Radiographic Findings

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

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

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.

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

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.

Crescent Sign

Flattening of joint surface Luscent areas

Flattening Snowcapping Luscent areas

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