Unicondylar sled prosthesis of the knee: The higher the case volume, the lower the number of revisions

In a series of commissions awarded by the Federal Joint Committee (G-BA) to the Institute for Quality and Efficiency in Health Care (IQWiG), the question is whether for certain surgical procedures, a correlation can be shown between the volume of services provided per hospital and the quality of treatment results. IQWiG's rapid report on the implantation of a unicondylar sled prosthesis as partial knee replacement (PKR), also called unicompartmental knee replacement, is now available.

According to the findings, there is a positive correlation between the volume of services and the quality of treatment: the higher the case volumes for PKR in a hospital, the less frequently renewed surgery is required to replace a component or the entire implant (revision) within 5 years of initial surgery. However, the only robust study on this topic only provides data with low informative value and solely on the risk of revisions.

The correlation of volume of services and quality of treatment with regard to the surgeon level and other relevant outcomes has thus not been investigated.

Partial joint replacement can preserve the natural range of motion

A common cause for knee replacement is a severe degeneration of the joint (gonarthrosis) with narrowing of the joint space, which is often accompanied by pain and limited mobility. If all joint surfaces (condyles) are affected by gonarthrosis, total knee replacement (TKR) is performed.

If radiographic imaging shows that only one side of the internal or lateral joint surface of the knee is affected by arthrosis, the sled prosthesis as PKR replaces only the degenerative joint surface. In contrast, the largely preserved joint surface on the other side usually remains untouched. PKR can preserve the natural range of motion in the joint better than TKR.

Minimum volumes for partial knee replacement have not yet been specified

In Germany in 2019, surgeons inserted 22,934 first-time unicondylar sled prostheses in patients with gonarthrosis or similar diagnoses in elective surgery, i.e. not in an emergency.

No minimum volumes have been specified for this type of surgery. For the present rapid report, IQWiG only considers first-time PKR. The Institute addresses the correlation between volume of services and quality of treatment for first-time TKR and for revisions of the knee in separate reports.

Only robust study provides data on solely one aspect

Although they screened more than 2000 abstracts and 44 full texts of scientific articles, IQWiG's researchers were only able to use one study for the present report. This was a retrospective cohort study on the use of unicondylar sled prostheses based on reimbursement data from Germany’s largest statutory health insurance fund (AOK), which only provided results on the impact of the volume of services per hospital on the revision rate within five years after first surgery. These data showed: the higher the case volume per hospital, the lower the number of revisions.

However, the informative value of the study results is considerably limited due to unclear data quality. For example, the analysis only adjusted for certain patient characteristics, but not for hospital and surgeon characteristics. For the latter, the necessary information is usually not available in routine data, or is sparse at best.

In addition, no correlation with quality of treatment was examined at either the surgeon level or the level of the combined volume of services of hospital and surgeon. In addition, there is a lack of data on most of the relevant outcomes, such as morbidity (e.g. loosening of the prosthesis or instability of the knee joint, fractures, pain or joint infections) and health-related quality of life (mobility and independence).

Due to the lack of informative studies, it is also not possible draw conclusions on the effects of specific minimum case volumes introduced into health care on the quality of treatment.

Process of report production

In March 2021, the G-BA commissioned IQWiG to prepare the report on the correlation between the volume of services and the quality of treatment results for PKR in an accelerated procedure as a so-called rapid report. Interim products were therefore not made available for a hearing. This rapid report was sent to the contracting agency, the G-BA, on 25 February 2022 and has now been published.

An extract of the final report will be soon be published in English. If you would like to be informed when it is published, please contact info@iqwig.de.