Quantification of patellofemoral joint contact area using magnetic resonance imaging.

To describe a method for quantifying patellofemoral joint contact area using magnetic resonance imaging (MRI), we used a repeated measures design using cadaver specimens. The use of contact area obtained from cadaveric specimens for biomechanical modeling does not permit investigators to assess the inter-subject variability in contact area as a result of patellofemoral pathology or malalignment. Therefore, a method for measuring patellofemoral joint contact area in-vivo is necessary. Six fresh frozen unmatched human cadaver knees were thawed at room temperature and minimally dissected to permit insertion of a pressure sensitive film packet into the suprapatellar pouch. A custom loading apparatus was designed to apply a compressive load to the patellofemoral joint at 30 degrees of flexion. Simultaneous measurement of contact area was made using both the pressure sensitive film technique and MRI. The intraclass correlation coefficient (ICC) and coefficient of variation were used to compare the agreement between the two methods and to assess the repeatability of the MRI method. Good agreement was found between the MRI and pressure sensitive film techniques (ICC 0.91; CV 13%). The MRI technique also was found to be highly reproducible (ICC 0.98; CV 2.3%). MRI assessment of patellofemoral joint contact area was found to be comparable to the established pressure sensitive film technique. These results suggest that this method may be a valuable tool in quantifying patellofemoral joint contact area in-vivo. Quantification of the patellofemoral joint stress has been dependent on patellofemoral joint contact area obtained from cadaver specimens, thereby negating the potential influence of subject specific variability. Developing a non-invasive technique to evaluate contact area will assist researchers and/or clinicians in obtaining patient-specific contact area data to be used in biomechanical analyses and clinical decision making.