It has been shown that a cognitive function (CF) loss can occur after hip or knee arthroplasty procedures, with an incidence of 40 to 70%. The pathogenesis remains unclear but studies suggest some form of brain emboli; although both trans-cranial doppler and trans-oesophageal doppler have both shown emboli per-operatively a correlation has never been shown with CF loss post-operatively. In contrast, in the cardiothoracic literature an embolic cause is widely accepted for detectable post-operative CF drop. The purpose of this study was to ascertain whether MRI could show evidence of embolic phenomena in patients undergoing hip or knee arthroplasty.

Twenty-five patients presenting for hip or knee arthroplasty procedures were consented for this study. Brain MRI scans and MR angiograms were performed 1 week pre-operatively and within 1 week post-operatively using a Phillips 1.5Tesla MRI unit. All scans recorded were independently reviewed by 2 radiologists. A series of tests to examine several modes of cognitive function were carried out by a clinical psychologist pre-operatively, and at 1 week post-operatively. The CF tests showed a clinically significant drop following surgery in 64% of cases – this is in keeping with other recently published data.

None of the post-operative scans or angiograms showed overt evidence of new lesions. Three Scans had equivocal tiny brainstem hypodensities on a single slice with no correlating abnormality on diffusion images to support the presence of new ischaemia.

We conclude that either the aetiology of post-operative CF drop following arthroplasty is not embolic in nature, or that with current technology MRI brain scans even with angiograms are not sensitive enough to show the corresponding abnormality. With currently available equipment there appears to be no benefit from using MRI as a tool to evaluate post-operative CF loss in this group of patients.

Introduction and Aims: The study was designed to compare the early results, prospectively, of the fixed-bearing Zimmer NexGen cruciate retaining (CR) and the Zimmer NexGen mobile-bearing knee (MBK) knee arthroplasty. The study was designed to determine whether differences exist in the clinical outcomes between patients receiving different types of bearings.

Method: Patients were randomly assigned to receiving either fixed or mobile bearings. Patients were blinded but not assessors to the type of arthroplasty. The study commenced in June 2000. By November 2002, 69 and 70 patients had been recruited into the CR and MBK groups respectively. Consultants were present in 92% of operations and the rest were performed by a senior registrar. The major indication was osteoarthritis (64 CR: 65 MBK). The surgical approach was medial parapatellar in 65 CR and 63 MBK the rest were subvastus, patella resurfacing was not routinely employed. Pre-operative, intra-operative and post-operative data was collated.

Results: The body mass index was 32 ± 7 CR and 32 ± 6 MBK. The average age was 67 ± 8 CR and 67 ± 8 MBK. Pain in the contralateral knee was present in 79.7% CR and 74.3% MBK group. Minimum post-operative follow-up was one year. There was no significant difference in the pre-operative and post-operative fixed flexion contracture, 4.3 ± 5.4 to 1.0 ± 2.9 CR and 6.2 ± 6.9 to 0.9 ± 2.8. The mean flexion pre-operatively and post-operatively between the two groups was not significantly different 108 ± 19 to 105 ± 16 CR and 107 ± 15 to 102 ± 13. Patello-femoral joint symptoms diminished from 67% to 12% CR and from 69% to 21% in the MBK group. The dependence on walking aids diminished from 50.7% to 16.7% CR and 51.4% to 26.9% MBK. At one year, nine percent and 21% were dissatisfied in the CR and MBK groups respectively. In the CR group, two revisions had been performed, one for infection and the other for arthrolysis and poly exchange. Two revisions had been carried out in the MBK group, one for extreme ‘clunking’ and the other for arthrolysis with poly exchange.

Conclusions: The one-year results suggest that the levels of dissatisfaction and patello-femoral problems are significantly greater in the mobile bearing group as opposed the fixed bearing. The early results would not encourage the use of the mobile bearings. We await the long-term results as regards survivorship of the bearings.