Increasing shape modelling accuracy by adjusting for subject positioning: An application to the analysis of radiographic proximal femur symmetry using data from the Osteoarthritis Initiative

Abstract

In total hip arthroplasty, the shape of the contra-lateral femur frequently serves as a template for preoperative planning. Previous research on contra-lateral femoral symmetry has been based on conventional hip geometric measurements (which reduce shape to a series of linear measurements) and did not take the effect of subject positioning on radiographic femur shape into account. The aim of this study was to analyse proximal femur symmetry based on statistical shape models (SSMs) which quantify global femoral shape while also adjusting for differences in subject positioning during image acquisition. We applied our recently developed fully automatic shape model matching (FASMM) system to automatically segment the proximal femur from AP pelvic radiographs to generate SSMs of the proximal femurs of 1258 Caucasian females (mean age: 61.3 SD = 9.0). We used a combined SSM (capturing the left and right femurs) to identify and adjust for shape variation attributable to subject positioning as well as a single SSM (including all femurs as left femurs) to analyse proximal femur symmetry. We also calculated conventional hip geometric measurements (head diameter, neck width, shaft width and neck-shaft angle) using the output of the FASMM system. The combined SSM revealed two modes that were clearly attributable to subject positioning. The average difference (mean point-to-curve distance) between left and right femur shape was 1.0 mm before and 0.8 mm after adjusting for these two modes. The automatic calculation of conventional hip geometric measurements after adjustment gave an average absolute percent asymmetry of within 3.1% and an average absolute difference of within 1.1 mm or 2.9° for all measurements. We conclude that (i) for Caucasian females the global shape of the right and left proximal femurs is symmetric without isolated locations of asymmetry; (ii) a combined left–right SSM can be used to adjust for radiographic shape variation due to subject positioning; and (iii) adjusting for subject positioning increases the accuracy of predicting the shape of the contra-lateral hip.

Investigation of Association Between Hip Osteoarthritis Susceptibility Loci and Radiographic Proximal Femur Shape

“…This study was conducted on radiographs of the OA–unaffected hip joint of subjects with unilateral hip OA on the assumption that the OA–unaffected side is a good predictor of the shape of the affected side before disease. This assumption was based on our prior analyses of the 2‐dimensional radiographic shape of left and right proximal femurs as captured by an SSM . Assuming radiographic proximal femur symmetry before the onset of disease, this raises questions as to what determines which side (left/right) will first develop OA, whether carriers of the risk allele of a susceptibility SNP are more prone to develop bilateral hip OA over time, and at what stage the morphology of the femur reflects changes as a consequence of disease rather than a predisposition.…”

“…This assumption was based on our prior analyses of the 2‐dimensional radiographic shape of left and right proximal femurs as captured by an SSM . Assuming radiographic proximal femur symmetry before the onset of disease, this raises questions as to what determines which side (left/right) will first develop OA, whether carriers of the risk allele of a susceptibility SNP are more prone to develop bilateral hip OA over time, and at what stage the morphology of the femur reflects changes as a consequence of disease rather than a predisposition. Future longitudinal studies will be needed to explore the interplay between genetically determined proximal femur morphology and the onset/progression of disease.…”

Methodology for Morphometric Analysis of Modern Human Contralateral Premolars

“…Faculty of Dentistry | University of Oslo | 2018 [36] also found that demographics (age, weight, height, ethnicity and gender) had no association with asymmetry. The bilateral matching symmetry of the femur is a valuable aid in reproducing the correct femoral size, shape and orientation in hip arthroplasty [37,38].…”

A simple method for restoring the femoral head center in hip arthroplasty: a 3-dimensional analysis in the Chinese population

“…Although preoperative planning of hip replacement using the contralateral side is common [ 23 – 25 ], the lateral discrepancies in the 3-dimensional geometry of the proximal femur may generate inaccuracies in various template approaches [ 26 – 28 ]. There are limited data on the lateral variability of LTFHC and GTFHC [ 18 ].…”