Polyethylene thickness in unicompartmental knee arthroplasty

Inadequate polyethylene thickness is a risk factor in the development of polyethylene wear in unicompartmental knee arthroplasty (UKA). The labelled thickness of polyethylene inserts often refers to the combined thickness of the insert and its metal backing. However specific information regarding the actual minimum thickness of the polyethylene is seldom available. We sought to determine the actual minimum thickness of polyethylene inserts used in five contemporary metal-backed UKA designs. The thinnest available insert from each of these designs was identified and measured at the lowest point of its concave articulating surface with a Kincrome electronic digital micrometer. The minimum thickness of the inserts ranged from 3.702 mm to 7.859 mm (mean values). In two of the inserts, the minimum thickness was found to be less than the recommended minimum thickness of 6mm. Implant manufacturers should clearly indicate the actual minimum thickness of polyethylene inserts on their product labels.