Mid-term Follow Up of a Highly Porous Acetabular Component for Primary Total Hip Arthroplasty

Introduction: As implant technology has continued to improve over the past decade, there has been an increase in the utilization of highly porous metal substrate acetabular components for primary total hip arthroplasty (THA). These implants have several theoretical benefits including a lower modulus of elasticity, which may result in a reduction in stress shielding, a higher coefficient of friction, which may enable better initial implant fixation, as well as higher porosity that may facilitate improved biological fixation. Although these components are implanted frequently, there are some studies that have posed concerns regarding radiographic evidence of loosening. Therefore, the purpose of this study was to assess: 1) The quality of fixation of porous metal acetabular components based on radiographs; 2) clinical outcomes; and 3) revision rates. Materials and Methods: A total of 159 patients (169 hips) who had undergone a primary THA utilizing a porous metal primary acetabular cup with minimum two-year follow up were assessed. The study cohort consisted of 51% women, had a mean age of 65 years (range, 30 to 92 years), a mean body mass index (BMI) of 29kg/m2 (range, 15 to 54), and a mean follow up of approximately four years (range, three to six years). Acetabular revision for component failure was documented. Radiographic assessments were independently performed by two fellowship-trained arthroplasty surgeons to determine implant stability and radiolucencies. Clinical evaluations were made by assessing the hip disability and osteoarthritis outcome score (HOOS-Jr) survey scores. Failure was defined as the need to revise the acetabular component, for either septic or aseptic pathology. Results: At final follow up, one patient had definitive loosening, one had probable loosening, and three patients had possible loosening. Only 3.0% had radiolucencies or radiosclerotic lesions in at least one zone. Of these patients, three developed progressive radiolucencies. All patients achieved excellent postoperative HOOS-Jr scores, and no significant differences were noted between patients who did not have loosening compared to patients who had possible or probable loosening. Only two patients underwent revision for aseptic loosening of the cup (success rate for this implant was 98.8% [2/169]). Discussion: There is a paucity of studies focused on the results of this porous metal substrate acetabular component, with some of the current literature reporting conflicting outcomes. Our study reported a low acetabular revision rate of only 1.2% at an approximate mean follow up of four years. The incidence of radiolucencies and progressive radiolucencies were lower (3.0%) than has been found in some studies. Overall, the results of this study support the utilization of this acetabular component in appropriately indicated patients. Conclusion: These data show a low rate of acetabular revision at mean four-year follow up.