Abstract: BACKGROUND: Previous studies have shown that early quadriceps weakness aggravation is associated with ischemia and reperfusion resulting from surgical trauma and/or tourniquet use after total knee arthroplasty, while intake of sufficient amounts of dietary n-3 polyunsaturated fatty acids can limit tissue damage associated with ischemia and reperfusion. 
OBJECTIVE: To explore the correlation between the level of serum n-3 polyunsaturated fatty acids and quadriceps weakness in the early stage after total knee arthroplasty. 
METHODS: A total of 66 patients with knee joint osteoarthritis admitted to the Second Affiliated Hospital of Hainan Medical University from March 2018 to March 2020 were selected. All of them received total knee arthroplasty. On postoperative day 1, serum n-3 polyunsaturated fatty acids levels were measured. Quadriceps strength, knee pain during quadriceps testing, and knee circumference were measured on preoperative day 1 and postoperative day 4. According to the testing result of quadriceps strength, the patients were divided into high quadriceps weakness group (<-63.7%, n=33) and low quadriceps weakness group (≥ -63.7%, n=33). Serum n-3 polyunsaturated fatty acids levels, knee pain during quadriceps testing, and knee circumference were compared between two groups. The correlation between the level of serum n-3 polyunsaturated fatty acids and quadriceps weakness was explored by Pearson correlation analysis. The influencing factors of quadriceps weakness were explored by multivariate Logistic regression analysis. The study was approved by the Ethics Committee of the Second Affiliated Hospital of Hainan Medical University. 
RESULTS AND CONCLUSION: (1) Compared with preoperatively, the quadriceps muscle strength decreased significantly, knee pain increased, and knee circumference increased after total knee arthroplasty in 66 patients (P < 0.01). (2) The level of n-3 polyunsaturated fatty acids and quadriceps strength in high quadriceps weakness group were lower than those in low quadriceps weakness group (P < 0.05). Knee pain was more serious in high quadriceps weakness group than that in low quadriceps weakness group (P < 0.05). The knee circumference was longer in high quadriceps weakness group than that in low quadriceps weakness group (P < 0.05). (3) Pearson correlation analysis showed that serum n-3 polyunsaturated fatty acids level was significantly positively correlated with quadriceps weakness (r= 0.356, P=0.004). (4) Multivariate logistic regression analysis showed that serum n-3 polyunsaturated fatty acids levels, knee pain, knee swelling and body mass index were independent influencing factors for quadriceps weakness after total knee arthroplasty (P < 0.05). (5) These results indicate that the level of serum n-3 polyunsaturated fatty acids was independent protective factors for quadriceps weakness after total knee arthroplasty.

Key words: bone, arthroplasty, arthritis, fatty acids, knee, quadriceps, myasthenia, correlation analysis