Introduction Patellofemoral joint osteoarthritis is common following anterior cruciate ligament reconstruction (ACLR) and may be linked with altered joint loading. We aimed to determine if altered patellofemoral joint loading is associated with prevalent and worsening early patellofemoral osteoarthritis following ACLR.

Materials and Methods Forty-six participants (mean age 27±5 years) one-year following primary ACLR (hamstring-tendon autograft) underwent magnetic resonance imaging (MRI) and biomechanical assessment of their reconstructed knee. Trunk and lower-limb kinematics plus ground reaction forces were recorded during the landing phase of a standardised forward hop task. These data were input into an established musculoskeletal model to calculate patellofemoral contact force. Follow-up MRI was acquired on 32 participants at five-years post-ACLR. Generalised linear models (Poisson) assessed the relationship between patellofemoral loading and prevalent early patellofemoral osteoarthritis (i.e., presence of a patellofemoral cartilage lesion one-year post-ACLR) and worsening patellofemoral osteoarthritis (i.e., incident/progressive patellofemoral cartilage lesion at 5-years post-ACLR).

Results Those with a lower peak patellofemoral contact force were more likely to have early patellofemoral osteoarthritis at 1-year post-ACLR (n=14 (30%); prevalence ratio 1.37; 95%CI 1.02 to 1.85). A lower peak patellofemoral contact force increased the risk of worsening patellofemoral osteoarthritis at 5-years post-ACLR (n=9 (28%); risk ratio 1.55, 95%CI 1.13 to 2.11).

Conclusion Young adults following ACLR who underload their patellofemoral joint during a hopping task are at high risk of early patellofemoral osteoarthritis onset and progression within the first 5-years after ACLR. These findings challenge traditional thinking that joint overloading drives post-traumatic osteoarthritis, and provides new targets for osteoarthritis prevention.