The validity of a novel radiological method for measuring femoral stem version on anteroposterior radiographs of the hip after total hip arthroplasty.
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.
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
M
M
Weber
University of Giessen and Marburg , Baldingerstraße, 35043 Marburg, Germany.
P
P
Lechler
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
F
F
von Kunow
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
F
F
Völlner
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
A
A
Keshmiri
Technische Universität München, Ismaninger Strasse 22, 81675 Munich, Germany.
A
A
Hapfelmeier
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
J
J
Grifka
Regensburg University Medical Centre, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany.
T
T
Renkawitz
D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery*; D005858:Germany; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging* / Q000601:surgery*; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D012399:Rotation; D014057:Tomography, X-Ray Computed
stem torsion; total hip arthroplasty; hip biomechanics; radiography