Abstract
BACKGROUND: While pronounced angiogenesis has been observed in the synovial tissues of adult patients with developmental dysplasia of the hip (DDH), the vascular supply to the infantile hip joint capsule remains unclear. This study aimed to investigate early microvascular alterations in DDH using super-resolution ultrasound imaging (SRUS). METHODS: A neonatal rabbit model of DDH was established by maintaining extreme hip flexion with medical tape for 10 days. Serial ultrasound evaluations, including conventional and SRUS, were performed at 0, 1, 2, and 4 weeks after constraint removal. Morphometric parameters (acetabular cartilage thickness, alpha angle) and SRUS-derived microvascular density in the joint capsule were analyzed and correlated with radiographic indices and histopathological validation. RESULTS: At the 4-week endpoint, dysplastic hips exhibited significantly thicker lateral acetabular cartilage (1.7 ± 0.4 mm vs. 1.3 ± 0.1 mm in controls, p < 0.001) and elevated microvascular density in the joint capsule (43 ± 20 a.u. vs. 23 ± 16 a.u., p < 0.001). Both cartilage thickness and microvascular density increased progressively with DDH severity (mild to dislocated). Histopathological scores confirmed worsening pathology with severity and correlated with imaging findings. Immunohistochemistry revealed increased α-SMA (alpha-smooth muscle actin) expression, supporting the presence of enhanced angiogenesis. CONCLUSIONS: SRUS enables the noninvasive visualization and quantification of increased microvascular density in the joint capsule of dysplastic hips. These microvascular alterations are present early in DDH progression and correlate with disease severity, offering a potential imaging biomarker for early detection and mechanistic study.