ORIGINAL ARTICLE
Chronic lateral ankle instability: review of anatomy,
biomechanics, pathology, diagnosis and treatment
J. Mangwani,* M. A. Hakmi,
{T. W. D. Smith
{*Senior House Officer, George Elliot Hospital, Nuneaton, UK CV10 7DJ;
{Specialist Registrar, Sheffield Children's Hospital, NHS Trust, Sheffield, UK; {Orthopaedic Surgeon,
Orthopaedic Department, Northern General Hospital, Sheffield, UK
SUMMARY. An ankle sprain is the most common injury encountered in athletes. Ten to twenty per cent develop chronic lateral ankle instability despite adequate non-operative treatment. An accurate diagnosis can usually be established by a detailed history, thorough physical examination and stress radiographs. Conservative treatment has a limited role in the management of chronic lateral instability. In the surgical treatment both anatomic and non-anatomic reconstructive procedures have reported excellent to good short-term results. However, longshort-term results favour the restoration of the normal anatomy and biomechanics by anatomic reconstruction of the lateral ankle ligaments. This review article will consider relevant surgical anatomy and biomechanics of the ankle joint and also address the pathology, diagnosis and various surgical options available for chronic lateral instability. ß 2001 Harcourt Publishers Ltd
INTRODUCTION
Lateral inversion ankle injury ± an ankle sprain ± is the most common injury in sports accounting for 16±21% of all athletic injuries.1±4Chronic instability
of the ankle is likely only if both anterior talo®bular ligament and calcaneo®bular ligament have been completely torn.5Symptomatic ankle instability
devel-ops in as many as 10±20% even after adequate non-operative treatment of acute sprain of lateral ankle
ligaments.6Although most patients may be
success-fully treated with a rehabilitative exercise programme and bracing, some may still require surgery for chronic functional instability. A proper history, physical examination, pre operative stress radiographs and other diagnostic procedures should be undertaken before embarking upon any surgical reconstruction. According to the literature, more than 50 surgical procedures for the treatment of chronic lateral ankle joint instability have been described. The methods can be divided into two groups: anatomic repairs and
non-anatomic reconstructions by tenodesis.7Excellent to
good results have been reported in over 90% of patients receiving a variety of anatomical and
non-anatomical reconstructive procedures.8However, the
increased morbidity and poor longterm results asso-ciated with non anatomic reconstructions swing the pendulum in favour of anatomic repair with shorten-ing, reinsertion and imbrication of the elongated liga-ments. Furthermore, biomechanical evaluations by
Wirth,9support the concept of anatomical
reconstruc-tion of ligaments in cases of ankle instability. ANATOMY
The so-called lateral collateral ligament of the ankle is actually composed of three main ligaments: the an-terior talo®bular, calcaneo®bular and posan-terior talo-®bular (Fig. 1). These ligaments vary in size, strength, relationship to ankle capsule and frequency of injury. The anterior talo®bular is the weakest, the calcaneo-®bular ligament (CFL) being 2.5 times and posterior talo®bular (PTFL) being twice as strong as the ATFL. (A) The anterior talo®bular ligament (ATFL) is 15±20 mm long and spans the anterior lateral ankle joint. The ligament is approximately 6±8 mm wide and 2 mm thick.10It originates at the distal anterior ®bula
and inserts on the body of talus just anterior to the articular facet. With the foot planti grade, its ®bres make an angle of approximately 758 with the ¯oor
from its ®bular origin.11 It originates at the distal
anterior ®bula and inserts on the body of talus just anterior to the articular facet and is most vulnerable Correspondence to: Mr M. A. Hakmi Specialist Registrar,
to injury in plantar¯exion, where the narrowest part of the talus is in the ankle mortise and the joint is mechanically least stable. It is the most frequently injured ligament and usually disrupted through its midsubstance.
(B) The calcaneo®bular ligament (CFL) originates from the anterior border of the distal lateral malleolus just below the origin of the ATFL and courses medi-ally, posteriorly, inferiorly to the calcaneal insertion. It is 2±3 cm long, 4±8 mm wide and 3±5 mm thick. The direction of the CFL ®bres is 108±458 posterior to the line of the longitudinal axis of the ®bula.10,12Another
important detail to remember during reconstruction is
that ATFL and CFL form an angle of 1048.13CFL is
lax in all positions except extremes of inversion. CFL crosses two joints: talocrural and talocalcaneal and prevents the calcaneus and talus from inverting with varus stress. However, there is some controversy as
regards its importance. According to Percy et al.,14
CFL is functionally the most important of the three lateral ligaments, but BrostroÈm15 denies its
signi®c-ance in chronic lateral ankle instability.
(C) The posterior talo®bular ligament (PTFL) is short, thick, the strongest of the three lateral ligaments and not surprisingly, the least injured. The PTFL is 3 cm long, 5 mm wide and 5±8 mm thick. It originates from the medial surface of the lateral malleolus and courses medially in a horizontal manner to the poster-ior aspect of the talus. PTFL is tensed only in extreme dorsi¯exion.16
BrostroÈm15in his report on the frequency of the
indi-vidual ligament ruptures stated that isolated ATFL injury occurred in 66%. A combined tear of ATFL and CFL was reported in 20%. It is the combined injury of both ATFL and CFL, which is responsible for the
development of chronic lateral ankle instability.5
Rupture of CFL alone is very rare as an isolated injury.15,17The PTFL is seldom injured.
BIOMECHANICS
The bony articulation along with surrounding liga-ments of the ankle represents a complex mechanical structure. Intact ligaments are essential for normal mechanics of the ankle joint. Each of the ligaments has a role in stabilizing the ankle joint.
In Biomechanical studies the ATFL has a lower load
to failure than does the CFL.18Conversely the ATFL
is capable of undergoing the greatest strain compared
with CFL and the PTFL.19,20The common
mechan-ism of injury of plantar¯exion and inversion together, with its lower maximum load to failure, accounts for the greater frequency of injuries to the ATFL.
Rasmussen21in his studies of sequential sectioning
of the lateral ligament concluded that the most import-ant function of ATFL was restriction of internal rota-tion of talus in the mortise. The ATFL also inhibits adduction in plantar¯exed ankle. The CFL acts against adduction force almost independently in the neutral and dorsi¯exed position. In a dorsi¯exed ankle, external rotation is prevented by PTFL.
With physiologic loading, the articular surface pro-vides 30% of stability to internal rotation and 100% stability to inversion.22It, therefore, means that joint
stabilizing function of the ligaments is most important in the unloaded ankle joint and ligament injuries occur when physiologic loading is exceeded or when the ex-tremity is being loaded or unloaded, e.g. during the initial phase of heel strike or ground contact.
Symptomatic instability can be caused by mechan-ical instability with demonstrable instability but it can also be present with no demonstrable instability. Therefore ankle instability can either be (a) mechan-ical or (b) functional. Mechanmechan-ical instability is the objective measurement (either clinical or roentgeno-graphic) whereas functional instability, ®rst described by Freeman et al.23,24is the patients' subjective
com-plaint of giving way in the ankle joint. Functional instability is the most common and serious residual disability after lateral ligament injuries of the ankle joint.6Tropp25de®ned functional instability as a
mo-tion beyond voluntary control but not exceeding the physiologic range of motion. Several causative fac-tors including proprioceptive disorders,23±26peroneal
muscle weakness,25 pain and mechanical instability,
i.e. rupture or elongation of the lateral ankle
liga-ments26have been proposed but the exact
pathophy-siologic factors responsible for functional instability still remain unknown. Mechanical instability of the ankle is motion beyond the physiologic range of mo-tion. Unfortunately, mechanical instability and func-tional instability are poorly correlated.23A correlation
between functional instability and isometric peroneal muscle weakness, measured with Cybex II
dynamo-meter has been shown by Tropp.25Freeman23,24found
a high incidence of functional instability after rupture of the lateral ankle joint ligaments. Karlsson et al.27
concluded that a combination of mechanical instability
A F E C J K L D I B H G
Fig. 1 Relevant surgical anatomy of the ankle. A: tibia; B: fibula; C: anterior talofibular ligament; D: calcaneofibular ligament; E: posterior talofibular ligament; F: anterior tibiofibular ligament; G: transverse tibiofibular ligament; H: posterior tibiofibular; I: lateral talocalcaneal ligament; J: cervical ligament; K: peroneus brevis; L: peroneus longus.
and proprioceptive de®cit, measured as an increased reaction time during an inversion torque, might be responsible for functional instability.
PATHOLOGY
Complete ligament disruption has been reported in
75% of common ankle sprains.28ATFL is the single
most frequently injured ligament. Midsubstance tears are common but bony avulsions of the talus and ®bula
have also been reported.29The second most common
injury is a combined tear of ATFL and CFL.28
Occa-sionally isolated tears of CFL have been reported and may be important in late subtalar instability.30,31
Other lesions commonly associated with lateral ligament injuries are: partial or complete rupture of peroneus longus and brevis tendon; chondral fractures of the talus; osteochondral fractures in talocrural joint; medial ligamentous and syndesmotic injuries, etc. These less common injuries must be kept in mind while evaluating these patients and radiographs.32
CLINICAL EVALUATION Symptoms
Patients with chronic lateral instability usually have a preceding history of signi®cant acute inversion ankle injury. In many cases, the acute injury was treated in-adequately. Patients often describe a feeling of `giving way' while the ankle is plantar¯exed and internally rotated. A history of insecurity, instability and giving way is far more important in diagnosis than the
phys-ical and radiographic examination.26 Apart from
in-stability, patients also complain of pain, intermittent swelling and recurrent ankle sprains. These symptoms may interfere with athletic or day-to-day activities. Physical examination
A positive history and thorough clinical examination helps to arrive at a proper diagnosis. The examination may reveal lateral tenderness but the most common and important tests for evaluation of instability are anterior drawer test and inversion stress test.33,34The
anterior drawer sign is used to evaluate the anterior movement of the talus compared with the tibia. A positive anterior drawer test signi®es disruption or instability of anterior talo®bular ligament. The inver-sion stress test evaluates the integrity of calcaneo®bu-lar ligament.
Anterior drawer test
In a relaxed patient, anterior subluxation of talus can be easily demonstrated, with the patient seated on a bench and the leg hanging off the end with the knee bent, tibia is stabilized with one hand while pulling the foot forward with the other hand behind the heel
(Fig. 2). The same can be performed with the patient lying supine.
Inversion stress test
Excessive inversion of the heel in plantigrade position can indicate laxity and positive inversions stress test. In patients with calcaneo®bular disruption, pain or frank instability may be demonstrated by this test (Fig. 3). However, it is very dif®cult to differentiate tibiotalar from talocalcaneal instability.
In addition to these, predisposing factors such as varus hindfoot alignment, hypermobile joints and tar-sal coalition should be appreciated. The integrity of peroneal or posterior tibial tendons should be included in a thorough physical examination.
RADIOGRAPHIC EVALUATION
Various imaging modalities including stress roent-genograms, ¯ouroscopy, arthrography, computed tomography, magnetic resonance imaging and MR arthrography have been used in the evaluation of lateral ankle ligament tears.
Fig. 2 Physical examination: Anterior drawer stress test.
Stress roentgenograms
Inversion stress view is an excessive talar tilt on an A P view of the ankle (Fig. 4) while an inversion force is applied. The inversion force can be applied manually or by using a jig with speci®cally de®ned stresses. Laurin et al.35have demonstrated similar results with
both the methods.
There is no consensus as to what is the normal range of talar tilt. Although a tilt of talus beyond 128 is noted tobemarkedlyabnormal,anormalvalueof238hasalso been quoted.35,36According to Cox and Hewes,37a ®ve
degree difference maybe clinically signi®cant. However side to side comparison is equally controversial.36,38
Anterior drawer or lateral stress X-rays (Fig. 5) are made in 108 to 208 of plantar ¯exion while the ankle is being subjected to an anterior displacement stress. Stress may be applied manually or by a jig. Normal value may range from 2 to 9 mm with the majority
being less than 4 mm for the maximum.39±41 ATFL
rupture is usually present, when anterior subluxation is more than 5 mm.
Broden's stress views may be helpful in identifying angular instability of the subtalar joint.35However,
re-centstudieshavequestionedthevalidityofsuchviews.42
The accuracy of the stress radiography has been questioned from time to time. In an extensive review
of literature by Frost and Amendola,43routine use of
stress X-rays in chronic lateral instability has been
condemned because of large variability in talar tilt and anterior drawer values.
Fluoroscopy
It is helpful in identifying the hypermobility and rota-tional instability of the subtalar complex. It is not of much value in chronic lateral ankle instability. Arthrography
Evaluation of chronic lateral instability by arthrogra-phy has limited value. One of the few applications includes detection of chronic subtalar instability. Also, for chronic tibio®bular instability, extension of the dye from the ankle joint more than 6 mm upward indicates signi®cant tibio®bular instability.
Computed tomography and magnetic resonance imaging
The primary application of either test is to exclude conditions presenting with the similar symptomatol-ogy such as peroneal tendon tears, osteochondral lesions and tarsal coalitions.44,45In a group of chronic
symptomatic patients after ankle sprain, Meyer46
reported intra- or juxta ± articular fragments in as many as 42%. Magnetic resonance imaging can de-monstrate ligamentous tears but its cost is a limiting factor in its application. Use of MR arthrography in identifying those patients who are most at risk from the development of chronic instability has
recently been emphasized.47
CLASSIFICATION
Several classi®cations have been proposed for lateral ankle ligament injuries based on anatomy, clin-ical symptoms and treatment. Most of these grade lateral ankle sprains from I to III or from mild to
severe.13,48±50 Uniform criteria for grading have not
been established and different authors have graded the injury by clinical signs and symptoms, degree of injury to the ligament(s) and the number of liga-ments ruptured.
Classification systems for lateral ankle sprains Based on the anatomy
Grade I: ATFL sprain
Grade II: ATFL and CFL sprains
Grade III: ATFL, CFL and PTFL sprains. Based on the degree of injury to the ligament (s)51
Grade 1: ligament stretched Grade 2: ligament partially torn Grade 3: ligament completely torn. Fig. 5 Radiograph of a normal ankle under inversion stress.
Based on the clinical signs and symptoms52
Mild sprain: minimal functional loss, no limp, minimal or no swelling, point tenderness, pain with reproduction of mechanism of injury;
Moderate sprain: moderate functional loss, unable to toe rise or hop on injured ankle, limp when walking, localized swelling, point tenderness;
Severe sprain: diffuse tenderness and swelling; crutches preferred by patient for ambulation.
Based on the treatment53
Type I: stable ankle by clinical testing (with anaesthesia if necessary); symptomatic treatment; Type II: unstable ankle with positive anterior drawer and/or positive talar tilt test by clinical examination. Group 1: nonathletic or older patient; functional treatment*;
Group 2: young athlete.
Type A: negative stress X-ray ®ndings; treat functionally;
Type B: positive tiboitalar stress X-ray ®ndings (talar tilt > 158; anterior drawer > 1 cm); treat by surgical repair;
Type C: subtalar instability; treat functionally. CONSERVATIVE TREATMENT
Symptomatic chronic lateral instability should ®rst be treated conservatively. Proprioceptive exercises, strengthening of peroneal muscles and ¯exibility may be suf®cient in relieving the disabling symptoms in some patients. Broadening and lowering the heel of the shoes in women and application of a lateral wedge to the shoe heel in men may improve the symptoma-tology. In sports activities, high top athletic shoe or taping of the ankle for chronic instability may be of
some bene®t. Larsen54 examined 20 patients with
chronic ankle instability with the ankle taped and un-taped. The measurable instability was signi®cantly de-creased after taping but after exercise, it was dede-creased only for talar tilting.
When disabling pain and instability persist, surgical stabilization using a suitable reconstructive procedure should be done.
SURGICAL TREATMENT
Aftercompletephysical,radiologicalevaluationawork-ing diagnosis is established. Failure of non-surgical
methods in improving symptoms leads the surgeon to plan a suitable reconstructive precedure. If any intraarticular pathology is suspected, a diagnostic
arthroscopy may be indicated. Kibler55 identi®ed
intraarticular problems in 83% of ankles undergoing modi®ed BrostroÈm reconstruction and believed that ¯uid extravasations did not compromise the ligament reconstruction. Taga et al.,56reported chondral lesions
in 95% of the chronically injured ankles examined by arthroscopy.
A clear indication for surgery is the presence of both functional and mechanical instability with failure of conservative treatment. More often than not, such a clear indication does not exist. In most of the reports, patient age appears to have little bearing on the out-come of surgery, however, in a study by Korkala et al.,57 lateral ligaments in patients over 40 years of
age showed a statistically signi®cant tendency to heal less well than that of younger patients.
A multitude of surgical methods for stabilization of lateral ankle ligaments is available. Almost all the procedures described in literature, report a success rate of more than 80%.24,39,58±66Operative procedures
are divided into two types: anatomic repairs and non-anatomic reconstructions.
TheanatomicrepairwaspopularisedbyBrostroÈm.61
He believed that direct repair of the lateral ankle liga-ments could be performed long after the injury because ligamentous tissue remained encased in scar tissue. His method of imbrication and suture of the torn ends of the ligament or suture of the ligament to bone has later
been modi®ed by many authors (Fig. 6).66±68Gould's
modi®cation39of BrostroÈm's procedure incorporates
ree®ng of the extensor retinaculum and provides sup-port to the subtalar joint.
Karlsson et al.27 have described the technique of
anatomic repair with transsection, shortening and im-brication of ATFL and CFL. In a large series, they reviewed 152 ankles after 2 to 10 years, an excellent or good result was reported in 87%. Generalized
ATFL:anteriortalofibularligament;CFL:calcaneofibularligament; PTFL: posterior talofibular ligament.
*Functional treatment in the unstable group includes 2 to 3 weeks of immobilization in a cast or walking boot followed by a stirrup brace and ankle rehabilitation with Achilles stretching, peroneal strengthening, and proprioceptive reduction.
D
A
B C
Fig. 6 Modified Brostrom anatomic reconstruction. A: imbrication of anterior talofibular ligament; B: imbrication of calcaneofibular ligament; C: peroneal tendons; D: extensor retinaculum.
hypermobility of the joints, long standing local liga-mentous insuf®ciency, and previously operated ankles accounted for unsatisfactory results. Reconstruction of both ligaments gave a better functional result than when only the anterior talo®bular ligament was recons-tructed. Attempts to recreate the ATFL and CFL using peroneus brevis tendon through bony tunnels
have been made by some surgeons.20,69Anatomic
re-construction can also be performed by using plantaris tendon.58,70,71By this technique, isometric
reconstruc-tion of ATFL and CFL is performed without causing any injury to peroneal muscles. This procedure is tech-nically demanding and plantaris tendon may be absent in 7±10% of the population.
In their study Okuda et al.72used palmaris longus
to reconstruct ATFL in 27 ankles with ligamentous instability. At a follow up of more than 2 years, func-tional evaluation showed excellent to good results in all ankles. In addition they stated that reconstruction of the calcano®bular ligament along with ATFL is not necessary for patients with chronic combined lateral ligament instability.
Excellent to good short-term results have been
reported with semitendinosus graft.73 At an average
follow-up of 24 months, 81% of the patients reported complete resolution or substantial improvement in in-stability, swelling and sharp pain.
Anatomic reconstruction of the lateral ligaments of the ankle using allograft tissue has been done in the
past.74 Recently, Nakata et al.75 have reported good
results using solvent dried and gamma ± irradiated allogenic fascia lata.
Non-anatomic reconstruction by tenodesis or checkrein use all or part of the peroneus brevis. The commonly used techniques of reconstruction are
Evans'76,77 (Fig. 7), Watson-Jones78 (Fig. 8),
Lar-sen64,79 and the Chrisman-Snook modi®cation62 of
the Elmslie procedure (Fig. 9). Encouraging short term results have been reported with Evans' tenod-esis76,80,81or its modi®cations.82,83However, longterm
studies have shown deterioration of function with
time. Cass et al.84 reviewed 19 patients at 9.5 years
follow up, 14 had unstable ankles and four had to use
ankle supports. Karlsson et al.85 reported only 50%
long-term satisfactory results. Marginal osteophytes
were found in many ankles. Rosenbaum et al.86
re-viewed 19 patients at 10 years follow up and reported a high rate of residual instability, pain and swelling. The gait analysis revealed reduced peak pressures under the lateral heel and increased values under the longitudinal arch. The persistent clinical problems, functional changes and disturbed ankle joint kine-matics permanently alters foot function and may subsequently lead to the development of arthrosis. The Evans' tenodesis reconstructs neither the ATFL nor the CFL, but aims to function as both. Orava
et al.87 noted a 50% incidence of radiographically
proved increased anterior drawer results after the Evans' procedure.
The Watson-Jones tenodesis78reconstructs ATFL
more effectively than CFL. Peters et al.,7in a review of
surgical treatments for chronic lateral ankle instability stated that 10 to 30% of the cases had restricted range of dorsi¯exion and inversion after Watson-Jones
B
A
C
Fig. 8 The Watson±Jones reconstruction. A: peroneus brevis; B: peroneus longus; C: 5th metatarsal.
B
A
C
Fig. 7 The Evans' reconstruction. A: peroneus bervis; B: peroneus longus; C: 5th metatarsal.
A
B
Fig. 9 The Chrisman±Snook reconstruction. A: peroneus brevis B: 5th metatarsal.
procedure. Although poor long-term results have
pre-viously been reported,88Bernhard and Burckhardt,89
in a recent study, have quoted 80% good or excellent results.
Chrisman-Snook modi®cation62of the Emslie
pro-cedure restores both ATFL and CFL and achieves better stability than Evans' reconstruction. Peters
et al.7reviewed 100 ankles treated by this procedure
and found that the stability was restored in 95% of the patients and 90% had good or excellent results. Com-plications such as problems with wound healing, skin sloughs, infection and sural nerve injury have been
reported. Snook et al.91have reported 94%
satisfact-ory results at 10 years follow-up. Chrisman et al. thought loss of 208 or less of inversion was inherent to the procedure and did not report it as a
complica-tion. Other authors90 have reported more than 80%
satisfactory results.
In a review of lateral ligament reconstruction
Hortsman et al.91 found a high incidence of
postoperative pain, 63% and 83% of patients with Chrisman-Snook and Evans' procedure respec-tively. Chrisman-Snook and Evans' procedure control talar tilt better than does the Watson-Jones procedure. Lowest incidence of instability, 12%, was reported with Chrisman-Snook procedure but had the highest incidence of loss of inversion. Overall satisfaction was reported in 90% of patients.
Anatomic versus non-anatomic reconstruction
Anatomic reconstruction of the lateral ankle ligaments is desirable. In a large series, Brunner and Gaechter70
compared anatomic plantaris repair to peroneal teno-desis and concluded that anatomic repair was superior. A revision rate of 9.4% in peroneal tenodesis was con-trasted with 1.9% in the anatomic plantaris repair. Unlike anatomic reconstructions, tenodesis do not re-store the normal anatomy of the lateral ankle liga-ments. The advantages of not sacri®cing normal tissue and not interfering with the ankle and subtalar joint biomechanics make anatomic reconstruction the pre-ferred choice of surgical intervention. Patients with hypermobile joints and de®cient or weak tissue for direct repair may be treated by augmented
reconstruc-tions.92The non-anatomic reconstruction by tenodesis
results in the restricted range of motion, reduced long-term stability, an increased risk of medially lo-cated degenerative changes, a larger number of reo-perations and less satisfactory overall results.93 The
anatomic reconstructions and augmentation restore the ligamentous force patterns more closely to normal
than do the tenodesis procedure.69
CONCLUSION
An ankle sprain contributes 16±21% to all the athletic injuries.1±4It results in chronic lateral ankle instability
in 10±20% of the patients.6 It is important for the
clinician to understand the relevant surgical anatomy, biomechanics and pathology of the chronic lateral ankle instability to establish an accurate diagnosis. The role of stress radiography in the diagnosis of chronic lateral instability is not clear.43Newer
imagin-ing modalities such as MR arthography in identifyimagin-ing the patients at risk for the development of chronic instability has recently been reported.47Conservative
treatment in the form of rehabilitative exercises and bracing has a role in less active population. Surgical treatment includes either anatomic reconstruction of the ligaments or non-anatomic reconstruction by tenodesis.24,39,58±66Anatomic reconstruction helps in
restoring the normal anatomy and biomechanics of the ankle joint and therefore, is the preferred method of surgical treatment.
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