Tag Archive | RSA

Preventing Acetabular Component Migration in Revision THA

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.

“New” but Not Necessarily “Improved”

A review of five hip- and knee-implant innovations, initiated by the FDA in reaction to serious problems with metal-on-metal hip bearings, found that none offered meaningful functional or patient-outcome benefits over older designs. The systematic review of 118 studies and more than 13,000 patients, published in the BMJ, also found that three of the new designs—ceramic-on-ceramic hip bearings, modular femoral necks, and high-flexion knee implants—were associated with higher revision rates relative to established designs. The other two innovations—uncemented monoblock acetabular cups and sex-specific knee implants—provided no benefit over older designs but had comparable revision rates.

The BMJ authors claim that the purpose of the review was not to “criticise the surgical community or orthopaedic industry,” but rather to “highlight that the status quo regarding the introduction of new device technologies is not acceptable.”

The BMJ authors cite stepwise introduction of new implant technologies as one way to avoid exposing large numbers of patients to innovations whose safety and efficacy are unproven. In a 2011 JBJS supplement, authors (two of whom also co-authored the BMJ study) proposed using roentgen stereophotogrammetric analysis (RSA) and national joint registry data to facilitate phased clinical introduction of new implants.