|Abstract / Summary
Data on patients with a Re-motion prosthesis – a third generation polyethylene-on-metal implant for TWA – have been collected in an multicenter international database, initiated by the author of this thesis in collaboration with Guillaume Herzberg from Lyon, France. This database constitutes a material on TWA that is far larger than in any other TWA-series ever published. The database is continuously updated and reanalyzed with an increasing follow-up time. The analyses published in paper II-IV, show that Re-motion TWA resulted in clinically and statistically significantly reduced disability, evaluated with a validated PROM – the QuickDASH questionnaire. Likewise, pain and grip strength improved significantly. This was the case in rheumatoid as well as in non-rheumatoid patients with severely destroyed wrists, including posttraumatic cases. Wrist motion however, did not improve. Nevertheless, motion after Re-motion TWA compared well with other currently available implants, published in series containing far smaller numbers, with the exception of the Maestro TWA, that in a single series of 23 patients yielded better motion. The question as to which extent and on what indications TWA is superior to TWF still needs to be answered.
The cumulated implant survival of the Re-motion was approximately 90 per cent at 9 years in the different diagnostic groups: RA, non-RA and posttraumatic. It is difficult to make a comparison with the longevity of no longer available implants of older generations, due to the modest information in the literature (paper I), with the exception of the Biax prosthesis, that had a comparable or somewhat lower implant survival (0.81 – 1.0 at 8 years). One implant, the APH, had a disastrous revision rate of 36/37 after 2 to 6.1 years. Another, the Meuli declined from 0.92 at 5 years to 0.77 at 8 years. Also concerning the longevity of available implants, only very few reports have been published. In fact, besides our reports on the Re-motion TWA, only information concerning the cumulated survival of the Universal prosthesis at 8 years or more was found through the systematic review of the literature in two papers: one paper, dealing with 24 Universal 1 cases and one with 21 Universal 2 cases, mostly in rheumatoid patients. For the Universal 1 the cumulated implant survival was 0.62 at 8 years and for the Universal 2 1.0. This discrepancy may be due to differences in prosthetic design, patient related factors, surgical techniques or decision making concerning revision: closer analysis is impossible in these small series.
The PROM used for the evaluation of disability/function – the QuickDASH – in paper II-IV, has been culturally adapted from US English to Danish according to the Guillemin guidelines on the initiative and under the guidance of the author of this thesis. In our analyses (paper VII and VIII) it has proven to have adequate psychometric properties in patients with TWA, assessed by classical methods and was of equal value as a PROM that is claimed to be more region specific: the PRWE.
PPO after TWA was a frequent occurrence frequently reported in the literature with varying implants (paper I). Its precise prevalence, location, natural history and clinical implications have not previously been analyzed systematically. According to our systematic measurements on serial (annual) radiographs after Re-motion TWA (paper V and VI), it is confined at the edges of the implant components close to the wrist joint in the vast majority of the cases and the radiolucent zone seems to stabilize at 1-2 mm within 3 years. More rarely it increases to higher levels, especially at the carpal side, but this seems not necessarily to lead to gross loosening of the components. The hypothesis that the development of PPO is related to the amount of polyethylene or metallic wear particles in the periprosthetic tissue, could not be confirmed (paper VI). It seems that other factors than polyethylene or metallic wear may cause loosening or at least contribute to loosening of the implants. Other factors may in theory be related to biomechanics or biocompatibility. For the time being we recommend close and continued observation of the patients with marked asymptomatic PPO but further investigations are needed.