Assessing ankle sprains

Some ankle sprains can lead to future arthritis and disability if not identified early and managed appropriately.

Dr Todd Gothelf
MD (USA), FRACS, FAAOS,  ABOS
Orthopaedic surgeon, Orthosports, Sydney
www.orthosports.com.au

Ankle sprains are among the most common injuries in sport and most can be treated non-operatively.

The correct rehabilitation of the majority of ankle sprains can lead to restoration of full function and return to sport can be achieved in 90% of patients within six weeks.

Some ankle sprains are not so forgiving. These can result in gross instability of the ankle, and if not treated urgently with surgery may lead to progressive arthritis and disability.

Last month, Gary Rohan, the promising AFL Swans rookie, sustained a horrific season-ending ankle injury (see the video at http://www.youtube.com/watch?v=f-9XssTeOa8).

A basic knowledge of the different types of ankle sprains is essential. This enables the physician to be able to identify those ankle injuries that require urgent surgical treatment, and those that can be conservatively treated initially with physiotherapy.

Types of ankle sprains
There are generally two types of ankle sprains. The low ankle sprain is the more common type and occurs when the ankle inverts, or turns inward. The anterior talo­fibular ligament (ATFL) and calcaneofib­ular ligament (CFL) are either partially or fully torn.

Regardless of the severity of injury to these ligaments, non-operative treatment usually results in stability of the ankle and return to sports in six weeks. Physiotherapy is recommended to encourage and restore function and to help prevent re-injury.

The high ankle sprain occurs with either a severe inversion, eversion or external rotation injury, i.e. when the ankle turns outward. Multiple ligaments are usually involved, including the medial deltoid ligament, and syndesmosis ligaments. These ligaments stabilise the tibia and fibula around the talus.

When these ligaments rupture, the fibula separates from the tibia and the box containing the talus is widened. As little as 1mm of lateral displacement of the fibula has been shown to reduce the available tibiotalar contact area in weight bearing by 42%. A failure to recognise this instability can result in chronic disability and early arthrosis of the ankle.

Syndesmosis sprain, diagnosed at arthroscopy. Fixation across the syndesmosis to stabilise the joint. Note the medial clear space is not wide.

History and examination
The medical history and physical examination will give clues that raise suspicion of a high ankle sprain. The patient may remember that the ankle twisted outward instead of inward. An inability to weight bear is generally more common with a high ankle sprain.

There are specific signs during physical examination that demonstrate a high ankle sprain. Tenderness when palpating the deltoid ligament and syndesmosis ligaments indicates injury to these structures. Other tests include:

The squeeze test: The tibia and fibula are compressed together above the ankle joint (away from the injury); reproduction of pain at the syndesmosis indicates a high ankle sprain.

The external rotation stress test: The leg is stabilised and the foot is forced into external rotation, stressing the deltoid and syndesmosis; reproduction of pain indicates injury to these ligaments.

Once a high ankle sprain is diagnosed, it is important to grade the injury. A high ankle sprain is classified into three grades, based on stability.

Grade I is a stable sprain, i.e. the ligaments are injured but the bones remain anatomically located. Grade III is grossly unstable, where widening is evident on a plain radiograph. Grade II sprains will have a normal x-ray but are unstable under stress. An urgent MRI will help to demonstrate the grade of syndesmosis injury.

A weight bearing radiograph will stress the syndesmosis and can demonstrate widening. Arthroscopic evaluation may be necessary to demonstrate instability of the syndesmosis.

Treatment of high ankle sprains
Treatment of a high ankle sprain varies based on the grade of injury. Grade I injuries can be treated non-operatively. A protective walking boot is used to allow weight bearing as tolerated. These patients must be warned of their lengthy recovery.

Treatment for grade II injuries is controversial and varies depending on the patient’s health and activity level. If the MRI demonstrates instability, I prefer arthroscopic evaluation for young active patients and rigid stabilisation if instability is detected.

Grade III injuries always require surgical fixation to restore the anatomy and prevent the development of arthritis.

KEY POINTS

• Low ankle sprains are more common, involve the ATFL and CFL ligaments, and are well treated with non-operative management. Physiotherapy can result in rapid restoration of function and return to sport.
• The high ankle sprain involves injury to the syndesmosis ligaments and, if missed, can result in chronic disability and early ankle arthritis.
• If suspicious of a high ankle sprain, an MRI and urgent referral to an orthopaedic surgeon is essential to determine proper treatment.