Effect of body mass index on knee function outcomes following continuous passive motion in patients with osteoarthritis after total knee replacement: a retrospective study

Obesity may influence postoperative rehabilitation outcomes after total knee replacement (TKR). The aim of this study was to evaluate the effects of body mass index (BMI) on the progression of inpatient rehabilitation using continuous passive motion (CPM) and its treatment outcomes.

A retrospective study was conducted in a rehabilitation centre. In total, 354 patients undergoing primary TKR were enrolled through medical chart review.

All patients commenced the CPM programme immediately after surgery and continued until hospital discharge.

Knee flexion, pain score, and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function score.

Patients were divided into five BMI groups: normal weight (n = 59), overweight (n = 95), Class I obesity (n = 90), Class II obesity (n = 82) and Class III obesity (n = 28). All outcome measures were recorded at admission; daily during the inpatient stay; at discharge; and at 1-, 3- and 6-month follow-up assessments.

During CPM exercises, obese patients had a smaller initial flexion angle (P < 0.001) and a smaller daily increment in the CPM motion arc (P < 0.001) compared with patients of normal weight. Severe obesity was associated with poor knee flexion [adjusted odds ratio (aOR) 11.9, 95% confidence interval (CI) 3.49 to 40.94, P < 0.001] and WOMAC physical function score (aOR 5.09, 95% CI 1.62 to 16.03, P = 0.005) at 6-month follow-up.

Obesity had a negative effect on progress during the CPM protocol, which commenced immediately after surgery and continued until discharge. Obesity was also associated with poorer self-reported function at 6-month follow-up.