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Session: Motion
Session starts: Thursday 26 January, 14:30
Presentation starts: 15:15
Room: Room 531

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Miriam Boot (Radboudumc)
Sebastiaan van de Groes (Radboudumc)
Hans Dunning (Radboudumc)
Esther Tanck (Radboudumc)
Dennis Janssen (Radboudumc)

Abstract:
Introduction Medial patellofemoral ligament (MPFL) reconstruction is the primary treatment for patients with recurrent patellofemoral instability. Still, the surgery is associated with high complication rates. Clinical outcomes can be improved by a better understanding of MPFL length changes during knee movement. Yet, a clear understanding of normal patellofemoral biomechanics of the MPFL is lacking. This study aimed to assess length changes of the MPFL from 0 to 90 degrees of flexion. Methods A high resolution static and medium resolution dynamic CT scan of both knees were obtained in 97 healthy subjects. Static CT scans were obtained in full extension. Dynamic CT scans were obtained during an active flexion-extension-flexion movement (full extension to 90° flexion) in 10s. Static and dynamic CT data were superimposed using image registration and transformations were interpolated to get 3D knee joint models per angle of flexion. Using the knee models, the MPFL length was measured based on anatomic studies from Schöttle’s point on the femur to three insertion points on the superomedial border of the patella (proximal, central, and distal). The shortest wrapping path around the femoral condyle was selected as the MPFL length. Subsequently, MPFL length changes were assessed per flexion angle and expressed as percentual length changes relative to the length in full extension. Results The average MPFL length changed less than 5% during knee movement (range: 0.8 – 20.6%). During the first 20-30° of flexion, the average MPFL length decreased with 2%. Beyond 20-30° of flexion, the elongation pattern depended on the patellar attachment site. For the central patellar attachment, the MPFL length restored to its initial length (0 ± 6%), whereas the length remained decreased for the proximal attachment (-3 ± 6%) and even increased for the distal attachment (+4 ± 7%). Conclusion The MPFL has on average a near-isometric behaviour during knee flexion but interindividual differences in elongation patterns are large. These findings suggest that a personalized surgical approach may be desirable for reducing complication rates. Future studies should focus on anatomical causes underlying to these differences in elongation patterns.