The relationship between external rotator strength to size of rotator cuff tear

Abstract

Clinically it was observed that patients with decreased static resisted external rotation strength o f the arm (tested in neutral) often had rotator cuff tears. 'In addition, it was observed that the size of the rotator cuff tear seemed to be correlated with the amount of loss of muscle strength. The purpose of this study of the shoulder was to ascertain: l.If static resisted external rotation strength of the arm (tested in neutral) can be used as a diagnostic test to ascertain if a tear of the rotator cuff is present. 2.1f a relationship exists between the decrease of strength of the arm when testing static resisted external rotation (in neutral) and the size of the cuff tear. Thirty- two subjects who had been selected by an orthopaedic surgeon to have their rotator cuff artbroscopically examined, were used for the study. Certain exclusion criteria were applied and twelve subjects were excluded from the study. The pre-operative testing consisted of a routine shoulder examination, which was expanded to include the Constant score method. Isometric muscle testing of the rotator cuff muscles was undertaken using a Nicholas hand held dynamometer. The opposite unaffected arm was used as a control. The force production of the affected arm was then calculated as a percentage of the control arm, thus resulting in a dimensioniess relative measurement of the strength of the affected arm. The intra-operative results of the arthroscopic examinations were obtained and if a tear was present, the size was calculated by multiplying the length and breadth of the tear. The preoperative findings and intra-operative results were analysed using the Pearson's correlation coefficient test. The results show that an inverse relationship exists between the size of the tear and the strength o f static resisted external rotation force o f the arm ( r = 0.62) >.e. the larger the tear, the less the strength of the arm when testing static resisted external rotation in neutral. The results also show that if the relative streng th (%) of the affected arm is known, then in 62 % of the cases the tear size can be accurately calculated. The statistical tests were unable to demonstrate any relationships between the other parameters tested (i.e. pain, function, abduction strength, internal rotator strength) and tear size. In addition it was found that when using static resisted external rotation strength o f the arm (tested in neutral) as a diagnostic test in isolation, it is difficult to differentiate accurately between no tear and a small tear of the cuff. A large or massive tear is easier to diagnose.