Original Article

Defining the dystrophic femoral neck in osteogenesis imperfecta: a radiographic and anatomical entity with diagnostic threshold

Service de Chirurgie orthopédique et traumatologie pédiatrique, Hôpital Necker Enfants malades - AP-HP, 149 Rue de Sèvres, 75015 Paris, France
² Genetics Department, Paris Cité University, INSERM UMR 1163, Imagine Institutee, 75015 Paris, France

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 11 August 2025
Accepted: 8 December 2025

Abstract

Introduction: Severe Osteogenesis Imperfecta (OI) can cause distinct proximal femoral deformities, but specific femoral neck changes remain poorly defined. This study aimed to characterize dystrophic femoral neck morphology and determine a diagnostic threshold. Methods: We retrospectively reviewed anteroposterior pelvic radiographs from patients >8 years old with severe OI (n = 24 hips) and age-matched controls (n = 24 hips). Measurements included femoral neck length, neck diameter, head diameter, neck-shaft angle, anterior lateral proximal femoral angle (aLPFA), and acetabular protrusion. Ratios of neck length-to-diameter and neck length-to-head diameter were calculated. Statistical comparisons used t-tests; ROC analysis identified the optimal threshold for distinguishing dystrophic necks. Results: OI patients had shorter femoral necks (52.7 ± 9.9 mm vs. 64.8 ± 9.6 mm, p < 0.001), smaller diameters (19.4 ± 4.7 mm vs. 32.8 ± 4.8 mm, p < 0.0001), and higher neck length-to-diameter ratios (2.82 ± 0.63 vs. 1.98 ± 0.19, p < 0.000001). A threshold of ≥2.35 (AUC = 0.90) identified dystrophic necks, associated with greater acetabular protrusion (–2.91 ± 12.33 mm vs. 4.42 ± 8.67 mm, p = 0.004). Discussion: A neck length-to-diameter ratio ≥ 2.35 reliably defines dystrophic femoral necks in OI and correlates with increased acetabular protrusion. Early recognition may guide surgical planning and help preserve hip function. Level of Evidence: Level IV – Retrospective comparative study.