The validity of a novel radiological method for measuring femoral stem version on anteroposterior radiographs of the hip after total hip arthroplasty

Bone Joint J. 2015 Mar;97-B(3):306-11. doi: 10.1302/0301-620X.97B3.34618.

Abstract

Femoral stem version has a major influence on impingement and early post-operative stability after total hip arthroplasty (THA). The main objective of this study was to evaluate the validity of a novel radiological method for measuring stem version. Anteroposterior (AP) radiographs and three-dimensional CT scans were obtained for 115 patients (female/male 63/72, mean age 62.5 years (50 to 75)) who had undergone minimally invasive, cementless THA. Stem version was calculated from the AP hip radiograph by rotation-based change in the projected prosthetic neck-shaft (NSA*) angle using the mathematical formula ST = arcos [tan (NSA*) / tan (135)]. We used two independent observers who repeated the analysis after a six-week interval. Radiological measurements were compared with 3D-CT measurements by an independent, blinded external institute. We found a mean difference of 1.2° (sd 6.2) between radiological and 3D-CT measurements of stem version. The correlation between the mean radiological and 3D-CT stem torsion was r = 0.88 (p < 0.001). The intra- (intraclass correlation coefficient ≥ 0.94) and inter-observer agreement (mean concordance correlation coefficient = 0.87) for the radiological measurements were excellent. We found that femoral tilt was associated with the mean radiological measurement error (r = 0.22, p = 0.02). The projected neck-shaft angle is a reliable method for measuring stem version on AP radiographs of the hip after a THA. However, a highly standardised radiological technique is required for its precise measurement.

Keywords: stem torsion; total hip arthroplasty; hip biomechanics; radiography.

Publication types

  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Aged
  • Arthroplasty, Replacement, Hip / methods*
  • Female
  • Femur / diagnostic imaging*
  • Femur / surgery*
  • Germany
  • Hip Prosthesis*
  • Humans
  • Imaging, Three-Dimensional
  • Male
  • Middle Aged
  • Osteoarthritis, Hip / diagnostic imaging*
  • Osteoarthritis, Hip / surgery*
  • Prospective Studies
  • Radiographic Image Interpretation, Computer-Assisted
  • Rotation
  • Tomography, X-Ray Computed