A preliminary examination of the CMS eligibility criteria in total-joint arthroplasty.

Objective: To analyze inpatient rehabilitation outcomes in total-knee arthroplasty (TKA) and total-hip arthroplasty (THA) patients using the 2004 Medicare 75% rule criteria.

Methods: This retrospective study compared outcomes in unilateral TKA (UTKA), bilateral TKA (BTKA), and THA after interdisciplinary inpatient rehabilitation (n = 867). Patients were separated into three comparison pairs: 1) UTKA or BTKA, 2) age <85 yrs or > or =85 yrs, and 3) body mass index (BMI) <50 or > or =50 kg/m. Length of stay (LOS), functional independence measure (FIM) scores (total, motor, and cognitive), hospital charges, FIM efficiency, and discharge disposition were analyzed.

Results: BTKA improved total FIM score more than UTKA (43 vs. 38%; P = 0.039). TKA with BMI > or =50 kg/m had similar admission and discharge FIM motor scores compared with BMI <50 kg/m (P > 0.05). TKA patients > or =85 yrs had lower admission FIM scores, longer LOS (11.3 vs. 9.4 days), and 22% higher total charges than TKA patients younger than 85 yrs (P = 0.042). THA patients > or =85 yrs had 6-10% lower total FIM, FIM motor, and FIM cognition scores and were discharged to home less frequently than younger patients (P < 0.05). Total and daily charges were 21-162% higher in THA patients with BMIs > or =50 kg/m than in THA patients with BMIs <50 kg/m (P < 0.045).

Conclusions: All patients made functional gains during rehabilitation. However, the most costly and lengthy rehabilitation occurred in TKA patients > or =85 yrs and THA patients with BMI > or =50 kg/m.