Loss of patellofemoral cartilage thickness over 5 years following ACL injury depends on the initial treatment strategy: results from the KANON trial

Objectives To evaluate changes in patellofemoral cartilage thickness over 5 years after anterior cruciate ligament (ACL) injury and to determine the impact of treatment strategy. Methods 121 adults (ages 18-35 years, 26% women) had an ACL injury and participated in the KANON randomised controlled trial. Of those, 117 had available MRIs at baseline (<4 weeks post-ACL rupture) and at least one follow-up measurement (2, 5 years). Patellofemoral cartilage thickness was analysed by manual segmentation (blinded to acquisition order). Patellar, trochlear and total patellofemoral cartilage thickness changes were compared between as-randomised (rehabilitation+early ACL reconstruction (ACLR) (n=59) vs rehabilitation+optional delayed ACLR (n=58)) and as-treated groups (rehabilitation+early ACLR (n=59) vs rehabilitation+delayed ACLR (n=29) vs rehabilitation alone (n=29)). Results Patellofemoral cartilage thickness decreased -58 mu m (95% CI -104 to -11 mu m) over 5 years post-ACL rupture, with the greatest loss observed in trochlea during the first 2 years. Participants randomised to rehabilitation+early ACLR had significantly greater loss of patellar cartilage thickness compared with participants randomised to rehabilitation+optional delayed ACLR over the first 2 years (-25 mu m (-52, 1 mu m) vs + 14 mu m (-6 to 34 mu m), p=0.02) as well as over 5 years (-36 mu m (-78 to 5 mu m) vs + 18 mu m (-7, 42 mu m), p=0.02). There were no statistically significant differences in patellofemoral cartilage thickness changes between as-treated groups. Conclusion Patellofemoral (particularly trochlear) cartilage thickness loss was observed in young adults following acute ACL rupture. Early ACLR was associated with greater patellofemoral (particularly patellar) cartilage thickness loss over 5 years compared with optional delayed ACLR, indicating that early surgical intervention may be associated with greater short-term structural patellofemoral cartilage deterioration compared with optional delayed surgery.