Rotator cuff tear pain and tear size and scapulohumeral rhythm

Abstract

Context: The body of knowledge concerning shoulder kinematics in patients with rotator cuff tears is increasing. However, the level of understanding regarding how pain and tear size affect these kinematic patterns is minimal.

Objective: To identify relationships between pain associated with a full-thickness rotator cuff tear, tear size, and scapulohumeral rhythm (SHR) and to determine whether pain and tear size serve as predictors of SHR.

Design: A test-retest design was used to quantify pain and SHR before and after a subacromial lidocaine injection. Correlation and multivariate analyses were used to identify relationships among pain, tear size, and SHR.

Setting: Orthopaedic biomechanics research laboratory.

Patients or other participants: Fifteen patients (age range, 40-75 years) with diagnosed full-thickness rotator cuff tears participated. They were experiencing pain at the time of testing.

Intervention(s): Shoulder kinematic data were collected with an electromagnetic tracking system before and after the patient received a lidocaine injection.

Main outcome measure(s): Pain was rated using a visual analog scale. Three-dimensional scapular kinematics and glenohumeral elevation were assessed. Scapular kinematics included anterior-posterior tilt, medial-lateral tilt, and upward-downward rotation. A regression model was used to calculate SHR (scapular kinematics to glenohumeral elevation) for phases of humeral elevation and lowering.

Results: Linear relationships were identified between initial pain scores and SHR and between tear size and SHR, representing an increased reliance on scapular motion with increasing pain and tear size. Pain was identified as an independent predictor of SHR, whereas significant findings for the effect of tear size on SHR and the interaction between pain and tear size were limited.

Conclusions: We noted an increased reliance on scapular contributions to overall humeral elevation with increasing levels of pain and rotator cuff tear size. Pain associated with a rotator cuff tear serves as a primary contributor to the kinematic patterns exhibited in patients with rotator cuff tears.

Keywords: biomechanics; scapula; shoulder kinematics.

Figure 1. Patient testing setup. Each patient performed the humeral elevation and lowering tasks between the anthropometrically assigned hand triggers. We attached electromagnetic tracking sensors to the sternum, upper arm, forearm, and scapula (not shown in photograph) of each patient while he or she sat in a wooden chair. Adapted from the Journal of Shoulder and Elbow Surgery, 17(1), Scibek JS, Mell AG, Downie BK, Carpenter JE, Hughes RE, Shoulder kinematics in patients with full-thickness rotator cuff tears following a subacromial injection, 172–181, 2008, with permission from Elsevier.

Figure 2. Arc of motion divided into phases for humeral elevation and lowering. Humeral motion was plotted against time, and the maximum point of elevation was determined for each trial. Total arc of motion achieved during the humeral elevation was calculated by subtracting the point at which humeral elevation was initiated (baseline) from the maximum point of elevation. The arc of motion was divided into 3 equal segments and labeled as phases I, II, and III for humeral elevation and phases IV, V, and VI for humeral lowering. Adapted from the Journal of Shoulder and Elbow Surgery, 17(1), Scibek JS, Mell AG, Downie BK, Carpenter JE, Hughes RE, Shoulder kinematics in patients with full-thickness rotator cuff tears following a subacromial injection, 172–181, 2008, with permission from Elsevier.

Figure 3. Diagram for scapulohumeral rhythm calculation with respect to the slope of the regression. The slope obtained during the simple linear regression analyses corresponded to scapulohumeral rhythm. These calculations represent scapular upward-downward rotation phase I. The solid line represents real motion for the humerus (elevation) and scapula (scapular rotation); the dashed line represents the line based on the slope for the linear regression. The same calculations also were performed for scapulohumeral rhythm for anterior-posterior tilt and scapulohumeral rhythm for medial-lateral tilt for each phase of elevation and lowering.

Figure 4. Positive linear relationship between preinjection pain and scapulohumeral rhythm for anterior-posterior tilt for phase II of scapular plane humeral motion.

Figure 5. Positive linear relationships between tear size and scapulohumeral rhythm for scapular-plane humeral elevation. A, Tear size versus scapular upward-downward rotation for phase IV. B, Tear size versus scapulohumeral rhythm for anterior-posterior tilt for phase V. C, Tear size versus scapulohumeral rhythm for medial-lateral tilt for phase II. 1 indicates small or moderate tears; 2, large tears; and 3, massive tears.