The Fate of Zone 2 Radiolucencies in Contemporary Highly Porous Acetabular Components: Not All Designs Perform Equally

Abstract

Background The enhanced frictional resistance of modern ultraporous acetabular components can impede complete seating; however, surgeons expect the enhanced ingrowth surface to resolve polar (zone 2) gaps over time via osseointegration. This study characterized zone 2 radiographic osseointegration in 3 acetabular component designs: 2 highly porous ingrowth and one traditional ongrowth. Methods A consecutive cohort of primary total hip arthroplasties was reviewed which utilized 3 different acetabular cup designs: ongrowth titanium with hydroxyapatite (HA), highly porous titanium with machined radial grooves (MRG), and dual-porous titanium substrate with micropore (MP). Radiographic analysis was performed using accepted measurement criteria with particular attention to radiolucent lines. Results Seven hundred ninety cases were available for analysis. Initial 1-month radiographs revealed 43.2% of HA, 78.2% of MRG, and 81.0% of MP cups exhibited zone 2 radiolucencies, consistent with incomplete seating. At 1 year, all HA radiolucencies resolved, whereas 46.2% and 34.7% of radiolucencies remained in MRG and MP cups, respectively ( P ≤ .005). At minimum 2 years, a significant proportion of zone 2 radiolucencies remained in 46.0% of MRG compared with 23.9% of MP cups and 3.0% of HA cups ( P ≤ .007). Conclusion The resolution of zone 2 radiolucencies at 1-year and minimum 2-year follow-up signified osseointegration for nearly all HA and most MP cups. Highly porous titanium cups with machined radial grooves demonstrated persistent zone 2 radiolucencies at 1 year and beyond. Given reports of early loosening with this particular acetabular implant, further follow-up is warranted as this study highlights that not all contemporary highly porous metal acetabular components perform equally. Level of Evidence III.

Novel nano‐hydroxyapatite coating of additively manufactured three‐dimensional porous implants improves bone ingrowth and initial fixation

“…Bioactive coatings that induce greater bone formation have been clinically reported to have a positive effect on radiographic signs around porous acetabular cups. 38 , 39 In over 70% of cases, a gap between the host bone and the alkali‐ and heat‐treated titanium acetabular cups was observed by radiographic evaluation immediately after surgery; however, all the gaps disappeared within a year. In HA‐coated acetabular cups, radiolucent lines observed at 1 month follow‐up decrease after 1 year, whereas the highly porous titanium cups remained radiolucent.…”