The length of the popliteus on sagittal views correlates with high tibiofemoral rotations and patellar instability

Purpose

This study evaluates the relationship between tibiofemoral rotation and the length of the popliteus on sagittal views to assess if there are significant length differences in the popliteus with different degrees of rotation.

Methods

MRIs were analyzed from two age-sex-matched cohorts: patellofemoral instability (PFI) patients and controls. Tibiofemoral rotation was measured by recording the angle between the femoral and tibial condylar lines. The popliteus length was measured by subtracting the distance from the popliteus sulcus to the femoral condyle and the sulcus to the posterior tibia on sagittal slices. Interrater reliability was calculated using intraclass correlation coefficients (ICC), a regression analysis described relationships between the metrics, and a Mann-Whitney U test compared median differences between cohorts. A significance level of 0.05 was used for all analyses.

Results

There were statistically significant positive relationships between rotation and length overall ($r^2$ = 0.49, p < 0.001), for the patient group ($r^2$ = 0.35, p < 0.001) and for the control group ($r^2$ = 0.52, p < 0.001). There was a significant difference between the PFI and control group for the rotation (p < 0.001) and length (p = 0.002). In total, seventy knees were included, 35 patients and 35 controls. The ICC for the rotation and length measurements were 0.87 (CI: 0.77–0.93) and 0.94 (CI: 0.89–0.97) respectively.

Conclusion

This study identified increased popliteus length associated with increased external tibiofemoral rotation as seen in patella instability patients. These findings demonstrate a further need to investigate the implications of advancing the popliteus for treatment of high tibiofemoral rotations.