Acetabular coverage differs between standing and supine positions: model-based assessment of low-dose biplanar radiographs and comparison with CT.
OBJECTIVES
To evaluate the feasibility of 2D and 3D acetabular coverage assessments based on low-dose biplanar radiographs (BPR) in comparison with CT, and to demonstrate the influence of weight-bearing position (WBP) on anterior and posterior acetabular coverages.


METHODS
Fifty patients (21 females, 29 males) underwent standing BPR and supine CT of the pelvis. Using dedicated software, BPR-based calculations of anterior and posterior 2D coverages and anterior, posterior, and global 3D coverages were performed in standardized anterior pelvic plane (APP) and WBP. CT-based anterior and posterior 2D coverages and global 3D coverage was calculated in APP and compared with BPR-based data. Statistics included intraclass correlation coefficients (ICC) and Bland-Altman plots.


RESULTS
Mean anterior 2D coverage was 21.2% (standard deviation, ± 7.4%) for BPR and 23.8% (± 8.4%) for CT (p = 0.226). Mean posterior 2D coverage was 54.2% (± 9.8%) for BPR and 61.7% (± 9.7%) for CT (p = 0.001). Mean global 3D coverage was 46.5% (± 3.0%) for BPR and 45.6% (± 3.6%) for CT (p = 0.215). The inter-method reliability between CT and BPR and inter-reader reliability for BPR-based measurements were very good for all measurement (all ICC > 0.8). Based on BPR, mean anterior and posterior 3D coverages were 20.5% and 26.0% in WBP and APP, while 25 patients increased anterior and 24 patients increased posterior 3D coverage from APP to WBP with a relative change of coverage of up to 11.9% and 10.0%, respectively.


CONCLUSIONS
2D and 3D acetabular coverages can be calculated with very good reliability based on BPR. The impact of standing position on acetabular coverage can be quantified with BPR on an individual basis.


KEY POINTS
• 2D and 3D acetabular coverages can be calculated with very good reliability based on biplanar radiographs in comparison with CT. • The impact of standing position on anterior and posterior acetabular coverages can be quantified with BPR on an individual basis.
['Fritz|Benjamin|B|http://orcid.org/0000-0001-8733-131X', 'Agten|Christoph A|CA|', 'Boldt|Franca K|FK|', 'Zingg|Patrick O|PO|', 'Pfirrmann|Christian W A|CWA|', 'Sutter|Reto|R|']
D000077:Acetabulum D000368:Aged D000369:Aged, 80 and over D005240:Feasibility Studies D005260:Female D006621:Hip Joint D006801:Humans D021621:Imaging, Three-Dimensional D007592:Joint Diseases D008297:Male D008875:Middle Aged D011859:Radiography D015203:Reproducibility of Results D016683:Supine Position D014057:Tomography, X-Ray Computed
Weight-bearing Acetabulum Hip joint Radiography Reproducibility of results