Workup/Staging

Question 1

How soon after Sg can radiologic evidence of HO be detected?

Answer 1

Radiologic evidence of HO can be detected 2–6 wks after Sg as calcified structures with blurred contours on x-ray. Bone scans typically show increased uptake in the STs adjacent to the hip and can detect HO several days before it becomes apparent on plain film.

Question 2

What is the most common staging system used for HO?

Answer 2

The most common staging system used for HO was developed by Brooker et al.

Grade 1: bone islands in ST around hip

Grade 2: exophytes in pelvis or proximal end of femur with at least 1 cm b/t opposing bone surfaces

Grade 3: exophytes in pelvis or proximal end of femur with <1 cm b/t opposing bone surfaces

Grade 4: bony ankylosis b/t proximal femur and pelvis

Grades 3–4 are considered clinically relevant even if there is no pain or impaired mobility.