BACKGROUND: Treatment of midportion Achilles tendinopathy is hampered by limited knowledge of the pathophysiology. HYPOTHESIS: Chondrogenic differentiation of tendon cells might take place in midportion Achilles tendinopathy and could be used as a target for drug treatment. An in vitro model for chondrogenic differentiation would be useful to evaluate existing and future treatment opportunities. Study: A controlled laboratory study. METHODS: Perioperatively harvested tissue from human midportion Achilles tendinotic lesions and healthy Achilles tendons was analyzed by microscopy and real-time reverse transcription polymerase chain reaction. In vitro chondrogenic differentiation of tendon explants was induced using transforming-growth-factor beta. This model was modulated by removing the chondrogenic stimulus or adding triamcinolone or platelet-rich plasma. RESULTS: Midportion Achilles tendinotic lesions had increased glycosaminoglycan staining and more rounded cell nuclei. Chondrogenic markers (sex-determining region Y)-box9, aggrecan, collagen 2, and RUNT-related transcription factor 2 were upregulated, but collagen 10 was not. Nondegenerative tendon explants cultured on chondrogenic medium had higher expression of aggrecan, collagen 2, and collagen 10 but not (sex-determining region Y)-box9 and RUNT-related transcription factor 2. Removing the chondrogenic stimulus decreased expression of aggrecan, collagen 2, and collagen 10. Both triamcinolone and platelet-rich plasma influenced the chondrogenic gene expression pattern in the in vitro model. CONCLUSION: Chondrogenic differentiation is present in midportion Achilles tendinopathy. An in vitro model to study this chondrogenic differentiation was developed. CLINICAL RELEVANCE: This model can be used to investigate chondrogenic differentiation as a possible target for drug treatment, contributing to the development of more successful mechanism-based treatment opportunities.

Additional Metadata
Keywords Achilles tendinopathy, chondrogenic differentiation, in vitro model, platelet-rich plasma (PRP), triamcinolone
Sponsor In 2009: Erasmus MC, Department of Orthopaedics, University Medical Centre Rotterdam
Persistent URL,
Journal American Journal of Sports Medicine
Note Epub 2009 Mar 11.
de Mos, M, Koevoet, J.L.M, van Schie, J.T.M, Kops, N, Jahr, H, Verhaar, J.A.N, & van Osch, G.J.V.M. (2009). In vitro model to study chondrogenic differentiation in tendinopathy. American Journal of Sports Medicine, 37(6), 1214–1222. doi:10.1177/0363546508331137