Computed Tomographic Measurement of Cementless Total Hip Replacement Implant Orientation

The aim of this study was to describe and assess a technique for the measurement of cementless (BioMedtrix Biologic Fixation [BFX]) total hip replacement implant orientation using computed tomography (CT). Postoperative CT studies of 15 dogs that had total hip replacement with a 24 mm BFX cup and BFX stem were reviewed retrospectively. Multiplanar reconstructed CT images were manipulated to generate standard positions of the pelvis and femur. Open face version, angle of lateral opening (ALO), inclination of the cup and stem anteversion were measured sequentially. Cases were anonymized, randomized and measured three times by two observers. Intraclass correlation coefficients for cup open face version, cup ALO, cup inclination and stem version were 1.0 and 1.0, 0.98 and 0.98, 0.99 and 0.99, and 1.0 and 0.97, for observers 1 and 2, respectively. The interclass correlation coefficients indicating interobserver variation for cup open face version, cup ALO, cup inclination and stem version were 1.0, 0.99, 0.99 and 0.99, respectively. The reported technique for measurement of BFX total hip replacement implant orientation is highly repeatable and allows objective measurement of implant orientation, including parameters which are not accessible radiographically.