Abstract
IntroductionHigh-volume unicompartmental knee arthroplasty (UKA) surgeons have lower revision rates, in part due to improved intra-operative component alignment. This study set out to determine whether PSI might allow non-expert surgeons to achieve the same level of accuracy as expert surgeons.Materials and methodsThirty-four surgical trainees with no prior experience of UKA, and four high-volume UKA surgeons were asked to perform the tibial saw cuts for a medial UKA in a sawbone model using both conventional and patient-specific instrumentation (PSI) with the aim of achieving a specified pre-operative plan. Half the participants in each group started with conventional instrumentation, and half with PSI. CT scans of the 76 cut sawbones were then segmented and reliably orientated in space, before saw cut position in the sagittal, coronal and axial planes was measured, and compared to the pre-operative plan.ResultsThe compound error (absolute error in the coronal, sagittal and axial planes combined) for experts using conventional instruments was significantly less than that of the trainees (11.6°±4.0° v 7.7° ±2.3º, p = 0.029). PSI improved trainee accuracy to the same level as experts using conventional instruments (compound error 5.5° ±3.4º v 7.7° ±2.3º, p = 0.396) and patient-specific instruments (compound error 5.5° ±3.4º v 7.3° ±4.1º, p = 0.3). PSI did not improve the accuracy of high-volume surgeons (p = 0.3).ConclusionsIn a sawbone model, PSI allowed inexperienced surgeons to achieve more accurate saw cuts, equivalent to expert surgeons, and thus has the potential to reduce revision rates. The next test will be to determine whether these results can be replicated in a clinical trial.
Highlights
High-volume unicompartmental knee arthroplasty (UKA) surgeons have lower revision rates, in part due to improved intra-operative component alignment
A virtual tibial bone cut for an Oxford medial compartment UKA (Zimmer Biomet, Bridgend, UK) was planned 4 mm below the joint line, with a coronal varus/valgus angulation of 0°, a posterior slope of 7°, and an axial orientation parallel to the anatomical tibial axis [16] (Fig. 1)
Higher UKA revision rates in inexperienced or low-volume surgeons has led to the suggestion that the procedure should only be carried out in expert centres [9,10,11]
Summary
High-volume unicompartmental knee arthroplasty (UKA) surgeons have lower revision rates, in part due to improved intra-operative component alignment. The aetiology of this caseload effect is likely to be multifactorial One of these factors is that UKA is a technically demanding procedure with a narrow tolerance for tibial component malpositioning; deviations of more than 3° from the native joint line in the coronal plane and 2° in the sagittal plane are associated with decreased prosthesis survival [12, 13]. In this context, the results of a randomised controlled trial RCT comparing conventional and patient-specific instrumentation for UKA are encouraging [14]. The authors, who are both high-volume UKA surgeons, found no difference in component alignment between the two techniques, suggesting that PSI might be able to replicate expert results [15]
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