In order to address high failure rates following rotator cuff repairs, a greater understanding is required of the underlying structural changes so that treatments can be appropriately targeted and biomarkers of failure can be identified. As collagen is the primary constituent of tendon and determines force transmission, collagen structural changes may affect responses to loading. For example changes in collagen 1 and 5 are associated with the hyperelastic Ehlers-Danlos syndrome, which is diagnosed by looking for pathopneumonic altered collagen fibres or ‘collagen flowers’ in skin using transmission electron microscopy (TEM). To date no study has been performed on the microstructure of torn human rotator cuff tendons using TEM. It was hypothesized that normal, small and massive human rotator cuff tendons tears will have altered microscopic structures. The unique study aimed to use TEM to compare the ultrastructure of small and massive rotator cuff tears, to normal rotator cuff tendons. Samples from 7 human rotator cuff tendons repairs were obtained, including 4 massive (>5 cm) and 3 small (< 1 cm) tears, and 3 matched normal controls with no history of connective tissue disorders. Specimens were fixed in 4% glutaraldehyde in 0.1M phosphate buffer, processed and examined blind using routine TEM examination. To assess whether changes in the relative expression of collagen 1 and 5 (COL1A1, COL5A1 and COL5A2) occurred in all tears, qPCR was performed on another 6 phenotypically matched patients.INTRODUCTION
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