Interchangeability of patellar height measurement using the Insall–Salvati ratio at 0° and 30° of knee flexion during weightbearing in total knee arthroplasty
Year: 2025
Type: article
Study design: Observational Study
Abstract: PURPOSE: To analyze the correlation and degree of agreement between the patellar heights measured at knee flexion of 0° and 30° before and after total knee arthroplasties (TKA) without patellar resurfacing. METHODS: One hundred primary TKAs with nonresurfaced patella were prospectively evaluated. We measured the Insall-Salvati ratio (ISR), modified ISR (mISR), Blackburne-Peel ratio (BPR), and Caton-Deschamps ratio (CDR) in weightbearing true lateral radiograph at knee flexion of 0° and 30°. The correlations between the patellar height measured at knee flexion of 0° and 30° were analyzed by Pearson correlation analysis. The degree of agreement between the patellar heights in knee flexion angles of 0° and 30° was analyzed using the limits of agreement (LoA) of Bland-Altman analysis; a difference of < ± 0.2 between the measurements at knee flexion of 0° and 30° was deemed clinically acceptable. RESULTS: Very strong correlations existed between the pre- and postoperative ISR (r = 0.826 and 0.823, p < 0.001, respectively), and the preoperative mISR (r = 0.802, p < 0.001) measured between knee flexion angles of 0° and 30°. Strong correlation was observed in the other pre- and postoperative measurements. The range between upper and lower LoAs of the ISR measured at knee flexion of 0° and 30° was < ± 0.20 preoperatively (-0.174 ~ 0.155) and postoperatively (-0.181 ~ 0.174), while the ranges for all other measurements did not lie within the clinically acceptable range. CONCLUSIONS: The ISR measured at 0° or 30° of knee flexion during weightbearing can be interchanged reasonably before and after TKA. Although knee flexion of 30° is the standard, lateral radiograph of 0° flexion can be a reasonable alternative for evaluating patellar height using the ISR. LEVEL OF EVIDENCE: Level II.
Authors: Sang Jun Song, Hyun Woo Lee, Cheol Hee Park
Institutions: Kyung Hee University, Kyung Hee University Medical Center
Language: English
Subfield: Surgery
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4414967437