The rotator cuff is a group of muscles and tendons that surround the shoulder joint, keeping the head of the upper arm bone (humerus) firmly positioned within its shallow socket and providing rotational strength to the shoulder. Through sudden trauma or repetitive use, these soft tissues can become damaged, sometimes to the point of tearing. This injury, which is known as a rotator cuff tear, is a common cause of shoulder pain and weakness. If these symptoms do not respond to conservative treatments, such as rest, medications, physical therapy, and injections, an arthroscopic rotator cuff tear repair may be considered.
A Renowned Orthopedic Surgeon on the Leading Edge of Shoulder Injury Treatment
Christopher C. Schmidt, MD, is a highly respected, board-certified orthopedic shoulder surgeon who practices in Pittsburgh, Pennsylvania, where he also serves as Director of the Shoulder and Elbow Fellowship in the Department of Orthopaedic Surgery of the University of Pittsburgh Medical Center (UPMC). In collaboration with a multidisciplinary team of orthopedic surgeons, bioengineers, mechanical engineers, fellows, and residents of UPMC, Dr. Schmidt performs extensive clinical and biomechanical research to continually improve arthroscopic rotator cuff tear repair techniques. The findings of these studies are integrated into best-practice guidelines that are utilized by his peers throughout the U.S.
Improving Shoulder Abduction After Rotator Cuff Tear Repair Surgery—the Role of the Rotator Crescent
Recently, Dr. Schmidt led an important research initiative to analyze the biomechanics of rotator cuff abduction. In essence, the study was based on the theory that, with an enhanced understanding of the intricacies of rotator cuff function, surgeons could improve surgical outcomes. Specifically, the objective of the study was to investigate the respective roles of the rotator cable and the lateral crescent area in force transmission and humeral abduction.
Through this study, Dr. Schmidt and his team found that the lateral crescent area appears to have a greater ability to transmit rotator cuff abduction force than the rotator cuff cable. This finding clarifies the reasons why superior abduction strength is often seen in healed rotator cuff tear repairs as compared to unhealed rotator cuff tear repairs, and also in graft-reconstructed repairs of irreparable rotator cuff tears as compared to partial repairs of irreparable rotator cuff tears.
Dr. Schmidt and his team have incorporated the results of this study into surgical techniques that are now being used by shoulder surgeons nationwide to improve abduction strength after rotator cuff tear repair surgery. The abstract of the study is reproduced below.
Rotator Crescent More Important Than the Rotator Cable for Shoulder Abduction
Schmidt CC, Spicer CS, Blake RJ, Zink TR, Davidson A, Smolinski PJ, Delserro SM, Miller MC, Smolinski MP
Shoulder and Elbow Laboratory, Department of Orthopaedic Surgery, University Pittsburgh Medical Center
Introduction: The rotator cable (RCa) is believed to function in load transfer from the supraspinatus (SS) and infraspinatus (IS) tendons to the greater tuberosity through its two humeral attachments: anteriorly (A) at the coracohumeral ligament (CHL) and posteriorly (P) between the IS and teres minor (TM) (Fig. 1) . The RCa has been likened to a suspension bridge, stress shielding the lateral crescent area (CA). A biomechanical study was performed to determine the roles of the RCa and CA in force transmission and humeral abduction. The underlying hypothesis was that the RCa generates greater humeral abduction force than the CA.
Methods: Thirteen fresh-frozen cadaveric specimens (average age 67 ± 13) without rotator cuff pathology were dissected to the level of the rotator cuff and capsuloligamentous tissues. All specimens were placed in a shoulder simulator (Fig. 2) and the upper and lower subscapularis, SS, IS, and TM were individually loaded with physiological force vectors [2,3]. The shoulders were positioned in neutral rotation, and loads were then applied at 0⁰ and 30º of scapular plane abduction. During testing, the abduction force was measured at the distal humerus using a 6 DOF load cell (accuracy ± 0.1 N). The specimens were tested first with the RCa intact and then after release of both the anterior and posterior cable insertions (Fig. 1).
Results: At 0⁰ of abduction the abduction force was greater after cable release than with the cable intact (*P > 0.012).
Discussion: This study showed that the release of the anterior and posterior RCa insertions, with an intact CA, yielded greater shoulder abduction force. This shows that the CA transmits load to the humerus and that it may be a more effective abductor than the RCa. Figure 4 illustrates that the RCa force at its insertions creates a moment that is not aligned with the abduction axis of rotation. When the RCa insertions are cut, all SS and IS load is transmitted through the CA which increases the moment that is aligned with the abduction axis of rotation leading to greater abduction force.
Figure 4: Arrow head dots on tendon force vectors (FRCaA, FRCaP and FCA) indicate directions are out of the page. Figure A 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. Figure B 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.
Clinical Relevance: The CA appears to have a greater ability to transmit rotator cuff abduction force than the RCa. This finding clarifies why superior abduction strength is seen with healed vs. unhealed rotator cuff repairs and graft reconstructed vs. partial repairs for irreparable tears [4,5].
References: (1) Arthroscopy 1993, 9; 611-16. (2) J Biomech 2007, 40; 2953-60. (3) J Anatomy 2010, 216; 643-49. (4) JBJS 2013, (95); 965-71. (5) Arthroscopy 2013, 29; 1911-21.
If you'd like to learn more about emerging techniques in arthroscopic rotator cuff tear repair surgery, contact Dr. Schmidt’s practice in Pittsburgh, PA, at (877) 471-0935 to request an appointment with Dr. Schmidt.
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