Effects of body mass index on postoperative outcome in patients with osteoarthritis after total knee arthroplasty

OBJECTIVE: To study effects of body mass index (BMI) on postoperative outcome in patients with osteoarthritis after total knee arthroplasty (TKA). METHODS: The data of 148 patients with osteoarthritis who underwent TKA from June 2006 to May 2009 in our hospital and had complete follow-up data were analyzed restrospectively, including 29 males and 119 females, ranging in age from 39 to 89 years old, with an average age of 71.2 years old. According to BMI classification standard, all the patients were divided into 4 groups: non-obese group (BMI ≤ 25.0 kg/m2), had 38 patients (45 knees), including 9 males and 29 females, with a mean age of (70.0 ± 8.2) years old; overweight group (BMI 25.1 to 27.0 kg/m2), had 40 patients (48 knees), including 10 males and 30 females, with a mean age of (72.6 ± 7.4) years old; obesity group (BMI 27.1 to 30.0 kg/ m2), had 30 patients (43 knees), including 7 males and 30 females, with a mean age of (70.4 ± 6.0) years old; morbidly obesity group (BMI > 30.0 kg/m2), 33 patients (39 knees), including 3 males and 30 females, with a mean age of (71.7 ± 6.4) years old. The index such as Knee Society Score (KSS), anterior knee pain and patella cartilage damage during surgery were recorded before surgery and at the time of follow-up. RESULTS: Postoperative KSS increased significantly compared to preoperative KSS, and the good rate reached to 97.1%. In the knee score, preoperative KSS and postoperative KSS had no significant differences among the four groups (preoperative P = -0.789; postoperative P = 0.133). However, compared with other groups, obesity group got the lowest preoperative function score (preoperative P = 0.036; postoperative P = 0.225). While the incidence of anterior knee pain was 9.7% (17/175), including 14 grade I and 3 grade II. There were no significant differences in incidence of anterior knee pain among four groups (χ2 = 0.764, P = 0.862). The average BMI of the patients with anterior knee pain was (27.4 ± 3.6) kg/m2, while the others' BMI was (27.5 ± 4.4) kg/m2. There was no statistically difference between two groups (t = -0.061, P = 0.951). There were no significant differences in patella cartilage damage among groups (χ2 = 7.070, P = 0.314). CONCLUSION: The KSS increases in all the different groups. Those patients get the benefit from TKA, and the obese patients can receive a similar postoperative outcome as the non-obese ones.