Expression of the mesenchymal stem cell marker Stro-1 in chronic tendinopathy

Abstract

Chronic tendon pain, frequently described as ‘tendinitis’, is common in the supraspinatus, Achilles and patella tendons, although little is known about the underlying pathology since painful tendons are not routinely biopsied and surgery is usually the last resort of treatment. Repeated microtrauma to the fibrillar matrix is thought to be the principal cause of most tendinopathy, although tendons are immensely strong under tension and do not normally rupture unless there has been prior degeneration of the matrix. Tendon cells (tenocytes) maintain the tendon matrix, and have been shown to have some capacity for remodelling the tendon in response to altered mechanical loads and injury. Tenocytes are not a homogenous cell population however, and there is evidence that, after injury, cells from the epitenon surrounding the fibre bundles are more active in the repair response than the mature tenocytes from within the fibre bundles (Gelberman et al. 1984). In chronic tendinitis, we and colleagues have shown an increase in cell number and activity associated with the lesion, although these cells have not yet been characterized. Having recently obtained access to tendon specimens from patients with mid-stage Achilles and patella tendinitis, the aim of this study was to characterize the cells proliferating within the lesion using a number of cell-specific immunocytochemical markers.