Purpose The purpose of this study was to investigate whether the vastus medialis oblique (VMO) compensates in patella dislocation patients with the increase of femoral anteversion angle (FAA).
Methods From January 2016 to January 2021, a total of 30 knees of 27 patients with recurrent patellar dislocation (RPD Group) were reviewed for this study. Among these patients, 13 patients with patellar dislocation and excessive FAA, >30° were assigned to A Group, and 17 patients with the patellar dislocation without excessive FAA,≤30 were assigned to B Group. And 27 age and sex matched knees without patellofemoral disorders were enrolled as control (C Group). The area of the VMO and vastus lateralis muscle (VLM) was measured 20 mm above the upper edge of the patella, and the ratio of the VMO and VLM area was calculated. The correlation relationship of FAA and VMO, VLM was analyzed.
Results Comparing with the C Group, the RPD Group had a significantly larger FAA (30.10± 9.61°vs 15.00± 1.85°, P< 0.05), and smaller VMO/VLM ratio (3.49±1.00/4.18±1.51, P< 0.05), and the VMO/VLM ratio was significantly greater in A Group than the B Group (3.97±1.11 vs3.12±0.70, P< 0.05). There was no statistically significant difference in VMO/VLM ratio among A Group and C Group (3.12±0.70/3.97±1.11, P> 0.05). And the VMO/VLM ratio was decreased in the B Group compared with the C Group (3.12±0.70/4.18±1.51, P< 0.05). The VMO/VLM ratio was positively correlated with the FAA(r=0.42) in the RPD Group.
Conclusion Compared with the C Group, the patients with recurrent patellar dislocation had a smaller VMO/VLM ratio. Moreover, the FAA was positively correlated with the VMO/VLM in patients with patella dislocation. This finding explained the compensatory thickening of the VMO in response to excessive FAA in patients with patella dislocation.