Abstract
Purpose of Study
To assess the incidence of radiolucency in cemented and cementless Oxford unicompartmental knee replacement at two years.
Introduction
Most unicompartmental knee replacements (UKRs) employ cement for fixation of the prosthetic components. The information in the literature about the relative merits of cemented and cementless UKR is contradictory, with some favouring cementless fixation and others favouring cemented fixation. In addition, there is concern about the radiolucency that frequently develops beneath the tibial component with cemented fixation. The exact cause of the occurrence of radiolucency is unknown but it has been hypothesised that it may suggest suboptimal fixation.
Method
Following ethical approval, 62 patients with medial OA were randomised to receive either cemented (n=32) or cementless components (n=30). All patients underwent an identical surgical procedure with either a cemented or cementless Oxford UKR. Patients were assessed clinically by a research physiotherapist and radiologically using screened radiographs. Thirty-eight patients from the trial with follow up of at least two years and well aligned radiographs were identified (cemented n=16, cementless n=22).
Results
The patients in the two groups were well matched. Radiological and clinical assessment was at a mean of 2.25 years. There was no significant difference in the clinical scores between the two groups. The median OKS for the cemented group was 43 and for the cementless group was 42.5. Narrow radiolucent lines were seen at the bone-implant interfaces of 63% of the cemented tibial components; partial in 38% and complete in 25%. In the cementless implants, partial radiolucencies were seen in 4.5% and complete radiolucencies in none. The differences are statistically highly significant (p< 0.0001). The lack of radiolucency beneath the cementless tibial components implies satisfactory bone ingrowth and hence fixation.
Conclusions
At 2 years the cementless components are well fixed and have similar clinical results to the cemented.
