THE SHAPE OF PATELLA RELATIVE TO FEMORAL EPICONDYLAR AXIS

Objective The aim of this study was to evaluate the shape of patella relative to the femoral epicondylar axis and to find sex differences. Materials and methods Computed tomography (CT) images of 100 knees with tibiofemoral osteoarthritis in 100 patients were prospectively collected. All patients were diagnosed as varus-type osteoarthritis with no destructive patellar deformity. Fifty patients were male and 50 female. The average male age was 70.8±14.6 (mean ± SD) years and the average female age was 73.3±6.7 years. Forty nine knees were right and 51 knees were left. The average height of males was 162.6±7.4 cm and that of females 149.6±5.7 cm. Males were significantly taller than females. The CT scan was performed with 2mm-interval slices in the vertical plane to the long axis of femoral shaft. Every CT image was examined to determine the maximum distance between the medial and lateral femoral epicondyle (inter-epicondylar distance, IED) along the epicondylar axis. The maximum patellar width and thickness were also measured at the image which had these maximum distances, while patellar cartilage thickness in anteroposterior diameter was not measured in this study. For evaluating the patellar size, each measured value was divided by IED and calculated each ratio. The ratio of patellar width to patellar thickness was also calculated. All parameters were compared between males and females. Statistical software Statview ver.5.0 (SAS Institute Inc.) was used for all analyses with significance being set at the 5% level. Results Measured values are presented on Table 1. The average IED, patellar width and patellar thickness of males were all significantly larger than those of females. As shown in Table 2, by contrast, each ratio to IED was almost the same between the sexes and there were no significant differences. The ratio of patellar width to patellar thickness was 46.7±2.6% in males and 46.6±2.9% in females. Discussion Although some studies have assessed the actual measurement values of patella, no prior study, to our knowledge, has morphologically evaluated the patella relative to the femur. This is the first study to investigate the configuration and location of patella relative to femoral epicondylar axis. Our results showed the configuration of patella relative to the femoral epicondylar axis was the same between sexes. The patellar width is approximately 56% and TGD is approximately 39% of IED. The most common complications after the surgery are related to patellofemoral problems. The ideal thickness of the resurfaced patella has not been clearly investigated. Patellar disabilities are associated with both decreased and increased patellar thickness— a thin patella could lead to anteroposterior patellar instability and a thick patella could increase the risk of stiffness of the knee and patellar subluxation. Therefore, it is desirable to restore the original patellar thickness during surgery. The results of current study showed that the ratio of patellar width to the patellar thickness was about 47%, which is useful to determine the thickness of patella during surgeries for severely damaged knees or revision surgeries.