Objectives: High external tibiofemoral rotations (external tibial rotations and/or internal femoral rotations) likely contribute to lateral patellofemoral instability (PFI). The popliteus musculotendinous complex is known to resist these rotations. However, to our knowledge no study has yet explored the relationship between rotation and the popliteus in cases where there is no known injury to the posterolateral corner, as in those with PFI. Thus, this study evaluates the relationship between tibiofemoral rotation and the length of the popliteus to assess if there are significant length differences in the popliteus with different degrees of rotation. This was done to better understand the plausibility of popliteus advancement or shortening in the treatment of high tibiofemoral rotations.

Methods

MRIs taken between the years 2015 to 2024 were analyzed from two matched cohorts: patellofemoral instability (PFI) patients and controls. All PFI knees had at least two dislocation events. 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 interclass correlation coefficients (ICC), a regression analysis was used to describe relationships between the metrics, and a Mann-Whitney U test was used to compare median differences between the 2 groups.

Significance

level of 0.05 was used for all analyses.

Results

There were statistically significant positive relationships between rotation and length overall (𝑟2=0.49, p=5.86×10-12), for the PFI patient group (𝑟2=0.35, p=9.96×10-5-5) and for the control group (𝑟2 =.52, p=6.86×10-7). There was a significant difference between the PFI and control group for the rotation (p=4.46×10-5) and length (p=0.002). Seventy total knees were included, 35 PFI 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. This demonstrates the need for further clinical research regarding how adjustment of the popliteus could be used to reduce high tibiofemoral rotations.

Level of Evidence: III; Case-Control Study