Abstract
Objectives:
Quadriceps tendon malalignment has been closely linked to chronic lateral patella tracking and the development of lateral patellar facet osteoarthritis. It is unknown what underlying deformity of the quadriceps muscle is associated with quadriceps tendon malalignment. A common assumption is that patella maltracking is associated with wasting of the vastus medialis relative to the rest of the quadriceps. The purpose was to 1) determine the association of the alignment of the proximal quadriceps musculature with quadriceps tendon alignment, 2) assess the torsional deformity of the quadriceps muscle along the femur in patients with quadriceps tendon malalignment, and 3) determine the association of quadriceps deformity with the relative volume of the four components of the quadriceps.
Method:
176 Computed Tomography (CT) scans were included in the study. Based on the measured Quadriceps Tendon Axial Angle (QTAx) cases were categorised into “lateralised”, “medialised”, and “normal” groups. 10 cases were selected from each group. The Quadriceps Muscle torsional angle (QMuscle) was measured at 7 points along the femur and compared to the QTAx groups. The cross-sectional area of the vastus intermedius (VI), vastus medialis, vastus lateralis and rectus femoris muscle bellies were also measured and compared between the QTAx groups.
Results:
There were significant differences in QMuscle between the three QTAx groups at all 7 points along the femur, with the lateralised group having the largest mean angle of 46.6° (SD=±7.5°) external rotation across all sections, compared to normal and medalised groups with external rotations of 37.6° (SD=±3.8°) and 30.6° (SD=±2.9°), respectively (p<0.001). The ratio of the vastus medialis to the total quadriceps muscle was significantly greater in the lateralised group, when compared to the normal group (p<0.001).
Conclusion:
Lateralisation or external rotation of the quadriceps tendon is highly correlated with the external rotation of the quadriceps muscle extending all the way up the thigh. Quadriceps malalignment is also associated with a larger vastus medialis muscle volume. These results demonstrate that chronic lateral patella tracking, which is closely associated with quadriceps malalignment, is likely to be due to a rotational deformity of the quadriceps muscle and not to wasting of vastus medialis.