The vastus medialis oblique compensates in current patellar dislocation patients with the increased femoral anteversion

Purpose The purpose of this study was to investigate whether the vastus medialis oblique (VMO) muscle compensates in patellar dislocation (PD) patients with the increased femoral anteversion angle (FAA). Methods Between 2021 and 2024, we included 60 patients with recurrent PD (RPD group). Inclusion criteria were at least two episodes of PD, as well as complete CT scans of the knee and hip. Exclusion criteria included traumatic or habitual dislocation, previous knee surgery, etc. Of these patients, 30 with excessive FAA (>= 30 degrees) were assigned to the A group, and 30 without excessive FAA (< 30 degrees) to the B group. A control group of 120 patients without patellofemoral disorders was also included (C group). The cross-sectional areas of the VMO and vastus lateralis muscle (VLM) were measured 20 mm above the patella on CT scans, and the VMO/VLM area ratio was calculated. The correlation between FAA and the VMO/VLM ratio was analyzed. Results The RPD group had a significantly larger FAA (15.0 +/- 1.9 degrees vs. 30.1 +/- 9.6 degrees, P = 0.040) and a smaller VMO/VLM ratio (4.2 +/- 1.5 vs. 3.5 +/- 1.0, P = 0.014) compared to the C group. Within the RPD group, the A group had a higher VMO/VLM ratio than the B group (4.0 +/- 1.1 vs. 3.0 +/- 0.7, P = 0.029). The B group's VMO/VLM ratio was lower than that of the C group (3.0 +/- 0.7 vs. 4.2 +/- 1.5, P = 0.004). However, there was no significant difference in the VMO/VLM ratio between the A group and the C group. The VMO/VLM ratio showed a moderate positive correlation with FAA in the RPD group, with a correlation coefficient of r = 0.4 (P = 0.012), indicating a statistically significant relationship between the two. Conclusion Patients with recurrent PD showed a smaller VMO/VLM ratio compared to controls. Increased FAA was correlated with compensatory thickening of the VMO and a higher VMO/VLM ratio in PD patients. This suggests that increased FAA may drive biomechanical adaptations in the quadriceps, stabilizing the patella. Clinicians should consider changes in FAA when assessing and treating PD. Level of evidenceLevel III.