Medicare HMO disenrollment and selective use of medical care: osteoarthritis-related joint replacement

Recent Medicare health maintenance organization (HMO) disenrollees use a high level of medical services. This study examined admissions for total hip arthroplasty (THA) and osteoarthritis-related knee replacements (OKR) among Medicare HMO disenrollees and continuously enrolled fee-for-service (FFS) beneficiaries to determine whether Medicare beneficiaries are returning to the FFS system to receive quality-of-life enhancing elective care.

Retrospective analysis of Medicare inpatient claims for elderly Medicare beneficiaries residing in South Florida between 1990 and 1993.

Inpatient admission rates for THA, OKR, and for 2 acute conditions--total hip replacements related to fracture of the hip (HRF) and acute myocardial infarction (AMI)--were estimated for Medicare HMO disenrollees over the 3-month period immediately following their disenrollment. These rates were compared with standardized rates for Medicare FFS enrollees.

The annualized adjusted rates of both THA and OKR were 3.5 to 4 times higher among Medicare HMO disenrollees than among FFS beneficiaries (P < or = .0001 for both procedures); substantially smaller differences were noted for HRF (P < or = .05), and no difference was present for AMI. HMO disenrollees and FFS enrollees did not differ in their levels of comorbidity at the time of admission.

These data provide indirect evidence that Medicare HMOs in South Florida are rationing THA and OKR and that beneficiaries respond by returning to the FFS system to seek care. This apparent rationing has important implications regarding for the management of serious, but nonemergent, medical conditions within the evolving Medicare system.