Bone scintigraphy as a prognostic indicator for bone collapse in the early phases of femoral head osteonecrosis.

Objective: Destructive and reconstructive processes at the reactive interface in femoral head osteonecrosis (FHO) are not well defined or predictable. The objectives of our study were to analyze scintigraphic characteristics of the reactive interface in the early stages of FHO and to assess the prognostic value of the reactive interface on scintigraphy (SC).

Methods: Thirty-six hips in 27 patients (21 men, 6 women; mean age 41 years, range 20 64 years) with a final diagnosis of radiographic stage 1 (4 hips) or stage 2 FHO (32 hips) were evaluated by planar and pinhole SC. Tracer uptake at the reactive interface on pinhole SC was assessed visually. Three categories were formed: normal, moderately increased, and highly increased activities. The time to head collapse was observed.

Results: Tracer uptake at the reactive interface was more frequently increased in hips with stage 2 of the disease than in those with stage 1. In hips with the same stage of the disease, different activities were detected [stage 1 FHO: moderately increased in 1 of 4 (25%) and highly increased in 1 of 4 (25%0) hips; stage 2 FHO: moderately increased in 8 of 32 hips (25%) and highly increased in 20 of 32 (631%/) hips]. Femoral heads with highly increased activity at the reactive interface collapsed more frequently and earlier: 13/15 conservatively treated hips in stage 2 collapsed in 1-6 months, whereas no hips with normal uptake at the reactive interface collapsed in 12 months follow-up and only one of six hips with moderately increased activity collapsed after 11.5 months (P < 0.05).

Conclusion: Our results indicate that the tracer uptake at the reactive interface can be different in the same stage of FHO. High tracer uptake at the reactive interface in the early phases of FHO seems to be a bad prognostic sign for femoral head collapse.