Articular Contact Area Before and After Deepening Trochleoplasty: 3D MRI Pilot Study and Considerations Regarding Pressure in the Patellofemoral Joint

Background: There is still a controversial debate regarding the pressure in the patellofemoral joint (PFJ) following deepening trochleoplasty (DTP). Objective: The purpose of this pilot study was to compare the PFJ contact area before and after DTP in patients treated for trochlear dysplasia and to discuss the biomechanical aspects regarding patellofemoral pressure. Methods: DTP was performed on four female patients to treat lateral patellar instability due to trochlear dysplasia. The preoperative and postoperative articular patellofemoral contact area was evaluated using three-dimensional (3D) MRI. Bone and cartilage were traced slice by slice in the acquired dimension, while the AMIRA segmentation software reconstructed the 3D model. This model was then transferred to the Rhinoceros software for measurement. Contour lines along the 3D model containing trochlear and patellar cartilage were placed, and the boundary and the curvature of the contact area were defined. The contact surfaces before and after DTP were compared. Results: The size of the articular contact area of the PFJ increased after DTP in three out of four cases compared to the preoperative condition. The preoperative average size of the contact area was 153 mm2 (range, 68–185); postoperatively, it was 289 mm2 (range, 200–370). The increase in contact area was, on average, 53% (−6% to 444%). Conclusions: The size of the articular contact area of the PFJ increased after DTP compared to the preoperative condition. The results provide biomechanical evidence that pressure in the PFJ decreases following DTP. The use of 3D MRI scans has demonstrated several advantages.