Abstract
Acetabular components used to treat large defects are at greater risk of loosening. Porous tantalum acetabular components have reported the most promising early to midterm revision rates. Early stability of acetabular components used at revision THR was shown to be a good predictor of later loosening. The primary aim was to assess the migration of porous acetabular component used to reconstruct severe acetabular defects. Secondarily, we investigated the effect of acetabular defect severity and type of component fixation on migration.
Radiosterometric analysis was used to measure migration at a mean follow-up of four years, (range 2–10) in 59 reconstructions of severe acetabular defects with porous tantalum components. Acetabular component fixation was classified as superior if augmented with screws through cup, augments or cage in the ilium only. Fixation was classified as combined, superior and inferior, if flanges and/or screws were also placed in the ischium and or pubis. Acceptable limits of proximal migration were defined as ≤1mm within 2 years and ≤2.5mm at any time point.
Eight hips had reconstruction of Paprosky II defects with superior fixation only. The mean proximal migration of the eight acetabular components was 0.25mm (0.08–0.40) at 2 years and 0.29mm (0.10–0.81) at last follow-up.
Fifty-one hips had reconstruction of Paprosky III defects. Seven of these reconstructions exceeded the migration thresholds. Five reconstructions (four with superior fixation and one cup cage construct with no inferior screw fixation) of hips with pelvic discontinuity developed pain and were re-revised for loosening. Two reconstructions are asymptomatic and migrated 2.68mm (cup-cage construct with superior screws) and 2.86mm (no pelvic discontinuity, superior fixation) at final follow-up. The mean proximal migration of the 51 Paprosky III reconstructions was 0.99mm (0.03 to 16.4) at 2 years and 1.92mm (0.01 to 29.4) at last follow-up. The mean proximal translation at 2 years of the 11 reconstructions with inferior screw fixation was 0.2mm (−0.6 to 0.7mm), compared with 0.9mm (−0.6 to 16.4mm) for the reconstructions without inferior screw fixation.
In conclusion, when used to reconstruct Paprosky II defects, porous tantalum acetabular components provide component stability similar to a good performing primary THR. These implants achieve adequate stability when used to treat Paprosky III defects, including those with pelvic discontinuity. For the most severe defects, combined fixation with inferior screws is recommended, particularly when reconstructing hips with pelvic discontinuity.
