Collagen fragmentation in ruptured canine cranial cruciate ligament explants

Collagen fragmentation in cranial cruciate ligament (CCL) explants and stifle synovial fluid was investigated in dogs with ruptured and intact CCL. Cathepsin K and tartrate-resistant acid phosphatase (TRAP) activities were determined in CCL explant supernatants. Formation of collagen fragments was determined in explant supernatants and stifle synovial fluid. Cathepsin K+ and TRAP+ cells were stained specifically in histological sections of CCL. Formation of telopeptide collagen fragments was increased in ruptured CCL explants and stifle synovial fluid from dogs with ruptured CCL. In ruptured CCL explants, release of collagen fragments was associated with extracellular release of TRAP and the presence of cathepsin K+ cells within CCL tissue. Cathepsin K+ and TRAP+ cells were only seen in ruptured CCL. It was concluded that infiltration of the CCL with TRAP+ cells in dogs with CCL rupture is associated with increased collagenolysis. It is hypothesized that recruitment and activation of TRAP+ mononuclear cells within the synovium and CCL precipitates CCL rupture through upregulation of collagenolytic enzymes and collagen degradation.