EARLY FILL-IN OF PERIACETABULAR GAP WITH UNCEMENTED CUP: IS IT THE CUP SETTLING WITHIN THE ACETABULUM?

Abstract

Introduction: Osseointegration is known to occur around the uncemented acetabular cups which results in fill-in of peri-acetabular gaps. The objective of this study was to assess the gaps around uncemented acetabular cups radiologically in early post-operative period.

Methods: 53 primary uncemented total hip arthroplasties were performed at our hospital by a single surgeon between February 2003 and august 2005. There were 29 females and 22 males. Two patients had bilateral surgeries. Mean age of patients was 70 years (range, 52–88 years). Primary osteoarthritis of the hip was the indication for surgery in all the patients. Peri-acetabular gaps were measured on the radiographs taken at day-1 post-operatively and at 3 months follow-up. All the measurements were taken independently by two investigators on two different occasions using a picture archiving & communications (PACS) system. The two sets of data from each investigator were compared for intra and inter-observer variability using independent-samples t test.

Results: in 24 cases, no gaps were found around the ace-tabular cups on day-1 post-operative radiographs. In 29 cases, the mean gap was 4 mm (range, 1–8 mm) on postoperative day-1. Five gaps were in zone one, 24 in zone two and none in zone three. At 3 months follow-up, the mean gap was found to be 0.6 mm (range, 0–3 mm). The reduction in gaps from day-1 post-op to 3 months follow-up was statistically significant (chi square test, p< 0.05).

Discussion: We found a significant reduction in peri-acetabular gaps as early as at 3 months following uncemented total hip arthroplasties. We feel that settling of the cup within the acetabulum is responsible, rather than osseointegration, for these fill-in of gaps in early postoperative period. A larger study is required to analyse this phenomenon as screws fixation of uncemented cups may compromise their settling within the acetabulum.