gms | German Medical Science

Objectives: Unicompartmental knee arthroplasty (UKA) has advantages over total knee arthroplasty (TKA) including a lower complication rate and faster return to work. However, joint registries show a lower survival rate. Possible explanations for this difference is the learning curve of the surgeon and the technical demanding surgery. An instrumentation method that has been available for about a decade is patient specific instruments (PSI). Cutting blocks are produced prior to surgery, based on a magnetic resonance imaging (MRI) scan or computed tomography (CT) scan. It is theoretically possible to accurately plan the position and size of the implants. As accurate positioning of the components is critical to the success and survival rate of UKA, PSI needs to be thoroughly investigated. However, no large prospective studies with mid- or longterm follow up are available at this moment. This study is a continuation of the study that was published in January 2021 that showed comparable rate of adverse events, radiological alignment and functional outcomes. This is the first independent two-center randomised controlled trial, assessing mid-term clinical and functional outcome of a large cohort comparing PSI with conventional instruments.

The aim of this two-centre RCT is to compare clinical (rate of adverse events, serious adverse events and revision rate) and functional outcomes (patient reported outcome measures) between patient specific instruments and conventional instruments in UKA. It is hypothesised that there will be comparable outcomes between both groups.

Methods: 120 patients were included in two different teaching hospitals and randomly allocated to the PSI or the CI group. All patients had surgery between April 2015 and July 2017. For blinding purposes, an MRI was done in all included patients in both the intervention and control group, according to the PSI scanning protocol. If the patient was allocated to the intervention group, a digital plan of the proposed per-operative positioning of the prosthesis was made available by a technician, based on the MRI scan. The surgeon approved every default setting and made adjustments in implant component size if necessary. Outcome measures were rate of (serious) adverse events, revision rate and patient reported outcome measures (PROMs) at 5 years follow up. Patients completed questionnaires at 1, 2 and 5 years follow up. Adverse events were retrieved from digital patient files.

Results: Preliminary outcomes (60% of the data) show comparable rates of adverse events, revision rates and patient reported outcomes measures between the PSI and CI group at 5 years follow up.

Currently, we are collecting the remaining data (40%). We expect to have the dataset complete by the end of May 2022. Therefore we will be able to present the full data at the DKOU 2022.

Preliminary conclusion: PSI does not have an advantage in clinical nor in functional outcome at mid-term follow up.

The definitive conclusions will be available in June 2022.