Obesity and inpatient rehabilitation outcomes following knee arthroplasty: a multicenter study

Objective: This multicenter study examined whether inpatient rehabilitation outcomes following total knee arthroplasty (TKA) were influenced by BMI. Methods and Procedures: This was a retrospective, comparative study conducted using a computerized medical database and medical records derived from TKA patients, at 15 independent rehabilitation hospitals (N = 5,428). Patients were separated into four groups based on BMI: non‐obese (BMI < 25 kg/m²), overweight (25–29.9 kg/m²), moderately obese (30–40 kg/m²), severely obese (BMI ≥ 40 kg/m²). All patients completed an interdisciplinary inpatient rehabilitation program post‐TKA. Total and individual functional independence measure (FIM) scores, length of stay (LOS), FIM efficiency scores, itemized hospital charges, and discharge disposition location, were collected. Results: The percentage of total FIM change was 7.5% greater by the time of discharge in the non‐obese than in the very severely obese (P < 0.05). FIM efficiency was lowest in the severely obese as compared to the remaining groups (3.7 points (pts)/day vs. 4.0–4.3 pts/day; P = 0.044). The change in the motor FIM score from admission to discharge was 6.7–15.6% greater in the non‐obese than in the remaining groups (P < 0.05). The changes in cognition FIM, toilet transfer and walking without assistance scores were higher in the non‐obese as compared to the severely obese group (P < 0.05). The severely obese group had higher total, physical and occupational therapy and pharmacy charges than the remaining groups (P < 0.05). Discussion: An excessive BMI does not prevent gains during inpatient rehabilitation; however, these gains are made less efficiently and at a higher cost than those made when the BMI is low.