Although healing is seen histologically, the possibility of resolution of radiologically positive asymptomatic lesions is less clear, although there are occasional reports in the literature. Nevertheless, the treatment of juxta-articular (A) lesions should be based on the finding that DON often progresses through the stages outlined later. One interesting study of the long-term outcome in affected divers who cease hyperbaric exposure after diagnosis suggests a high likelihood of further progression of lesions, and it has been suggested that progress may be unrelated to further diving exposure10. The asymptomatic head, neck and shaft lesions require no active therapy.
Hyperbaric oxygen therapy has been used successfully to treat the early stages of avascular necrosis (Ficat stages 1 and 2 – see the next section), but it is not clear whether DON is likely to respond in the same way.
Surgical treatment of disabling aseptic osteonecrosis must be based on the aetiology and may therefore have a rational basis in DON that is absent in idiopathic disease. Conversely, most surgical experience is with idiopathic osteonecrosis of the femoral head – the site at which osteonecrosis produces the most devastating disability. It is not yet clear whether the same approach will be more or less successful following DON. The type of treatment is determined by the staging of the disease process (as described by Ficat11), the age of the patient and the joints involved.
STAGING (FROM FICAT11)
0 – Asymptomatic, pre-radiological (i.e. high index of suspicion confirmed by raised intramedullary pressure or positive scan).
1 – Symptomatic, pre-radiological.
2 – Symptomatic, radiological pre-destruction.
3 – Collapse of articular surface.
4 – Destruction of joint.
Core decompression has its advocates, but the value of the procedure is still questionable. If accepted, it is indicated for stage 0 to 2. The results are, as expected, better for the earliest stages.
Vascularized fibular graft procedure has been used for stage 0 to 2 disease, mainly that affecting the hip. One comparative study suggests that results are better with this procedure than with core decompression12.
When gross damage to the articular surfaces exists, reconstructive techniques offer the best chance of rehabilitation.
- Osteotomy of the femoral neck, either rotation or wedge, endeavours to move the weight-bearing axis away from a localized necrotic area.
- Arthrodesis is possible for a young patient, with destruction of one hip only.
- Arthroplasty is indicated for ‘end-stage’ joints especially if the patient is old or the disease is bilateral. Total joint replacement has proved useful in replacing severely affected hip and shoulder joints. The concern about this form of surgery is that the life of the prosthesis is unknown because it is used in a relatively young population with a long life expectancy.