MORPHOLOGY OF THE TORN ROTATOR CUFF

The morphological characteristics of shoulders with torn rotator cuffs were determined using 41 embalmed specimens. The following parameters were measured in the supraspinatus (SSP), infraspinatus (ISP) and sub scapularis (SSC) muscles: the length, thickness and width of the extra muscular tendon; the length of the intramuscular tendon; the length an d width of a tear, if present, muscle fibre length; and muscle volume. The cross-sectional area (CSA) of the tendon was measured on the phot ographic image of slices of the tendon using an image analysis system, and the CSA of the muscle was calculated by dividing the muscle volum e by muscle fibre length. The rotator cuff was intact in 11 shoulders. A partial-thickness tear of the cuff was present in 12 shoulders, a f ull-thickness tear of the SSP in 11 shoulders, and a full-thickness te ar of more than 2 tendons in 7. Overall incidence of full-thickness te ars of the rotator cuff was 44%, and that of partial-thickness tears 2 9%. With increase of tear size, the functional tendon length (extramus cular tendon length plus tear length) increased by a statistically sig nificant amount in the SSP, ISP and SSC, whereas muscle fibre length d ecreased in SSP and ISP. It is concluded that the increased functional tendon length and decreased muscle fibre length are the main morpholo gical changes that make the rotator cuff a physiologically abnormal un it. Surgical repair of the torn cuff would be expected to improve thes e anatomical changes and restore the kinetics of the glenohumeral join t. Our data encourage early repair of rotator cuff tears at a stage wh en these anatomical changes are still reversible in patients, such as manual labourers and athletes, who need functional shoulders.