Evaluation of patellar dimension and Bristol Index in Asian population: An MRI study

BACKGROUND: Restoration of patellar thickness is pivotal during a total knee arthroplasty (TKA). Several studies showed there are differences in the knee measurements between Asian and Western population. PURPOSE: This study aims to evaluate the patellar dimension and Bristol Index of patellar width to thickness (BIPWiT) using magnetic resonance imaging (MRI) in Asian population. STUDY DESIGN: This is a descriptive epidemiology study. METHODS: 101 MRI scans of young adult patients with normal patellofemoral joint (PFJ) age 17–40 were evaluated from January 2019 to December 2020. Exclusion criteria included patella-femoral pathology and degenerative joint disease. Data of gender, body height and weight were obtained from physical examination, while patella height, width and thickness were obtained using MRI measurement. Descriptive analysis was used to get the mean and standard deviation of patella dimension, whereas correlation between patella thickness with patella width and length were analyzed using Pearson correlation and BIPWiT ratio was obtained by dividing the patellar width and patellar thickness. RESULTS: Mean patellar length was 30.06 ± 2.94 (29.48–30.64); patellar width was 44.13 ± 4.44 (43.26–45.01); and patellar thickness was 23.89 ± 2.33 (23.43–24.35). Patellar dimension in male were significantly larger compared to female (P < 0.001). However, there was no difference in cartilage thickness between male and female (P = 0.305). There was strong correlation between patellar width and patellar thickness (r = 0.66; P < 0.001) with BIPWiT ratio of 1.85 ± 0.15. CONCLUSION: BIPWiT of 1.8:1 between patellar width and patellar thickness was recommended as a guide for patellar thickness restoration during TKA. There is no difference of patellar dimension between Asian and Western population in a healthy knee. CLINICAL RELEVANCE: The result of BIPWiT ratio found in this study may aid upon pre-operative planning prior TKA for surgeons in order to achieve optimal patellar thickness and avoid patellofemoral problem. WHAT IS KNOWN ABOUT THE SUBJECT: Currently there are raising concerns about the different sizes of knee measurements between Asian and Western population which will affect techniques during TKA to achieve optimum result. WHAT THIS STUDY ADDS TO THE EXISTING KNOWLEDGE: This study not only prove that there is no difference between patellar dimension of Asian and Caucasian but also found a similar BIPWiT ratio for patellar resection during TKA with previous literature. LEVEL OF EVIDENCE: Level III.