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Abstract

Introduction: Dysfunction of the subscapularis following total shoulder replacement has become a concern and may represent poor healing following surgical repair. The objective of this study was to evaluate the restoration of the subscapularis footprint anatomy and failure strength for subscapular repair using transosseous tunnels and a second anatomical repair using combined transosseous tunnels and direct tendon to tendon repair. Methods: Six matched pairs of fresh-frozen human cadaver shoulders were dissected. The footprint of the subscapularis’ native insertion on the humerus was outlined with India ink and digitized. One shoulder from each pair was randomly assigned to a transosseous repair and the contralateral shoulder to a combined transosseous tunnel and direct tendon to tendon repair. For the tendon to tendon repair, the subscapularis was released from its attachment on the lesser tuberosity, leaving 1 cm of cuff tissue. For the isolated transosseous tunnel repair, the entire subscapularis tendon was released off the lesser tuberosity. The repair footprint was then digitized. The humerus was prepared similar to an actual shoulder replacement procedure. The belly of the subscapularis muscle was then fixed in a freezing clamp and material testing was performed with cyclic tensile loading under force control using an MTS machine. After cyclic loading, a constant ramp displacement was applied to the specimen until the repair failed. Results: The tendon to bone repair insertional footprint area (228.6 mm2) was significantly less than that of the native footprint (697.3 mm2). Centroid data showed that the isolated transosseous repair moved the centroid of the footprint medially an average of 9 mm and superiorly an average of 5.5 mm on the humerus. The combined direct tendon and transosseous repair required a statistically significant greater (p = 0.03) number of cycles to reach a 5 mm gap (205.7 ± 65.1) than did the isolated transosseous technique (76.4 ± 34.2). Similarly, a greater number of cycles was observed for the 10 mm gap (p=0.03); combined tendon to tendon and transosseous repair (307.5 ± 82.4 cycles) compared to isolated transosseous repair (166.2 ± 85.8 cycles). Conclusion: Subscapularis dysfunction following shoulder arthroplasty has become a recognized problem. This study has demonstrated that transosseous tunnel repair alters subscapularis insertional anatomy that results in weaker strength of fixation and less contact area when compared to combined direct tendon-tendon and transosseous tunnel repair. If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use).