Osteonecrosis (Avascular necrosis)

Avasclar necrosis (AVN) of bone is a family of conditions where bones in typical parts of the body may die. The most classic of this occurence is in the hip where blood supply is vulnerable but similar phenomenon occur in the talus, scaphoid, humeral head, femoral and tibial condyle. This is one of the most common causes of hip pain in the Asian community and is has been described to the indiscriminate use of steroid medication in traditional therapies. Nevertheless there are other common associations like alcohol intake (Figure 1), trauma, deep sea diving and certain metabolic diseases (very rare). Synonyms of the condition include aseptic necrosis and osteonecrosis.


Figure 1. This gentleman had bilateral hip pains. Xrays were normal (a). He had a significant history of heavy alcohol intake and and MRI was done (b) which confirmed the presence of osteonecrosis or avascular necrosis of both hips. The surgeon opted for the unusual practice of a pin placement which while theoretically achieving the same goal of core decompression (c) is somewhat unorthodox. This was subsequently removed but the pain persisted and the patient sought treatment for his ailment with us (second opinion).

Classification
The two common classifications are the Ficat-Arlet and ARCO classifications. The latter is easier to understand and related here:

 Stage   

 Description

 Treatment

0

 Hip at risk

 Observation

 I

Changes on MRI or bone scan but not on xray 

 Core decompression

 II

Changes on Xray 

 Core decompression 

 III

Collapse of the head

 Hip replacement

IV 

 Arthritis

 Hip replacement

Treatment 
Symptomatic treatment with pain killers and reduced weight bearing is probably the most suited to Stage 0 disease. In this stage by definition the other hip has avascular necrosis and this hip is "at risk" for developing AVN. The problem with this regime is one does not when to stop - how long does the patient remain off his feet? In Stage I and II disease core decompression is performed where the hip is drilled out from the side (Figure 2). This serves to 'reactivate' blood flow into the area by reducing the pressure in the canal. This understanding is probably crude and the truth is more akin to a remodeling process that extends into the head. Nevertheless the method has stood the test of time. Attempts at adding a strut graft into the centre of the defect have not improved results. Nevertheless the introduction of bone grafts carrying growth factors have recently been seen to improve the results of grafting alone. The most successful variants of these are to insert the patient's own fibula into the defect and hook up the blood vessel to a nearby artery or vein . This so called "vascularised fibula graft" has been shown to be highly successful but results in the patient's loss of a fibula in an uncertain fashion and has not been widely advocated. Hip replacements are done for Stage III and IV diseas and are covered elsewhere in this website (Figure 3).


Figure 2. We opted to perform a core decompression with growth factor therapy. The area of necrosis is guided by a pin and drilled out (a). The same channel is then used to burr out the dead tissue (b). Subsequently the space in the hip is packed with growth factors (demineralized bone matrix or stem cell carriers) and the channel packed with a bone transplant.

Results
Treatment of avascular necrosis has been relatively stagnant until the last few years. The Stage 0 lesion can remain stable indefinitely and can be difficult to advise on. Certainly offending agents if possible should be removed.Stage I and I disease usually yields a 70% success rate with core decompression alone. Recently the use of allografts with growth factor rich supplements have brought the success rate of core decompressions up to 80% and is the method of choice practiced at Limb Salvage and Revision Arthroplasty Surgery (Figure 3). Inserting a vascularised fibular graft is very successful and close to 90% success but results in loss of the patient's fibula.


Figure 3. The results of the procedure are very satisfactory in up to 80% of cases selected at the right time. It is critical to get the graft in the exact centre of the neck (a) for strength to allow efficient weight bearing (a). The procedure was unfortunately too late to save the other hip where a replacement had to be done (c).