Due to the intricacy and complexity of the shoulder structure, rotator crescent tears require specialized medical attention. In Pittsburgh, Pennsylvania, world-class shoulder care is available from Christopher C. Schmidt, MD, a board-certified orthopedic surgeon who consistently ranks among the top shoulder specialists in the United States.
Widely regarded as an expert among experts, Dr. Schmidt has published more than 150 book chapters and peer-reviewed scientific articles and abstracts on rotator cuff surgery and related topics. With a goal to continually further his field, Dr. Schmidt performs extensive research in his role as the Director of the Shoulder and Elbow Fellowship, Department of Orthopaedic Surgery at the University of Pittsburgh Medical Center.
Investigating the “Suspension Cable” Concept
In a recent study, Dr. Schmidt explored the biomechanics of the rotator cable and the rotator crescent, which together function as the shoulder’s “suspension bridge.” More specifically, he tested the prevalent theory that the rotator cable serves as the main structure that transmits load to the humerus and strain-shields the rotator crescent during abduction, much like the suspension cable of a bridge.
Based on extensive testing and analyses, Dr. Schmidt and his team concluded that the rotator crescent is a load-bearing structure in and of itself. As such, rotator crescent tears are mechanically significant injuries that should be clinically addressed.
The abstract of the study is reproduced below:
Abduction Force Transmission Through the Rotator Cable
R Blake1, M Smolinski1, C Spicer1, A Davidson MC Miller1, P Smolinski1,2, T Zink2, D Papadopoulos2, CC Schmidt1,2
1 Department of Mechanical Engineering and Material Science, University of Pittsburgh, PA
2 Department of Orthopedic Surgery, University of Pittsburgh, Pittsburgh, PA
Disclosures: None
INTRODUCTION: It is believed that the rotator cable (RCa), which originates at the coracohumeral ligament (CHL) insertion and terminates between the infraspinatus (IS) and teres minor (TM) footprints, is the main structure transmitting load to the humerus and strain shields the lateral cuff similar to a bridge suspension cable [1]. To investigate the cable concept, direction of strain was measured in the RCa under rotator cuff loading.
METHODS: With approval from the institutional review board, 18 fresh-frozen cadaveric specimens (average age 67 ± 17) without rotator cuff pathology were dissected keeping the shoulder joint and rotator cuff complex intact. The specimens were placed in a shoulder simulator. The upper and lower subscapularis (SubS), supraspinatus (SS), IS, and TM were individually loaded with physiological force vectors [2,3] (Fig. 1). The shoulders were positioned in neutral rotation and flexion and tested at 0° and 30° of scapular plane abduction. During loading, the strain of the RC (Fig. 1) using a digital image correlation technique with a Vic-3D 8 system [accuracy ± 10µm] (Correlated Solutions Inc, Irmo, SC). After testing the native intact condition, the specimens had both the anterior and posterior cable insertions (full) released. The directions of the maximum principal strains (averaged over a 2 mm radius circle) were taken in the center of the RCa at five different angular positions evenly spaced throughout the RCa. Statistical comparisons were made using paired t-tests with cable state as the variable with significance set at p < 0.05.
Figure 1: Specimen in testing system (left) and contour plot of the maximum principal strain in the rotator cuff (right).
RESULTS SECTION: The directions of maximum principal strain in the cable as a function of insertion condition and flexion angle is given in Figure 2 and Table 1. There was no significant difference in strain direction with cable state.
Table 1: Maximum principal strain direction by rotator cable position and rotator cuff state
DISCUSSION: Based upon the hypothesis that the rotator cable transmits the load, it would be thought that the largest (principal) strain in the cable would be along the direction of the cable and its fibers (Fig. 2A). However, the native condition resulted in medially directed strain and our results show that strain direction shifted posteriorly at 0° (Fig. 2B) and anteriorly at 30° with transection of the cable insertions, but the change is not significant.
CLINICAL RELEVANCE: Due to the direction of strains in the rotator cable, tears in the crescent area are mechanically significant and should be repaired accordingly.
REFERENCES: 1. Burkhart, et al., Arthroscopy 1993 2. Kedgley, et al., J Biomech. 2007 3. Omi, et al., J Anatomy 2010
If you would like to explore your treatment options for a rotator cuff tear with Dr. Schmidt, call (877) 471-0935 to request an appointment at one of his office locations in the greater Pittsburgh, PA, area.
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