A New Tool for Measuring Cup Orientation in Total Hip Arthroplasties from Plain Radiographs

Orientation of the hip cup is important in total hip arthroplasties. Orientation includes abduction (inclination) and anteversion. Anteversion can be considered as true (anatomic) and planar (radiographic) anteversion. Some measurement methods either are too complicated or are less precise. We developed a new protractor to measure cup orientation using postoperative anteroposterior radiographs centered at the hip. The new protractor measures true and planar anteversion and abduction easily and precisely. We verified its accuracy using a software simulator and simulated 45 radio- graphs of total hip arthroplasties with 15 different anteversions ranging from 15°-29° and 45 actual radiographs of total hip arthroplasties. We then measured the planar ante- version with our method and the method of Lewinnek et al. Maximal errors were 3° and 2.61°, respectively, and mean errors were 0.96° and 1.2°, respectively. The standard deviations were 0.74° with our method and 0.57° with the method of Lewinnek et al. For the real radiographs, the mean of absolute difference between the two methods was 1.34°, and the standard deviation was 1.13°. We found no difference between the two methods and no difference in our findings compared with those of Pradhan.Level of Evidence: Diagnostic study, level II.

[1]  H. Uhthoff,et al.  Anteversion of the acetabular cup. Measurement of angle after total hip replacement. , 1986, The Journal of bone and joint surgery. British volume.

[2]  J. Lewis,et al.  Dislocations after total hip-replacement arthroplasties. , 1978, The Journal of bone and joint surgery. American volume.

[3]  L. Fabeck,et al.  A method to measure acetabular cup anteversion after total hip replacement. , 1999, Acta orthopaedica Belgica.

[4]  J. Visser,et al.  A new method for measuring angles after total hip arthroplasty. A study of the acetabular cup and femoral component. , 1981, The Journal of bone and joint surgery. British volume.

[5]  R. Beckenbaugh,et al.  2,012 total hip arthroplasties. A study of postoperative course and early complications. , 1974, The Journal of bone and joint surgery. American volume.

[6]  Karl-Heinz Widmer,et al.  A simplified method to determine acetabular cup anteversion from plain radiographs. , 2004, The Journal of arthroplasty.

[7]  R. Pradhan,et al.  Planar anteversion of the acetabular cup as determined from plain anteroposterior radiographs. , 1999, The Journal of bone and joint surgery. British volume.

[8]  D. Murray The definition and measurement of acetabular orientation. , 1993, The Journal of bone and joint surgery. British volume.

[9]  Gerald Q. Maguire,et al.  A new CT method for measuring cup orientation after total hip arthroplastyA study of 10 patients , 2004, Acta orthopaedica Scandinavica.

[10]  Frank Langlotz,et al.  Anatomic Referencing of Cup Orientation in Total Hip Arthroplasty , 2005, Clinical orthopaedics and related research.

[11]  R. McLaren Prosthetic hip angulation. , 1973, Radiology.