As a primary pathology of the rotator cuff irreparable suscapularis ruptures are rare. However insufficiency of this muscle-tendon unit has been described as one of the most frequent complications after total shoulder arthroplasty or open instability surgery1-3 and the incidence of chronic irreparable lesions is increasing.
In revision surgery there is a potential risk for denervation of the muscle. In the first chapter, it could be demonstrated that the superior and middle subscapular nerves are at risk when extensive release is required at the anterior surface of the muscle. This was especially true when the subscapularis tendon was pulled laterally. In this situation the „safe harbor“ turns out to be the lateral border of the base of coracoid process.
If a chronic subscapularis tear requires surgical treatment , reconstruction with a tendon transfer has been proposed. Unfortunatly there is no optimal transfer for the subscapularis muscle. In chapters 2.2, 3.1 and 3.2 the anatomical and biomechanical basis for a new concept of selective subscapularis reconstruction have been established. Based on these studies it could be demonstrated that the teres major is a safe and biomechanically logical transfer for reconstruction of the lower part of the subscapularis. The analysis was carried on to define the optimal transfer for reconstruction of the upper part of the subscapularis. In Chapter 3.2 it was possible to determine the biomechanical effect of rerouting procedures of the pectoralis major transfer. Passing the tendon underneath the conjoined tendon seems to be the most effective way to improve the direction of the pectoralis major transfer for subscapularis reconstruction. However this technique is demanding when the plane underneath the conjoined tendon is scarred and the pectoralis major is bulky . In such cases there is a risk to injure the musculocutaneous nerve.4 Therefore, the split pectoralis major tendon may be a safer option.
Although the clinical series presented in chapter 4.1 is small, the combined TM-sPM transfer appears to be a valuable and a safe alternative to treat irreparable subscapularis tears. An interesting observation in this study was that the transfer was able to recenter the statically subluxed humeral head in two cases. This could be attributed to the dynamic hammock built by the transferred teres major. The early promising subjective and objective results presented here encourage for further investigation.
For the sake of completeness it should be emphasized that together with improvement of surgical technique, careful patient selection and scrupulous postoperative rehabilition are essential to achieve an optimal clinical outcome. Furthermore, the subscapularis insufficiency is a unequivocal clinical entity which should be diagnosed early to allow primary repair.
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der Humboldt-Universität zu Berlin