Increased cell proliferation and associated expression of PDGFRβ causing hypercellularity in patellar tendinosis

Objective. This study assessed cellularity in patellar tendinosis with respect to cell proliferation and the expression of platelet-derived growth factor receptor beta (PDGFR beta). Methods. Surgical samples were taken from 11 patients fulfilling criteria of patellar tendinosis and from 12 matched controls. Standard immunohistochemistry methods were used to detect expression of PDGFR beta and proliferation cell nuclear antigen (PCNA). Results were analysed by computer-assisted microscopy. Tendon cells were isolated from nine tendinosis and eight control tissues for cell culture. Results. Increased cellularity (P < 0.001) was observed in tendinosis tissues compared with controls, and also a higher proliferative index (P < 0.001). Increased expression of PDGFR beta was demonstrated (P < 0.001). Cultured tendinosis cells showed a higher proliferation rate than controls (P < 0.001). This was maintained when the cells were cultured under various conditions of serum supplementation (P < 0.01). Tendinosis cells also showed a higher proliferation rate (P < 0.01) in medium containing 10 ng/ml PDGF. Conclusion. Hypercellularity in patellar tendinosis is caused by increased cell proliferation and is associated with increased expression of PDGFR beta.