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How are dysplastic hips different? A three-dimensional CT study
Harold van Bosse1, John H Wedge, Paul Babyn
1Shriners Hospitals for Children-Philadelphia, 3551 N Broad Street, Philadelphia, PA, 19140, USA, hvanbosse@shrinenet.org.
Insights
Developmentally dysplastic hips exhibit global deficiencies, not just single-dimension issues. Early detection and treatment are crucial for managing acetabular dysplasia and preventing joint degeneration.
Area of Science:
- Orthopedic surgery
- Developmental hip dysplasia research
- 3D imaging in orthopedics
Background:
- Acetabular dysplasia is a developmental condition affecting hip joint integrity.
- Surgical correction aims to prevent or postpone joint degeneration.
- The precise anatomical abnormalities in dysplastic hips remain debated.
Purpose of the Study:
- Characterize the typical size, shape, and orientation of nondysplastic hips.
- Identify differences in these variables in developmentally dysplastic hips.
- Investigate version differences and inter-variable relationships in dysplastic vs. nondysplastic acetabuli.
Main Methods:
- Retrospective analysis of 48 dysplastic and 55 nondysplastic hip 3D CT scans.
- Standardized anatomical orientation of 3D reconstructions for measurement.
- Measurement of dimensional and positional information from acetabular volumes.
Main Results:
- Dysplastic acetabuli are globally deficient, elongated, and shallower than nondysplastic hips.
- Acetabular openings are more vertical in females with dysplasia.
- Dysplastic hips show reduced volume and femoral head coverage, with specific version differences.
Conclusions:
- Developmentally dysplastic acetabuli are globally deficient, not just in one dimension.
- The subluxated femoral head articulates with an elongated, retroverted, and shallow acetabulum.
- Early detection and intervention are vital for effective management of acetabular dysplasia.
Background:
Surgical correction of acetabular dysplasia can postpone or prevent joint degeneration. The specific abnormalities that make up the dysplastic hip are controversial.
Questions/Purposes:
(1) What are the relative size, shape, and orientations of the typical nondysplastic hip? (2) How do these variables differ in the developmentally dysplastic hip? (3) Are there version differences between the acetabuli of dysplastic and nondysplastic hips? (4) Are there pairs of variables in which the change in one is always accompanied by a change in the other for both nondysplastic and dysplastic acetabuli?
Methods:
Of 117 consecutive three-dimensional (3-D) CT scans performed for hip dysplasia between March 1988 and October 1995, 48 met criteria of developmentally dysplastic hips by plain radiography. These were retrospectively compared with 55 pelvic 3-D CT scans culled from 81 consecutive scans performed for reasons other than hip dysplasia (ie, hip pain, trauma, infection) that did not affect the hip or pelvic landmarks. The 3-D reconstructions were orientated anatomically for standardization of the measurements to be compared. Representative 3-D volumes of the acetabular space were constructed from which we could measure anatomic positions and dimensional information. One author performed all image orientation and measurements.
Results:
Nondysplastic acetabuli are essentially hemispheric with height equal to width and twice the depth. The dysplastic acetabuli were elongated in females (52.4 ± 6.2 mm for dysplastic versus 46.5 ± 4.6 mm for nondysplastic (mean difference, 5.0; 95% confidence interval [CI], 1.9-8.0; p = 0.002) and shallower in both females (18.7 ± 4.9 mm for dysplastic versus 23.6 ± 4.0 mm for nondysplastic; mean difference, 6.5; 95% CI, 4.4-8.5; p < 0.0001) and males (21.1 ± 4.8 mm for dysplastic versus 25.0 ± 4.3 mm for nondysplastic, mean difference, 5.3; 95% CI, 2.6-8.1; p = 0.0002); width was similar to that of nondysplastic hips. Acetabular openings were slightly more vertical than nondysplastic hips in females (5°; 95% CI, 1.9-8.1; p = 0.002) but not in male subjects. The dysplastic acetabuli were smaller in volume (18% in females, p = 0.002, and 19% in males, p = 0.0012) and had less space occupied by the femoral head compared with nondysplastic hips (p < 0.0001 for females, p < 0.0001 for males). Dysplastic hip midacetabulum was 4° more anteverted in females (95% CI, 0.5-6.8; p = 0.022) but not for males (p = 0.538). The upper dysplastic acetabulum was more retroverted in females and males (10.2°; 95% CI, 5.5-15; p < 0.0001, and 7.0°; 95% CI, 0.6-13.4; p = 0.032, respectively). Acetabular volumes in nondysplastic and dysplastic hips were related to acetabular width but not to length.
Conclusions:
Developmentally dysplastic acetabuli are not deficient in merely a single dimension but are globally deficient. The subluxated femoral head lies in the elongated and retroverted superior acetabulum, which becomes progressively shallower as the acetabulum increases in length. Focally deficient anterior or posterior femoral head coverage is uncommon. Current procedures that redirect the acetabulum, no matter how technically successful, cannot fully compensate for the incongruence of a spherical femoral head within a shallow and elongated acetabulum unless corrected at an early age when acetabular remodeling is possible. Early detection and treatment of acetabular dysplasia should be emphasized.
Level Of Evidence:
Level III, prognostic study.
