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Microangiographic, histological and radiographic study of the femoral head following experimental hip dislocation in rabbits Duncan, Clive P.

Abstract

In 220 rabbits (65 mature and 155 immature) the effects of dislocation, persistant dislocation and reduction at varying intervals (immediately, 12, 24 and 48 hours after dislocation) of the left hip were studied by microangiographic, histological and radiographic examination. Dislocation of the left hip was induced manually under anaesthesia by a doraally applied force with the hip held adducted and internally rotated. Reduction was effected by ventral traction with the hip in the same position. The right hip was untouched and used as a control in all cases. In 135 animals, a tracer dye was infused into the abdominal aorta proximal to its bifurcation under standard conditions of temperature and pressure. This infusion was done at 10 minutes, and at 1, 3, 5, and 7 days after dislocation or reduction. The femoral heads were then processed and studied under stereomicroscopy. Histological and radiographic studies were made in the remaining 85 animals at intervals between 3 and 10 weeks after dislocation or reduction. In immature animals, severe dye perfusion defecit was observed in all cases within 10 minutes of dislocation. This was maximal in the antero-medial half of the femoral head. The defecit was increased at 24 hours and persisted until 5 days after dislocation. At the seventh day recovery had commenced. A profound perfusion defecit was also noted within 10 minutes of immediate reduction, however, recovery was observed at 24 hours and was almost complete at 5 - 7 days. The rate of recovery in those animals in which the dislocation was reduced at 12, 24 and 48 hours did not differ from that observed in unreduced animals. In adult animals, significant circulatory disturbance was infrequently observed after dislocation and persistant dislocation. Consequently, the beneficial effects of reduction, if any, were obscured. The epiphyseo-metaphyseal vascular anastomoses across the epiphyseo scar were filled with dye in all mature rabbits and seemed to act as a route of blood supply and drainage in adult animals.. Extensive histological avascular necrosis of the femoral head was observed in the majority of animals, but was significantly more common in immature rabbits. Less extensive and less common avascular necrosis was observed in immature animals after immediate reduction. However, reduction delayed to 12 hours or later was not associated with a lower incidence of bone death. Abnormal radiological findings were common and varied. Specific alteration in density and outline of the femoral head was however infrequently observed, but corelated well with the histological findings. Decreased biodensity was associated with inbalanced bone resorption and hyperaemia, and increased radiodensity with bone death and new bone apposition. It is concluded that traumatic dislocation causes embarassment and sequential changes in the circulation within the femoral head in rabbits. The perfusion defecit is more severe in immature animals as the intra-osseous epiphyseo-metaphyseal vessels minimize this circulatory disturbance in adult animals. Early reduction enhances early and complete recovery of blood supply in immature animals. Varying degrees of avascular necrosis of the femoral head occur in both adult and immature animals with and without reduction, but is more common and extensive in immature animals. Abnormal radiological features within the femoral head are infrequently observed up to ten weeks after dislocation but correlate well with the histological findings when present.

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