Ligament repair for ankle sprains: ‘A square peg in a round hole’? Is surgery justified?

Ligament repair for ankle sprains: ‘A square peg in a round hole’?  Is surgery justified?

              Dr K S Dhillon. FRCS, LLM.

Introduction

Ankle sprain is the most common sports injury and in 95% of the sprains the lateral ligament is involved. Anecdotal observations suggest that there is a trend towards increasing use of magnetic resonance imaging in the diagnosis of ankle instability as well as an increasing use of surgical intervention in the treatment of ankle instability. The reality is that an MRI is not necessary for the diagnosis of ankle instability and there is no scientific evidence that surgical intervention provides better outcome compared to functional treatment in the treatment of acute or chronic instability of the ankle. The cause of ankle instability is multi-factorial. Ligament laxity is only one of the factors and other factors include the complex morphology and biomechanics of the ankle, muscular weakness, diminished proprioception and postural deficits. Ligament laxity is easy to diagnose hence it becomes the target of surgical intervention. The other factors are difficult to assess clinically and are often neglected. This is probably the reason why surgical treatment of the ligament laxity does not provide the desired outcome. Repairing the ligament to solve the problem of ankle instability is akin to squeezing a square peg into a round hole. A more rounded approach is needed to resolve the problem.

Epidemiology and clinical course of ankle sprains

Ankle sprain is the most common sports injury. In about 95% of ankle sprains the lateral ligament is involved and in the remaining 5% the medial ligament is involved. Swenson et al¹ in an epidemiological survey of US high school athletes found that there were 5,373 ankle sprains in 17,172,376 athlete exposures (AEs) which works out to 3.13 ankle sprains per 10,000 AEs. Girls had higher rates of ankle sprain than boys and the rates were higher with competition than practice.

Their survey found that the anterior talofibular ligament (ATFL) was involved in 85.3% of the sprains. The rates for the posterior talofibular ligament (PTFL) was 12.3%, anterior inferior tibiofibular ligament 26.4%, posterior inferior tibiofibular ligament 4.1%, calcaneofibular ligament (CFL) 34.5% and for the deltoid ligament 5.4%.

Following an ankle sprain there is a rapid improvement of the pain within 2 weeks. A systematic review of the literature by van Raijn et al showed that 5 to 33% of the patients still have pain after 1 year. Full recovery was reported in 36 to 85% of the patients within one year period. The risk of resprain after the initial injury varied from 3% to 34% of the patients and the span from initial injury to resprains ranged from 2 weeks to 96 months².

Classification

Lateral ligament injuries are usually graded into three³.

·         Grade 1 The ligament is stretched and involves the ATFL

·         Grade 2 The ligament is partially torn and involves the AFTL and the CFL

·         Grade 3 The ligament is completely torn and involves the AFTL, CFL and the PTFL

Chronic ankle instability can be mechanical or functional. Mechanical instability is said to be present when there is about 10 degrees or more of talar tilt or there is a 10mm or more of anterior shift of the talus when compared to the contralateral ankle on clinical examination⁴. Functional instability on the hand is a subjective complaint of ankle instability which is believed to be due to sensorimotor and neuromuscular deficit. This is supported by evidence of increased reaction time of the Peroneal Longus muscle³.

Diagnosis of chronic ankle instability

Chronic ankle instability is not the consequence of a single factor such as ligament laxity, muscle weakness, diminished proprioception or postural deficits but there is evidence that all these factors are associated with chronic ankle instability.

Diagnosis of chronic instability is essentially clinical. The patient usually gives a history of persistent ankle pain, recurrent sprains and repeated episodes of giving way of the ankle. Giving way of the ankle can be due to mechanical, dynamic instability or reflex inhibition because of pain due to various causes including anterior or posterior impingement. In mechanical/dynamic instability the pain and giving way comes after the episode while with reflex inhibition the pain comes before the episode of giving way⁵.

Testing for the ATFL is done by an anteromedial rotatory drawer test of a plantar flexed ankle while testing for laxity of the CFL is done by inverting the hind foot with the ankle in dorsiflexion⁵. X-rays of the ankle in the anteroposterior, lateral weight bearing (with patient leaning forward) and oblique projections can be useful to assess the syndesmotic alignment, angular malalignment and the ankle mortise congruency⁵. Various manual and mechanical stress radiographic tests have been described but unfortunately meta-analysis shows that these radiographic testing is not sufficiently robust to be of much use in treatment of patients with ankle instability⁶. It is often difficult to obtain reliable and reproducible magnetic resonance images of the ankle. Such images do not give us more information about the ligament injury than what is available on clinical examination. However an MRI can be useful to exclude other causes of ankle pain such as osteochondral lesions and tendon pathology⁵.

Subtalar sprains must be kept in mind in patients with ankle pain after lateral ligament injuries. Subtalar sprains are common in patients with acute lateral ligament injuries. Assessment of subtalar sprains is difficult and unreliable; hence the true incidence of these sprains is unknown⁴. Meyer et al⁷ did arthrograms in patients with acute ankle injuries and found that 43% of patients with lateral ligament injuries had subtalar sprains. Little attention is given to subtalar injuries presumably because they heal with conservative treatment just as most lateral ligament injuries do.

Treatment of acute lateral ligament injuries

There is good level 1 evidence that stable grade 1 injuries of the lateral ligament can be treated conservatively, with protection, rest, ice, compression and elevation (PRICE), and the outcome can be expected to be good⁸. The question is how unstable grade 2 and 3 injuries should be treated?

Kerhoffs et al⁹ in 2007 did a meta-analysis comparing conservative to surgical treatment of lateral ligament injuries of the ankle. They found that all the trials had methodological weakness and were not robust enough to show superiority of one form of treatment over the other. There was decreased incidence of objective instability after surgical treatment but there was no difference in subjective instability between the two groups. Surgery was however associated with slower return to normal activity, and a higher incidence of ankle stiffness and impaired ankle mobility. Besides the higher cost of surgery, there were complications in the surgical group.

To overcome the problems of methodological weakness, such as randomization, heterogeneity of study samples, non-blinded research and short follow up of previous studies, Pihlajamaki et al¹⁰ did a prospective randomized controlled trial to compare surgical versus functional treatment for acute ruptures of the lateral ligament of the ankle in young men.

The study conducted between 1991 and 1992 recruited physically active Finnish male defence forces personnel with an average age of 20.4 years. All the patients had a grade 3 tear of the lateral ligament of the ankle which was confirmed by stress radiography. Twenty five patients were randomly allocated to the surgical repair of ligament group while 26 were allocated to functional conservative treatment group.

At a mean follow up of 14 years, 60% of the surgical group patients and 69% of the functional treatment group were available for review. All patients in both groups had recovered the preinjury activity level and they could walk and run normally. There was no significant difference in the ankle scores and the findings on stress radiography between the two groups. However the reinjury rate was significantly higher in the functional treatment group. In the surgical group about 27% had evidence of osteoarthritis but none of the patients in the functional group had evidence of osteoarthritis.

The authors of this level 1 study concluded that in terms of recovery of preinjury activity level the long term results were the same in both groups. There was no difference in the objective ankle stability on stress testing in both groups. There was a risk of osteoarthritis in the surgically treated patients whereas there was no osteoarthritis in the conservatively treated group at a mean follow up of 14 years. There was a significantly higher rate of reinjury in the non-surgical group but the reinjury posed no major problem since the subjective recovery and physical activity level was the same in both groups. None of the patients in either group had surgery for ankle instability.

Takao et al¹¹ in a level 3 cohort study of 132 patients comparing surgical with functional treatment of lateral ligament injuries found no difference in the mean results of the clinical scores and ankle stability on stress radiography between the two groups at 2 years follow up. However in this study 10% of the patients (8 of 78 patients) in the functional group had a functional score of less than 80 points and had instability on follow up.

A higher rate of reinjury or instability on follow up in patients treated conservatively after an acute tear of the lateral ligament should not be construed as an indication for surgery of acute tears because surgery can always be carried out at a later date if instability persists without jeopardizing the long term outcome. Kitaota et al¹² did a retrospective; 10 years follow up study, comparing the outcome of acute and delayed reconstruction for lateral ligament instability and found that the radiological and clinical results were similar in the two groups.

One of the problems with these studies comparing surgical to functional treatment is that the number of patients recruited are rather small and this does not provide sufficient analytic power to assess the differences in clinical scores¹³.

Treatment of chronic ankle instability

Chronic ankle instability occurs in about 10 to 20% of patients after an acute ankle sprain. Surgical intervention is considered in these patients when ligament instability is present and conservative treatment fails. How successful is treatment for chronic ankle instability?

Jasper de Vries et al¹⁴ published the Cochrane collaborative review of intervention for treating chronic ankle instability in 2011. Ten randomised or quasi-randomised trials were available for review. There was ‘limitations in the design, conduct and reporting of these trials’ which  ‘resulted in unclear or high risk of bias assessments relating to allocation concealment, assessor blinding, incomplete and selective outcome reporting’.

The studies were divided into three groups. The first group of 4 studies evaluated conservative treatment in the form of neuromuscular training, the second group of 4 studies compared repair and tenodesis as a form of surgical treatment and the last group of 2 studies compared early mobilization in a brace and immobilization in a cast after surgery.

There were no studies comparing surgical and conservative treatment of chronic ankle instability. There were no systematic reviews of surgical treatment of chronic ankle instability.

Neuromuscular rehabilitation appears to improve function in the short term but the long term outcome of rehabilitation is not known. There is no evidence to support the benefits of one form of surgical treatment over another but tenodesis imposes practical limitation in some patients due to the small size of the tendon. To reduce the time to return to work and sports, functional post- operative rehabilitation with early mobilization is preferred. What is the best way to treat chronic ankle instability remains unanswered. Given the cost, risks and complications associate with surgery, logic dictates that the trend should favour conservative treatment.

Why is ligament surgery not able to restore stability of the ankle?

Repair of the lateral ligament of the ankle should restore stability but the outcome of surgery is not superior to non-surgical intervention. The reason appears to lay in the complex morphology and biomechanics of the ankle and the foot. The ankle has a very important role in transmitting vertical stresses produced by the weight of the body into horizontal stresses in a plantigrade foot. This is made possible by a complex interaction between the bony, ligamentous, muscular and neurological structures around the ankle and the foot.

The bone and ligamentous structures provide mechanical stability while the musculotendinous structures around the joints provide the functional stability. Repair of the lax lateral ligaments of the ankle only corrects one of the elements responsible for ankle and foot stability. Abnormalities of the lateral ligament of the ankle are easily detected but abnormalities of the other structures are difficult to detect, and this includes the laxity of the subtalar joint ligaments.

The talocrural joint is not a simple hinge which allows dorsiflexion and plantar flexion of the ankle. It has, according to many authors, a multi-axial mobility. In flexion/extension rolling movements occur, and there is sliding motion (horizontal rotation), as well as abduction/adduction motion in the coronal plane¹⁵.

The morphology of the talus has now been studied in more details and the morphology can vary between individuals where some types of morphology favours instability. The talus is shaped like a truncated cone with a complicated axis of movements. The radii of curvature of the dome of the talus has a variable medial/lateral distribution with the medial radius of curvature inferior to the lateral curvature in 66% of individuals, equal in 19% and inverted in 15% of individuals¹⁵.  The type 3 morphotype where the medial radius of curvature is greater, medial rotation and supination is reduced, and this protects the anterior talofibular ligament and the cervical ligament of the subtalar joint. In type 2 talus, where the two radii of curvatures are the same, the rotatory stress is less and this places higher stress on the anterior talofibular ligament. In type 1 talus there is true rotatory stability and the deltoid ligament becomes the main anchor point¹⁵. This variable morphology of the talus has differing biomechanical consequences. Instability can also occur when there is ankle joint incongruence, produced by a wider talar dome and reduced talar coverage, as well as when the talus is placed more anteriorly in relation of the tibia. Tibiofibular diastasis, malunion of the lateral malleolus and medial rotation of the talus as in pes cavus are other factors that can contribute to instability¹⁵.

Besides the bony morphology, the ligamentous morphology can also contribute to joint instability. Marfan type generalised hyper laxity and defects of mechanoreceptors and proprioception can contribute joint instability. Subtalar joint instability is now believed to contribute to chronic ankle instability although it is difficult to evaluate clinically¹⁵.

Limitation of dorsiflexion of the ankle caused by anterior osteophytes and synovial hypertrophy (fibrous impingement) can lead to mechanical joint instability. Shortening of the gastrocnemius will produce limitation of ankle dorsiflexion leading to sensation of overall instability as well as ankle instability¹⁵.

Varus of the hind foot has been shown to produce failure of ligament reconstruction of the ankle. Varus of the hind foot cause excessive pressure on lateral side of the foot and postural imbalance when weight bearing on one foot which can lead to stresses on the lateral structures of the ankle including the lateral ligament. Limb length discrepancy can lead to equinovarus positioning of the ankle in the shorter limb producing similar stresses on the ankle¹⁵.

Finally, neuromuscular incoordination, due to weakness of the peroneal muscles and abnormal proprioception due to any cause, can lead to ankle instability.

The cause of chronic ankle instability is multi-factorial and includes ankle and foot morphology, ligament laxity, muscle weakness, diminished proprioception as well as postural deficits. However the ligament laxity is easy to diagnose and consequently it becomes the target of treatment in the hope that it will solve the problem of ankle instability. It is quite obvious that repair of the ligament does not provide better outcome than functional treatment. There is a need for a more thorough assessment of the patient to evaluate the causes of the instability to achieve a better outcome for patients with chronic ankle instability. The subtalar joint, foot abnormalities and neuromuscular status of the patients need greater attention than is presently given to these structures that contribute to the instability.

Conclusion

Ankle sprain is the most common sports injury and in 95% of the sprains the lateral ligament is involved. The diagnosis is essentially clinical and magnetic resonance imaging and stress radiographs are of not much value in diagnosing ankle instability. There is a growing trend in treatment of ankle instability (acute and chronic) with surgery. However there is no good quality evidence that surgery produces better outcome compared to functional treatment in the treatment of ankle instability. There is level 1 scientific evidence that the outcome in terms of ankle scores and findings on stress radiography are not significantly different when surgical treatment for acute lateral ligament injury is compared to functional treatment on long term (14 years) follow up. Surgical treatment is associated with higher cost; surgical complications and in the long term surgically treated patients develop osteoarthritis of the ankle. There is a higher incidence of reinjury in patients treated conservatively but this poses on major problem because the subjective recovery and return to activity is not dissimilar in the two groups of patients.

Chronic ankle instability occurs in 10 to 20% of the patients with acute ankle sprains. Though surgical intervention is considered in patients with chronic ankle instability there is no scientific evidence that surgery provides better outcome as compared to functional treatment.

The cause of ankle instability is multifactorial. Besides ligament laxity other factors responsible for instability include complex morphology and biomechanics of the ankle, muscular weakness, diminished proprioception and postural deficits. Ligament laxity is easy to diagnose hence it becomes the target of surgical intervention. The other factors are difficult to assess clinical and are often neglected. This is probably the reason why surgical treatment of the ligament laxity does not provide the desired outcome. Repairing the ligament to solve the problem of ankle instability is akin to squeezing a square peg into a round hole. A more rounded approach is needed to resolve the problem.

References

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12.  Kitaoka HB, Lee MD, Morrey BF, Cass JR. Acute repair and delayed reconstruction for lateral ankle instability: twenty-year follow-up study. J Orthop Trauma. 1997 Oct;11(7):530-5.

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