Quantification of patellofemoral joint stress in females who have undergone ACL reconstruction: Implications for early onset osteoarthritis.

Abnormal patellofemoral joint (PFJ) stress (defined as the PFJ reaction force divided by the PFJ contact area) may be contributory to early-onset PFJ osteoarthritis in persons who have undergone anterior cruciate ligament reconstruction (ACLr). Using a model of the PFJ that takes into consideration subject-specific contact area, the purpose of this study was to compare peak PFJ stress during functional tasks between females who have undergone ACLr and healthy controls. It was hypothesized that persons post-ACLr would exhibit higher peak PFJ stress during walking, running, and drop landing tasks and that increased PFJ stress would be driven primarily by reduced PFJ contact area. Forty female athletes between the ages of 18-35 who participated in field or court sports participated. Twenty had previously undergone ACLr during the last 6-12 months and 20 were matched to healthy controls. Participants completed two phases of data collection: 1) loaded MRI assessment of the PFJ (35 % bwt) to quantify contact area, and 2) biomechanical assessment of walking, running and a single leg drop land task. A previously described subject-specific model of the PFJ was used to calculate PFJ stress. Peak PFJ stress did not differ between females post-ACLr and healthy controls across tasks. Lower PFJ reaction forces at the time of peak stress were observed in the ACLr group for each task, however this was offset by significantly lower utilized PFJ contact area. Large variability in peak stress was observed in the ACLr group suggesting that a subset of individuals may be at risk of overloading of the PFJ.