Abstract
ObjectiveTo evaluate the impact of body mass index (BMI) on the mid-term clinical outcomes and survival in patients receiving a mobile-bearing unicompartmental knee arthroplasty (UKA).MethodsWe retrospectively collected data from 355 patients who underwent UKA from June 2006 to June 2015, with a mean follow-up of 106.5 ± 22.5 months. Patients were assigned into four groups based on their BMI before surgery: normal weight group (BMI 18.5 ~ 22.9 kg/m2), overweight group (23 ~ 24.9 kg/m2), obesity group (25 ~ 29.9 kg/m2), and severe obesity group (≥ 30 kg/m2). The knee society score (KSS), knee society function score (KSFS), hospital for special surgery score (HSS), and range of motion (ROM) were assessed before the operation and at the last follow-up. The femorotibial angle (FTA) was assessed after the operation immediately and at the last follow-up. Kaplan–Meier survival analysis was performed among the four groups.ResultsThe KSS, KSFS, and HSS in all groups were markedly improved compared with the preoperative values (p<0.001), but the ROM score was not significantly different (p>0.05). There were significant differences in KSS (p<0.001) and HSS (p = 0.004) across the four BMI groups, and these differences were due to the severe obesity group. All groups exhibited an inclination of knee varus deformity at the last follow-up (p < 0.05). Moreover, no marked difference in the implant survival rate was found among the different groups (p = 0.248), or in the survival curves (p = 0.593).ConclusionsBMI does not influence the implant survival rate. The postoperative functional and quality-of-life scores were significantly improved in all groups. Obese (BMI ≥30 kg/m2) individuals should not be excluded from UKA.
Highlights
Obesity plays a significant role in the occurrence and progression of knee osteoarthritis (OA) [1,2,3], and globally, obesity has been predicted to enhance the demand for knee replacement surgery [4,5,6]
According to the body mass index (BMI) classification standards of Asian adults defined by the World Health Organization (WHO) [14], the patients were assigned into four categories: normal body mass group (BMI 18.5–22.9 kg/m2, 33 cases with 38 knees), overweight group (BMI 23–24.9 kg/m2, 35 cases with 43 knees), obesity group (BMI 25–29.9 kg/m2, 97 cases with 110 knees), and severe obesity group (BMI ≥30 kg/m2, 28 cases with 38 knees)
Cohort demographics A total of 355 patients (408 knees) with medial compartment OA of the knee, who were treated with mobile-bearing unicompartmental knee arthroplasty (UKA) from June 2005 to June 2015, were selected as the research subjects in the present study
Summary
Obesity plays a significant role in the occurrence and progression of knee osteoarthritis (OA) [1,2,3], and globally, obesity has been predicted to enhance the demand for knee replacement surgery [4,5,6]. Morbid obesity is traditionally considered a contraindication to knee replacement surgery due to low long-term. Compared to fixed-bearing UKA, mobile-bearing UKA has less bearing abrasion but a higher bearing dislocation rate. Mobile-bearing prevents higher maximum peak pressures to concentrate on a small area and reduces bearing abrasion [13], but whether this change will benefit obese patients is unclear due to the possibility of increasing bearing dislocationinduced prosthesis revision [13]. We propose the hypothesis that a high BMI does not increase the revision rate, and is not a contraindication to mobile-bearing UKA. We focused on the impact of BMI on mid-term clinical outcomes of UKA and performed a retrospective comparative study composed of 355 patients undergoing medial UKA
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