Summary

Body mass index has no significant effect on either the radiological corrections, clinical outcomes, complications, or survivorship of MOWHTO at short to medium term follow up

Abstract

Purpose

This study investigates the effect of the body mass index (BMI) on the early (2 years) to midterm (5 years) results of medial opening wedge high tibial osteotomy (MOWHTO) .

Methods

A prospectively maintained single-centre database of 1138 knee osteotomies, between 2002 to 2022, was retrospectively reviewed. Adult patients who underwent MOWHTO for symptomatic unicompartmental medial knee osteoarthritis (OA), with varus knee malalignment, having failed conservative management were included. Patients were categorized into 3 groups according to their BMI as per the classification from the National Institute for Health and Care Excellence (NICE): The healthy weight (HW) group (BMI of 18.5-24.9 kg/m2), the overweight (OW) (BMI of 25-29.9 kg/m2) , and the obesity (OB) group (BMI = 30 kg/m2). Multiple PROMs (n = 6) were recorded preoperatively and at 2 and 5 years postoperatively. Deformity analysis was undertaken preoperatively and postoperatively. The relative risk (RR) of the complications between the HW, OW and OB groups was calculated. The rate of conversion to arthroplasty, and 5, and 10 years survivorship were recorded, as well as the hazard ratio (HR) of BMI on survivorship.

Results

A total of 547 cases were included in the study: the HW group (n =96), the OW group (n = 233), and the OB group (n = 245), with a mean BMI of 23 ± 1.5 kg/m2 , 27.4 ± 1.4 kg/m2 and 34.4 ± 3.8 kg/m2, respectively. The mean follow up was 13.3 years (4.8 -20.3). The mean mechanical tibiofemoral angle corrections were in the HW group : 7.1 ±3°, OW group : 6.6 ± 3.5°, OB group: 7.1± 3.8 °, with no intergroup significant difference (p = n.s.). Clinically, despite lower preoperative scores in the OW and OB groups, no difference was observed postoperatively among the three groups. The overall complication rate was 12.5% in the HW group , 6.8 % in the OW group and 9.8% in the OB group. There was no significant difference in the RR of complications between the HW and OW groups (RR 0.6, [95% CI: 0.3, 1.3], (p = 0.2), and the HW and OB groups ( RR = 0.8 [95% CI: 0.3, 2.2], (p = 0.7). There was no overall significant difference in survival outcomes based on the BMI between the 3 groups (p = 0.4). The HR of conversion to arthroplasty between the HW and OW groups was 1.4 [95% CI: 0.6, 3.5] ,(p = 0.5), and between the HW and OB groups was 1.8 [95% CI: 0.8, 4.4] (p = 0.2).

Conclusion

Body mass index has no significant effect on either the radiological corrections, clinical outcomes, complications, or survivorship of MOWHTO at short to medium term follow up. No specific cut off point for BMI can be recommended as a contraindication to MOWHTO.