Head penetration into Hylamer acetabular liner sterilized by gamma irradiation in air and in a nitrogen atmosphere

We reviewed 25 consecutive primary cementless total hip arthroplasties with Hylamer acetabular liners (Hylamer group) and 12 with conventional ultra-high molecular weight polyethylene (Enduron group). Two-dimensional penetration of the femoral head into the liner was determined from anteroposterior radiographs of the pelvis. Head penetration rate was 0.37 mm/y in the Hylamer group sterilized by gamma irradiation in air (n = 6; mean length of follow-up, 3 years), 0.21 mm/y in the Hylamer group sterilized by gamma irradiation in a nitrogen atmosphere (n = 19; mean length of follow-up, 2.7 years), and 0.11 mm/y in the Enduron group (n = 12; mean length of follow-up, 3.9 years). Osteolysis was identified in 6 of the 25 hips with Hylamer liners and 1 of the 12 hips with conventional liners. There was a positive linear correlation between period from production to operation and head penetration rate with Hylamer liner sterilized by gamma irradiation in air and no correlation in a nitrogen atmosphere. Rapid oxidation by irradiation in air might not be the main cause of high rate of wear in Hylamer liners.