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To the Editor

I read with interest the study on long-term outcome of silicone metacarpophalangeal implant surgery published recently in Arthritis Care & Research (Chung KC, Burns PB, Kim HM, Burke FD, Wilgis EF, Fox DA. Long-term followup for rheumatoid arthritis patients in a multicenter outcomes study of silicone metacarpophalangeal joint arthroplasty. Arthritis Care Res [Hoboken] 2012;64:1292–300). The study was large, had a long-term followup period, and included a comparator group. However, I have some issues with the analysis strategy used by the authors and their subsequent conclusions.

Because this study is not a randomized trial, the comparison between the groups must be made with great caution. Clearly at baseline, the patients who elected to have surgery had much worse hand function (in all aspects measured) than patients who declined surgery. The improvement in the surgery group is notable and contrasts with the stable course in the control group. However, in my view, the key finding is not (as reported) the difference in change between the groups, but the fact that the surgery group was able to improve to the level of the control group.

It would be interesting to learn the results of surgery performed in the subgroup of patients with hand function as good as the nonsurgery group at baseline. Did the patients in this subgroup show as much improvement as the patients with worse hand function? Also, the decrease in improvement over time suggests that a stable state was not reached and the surgery group needed to be followed up for even longer.

Finally, the analysis comparing the outcomes of the study (surgical) hand with the contralateral (nonsurgical) hand was unfortunately only briefly described and shown in a supplementary table. I think this analysis has greater validity than the main analysis because the variability between the hands of one patient is likely to be less than the variability between the hands of separate patients. For instance, the contralateral hand is more likely to also show poor function and thus more resemble the surgical hand. Also, the influences working at the patient level are likely the same in both hands. Supplementary Table 1 of the article did not show the baseline data for the nonsurgical hand; however, it did show that the surgical hand improved or maintained function better than the control hand, confirming the main study findings. Interestingly, the supplementary table also confirmed a finding not highlighted by the authors. In the main analysis, grip strength was, not unexpectedly, less at baseline in the hands of the surgical group compared to the hands of the control group. However, grip strength increased more in the control group than in the surgical group, and this was mirrored in the within-patient analysis; namely, grip strength increased in both hands, but more in the nonsurgical hands than in the surgical hands (P = 0.06).

In conclusion, this study adds to our knowledge of the pros and cons of silicone implant surgery. Readers should certainly look at Supplementary Table 1. Overall, I think there is enough equipoise to perform a randomized trial on the balance of benefit and harm of this procedure.

  • Maarten Boers, MSc, MD, PhD

  • VU University Medical Center

  • Amsterdam, The Netherlands