A New Technique for Radiographic Measurement of Acetabular Cup Orientation

Two Year Average Follow Up of Supercapsular Percutaneously Assisted Total Hip Arthroplasty; Zero Dislocations

“…Standing radiographs taken in clinic 3 weeks post-operatively were reviewed and analyzed with commercially available templating software (Traumacad®, Brainlab, Munich, DE) to measure cup abduction, anteversion, and leg length discrepancy, a method that has been found to correlate well with CT-based measurements of implant position. [44][45][46] Number of dislocations were con rmed through telephone interviews with the patients one year or more after surgery. During telephone interviews, patients were also asked if the operative hip had experienced any dislocations, secondary surgery or any other complications in order to assess for any treatments that may have been rendered at outside institutions.…”

Validation of a new 2-D technique for radiographic wear measurement of cemented, highly cross-linked polyethylene acetabular cups

“…Before triggering the edge-detection routine and fitting an ellipse to the wire marker image, the image of the femoral head is masked by manually setting points where it intercepts the wire marker image. The shape and orientation parameters of the fitted ellipse enable the calculation of the cup version (sin −1 (b/a)) and inclination (corrected for X-ray beam offset [ 12 , 13 ]).…”

2D measurements of cup orientation are less reliable than 3D measurements (Acta Orthop 2015; 86 (4): 485–90.)

“…They would seem to have overlooked our laboratory study – published online 1 year before their submission date – in which we measured the orientations of 2 types of MoM resurfacing cup (Birmingham Hip and ASR) and compared the EBRA technique with our new, 2D Wrightington Cup Orientation software (WCO) (Derbyshire et al. 2014 ). Although measurement of MoM cup orientation using EBRA has been validated in laboratory studies, the same cannot be said for MoM cup measurement using their 3D CT technique – as the authors acknowledge.…”

“…The WCO software can correct version and inclination for X-ray focus point offset from the hip (Derbyshire 2008 , Derbyshire et al. 2014 ). I estimate that, for the cup in Figure 1, the anteversion measurement would have needed a correction of about +4° (+2° if focused at the middle of the pubic symphysis).…”

“…However, it is possible to distinguish retroversion reliably using the WCO system – provided that a second antero-posterior X-ray examination is taken with the beam focused at a different location from the first (Derbyshire et al. 2014 ). It is not clear what point the authors were trying to make with their version/inclination scatter graphs.…”