OBJECTIVES : While treatment algorithms and guidelines exist for osteoarthritis (OA), it is challenging to classify OA severity to study treatment approaches. Our goal was to stratify OA patients using a treatment-based severity definition and compare healthcare utilizations and costs.

METHODS : This was a retrospective study from 2001-2018 at a large U.S. integrated health system. Patients age 18+ with ≥1 month of insurance and diagnosis code for OA (ICD-9: 715.*, ICD-10 M15-19) or joint surgery were included. Patients were categorized as mild OA at index date and moderate-severe OA when any of eight literature-based criteria were met (hip/knee procedure, two anxiety/depression encounters, two prescriptions for opioid or nonsteroidal anti-inflammatory drug, two intra-articular injections, mobility aid, physical therapy referral, or two x-rays), thus forming one or two time periods per patient. All-cause outpatient visits (OP), emergency department visits (ED), inpatient days hospitalized (IP), total allowed medical cost, and total allowed pharmacy cost (per-member per-year, PMPY) between mild vs. moderate-severe periods. Claims for OA-related procedures, encounters or medications were re-analyzed as a subset.

RESULTS : We identified 127,656 patients, of whom 18% progressed from mild to moderate-severe and 31% were moderate-severe at initial diagnosis. Moderate-severe OA patients had higher rates of OP visits and IP days than mild OA patients (OP: 9.8 vs. 8.7; IP: 12.2 vs. 4.3) and higher total pharmacy cost ($6212 vs. $4817 PMPY). All categories of OA-related utilization and costs were significantly higher for moderate-severe vs. mild (OP: 0.96 vs. 0.42, IP: 1.02 vs. 0.04, ED: 0.19 vs. 0.13, pharmacy: $613 vs. $437, medical: $1631 vs. $411). All significant findings were p<0.001.

CONCLUSIONS : Treatment-based severity level was strongly associated with patients' OA-related utilization and costs, and, in most cases, all-cause utilization and costs. Understanding patients' disease progression is important for better managing and treating disease burden in the future.