Open-Source and Commercial 3-Dimensional Computed Tomography Methods Show Limited Agreement for Classifying Acetabular Morphology in Patients Undergoing Hip Arthroscopy
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Updated: Nov 5, 2026
In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
Published on: July 2, 2021
Ashley A Ellingwood1, Rajvarun S Grewal2, Henry M Gass3
1Division of Orthopedics Rady Children's Hospital-San Diego San Diego California U.S.A.
Purpose:
To compare acetabular morphology classifications derived from a validated open-source (freely available) method with those derived from commercially available software in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome.
Methods:
We analyzed preoperative 3-dimensional computed tomography imaging in patients with femoroacetabular impingement syndrome using open-source and commercial software. The open-source method calculated acetabular coverage across 5 regions and generated z-scores relative to an internal normative database. Hips with z-scores ≥2 or ≤-2 were classified as abnormal. The commercial method categorized hips as normal, undercovered, or overcovered based on published thresholds (lateral center-edge angle, Tönnis angle, coverage percentage, and crossover sign) and focal depth mapping. The primary outcome was categorical agreement between methods.
Results:
Seventy-six hips (55 women, 21 men; mean age 35.5 ± 12.3 years) were included. The open-source method classified 58/76 hips as normal, 10/76 as dysplastic, and 8/76 as overcovered. The commercial method classified 14/76 hips as normal, 29/76 as undercovered, and 33/76 as overcovered. A total of 23/76 hips were classified the same in both systems and called agreed. Disagreements (53/76 hips) fell into 3 categories: (1) essentially similar despite different labels because of borderline z-scores or small focal areas (n = 24), (2) disagreements driven by Tönnis angle alone (n = 8), and (3) true disagreements (n = 21). Notably, 5 hips (6.6%) showed opposite classifications (e.g., dysplastic vs overcovered). Subanalysis of z-scores showed that 69.8% of disagreements reflected borderline morphology (z-scores of ±1-2).
Conclusions:
Although both open-source and commercial methods provide 3-dimensional classification of acetabular morphology, categorical agreement was limited. Most disagreements reflected borderline morphology or small focal areas of uncertain clinical relevance. A minority showed true classification opposites.
Clinical Relevance:
Awareness of the methodological differences between open-source and commercial 3-dimensional computed tomography platforms may help surgeons appropriately interpret acetabular morphology classifications during preoperative planning for patients undergoing hip arthroscopy for femoroacetabular impingement syndrome.
