Influence of Medial Patellofemoral Ligament Reconstruction on Patellofemoral Contact in Patients With Low-Flexion Patellar Instability: An MRI Study

Background:Medial patellofemoral ligament (MPFL) reconstruction is a well-established procedure for the treatment of patients with patellofemoral instability (PFI) at low flexion angles (0 degrees-30 degrees). Little is known about the effect of MPFL surgery on patellofemoral cartilage contact area (CCA) during the first 30 degrees of knee flexion. Purpose/Hypothesis:The purpose of this study was to investigate the effect of MPFL reconstruction on CCA using magnetic resonance imaging (MRI). We hypothesized that patients with PFI would have a lower CCA than patients with healthy knees and that CCA would increase after MPFL reconstruction over the course of low knee flexion. Study Design:Cohort study; Level of evidence, 2. Methods:In a prospective matched-paired cohort study, the CCA of 13 patients with low-flexion PFI was determined before and after MPFL reconstruction, and the data were compared with those of 13 healthy volunteers (controls). MRI was performed with the knee at 0 degrees, 15 degrees, and 30 degrees of flexion in a custom-designed knee-positioning device. To suppress motion artifacts, motion correction was performed using a Moire Phase Tracking system via a tracking marker attached to the patella. The CCA was calculated on the basis of semiautomatic cartilage and bone segmentation and registration. Results:The CCA (mean +/- SD) at 0 degrees, 15 degrees, and 30 degrees of flexion for the control participants was 1.38 +/- 0.62, 1.91 +/- 0.98, and 3.68 +/- 0.92 cm(2), respectively. In patients with PFI, the CCA at 0 degrees, 15 degrees, and 30 degrees of flexion was 0.77 +/- 0.49, 1.26 +/- 0.60, and 2.89 +/- 0.89 cm(2) preoperatively and 1.65 +/- 0.55, 1.97 +/- 0.68, and 3.52 +/- 0.57 cm(2) postoperatively. Patients with PFI exhibited a significantly reduced preoperative CCA at all 3 flexion angles when compared with controls (P <= .045 for all). Postoperatively, there was a significant increase in CCA at 0 degrees of flexion (P = .001), 15 degrees of flexion (P = .019) and 30 degrees of flexion (P = .026). There were no significant postoperative differences in CCA between patients with PFI and controls at any flexion angle. Conclusion:Patients with low-flexion patellar instability showed a significant reduction in patellofemoral CCA at 0 degrees, 15 degrees, and 30 degrees of flexion. MPFL reconstruction increased the contact area significantly at all angles.