Rotator Cuff Tear Kinematics: an In-vitro Study of Rotator Cuff Tear and Repair Kinematics

*Shore, BJ; +**Kedgley, AE;*Drosdowech, DS; *King, GJW; *Athwal, GS; **Johnston, JA; *Faber, KJ *Hand and Upper Limb Centre, Department of Orthopaedics, University of Western Ontario. +**Bioengineering Research Laboratory, St. Joseph’s Health Care London, Hand and Upper Limb Centre, 268 Grosvenor Street, London, Ontario, CANADA, N6A 4L6, 519-646-6000, Fax: 519-646-6049 [email protected] INTRODUCTION: Rotator cuff tears are a common cause of shoulder pain and dysfunction. The prevalence of full and partial thickness tears increases linearly with age after 50 years, and by the age of 80, they exist in 80% of the population. Despite the prevalence of rotator cuff disease in our population, there is little literature on the effect of rotator cuff tears on active shoulder kinematics in a cadaver model. Furthermore, there are apparently no studies comparing the differences in active shoulder kinematics following different repair techniques. We hypothesized that double row suture anchor repairs of rotator cuff tendon tears will more closely restore normal active glenohumeral joint kinematics to those observed in the intact state than a single row suture anchor repair. Therefore, the purpose of this in-vitro biomechanical study was conducted to determine the effects of simulated tears and subsequent repairs of the rotator cuff tendons on joint kinematics. METHODS: Eight paired fresh-frozen cadaveric shoulder specimens (mean age: 66.0 ± 8.7 years) were tested using a custom loading apparatus designed to simulate unconstrained motion of the humerus. Cables were sutured to the tendons of the supraspinatus, subscapularis, and infraspinatus/teres minor muscles. Three cables were attached to the deltoid tuberosity to replicate the anterior, middle and posterior thirds of the deltoid muscle. Loads were applied to the cables to simulate the muscle loading in ratios with respect to the middle deltoid based on variable ratios of electromyographic (EMG) data and average physiological crosssectional area (pCSA) of the muscles. An electromagnetic tracking device (Flock of Birds, Ascension Technologies, VT) was used to provide real-time feedback of abduction angle, to which the loading ratio was varied correspondingly. An anterolateral deltoid muscle splitting incision was utilized,, to access the rotator cuff interval and supraspinatus tendon. A 2cm tear was made in the supraspinatus tendon insertion, beginning at the rotator cuff interval and extending in a posterior direction, and 1cm of tendon was resected to simulate the clinical arthroscopic scenario of tendon retraction. The deltoid muscle and skin incisions were then sutured and simulated active glenohumeral abduction was performed with data collected. Specimens were randomized to receive either single or double suture anchor repair (Figure 1).