Avascular
necrosis of the hip
Epidemiology
Pathophysiology
The head of the femur is one of the areas of the body most susceptible
to avascular necrosis. The underlying pathophysiology of the condition is not
known but it is believed that the blood supply to the femoral head is lost
either through thrombosis of the vessels entering the head or because of
interosseous hypertension. The marrow of the femoral head becomes replaced with
fat and the bone dies. Subsequently, there will be a zone of revascularisation
which will be incomplete if the avascular area is large. Finally, there is a
zone of reossification. During this period the joint is at risk of collapse.
Once collapse has occurred full recovery is not possible and secondary arthritis
sets in.
History
The patient may complain of sudden onset of pain in the hip or gradually
increasing joint pain.
A careful family history will be needed to exclude sickle cell and
thalassaemia. A social history should carefully cover alcohol intake, and a
history of having worked underground or under water using high pressure. This
exposure might have taken place some years before the onset of symptoms in the
joint.
Medical history should specifically cover treatment with steroids.
Examination
On examination there may be nothing to find, except for a painful
limitation of range of movement.
Investigation
Ultrasound may reveal a small effusion around the hip but X-rays are
normal unless the avascular necrosis has been caused by a fracture. A
radioisotope scan will show a dead area of the femoral head later surrounded by
a hyperaemic area of revascularisation. Magnetic resonance imaging (MRI) may
also show one or more avascular areas. If
Treatment
If the femoral head has not collapsed a ‘forage’ operation (where a
core of bone is removed from the femoral neck and femoral head through a window
in the lateral femoral cortex) can be used to decompress the femoral head. There
is no clear evidence that this operation makes any difference to the natural
history of avascular necrosis. If the avascular area is in the main
weight-bearing area of the femoral head a further option is to perform an
osteotomy. The head is rotated to bring a healthier part of the head into the
main weight-bearing area of the hip joint to prevent collapse.
Problems
Once the femoral head has collapsed osteoarthritis is inevitable, with
pronounced shortening as the hip collapses followed by stiffness as the joint
becomes incongruent and osteoarthritis sets in. The options then are an
arthrodesis or a hip replacement. Osteotomy is unlikely to help at this stage.
Avascular
necrosis
• Idiopathic in children = Perthes’ disease
• Complication of alcohol and steroids in adults
• Complication of sickle cell and thalassaemia in all ages
• Avoided by hemiarthroplasty following subcapital fracture in
the elderly
Pertrochanteric
fractured neck of femur
Epidemiology
Fractures through the trochanters of the femur are as common as
subcapital fractured neck of femur. They can occur in patients with
osteoarthritis of the hip and are caused by a trip or a fall on to the hip.
Unlike subcapital fractures these can occur in association with
arthritis of the hip. In the younger adult they can occur with high-velocity
trauma.
History
The patient complains of sudden severe onset of pain in the hip and is
unable to weight-bear.
Examination
On examination the leg is often short and internally rotated.
Treatment
The fracture is highly unstable (Fig. 23.20) and the patient cannot
mobilise until it has been stabilised. This fracture can be managed on traction
but it is very difficult to reduce the
The
patient is usually very elderly and this length of time in bed would destroy
their sense of independence and put them at risk for developing hypostatic
pneumonia, urinary tract infection and bed sores. The blood supply of the
femoral head is not affected by this fracture and therefore avascular necrosis
is not a problem. However, the fracture requires a very strong fixation because
of the enormous forces which go through the hip. The dynamic hip screw (DHS) is
made up of two parts which can slide in relation to each other but do not allow
binding (Fig. 23.20). The first part is a heavy-duty plate which is fixed to the
lateral cortex of the femur with cortical screws. The second part is a rod which
passes up through a slot in the plate into the femoral neck. Its threaded end
crosses the fracture line to engage and hold the femoral head. As the patient
weight-bears on the healing fracture the broken ends of the bone collapse into
each other and compress the fracture. The sliding-rod mechanism of the DHS
allows this to happen without allowing the hip to fall into varus. This prevents
the plate breaking at the fracture, or indeed the rod penetrating through into
the femoral head and acetabulum.
Some fractures are difficult to reduce and can result in poor placement
of the DHS. If this happens the fixation will fail, and the fracture collapses
into a painful nonunion which is difficult to reconstruct.
Pertrochanteric
fractured neck of femur
•
Common in the elderly
•
Does not cause avascular necrosis
• Nonoperative treatment is slow and difficult