[Volume-Outcome Effects in Primary and Revision Hip Arthroplasty: Evidence for Minimum Volume Thresholds in German...

BACKGROUND: In Germany, hospital services will generally only be reimbursed within designated service groups (SGs) in the future. The assignment of SG is tied to various requirements ensuring quality of care, including provision of minimum volume thresholds. Although evidence on the relationship between case volume and outcome quality exists for many indications and procedures, this evidence is lacking at the SG level. Using hip arthroplasty as an example, this study is the first to examine, at the SG level, the effect of minimum case-volume thresholds on outcome quality and population accessibility, thereby providing indications for potential minimum volume thresholds.

METHODS: Outcome quality was measured using the MTL30 and MTL21 indicators, which describe the composite outcome of in-hospital mortality and external transfer within 30 or 21 days, and length of stay beyond the expected duration. Based on nationwide hospital service data for the year 2024, the risk of MTL30 and MTL21 was estimated as a function of hospital case volume and relevant patient-level risk factors using Poisson regression. For various case-volume thresholds, accessibility analyses were conducted using travel-time data at the market-cell level. The findings serve as a basis for recommendations by the relevant scientific medical societies regarding future minimum capacity thresholds in SG 23 (primary hip arthroplasty) and SG 25 (revision hip arthroplasty).

RESULTS: The analysis of 221,698 cases performed in 2024 across a total of 1,062 hospital sites in SG 23 and SG 25 nationwide showed a clear positive association between case volume and outcome quality. Patients undergoing elective primary hip arthroplasty in SG 23 had a 44% lower risk of MTL21 at institutions with at least 100 cases per year compared with sites with fewer than 100 cases per year (RR = 0.56 [95% CI: 0.53, 0.59]). For elective revision procedures in SG 25, the risk of MTL30 decreased by 24% (RR = 0.76 [95% CI: 0.68, 0.83]) when the institution performed at least 15 cases per year. At these case-volume thresholds, the average travel time to the nearest hospital site was less than 20 minutes in both SGs. Further quality gains in SG 23 and SG 25 were observed at minimum case volumes of 150 and 25 cases, respectively, while average travel time remained below 25 min.

CONCLUSION: This study demonstrates substantial potential for quality improvement in SG 23 (primary hip arthroplasty) and SG 25 (revision hip arthroplasty) under moderate concentration of care. The authors recommend minimum case-volume thresholds of at least 100 cases, preferably 150, for primary hip arthroplasty, and at least 15 cases, preferably 25, for revision hip arthroplasty, given accessibility within an average travel time of less than 20 and 25 min, respectively. These findings are associated with clear improvements in quality without meaningfully compromising population accessibility.