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A new California Workers’ Compensation Institute (CWCI) study finds that after across-the-board declines in California inpatient hospitalizations during the COVID-19 health care crisis of 2020, the number of inpatient stays paid under Medicare, Medi-Cal, and private coverage all began to rebound in 2021, but the number of workers’ compensation hospitalizations fell an additional 5.7%.

The latest results come from a CWCI study that measures and compares the use of inpatient services and procedures in different systems using data compiled by the state on more than 35.3 million hospital stays with 2012 through 2021 discharge dates.

The 2021 decline in workers’ compensation hospitalizations brought the total decline over the past decade to 48.1%, more than triple the 10-year decline of 15.0% noted for hospital stays paid under private coverage, while hospitalizations paid under Medicare were only down 5.2% and those paid by Medi-Cal increased by 11.7%.

Workers’ compensation is by far the smallest program analyzed, representing just 163,249 (<0.5 %) of the California inpatient stays over the 10-year study period, and just 0.3 % in 2021.

Most workers’ compensation hospital stays are for the treatment of musculoskeletal and connective tissue disorders (between 58.1% and 66.0% of the stays since 2012), but COVID’s impact is evident in the recent data, as the percentage of injured worker inpatient stays for the treatment of diseases and disorders of the respiratory system nearly tripled from 2.6% in 2019 to 7.4% in 2020 and remained at an elevated level (7.0%) in 2021.

A review of the hospital stays for diseases and disorders of the respiratory system found that half were for respiratory infections and inflammation, though injured worker hospitalizations in this diagnostic category included a larger share of collapsed lungs or major chest traumas.

Surgical stays are far more prevalent in workers’ compensation than in other systems, with the data showing they accounted for more than 2/3 of injured workers’ inpatient hospitalizations in 2021, versus 24.7% for Medicare, 21.1% for Medi-Cal, and 31.5% for private coverage.

Workers’ compensation inpatient surgeries continue to be led by spinal fusions (17.6% of the 2021 surgeries) and major joint replacements (10.7%).

Despite a sharp decline in workers’ compensation spinal fusions (-59.1% since 2012), they are still far more prevalent among the injured worker inpatient population than among inpatients covered by Medi-Cal (0.6%), Medicare (1.3%); or private coverage (1.8%).

As for workers’ compensation joint replacement surgeries, the Institute found that 87.9% of all injured workers who underwent knee or hip replacements in 2021 were diagnosed with primary osteoarthritis, which tends to develop from mechanical wear and tear, structural degeneration, and joint inflammation, rather than from an acute, direct trauma to the joint associated with a specific injury.

Furthermore, the decline in workers’ compensation inpatient surgeries has been somewhat offset by an increase in the number of injured worker spinal fusions and total joint replacements performed on an outpatient basis..

More detailed findings from the CWCI study have been released in a Research Update Report, “Trends in the Utilization of Inpatient Care in California Workers’ Compensation.”