Abstract
External rotation of the shoulder is commonly measured in two ways, with the arm adducted or with the arm abducted to 90°. The measurement forms an important part of the assessment of shoulder function, but has been shown to be unreliable. Following the observation that, with the arm adducted, the range of external rotation alters according to the exact position of the arm in the sagittal plane, we conducted a study to quantify the effect on the range of external rotation of a small increment in forward flexion (15°).
With the arm first in a vertical position and then in 15° of forward flexion, external rotation was measured in 40 asymptomatic and 20 ‘frozen’ shoulders. With forward flexion, the range of external rotation decreased by a mean of 16.9° in the asymptomatic and 13.5° in the ‘frozen’ shoulders.
We postulate that some of the variation is a function of scapular positioning. With arm flexion, the scapula protracts, resulting in alteration in glenoid version. However, some difference is due also to alteration in soft tissue tension in the two arm positions.
The sagittal position of the arm affects the range of external rotation of the adducted shoulder. This variation in measurement may affect the scores of certain outcome measures.
Secretary: Dr H.J.S. Colyn, Editor: Professor M.B.E. Sweet. Correspondence should be addressed to SAOA, Box 47363, Parklands, Johannesburg, 2121, South Africa.
