). The average distance measured from the top of the humerus to the center of the tenodesis site (described in the Methods section) in the arthroscopic suprapectoral group of cadaveric specimens (n ¼ 9) was 4.68 cm 0.97 cm. In the open subpectoral group (n ¼ 9), this moved to 7.46 cm 1.7 cm. The difference was statistically significant (P < .0001).
Statistical Methods An a priori power analysis was completed to determine an appropriate number of specimens, with ultimate load to failure as the primary variable. Based on
Restoration of Biceps Length-Tension Relationship In the arthroscopic suprapectoral group, the average change in location of the metallic marker from the preoperative to the postoperative image was 2.15
results of similar published studies, this study was powered to detect a mean difference of 45 N between groups, with an average standard deviation of 35 N for each group. To achieve 80% power with a ¼ 0.05, 9 specimens were required in each group. This equates to a very large effect size (Cohen’s d ¼ 1.29). A reliability analysis for the pre- and postoperative length-tension measurements was completed to determine absolute agreement using the intraclass correlation coefficient (ICC[2,1]). Means and standard deviations were calculated and compared using a Mann Whitney U test. A nonparametric test was chosen given the smaller sample sizes. For all statistical tests, P < .05 was considered significant. Statistical analysis was performed using IBM SPSS Statistics, version 21 (SPSS, Chicago, IL).
Results
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difference between the ASPBT and OSPBT ultimate load to failure was statistically significant (P ¼ .005).
Discussion
Fig 4. In addition to ultimate load to failure, the mode of failure for each specimen was recorded. Seven of the 9 arthroscopic suprapectoral specimens failed because of implant pullout, as seen in this image.
0.62 cm in a proximal direction, representing a potential overtensioning of the biceps. The average change in location in the open subpectoral group was 0.78 0.35 cm, also in a proximal direction, representing overtensioning, although to a lesser magnitude. This difference was statistically significant (P ¼ .002). The measurement technique as described had excellent reliability, with an ICC(2,1) for absolute agreement of repeated preoperative measurements of 0.99 and an ICC(2,1) for absolute agreement of repeated postoperative measurements of 0.99. Biomechanical Comparison of Suprapectoral and Subpectoral Locations The average load to failure in the arthroscopic suprapectoral group was 138.8 29.1 N. The mode of failure was implant pullout in 7 of 9 specimens (Fig 4). The remaining 2 specimens in this group failed at the tendon-implant interface, with catastrophic failure of the tendon at this location. The average load to failure in the open subpectoral group was 197 38.6 N. The mode of failure was implant pullout in 1 of 9 specimens. The remaining specimens in this group also failed at the tendon-implant interface with tendinous rupture. The
This study revealed 2 significant biomechanical differences between the arthroscopic suprapectoral and open subpectoral biceps tenodesis techniques: The described ASPBT technique has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with the OSPBT technique. The average tenodesis location of the arthroscopic suprapectoral group of cadaveric specimens was 4.68 cm. Murachovsky et al.44 described the distance between the pectoralis major tendon and the top of the humeral head in a cadaveric study of 40 shoulders to be 5.6 cm (range, 5.0 to 7.0 cm; SD, 0.5 cm), with little variation noted with age, sex, and patient height. This finding was confirmed in an additional study, which reported an average of 5.64 cm.45 The tenodesis location achieved in the described arthroscopic suprapectoral technique represents a location within 1 cm of the superior border of the pectoralis major tendon, indicating reliable placement at the desired suprapectoral location. The average tenodesis location of the open subpectoral group of cadaveric specimens was 7.46 cm. A recent anatomic study by Lafrance et al.43 described the height of the pectoralis major tendon to be 3.73 0.83 cm in the region of the biceps tendon, where open subpectoral tenodesis is performed. Combining this with the measurements of Murachovsky et al.,44 the average distance from the top of the humerus to the inferior border of the pectoralis major tendon is 8.49 cm. Our data show extremely accurate localization of the tenodesis site using an open subpectoral technique approximately 1 cm proximal to the inferior border of the pectoralis major tendon as described by numerous authors.20,31 Our data indicate an average difference in location between techniques of 2.74 cm, which was statistically significant. This is similar to the findings of Johannsen et al.,9 who recently reported that the open subpectoral approach placed the tenodesis tunnel on average 2.2 cm further distal than the arthroscopic suprapectoral approach. The importance of re-establishing the length-tension relationship of the long head biceps during tenodesis has been increasingly recognized.22,42 Undertensioning of the biceps during tenodesis can result in a persistent deformity, early muscle fatigue, or cramping.46,47 With overtensioning, pullout forces at the site of the tenodesis increase, which can predispose to fixation failure, among other potential complications.22 Using a novel technique with a metallic marker and static fluoroscopy, we found that the described arthroscopic
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suprapectoral technique brings the tendon proximally and overtensions the long head biceps by 2.15 cm. This overtensioning phenomenon occurred to a lesser degree in the open subpectoral group, in which the metallic marker was displaced only 0.78 0.35 cm on average (P < .001). This study did not dynamically evaluate the metallic marker during the tenodesis process to determine during which step or steps the overtensioning occurred; however, one potential explanation for the observed differences in tensioning is the “double-drop” phenomenon. This occurs as the tendon is docked in the tunnel during the ASPBT technique. The tendon is pushed into the tunnel from a superior and inferior direction, thus pulling in twice as much tendon. This will likely lead to the overtensioning found in the present study and may also greatly contribute to the poorer biomechanical strength with the ASPBT technique, because there is significantly more tendon in the tunnel and thus less circumference for purchase of the screw to bone. Based on the results of this study, we have modified our clinical technique for arthroscopic tenodesis, first stabilizing the biceps tendon proximally in the joint using a spinal needle before performing tenotomy. This approximates the previous or native length-tension relationship while performing tenodesis. We are then careful when “docking” the tendon in the drilled tunnel, securing the tendon approximately 2 cm proximal to the tunnel aperture with an aim to match this length and tension as closely as possible and avoid bringing too much distal tendon into the tunnel. Because open tenodesis resulted in only mild overtensioning, we do not similarly anchor the tendon in the joint after tenotomy; this modification would not be feasible because the tendon needs to be drawn into the incision for placement of sutures and blind-end docking. We continue to use the technique as described earlier and are careful to match the previous tension of the biceps as closely as possible. Restoration of biceps tendon tension during tenodesis has not previously been well evaluated. Johannsen et al.9 discussed potential implications of tenodesis technique on the length-tension relationship in their recent cadaveric study but did not rigorously or quantitatively evaluate it as a study objective. David et al.22 described a surgical technique for arthroscopic biceps tenodesis with an interference screw focused on the restoration of appropriate length-tension but again did not quantitatively evaluate whether it was actually achieved. Several known factors contribute to the biomechanical strength of a tenodesis construct, including bone or tissue quality, implant type, and tensioning. Although numerous studies have investigated these variables for tenodesis techniques in isolation, no previous studies have compared the isolated effect of the suprapectoral or subpectoral tenodesis location in a clinically
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relevant cadaveric model. For the tenodesis techniques described here that use an interference screw implant, our study found that the suprapectoral tenodesis location resulted in inferior ultimate load to failure compared with a subpectoral tenodesis (138.8 29.1 N v 197 38.6 N; P ¼ .002). The predominant mode of failure interestingly differed between the 2 techniques as well, with failure caused by implant pullout in 7 of 9 suprapectoral tenodesis specimens compared with only one of 9 subpectoral specimens. Previous studies have investigated ultimate load to failure for biceps tenodesis using interference screw fixation. Mazzocca et al.11 compared load to failure in 20 cadaveric shoulder specimens, including 5 using an open subpectoral technique with an interference screw and 5 using an arthroscopic suprapectoral technique with an interference screw. The authors reported load to failure of 252.4 68.63 N in the OSPBT group and 237.6 27.58 N in the ASPBT group and concluded that no significant differences existed in ultimate failure strength between methods. Richards and Burkhart48 evaluated load to failure in 11 cadaveric specimens, 5 of which were tenodesed in an open manner using an interference screw in a proximal location. The authors reported a load to failure of 233.5 55.5 N for the interference screw tenodesis, which was significantly better than that for suture anchor fixation. Golish et al.7 also found a load to failure of 169.6 50.5 N for open subpectoral biceps tenodesis with an interference screw in 9 cadaveric specimens, which was likewise significantly better than suture anchor fixation. Recently, Patzer et al.16 biomechanically compared several biceps tenodesis options, including 7 cadaveric specimens with suprapectoral tenodesis using an interference screw and 7 specimens with a subpectoral tenodesis using an interference screw. The ultimate load to failure in the suprapectoral group was 218.3 59.7 N and was 200.7 38.6 N in the subpectoral group. This was significantly higher than seen in suture anchor techniques. The observed load to failure in our study was similar to those previously reported; however, we found a significantly lower load to failure in the ASPBT group compared with those previously reported. This difference may be technique related, because the described ASPBT technique results in more tendon remaining in the tunnel, which can lead to decreased bony contact for the tenodesis implant. In addition, implant differences (SwiveLock v BioTenodesis Screw; Arthrex, Naples, FL) might also contribute to the observed difference in biomechanical strength. Finally, the bone quality at the site of tenodesis may be a factor in this observed biomechanical strength difference because the more proximal tenodesis location of the ASPBT technique has potentially weaker metaphyseal bone than does the diaphyseal bone of the OSPBT location.
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Limitations This study has several limitations. First, this is a timezero study, which can investigate only the initial fixation of the tendon, implant, and bone. Biological factors such as tendon ingrowth or soft tissue effects cannot be predicted based on these experiments. Additionally, clinical results likewise cannot be determined. Future comparative clinical studies are necessary to determine what result tenodesis location will have on postoperative function and patient satisfaction. Second, the biomechanical testing was performed after dissection of the remaining soft tissue structures, which could contribute to the overall strength of the tenodesis construct. Clinical failures primarily occur at the suturetendon interface, as opposed to the implant pullout observed in this biomechanical study, which could also be related to dissection of the surrounding soft tissues before biomechanical testing. Third, our novel technique for assessing the length-tension relationship has not previously been validated. Fourth, the study measurements, including measurement of the lengthtension relationship and biomechanical measurements, were not able to be performed in a blinded fashion. Finally, although 2 fellowship-trained surgeons performed all study procedures, and cadavers and surgeons were randomized to techniques, having 2 surgeons does add variability that must be considered.
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Conclusions The described ASPBT technique using an interference screw implant has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaveric specimens.
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COMPARISON OF BICEPS TENODESIS TECHNIQUES 23. Elkousy HA, Fluhme DJ, O’Connor DP, Rodosky MW. Arthroscopic biceps tenodesis using the percutaneous, intra-articular trans-tendon technique: Preliminary results. Orthopedics 2005;28:1316-1319. 24. Gartsman GM, Hammerman SM. Arthroscopic biceps tenodesis: Operative technique. Arthroscopy 2000;16: 550-552. 25. Kim SH, Yoo JC. Arthroscopic biceps tenodesis using interference screw: End-tunnel technique. Arthroscopy 2005;21:1405. 26. Klepps S, Hazrati Y, Flatow E. Arthroscopic biceps tenodesis. Arthroscopy 2002;18:1040-1045. 27. Lafosse L, Shah AA, Butler RB, Fowler RL. Arthroscopic biceps tenodesis to supraspinatus tendon: Technical note. Am J Orthop (Belle Mead NJ) 2011;40:345-347. 28. Lo IK, Burkhart SS. Arthroscopic biceps tenodesis using a bioabsorbable interference screw. Arthroscopy 2004;20:85-95. 29. Nord KD, Smith GB, Mauck BM. Arthroscopic biceps tenodesis using suture anchors through the subclavian portal. Arthroscopy 2005;21:248-252. 30. Patzer T, Kircher J, Krauspe R. All-arthroscopic suprapectoral long head of biceps tendon tenodesis with interference screw-like tendon fixation after modified lasso-loop stitch tendon securing. Arthrosc Tech 2012;1:e53-e56. 31. Romeo AA, Mazzocca AD, Tauro JC. Arthroscopic biceps tenodesis. Arthroscopy 2004;20:206-213. 32. Scheibel M, Schroder RJ, Chen J, Bartsch M. Arthroscopic soft tissue tenodesis versus bony fixation anchor tenodesis of the long head of the biceps tendon. Am J Sports Med 2011;39:1046-1052. 33. Verma NN, Drakos M, O’Brien SJ. Arthroscopic transfer of the long head biceps to the conjoint tendon. Arthroscopy 2005;21:764. 34. Lutton DM, Gruson KI, Harrison AK, Gladstone JN, Flatow EL. Where to tenodese the biceps: Proximal or distal? Clin Orthop Relat Res 2011;469:1050-1055. 35. Franceschi F, Longo UG, Ruzzini L, Rizzello G, Maffulli N, Denaro V. Soft tissue tenodesis of the long head of the biceps tendon associated to the roman bridge repair. BMC Musculoskelet Disord 2008;9:78. 36. Ahmed M, Young BT, Bledsoe G, Cutuk A, Kaar SG. Biomechanical comparison of long head of biceps tenodesis with interference screw and biceps sling soft tissue techniques. Arthroscopy 2013;29:1157-1163. 37. Arora AS, Singh A, Koonce RC. Biomechanical evaluation of a unicortical button versus interference screw for subpectoral biceps tenodesis. Arthroscopy 2013;29:638-644.
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38. Slabaugh MA, Frank RM, Van Thiel GS, et al. Biceps tenodesis with interference screw fixation: A biomechanical comparison of screw length and diameter. Arthroscopy 2011;27:161-166. 39. Patzer T, Rundic JM, Bobrowitsch E, Olender GD, Hurschler C, Schofer MD. Biomechanical comparison of arthroscopically performable techniques for suprapectoral biceps tenodesis. Arthroscopy 2011;27: 1036-1047. 40. Lopez-Vidriero E, Costic RS, Fu FH, Rodosky MW. Biomechanical evaluation of 2 arthroscopic biceps tenodeses: Double-anchor versus percutaneous intraarticular transtendon (PITT) techniques. Am J Sports Med 2010;38:146-152. 41. Ozalay M, Akpinar S, Karaeminogullari O, et al. Mechanical strength of four different biceps tenodesis techniques. Arthroscopy 2005;21:992-998. 42. Denard PJ, Dai X, Hanypsiak BT, Burkhart SS. Anatomy of the biceps tendon: Implications for restoring physiological length-tension relation during biceps tenodesis with interference screw fixation. Arthroscopy 2012;28: 1352-1358. 43. Lafrance R, Madsen W, Yaseen Z, Giordano B, Maloney M, Voloshin I. Relevant anatomic landmarks and measurements for biceps tenodesis. Am J Sports Med 2013;41:1395-1399. 44. Murachovsky J, Ikemoto RY, Nascimento LG, Fujiki EN, Milani C, Warner JJ. Pectoralis major tendon reference (PMT): A new method for accurate restoration of humeral length with hemiarthroplasty for fracture. J Shoulder Elbow Surg 2006;15:675-678. 45. Torrens C, Corrales M, Melendo E, Solano A, RodriguezBaeza A, Caceres E. The pectoralis major tendon as a reference for restoring humeral length and retroversion with hemiarthroplasty for fracture. J Shoulder Elbow Surg 2008;17:947-950. 46. Lim TK, Moon ES, Koh KH, Yoo JC. Patient-related factors and complications after arthroscopic tenotomy of the long head of the biceps tendon. Am J Sports Med 2011;39: 783-789. 47. Kelly AM, Drakos MC, Fealy S, Taylor SA, O’Brien SJ. Arthroscopic release of the long head of the biceps tendon: Functional outcome and clinical results. Am J Sports Med 2005;33:208-213. 48. Richards DP, Burkhart SS. A biomechanical analysis of two biceps tenodesis fixation techniques. Arthroscopy 2005;21:861-866.
Purpose: This study aimed to (1) evaluate the ex vivo restoration of the long head biceps length-tension for both arthroscopic suprapectoral biceps tenodesis (ASPBT) and open subpectoral biceps tenodesis (OSPBT) techniques and (2) assess how location in the proximal humerus affects pullout strength for tenodesis using an interference screw implant. Methods: Eighteen matched cadaveric shoulders were randomized to OSPBT or ASPBT groups (9 each). Tenodesis was performed using clinical techniques. Preoperatively, a metallic bead was placed in the biceps tendon and a fluoroscopic image was obtained. Postoperatively, an image was obtained to evaluate the location of the tenodesis and the metallic bead and determine tensioning. Biomechanical load-to-failure testing was then performed. Results: The ASPBT technique resulted in an average of 2.15 0.62 cm of biceps overtensioning compared with 0.78 0.35 cm (P < .001) in the OSPBT group. The average load to failure in the ASPBT group was 138.8 29.1 N compared with 197 38.6 N (P ¼ .002) in the OSPBT group. Failure caused by implant pullout was significantly more frequent in the ASPBT group (7 of 9) than in the OSPBT group (1 of 9). Conclusions: The described ASPBT technique using an interference screw implant has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaveric specimens. Clinical Relevance: This study shows differences in the biomechanical properties of OSPBT and ASPBT. Modification of currently published ASPBT techniques may be necessary to improve restoration of the physiological length-tension relationship of the biceps. Clinical studies may need to clarify if the lower ultimate load to failure for the ASPBT technique is clinically significant.
L
ong head biceps tenodesis has gained considerable popularity in the surgical management of a spectrum of disorders including biceps instability, biceps tendinopathy, biceps tears, superior glenoid labrum/ biceps anchor pathologic processes, massive rotator cuff tears, and associated subscapularis tears.1 Tenodesis is promoted as preferable to biceps tenotomy in young
From Department of Orthopaedic Surgery, University of Virginia Health System, Charlottesville, Virginia, U.S.A. The authors report the following potential conflict of interest or source of funding: S.F.B. receives support from Arthrex, MicroAire Surgical Instruments, Tornier, and Springer. Received May 20, 2014; accepted October 23, 2014. Address correspondence to Stephen F. Brockmeier, M.D., Department of Orthopaedic Surgery, Sports Medicine and Shoulder Surgery, University of Virginia Health System, 400 Ray C Hunt Dr, Ste 330, Charlottesville, VA 22908, U.S.A. E-mail: [email protected] Ó 2015 by the Arthroscopy Association of North America 0749-8063/14426/$36.00 http://dx.doi.org/10.1016/j.arthro.2014.10.012
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and active patients, thin patients, and patients concerned with cosmetic deformity; it is also used to reduce the possibility of cramping with repetitive use.2 Numerous options for surgical approach, location, and method of fixation have been investigated for biceps tenodesis in both cadaveric and clinical studies. Long head biceps tenodesis can be performed with an open3-18 or arthroscopic technique9,18-33 and can be positioned high at the entrance of the bicipital groove, in the suprapectoral location just proximal to the pectoralis major tendon,9,16,22,30,31,34 in a subpectoral location at or distal to the pectoralis major tendon,6,10,12,15,16,34 or in other positions, including the conjoint tendon or soft tissue tenodesis sites.27,32,33,35 Arthroscopic suprapectoral and open subpectoral techniques are 2 common distal techniques for biceps tenodesis.9 Although numerous cadaveric and biomechanical studies have assessed these methods in isolation,4,7,17,36-41 few studies are available that directly compare the 2 techniques.9,39 Additionally, there has
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been increasing recognition that restoration of the anatomic length-tension relationship of the long head biceps is a critical aspect of the tenodesis procedure.22,42,43 These data are valuable to orthopaedic surgeons using these techniques, because little data exist guiding practitioners regarding the differences in these commonly used methods. The purposes of this study were to (1) evaluate the ex vivo restoration of the long head biceps lengthtension for both ASPBT and OSPBT techniques and (2) assess how location in the proximal humerus (suprapectoral or subpectoral) and surgical technique affect pullout strength for biceps tenodesis using an interference screw implant. Our null hypothesis was that no difference existed between ASPBT and OSPBT regarding restoration of the length-tension relationship and pullout strength.
Methods Specimens Nine matched pairs (n ¼ 18) of fresh-frozen cadaveric arms (including shoulder and forearm) without evidence of significant previous trauma were obtained for this study. Right and left shoulders were randomized to either the arthroscopic suprapectoral biceps tenodesis (ASPBT) group or the open subpectoral biceps tenodesis (OSPBT) group, such that within each pair, one shoulder underwent an ASPBT and the other underwent an OSPBT. Before any study procedures, dualenergy x-ray absorptiometry (DEXA) scanning was completed on all specimens, and T scores were calculated. The specimens were thawed for 24 hours before testing. Preoperative Preparation Before each tenodesis procedure, a spherical metallic marker was placed 1 cm distal to the long head biceps musculotendinous junction using a nonabsorbable suture. A small incision was made in the area of the musculotendinous junction, and the soft tissues were dissected until the location was confirmed. After the metallic marker was stitched in place, the skin was closed with nonabsorbable suture. This procedure was repeated for all cadaveric specimens in both the ASPBT and OSPBT groups. After placement of the metallic marker, a fluoroscopic image of each shoulder was obtained and saved for later measurement. Operative Technique Cadaveric shoulders were secured to a mounted fixture to approximate a beach-chair position to maintain a consistent orientation among procedures. Two senior sports fellowship-trained orthopaedic surgeons (M.D.M., S.F.B.) performed the procedures. Each surgeon was randomly assigned to the procedure
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(ASPBT or OSPBT) to be performed on each cadaveric shoulder pair. For each tenodesis technique, standard arthroscopic portals were established. A spinal needle was placed percutaneously through the long head biceps tendon between 1 and 2 cm distal to its superior labral attachment. A polydioxanone suture was passed through the tendon using a needle to facilitate retrieval (for OSPBT) or for control of the tendon (for ASPBT). The biceps was then released from its superior labral attachment. Arthroscopic Suprapectoral Tenodesis. For the arthroscopic technique, the arthroscope was redirected into the subacromial space. Using a direct lateral portal, a bursectomy was performed to facilitate visualization of the biceps tendon in the subdeltoid space. The camera was then repositioned in the lateral portal, and the biceps tendon was identified in its sheath within the intertubercular groove. Cautery was used to release the biceps from its sheath, and an appropriate site for tenodesis was localized just proximal to the pectoralis major tendon, which was easily visible using this approach. A spinal needle was used to localize an appropriate position and angle through which tenodesis fixation could be performed. A portal was established at this location, and a sharp-tipped 7.5-mm reamer was drilled to a depth of 20 mm. The proximal tendon was held to native tension using the previously placed polydioxanone suture. A 7 mm 19.5 mm forked Arthrex SwiveLock PEEK anchor (Arthrex, Naples, FL) was then used to affix the tendon to the reamed tenodesis site. The tendon was pushed into the tunnel using the fork of the implant, typically from a superior and inferior direction. Care was taken to avoid wrapping the tendon with the implant as the implant was tightened. Open Subpectoral Tenodesis. For the open subpectoral technique, the long head biceps was tenotomized arthroscopically as described for the arthroscopic technique. After this, a 3-cm vertical incision was made near the axillary fold. The overlying fascia and fatty tissue were incised. A pointed Hohmann retractor was placed under the pectoralis major and a Chandler retractor was placed over the medial aspect of the humerus to assist in visualization. The soft tissues were dissected, and the long head biceps was isolated just posterior to the pectoralis major insertion. A right-angle clamp was used to pull the biceps tendon from underneath the pectoralis major and deliver it through the incision. The bicipital groove was palpated, and the periosteum was reflected using an elevator at a point just proximal to the inferior edge of the pectoralis major. The musculotendinous transition site was identified, and the distal 20 mm of the tendinous portion of the biceps was whip-stitched. The remaining biceps tendon was
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Assessment of Tenodesis Location A standard anteroposterior fluoroscopic image was obtained after the procedure to determine the location of the tenodesis site (observed as a translucent circle in the humerus). The location was measured as the distance from the top of the humeral head to the center of the circular tenodesis site (tenodesis distance on the humerus). A line was drawn from the most proximal aspect of the humeral head to a horizontal line drawn through the center of the tenodesis site perpendicular to the vertical line drawn from the most superior aspect of the humerus (Fig 1).
Fig 1. Postoperative cadaveric anteroposterior fluoroscopic image showing the method for determining the location of the biceps tenodesis site in relation to the humeral head. This was repeated for all cadaveric specimens.
then amputated. A guidewire was placed, and a 7.5-mm cannulated reamer was drilled to a depth of 20 mm. A 7 mm 15 mm Arthrex PEEK Bio-Tenodesis Screw (Arthrex, Naples, FL) was then used to affix the tendon to the reamed tenodesis site after docking the tendon stump in the prepared tunnel. Again, care was taken to avoid tendon wrapping during final fixation.
Assessment of Length-Tension Relationship The ex vivo restoration of the long head biceps length-tension relationship was assessed using the preoperatively placed spherical metallic marker. The preoperative and postoperative digital fluoroscopic images were evaluated for the location of the metallic marker. For consistency, the location of the marker was measured as the distance from the top of the humeral head to the location of the metallic marker (Fig 2). Fluoroscopic images were obtained at a standard distance from the radiographic source. To further reduce the chance for error based on imaging technique, all measurements were normalized to the known diameter of the metallic marker, which was 5 mm. The difference in location of the metallic marker from preoperatively to postoperatively was considered to reflect the underor overtensioning of the biceps tendon during tenodesis. Each fluoroscopic image was digitized and processed using Adobe Photoshop CS6 (Adobe Systems, San Jose, CA). Two evaluators (B.C.W., M.L.L.) independently performed all measurements; these were averaged to yield the final measurement for each preoperative and postoperative specimen.
Fig 2. Anteroposterior preoperative (left) and postoperative (right) fluoroscopic images showing the change in position of the metallic marker during the tenodesis procedure. The location of the metallic marker was measured on both images, and the absolute difference between the preoperative and postoperative measurements indicated the change in length/tension on the biceps resulting from the tenodesis procedure.
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Fig 3. Setup for biomechanical testing. The humerus was potted and then mounted in an inverted position into an MTS machine. The biceps tendon was whip-stitched and then placed in the tendon clamp for the MTS machine.
Biomechanical Technique and Measurements After completion of the preceding in vivo measurements, the humeri were dissected to remove all tissue other than that of the biceps tendon and tenodesis site and were frozen until testing. Each specimen was thawed to room temperature for at least 24 hours before testing. The shaft of each humerus was amputated just proximal to the epicondyles of the distal humerus, and the distal end was potted in a fast-setting resin in a custom-fashioned polyvinyl chloride cylinder. Each humerus was then mounted in an MTS 858 Mini Bionix materials testing machine (MTS, Eden Prairie, MN). The humerus was mounted in an inverted manner so that the cyclic and load-to-failure forces were close to parallel to the longitudinal axis of the humerus to approximate the in vivo loading of the long head biceps tendon at an angle of about 30 to the humeral shaft, which was the same between groups (Fig 3). A low-force (2.5 kN) load cell was used. An MTS tendon clamp was used to attach the distal end of the biceps tendon to the MTS machine (Fig 3). All testing was performed at room temperature. Care was taken to keep the specimens moist to avoid degradation. The tendons were first cycled from 0 to 10 N of load at a frequency of 1.0 Hz for 100 cycles. After the cyclic loading, a load-to-failure test was conducted on the same specimens at a rate of 1.0 mm/s until a peak load was observed. Data recorded for the load-tofailure testing included the ultimate failure load and the mode of failure.
Dual-energy x-ray absorptiometry of the proximal humerus revealed no significant differences between the ASPBT and OSPBT groups. The average T score in the ASPBT group was 2.7 1.0; the average T score in the OSPBT group was 2.7 0.8 (P ¼ 1.000). The average distance measured from the top of the humerus to the center of the tenodesis site (described in the Methods section) in the arthroscopic suprapectoral group of cadaveric specimens (n ¼ 9) was 4.68 cm 0.97 cm. In the open subpectoral group (n ¼ 9), this moved to 7.46 cm 1.7 cm. The difference was statistically significant (P < .0001).
Statistical Methods An a priori power analysis was completed to determine an appropriate number of specimens, with ultimate load to failure as the primary variable. Based on
Restoration of Biceps Length-Tension Relationship In the arthroscopic suprapectoral group, the average change in location of the metallic marker from the preoperative to the postoperative image was 2.15
results of similar published studies, this study was powered to detect a mean difference of 45 N between groups, with an average standard deviation of 35 N for each group. To achieve 80% power with a ¼ 0.05, 9 specimens were required in each group. This equates to a very large effect size (Cohen’s d ¼ 1.29). A reliability analysis for the pre- and postoperative length-tension measurements was completed to determine absolute agreement using the intraclass correlation coefficient (ICC[2,1]). Means and standard deviations were calculated and compared using a Mann Whitney U test. A nonparametric test was chosen given the smaller sample sizes. For all statistical tests, P < .05 was considered significant. Statistical analysis was performed using IBM SPSS Statistics, version 21 (SPSS, Chicago, IL).
Results
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difference between the ASPBT and OSPBT ultimate load to failure was statistically significant (P ¼ .005).
Discussion
Fig 4. In addition to ultimate load to failure, the mode of failure for each specimen was recorded. Seven of the 9 arthroscopic suprapectoral specimens failed because of implant pullout, as seen in this image.
0.62 cm in a proximal direction, representing a potential overtensioning of the biceps. The average change in location in the open subpectoral group was 0.78 0.35 cm, also in a proximal direction, representing overtensioning, although to a lesser magnitude. This difference was statistically significant (P ¼ .002). The measurement technique as described had excellent reliability, with an ICC(2,1) for absolute agreement of repeated preoperative measurements of 0.99 and an ICC(2,1) for absolute agreement of repeated postoperative measurements of 0.99. Biomechanical Comparison of Suprapectoral and Subpectoral Locations The average load to failure in the arthroscopic suprapectoral group was 138.8 29.1 N. The mode of failure was implant pullout in 7 of 9 specimens (Fig 4). The remaining 2 specimens in this group failed at the tendon-implant interface, with catastrophic failure of the tendon at this location. The average load to failure in the open subpectoral group was 197 38.6 N. The mode of failure was implant pullout in 1 of 9 specimens. The remaining specimens in this group also failed at the tendon-implant interface with tendinous rupture. The
This study revealed 2 significant biomechanical differences between the arthroscopic suprapectoral and open subpectoral biceps tenodesis techniques: The described ASPBT technique has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with the OSPBT technique. The average tenodesis location of the arthroscopic suprapectoral group of cadaveric specimens was 4.68 cm. Murachovsky et al.44 described the distance between the pectoralis major tendon and the top of the humeral head in a cadaveric study of 40 shoulders to be 5.6 cm (range, 5.0 to 7.0 cm; SD, 0.5 cm), with little variation noted with age, sex, and patient height. This finding was confirmed in an additional study, which reported an average of 5.64 cm.45 The tenodesis location achieved in the described arthroscopic suprapectoral technique represents a location within 1 cm of the superior border of the pectoralis major tendon, indicating reliable placement at the desired suprapectoral location. The average tenodesis location of the open subpectoral group of cadaveric specimens was 7.46 cm. A recent anatomic study by Lafrance et al.43 described the height of the pectoralis major tendon to be 3.73 0.83 cm in the region of the biceps tendon, where open subpectoral tenodesis is performed. Combining this with the measurements of Murachovsky et al.,44 the average distance from the top of the humerus to the inferior border of the pectoralis major tendon is 8.49 cm. Our data show extremely accurate localization of the tenodesis site using an open subpectoral technique approximately 1 cm proximal to the inferior border of the pectoralis major tendon as described by numerous authors.20,31 Our data indicate an average difference in location between techniques of 2.74 cm, which was statistically significant. This is similar to the findings of Johannsen et al.,9 who recently reported that the open subpectoral approach placed the tenodesis tunnel on average 2.2 cm further distal than the arthroscopic suprapectoral approach. The importance of re-establishing the length-tension relationship of the long head biceps during tenodesis has been increasingly recognized.22,42 Undertensioning of the biceps during tenodesis can result in a persistent deformity, early muscle fatigue, or cramping.46,47 With overtensioning, pullout forces at the site of the tenodesis increase, which can predispose to fixation failure, among other potential complications.22 Using a novel technique with a metallic marker and static fluoroscopy, we found that the described arthroscopic
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suprapectoral technique brings the tendon proximally and overtensions the long head biceps by 2.15 cm. This overtensioning phenomenon occurred to a lesser degree in the open subpectoral group, in which the metallic marker was displaced only 0.78 0.35 cm on average (P < .001). This study did not dynamically evaluate the metallic marker during the tenodesis process to determine during which step or steps the overtensioning occurred; however, one potential explanation for the observed differences in tensioning is the “double-drop” phenomenon. This occurs as the tendon is docked in the tunnel during the ASPBT technique. The tendon is pushed into the tunnel from a superior and inferior direction, thus pulling in twice as much tendon. This will likely lead to the overtensioning found in the present study and may also greatly contribute to the poorer biomechanical strength with the ASPBT technique, because there is significantly more tendon in the tunnel and thus less circumference for purchase of the screw to bone. Based on the results of this study, we have modified our clinical technique for arthroscopic tenodesis, first stabilizing the biceps tendon proximally in the joint using a spinal needle before performing tenotomy. This approximates the previous or native length-tension relationship while performing tenodesis. We are then careful when “docking” the tendon in the drilled tunnel, securing the tendon approximately 2 cm proximal to the tunnel aperture with an aim to match this length and tension as closely as possible and avoid bringing too much distal tendon into the tunnel. Because open tenodesis resulted in only mild overtensioning, we do not similarly anchor the tendon in the joint after tenotomy; this modification would not be feasible because the tendon needs to be drawn into the incision for placement of sutures and blind-end docking. We continue to use the technique as described earlier and are careful to match the previous tension of the biceps as closely as possible. Restoration of biceps tendon tension during tenodesis has not previously been well evaluated. Johannsen et al.9 discussed potential implications of tenodesis technique on the length-tension relationship in their recent cadaveric study but did not rigorously or quantitatively evaluate it as a study objective. David et al.22 described a surgical technique for arthroscopic biceps tenodesis with an interference screw focused on the restoration of appropriate length-tension but again did not quantitatively evaluate whether it was actually achieved. Several known factors contribute to the biomechanical strength of a tenodesis construct, including bone or tissue quality, implant type, and tensioning. Although numerous studies have investigated these variables for tenodesis techniques in isolation, no previous studies have compared the isolated effect of the suprapectoral or subpectoral tenodesis location in a clinically
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relevant cadaveric model. For the tenodesis techniques described here that use an interference screw implant, our study found that the suprapectoral tenodesis location resulted in inferior ultimate load to failure compared with a subpectoral tenodesis (138.8 29.1 N v 197 38.6 N; P ¼ .002). The predominant mode of failure interestingly differed between the 2 techniques as well, with failure caused by implant pullout in 7 of 9 suprapectoral tenodesis specimens compared with only one of 9 subpectoral specimens. Previous studies have investigated ultimate load to failure for biceps tenodesis using interference screw fixation. Mazzocca et al.11 compared load to failure in 20 cadaveric shoulder specimens, including 5 using an open subpectoral technique with an interference screw and 5 using an arthroscopic suprapectoral technique with an interference screw. The authors reported load to failure of 252.4 68.63 N in the OSPBT group and 237.6 27.58 N in the ASPBT group and concluded that no significant differences existed in ultimate failure strength between methods. Richards and Burkhart48 evaluated load to failure in 11 cadaveric specimens, 5 of which were tenodesed in an open manner using an interference screw in a proximal location. The authors reported a load to failure of 233.5 55.5 N for the interference screw tenodesis, which was significantly better than that for suture anchor fixation. Golish et al.7 also found a load to failure of 169.6 50.5 N for open subpectoral biceps tenodesis with an interference screw in 9 cadaveric specimens, which was likewise significantly better than suture anchor fixation. Recently, Patzer et al.16 biomechanically compared several biceps tenodesis options, including 7 cadaveric specimens with suprapectoral tenodesis using an interference screw and 7 specimens with a subpectoral tenodesis using an interference screw. The ultimate load to failure in the suprapectoral group was 218.3 59.7 N and was 200.7 38.6 N in the subpectoral group. This was significantly higher than seen in suture anchor techniques. The observed load to failure in our study was similar to those previously reported; however, we found a significantly lower load to failure in the ASPBT group compared with those previously reported. This difference may be technique related, because the described ASPBT technique results in more tendon remaining in the tunnel, which can lead to decreased bony contact for the tenodesis implant. In addition, implant differences (SwiveLock v BioTenodesis Screw; Arthrex, Naples, FL) might also contribute to the observed difference in biomechanical strength. Finally, the bone quality at the site of tenodesis may be a factor in this observed biomechanical strength difference because the more proximal tenodesis location of the ASPBT technique has potentially weaker metaphyseal bone than does the diaphyseal bone of the OSPBT location.
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Limitations This study has several limitations. First, this is a timezero study, which can investigate only the initial fixation of the tendon, implant, and bone. Biological factors such as tendon ingrowth or soft tissue effects cannot be predicted based on these experiments. Additionally, clinical results likewise cannot be determined. Future comparative clinical studies are necessary to determine what result tenodesis location will have on postoperative function and patient satisfaction. Second, the biomechanical testing was performed after dissection of the remaining soft tissue structures, which could contribute to the overall strength of the tenodesis construct. Clinical failures primarily occur at the suturetendon interface, as opposed to the implant pullout observed in this biomechanical study, which could also be related to dissection of the surrounding soft tissues before biomechanical testing. Third, our novel technique for assessing the length-tension relationship has not previously been validated. Fourth, the study measurements, including measurement of the lengthtension relationship and biomechanical measurements, were not able to be performed in a blinded fashion. Finally, although 2 fellowship-trained surgeons performed all study procedures, and cadavers and surgeons were randomized to techniques, having 2 surgeons does add variability that must be considered.
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Conclusions The described ASPBT technique using an interference screw implant has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaveric specimens.
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