ABSTRACT
Objective:To analyze the factors affecting the relative height change of the patella after primary robotic-assisted total knee arthroplasty (R-TKA).Methods:The data of 97 patients with osteoarthritis of the knee treated with R-TKA admitted from June 2021 to March 2022 were retrospectively analyzed, including 15 males and 82 females, aged 70.0±5.4 years (range, 58-80 years). The bone resection parameters of the robotic system were recorded intraoperatively, including the bone resection amount of the medial and lateral distal femur, medial and lateral posterior femoral condyle and medial and lateral tibial plateau. The Blackburne-Peel index (BPI) and Caton-Deschamps index (CDI) were used to measure the preoperative and postoperative relative patellar height on lateral radiographs, as well as the posterior tibial slope (PTS) and the change in patellar ligament length before and after surgery. The relationship between the change in relative patellar height and the variables of interest was analyzed using partial correlation and multiple linear regression.Results:The mean postoperative CDI was lower than preoperatively (0.79±0.15 vs. 0.91±0.13, t=9.69, P<0.001), and the percentage of patients with postoperative CDI<0.6 was higher than preoperatively (9.3% vs. 0; χ 2=12.92, P<0.001); the differences in mean postoperative BPI and percentage of patients with postoperative BPI<0.45 were not statistically significant compared to preoperatively (0.69±0.13 vs. 0.71±0.17, t=1.35, P=0.182; 11.3% vs. 17.5%, χ 2=1.50, P=0.220). The mean patellar ligament length on the first postoperative day was 2.29 mm shorter than preoperatively, there was a statistically significant difference ( t=5.90, P<0.001). Partial correlation analysis showed that the amount of patellar ligament length change was positively correlated with the amount of BPI and CDI change ( r=0.84, P<0.001; r=0.70, P<0.001), and the amount of PTS change and the mean distal femoral bone resection were negatively correlated with the amount of BPI ( r= -0.41, P<0.001; r=-0.32, P=0.002) and CDI ( r=-0.23, P=0.029; r=-0.25, P=0.017) change. In contrast, the amount of posterior femoral condyle bone resection and tibial plateau bone resection did not correlate with the change of BPI and CDI. Multiple linear regression analysis showed that the amount of patellar ligament length change, PTS change and the distal femoral bone resection were factors influencing the change of BPI ( β=0.03, P<0.001; β=-0.01, P<0.001; β=-0.02, P=0.021) and CDI ( β=0.02, P<0.001; β=-0.01, P=0.001; β=-0.02, P=0.008). Conclusion:Amount of patellar ligament length change, PTS change and the distal femoral bone resection are factors affecting the BPI. In order to obtain a better relative patellar height in the primary R-TKA, attention should be paid to the adjustment of the distal femoral bone resection and PTS, while taking the necessary measures to reduce the postoperative patellar ligament length changes.