Dynamics of Technetium-99m Methylenediphosphonate Imaging of the Femoral Head After Hip Fracture

Abstract

A prospective study of the development of necrosis of the femoral head was performed in 34 patients with fractures of the femoral neck. Technetium-99m MDP images of the hip regions were obtained immediately after nailing of the hip and at four, eight and 12 months. There was a good correlation between qualitative and numeric evaluation of isotope uptake in the femoral heads. Comparison of the activity level in the femoral head on the fracture side with that in the contralateral control site showed activity ratios to vary between < 1.0 for those heads showing a general reduction in activity on conventional images to > 1.4 with a mean of 2.0 for those showing increased activity. The initial postoperative images in 2/7 undislocated fractures showed a marked depression in femoral head activity on the fracture side; 13/21 dislocated fractures showed a similar defect suggesting a significant loss of bone remodeling. Normal Tc-99m activity in the femoral head (category 2) was observed in two fracture cases imaged within 24 hours of fracture, just prior to nailing. Repeat studies within one week of fracture and nailing demonstrated a marked depression in activity (category 0). Radiographic evidence of collapse later developed in both patients. The perfusion and blood pool images were useful for identifying femoral heads with deficient circulation. This investigation has demonstrated that the nailing procedure may threaten the vascular condition of the femoral head in hip fracture, that a dead head may be radiographically normal and clinically asymptomatic, and that the metabolic condition of the femoral head may be expressed in numeric terms suitable for statistical analysis.