Expression of type VI collagen in arthrofibrotic tissue. An immunhistochemical study

Arthrofibrosis is a disabling complication after trauma and surgery due to massive connective tissue proliferation. The etiology and pathogenesis have never been fully understood. A strong immune response may lead to activati on and proliferation of fibroblasts with excessive and disordered depositio n of matrix proteins. In similar pathological conditions, like lung fibrosi s or superficial fibromatoses with fibrotic transformation an increased exp ression of collagen type VI has been reported. We investigated fibrotic tis sue samples taken from 18 patients (average age: 32,7 years), who underwent arthrolysis of the knee joint because of symptomatic arthrofibrosis follow ing ligament injury. The mean interval between trauma and arthrolysis was 1 3,8 months (range 4-50 months). Tissue samples were taken from the infrapat ellar fat pad and intercondylar connective tissue. All samples were stained with HE. The expression of type III and VI collagen was studied immunohist ochemically using an immunoperoxidase method for light microscopic visualiz ation. Histologic analysis from patients with arthrofibrosis showed a synov ial hyperplasia with cell infiltration and vascular proliferation compared to synovial tissue samples from knee joints without any detectable patholog y. Subsynovial an increased deposition of matrix proteins was visible. Type VI collagen was widely distributed as a network subsynovial and around cap illary walls. Type III collagen showed a diffuse distribution. Arthrofibrot ic tissue is, similar to pathological conditions with fibrotic transformati on characterized by an increased expression of collagen type VI. Collagen t ype VI may play an important role in matrix homeostasis. It serves as an an choring element between collagen fibers and as a cell binding structure.