Injuries produced by blunt trauma to the human patellofemoral joint vary with flexion angle of the knee

Patellofemoral joint impact trauma during car accidents. sporting activitie s, and falls can produce acute gross fracture of bone, microfracture of bon e, and soft tissue injury. Field studies of car accidents, however, show th at most patellofemoral traumas are classified as 'subfracture' level injuri es. While experimental studies have shown that the influence of flexion ang le at impact is not well understood. flexion angle may influence injury loc ation and severity. In the current study, 18 pairs of isolated human cadave r knees were subjected to blunt impact at flexion angles of 60 degrees. 90 degrees. or 120 degrees. One knee from each cadaver was sequentially impact ed until gross fracture of bone was produced. The contralateral knee was su bjected to a single. subfracture impact at 45% of the impact energy produci ng fracture in the first knee. The fracture experiments produced gross frac ture of the patella and femoral condyles with the fracture plane positioned largely within the region of patellofemoral contact. The fracture location and character changed with flexion angled at higher flexion angles the pro ximal pole of the patella and the femoral condyles were more susceptible to injury. For the 90 degrees flexion angle, the patella was fractured centra lly, while at 60 degrees the distal pole fractured transversely at the inse rtion of the patellar tendon. In addition, the load magnitude required to p roduce fracture increased with flexion angle. In the 'subfracture' knees, i njuries were documented for all flexion angles: occult microfractures of th e subchondral and trabecular bone and fissures of the articular surface, Si milar to the fracture-level experiments, the injuries coincided with the pa tellofemoral contact region These data show that knee flexion angle plays a n important role in impact related knee trauma. Such data may be useful in the clinical setting, as well as in the design of injury prevention strateg ies. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science L td. All rights reserved.