Revision total hip arthroplasty (THA) is a challenging procedure for many reasons, not the least of which is the risk of aseptic loosening leading to re-revision, especially in patients with severe acetabular defects. Acetabular components made of porous tantalum have a developed a good reputation for lower rates of re-revision, relative to components made of other materials. In the November 21, 2018 issue of The Journal of Bone & Joint Surgery, Solomon et al. bolster the evidence base regarding the success of porous tantalum acetabular components in revision THA.
The authors conducted a single-center prospective cohort study that used radiostereometric analysis (RSA) to accurately measure acetabular component migration in 55 revision THAs that involved a porous tantalum acetabular component. Over a mean follow-up of 4 years, 48 of the 55 components migrated <1 mm, the threshold that, based on previous findings in the literature, the authors defined as predicting later loosening. Five of the 7 components that exceeded the threshold were re-revised for loosening related to patient symptoms.
The RSA data for the 5 components that required re-revision revealed large proximal translations and sagittal rotations that increased over time until re-revision, although the RSA readings revealed that the majority of the migration occurred in the first 6 weeks. Among the components that did not exceed the 1 mm threshold for migration at 2 years, none have been subsequently re-revised for loosening.
The authors also analyzed fixation methods in this cohort. They found that, at 2 years, the median proximal translation of components that used inferior screw fixation was significantly lower than that of components without inferior screw fixation. The take-home messages from this study seem to be as follows:
- Porous tantalum acetabular components really do perform well in revision THA.
- When indicated, inferior screw fixation lowers the risk of component migration.
- Early component migration is a good predictor of long-term component survivorship.
One key question for orthopaedic surgeons regarding revision total knee arthroplasty (TKA) is how best to affix femoral and tibial stems. The August 17, 2016 edition of the Journal of Bone & Joint Surgery contains findings from a Level I randomized trial by Heesterbeek et al . that addresses this clinical conundrum.
Thirty-two patients with Type-I or II bone defects who needed a revision TKA received the same basic implant, with the femoral components and tibial baseplates being cemented in all cases. However, in half the patients the femoral and tibial stems were cemented, and in the other half the stems were press-fit (so-called hybrid fixation).
Measuring micromotion with radiostereometric analysis (RSA) at baseline, 6 weeks, and 3, 6, 12, and 24 months, the authors found no significant between-group differences in component migration. Similarly, at the 2-year follow-up, there were no significant between-group differences in clinical scores, including KOOS and visual analog ratings of pain and satisfaction.
The authors expressed concern about what they deemed the “relatively high” number of components in both groups that migrated > 1 mm (translation) or > 1° (rotation), and they are continuing to follow all these patients to determine whether clinically relevant component loosening eventually ensues.