Chronic Achilles tendinopathy. A survey of surgical and histopathologic findings.

The surgical findings and the histopathology are reported for 163 patients (134 males, 29 females; mean age, 38 years; range, 13-72 years; 75% athletes) with chronic Achilles tendinopathy. Biopsy specimens from symptomatic (155 cases) and nonsymptomatic (90 cases) parts of the tendon and from the paratenon (97 cases) were obtained. Surgical reports were reviewed and histopathology was evaluated according to a standardized protocol. Eighteen tendons also were analyzed by immunofluorescence for fibrinogen, immunoglobulins, and complement. Degenerative changes (tendinosis) characterized by abnormal fiber structure, focal hypercellularity, and vascular proliferation were noted in 90% of biopsy specimens from symptomatic parts of the tendons and, to a lesser degree, in 20% from nonsymptomatic parts. Fibrinogen could be identified in most lesion biopsy specimens. Partial tendon ruptures were present in 19% of the patients and always occurred in areas afflicted with tendinosis. The paratenon was mostly normal or revealed only slight changes. Increasing age and male gender were associated with more pronounced histopathologic changes. Tendinosis, sometimes complicated by partial rupture, appears to be the major lesion in chronic Achilles tendinopathy; the paratenon is rarely involved. Important features are a lack of inflammatory cells and a poor healing response.