Lateral Ankle Instability

Etiology

Lateral ligament instability can result from either of two means; functional or mechanical instability. Mechanical instability arises either via an acute injury or chronic repetitive stress resulting in attenuation and alteration of the mechanical structures of the ligaments. The most common mechanism of injury in lateral ankle sprain occurs with a plantar-flexory force on an inverted ankle as the body moves over the foot. The ATFL is the most commonly injured ligament followed by the CFL, and then the PTFL [1]. Ligaments often heal in an elongated position which can lead to plastic deformation, which further reduces the ability to provide restraint. Functional instability is the feeling of ankle instability or recurrent, symptomatic ankle sprains due to proprioceptive deficits. Lateral ankle instability can also be caused by hereditary ligamentous laxity that is associated with Ehlers-Danlos syndrome, Marfan’s syndrome and Turner’s syndrome.

Epidemiology

40% of all athletic injuries are ankle sprains, making ankle sprains the most commonly sustained injury during sporting events[2]. Over 50% of basketball injuries and almost 30% of soccer injuries can be attributed directly to ankle injuries[3]. Over 10% of the emergency room visits in the United States are due to ankle sprains with an incidence of 30,000 per day[4]. 75% of ankle injuries involve the lateral ankle with an equal distribution between male and females.  Some literature has reported a 25% higher rate of grade I sprains in females compared to males, and a higher predisposition to suffering future sprains once having sustained an ankle sprain [5][6][7][8].  90% of all ankle sprains involve the ATFL, while 50-75% of the time the CFL is engaged, and only 10% of the time is the PTFL involved[9][10][11][12]. 55-72% of patients who sustain a lateral ankle sprain suffer residual symptoms. In the USA the estimated incidence rate of ankle sprains in the general population presenting to emergency departments is 2.15 per 1,000 person- per year. The incidence of ankle sprains in the military has been reported to be up to 27-fold higher than in the general population. [13]

Pathophysiology

As previously stated, ankle sprains are a common injury, which can lead to ligament attenuation of the lateral ankle and can further propagate ankle instability.  An injury to the lateral ankle can lead to both functional and mechanical instability of the ankle. Lateral ankle instability can also be caused by hereditary ligamentous conditions such as Ehlers-Danlos syndrome, Marfan’s syndrome and Turner’s syndrome.

History and Physical

A thorough history can point practitioners in the right direction when evaluating a patient with ankle instability or pain. A history of recurrent or recent ankle sprains can raise a red flag to guide a physician for a more in-depth examination of the ankle and its stability. Patients will often report repeated episodes of the ankle “giving way” on uneven terrain or a feeling of looseness and may be especially mindful of specific activities in which they are aware they may have the potential for injuries. Pain itself can also be a complaint, though generally not the chief complaint.

Physical of examination of the foot and ankle when approaching ankle instability should always include assessment of alignment, as individual factors such as cavus or varus may predispose patient to recurrent instability. Hypermobility should also be a consideration when initially evaluating patients as laxity may predispose to further injury. The range of motion and strength are also crucial to a full examination, especially when compared to the contralateral extremity. Stress examinations including the talar tilt and anterior drawer test individually evaluate the lateral ankle ligaments. The Anterior drawer should be performed with the foot in 20 plantarflexion, and then compared to the contralateral extremity. A shift during the anterior drawer test of more than 8mm is considered pathological. The talar tilt examination assesses CFL integrity, and a value of greater than 10 degrees or more than 5 degrees compared to the contralateral side is considered pathological when viewed on a radiograph. Physiological talar tilt can range from 5 to 23 degrees.

Evaluation

Evaluation of lateral instability consists of the history, and physical described previously but also includes radiographs of the ankle to assess for syndesmosis widening, foot or ankle deformities which may predispose patients to instability. Stress radiographs such as with the anterior drawer test or talar tilt test are also essential to evaluate for structural abnormalities. Patients with mechanical instability will display radiological evidence, patients with functional instability may have a negative anterior drawer or talar tilt tests. MRI can be useful to evaluate the lateral ankle complex, and it can also identify concomitant pathologies such as talar dome osteochondral defects, peroneal tendon pathology and can be of assistance in surgical planning. Evaluation can consist of the staging of the injury to the lateral ankle, and there have been many classification descriptions over the years.

Anatomic

• Grade I - stretching of the lateral ligament complex
• Grade II - Partial tearing of one or several of the ligaments in the lateral ligament complex
• Grade III - Complete rupture of the lateral ligament complex.

Functional

• Grade I - the patient can fully bear weight and walk.
• Grade II - patient walks with a noticeable limp.
• Grade III - patient unable to walk

Stage I - ATFL involvement - microscopic tears

Stage II - ATFL involvement predominantly with CFL injury

Stage III - ATFL and CFL involvement with complete disruption of both ligaments and gross laxity noted upon examination.

Treatment / Management

Conservative treatment of lateral ankle instability consists of early functional rehabilitation; including rest, ice, elevation, compression, initial range of motion, progressive weight-bearing guided by symptom tolerance, and physical therapy. Even with proper functional rehabilitation 10 to 40% of patients will go on to develop chronic ankle instability following acute ankle sprains. Multiple studies have been published which show both the benefits of conservative therapy as well as surgical treatment for cases that do not adequately respond to conservative treatment.

There have been more than 70 different operative techniques described in the literature for correcting ankle instability, and can be divided into three main categories; anatomic, non-anatomic, and anatomic augmented tenodesis reconstruction.

Anatomic reconstruction consists of the Brostrom procedure, which includes direct repair of the ATFL in pants over vest fashion, this reduces any redundancy due to ligamentous laxity and can be used for completely torn ligaments. The Brostrom procedure has been modified and can include the use of the extensor retinaculum to increase the efficacy of the repair.

Non-anatomic reconstructions are aptly named because they do not repair or recreate the native lateral ligament complex. The use of the peroneus brevis tendon in the Evans and Christman-Snook procedure recreates stability to the lateral ankle.

Anatomic augmented tenodesis reconstructions typically combine a traditional Brostrom procedure with either autograft or allograft tissue and can be accomplished via suture anchors or interference screws.

Differential Diagnosis

Differential diagnosis of lateral ankle instability includes other conditions which can cause pain and weakness to the lateral ankle including:

• Hereditary ligamentous laxity disorders (Ehlers-Danlos syndrome, Marfan's syndrome, and Turner's syndrome)
• Acute ankle injury/instability
• Chronic ankle instability
• Fracture
• Sinus tarsi syndrome
• Osteochondral defects
• Peroneal tendinopathy
• Subtalar instability

Prognosis

Literature reveals that anatomic repairs faired with the best results, averaging 85-95% good to excellent postoperative results, however patients who had poor tissue quality, long-standing instability, or cavovarus foot type with ligamentous laxity failed to recover as well following repair.  Surgical repair was utilizing other than anatomic reconstruction, still showed promising results with about 88% of patients relating good to excellent results. Another article which employed high demand athletes with chronic lateral ankle instability reported a 94% return to previous sports after surgical repair[14].

Complications

Complications of surgery can include; continued pain, infection, failure of procedure (continued instability), nerve injury (3.8-9.7%)[15], wound healing complications (4%), stiffness, impingement from overtightening, amputation, and death.

Chronic lateral ankle instability without surgical intervention may lead to an unbalance ankle and subtalar joint thus resulting in early-onset of degenerative joint disease.