Contribution to the initial pathodynamics of hip luxation in young rats.

BACKGROUND: An anatomo-functional system has been described for the normal hip of some young mammals. This system includes the ligamentum teres, the transverse acetabular ligament, and the meniscoid of the hip.

PURPOSE: This report analyzes morphologic changes in the anatomo-functional system of young rats in an experimental model of hip luxation, and on the initial pathodynamics of luxation produced experimentally.

METHODS: Hyperextension of the left knee was induced in 58 young rats through fixation of the tibia and femur with Kirschner wire. Radiographic, macroscopic, and microscopic parameters were analyzed for 3 study periods (group 1: 4 d, group 2: 1 wk, group 3: 2 wk), and macroscopic parameters were studied in a late group (group 4: 6 wk).

RESULTS: Breaks in the Shenton line were observed from group 1 (subluxation) onward (luxation). Hypertrophy of the round and transverse acetabular ligaments of the acetabulum and meniscoid, progressive elevation of the meniscoid, and fibrosis of the fibrofatty (pulvinar) tissue occurred from group 1 onward. Radiographic and morphometric studies showed triplane innominate bone deformation (anterior bending, lateral tilt, and rotation of the ischium), which resulted in decreased joint space. As time progressed, the increase in these injuries was accompanied by morphologic changes in the acetabulum, posterosuperior displacement and reorientation of the acetabulum and extrusion of the femoral head.

CONCLUSIONS: Under the conditions of this study, the temporospatial morphologic changes in the acetabulum due to injury of the anatomo-functional system, and the triplane pelvic deformity in the initial period of the injury, produced femoral head extrusion of the acetabulum. RELEVANT SYMPTOMS: These disorders may help us understand the pathogenic and clinical phenomena that appear in early stages of hip luxation disease.