Intracapsular hip pressure after femoral neck fracture

A consecutive series of 34 patients with femoral neck fractures was included in a prospective study aimed at evaluating preoperative variations in intracapsular pressure after changes in hip position, hip traction, and aspiration of hemarthrosis and their influence on the development of femoral head necrosis. Patients were observed for 7 years after surgery. Before aspiration, the mean intracapsular pressure in the antalgic physiologic position was 44.4 mm Hg. There were no differences between displaced and undisplaced fractures. The pressure was a maximum (mean value, 124.8 mm Hg) with the hip in extension and inward rotation, this pressure being greater than the blood systolic pressure in most cases. Hip traction of 3 kg in the antalgic physiologic position was found to be highly effective in preventing any bone flow tamponade effect in displaced and undisplaced femoral neck fractures: the mean intracapsular pressure decreased to 28.5 mm Hg. Aspiration of the hemarthrosis induced a significant decrease in intracapsular pressure only in cases with impaired vascularity of the femoral head as measured by scintigraphy using 99mTc labeled methyldiphosphonate. Aspiration of the hemarthrosis therefore is indicated only in the above cases, although it is less effective than hip traction in the antalgic position. There was no significant correlation between intracapsular pressure and the scintigraphy ratio. Avascular necrosis of the femoral head was detected in six cases. Among these, five patients had an intracapsular pressure below their diastolic blood pressure. This could indicate that vascular damage related to the fracture could be an important cause of bone necrosis despite that blood supply can be decreased by a tamponade effect.