Abstract
The orientation of the acetabular component in metal-on-metal hip resurfacing arthroplasty affects wear rate and hence failure. Correct assessment of acetabular orientation is key in assessing the painful hip resurfacing. This study aimed to establish if interpretation of pelvic radiographs with TraumaCad software can provide a reliable alternative to computed tomography (CT) in measuring the acetabular inclination and version.
TraumaCad was used to measure the acetabular orientation on AP pelvis radiographs of 14 painful hip resurfacings. Four orthopaedic surgeons performed each measurement twice. These were compared with measurements taken from CT reformats performed by an experienced musculoskeletal radiologist. The correlation between TraumaCad and CT was calculated, as was the intra- and inter-observer reliability of TraumaCad.
There is strong correlation between the two techniques for the measurement of inclination and version (p<0.001). Intra- and inter-observer reliability of TraumaCad measurements are good (p<0.001). Mean absolute error for measurement of inclination was 2.1°. TraumaCad underestimated version compared to CT in 93% of cases, by 12.6 degrees on average.
When assessing acetabular orientation in hip resurfacing, the orthopaedic surgeon may use TraumaCad in the knowledge that it correlates well with CT and has good intra- and inter-observer reliability but underestimates version by 12° on average. This underestimation may be contributed to by the natural divergence of the X-ray beam, the short arc of the ellipse left exposed by the large diameter head, and the non-hemispherical resurfacing cup.
