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Effect of combined flexion and external rotation on measurements of the proximal femur from anteroposterior pelvic radiographs - 11/06/18

Doi : 10.1016/j.otsr.2018.03.004 
J.D. O’Connor a, M. Rutherford a, J.C. Hill b, D.E. Beverland b, N.J. Dunne c, d, e, f, A.B. Lennon a,
a School of Mechanical and Aerospace Engineering, Queen's University Belfast, 125, Stranmillis road, BT9 5AH, Belfast, United Kingdom 
b Primary Joint Unit, Musgrave Park Hospital, Stockman's Lane, Belfast, BT9 7JB, United Kingdom 
c School of Mechanical & Manufacturing Engineering, Dublin City University, Glasnevin, Dublin 9, Ireland 
d Centre for Medical Engineering Research, Stokes Building, School of Mechanical & Manufacturing Engineering, Dublin City University, Collins avenue, Dublin 9, Ireland 
e Trinity Centre for Bioengineering, Trinity College Dublin, 152-160, Pearse street, Dublin 2, Ireland 
f School of Pharmacy, Queen's University Belfast, 97, Lisburn road, BT9 7BL, Belfast, United Kingdom 

Corresponding author.

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Abstract

Introduction

Fixed flexion and external rotation contractures are common in patients with hip osteoarthritis and, in particular, before total hip replacement (THR). We aimed to answer the following question: how does combined flexion and external rotation of the femur influence the radiographic assessment of (1) femoral offset (FO) (2) neck-shaft angle (NSA) and (3) distance (parallel to the femoral axis) from greater trochanter to femoral head center (GT-FHC)?

Hypothesis

Combined flexion and external rotation impact the accuracy of two-dimensional (2D) proximal femur measurements.

Materials and methods

Three-dimensional (3D) CT segmentations of the right femur from 30 male and 42 female subjects were acquired and used to build a statistical shape model. A cohort (n=100; M:F=50:50) of shapes was generated using the model. Each 3D femur was subjected to external rotation (0°–50°) followed by flexion (0°–50°) in 10° increments. Simulated radiographs of each femur in these orientations were produced. Measurements of FO, NSA and GT-FHC were automatically taken on the 2D images.

Results

Combined rotations influenced the measurement of FO (p<0.05), NSA (p<0.001), and GT-FHC (p<0.001). Femoral offset was affected predominantly by external rotation (19.8±2.6mm [12.2 to 26.1mm] underestimated at 50°); added flexion in combined rotations only slightly impacted measurement error (20.7±3.1mm [13.2 to 28.8mm] underestimated at 50° combined). Neck-shaft angle was reduced with flexion when external rotation was low (9.5±2.1° [4.4 to 14.2°] underestimated at 0° external and 50° flexion) and increased with flexion when external rotation was high (24.4±3.9° [15.7 to 31.9°] overestimated at 50° external and 50° flexion). Femoral head center was above GT by 17.0±3.4mm [3.9 to 22.1mm] at 50° external and 50° flexion. In contrast, in neutral rotation, FHC was 12.2±3.4mm [3.9 to 22.1mm] below GT.

Discussion

This investigation adds to current understanding of the effect of femoral orientation on preoperative planning measurements through the study of combined rotations (as opposed to single-axis). Planning measurements are shown to be significantly affected by flexion, external rotation, and their interaction.

Level of evidence

IV Biomechanical study.

Le texte complet de cet article est disponible en PDF.

Keywords : Femoral orientation, Preoperative planning, Femoral offset, Neck-shaft angle


Plan


 Presented to Closed Meeting International Hip Society, London September 2017.


© 2018  Elsevier Masson SAS. Tous droits réservés.
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Vol 104 - N° 4

P. 449-454 - juin 2018 Retour au numéro
Article précédent Article précédent
  • Impact of operative time on early joint infection and deep vein thrombosis in primary total hip arthroplasty
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