Assessing Femoral Anteversion in Patients With Bilateral Recurrent Patellar Dislocations.

Background: After first-time lateral patellar dislocation, 44% to 70% of patients sustain redislocations. Increased femoral anteversion (FA) is considered to result in increased lateralizing forces on the patella, which might predispose one to patellar instability. When recurrent patellar dislocations (RPDs) are bilateral, it is unclear if the FA is even more increased.

Hypothesis: Patients with bilateral RPD would have greater FA than patients with unilateral RPD.

Study design: Case-control study; Level of evidence, 3.

Methods: A total of 52 skeletally mature patients with RPD and a clinical suspicion of rotational malalignment underwent rotational computed tomography or magnetic resonance imaging. The uni- or bilaterality of the RPD was determined. A control group comprising 54 adult patients with trauma underwent computed tomography of both lower extremities as part of a multitrauma protocol. The FA values of both lower extremities were evaluated separately.

Results: In total, 20 of 52 (38.5%) patients in the study group had a history of unilateral RPD and 32 of 52 (61.5%) patients had a bilateral RPD diagnosis. The mean FA of the asymptomatic limb in unilaterally symptomatic patients was 18.0° (SD, 11.2°; range, 0.5°-40.0°; median, 16.5°). In the symptomatic limb, the mean FA was 19.2° (SD, 9.1°; range, 2.0°-33.0°; median, 19.0°) (mean difference, 1.2°; 95% CI -1.3° to 3.8°). In bilaterally symptomatic patients, the mean FA on the right side was 23.2°, and 22.5° on the left. The mean differences between the symptomatic limbs in the unilateral RPD group and the right or left limbs in the bilateral RPD group were 4.0° (P = .263) and 3.3° (P = .326), respectively. In the control group without RPD, the mean FA was 12.5° (SD, 8.5°; range, 0.8°-33.0°; median, 10.9°). The mean difference between right limbs of the patients with bilateral RPD and right limbs of controls was 10.8° (P = .001).

Conclusion: Patients with bilateral RPD have bilaterally greater FA than patients without a history of RPD. Patients with unilateral RPD have greater FA on both sides compared with the control group without a history of lateral patellar dislocation. No statistically significant difference of FA can be seen between patients with bilateral or unilateral RPD.