Background: We have previously reported that 6 months of oral treatment with clodronate reduced the migration of the NexGen total knee prosthesis during the first postoperative year, as measured by radiostereometry (RSA). We now report the 4-year results.
Methods: This was a double-blind randomized study, using RSA with maximal total point motion (MTPM).
Results: With analysis according to the "intention to treat" principle, the only remaining difference between the groups at 4 years was reduced rotation around the transverse axis (a secondary variable) in the clodronate group. However, 3 patients (all clodronate) did not take any tablet after surgery. If they are excluded, there was an almost statistically significant difference between the groups at 4 years regarding MTPM from baseline, with the clodronate group showing 25% less migration. From 1 to 4 years, there was no difference in migration rate by MTPM, but there was a continuous increase in rotation around the transverse axis in the controls, which differed from the clodronate group. There were no cases of aseptic loosening. 2 patients had migration of more than 1.3 mm from baseline to 4 years; neither of them had taken clodronate. The others had migration of less than 0.9 mm.
Interpretation: Because migration was clearly reduced by clodronate during the first postoperative year, and there was still a difference at 4 years when analyzed per protocol, it appears likely that this treatment can diminish the risk of loosening. The difference in the number of outliers also points in this direction, and may be more relevant than mean migration values.