ANKLE INSTABILITY

ANKLE INSTABILITY CONDITION

Currently, there is great heterogeneity regarding the exact definition of CAI (chronic ankle instability).  In this review, CAI will be defined as recurrent ankle instability episodes occurring for a minimum of 1 year after an initial injury.  CAI has been traditionally classified as either mechanical or functional instability.  Mechanical instability may occur as a result of adverse anatomical changes such as ligamentous laxity and impaired arthrokinematics.  Functional instability may be a result of adverse neuromuscular changes such as impaired proprioception and neuromuscular control.  Functional instability has also been described as persistent symptoms without pathological laxity on examination.  However, it is now understood that mechanical and functional instability can exist at the same time, together. 

Most patients with CAI are initially treated conservatively via a rehabilitation program. However, those who do not respond favorably to conservative measures are candidates for surgical intervention. 

The lateral ligaments of the ankle include the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL).  The ATFL is contiguous with the joint capsule and has a variable number of bands.  In a cadaveric study of the human lateral ankle ligaments, the authors found that 50% (7 of 14) of the specimens had a single-banded ATFL, with the remaining having 2 bands.  A single-banded ATFL’s origin is located on the fibula’s anterior margin approximately 13.8 mm from the lateral malleolus’s inferior tip.  The ATFL inserts just anterior to the lateral articular surface of the talus.  The CFL’s origin is approximately 5.3 mm anterior to the lateral malleolus’s inferior tip.  The CFL crosses both the subtalar and talocrural joint and lies underneath the peroneal tendons. The CFL courses posteroinferiorly to insert onto the lateral aspect of the calcaneal body.  The PTFL’s origin is located approximately 4.8 mm superior to the lateral malleolus’s inferior tip on the medial aspect of the lateral malleolus, and its fibers spread onto the posterolateral aspect of the talus. 

Ankle stability is conferred by passive ligamentous restraints, articular surface congruity, and active musculotendinous units.  The ATFL, CFL, and PTFL provide static restraint to the lateral aspect of the ankle. The ATFL is taut in plantarflexion and prevents anterior talar displacement and excessive plantarflexion.  Following an inversion injury of a plantarflexed foot, the ATFL is at risk of rupture.  It is also the weakest of the 3 ligaments. In a biomechanical study on the human ankle ligaments, the ATFL exhibited the lowest load to failure (138.9 N) compared to the CFL (345.7 N) and the PTFL (261.2 N).  In contrast, the CFL is taut in dorsiflexion; it prevents excessive subtalar and talocrural joint supination, excessive hindfoot inversion and internal rotation, and assists with subtalar joint stability.  The PTFL is also tight in dorsiflexion; however, it helps prevent excessive ankle internal rotation and inversion.  The PTFL is rarely affected, and it usually ruptures only after severe injuries such as ankle dislocation. 

The inferior extensor retinaculum (IER) is an important secondary static stabilizer. It is composed of several bands (lateral, intermediate, and medial) and its characteristic shape secures the peroneus tertius and extensor digitorum longus tendon.  Like the CFL, the IER’s lateral band stabilizes the subtalar joint. 

In contrast to the static stabilizers, the musculotendinous units provide stability via muscular contractions.  The peroneal muscles are important active stabilizers of the lateral ankle. During a sprain, the peroneal muscles serve as a major line of defense to counteract the excessive inversion force on the ankle.  A delayed peroneal reaction time is associated with CAI. There is some evidence that the ankle’s sensory fibers and mechanoreceptors are also damaged during a sprain.  This can potentially compromise the ankle’s proprioceptive reflex mechanism and lead to a disruption of peroneal reaction time. 

Associated occurring disorders include bony and soft tissue ankle impingement, osteochondral lesions of talus (OLT), loose bodies, peroneal tenosynovitis, and peroneus brevis tears.  It is suggested that certain disorders predict unsatisfactory outcomes following surgery.  However, a more recent retrospective case series (Level IV) revealed that the reoperation rate was lower in patients with peroneal pathology compared with others (8.7% vs 27.5%, P = .032) which was attributed to a more comprehensive initial surgery.  The senior authors routinely perform ankle arthroscopy at the time of ligamentous stabilization because of the high rate of intra-articular lesions in this patient population, including OTLs and soft-tissue or bony impingement.

Another condition commonly associated with CAI is known as subtalar joint instability (STJI) which occurs in 10% to 30% of patients who have CAI.  The subtalar joint has an extensive amount of ligamentous support from the interosseous talocalcaneal ligament, cervical ligament, deltoid ligament’s tibiocalcaneal fascicle, CFL, and the lateral root of the IER.  Although an ATFL and CFL injury primarily compromises the stability of the talocrural joint, ^a CFL injury can also present as STJI.  STJI and CAI present very similarly where patients complain of their ankle “giving way” in the setting of recurrent sprains. 

Traditionally, stress radiography has been used to delineate CAI from STJI by objectively evaluating both the talocrural and talocalcaneal joints.  The Broden projection is a popular subtalar stress view and a nonparallelism between the talus and calcaneus is suggestive of STJI.  However, its utility has since been questioned because it only evaluates the posterior facet of the subtalar joint.  Thus, little is known about effective diagnostic methods to clinically differentiate STJI from CAI.

A potential sequela of CAI is osteoarthritis and hindfoot varus or valgus malalignment. In a case series (Level IV) evaluating posttraumatic ankle osteoarthritis, 13% were attributed to a ligamentous lesion, with the majority involving the lateral ligaments.  Notably, the time span for developing arthritis was shorter in those with a single severe sprain compared to chronic lesions (mean latency of 25.7 vs 38.0 years, P < .05).  The authors also found that approximately 67% of patients with chronic lateral ankle instability had varus malalignment. The varus malalignment was attributed to progressive degenerative changes on the medial ankle’s cartilaginous surface as a result of peroneal muscle dysfunction and abnormal ankle kinematics. 

Nonoperative Intervention

After a sprain, patients are initially treated conservatively. An individualized rehabilitation program for at least 3 months is a key component of nonoperative intervention, because it addresses each patient’s exercise needs accordingly.  The rehabilitation program for CAI is composed of a functional and a preventative component.  During both phases, the patient performs multidirectional strengthening exercises with an emphasis on proprioceptive training, peroneal muscle strengthening, and sport-specific training for athletes. 

Addressing risk factors for recurrent sprains (eg, proprioception deficits) are important for both preventive and treatment strategies.  The use of either bracing or taping is also effective in preventing recurrent sprains.  In a randomized controlled study (Level I) evaluating the preventive role of a brace alone to neuromuscular training and combination of the two, the authors found that a brace alone was superior to neuromuscular training in decreasing the incidence but not the severity of the sprains.  Compared to the neuromuscular training group, the patients who received a combination of the 2 methods had a lower incidence of recurrence; however, it was not statistically significant.  In another study (Level I), the authors evaluated the effect of a semirigid orthosis on the incidence of ankle sprains in soccer players.  They found a significantly lower incidence of recurrent sprains in the orthotic group. However, the use of semirigid orthosis did not affect the incidence in patients without a history of sprain.  The authors suggested that orthosis provides both proprioception and mechanical support to an ankle with a prior history of sprain.  Preventive programs have also been found to reduce the rate and recurrence of ankle sprains. 

Operative Intervention

There are several surgical options for patients who do not respond to rehabilitation.  These techniques are broadly categorized into nonanatomic versus anatomic approaches. Nonanatomic approaches do not re-create the ligaments’ normal anatomic insertion points; these procedures rely on local grafts (eg, peroneus brevis tendon autograft) to reconstruct the attenuated ligaments.  Nonanatomic procedures have several clinical disadvantages, such as the sacrifice of a normal tendon to use as a graft, impaired ankle range of motion, and long-term degenerative changes.  In contrast, anatomic procedures are preferred as they attempt to re-create the normal ankle’s biomechanics,  and these procedures will be described here.

Direct lateral structure repair depends on the quality of the ligamentous tissue. In the 1960s, Broström  first described an anatomic technique that directly repaired the ATFL and CFL. In this technique, the ends of the attenuated ATFL are oversewn and tightened using continuous sutures. However, this was later modified with the Gould technique, which involves reinforcing the repair by suturing the IER to the fibula. 

The open Broström-Gould anatomic repair is one of the most common techniques used for lateral ankle instability. However, an alternative anatomic technique involving the use of an autograft or allograft is occasionally necessary, usually in the setting of revision surgery, longstanding instability, and generalized ligamentous laxity.  In a comparative (Level III) study evaluating clinical outcomes following Broström repair versus anatomic reconstruction with allograft tendons, the two groups had similar function and activity levels at a minimum of 2 years follow-up, which suggests that reconstruction is a reliable option for those at risk of failure with a standard anatomic repair.  However, it is unclear which anatomical procedure is most appropriate for CAI due to study heterogeneity and limited high-quality studies. 

The use of a suture tape and/or suture anchor augmentation for lateral ligament reinforcement has also been evaluated. In a cadaveric study comparing the traditional Broström repair to suture anchor and suture anchor with tape augmentation, the authors found that the tape augmentation group was biomechanically superior to the others.  The addition of a suture tape material may be particularly useful in cases where a standard Broström repair has a higher risk of failure, such as connective tissue disorders, revision surgery, or generalized ligamentous laxity. In a prospective case series (Level IV) of twenty-eight patients with generalized ligamentous laxity treated with suture tape augmentation (mean follow-up of 35.8 months), the authors found significantly improved Foot and Ankle Outcome Scores and Foot and Ankle Ability Measure scores from baseline.  Only one subject in the series experienced recurrence of CAI.  This suggests that suture tape augmentation is an effective adjuvant to the modified Broström repair.

In the past decade, there has been an increased interest in arthroscopic surgery because of its minimally invasive nature and its potential to decrease patients’ recovery time and morbidity.  Arthroscopic intervention also allows the surgeon to concurrently diagnose and treat intra-articular disorders while addressing the damaged ligaments.  In a randomized controlled study (Level I) comparing an “all-inside” arthroscopic modified Broström to the open technique, at 1 year after surgery there was no difference in clinical or radiologic outcomes.  In another study (Level IV), the authors compared clinical outcomes of the open Broström-Gould repair to an all-inside arthroscopic Broström.  The data showed no observable differences between the 2 approaches with respect to pain, American Orthopaedic Foot & Ankle Society (AOFAS) Ankle-Hindfoot Score, and Karlsson-Peterson scores.  However, compared to the open procedure, the authors found that the arthroscopic group exhibited earlier time to ambulation (12 vs 22 days).  In a case series (Level IV) of patients treated with an “all-inside” arthroscopic knotless suture-anchor technique, not only did all the patients report subjective improvement in their ankle stability and ability to return to their normal activities but the technique also avoided the suture knot prominence that is often associated with postoperative neuritis. 

Arthroscopic procedures also have their disadvantages. The suture anchors’ knots can entrap nearby structures such as the extensor tendons, superficial peroneal nerve, and peroneus tertius.  Although a recent systematic review comparing open to arthroscopic techniques showed higher complication rates for arthroscopic studies, the review was mostly limited to level IV studies and by statistical heterogeneity.  The complications did not impact patients’ functional scores. 

Ankle Osteochondral defects

The understanding of osteochondral lesions of the talus has developed gradually over the past several centuries. Monro was the first to describe talar osteochondral injury when he removed loose fragments from an ankle in 1737. In 1888, König coined the term osteochondritis dissecans (OCD), referring to loose bodies within a knee joint that he believed to be secondary to avascular necrosis. It was not until 1922 when OCD was first described in the ankle by Kappis, and in 1924 Phemister proposed a traumatic etiology for such talar lesions, a hypothesis that was supported by Fairbank in 1933 and later in 1959 by Berndt and Harty.

Our current definition of an osteochondral lesion (OCL) is any defect involving both the articular surface and the subchondral bone of the talus. This definition recognizes that there are a variety of etiologic pathways that result in similar lesions within the dome of the talus. Many of these lesions are associated with traumatic events and are prevalent within active populations. In fact, concomitant OCLs have been reported in 50% to 73% of acute ankle injuries. Less frequent causes of OCLs include genetic predisposition, degenerative joint disease, joint malalignment, avascular necrosis, peripheral vascular disease, and endocrine or metabolic abnormalities. Treatment of osteochondral lesions of the talus has been traditionally difficult due to the limited healing potential of the talar articular surface and the massive forces transmitted through the ankle joint. However, during the past 10 to 15 years, significant advancements have been made in understanding the pathophysiology of osteochondral injury and modern surgical techniques have continued to evolve to provide a more durable and functional repair.

Treatment for osteochondral lesions of the talus continues to improve as studies have demonstrated increasing clinical efficacy. Nonoperative treatment is the ideal primary protocol, with the hope that patients will be able to regain function and shed painful symptoms to return to daily activities. However, the lackluster healing properties of articular cartilage have rendered non-operative treatment limited in its power at best, and operative treatment has become increasingly common. Microfracture, drilling, and other bone marrow stimulating techniques yield positive results for smaller lesions, and autologous and cadaveric bone grafts may be necessary for failed bone marrow stimulation procedures or larger lesions. Other methods remain in their early developmental stages. Cell-based repair strategies have sparked interest among scientists and clinicians, but clinical applications and substantial studies are still lacking. PRP and hyaluronate therapy have also shown promise as useful therapy down the road. With the large incidence of ankle trauma and an increasing demand for the proper treatment of OCLs, operative techniques are continuing to evolve in hopes of improving pain and function while effectively halting degenerative arthritis changes in the ankle.