Internal versus external femorotibial rotation an anterior cruciate ligament rupture and patellofemoral instability on preoperative standing radiographs.

Abstract

Previous literature has identified non-modifiable risk factors for anterior cruciate ligament (ACL) rupture and patellofemoral instability (PFI), such as sex, joint laxity, tibial slope, variations in the intercondylar notch, patella alta, trochlear dysplasia, distance from the tibial tubercle to the trochlear groove, and posterior cruciate ligament morphology. The primary aim of this study was to compare femorotibial rotation among pediatric patients with ACL rupture, PFI, and a comparison cohort. The authors hypothesized there would be differences in femorotibial rotation measurements between patients with ACL rupture, PFI, and a comparison cohort. A retrospective review was conducted, where patients aged 8-21 years at a single institution who sustained an ACL rupture or PFI injury between January 2015 and August 2022 were identified. Participants were included if they had a preoperative EOS lower limb x-ray. Participants with a history of previous knee surgery to either knee, or more than one diagnosis of either ACL rupture or PFI were excluded. Participants were compared to a cohort of scoliosis patients with a Cobb angle less than 20° who had biplane EOS radiographs (Controls). All preoperative radiographs were sent for EOS three-dimensional reconstructions. Data outputs with a specific focus on femorotibial rotation, femoral anteversion, and tibial torsion were acquired and analyzed. The femorotibial rotation output measurements were positive or negative, representing external and internal rotation, respectively. A Kruskal-Wallis Test was run to compare femorotibial rotation between the three groups (ACL, PFI, Controls), and pairwise comparisons were also analyzed. Statistical significance was set to p ≤ 0.05. Univariate and multivariable linear regression analyses were performed to assess the association between femorotibial rotation and group, age, sex, BMI, and mechanical axis alignment. Of the identified patients, 197 met final inclusion and exclusion criteria (60 ACL, 92 PFI, 45 Controls). The mean age at time of imaging for all patients was 14.4 ± 2.2 years (ACL: 14.3 ± 1.8 years; PFI: 14.3 ± 2.4 years; Controls: 14.9 ± 2.4 years), and 50.8% were female (ACL: 43.3% female; PFI: 58.7% female; Controls: 44.4% female). The median femorotibial rotation was 4.8° (ACL: -2.1°; PFI: 10.2°; Controls: 4.4°). Femorotibial rotation was noted to be significantly different between cohorts (p < 0.001), and the pairwise comparisons between each group were also significant (ACL-Control: p < 0.001, ACL-PFI: p < 0.001, Control-PFI: p < 0.001). These differences remained significant after multivariable adjustment for age, sex, BMI, and mechanical axis alignment (ACL vs. Control: p < 0.001; PFI vs. Control: p = 0.001). Femorotibial rotation differed significantly between patients with ACL rupture, PFI, and a comparison cohort. Most ACL patients had internal femorotibial rotation, while most PFI patients had external femorotibial rotation.