X-ray examination and clinical manifestations of staging
(I) Stage I (ultrastructural variant stage of femoral head necrosis): X-ray film shows disorganized and broken structure of bone trabeculae in the bearing system of the femoral head, appearing hairy edge of the femoral head, with or without limited mild pain clinically.
(II) Stage II (sensitized stage of femoral head necrosis): X-ray film shows that small cystic change shadow will appear inside the femoral head, and the density around the cystic area is uneven. The bone trabecular structure is disturbed, sparse or blurred, and fine collapse may also appear, which is clinically accompanied by significant pain and mild limitation of movement.
(III) Stage III (necrosis and necrosis of femoral head): X-ray film shows morphological changes of femoral head, including incomplete, wormy or flattened edges, partial loss of trabecular structures, uneven bone density, widening or narrowing of the acetabulum and femoral head gap, and formation of superfluous bone, with pain, intermittent claudication, restricted joint movement, and shortening of the affected limb to different degrees.
(D) Stage IV (femoral head necrosis disabling stage): the morphology and structure of the femoral head are obviously changed, with large irregular collapse or flattening, and structural variation of bone trabeculae. The gap between the acetabulum and the femoral head disappears, etc. Clinical manifestations are pain, functional impairment, stiffness and inability to walk, dislocation or subluxation, and limitation of functional activities of the involved knee joint.
The clinical staging of femoral head necrosis is important for judging the prognosis and determining the treatment plan.
ARCO staging is the current common staging method
Stage 0: biopsy results consistent with necrosis, the rest of the examination is normal
Stage 1: Positive bone scan or/and MRI
A Magnetic resonance femoral head lesion extent <15%
B Femoral head lesion extent 15-30%
C Extent of femoral head lesion >30%
Stage 2: patchy femoral head with uneven density, sclerosis and cyst formation, no collapse on plain film and CT, positive MRI and bone scan, no change in acetabulum
A MRI femoral head lesion extent <15%
B MRI femoral head lesion range 15-30%
C Magnetic resonance femoral head lesion range >30%
Stage 3: Crescentic sign on frontal and lateral views
A Crescent length <15% Articular surface or collapse less than or <2-mm
B Crescent length – 15-30% of articular surface length or collapse 2-4mm
C Crescent length >30% of articular surface length or collapse >4-mm
Stage 4: Collapse and flattening of the articular surface, narrowing of the joint space, necrotic changes in the acetabulum, cystic changes, cysts and bone spurs
Grading.
1) Grade I (localized ischemic necrosis).
2) Grade II (massive ischemic necrosis).
3) Grade 3 (whole head ischemic necrosis).
In addition, according to the site of necrosis, it is divided into
(1) Medial necrosis: Necrosis occurs in the medial non-weight-bearing area of the femoral head.
(2) lateral necrosis: necrosis occurs in the lateral part of the femoral head and is the main cause of femoral head collapse.
(3) Central necrosis: necrosis occurs in the central part of the femoral head.
(4) Central parietal necrosis: necrosis occurs in the top central part of the femoral head.