ANATOMY & FUNCTION

The ankle is a joint which is formed by the tibia and fibula (bones above the ankle in the foreleg) and the talus (below the ankle joint). The ankle joint allows for the upwards (dorsiflexion) and downwards (plantarflexion) motion. The end of the shin bone (tibia) forms the inner bony prominence of the ankle called the medial malleolus. The outer bony prominence is called the lateral malleolus and is formed by the small outer bone in the foreleg called the fibula. Stability of the joint comes from several factors:

• the unique structural arrangement of the bones forming the joint
• the surrounding ligaments.

Joint instability may develop after damage occurs to one or more of the bones surrounding the joint. This type of damage is termed a fracture. The joint may also become unstable when the surrounding ligaments are damaged.

On the lateral (outside) of the ankle is a complex of three ligaments. These three ligaments provide stability by attaching the lateral malleolus to the bones below the ankle joint (talus and calcaneus). They are the:

• anterior talo-fibular ligament (goes from the talus to the fibula)
• calcaneo-fibular ligament (goes from the calcaneus to the fibula)
• posterior talo-fibular ligament (goes from the talus to the fibula). 
  • A joint is formed where the bones come together. (For more information on joints: WHAT IS A JOINT?) The bones are held together by tissue called ligaments. The ligaments allow for motion of the boned at the joint, but only within certain ranges of motion. Sprains occur when the ligaments are stretched more then normal. This results in a partial tear or complete tear of the ligament. This ligament damage results in the development of abnormal motion at the joint due to the loss of stability.

    The term sprain merely indicates that a ligament has been damaged. Sprains are divided into several groups depending on the severity of damage to the involved ligament.

    Grade I Sprain

    A Grade I (First Degree) sprain is the most common and requires the least amount of treatment and recovery. The ligaments connecting the ankle bones are often over-stretched, and damaged microscopically, but not actually torn. The ligament damage has occurred without any significant instability developing.

    Grade II Sprain

    A Grade II (Second Degree) injury is more severe and indicates that the ligament has been more significantly damaged, but there is no significant instability. The ligaments are often partially torn.

    Grade III Sprain

    A Grade III (Third Degree) sprain is the most severe. This indicates that the ligament has been significantly damaged, and that instability has resulted. A grade III injury means that the ligament has been torn.

    The lateral ligaments are the most commonly injured. On the lateral side, the ligaments are typically damaged in a direction that goes from the front to the back, with the most severe injury being in the front (anterior) and the least severe being in the back (posterior). Therefore, the most commonly damaged ligament is the anterior talo-fibular ligament and the least commonly damaged is the posterior talofibular ligament.

    The sprain occurs when the ankle is turned unexpectedly in any direction that is further than he ligaments are able to tolerate. Typically, the sprain occurs with running, jumping, sharp direction changes, or stepping on uneven ground. The risk factors for having an ankle sprain include, uneven ground, previous untreated ankle injuries, being overweight, or using poorly fitting or worn out shoes. 

    DIAGNOSIS 

    Diagnosis of the injury is determined by examination of the location of the bruising (ecchymosis), swelling, and tenderness. It is also necessary to perform stress testing of the ligaments to determine whether the ligament has been torn. Stress testing of the ligaments is done by pushing on the ankle and attempting to determine if there is any abnormal motion at the joint which would indicate that a ligament has been torn. In addition, x-rays are often performed to check for the possibility of a chipped bone or fracture.

    When performing a stress test of the ligaments, a posteriorly directed force is applied to the front of the tibia (shin bone). If the ankle ligaments are completely torn, the tibia will visibly shift backwards at the ankle joint. When the force is removed, the tibia will snap back into its proper position at the ankle joint. When this abnormal motion occurs, the anterior talo-fibular ligament (ATFL) has been torn. 

    Depending on the severity of the sprain, treatment may range from simply wearing a supportive brace, to using a walking cast, or even having the ankle operated on. The type of treatment depends on several factors including severity of injury, presence of associated injuries, the routine stresses that are placed upon the ankle, and the general medical condition of the injured patient. At some point,

    • Rest,
    • Ice,
    • Compression, and
    • Elevation

       

    (RICE) is used in the treatment program. As the healing progresses, the exercises that may be involved include range of motion exercises, strengthening exercises, and exercises developed to restore balance and agility.

    Each injury is different and the time to return to full activity depends upon the severity of the injury and the restoration of motion and strength. As a general rule, the minimum time required for satisfactory healing is 6 weeks.

    RESIDUAL ANKLE INSTABILITY

    Occasionally, when the ligaments heal, they are weaker or looser then prior to the injury. This results in an ankle that is more likely to be unstable and twist more easily. When this happens, PT often allows the adjacent muscles to strengthen and stabilize that joint. Sometimes, it is necessary to wear a brace when walking on uneven ground or during sports to support the ankle. Rarely, it is necessary to surgically reconstruct the ligaments. However, when it does become necessary to reconstruct the torn ligaments, the reconstruction may be done in several ways. One of the methods of reconstruction involves harvesting a portion of the peronus brevis tendon at the lateral aspect of the ankle, and then placing several drill holes around the bones of the ankle. The harvested tendon is then passed through the drill holes to reconstruct the damaged ligaments. Post operatively, a short leg cast is usually applied for approximately 6 weeks. Following this, physical therapy is initiated to rehabilitate the ankle.