Due to the unique and complex anatomy of the rotator cuff and its essential role in shoulder abduction, highly specialized expertise is necessary to effectively treat rotator cable injuries. Christopher C. Schmidt, MD, is a board-certified orthopedic surgeon who specializes in rotator cuff tear repair in Pittsburgh, Pennsylvania. Widely regarded as one of the best shoulder surgeons in the nation, Dr. Schmidt performs extensive clinical and biomechanical research with an aim to continually advance his field, and he regularly contributes to guidelines used by his peers to improve patient care through evidence-based medicine.
Exploring the Role of the Rotator Cable in Shoulder Abduction
A thick fibrous structure, the rotator cable functions much like a weight-bearing suspension bridge in carrying applied forces to the rotator cuff. Situated at the distal end of the supraspinatus tendon, the rotator cable is believed to be susceptible to strain because it stress-shields the rotator crescent, an avascular area of the rotator cuff that is prone to tears.
Recently, Dr. Schmidt led a biomechanical study to further explore the respective roles of the rotator cable and the rotator crescent in force transmission for shoulder abduction. Through extensive testing, Dr. Schmidt and his team found that the rotator crescent alone can transmit sufficient load for shoulder abduction without the aid of the rotator cable. The team also concluded that the rotator crescent is a more effective abductor than the rotator cable.
The abstract of the study is reproduced below:
Rotator Cable Injury Does Not Reduce Abduction Force
MP Smolinski1, CS Spicer1, R Blake1, A Davidson2, MC Miller1, P Smolinski1, T Zink2, D Papadopoulos2, CC Schmidt1,2
1 Department of Mechanical Engineering and Material Science, University of Pittsburgh, PA
2 Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA
INTRODUCTION: The rotator cable (RCa) has been suggested as a major load bearing tissue structure from the supraspinatus (SS) and infraspinatus (IS) to the greater tuberosity through its two humeral attachments: the anterior insertion (A) at the coracohumeral ligament (CHL) and the posterior insertion (P) between the IS and teres minor (TM) insertions (Fig. 1A) . The crescent area (CA) is lateral to the cable. A biomechanical study was done to determine the roles of the RCa and CA in force transmission for humeral abduction.
METHODS: Ten fresh-frozen cadaveric specimens (74 ± 17 years) without rotator cuff pathology were dissected to the level of the rotator cuff and capsuloligamentous tissues. The shoulders were tested in a shoulder simulator (Fig. 1B) with physiological load vectors applied to the upper and lower subscapularis, SS, IS, and TM [2,3]. The shoulders were tested at both 0⁰ and 30º of scapular plane abduction in neutral rotation. With the applied muscle loads, the abduction force was measured at the distal humerus using a 6 DOF load cell (accuracy ± 0.1 N). The RCa states of intact (n=10) and anterior and posterior insertion release (Fig. 1A).
Figure 1: A) Identification of the rotator cable and anterior (A) and posterior (P) insertions and B) shoulder simulator.
RESULTS: At 0⁰ of abduction the abduction force was significantly greater after cable release than with the cable intact (*p = 0.003) (Fig. 2).
Figure 2: Abduction force at 0° and 30° of abduction for intact cable and cable with anterior and posterior insertions cut. (*p < 0.05).
DISCUSSION: This study found that the release of the anterior and posterior RCa insertions resulted in greater shoulder abduction force. Thus, the crescent area is able to transmit load to the humerus and was a more effective abductor than the RCa. Figure 3 illustrates that the RCa force at the insertions creates a moment that is not aligned with the abduction axis of rotation, and when the RCa insertions are transected, load from the SS and IS are transmitted through the CA.
Figure 3: Arrowhead dots on tendon force vectors (FRCaA, FRCaP and FCA) indicate directions are out of the page. Left figure shows that the axes of the moments (MRCaA and MRCaP) caused by the RCa anterior and posterior forces are not aligned with the axis of rotation for abduction. Right figure shows when RCa insertions are cut, all RCa forces are transmitted through the CA and moments from all forces are now aligned along the axis of rotation.
SIGNIFICANCE/CLINICAL RELEVANCE: This study found that the crescent area can alone transmit load for abduction without the aid of the cable.
REFERENCES: (1) Arthroscopy 1993, 9; 611-16. (2) J Biomech 2007, 40; 2953-60. (3) J Anatomy 2010, 216; 643-49.
If you would like to learn about arthroscopic rotator cuff tear repair and the innovative surgical techniques performed by Dr. Schmidt, call (877) 471-0935 to request a personal consultation at one of his three office locations in the greater Pittsburgh, PA, area.
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