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Femurs in patients with hip dysplasia have fundamental shape differences compared with cam femoroacetabular
Michael D Harris1, Brecca M M Gaffney2, John C Clohisy3
1Program in Physical Therapy, Department of Orthopaedic Surgery, Washington University School of Medicine, 4444 Forest Park Ave, St Louis, MO 63108, USA.
Insights
Developmental dysplasia of the hip (DDH) and cam femoroacetabular impingement (FAI) show distinct proximal femur shape variations. Understanding these differences is crucial for developing unique treatment strategies for each condition.
Area of Science:
- Orthopedics
- Biomedical Engineering
- Radiology
Background:
- Femoral deformities are common in developmental dysplasia of the hip (DDH), but treatment is not standardized.
- Deformities in DDH can resemble cam femoroacetabular impingement (FAI).
- Clarifying shape variations is essential for targeted treatment.
Purpose of the Study:
- To differentiate proximal femur shape variations between female patients with DDH and cam FAI.
- To compare 3D and 2D morphometric measures in DDH and cam FAI.
- To inform distinct treatment approaches based on unique biomechanical features.
Main Methods:
- Utilized 3D statistical shape modeling and principal component analysis (PCA) on 68 DDH and 60 cam FAI female patients.
- Quantified femoral head asphericity, α-angle, head-neck offset (HNO), and neck-shaft angle (NSA).
- Analyzed shape variations in both articular and extra-articular proximal femur regions.
Main Results:
- Shared variations included lesser trochanter to femoral head length and greater trochanter height.
- DDH showed unique head irregularities, while FAI had variations at the lateral head-neck junction and greater trochanter.
- DDH hips were less spherical (larger sphere-fitting errors), with smaller α-angles, larger HNO, and larger NSAs compared to FAI.
Conclusions:
- Distinct articular and extra-articular proximal femur shape features characterize DDH and cam FAI.
- These unique features influence the biomechanics of each disorder.
- Treatment strategies for DDH and cam FAI should be individualized based on their specific morphologic characteristics.
Abstract:
Femoral deformities are common in developmental dysplasia of the hip (DDH), but decisions about how to treat them are not standardized. Of interest are deformities that may be akin to cam femoroacetabular impingement (FAI). We used three-dimensional and two-dimensional measures to clarify the similarities and differences in proximal femur shape variation among female patients with DDH (n = 68) or cam FAI (n = 60). Three-dimensional measures included femoral head asphericity, as well as shape variation using statistical shape modeling and principal component analysis (PCA). Two-dimensional measures included the α-angle, head-neck offset (HNO) and the neck-shaft angle (NSA). Significant shape variations were captured in the first five PCA modes, with the greatest shared variation between groups being the length from the lesser trochanter to the femoral head and greater trochanter height. Variations unique to DDH were irregularities at different areas of the femoral head, but not at the lateral femoral head-neck junction where variation was strong in FAI. The FAI group also had unique variations in greater trochanter shape. DDH femoral heads were less spherical, as indicated by larger sphere-fitting errors (P < 0.001). Radiographically, the DDH group had significantly smaller α-angles (P < 0.001), larger head-neck offsets (P = 0.02) and larger NSAs (P < 0.001). Both the articular and extra-articular regions of the proximal femur have distinct shape features in DDH and cam FAI that can uniquely affect the biomechanics of each disorder. Accordingly, approaches to addressing each disorder should be unique.
