1. Radiographic Findings

2. AVASCULAR NECROSIS (AVN)
Osteonecrosis, aseptic (bone) necrosis, ischemic bone necrosis
Cellular death of bone components due to interruption of the blood supply
Bone structures collapse --> bone destruction, pain and loss of function
Affects bones with a single terminal blood supply
Head of the femur and proximal humerus

3. Principal Causes Acute trauma (Fx or dislocation) Steroid therapy
Alcoholism
Pancreatitis
Sickle Cell Anemia
Cushing’s disease
Collagen vascular disease (e.g. SLE)
Caisson disease
Gaucher’s disease
Radiation therapy

4. Pathophysiology Vascular occlusion Altered lipid metabolism
Intravascular coagulation
Healing process
Primary cell death
Mechanical stress
Vascular occlusion:interruption of the extraosseous blood supply due to direct trauma, nontraumatic stress, and stress fracture.
tackle from behind (may cause an anterior hip subluxatioN)
extreme abduction or external rotation (may result in an anterior dislocation)
Altered lipid metabolism:increased levels of serum lipids  lipid deposition in the femoral head  femoral hypertension & ischemia.
Intravascular coagulation: thrombosis, infection, malignancy, pregnancy
Healing process:Necrotic bone  process of repair [osteoclasts, osteoblasts, histiocytes, and vascular elements] Osteoblasts build new bone on top of the dead bone  thick scar  prevents revascularization of necrotic bone  resultant abnormal joint remodeling and joint dysfunction.
Primary cell death:Osteocyte death
Mechanical stress:increased weight bearing of the femoral head.

5. Clinical Findings Initial PE maybe unrevealing or asymptomatic
Tenderness around affected joint
Restricted and painful active and passive movements
Neurologic deficit
Joint deformity and swelling

6. Flattening of joint surface
Crescent Sign
Snowcapping
Areas of lucency
Flattening of joint surface
CRESENT SIGN
Earliest sign of AVN of femoral head
Thin radioluscent line beneath articular cortex
Best visualized in frog-leg position
SNOWCAPPING
Diffuse homogenous increase in density
Represents deposition of reparative bone
Seen without crescent sign or collapse
Most commonly seen in head of humerus
LUSCENT AREAS– site of resorption of necrotic marrow and trabecular.

7. Crescent Sign

8. Flattening of joint surface
Luscent areas

9. Flattening
Snowcapping
Luscent areas

11. AVN Classification (FICAT System)
Stage I
conventional radiograph is normal, but MRI or radionuclide imaging findings will confirm AVN
Stage II
cystic and sclerotic changes are seen on conventional radiographs
Stage III
crescent sign is seen
Stage IV
flattening of the femoral head, narrowing of the hip joint, severe joint destruction