Asymmetrical Patellofemoral Joint Loading Persists Through Return to Sport After Anterior Cruciate Ligament...

Patellofemoral joint loading after anterior cruciate ligament reconstruction (ACLR) remains poorly understood, despite the high prevalence of patellofemoral joint complications following surgery. With an observational cohort design, we compared patellofemoral joint stress (PFJS) and reaction force (PFJRF) between surgical and nonsurgical limbs during a double-limb squat at 12 weeks postsurgery and return to sport (RTS), with sex-based comparisons.

Forty-seven athletes (21 males and 26 females) aged 12-25 years performed a body weight double-limb squatting task at 12 weeks postoperatively and RTS. Maximal knee extensor strength was assessed at both time points with isokinetic dynamometry. Ground reaction forces and kinematic data were used to compute patellofemoral loading. Mixed factorial analyses of variance compared patellofemoral loading and knee extension strength, and Pearson correlations examined associations between patellofemoral loading and knee extensor strength.

The surgical limb demonstrated lower PFJS (P < .001, ηp2=.439) and PFJRF (P < .001, ηp2=.423) at both time points, though these measures increased over time without significant changes in the nonsurgical limb. Females exhibited lower PFJS (P < .001, d = 0.73) and PFJRF (P = .032, d = 0.52) than males across limbs and time points. Knee extensor strength was positively associated with PFJS (r = .697; r = .616) and PFJRF (r = .605; r = .531, all P < .01) at both 12 weeks postsurgery and RTS, respectively.

Athletes demonstrate decreased patellofemoral joint loading in the surgical versus the nonsurgical limb through RTS. Females exhibit lower patellofemoral loading after ACL reconstruction, which may be linked to their higher prevalence of posttraumatic osteoarthritis and patellar abnormalities-supporting the paradoxical hypothesis that underloading, rather than overloading, may promote osteoarthritis development.