Histopathological assessment and pathological significance of matrix degeneration in supraspinatus tendons

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Abstract
Sir, Although histological abnormalities of the supraspinatus tendon are a frequent finding in cadaver studies, the relationship between age, specific matrix changes and the development of clinical tendinopathy (tendinitis) has not been rigorously investigated. We conducted a histopathological analysis of 85 supraspinatus tendons from cadavers (aged 11–96 yr) and 33 specimens from patients with degenerate rotator cuff tears (aged 38–81 yr). Representative sections of each specimen were examined by two blinded observers independently and graded according to a four‐point scale based on the organization of the tendon fibre bundles. Normal tendons were designated grade 1 and comprised bundles of fibres with a wavy outline, with individual fibres easily discernible within the bundles. Tenocyte nuclei were elongated with an unremarkable chromatin pattern and lay with their long axis parallel to the bundles of collagen. Mild degeneration, designated grade 2, showed collagen fibres still relatively well aligned, although the waviness was patchy and individual fibres could not be readily identified in all fields. The cell nuclei were shorter but still oval, with darker‐staining chromatin. The relationship to collagen fibres was maintained but often the nuclei were arranged in short chains to give an Indian‐file appearance. Moderate degeneration, designated grade 3, showed increasing hyalinization of the collagen to produce areas of smudgy, homogeneous eosinophilic staining in the haematoxylin/eosin preparation. Cell nuclei were often increased in number and were round to oval in outline with a darkly staining chromatin pattern. There was some loss of orientation of the collagen bundles and loss of orientation of the nuclei in relation to the collagen bundles. Severe degeneration, designated grade 4, showed diffuse hyalinization of the collagen throughout the tendon, with a homogeneous appearance. There was complete loss of orientation of collagen bundles within the tendon, as assessed by polarized light microscopy. The number of nuclei was reduced and those present were small, dark and rounded.