Introduction and Aims: A recently reported study and reports in the German lay press have indicated that there may be an increased incidence of limp following Robodoc THR. This paper presents the detailed functional aspects from the first randomised US FDA multicentre trial.

Method: The controlled randomised trial was conducted from 1994–98, with 136 hip replacements performed on 119 patients at three centres. The implants were either AML (Depuy) or Osteoloc (Howmedica). Twenty-eight patients were lost to follow-up at two years. Twenty-four month Harris hip score surveys for the remaining 108 patients – 53 Robodoc and 55 Control – were reviewed and relevant scores were tabulated for limp and use of support aids.

Results: In the Robodoc group, 45 patients had no limp and eight patients had slight to moderate limp. In the control group, 44 patients had no limp, and 11 patients had slight to moderate limp. The average Harris limp score was 10.49 for the Robodoc group and 10.24 for the control group (NS). In the use of supportive aids and canes, at 24 months, there was essentially no difference between the average of the scores. In the Robodoc group,47 patients required no aids, and six required the use of a cane. In the control group, 49 patients required no supportive aids, and six patients required the use of a cane.

Conclusions: In this randomised controlled study no statistically significant difference was found between the Robodoc and the manual method in the incidence of limp and use of supportive aids, following primary Total Hip Arthroplasty. This data is also consistent with other published studies using Robodoc and is in contrast to a recent study from one centre.

Ferrography is a technique for analysing wear by means of the magnetic separation of wear particles. To evaluate its application in human joints, the results of the ferrographic analysis of saline washings of symptomatic human knees were compared with the results of the arthroscopic examination of the same knees. Ferrography was found to be an extremely sensitive monitor of articular erosion, with a resolution far greater than that of arthroscopy. This was particularly apparent with knees suffering from a torn anterior cruciate ligament: arthroscopy detected no damage to the cartilaginous surfaces whereas ferrography detected a substantial level of "microdamage". The spectrum of wear particles showed qualitative and quantitative alterations depending upon the condition of the knee. Ferrography thus holds much promise as a potential differential diagnostic technique of great sensitivity, with particular relevance to the very early changes which precede clinical symptoms. Study of wear particles is also justified by evidence indicating an active role in the pathophysiological progression of arthritis.