Patellofemoral joint (PFJ) instability occurs as a result of multiple risk factors including boney and soft tissue pathoanatomy, and mechanical relationships, notably affecting the paediatric population with an incidence rate of 147.7/100,000 person years. Patellofemoral instability is known to be positivity related to the force exerted by the quadriceps in the coronal plane (described by the Q-angle), the Quadriceps Torsion Angle (QTA) in the axial plane as well as the degree of femoral torsion (FT). This investigation aims to develop a better understanding of the relationship between the quadriceps positional anatomy and quadriceps mechanism in the context of paediatric patellofemoral instability utilising a specific-specific coordinate system. Twelve knees were assessed in 12 participants with PFJ instability. Participants were divided into groups: six with femoral torsion 25° (15.02 ±2.53 years, 59.77 ±10.37kg). Five controls were also selected (13.80 ±3.22 years, 48.58 ±12.36kg). MRI imaging was conducted for each participant. 3D reconstruction of the femur, vastus lateralis and medialis was obtained using Mimics 26.0 (Materialise, Leuven). A subject-specific, cartesian reference system was defined using the posterior femoral condylar axis (PCA), the mechanical axis (MA) in the coronal plane and the perpendicular bisector of the PCA at the level of the MA intersection as the “z”, “x” and “y” axes, respectively. The muscles for each participant were divided into 50 slices along the MA and the centroid lines of the vastii were defined as the centre of the muscle area for each slice. The vastii distribution was compared axially and position of the centroid line-of-best-fit with respect to the MA were compared across the coronal and sagittal views between groups. The vastus lateralis was distributed across the anterio- and posteriolateral segments of the femur. The distribution in the anterior-lateral quadrant between Group 1 (63.67 ±13.18%) and Group 2 (44.23 ±15.72%) was statistically significant (p = 0.042). Axially, the vastus medialis was distributed in all four quadrants with respect to the reference system with the anterior-medial quadrant contributing to the largest proportion across all participant groups (41.05–75.49%) compared to the anterior-lateral (7.73–58.40%), posterior-lateral (0.40–5.89%) and posterior-medial (0.00–14.00%). The mean angle between the medialis centroid and MA viewed coronally was calculated as 7.43 ±1.21° for Group 1, 7.19 ±0.90° for Group 2 and 8.46 ±0.53° for the controls. The results between Group 2 and the controls were statistically significant (p = 0.02). In the sagittal view, the angle was calculated as 0.92 ±1.00° for Group 1, 2.07 ±1.47° for Group 2 and 1.40 ±0.43° for the controls. These results demonstrate both qualitative and quantitative differences between participants with varying levels of femoral torsion and quadriceps torsion angle. Results demonstrate that a FT < 1 5° and QTA < 5 0° may impact lateralis axial distribution while FT < 25° may impact medialis centroid proximity to the mechanical axis. These results provide a foundation for further investigation into the complex relationship between boney and soft tissue pathoanatomy with implications for surgical planning.
Aulakh et al. (Wed,) studied this question.