A Guide To Addressing Lateral Ankle Instability
Given the common nature of lateral ankle sprains and the development of chronic ankle instability in some of these patients, these authors offer key diagnostic tips, share their thoughts on conservative modalities and review the literature on surgical options.
Ankle sprains are reportedly the most common musculoskeletal injury in the United States. Approximately 30,000 occur each day and account for 40 percent of sports medicine injuries.1,2 Researchers have estimated that 85 percent of ankle sprains are lateral ligamentous injuries, 10 percent are tibiofibular syndesmotic injuries and 5 percent are medial deltoid ligament injuries.3
The majority of these injuries heal uneventfully with traditional methods of conservative treatment such as temporary immobilization, rest, ice, compression, elevation and either home or formal physical therapy exercises. However, some patients develop recurrent sprains or chronic ankle instability.4 When it comes to the patient with an unstable ankle, one would employ conservative treatment modalities first. However, if the condition persists, there are numerous surgical options ranging from open or arthroscopic repair of the ligamentous complex to secondary repair utilizing tendon grafts or tissue substitutes.5 Regardless of which treatment modality one ultimately employs, excellent outcomes in stability and function can occur when treating chronic lateral ankle instability.
Salient Pointers On Mechanical And Functional Instability
Lateral ankle instability, whether chronic or acute, can be defined as mechanical or functional.
Mechanical instability is excessive motion beyond normal physiologic ranges.6 One can observe this either clinically by performing the anterior drawer test and/or radiographically using stress inversion and anterior drawer techniques. This abnormal motion is frequently present following an acute injury but typically resolves after up to 12 weeks of conservative care. Chronic mechanical instability may arise from a singular incident but it typically follows a pattern of repeated injury.
Functional instability is a chronic disorder defined as a subjective complaint of the ankle “giving way” without any clinical or radiographic findings of instability. This represents a loss of neuromuscular control. This has typically been regarded as a loss of proprioceptive input secondary to ligamentous injury. (See “A Pertinent Overview Of Anatomical Insights” on page 54.)
However, the location of the end proprioceptive organs is a subject of debate. While there is no debate that numerous nerve fibers are in the mechanoreceptors of the joint capsule and ligaments, recent studies have demonstrated that proprioceptive input arises from the skin and muscle, and may not depend on the capsular or ligamentous fibers. The afferent signals from proprioceptors, especially pressure receptors on the plantar foot, trigger a peripheral reflex and muscle activation, specifically the peroneal muscles, following an unexpected inversion movement at the ankle joint. The peroneal musculature provides the “dynamic defense system,” a strong contraction triggered by the proprioceptive reflex arc.
The typical position of the foot at injury, plantarflexed and inverted, prepares the foot to be supported by this dynamic defense system by preactivating the peroneals prior to ground contact. This increases segmental reflex activity and stretch velocity of these muscles. Research has demonstrated that braces and tape shorten the peroneal reaction time. Also bear in mind that the peroneal tendons provide five times greater resistance to inversion to protect the ankle than any tape, brace or shoe.