Computed tomography evaluation of the periacetabular gap of a porous tantalum acetabular component.

The periacetabular gap is an inherent consequence of the peripheral rim press-fit of the porous tantalum acetabular component. The circumference of the prosthesis is clearly depicted with computed tomography (CT) images that have been optimised to reduce metal artefacts. This case report highlights the utility of single-energy metal artefact reduction (SEMAR) for CT evaluation of the periacetabular gap by comparing CT images with and without SEMAR. A 70-year-old woman with a 5-year history of rheumatoid arthritis underwent total hip arthroplasty with a porous tantalum modular acetabular component. A periacetabular gap was suspected by plain radiography 2 weeks postoperatively. The metal artefacts rendered evaluation of the circumference of the acetabular component difficult in CT images acquired without SEMAR. In contrast, there were fewer metal artefacts, and a periacetabular gap (depth of 6.5 mm in DeLee and Charnley zone 2) was clearly depicted in CT images with SEMAR 2 weeks postoperatively. The porous surface of the acetabular component was in contact with the anterior and posterior rims of the acetabulum. Gap filling with bone and bone ingrowth into the porous surface were observed on CT images with SEMAR 24 weeks postoperatively. In conclusion, SEMAR reduces metal artefacts and improves CT image quality around the circumference of the acetabular component. The periacetabular gap and its filling with bone are clearly depicted in CT images with SEMAR, but not without SEMAR.