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Biomechanical analysis of anterior capsule reconstruction and latissimus dorsi transfer for irreparable subscapularis tears
J Shoulder Elbow Surg (2019) -, 1–7
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Biomechanical analysis of anterior capsule reconstruction and latissimus dorsi transfer for irreparable subscapularis tears Reza Omid, MDa, Michael A. Stone, MDb,*, Charles C. Lin, MDc,d, Nilay A. Patel, MDe,d, Yasuo Itami, MDf,d, Michelle H. McGarry, MSd, Thay Q. Lee, PhDd a
Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA Division of Shoulder and Elbow Surgery, Rothman Orthopaedic Institute, Thomas Jefferson University Hospitals, Philadelphia, PA, USA c Department of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, NY, USA d Orthopaedic Biomechanics Laboratory, Congress Medical Foundation, Pasadena, CA, USA e Department of Orthopaedic Surgery, University of California, Irvine, Orange, CA, USA f Department of Orthopaedic Surgery, Osaka Medical College, Takatsuki, Japan b
Background: Anterior capsule reconstruction (ACR) and latissimus dorsi transfers (LTs) have been proposed as solutions for irreparable subscapularis tears. The purpose of this study was to biomechanically assess the effects of ACR and LT separately and together for treatment of irreparable subscapularis tears. Materials and method: Eight cadaveric shoulders underwent 5 testing conditions: (1) intact, (2) irreparable subscapularis tear, (3) ACR, (4) ACRþLT, and (5) LT alone. Anteroinferior translation loads of 20, 30, and 40 N were applied. Range of motion and magnitudes of glenohumeral anterior and inferior translation at 0 , 30 , and 60 of abduction and at 30 and 60 of external rotation were measured for each testing condition. Results: At 30 of abduction and 60 of external rotation, ACR and ACRþLT restored anterior and inferior translation to intact (P > .702) for 30 and 40 N of anteroinferiorly directed force. LT alone did not restore anteroinferior stability at 30 N of distraction force at 30 of glenohumeral abduction and 60 of external rotation (P < .001). However, ACR and ACRþLT led to significant decreases in total range of motion compared to intact at 0 and 30 of abduction (P < .007). Conclusions: ACR with dermal allograft was able to restore anteroinferior stability in the setting of irreparable subscapularis tears but resulted in decreased total range of motion. LT alone was less effective than ACR in restoring glenohumeral stability. The addition of LT as a dynamic restraint did not increase the efficacy of ACR. Level of evidence: Basic Science Study; Biomechanics Ó 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Anterior capsule reconstruction; subscapularis tear; rotator cuff; cadaveric study; latissimus dorsi; tendon transfer
Institutional review board approval was not required for the basic science study.
*Reprint requests: Michael A. Stone, MD, Rothman Orthopaedic Institute, 925 Chestnut Street, 5th floor, Philadelphia, PA 19107, USA. E-mail address: [email protected] (M.A. Stone).
1058-2746/$ - see front matter Ó 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. https://doi.org/10.1016/j.jse.2019.07.033
2 The anterior glenohumeral capsule, glenohumeral ligaments, and the subscapularis play key roles in maintaining anterior glenohumeral joint stability. Failure of these structures leads to altered kinematics of the shoulder, which can result in severe functional deficits, particularly in young, active patients. Subscapularis tears can be isolated or present in conjunction with other rotator cuff tears, and in one series of 580 patients undergoing rotator cuff operations, 6.2% had irreparable tears.5 These irreparable subscapularis tears can be the result of prior failed repair or neglected massive tear and present as a challenging treatment dilemma.3 Muscle transfers, such as the pectoralis major transfer, and more recently the latissimus dorsi tendon transfer (LT), may be used to improve glenohumeral stability and have been described with transfer of varying portions and muscle trajectories.5,8,15,19 The LT has a line of pull that more closely resembles the pull of the native subscapularis, passing behind the chest wall rather than in front of it in the case of the pectoralis major transfer.4,9,13 Although these options have been used to varying levels of success, they are associated with significant retear rates and complications such as musculocutaneous or axillary nerve injury.4-6,17 Additionally, they are nonanatomic and alter the normal biomechanics of the shoulder, which requires more aggressive salvage procedures in case of failure. More anatomic reconstruction options exist, including soft tissue procedures such as capsular shifts or stabilization using autografts (IT band or hamstring) or allografts (tibialis anterior or Achilles tendon).2,7 However, these procedures often require complex folding of the graft material to generate enough coverage to re-create the various glenohumeral ligaments.2,7 Drawing from the promising outcomes of superior capsule reconstruction for irreparable supraspinatus tears, anterior capsule reconstruction (ACR) has been more recently suggested as a possible solution. The main benefits of this technique are that it restores normal anatomy, thereby preserving kinematics more similar to the native shoulder, and has a lower risk of neurovascular injury.10,14,16 An irreparable subscapularis tear represents an anatomic disruption of not just the subscapularis but also a tear of the underlying capsule and glenohumeral ligaments. Therefore, these lesions are a disruption of both static stabilizers (anterior capsule and glenohumeral ligaments) and dynamic stabilizers (subscapularis muscle). Most proposed solutions attempt to restore this deficiency with only a single type of stabilization, with muscle transfers only restoring the dynamic stabilizer and grafts restoring only the static stabilizers. It is possible that restoration of both a static stabilizer using ACR and adding a dynamic stabilizer such as an LT may allow for restoration of shoulder biomechanics closer to the intact state than either procedure alone.
R. Omid et al. The purpose of this study was to evaluate the effect of the ACR, LT, and the combined effect in a cadaveric model for irreparable subscapularis tears. We hypothesized that the ACR would be more effective at restoring glenohumeral stability than the LT alone, and the addition of the LT would increase range of motion and further reduce anteroinferior translation.
Materials and methods Specimen preparation Eight shoulder specimens (7 male and 1 female, average age 64 years) were used for this cadaveric biomechanical study. The shoulders were stored at –20 C and thawed overnight before testing. Each shoulder was grossly assessed for any evidence of previous injury or surgery. Shoulders were then dissected free of all soft tissue, taking care to leave the tendinous insertions of the pectoralis major, latissimus dorsi, deltoid, supraspinatus, infraspinatus, teres minor, and subscapularis muscles intact along with the coracoacromial ligament.
Testing setup A previously validated custom shoulder testing system was used for this study.11 The scapula was mounted in 20 of anteversion, and the muscles were loaded using lines through metal guides and over pulleys to simulate the natural vectors of the shoulder muscles. Muscle loading was determined using the crosssectional area of the muscles, similar to previous studies, and were applied through lines of pull sutured to the tendinous insertions as follows: supraspinatus (10 N), subscapularis (10 N), infraspinatus (5 N), teres minor (5 N), deltoid (36 N), latissimus dorsi (10 N), and pectoralis major (10 N).1,18 After the irreparable subscapularis tear condition was created, the subscapularis was unloaded. Three screws were placed on the scapula and three screws were placed on the humerus to track the relative position of the humeral head and the glenoid. A Microscribe 3Dx (Revware, Inc, Raleigh, NC, USA), with accuracy within 0.3 mm, was used to digitize each point in space. All measurements were taken twice. After testing of all conditions, the articular geometry of the glenoid and the humeral head were then collected and the position of the center of the humeral head was assessed. The movement of the humerus with respect to the scapula was then calculated.
Biomechanical testing Each condition was tested at 0 , 30 , and 60 of glenohumeral abduction. Maximum internal and external rotation (ER) were determined by applying 1.5 Nm of torque. Anteroinferior translation was assessed using anteroinferior translation loads of 20, 30, and 40 N applied through a line tied around the surgical neck of the humerus and guided through a pulley to create an anterior vector directed 20 inferiorly.
ACR vs. Lat transfer for subscapularis tears
3
Figure 1 Testing conditions. Five conditions were tested sequentially in this study: (A) Intact, (B) irreparable subscapularis tear, (C) anterior capsule reconstruction with human dermal allograft, (D) anterior capsule reconstruction with the addition of a latissimus dorsi transfer, (E) latissimus dorsi transfer alone.
Testing conditions
Anterior capsule reconstruction with latissimus dorsi transfer condition
Each specimen sequentially underwent 5 testing conditions: (1) intact, (2) irreparable subscapularis tear (SubT), (3) anterior capsule reconstruction with human dermal allograft (JRF Ortho, Centennial, CO, USA) (ACR), (4) anterior capsule reconstruction with the addition of a latissimus dorsi transfer (ACRþLT), and (5) latissimus dorsi transfer alone (LT).
Irreparable subscapularis tear condition The subscapularis and anterior capsule were sharply incised and released from the superior three-fourths of the lesser tuberosity (Fig. 1, B). At the glenoid, the capsule was resected off the glenoid from 1 o’clock to 5:30 o’clock while taking care to leave the labrum intact.
Anterior capsule reconstruction dermal allograft condition
with
human
Two 4.5-mm double-loaded Corkscrew FT anchors (Arthrex, Inc, Naples, FL, USA) were inserted at the 1:30 o’clock and 5 o’clock positions on the anterior glenoid, just medial to the labrum (Fig. 1, C). Two 4.75-mm triple-loaded SwiveLock anchors (Arthrex, Inc) were inserted on the humeral head at the medial margin of the lesser tuberosity. The size of the allograft was measured based on the locations of these anchors while the humerus was in 30 of glenohumeral abduction and at the midpoint of the total range of motion to prevent an overconstrained joint while maintaining graft tension. The graft was oversized by adding 5 mm medially, 5 mm superiorly, 10 mm inferiorly, and 10 mm laterally to ensure adequate coverage. The graft was first fixed to the glenoid using a double-pulley technique and then fixed to the lesser tuberosity using 2 horizontal mattress stitches. One superior side-to-side suture was placed to close the rotator interval. One inferior sideto-side suture was placed to create capsular continuity between the graft and the remaining inferior capsular tissue at the articular margin.
The latissimus dorsi insertion was sharply dissected from its insertion onto the humerus (Fig. 1, D). It was then transferred anterosuperiorly and placed over the anterior capsule reconstruction construct. A horizontal mattress stitch was used to secure the tendon transfer. One superior side-to-side suture through the transferred tendon and remaining superior capsule was added to replicate the subscapularis muscle vector. Inferior side-to-side suturing was not performed because of lack of transferred tendon width.
Latissimus dorsi transfer condition The dermal allograft was removed by sharply dissecting the allograft from beneath the LT, taking care to retain all the sutures keeping the muscle transfer in place (Fig. 1, E). This was done to ensure that the tendon transfer remained in the same place between conditions and thus avoiding a change in force vectors.
Statistical analysis A 2-way repeated measures analysis of variance test with Tukey post hoc tests (SigmaPlot; Systat Software Inc, San Jose, CA, USA) were used to compare the various conditions. Statistical significance was set at P < .05.
Results Total range of motion The subscapularis tear resulted in an increase in the total range of motion at all degrees of shoulder abduction (P < .042) (Fig. 2). The ACR and ACRþLT conditions both resulted in significantly decreased total range of motion at 0 and 30 of abduction (P < .007). However, at 60 of abduction, both were able to restore the total range of motion back to the intact state (P > .066). Latissimus transfer alone was able to restore the total
4
R. Omid et al.
Figure 2 Total range of motion (*P < .05 vs. Intact; yP < .05 vs. SubT; zP < .05 vs. ACR; xP < .05 vs. ACRþLT). abd, abduction; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer.
range of motion to intact states at all degrees of abduction (P > .104).
Anterior glenohumeral translation The differences in anterior translation between conditions were greater at 60 of ER than at 30 of ER (Table I). At 60 of ER with 20 N of pull, there were no significant differences between conditions in anterior translation at any degree of shoulder abduction. At both 30 and 40 N of anteroinferior force, the subscapularis tear condition resulted in significantly greater anterior translation at 0 of abduction and 30 of abduction and 60 of ER (0 abd-60 ER and 30 abd60 ER, respectively). The ACR and ACRþLT conditions were able to restore anterior translation back to intact states at each of these shoulder positions. However, there were no significant differences between the ACR and ACRþLT conditions. Latissimus transfer alone was unable to resist significant anterior translation at 30 and 40 N for 0 abd60 ER and 30 N for 30 abd-60 ER.
Inferior glenohumeral translation For inferior translation, the differences between conditions were also more substantial at 60 ER than 30 ER (Table II). Subscapularis tear resulted in a significant increase in inferior translation at 30 and 40 N for both 0 abd-60 ER and 30 abd60 ER. ACR and ACRþLT were able to restore inferior translation to the intact state at each of these loads and angles.
However, there was no significant difference between the ACR and ACRþLT conditions. Latissimus transfer alone still resulted in significant inferior translation compared to intact at 30 N in 0 abd-60 ER and 30 abd-60 ER.
Discussion We found that ACR was more effective than LT at restoring glenohumeral kinematics when subjected to a translation force. Furthermore, the addition of the LT on top of the ACR did not significantly improve construct performance against anterior translation. Anterior capsule reconstruction with dermal allograft resulted in a reduction in total range of motion, whereas LT alone resulted in a restoration of total range of motion. Clinically, LT for irreparable subscapularis tears are usually associated with increases in active range of motion because of the increase in ability to perform active internal rotation.13 However, in this model only passive range of motion was assessed. Variations in ACR technique may change the amount of range of motion lost with ACR. Position of the arm during graft sizing affects graft tension and thus range of motion. Additionally, side-toside suturing has been shown to affect graft performance in superior capsule reconstruction and could also affect capsular tightness in ACR.12 This change in capsular tightness could result in decreased range of motion. Although there was no significant difference in range of motion between the ACR and ACRþLT conditions,
ACR vs. Lat transfer for subscapularis tears Table I
5
Anterior glenohumeral translation
0 abd-30 ER 20 N 30 N 40 N 30 abd-30 ER 20 N 30 N 40 N 60 abd-30 ER 20 N 30 N 40 N 0 abd-60 ER 20 N 30 N 40 N 30 abd-60 ER 20 N 30 N 40 N 60 abd-60 ER 20 N 30 N 40 N
Intact
SubT
ACR
ACRþLT
LT
1.5 0.2 3.3 0.6 10.5 3.3
1.8 0.3 9.8 3.6) 19.3 3.0)
1.7 0.3 9.0 3.0 16.6 2.4)
1.5 0.2 6.3 2.5 12.7 2.9y
1.6 0.2 10.2 3.4) 19.2 3.7),z
1.4 0.2 3.1 0.8 9.6 2.7
1.5 0.2 8.1 3.4 21.6 2.9)
1.5 0.2 8.5 3.5 17.2 3.2)
1.8 0.3 9.1 2.5) 15.7 2.7),y
1.8 0.3 12.4 4.2) 18.8 3.7)
1.6 0.3 3.9 0.9 7.3 1.3
1.8 0.3 5.8 2.0 11.0 2.6
2.3 0.7 6.9 2.1 10.1 2.2
1.7 0.3 6.2 1.7 9.6 1.8
1.8 0.3 5.1 1.3 11.4 3.2
2.5 0.4 16.3 4.0) 24.9 3.2)
2.2 0.3 10.1 3.1y 12.2 3.4y
2.3 0.3 10.5 3.2y 12.8 3.3y
2.7 0.6 16.5 4.6),z,x 17.8 4.3),y,z,x
1.5 0.3 6.5 2.4 14.1 3.1
2.5 0.6 18.4 4.0) 25.2 2.2)
2.2 0.5 9.7 2.7y 13.8 2.8y
2.2 0.2 10.4 2.5y 14.7 2.6y
2.1 0.4 17.7 3.9),z,x 18.4 4.0y
1.7 0.5 5.6 1.5 9.4 1.7
3.1 0.9 11.4 2.4 18.0 2.5)
2.8 1.0 8.7 2.1 13.3 2.6
2.4 0.6 6.9 1.9 9.7 1.8y
2.2 0.6 7.8 2.3 13.2 2.9)
2.5 0.8 9.5 2.4 14.2 2.4
abd, abduction; ER, external rotation; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer. Results are reported in millimeters. * P < .05 vs. Intact. y P < .05 vs. SubT. z P < .05 vs. ACRþLT. x P < .05 vs. ACR.
adding the LT on top of the ACR adds additional sutures to the construct and could affect passive range of motion, although it may possibly improve active range of motion clinically as the transfer would add a muscular component to the anterior shoulder. The ACR was able to restore anterior and inferior translation back to the intact state in the setting of an anteroinferior translation force. In contrast, the LT alone was not as effective as the ACR at resisting anterior and inferior translation. The difference in efficacy was particularly notable at lower ranges of abduction. At greater translation loads of 40 N, the effects of the LT were more evident, suggesting that the effect of the LT may be greater at the extremes of instability. Combining the effect of the ACR with the LT also did not result in a significant difference from the ACR alone. Although it was theorized that the dynamic stabilizing effect of an LT added to the static stabilizing effect of the ACR, it is possible that most of the combined stabilization effect is dominated by the ACR, and therefore the lesser effect contributed by the LT was not seen.
LT has been demonstrated as an option for irreparable subscapularis tears and has yielded promising short-term results when the transfer remains intact.9,13 However, longterm results of this technique are yet to be reported. Anatomically, it has been suggested to be superior to pectoralis major transfers because of the force vector being more similar to the native subscapularis as it passes posterior to the chest wall rather than anterior to it.4 In our study, we did not find the LT alone to be particularly effective in resisting anterior or inferior translation at loads that resulted in significant translation of the humeral head. LTs are associated with complications such as axillary nerve entrapment or tendon transfer rupture, which results in poor outcomes.6,9 Similar to LTs, ACRs are also still in nascent stages of utilization. Although there have been studies demonstrating various techniques for ACR, there are no long-term studies demonstrating its efficacy.10,14,16 In this study, we found that ACRs could be a viable option to reduce or prevent anterior or inferior translation of the humeral head while reducing the risk of nerve entrapment and without altering normal shoulder anatomy.
6
R. Omid et al. Table II
Inferior glenohumeral translation Intact
0 abd-30 ER 20 N 30 N 40 N 30 abd-30 ER 20 N 30 N 40 N 60 abd-30 ER 20 N 30 N 40 N 0 abd-60 ER 20 N 30 N 40 N 30 abd-60 ER 20 N 30 N 40 N 60 abd-60 ER 20 N 30 N 40 N
SubT
ACR
ACRþLT
LT
0.5 0.1 1.5 0.4 9.0 4.1
0.7 0.1 8.6 4.5) 18.3 4.2)
0.7 0.2 9.0 4.4) 17.5 4.2)
0.5 0.1 5.6 3.7 13.0 4.6
0.7 0.1 9.6 4.6) 19.8 4.7),y
0.5 0.1 1.6 0.6 8.8 3.1
0.6 0.1 7.5 4.0 20.0 3.2)
0.6 0.1 6.9 3.5 15.5 3.2)
0.7 0.2 7.2 3.0 13.8 3.2z
0.8 0.2 11.6 4.8) 17.5 3.9)
0.6 0.2 1.8 0.6 4.2 1.2
0.7 0.2 2.6 0.9 7.1 2.8
0.9 0.4 3.8 1.4 5.9 2.0
0.6 0.1 3.7 1.7 5.5 1.8
0.8 0.3 5.2 2.6 9.1 3.1
0.4 0.1 2.3 0.9 9.5 3.6
0.7 0.1 12.9 3.9) 20.2 3.4)
0.8 0.3 8.4 3.2 10.8 3.9z
0.7 0.1 8.2 3.9z 10.4 4.3z
0.9 0.3 13.8 4.3),y 15.1 4.3y
0.5 0.1 5.0 2.8 11.5 3.1
1.0 0.3 13.7 3.3) 19.1 2.4)
0.8 0.3 7.3 2.7z 12.1 3.4z
0.7 0.1 7.5 2.9z 11.9 3.4z
0.6 0.2 13.8 3.4),y,x 14.2 3.5
1.0 0.4 4.8 1.7 7.6 2.2
0.9 0.4 3.8 1.6 5.1 1.7
0.6 0.2 2.9 1.4 5.3 1.6
1.1 0.5 6.0 1.8 10.2 2.3
0.9 0.4 5.4 1.9 7.9 2.1
abd, abduction; ER, external rotation; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer. Results are reported in millimeters. * P < .05 vs. Intact. y P < .05 vs. ACRþLT. z P < .05 vs. SubT. x P < .05 vs. ACR.
There were several limitations to this study. As this was a cadaveric biomechanical study, it represents only timezero conditions and does not take into consideration healing or physical rehabilitation after surgery. For tendon transfers in particular, outcomes rely on patient adherence to rigorous physical therapy and muscle retraining. Therefore, the outcomes after LT may vary from patient to patient and may be more effective over time. Reductions in range of motion were seen with ACR in this time-zero study. These limitations should be less in clinical situations, as the graft will stretch over time. Furthermore, the optimal technique for placement of ACR has not yet been fully elucidated. Factors such as graft tension or side-to-side suturing could affect the efficacy of the reconstruction technique. In this study, shoulder specimens without full torsos were used. Although the biomechanical testing jig used lines of tension to simulate all native muscle vectors, these could only be approximated without the torso intact. Additionally, the muscle transfer in this study was not subject to soft tissue limitations that would be seen in vivo, which could affect muscle vectors, as the surrounding tissue was dissected away during specimen preparation. Another limitation is
that in this study, all testing occurred in a single sequence to ensure repeatability. However, viscoelastic effects that occur during testing could have systematically propagated throughout the study. This study also only assessed a single graft type. Although human dermal allograft has emerged as a popular option for reconstructive procedures in the shoulder, the use of other graft types may alter the kinematics of the resulting procedure and result in varying results.
Conclusion Anterior capsule reconstruction with dermal allograft was able to restore anteroinferior stability in the setting of irreparable subscapularis tears but resulted in decreased total range of motion. Latissimus dorsi transfer alone was less effective than anterior capsule reconstruction in restoring glenohumeral stability. The addition of latissimus dorsi transfer as a dynamic restraint did not increase the efficacy of the anterior capsule reconstruction.
ACR vs. Lat transfer for subscapularis tears
Disclaimer Reza Omid receives royalties from Medacta and Integra and has consultant agreements with Wright/Tornier, Medacta, and Integra. All the other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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7 8. Jost B, Puskas GJ, Lustenberger A, Gerber C. Outcome of pectoralis major transfer for the treatment of irreparable subscapularis tears. J Bone Joint Surg Am 2003;85:1944-51. https://doi.org/10.2106/ 00004623-200310000-00012 9. Kany J, Guinand R, Croutzet P, Valenti P, Werthel JD, Grimberg J. Arthroscopic-assisted latissimus dorsi transfer for subscapularis deficiency. Eur J Orthop Surg Traumatol 2016;26:329-34. https://doi.org/ 10.1007/s00590-016-1753-3 10. Kwapisz A, Tokish JM. Anterior capsule reconstruction technique with an acellular dermal allograft. Arthrosc Tech 2017;6:e1945-52. https://doi.org/10.1016/j.eats.2017.07.012 11. Lee YS, Lee TQ. Specimen-specific method for quantifying glenohumeral joint kinematics. Ann Biomed Eng 2010;38:3226-36. https:// doi.org/10.1007/s10439-010-0074-7 12. Mihata T, McGarry MH, Kahn T, Goldberg I, Neo M, Lee TQ. Biomechanical role of capsular continuity in superior capsule reconstruction for irreparable tears of the supraspinatus tendon. Am J Sports Med 2016;44:1423-30. https://doi.org/10.1177/0363546516 631751 13. Mun SW, Kim JY, Yi SH, Baek CH. Latissimus dorsi transfer for irreparable subscapularis tendon tears. J Shoulder Elbow Surg 2018; 27:1057-64. https://doi.org/10.1016/j.jse.2017.11.022 14. Pogorzelski J, Hussain ZB, Lebus GF, Fritz EM, Millett PJ. Anterior capsular reconstruction for irreparable subscapularis tears. Arthrosc Tech 2017;6:e951-8. https://doi.org/10.1016/j.eats.2017.03.008 15. Resch H, Povacz P, Ritter E, Matschi W. Transfer of the pectoralis major muscle for the treatment of irreparable rupture of the subscapularis tendon. J Bone Joint Surg Am 2000;82:372-82. 16. Rogers JP, Kwapisz A, Tokish JM. Anterior capsule reconstruction for irreparable subscapularis tears. Arthrosc Tech 2017;6:e2241-7. https:// doi.org/10.1016/j.eats.2017.08.017 17. Ruiz-Iban MA, Murillo-Gonzalez JA, Diaz-Heredia J, AvilaLafuente JL, Cuellar R. Pectoralis major transfer for subscapular deficiency: anatomical study of the relationship between the transferred muscle and the musculocutaneous nerve. Knee Surg Sports Traumatol Arthrosc 2013;21:2177-83. https://doi.org/10.1007/s00167013-2432-0 18. Veeger HE, Van der Helm FC, Van der Woude LH, Pronk GM, Rozendal RH. Inertia and muscle contraction parameters for musculoskeletal modelling of the shoulder mechanism. J Biomech 1991;24: 615-29. 19. Wirth MA, Rockwood CA Jr. Operative treatment of irreparable rupture of the subscapularis. J Bone Joint Surg Am 1997;79:722-31.
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Biomechanical analysis of anterior capsule reconstruction and latissimus dorsi transfer for irreparable subscapularis tears Reza Omid, MDa, Michael A. Stone, MDb,*, Charles C. Lin, MDc,d, Nilay A. Patel, MDe,d, Yasuo Itami, MDf,d, Michelle H. McGarry, MSd, Thay Q. Lee, PhDd a
Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA Division of Shoulder and Elbow Surgery, Rothman Orthopaedic Institute, Thomas Jefferson University Hospitals, Philadelphia, PA, USA c Department of Orthopedic Surgery, NYU Langone Orthopedic Hospital, New York, NY, USA d Orthopaedic Biomechanics Laboratory, Congress Medical Foundation, Pasadena, CA, USA e Department of Orthopaedic Surgery, University of California, Irvine, Orange, CA, USA f Department of Orthopaedic Surgery, Osaka Medical College, Takatsuki, Japan b
Background: Anterior capsule reconstruction (ACR) and latissimus dorsi transfers (LTs) have been proposed as solutions for irreparable subscapularis tears. The purpose of this study was to biomechanically assess the effects of ACR and LT separately and together for treatment of irreparable subscapularis tears. Materials and method: Eight cadaveric shoulders underwent 5 testing conditions: (1) intact, (2) irreparable subscapularis tear, (3) ACR, (4) ACRþLT, and (5) LT alone. Anteroinferior translation loads of 20, 30, and 40 N were applied. Range of motion and magnitudes of glenohumeral anterior and inferior translation at 0 , 30 , and 60 of abduction and at 30 and 60 of external rotation were measured for each testing condition. Results: At 30 of abduction and 60 of external rotation, ACR and ACRþLT restored anterior and inferior translation to intact (P > .702) for 30 and 40 N of anteroinferiorly directed force. LT alone did not restore anteroinferior stability at 30 N of distraction force at 30 of glenohumeral abduction and 60 of external rotation (P < .001). However, ACR and ACRþLT led to significant decreases in total range of motion compared to intact at 0 and 30 of abduction (P < .007). Conclusions: ACR with dermal allograft was able to restore anteroinferior stability in the setting of irreparable subscapularis tears but resulted in decreased total range of motion. LT alone was less effective than ACR in restoring glenohumeral stability. The addition of LT as a dynamic restraint did not increase the efficacy of ACR. Level of evidence: Basic Science Study; Biomechanics Ó 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Anterior capsule reconstruction; subscapularis tear; rotator cuff; cadaveric study; latissimus dorsi; tendon transfer
Institutional review board approval was not required for the basic science study.
*Reprint requests: Michael A. Stone, MD, Rothman Orthopaedic Institute, 925 Chestnut Street, 5th floor, Philadelphia, PA 19107, USA. E-mail address: [email protected] (M.A. Stone).
1058-2746/$ - see front matter Ó 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. https://doi.org/10.1016/j.jse.2019.07.033
2 The anterior glenohumeral capsule, glenohumeral ligaments, and the subscapularis play key roles in maintaining anterior glenohumeral joint stability. Failure of these structures leads to altered kinematics of the shoulder, which can result in severe functional deficits, particularly in young, active patients. Subscapularis tears can be isolated or present in conjunction with other rotator cuff tears, and in one series of 580 patients undergoing rotator cuff operations, 6.2% had irreparable tears.5 These irreparable subscapularis tears can be the result of prior failed repair or neglected massive tear and present as a challenging treatment dilemma.3 Muscle transfers, such as the pectoralis major transfer, and more recently the latissimus dorsi tendon transfer (LT), may be used to improve glenohumeral stability and have been described with transfer of varying portions and muscle trajectories.5,8,15,19 The LT has a line of pull that more closely resembles the pull of the native subscapularis, passing behind the chest wall rather than in front of it in the case of the pectoralis major transfer.4,9,13 Although these options have been used to varying levels of success, they are associated with significant retear rates and complications such as musculocutaneous or axillary nerve injury.4-6,17 Additionally, they are nonanatomic and alter the normal biomechanics of the shoulder, which requires more aggressive salvage procedures in case of failure. More anatomic reconstruction options exist, including soft tissue procedures such as capsular shifts or stabilization using autografts (IT band or hamstring) or allografts (tibialis anterior or Achilles tendon).2,7 However, these procedures often require complex folding of the graft material to generate enough coverage to re-create the various glenohumeral ligaments.2,7 Drawing from the promising outcomes of superior capsule reconstruction for irreparable supraspinatus tears, anterior capsule reconstruction (ACR) has been more recently suggested as a possible solution. The main benefits of this technique are that it restores normal anatomy, thereby preserving kinematics more similar to the native shoulder, and has a lower risk of neurovascular injury.10,14,16 An irreparable subscapularis tear represents an anatomic disruption of not just the subscapularis but also a tear of the underlying capsule and glenohumeral ligaments. Therefore, these lesions are a disruption of both static stabilizers (anterior capsule and glenohumeral ligaments) and dynamic stabilizers (subscapularis muscle). Most proposed solutions attempt to restore this deficiency with only a single type of stabilization, with muscle transfers only restoring the dynamic stabilizer and grafts restoring only the static stabilizers. It is possible that restoration of both a static stabilizer using ACR and adding a dynamic stabilizer such as an LT may allow for restoration of shoulder biomechanics closer to the intact state than either procedure alone.
R. Omid et al. The purpose of this study was to evaluate the effect of the ACR, LT, and the combined effect in a cadaveric model for irreparable subscapularis tears. We hypothesized that the ACR would be more effective at restoring glenohumeral stability than the LT alone, and the addition of the LT would increase range of motion and further reduce anteroinferior translation.
Materials and methods Specimen preparation Eight shoulder specimens (7 male and 1 female, average age 64 years) were used for this cadaveric biomechanical study. The shoulders were stored at –20 C and thawed overnight before testing. Each shoulder was grossly assessed for any evidence of previous injury or surgery. Shoulders were then dissected free of all soft tissue, taking care to leave the tendinous insertions of the pectoralis major, latissimus dorsi, deltoid, supraspinatus, infraspinatus, teres minor, and subscapularis muscles intact along with the coracoacromial ligament.
Testing setup A previously validated custom shoulder testing system was used for this study.11 The scapula was mounted in 20 of anteversion, and the muscles were loaded using lines through metal guides and over pulleys to simulate the natural vectors of the shoulder muscles. Muscle loading was determined using the crosssectional area of the muscles, similar to previous studies, and were applied through lines of pull sutured to the tendinous insertions as follows: supraspinatus (10 N), subscapularis (10 N), infraspinatus (5 N), teres minor (5 N), deltoid (36 N), latissimus dorsi (10 N), and pectoralis major (10 N).1,18 After the irreparable subscapularis tear condition was created, the subscapularis was unloaded. Three screws were placed on the scapula and three screws were placed on the humerus to track the relative position of the humeral head and the glenoid. A Microscribe 3Dx (Revware, Inc, Raleigh, NC, USA), with accuracy within 0.3 mm, was used to digitize each point in space. All measurements were taken twice. After testing of all conditions, the articular geometry of the glenoid and the humeral head were then collected and the position of the center of the humeral head was assessed. The movement of the humerus with respect to the scapula was then calculated.
Biomechanical testing Each condition was tested at 0 , 30 , and 60 of glenohumeral abduction. Maximum internal and external rotation (ER) were determined by applying 1.5 Nm of torque. Anteroinferior translation was assessed using anteroinferior translation loads of 20, 30, and 40 N applied through a line tied around the surgical neck of the humerus and guided through a pulley to create an anterior vector directed 20 inferiorly.
ACR vs. Lat transfer for subscapularis tears
3
Figure 1 Testing conditions. Five conditions were tested sequentially in this study: (A) Intact, (B) irreparable subscapularis tear, (C) anterior capsule reconstruction with human dermal allograft, (D) anterior capsule reconstruction with the addition of a latissimus dorsi transfer, (E) latissimus dorsi transfer alone.
Testing conditions
Anterior capsule reconstruction with latissimus dorsi transfer condition
Each specimen sequentially underwent 5 testing conditions: (1) intact, (2) irreparable subscapularis tear (SubT), (3) anterior capsule reconstruction with human dermal allograft (JRF Ortho, Centennial, CO, USA) (ACR), (4) anterior capsule reconstruction with the addition of a latissimus dorsi transfer (ACRþLT), and (5) latissimus dorsi transfer alone (LT).
Irreparable subscapularis tear condition The subscapularis and anterior capsule were sharply incised and released from the superior three-fourths of the lesser tuberosity (Fig. 1, B). At the glenoid, the capsule was resected off the glenoid from 1 o’clock to 5:30 o’clock while taking care to leave the labrum intact.
Anterior capsule reconstruction dermal allograft condition
with
human
Two 4.5-mm double-loaded Corkscrew FT anchors (Arthrex, Inc, Naples, FL, USA) were inserted at the 1:30 o’clock and 5 o’clock positions on the anterior glenoid, just medial to the labrum (Fig. 1, C). Two 4.75-mm triple-loaded SwiveLock anchors (Arthrex, Inc) were inserted on the humeral head at the medial margin of the lesser tuberosity. The size of the allograft was measured based on the locations of these anchors while the humerus was in 30 of glenohumeral abduction and at the midpoint of the total range of motion to prevent an overconstrained joint while maintaining graft tension. The graft was oversized by adding 5 mm medially, 5 mm superiorly, 10 mm inferiorly, and 10 mm laterally to ensure adequate coverage. The graft was first fixed to the glenoid using a double-pulley technique and then fixed to the lesser tuberosity using 2 horizontal mattress stitches. One superior side-to-side suture was placed to close the rotator interval. One inferior sideto-side suture was placed to create capsular continuity between the graft and the remaining inferior capsular tissue at the articular margin.
The latissimus dorsi insertion was sharply dissected from its insertion onto the humerus (Fig. 1, D). It was then transferred anterosuperiorly and placed over the anterior capsule reconstruction construct. A horizontal mattress stitch was used to secure the tendon transfer. One superior side-to-side suture through the transferred tendon and remaining superior capsule was added to replicate the subscapularis muscle vector. Inferior side-to-side suturing was not performed because of lack of transferred tendon width.
Latissimus dorsi transfer condition The dermal allograft was removed by sharply dissecting the allograft from beneath the LT, taking care to retain all the sutures keeping the muscle transfer in place (Fig. 1, E). This was done to ensure that the tendon transfer remained in the same place between conditions and thus avoiding a change in force vectors.
Statistical analysis A 2-way repeated measures analysis of variance test with Tukey post hoc tests (SigmaPlot; Systat Software Inc, San Jose, CA, USA) were used to compare the various conditions. Statistical significance was set at P < .05.
Results Total range of motion The subscapularis tear resulted in an increase in the total range of motion at all degrees of shoulder abduction (P < .042) (Fig. 2). The ACR and ACRþLT conditions both resulted in significantly decreased total range of motion at 0 and 30 of abduction (P < .007). However, at 60 of abduction, both were able to restore the total range of motion back to the intact state (P > .066). Latissimus transfer alone was able to restore the total
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R. Omid et al.
Figure 2 Total range of motion (*P < .05 vs. Intact; yP < .05 vs. SubT; zP < .05 vs. ACR; xP < .05 vs. ACRþLT). abd, abduction; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer.
range of motion to intact states at all degrees of abduction (P > .104).
Anterior glenohumeral translation The differences in anterior translation between conditions were greater at 60 of ER than at 30 of ER (Table I). At 60 of ER with 20 N of pull, there were no significant differences between conditions in anterior translation at any degree of shoulder abduction. At both 30 and 40 N of anteroinferior force, the subscapularis tear condition resulted in significantly greater anterior translation at 0 of abduction and 30 of abduction and 60 of ER (0 abd-60 ER and 30 abd60 ER, respectively). The ACR and ACRþLT conditions were able to restore anterior translation back to intact states at each of these shoulder positions. However, there were no significant differences between the ACR and ACRþLT conditions. Latissimus transfer alone was unable to resist significant anterior translation at 30 and 40 N for 0 abd60 ER and 30 N for 30 abd-60 ER.
Inferior glenohumeral translation For inferior translation, the differences between conditions were also more substantial at 60 ER than 30 ER (Table II). Subscapularis tear resulted in a significant increase in inferior translation at 30 and 40 N for both 0 abd-60 ER and 30 abd60 ER. ACR and ACRþLT were able to restore inferior translation to the intact state at each of these loads and angles.
However, there was no significant difference between the ACR and ACRþLT conditions. Latissimus transfer alone still resulted in significant inferior translation compared to intact at 30 N in 0 abd-60 ER and 30 abd-60 ER.
Discussion We found that ACR was more effective than LT at restoring glenohumeral kinematics when subjected to a translation force. Furthermore, the addition of the LT on top of the ACR did not significantly improve construct performance against anterior translation. Anterior capsule reconstruction with dermal allograft resulted in a reduction in total range of motion, whereas LT alone resulted in a restoration of total range of motion. Clinically, LT for irreparable subscapularis tears are usually associated with increases in active range of motion because of the increase in ability to perform active internal rotation.13 However, in this model only passive range of motion was assessed. Variations in ACR technique may change the amount of range of motion lost with ACR. Position of the arm during graft sizing affects graft tension and thus range of motion. Additionally, side-toside suturing has been shown to affect graft performance in superior capsule reconstruction and could also affect capsular tightness in ACR.12 This change in capsular tightness could result in decreased range of motion. Although there was no significant difference in range of motion between the ACR and ACRþLT conditions,
ACR vs. Lat transfer for subscapularis tears Table I
5
Anterior glenohumeral translation
0 abd-30 ER 20 N 30 N 40 N 30 abd-30 ER 20 N 30 N 40 N 60 abd-30 ER 20 N 30 N 40 N 0 abd-60 ER 20 N 30 N 40 N 30 abd-60 ER 20 N 30 N 40 N 60 abd-60 ER 20 N 30 N 40 N
Intact
SubT
ACR
ACRþLT
LT
1.5 0.2 3.3 0.6 10.5 3.3
1.8 0.3 9.8 3.6) 19.3 3.0)
1.7 0.3 9.0 3.0 16.6 2.4)
1.5 0.2 6.3 2.5 12.7 2.9y
1.6 0.2 10.2 3.4) 19.2 3.7),z
1.4 0.2 3.1 0.8 9.6 2.7
1.5 0.2 8.1 3.4 21.6 2.9)
1.5 0.2 8.5 3.5 17.2 3.2)
1.8 0.3 9.1 2.5) 15.7 2.7),y
1.8 0.3 12.4 4.2) 18.8 3.7)
1.6 0.3 3.9 0.9 7.3 1.3
1.8 0.3 5.8 2.0 11.0 2.6
2.3 0.7 6.9 2.1 10.1 2.2
1.7 0.3 6.2 1.7 9.6 1.8
1.8 0.3 5.1 1.3 11.4 3.2
2.5 0.4 16.3 4.0) 24.9 3.2)
2.2 0.3 10.1 3.1y 12.2 3.4y
2.3 0.3 10.5 3.2y 12.8 3.3y
2.7 0.6 16.5 4.6),z,x 17.8 4.3),y,z,x
1.5 0.3 6.5 2.4 14.1 3.1
2.5 0.6 18.4 4.0) 25.2 2.2)
2.2 0.5 9.7 2.7y 13.8 2.8y
2.2 0.2 10.4 2.5y 14.7 2.6y
2.1 0.4 17.7 3.9),z,x 18.4 4.0y
1.7 0.5 5.6 1.5 9.4 1.7
3.1 0.9 11.4 2.4 18.0 2.5)
2.8 1.0 8.7 2.1 13.3 2.6
2.4 0.6 6.9 1.9 9.7 1.8y
2.2 0.6 7.8 2.3 13.2 2.9)
2.5 0.8 9.5 2.4 14.2 2.4
abd, abduction; ER, external rotation; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer. Results are reported in millimeters. * P < .05 vs. Intact. y P < .05 vs. SubT. z P < .05 vs. ACRþLT. x P < .05 vs. ACR.
adding the LT on top of the ACR adds additional sutures to the construct and could affect passive range of motion, although it may possibly improve active range of motion clinically as the transfer would add a muscular component to the anterior shoulder. The ACR was able to restore anterior and inferior translation back to the intact state in the setting of an anteroinferior translation force. In contrast, the LT alone was not as effective as the ACR at resisting anterior and inferior translation. The difference in efficacy was particularly notable at lower ranges of abduction. At greater translation loads of 40 N, the effects of the LT were more evident, suggesting that the effect of the LT may be greater at the extremes of instability. Combining the effect of the ACR with the LT also did not result in a significant difference from the ACR alone. Although it was theorized that the dynamic stabilizing effect of an LT added to the static stabilizing effect of the ACR, it is possible that most of the combined stabilization effect is dominated by the ACR, and therefore the lesser effect contributed by the LT was not seen.
LT has been demonstrated as an option for irreparable subscapularis tears and has yielded promising short-term results when the transfer remains intact.9,13 However, longterm results of this technique are yet to be reported. Anatomically, it has been suggested to be superior to pectoralis major transfers because of the force vector being more similar to the native subscapularis as it passes posterior to the chest wall rather than anterior to it.4 In our study, we did not find the LT alone to be particularly effective in resisting anterior or inferior translation at loads that resulted in significant translation of the humeral head. LTs are associated with complications such as axillary nerve entrapment or tendon transfer rupture, which results in poor outcomes.6,9 Similar to LTs, ACRs are also still in nascent stages of utilization. Although there have been studies demonstrating various techniques for ACR, there are no long-term studies demonstrating its efficacy.10,14,16 In this study, we found that ACRs could be a viable option to reduce or prevent anterior or inferior translation of the humeral head while reducing the risk of nerve entrapment and without altering normal shoulder anatomy.
6
R. Omid et al. Table II
Inferior glenohumeral translation Intact
0 abd-30 ER 20 N 30 N 40 N 30 abd-30 ER 20 N 30 N 40 N 60 abd-30 ER 20 N 30 N 40 N 0 abd-60 ER 20 N 30 N 40 N 30 abd-60 ER 20 N 30 N 40 N 60 abd-60 ER 20 N 30 N 40 N
SubT
ACR
ACRþLT
LT
0.5 0.1 1.5 0.4 9.0 4.1
0.7 0.1 8.6 4.5) 18.3 4.2)
0.7 0.2 9.0 4.4) 17.5 4.2)
0.5 0.1 5.6 3.7 13.0 4.6
0.7 0.1 9.6 4.6) 19.8 4.7),y
0.5 0.1 1.6 0.6 8.8 3.1
0.6 0.1 7.5 4.0 20.0 3.2)
0.6 0.1 6.9 3.5 15.5 3.2)
0.7 0.2 7.2 3.0 13.8 3.2z
0.8 0.2 11.6 4.8) 17.5 3.9)
0.6 0.2 1.8 0.6 4.2 1.2
0.7 0.2 2.6 0.9 7.1 2.8
0.9 0.4 3.8 1.4 5.9 2.0
0.6 0.1 3.7 1.7 5.5 1.8
0.8 0.3 5.2 2.6 9.1 3.1
0.4 0.1 2.3 0.9 9.5 3.6
0.7 0.1 12.9 3.9) 20.2 3.4)
0.8 0.3 8.4 3.2 10.8 3.9z
0.7 0.1 8.2 3.9z 10.4 4.3z
0.9 0.3 13.8 4.3),y 15.1 4.3y
0.5 0.1 5.0 2.8 11.5 3.1
1.0 0.3 13.7 3.3) 19.1 2.4)
0.8 0.3 7.3 2.7z 12.1 3.4z
0.7 0.1 7.5 2.9z 11.9 3.4z
0.6 0.2 13.8 3.4),y,x 14.2 3.5
1.0 0.4 4.8 1.7 7.6 2.2
0.9 0.4 3.8 1.6 5.1 1.7
0.6 0.2 2.9 1.4 5.3 1.6
1.1 0.5 6.0 1.8 10.2 2.3
0.9 0.4 5.4 1.9 7.9 2.1
abd, abduction; ER, external rotation; SubT, irreparable subscapularis tear; ACR, anterior capsule reconstruction; ACRþLT, anterior capsule reconstruction with latissimus dorsi transfer; LT, latissimus dorsi transfer. Results are reported in millimeters. * P < .05 vs. Intact. y P < .05 vs. ACRþLT. z P < .05 vs. SubT. x P < .05 vs. ACR.
There were several limitations to this study. As this was a cadaveric biomechanical study, it represents only timezero conditions and does not take into consideration healing or physical rehabilitation after surgery. For tendon transfers in particular, outcomes rely on patient adherence to rigorous physical therapy and muscle retraining. Therefore, the outcomes after LT may vary from patient to patient and may be more effective over time. Reductions in range of motion were seen with ACR in this time-zero study. These limitations should be less in clinical situations, as the graft will stretch over time. Furthermore, the optimal technique for placement of ACR has not yet been fully elucidated. Factors such as graft tension or side-to-side suturing could affect the efficacy of the reconstruction technique. In this study, shoulder specimens without full torsos were used. Although the biomechanical testing jig used lines of tension to simulate all native muscle vectors, these could only be approximated without the torso intact. Additionally, the muscle transfer in this study was not subject to soft tissue limitations that would be seen in vivo, which could affect muscle vectors, as the surrounding tissue was dissected away during specimen preparation. Another limitation is
that in this study, all testing occurred in a single sequence to ensure repeatability. However, viscoelastic effects that occur during testing could have systematically propagated throughout the study. This study also only assessed a single graft type. Although human dermal allograft has emerged as a popular option for reconstructive procedures in the shoulder, the use of other graft types may alter the kinematics of the resulting procedure and result in varying results.
Conclusion Anterior capsule reconstruction with dermal allograft was able to restore anteroinferior stability in the setting of irreparable subscapularis tears but resulted in decreased total range of motion. Latissimus dorsi transfer alone was less effective than anterior capsule reconstruction in restoring glenohumeral stability. The addition of latissimus dorsi transfer as a dynamic restraint did not increase the efficacy of the anterior capsule reconstruction.
ACR vs. Lat transfer for subscapularis tears
Disclaimer Reza Omid receives royalties from Medacta and Integra and has consultant agreements with Wright/Tornier, Medacta, and Integra. All the other authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
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