Avascular Necrosis

Definition

AVN OF BONE/OSTEONECROSIS means “BONE DEATH”

Sudden Obstruction in arterial blood supply to a part of bone

O S T E O N E C R O S I S

Causes Traumatic: Fracture -Femur Neck, Talus, Scaphoid. Dislocations – hip Non-Traumatic : Caisson Disease Sickle Cell Disease Gaucher’s Disease Coagulation Disorders Cortisone Administration Organ /Bone transplantation Metal corrosion Alcoholism Exposure to xrays and radioactive substances

Common sites of predilection

-Femoral head

-Scaphoid(Preiser’s Disease)

-Talus

-Segmental fracture

-Others – capitellum , radial head , lateral femoral condyle

Pathogenesis

BONE ISCHAEMIA is due to

- Interruption of arterial inflow - Occlusion of Venous Outflow - Intravascular Blockage of arterioles & capillaries- Increase in marrow pressure

Repair process in a cancellous bone

• Proliferating capillaries and fibrous stroma penetrate marrow space of dead bone

• Phagocytes remove the marrow debris

• Osteoblasts lay down immature woven bone

• All these process further increases the radiodensity of necrotic bone

• Later osteoclastic resorption removes the woven bone as well as the old trabaeculae

• This is replaced by well organised lamellar bone

• This process of apposition of new bone on some surface and osteoclastic resorption on other surface is called CREEPING SUBSTITUTION

Repair process in cortical bone

• Excavation of haversian canal by osteoclastic resorption proceeds

• This enlarges the canal which multiple in number and uniform in size

• Later osteoblasts lay down concentric rings of new bone

Pathology• Microscopically 4 stages are recognised -Stage of marrow necrosis and cell death.

-Reactive vascularisation and infiltration.

-Distortion of shape by collapse and compression of trabeculae

-Subchondral collapse

Deformation of articular cartilage

Dysbaric osteonecrosis Caisson disease /Decompressionsickness/

Aeroembolism. Seen in deep sea divers , tunnel workers,

working in unpressurized aircrafts. Nitrogen gas bubbles liberated in a

concentration that cannot be readily absorbed by blood stream or excreted by lungs.

As a result gas bubbles accumulate in tissues causing local ischemia or intravascular occlusion

Corticosteroid induced AVN1. Fat embolism theory :

• Fat accumulates in liver in patients treated with steroid , and serum lipid concentration also increases

• It gives rise to fat embolism and AVN

2. Subchondral osteoporotic fracture :

Steroids induce protein catabolism Resulting in generalised osteoporosis

Produces subchondral fractures and aseptic necrosis

Clinical Features

Early stages: Pain-near joint

Later stages: Stiffness, Limitation of movements

Advanced stage: Fixed Deformities

Radiological features

• Initially necrotic bone appears radiodense

• Surrounding vascular bone shows relative osteoporosis

• In Early stages- Articular cartilage is not affected - so joint space is normal

• In later stages -Partial collapse,flattening of head,joint space narrowing,osteoarthotic changes

AVN of femoral head

• Occurs mainly due to femur neck fracture and hip dislocation

• Due to disruption of vascular channel in femoral neck

Vascular supply around femoral neck

Vascular disruption following #

Radiography of femur head - AVN

Treatment

Core Decompression.

Vasularised Fibular Graft.

Hemiarthroplasty .

Total hip arthroplasty.

Legg-calve perthe’s disease AVN of ossification centre of capital epiphysis of femoral

head. 3-12 age group. c/f: Limp, antalgic gait, limited motion HIP DEFORMITY xray: Early findings include Medial joint space widening irregularity of femoral head ossification cresent sign (represents a subchondral fracture)

Treatment: Aim- preserve the femoral head, acetabular

congruity, eliminate or reduce weight bearing.Nonoperative -observation, activity restriction, partial weight bearing, traction, and physical therapy. .Ambulation-Abduction Brace

Operative- children > 8 years of age.

-Femoral Osteotomyproximal femoral varus osteotomy

-Pelvic Osteotomy.

AVN of scaphoid

Vascular supply of scaphoid

Vascular disruption in # scaphoid

Radiography of scaphoid # AVN

AVN of talus

Vascular supply of talus

Radiography showing AVN

Other bones susceptible for AVN

Lateral femoral condyle Capitellum

The goal in treating avascular necrosis

Is to improve the patient's use of the affected joint,

Stop further damage to the bone and

Ensure bone and joint survival.

• Various methods for delaying disease progression• Non surgical –

• Bisphosphonate• Anticoagulants• Vasodilators• Biophysical modalities

• Surgical – • Core decompression• Vascularised bone graft/muscle pedicle graft

Usually arthroplasty is awaited without any big surgical intervention