Summary

In this dynamic shoulder model, superior capsular reconstruction only partially restored native glenohumeral joint loads. However, glenohumeral contact pressure, compensatory deltoid forces and superior migration were significantly reduced, while increasing abduction motion, when compared to the posterosuperior rotator cuff tear.

Abstract

Background

Although clinical and biomechanical evidence suggests that superior capsular reconstruction (SCR) for irreparable posterosuperior rotator cuff tears (PSRCT) holds considerable joint preserving potential, its true effect on glenohumeral contact mechanics during dynamic abduction motion remains largely unknown. The purpose of the study was to evaluate the effect of an irreparable PSRCT on glenohumeral joint loads and to quantify improvement following SCR using an acellular dermal allograft. It was hypothesized that performing an SCR would reverse increased glenohumeral joint loads caused by an irreparable PSRCT.

Methods

Ten fresh-frozen cadaveric shoulders were tested using a validated dynamic shoulder simulator. A pressure mapping sensor was placed between the humeral head and glenoid surface. Each specimen underwent the following conditions: (1)native, (2)irreparable PSRCT, (3)SCR using an acellular dermal allograft. Glenohumeral abduction angle (gAA) and superior humeral head migration (SM) were measured using 3D motion tracking software. Cumulative deltoid force (cDF) and glenohumeral contact mechanics, including contact area (gCA) and contact pressure (gCP), were assessed at rest,15°,30°,45°, and maximum angle of glenohumeral abduction.

Results

The PSRCT resulted in a significant decrease of gAA along with an increase in SM, cDF, and gCP (P<.001, respectively). SCR did not restore native gAA (P<.001), however, SM was significantly reduced (P<.001). Further, SCR significantly reduced deltoid forces at 30° (P=.007) and 45° of abduction (P=.007) when compared to the PSRCT. SCR did not restore native cDF at 30° (P=.015,), 45° (P<.001), and maximum angle (P<.001) of glenohumeral abduction. Compared to the PSRCT, SCR resulted in a significant decrease of gCP at 15° (P=.008), 30° (P=.002), and 45°(P=.006). However, SCR did not completely restore native gCP at 45° (P=.038) and maximum abduction angle (P=.014).

Conclusion

In this dynamic shoulder model, performing an SCR only partially restored native glenohumeral joint loads. However, SCR significantly decreased gCP, cDF and SM, while increasing abduction motion, when compared to the PSRCT. These observations raise concerns regarding the true joint preserving potential of SCR for an irreparable PSRCT, along with its ability to delay progression of cuff tear arthropathy and eventual conversion to reverse shoulder arthroplasty.