ACETABULAR OSTEOLYSIS OF NONCEMENTED HIP PROSTHESIS

Abstract

Purpose: Osteolysis is one of the important issues during the life of noncemented total hip arthroplasty (THA). The purpose of this study was to evaluate a series of 228 THA using an ABG-1 implant to determine the incidence of osteolysis and contributive factors.

Material and methods: This series of 228 THA using noncemented ABG-1 anatomic implants coated with hydroxyapatite was implanted in 210 patients, 116 women and 112 men, mean age 62.2 years. The indication was primary osteoarthritis (53.6%), primary necrosis (21.5%), posttraumatic osteoarthritis (11.8%), rheumatoid disease (8.3%) and hip dysplasia (4.8%). The bearings were, 200 zirconium-polyethylene (87.7%), 28 metal-polyethylene (12.3%). At mean 88.6 months follow-up, a minimum 60 months postoperatively, we reviewed 163 patients (37 patients died without revision, 28 (12.3%) were lost to follow-up, and 17 had undergone a revision procedure). We analyzed osteolysis on the digitalized radiograms using the Delee-Charnley classification to which we added a fourth retroacetabular zone. Polyethylene wear was measured with the Imagika(r) software using the method described by Martell.

Results: The 17 cup revisions (8.5%) were required for instability (4 pt), loosening (4 pt), osteolysis (4 pt), infection (3 pt), and limping (1 pt). Overall implant survival was 92.1%. Implant survival, considering loosening and osteolysis as failure, was 96.1%. Mean wear at last follow-up was 1.26 mm, for an annual average of 0.17 mm (0.04 – 0.69 mm/yr). Acetabular osteolysis was observed in 41.6% of cases, mainly in the Delee-Charnley zone 1, but was also found in all the other zones. The average surface area was an estimated 223 mm2. Possible factors favoring osteolysis were: aetiology, age, gender, activity level, body mass index, Charnley ABC classification, presence of preoperative acetabular defects, cup size, polyethylene insert thickness, position of the insert rim, cup inclination, complementary fixation, bearing type, polyethylene offset and wear. There was a statistically significant relationship between osteolysis and: the Charnley classification (p=0.012), presence of preoperative acetabular defects (p=0.0034), cup inclination angle (p=0.035), cup size (p=0.042), polyethylene thickness (p< 0.01), use of complementary fixation (p=0.048), and polyethylene wear (p=0.0011). Paradoxically, we did not find any relationship with gender, age, body mass index, and the other factors.

Discussion: This analysis demonstrated the determining causes of osteolysis: time, polyethylene thickness, polyethylene wear, the Zicronium-polyethylene bearing. Wear was probably not only the consequence of the Zicronium-polyethylene bearing but was also related to the quality of the polyethylene, and the instability of the insert. Diffuse osteolysis is favored by orifices in the first-generation cups which have been eliminated in the ABG-2 cups.