Prediction of femoral head avascular necrosis following neck fracture with Tc-99m-HDP pinhole bone scan after metallic fixation

Objectives To evaluate the predicting value of Tc-99m-hydroxydiphosphonate (HDP) pinhole bone scan in development of avascular necrosis in patients with femoral neck fracture after cannulated screw fixation.

Methods Pinhole bone scan of patients with metallically fixed femoral neck fracture from 2008 to 2011 were retrospectively reviewed. Initial pinhole bone scan was obtained within 2-3 weeks after surgery. Findings of initial pinhole bone scan were divided in to 3 groups. Group A included cold defect in affected femoral head, group B with no increased or decreased uptake and group C with increased uptake along the inserted screw. More than 6 months of follow-up with pinhole bone scan and clinico-radiological evidence for avascular necrosis (AVN) was analyzed.

Results 35 patients (mean age 54.5 ± 10.2, male 11, female 24) were included. 9 patients were in group 1, one in group 2 and 25 in group 3. During the follow-up, 10 patients were diagnosed as AVN. In group 1, 8 out of 9 patients (89%) and total hip arthroplasty was performed in 3 patients. In group 3, only 2 patients (0.09%) developed AVN.

Conclusions To predict AVN of femoral head followed by neck fracture, many imaging techniques with variable results were known. In this study, cold defect in early post-operative pinhole bone scan could predict AVN and increased uptake along screw inserted site could be a sign of good prognosis. More intensive care might be needed for the patients with cold defect in femoral head on pinhole bone scan. Further evaluation with larger population is necessary.