Abstract
Background:
The purpose of this study was to compare the biomechanical effects of the trapezius transfer and the latissimus dorsi transfer in a cadaveric model of a massive posterosuperior rotator cuff tear.
Methods:
Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane with anatomically based muscle loading. Humeral rotational range of motion and the amount of humeral rotation due to muscle loading were measured. Glenohumeral kinematics and joint reaction forces were measured throughout the range of motion. After testing in the intact condition, the supraspinatus and infraspinatus were resected, simulating a massive rotator cuff tear. The lower trapezius transfer was then performed. Three muscle loading conditions for the trapezius (12N, 24N, 36N) were applied to simulate a lengthened graph as a result of excessive creep, a properly tensioned graph exerting a force proportional to the cross-sectional area of the inferior trapezius, and an over-constrained graph respectively. Next the latissimus dorsi transfer was performed and tested with one muscle loading condition 24N. A repeated-measures analysis of variance was used for statistical analysis.
Results:
The amount of internal rotation due to muscle loading increased with massive cuff tear at 0°, 30°, 60° abduction (p < 0.05), and was restored with the latissimus transfer at 0° abduction and the trapezius transfer at all abduction angles. (Figure 1) The cuff tear decreased glenohumeral joint compressive force, which was restored with the trapezius transfer at all positions; however, the latissimus transfer failed to restore the intact compressive force (p < 0.05). (Figure 2) At neutral rotation and 0° abduction, there was an increase in the anteriorly directed force for the rotator cuff tear and latissimus transfer conditions, that was restored to intact values by the trapezius transfer (p < 0.05). (Figure 3) At maximum internal rotation and 0° of abduction, the apex of humeral head shifted superiorly and laterally after massive cuff tear (p < 0.05); this abnormal shift was more closely restored to intact values by the trapezius transfer than the latissimus transfer in directions (p < 0.05).
Conclusion:
The trapezius transfer for massive cuff tear restores native glenohumeral forces better than the latissimus transfer by recruiting an exogenous force across the glenohumeral joint. However, the increase in compressive force seen with the trapezius transfer may be problematic in patients with osteoarthritis. Clinical studies to evaluate the results of the trapezius transfer are warranted.
