Osteonecrosis (aseptic necrosis) of the ankle occurs due to temporary or permanent loss of blood supply to the ankle area. As a result, the bone becomes dead and collapses. Ankle osteonecrosis often leads to destruction of the cartilage, resulting in arthritis and pain. In the case of the ankle, three joints can be affected: the ankle, the ankle joint, the ankle socket and the subtalar joint.
Ankle osteonecrosis is difficult to diagnose and treat because of the anatomical position of the ankle and its precarious blood supply. The incidence of ankle osteonecrosis is increasing as the incidence of high-energy injuries increases. Ankle injuries are caused by high-energy injuries such as falls from height and traffic accidents. The use of highly sophisticated imaging techniques has led to an increase in the number of patients diagnosed with early injury.
Ankle osteonecrosis has three main causes. Approximately 75% of patients have a history of neck or ankle body fracture. The incidence of osteonecrosis after an ankle neck fracture increases the greater the initial misalignment of the fracture. 15% of patients suffer from a comorbidity or have a history of steroid use. Other causes of the disease are sickle cell anaemia, chronic renal failure, haemophilia, hyperuricaemia or lymphoma.
Pain is the most common symptom of ankle osteonecrosis and is strongly associated with loss of joint integrity. Prior to the collapse of the articular surface, the patient may be asymptomatic. With subchondral osteonecrosis, subchondral collapse may occur due to lack of structural support, resulting in a subchondral fracture, which can cause pain as well as mechanical symptoms.
Although MRI and bone scintigraphy are useful for early detection of ankle osteonecrosis, evaluation should begin with plain radiographs. Early sclerotic changes, cysts and hypochondrium collapse can be seen on plain radiographs. Hawkins’ sign (a radiolucent band in the ankle dome) can provide evidence of revascularisation and is considered to be a reliable early indicator of vascular viability. MRI is considered a key diagnostic tool in the early stages of the disease. It is used to diagnose and quantify the extent of osteonecrosis. Radioactive technetium scintigraphy is also useful for the diagnosis of ankle osteonecrosis in early stages. It is usually performed 6 to 12 weeks after internal osseointegration of the ankle fracture and shows reduced uptake in the ankle body.
Treatment options for ankle osteonecrosis include conservative and surgical methods. Conservative treatment includes the use of orthotics and guardianship. Surgical treatment includes core decompression, implantation of vascularized grafts, arthroplasty and ankle arthrodesis.