Acute Ankle Sprain, Chronic Ankle Instability, and Subtalar Laxity

Gregory C. Berlet

G. Alexander Simpson

ACUTE ANKLE SPRAINS AND CHRONIC ANKLE INSTABILITY

PATHOGENESIS

Ankle sprains are the most common sports-associated injury, accounting for as much as 40% of all athletic injuries. It has been estimated that ankle sprains account for up to 10% of all visits to the emergency department and have an incidence of up to one inversion injury of the ankle per 30,000 people each day and 2 million per year.

Epidemiology

Sprains of the ankle occur in many sports. The incidence of ankle injuries appears to be equal among males and females when compared within specific sporting activities. The peak ages of injury range between 10 and 19 years. They account for 45% of all basketball injuries and 31% of soccer injuries. In football, 10% to 15% of all time lost to injuries is attributable to ankle injuries. One-third of all military recruits sustain an inversion ankle injury that requires medical care during a 4-year tenure.

Long-term sequelae from lateral ankle sprains have been estimated to occur in up to 60% of patients. The grade of acute ankle sprains does not correlate well with chronic symptoms. Interestingly, the factor most predictive of residual symptoms, 6 months following an ankle injury, was a syndesmosis sprain and not mechanical instability. The most common complaints in patients with chronic ankle instability are swelling, giving way, frank instability, and pain.

Anatomy

The lateral ankle is supported by both static and dynamic restraints. The static restraints are provided by the bony configuration of the ankle and the ligaments. The dynamic restraints are the peroneal tendons—longus and brevis. The shape of the joint contributes about 30% of the resistance to rotational forces about the ankle, whereas the soft tissues provide the other 70%.

The configuration of the talus, with its flared anterior half, provides a bony restraint to lateral motion when the talus is engaged in the mortise in dorsiflexion. In plantarflexion, the narrowest surface of the talus is in the mortise, rendering less bony stability and an increased risk to inversion injury.

The lateral collateral ligaments of the ankle include (Fig. 12.1) the following:

Anterior talofibular ligament (ATFL) from the anterior border of the lateral malleolus to the lateral talar body
Calcaneofibular ligament (CFL) from the anterior tip of the lateral malleolus to the lateral posterior calcaneus
Posterior talofibular ligament (PTFL)

In neutral position, the ATFL runs parallel to the axis of the foot, whereas in plantarflexion, it is vertical and functions as a collateral ligament. The CFL is taut in dorsiflexion. The CFL works in concert with the ATFL and is rarely injured alone. The ATFL is the primary restraint to inversion throughout ankle plantarflexion and dorsiflexion.

Figure 12.1 Lateral aspect of the ankle. The anterior half of the peroneus brevis tendon is harvested. The superior peroneal retinaculum is preserved.

At the lateral malleolus, the peroneal tendons run through a fibro-osseous tunnel under the superior peroneal retinaculum, and distally they pass deep to the inferior peroneal retinaculum. The superior peroneal retinaculum and CFL run parallel. Anteriorly, the peroneal tendons are stabilized by the posterior surface of the distal fibula in the retromalleolar sulcus. The peroneus brevis inserts on the base of the fifth metatarsal, and the peroneus longus courses under the cuboid to insert on the base of the first metatarsal and medial cuneiform. The peroneals act primarily as evertors, with the peroneus brevis being the stronger of the two. The peroneal muscles work dynamically to stabilize both the ankle and the subtalar joint.

Classification

A classification scheme for ankle sprains is given in Table 12.1. Chronic ankle instability has been estimated to occur in up to 40% of patients with acute ankle sprains with two types of instability: mechanical and functional (Box 12.1).

TABLE 12.1 CLASSIFICATION SCHEME FOR ANKLE SPRAINS

Grade	Description
I	Mild ligamentous stretch, minimal swelling and tenderness, no instability, little functional loss
II	Partial tears, increased swelling and tenderness, mild to moderate instability
III	Complete rupture of the ATFL with variable injury of CFL with severe swelling and tenderness, loss of function, significant instability
ATFL, anterior talofibular ligament.

BOX 12.1 TYPES OF ANKLE INSTABILITY

Functional Instability

Subjective giving way
Motion beyond voluntary control but not necessarily exceeding the physiologic range of motion
Peroneal muscle weakness
Decreased peroneal reaction time
Subtalar instability
Proprioceptive defects
Poor balance
Physical therapy is mainstay of treatment

Mechanical Instability

Motion beyond the normal physiologic limits
Excessive anterolateral laxity
Physical therapy program tried
Persistent mechanical lateral ankle instability is an indication for surgical stabilization of the ankle

DIAGNOSIS

History and Physical Examination

The physical examination is used to confirm the working diagnosis and to rule out associated injuries.
Patients with chronic ankle instability typically present with pain, instability, or a combination of pain and instability.
Patients will typically provide a history of severe inversion injury or a history of multiple ankle sprains.
A key feature of the history is whether pain is present in the intervals between ankle sprains.
- If pain is present in the intervals between sprains, a secondary diagnosis, in addition to ligamentous instability, should be entertained (Table 12.2).

Clinical Features

A complete physical examination of the ankle includes the following:
- Examination of the joint above (knee) and below (subtalar)
- Assessment of lower extremity alignment
- Ankle range of motion
- Eliciting the point of maximal tenderness
- Anterior drawer and varus stress test
- Assessing for peroneal pathology
- Assessment of ankle proprioception
The assessment of point tenderness includes a systematic examination of the bony and soft-tissue anatomy of the foot and ankle with palpation of the following:
- ATFL
- PTFL
- CFL
- Syndesmosis
- Calcaneocuboid joint
- Posterior tibial and peroneal tendons
- The base and shaft of the fifth metatarsal
- Medial and lateral malleoli
Lower extremity alignment should be assessed with the patient both weight bearing and seated.
Varus hindfoot alignment should be assessed, as it predisposes the ankle to inversion injury.
Tarsal coalitions may present as recurrent sprained ankles.
- A patient with a tarsal coalition will most commonly have hindfoot valgus with a variable but decreased amount of subtalar motion.
- Hindfoot malalignment needs to be assessed for flexibility.
- The hindfoot malalignment may need to be corrected at the time of ligamentous reconstruction.
- The functional range of motion is 10° of dorsiflexion to 25° of plantarflexion.
Subtalar motion is rotation around an oblique axis running from the medial side of the talar neck to the posterolateral aspect of the calcaneus.
- Total subtalar motion is around 20°, but is difficult to accurately measure clinically.
- Subtalar motion is often referred to as a percentage of the contralateral limb.
The anterior drawer test is designed to test the competency of the ATFL.
- The test is performed with the patient sitting and the knee flexed at 90°.
- The tibia is stabilized and an attempt is made to draw the talus forward.
- With intact medial structures and incompetent lateral ligaments, the displacement is rotatory.
- More anterior displacement of the talus relative to the tibia on the injured side compared with the contralateral side or excessive displacement signifies a positive test.
- A positive anterior drawer test has been described to be translation of 5 mm more than on the contralateral side or an absolute value of 9 to 10 mm.
- A firm end point on stressing is less likely to indicate instability of the ATFL.
- A positive test is significant only when it correlates with symptoms because only one-half of patients with a positive anterior drawer test have symptomatic instability.
Peroneal tendon assessment includes strength of eversion, stability of the tendons behind the fibula, and tenderness along the course of the tendons.
- Patients with chronic tendon subluxation may describe snapping and discomfort with repeated episodes of giving way in the ankle.
- The best provocative test for subluxation or dislocation of the tendons is active eversion of the foot with ankle dorsiflexion against resistance.
- Peroneal eversion strength is considered adequate if the examiner is unable to overcome the peroneals with a maximal eversion effort.
- Weakness should mandate a search for peroneal pathology before a diagnosis of deconditioned peroneal muscles is made.
Proprioceptive defects may present as giving way.
- The mechanism of nerve injury is traction with damage occurring after as little as 6% nerve elongation.
- Severe (grade III) ankle sprains have been associated with more than 80% injury rate to the tibial and peroneal nerves.
- Proprioception can be assessed with a modified Romberg test by having the patient stand first on the uninjured limb and then on the injured limb with eyes open and then closed.
- Stabilometry is an objective means to measure postural equilibrium and has been shown to correlate with functional instability.

TABLE 12.2 LESIONS TO CONSIDER IN PATIENTS WITH CHRONIC SYMPTOMS FOLLOWING ANKLE INSTABILITY

Type	Characteristics
Bone	Anterior process of the calcaneus fracture Lateral and posterior talar process fracture Malleoli fracture Base of fifth metatarsal fracture Tibiotalar bony impingement Osseous and fibrous tarsal coalition
Cartilage	Osteochondral lesions (i.e., OCD) of the talus and tibia
Ligamentous	Functional lateral ligamentous instability Mechanical lateral ligamentous instability Subtalar instability Syndesmosis injury
Neural	Neurapraxia of the superficial peroneal nerve
	Neurapraxia of the sural nerve
Tendinous	Os peroneum syndrome
	Tear of the peroneus longus at the peroneal tubercle
	Peroneal brevis tear
	Peroneal instability at the superior peroneal retinaculum
Soft tissue	Sinus tarsi syndrome
	Anterolateral ankle soft-tissue impingement