hip pathology

Flashcards covering the definition, aetiology, pathology, and radiological stages of osteonecrosis and Legg-Calvé-Perthes disease as described in the lecture.

Osteonecrosis (Avascular Necrosis)

The death of a segment of bone caused by the interruption of blood supply to the marrow, medullary bone, or cortex.

Aetiology of Osteonecrosis

The causes include spontaneous/idiopathic factors, trauma, haematological disorders, alcoholism, and steroid therapy.

Common Anatomical Sites of Osteonecrosis

Primarily the head of femur, body of talus, and scaphoid; also occurs in the body of the lunate and the head of the second metatarsal.

Articular Cartilage in Pathology

Areas at high risk of avascular necrosis often have a very large portion of their total surface covered with this tissue, which limits the space for blood vessels to enter.

Revascularisation Process

A very slow process where an attempt to restore blood flow extends inward from adjacent viable bone following the death of osteocytes.

Hyperaemia and X-ray Density

Increased blood flow in surrounding bone causes osteoporosis of living bone, making infarcted bone appear whiter or denser on an X-ray by comparison.

Sub-articular Collapse

A weakening that occurs as vessels approach a necrotic area and osteoclastic resorption of dead bone takes place, leading to an irregular surface and painful degenerative arthritis.

Juvenile Osteonecrosis

A group of paediatric diseases where growth ossification centres undergo degeneration, necrosis, or inactivity, followed by regeneration and deformity.

Legg-Calvé-Perthes Disease (LCPD)

Avascular necrosis of the femoral capital epiphysis occurring before the closure of the growth plate.

LCPD Incidence and Demographics

Occurs in $1\text{ of }1200$ children, primarily between $2$ and $13\text{ years}$ of age (peak $4$ to $9\text{ years}$), with a $5:1$ ratio of boys to girls and a $6\%$ family history association.

Transient Synovitis

Synovial inflammation and joint fluid lasting $1$ to $3\text{ weeks}$ in children $<10$ years; if symptoms progress rather than resolve, it may lead to avascular necrosis.

Avascular Stage of LCPD

The first stage lasting several months to a year where the ossification centre becomes necrotic; X-rays may remain normal despite the death of the femoral head.

Revascularisation Stage of LCPD

The second stage lasting $1$ to $4\text{ years}$ involving resorption of necrotic bone, replacement by immature bone cells, and remodeling of bone contour.

Remodelling/Repair Stage of LCPD

The third stage where immature bone cells are replaced by normal bone cells and the femoral head is reshaped throughout the growing years.

Deformity Stage in LCPD Pathology

The final stage where the femoral head is flatter and enlarged, the acetabulum is shallow, the femoral neck is shorter (coxa vara), and the greater trochanter is enlarged.

Apparent Joint Space Increase

An X-ray finding in the avascular stage where the bony head stops growing but the cartilage continues to be nourished by diffusion, making the space between bones appear larger.

Crescent Sign

A tangential line seen in radiology during the revascular stage caused by fractures in the subchondral region of dead bone trabeculae.

Coxa Vara

A deformity of the hip where the femoral neck is more acutely angled, often seen in the repair/remodelling stage of Legg-Calvé-Perthes disease.