Uncemented total hip arthroplasty for primary osteoarthritis in young patients: a mid-to long-term follow-up study from the Finnish Arthroplasty Register.

INTRODUCTION: The survival of total hip arthroplasties (THAs) has been considered to be poor in young patients. We evaluated the population-based survival of uncemented THA for primary osteoarthritis (OA) in patients under 55 years of age and the factors affecting survival.

METHODS: The Finnish Arthroplasty Register was established in 1980. Between that year and 2003, 92,083 primary THAs were entered in the register, 5,607 of which were performed for primary OA in patients under 55 years of age. Using records from these 5,607 THAs, we selected uncemented femoral and acetabular components that had been used in more than 100 operations during the study period. Survival of both components (cup/stem) and their combinations were analyzed separately with the Kaplan-Meier analysis and the Cox regression model.

RESULTS: All uncemented stems studied showed a survival rate of over 90% at 10 years. The Biomet Bi-Metric stem had a 95% (95% CI 93- 97) survival rate even at 15 years. Overall survival of the extendedly porous-coated Lord Madréporique stem (p = 0.003) and the proximally porous-coated Anatomic Mesh stem (p = 0.0008) were poorer than that of the Biomet Bi-Metric stem. When endpoint was defined as stem revision for any reason, results were generally similar; there was no difference, however, between the survival rates of the Lord Madréporique stem and the Bi-Metric stem. Of the acetabular components, the Biomet Universal, the ABG Il and the Harris-Galante II cups showed < 90% survival rates at 10 years with aseptic loosening as endpoint; at 13 years the corresponding survival rates were 94% (95% CI 91-97) for the Biomet Universal and 95% (95% CI 91-98) for the Harris-Galante II cups with aseptic loosening as endpoint. The PCA Pegged porous-coated uncemented cup showed a poor 13-year survival rate of 68% (95% CI 59-78) with aseptic loosening as endpoint. However, when endpoint was defined as any revision (including exchange of liner), the 10-year survival rates of all brands of cup except Harris-Galante II declined to under 80%.

INTERPRETATION: Modern second-generation uncemented stems, with proximal circumferential porous- or HA-coating, seem to be a good choice for young patients with primary OA. Similarly, modern press-fit porous- and HA-coated cups appear to have good endurance against aseptic loosening in these young patients. However, liner revisions were common; thus, survival rates of uncemented cups were unsatisfactorily low. Polyethylene wear and unfavorable locking mechanisms between the metal shell and the polyethylene liner and their sequelae remain matters of concern in this young and active group of patients.