Page 100 - ASOP ROT Study Guide

5 . 1 . 1 Post traumatic avascular necrosis

Areas at risk following trauma include:- the femoral head, the proximal part of the scaphoid in the wrist and the
proximal part of the talus. In these situations the trauma can cut the blood supply. In femoral neck fractures the
damage to the capsular blood vessels puts the femoral head at risk and in the other two sites a distal blood
supply is severed from the proximal part of the bone.

5 . 1 . 2 Avascular necrosis of unknown cause

In other areas such as the lunate (one of the small carpal bones in the wrist) and the femoral head, avascular
necrosis occurs in less obvious circumstances. Avascular necrosis of the head of the femur is seen following
chronic alcohol abuse, high dose steroid therapy and in deep sea divers (Caisson's disease). The cause and
effect in these diverse situations remains a mystery. The patient presents with acute and often severe joint
pain which is made worse by movement and to some degree relieved by rest. With the passage of time
symptoms become indistinguishable from osteoarthritis and then it may be treated as such. Unfortunately
many patients with avascular necrosis are young.

5.2. Diagnosis

Diagnosis can be very difficult initially as there are no changes to be seen on an X-ray. Later the bone
appears dense, reflecting the absence of blood vessels.

Avascular necrosis may be reversed if a blood supply can be re-established naturally. However, in the
re-vascularizing phase the bone is very soft and prone to distort, with secondary arthritic changes. The
surgical restoration of bone blood supply is not possible at the moment.

5.3 Management

Treatment is non-specific. If possible the affected joint should be rested. Surgery is of no value in treating the
underlying condition and often the surgeon is left to salvage the situation with a joint replacement. As such
patients are often young this is, as explained above in the management of osteoarthritis, highly problematical.

6. CRYSTAL ARTHROPATHIES

In these conditions, crystals of the by-products of body metabolism are deposited in the joints, on the surface
of the articular cartilage and within the synovial fluid. This occurs either because of some abnormality of
metabolism resulting in excess production, or because the kidneys are failing to eliminate them.

They cause a chronic degenerative change in the joint and may be a cause of secondary arthritis. They also
cause acute inflammations which tend to settle spontaneously although it is common to reduce the painful
effects with drugs.

6 . 1 Gout

Gout is caused by urate crystal deposition. Urate is a waste product of cell metabolism. It becomes
deposited in circumstances such as dehydration (particularly post-surgery), and after chemotherapy for cancer.
Probably the commonest cause in the west is the injudicious over-use of diuretics, which are drugs used to treat
high blood pressure and mild heart failure.

It presents with a hot, tender and swollen joint. Any joint can be affected but it is seen commonly in the knee
and less commonly in the first metatarsophalangeal joint. It is important to exclude infection early as this
condition tends to mimic gout. If infection is missed it can do a lot of damage to the articular cartilage before
treatment is started.

Diagnosis is made by detecting the presence of a high level of uric acid in the blood. Normally this waste product
is passed out in the urine. A diagnosis is more accurately made by extracting joint fluid through a syringe and
testing for the presence of urate crystals.

Gout may be treated using anti-inflammatory drugs which, as well as reducing inflammation, also help the
kidneys eliminate urate.