Current Concepts In Treating Syndesmotic Ankle Injuries

In the quest to promote normal biomechanics and avoid complications, surgeons continue to debate appropriate fixation, screw size and other components of surgical repair for syndesmotic ankle injuries. Accordingly, these authors offer pertinent surgical pearls, discuss the intricacies of screw fixation and provide two helpful case studies.

Syndesmotic injuries or high ankle sprains are common and can be very debilitating. Every two minutes, an individual in the United States sustains an ankle fracture.¹ An estimated 10 percent of all ankle sprains involve injury to the syndesmosis. Approximately every 20 minutes in the United States, there is an ankle injury that may require fixation of the distal tibiofibular syndesmosis.¹

There is controversy and debate in the literature regarding the need for fixation, position and method of fixation, screw sizes, number of screws, how many cortices the screws should engage, and whether and when one can remove the screws. Detection of this injury, appropriate treatment and adequate, stable fixation will reduce long recovery times and poor outcomes.

Understanding The Anatomy And Mechanism Of Injury

Syndesmosis is a fibrous articulation in which ligaments unite opposing surfaces.² The distal tibiofibular syndesmosis is important for stability of the ankle mortise and is extremely important for weight transmission and walking. The syndesmosis consists of the anterior inferior tibiofibular ligament, the posterior inferior tibiofibular ligament and the interosseous membrane. We can consider the inferior transverse tibiofibular ligament as a fourth ligament and a continuation of the distal posterior inferior tibiofibular ligament.³

Although the syndesmotic ligaments provide stability, they also permit the distal fibula to rotate approximately 12 degrees relative to the tibia. The anterior inferior tibiofibular ligament originates from the anterolateral tubercle (Chaput’s tubercle) of the tibia and inserts on the anterior tubercle of the fibula (Wagstaffe’s tubercle). The posterior inferior tibiofibular ligament originates from the posterior tubercle (Volkmann’s tubercle) of the tibia and inserts into the posterior portion of the lateral malleolus. The anterior inferior tibiofibular ligament and posterior inferior tibiofibular ligament are the primary stabilizers of the distal tibiofibular articulation. The interior transverse ligament forms the distal portion of the posterior inferior tibiofibular ligament. These ligaments stabilize the ankle mortise by providing strong opposition of the fibula to the fibular notch of the tibia and strong dynamic support to the ankle mortise.²

The interosseous ligament, which is a thickened portion of the distal interosseous membrane, acts as a buffer to axial tibial loading because it transfers a portion of the weightbearing load from the tibia to the fibula. Disruption of this ligament may result in increased compressive stress within the tibia, which will in turn increase the lateral dislocation of the distal fibula and incongruence of the ankle joint. This may disrupt dynamic ankle joint motion and joint position of the talus within the mortise, which can cause abnormal contact pressures and the development of arthritis in the ankle joint.⁴ Another important anatomic consideration is the talus itself. Since the talar dome is wider anteriorly than posteriorly, extreme dorsiflexion can cause separation of the distal tibiofibular articulation and injure the ligamentous structures that stabilize the distal tibia and fibula.

Syndesmotic injuries usually occur when an external rotation force acts on the foot relative to the tibia. Syndesmotic ligament damage may occur with or without a concomitant fracture. Fractures that are typical with this mechanism include pronation-external rotation ankle fractures (Weber C) and fractures of the proximal fibula (Maisonneuve fractures). Isolated syndesmotic injuries mostly result from hyperdorsiflexion with external rotation and axial compression of the tibiotalar joint.³ Syndesmotic injuries can happen in individuals who participate in sports such as football, skiing and soccer that may require planting of the foot and cutting.⁵ However, injuries can also occur with direct blows to the leg, falls, twisting weightbearing injuries and motor vehicle accidents.⁴

Essential Diagnostic Tips

When the surgeon is diagnosing syndesmotic injuries, he or she must perform a thorough lower extremity physical examination along with radiographic evaluation. The literature has described the “squeeze test” and “external rotation test” as being useful in diagnosing syndesmotic injuries.^2,6 In the squeeze test, compression of the fibula and the tibia above the midpoint of the calf causes a slight separation of the two bones distally, resulting in pain at the level of the syndesmosis. In the external rotation test, stabilize the leg with the knee flexed at 90 degrees and externally rotate the foot on the leg. If this elicits pain, the test is positive.

There are also radiographic parameters to diagnose syndesmotic injuries. These include increased tibiofibular clear space, decreased tibiofibular overlap and increased medial clear space.² The anteroposterior view best demonstrates the ankle mortise and tibiofibular syndesmosis. Measure the tibiofibular overlap from the medial aspect of the fibula to the lateral border of the anterior tibial prominence 1 cm above the plafond. This distance should be greater than 10 mm. To adequately measure the tibiofibular clear space, take the width between the medial aspect of the fibula and lateral border of the posterior tibia malleolus 1 cm proximal to the plafond. Ideally, this distance should be less than 5 mm. The medial clear space is the distance between the lateral border of the medial malleolus and the medial border of the talus, which one measures at the level of the talar dome. Widening of the medial joint space greater than 4 mm indicates deltoid ligament injury and lateral talar translation.^2,7

Computed tomography (CT), magnetic resonance imaging (MRI) and arthroscopy may also aid in detecting syndesmotic injuries.^2,8 We recommend these advanced imaging studies in patients who have persistent pain and in whom a clinical and radiographic diagnosis are not definitive. The CT scans are particularly sensitive for minor or partial ruptures, and to assess diastasis. Analysis with MRI can be beneficial because it can aid in revealing secondary findings such as osteochondral lesions and ligamentous injury. Arthroscopy allows clear visualization of the injured site and researchers have shown that it assists in measuring dynamic movements between the tibia and fibula.⁴

Clinicians can also use the Cotton test intraoperatively to assess syndesmotic stability.^2,3,9 This test involves placing a bone hook on the fibula and applying a lateral distraction force in an attempt to separate the fibula from the tibia. A 3 to 4 mm lateral shift indicates syndesmotic instability.³ The surgeon can also perform an intraoperative stress test, which involves applying an external rotation stress on the ankle joint. This may demonstrate an increase in tibiofibular clear space, decreased tibiofibular overlap and increased medial clear space, which would suggest injury to the syndesmotic ligaments. All of these maneuvers are beneficial in diagnosing syndesmotic instability.²

Key Insights On Surgical Management

The goals of treatment for syndesmotic injuries are reduction and maintenance of proper alignment of the ankle joint.¹⁰ At our institution, we surgically treat ankle fractures with a syndesmotic injury. Initially, one has to reduce the fibula, restore its length and stabilize the fracture with appropriate fixation.

Reduce the fibula by putting it back into the fibular notch of the tibia. This involves applying a compressive force between the fibula and tibia, and evaluating the alignment via fluoroscopy. If this does not reduce the fibula, one can apply a downward force to the fibula and this should reduce the fibula into the notch. During the reduction maneuver, leave the foot in a natural plantarflexed position. In preparation for fixation, one can ensure stability of the reduction with a large bone clamp.

During screw insertion, the clamp should hold the reduction to avoid shifting and maintain proper alignment and length. The ankle joint should be dorsiflexed during screw insertion due to the posterior portion of the talar dome being 2.5 mm narrower than the anterior portion. The theory was that if one inserted the screw while the ankle joint was plantarflexed, it would cause limitation in dorsiflexion and pain and stiffness of the ankle.

However, Tornetta and colleagues in a cadaveric study found that screw insertion with the foot plantarflexed does not lead to loss of dorsiflexion.¹¹ Actually, it recreates the deforming force of external rotation and may lead to malreduction of the unstable syndesmosis. It is thus likely that the most important aspect of syndesmotic fixation is anatomical reduction of the syndesmosis and not the degree of ankle dorsiflexion during fixation.³ In our institution, we have inserted screws with the ankle joint in dorsiflexion, plantarflexion and in neutral position, and found no limitation in dorsiflexion at the ankle joint. In fact, we have had difficulty reducing the fibula when the foot is dorsiflexed.

There is debate in the literature on the method of fixation for these injuries and a considerable amount of research has been devoted to determine the best fixation technique for syndesmotic injuries. Surgeons have used both 3.5 and 4.5 mm cortical screws for syndesmotic fixation.^1-3,10,12-14 Fixation may involve either three or four cortices of the fibula and tibia. Authors have suggested that engaging three cortices permits physiologic motion but may also lead to hardware loosening and loss of alignment. Researchers have shown that engaging four cortices improves syndesmosis stability.¹⁵ Surgeons usually use metal screws for syndesmosis fixation but these may eventually require removal so they do not break or loosen. Authors have advocated bioabsorbable screws because they eliminate the need for removal but hydrolysis and degradation may gradually reduce their strength prior to healing.^2,15

FiberWire (Arthrex) may also stabilize the syndesmosis and does not require removal.^16,17 The FiberWire is a surgical implant based on the suture EndoButton design. Authors have described it as an effective technique to fix syndesmotic injuries while avoiding complications associated with the use of traditional metallic screws, specifically screw breakage, stiffness and hardware pain.^16-18 Cottom and colleagues studied 25 patients with disruption of tibiofibular articulation who had fixation using FiberWire.¹⁶ They stated that the FiberWire allows for stability in the syndesmosis with the implant remaining in place until there is full ligament healing. The study related that the FiberWire provided semi-rigid dynamic stabilization. The benefits were that FiberWire provided consistent and accurate reduction of the syndesmosis, and would obviate the need for hardware removal.^16,17

Should You Remove Syndesmotic Screws?

There is ongoing debate in the literature as to whether one should remove syndesmotic screws and even whether patients should bear weight prior to screw removal. Qamar and coworkers related that although routine removal of syndesmotic screws is not required, surgeons typically remove screws due to the possibility of hardware irritation or reduced range of motion after four to six months.¹⁹ In their study, the authors stated several problems that have been associated with syndesmotic screw fixation, which include lack of motion that may result in synostosis, screw loosening and screw breakage. Some authors advocate removal of screws to restore normal biomechanics of the syndesmosis and improve function.³ The theory is that premature weightbearing could cause abnormal ankle motion and result in possible fatigue failure of the screw.

In our institution, we routinely remove screws three months after fixation to avoid breakage and loosening. If a screw does break when one uses four cortices, it is easier to remove it through the medial or lateral approach.

Other factors to consider are patient preference and complaints of painful retained hardware. There is no consensus regarding weightbearing status after repair of the syndesmosis with screw fixation. Some studies suggest that patients should only bear weight after syndesmotic screw removal because studies have shown syndesmotic fixation to help limit tibiotalar external rotation, increase talar inversion and impart compressive strains on the lateral aspect of the fibula.¹³ In our institution, we have allowed patients to bear weight after fracture healing and before routine syndesmotic screw removal, and have found no significant disruption in the ankle mortise or retained hardware.

Current Insights On Surgical Technique And Screw Selection

Once you have achieved accurate reduction, insert syndesmotic screws parallel to the ankle joint in the coronal plane to maintain reduction. Ideally, place the screw 2 to 4 cm proximal to the ankle joint and 25 to 30 degrees from the posterolateral position to anteromedial, keeping in mind that the tibia is located anterior to the fibula.^2,3,13 During screw insertion, a clamp should hold the reduction to avoid shifting and maintain proper alignment and length. It is thus likely that the most important aspect of syndesmotic fixation is anatomical reduction of the syndesmosis and not the degree of ankle dorsiflexion during fixation.³

Screw selection, the number of screws used and the number of cortices that the screws engage all depend on patient variables. These include body mass index, comorbidities including osteoporosis, neuropathy, smoking, activity level, fracture pattern, and degree of the fracture and syndesmotic instability.¹⁰

A survey by Bava and colleagues found that surgeons used 3.5, 4.0, 4.5 and 6.0 mm non-cannulated screws to fix syndesmotic injuries.¹⁰ The report found that the larger screws were more prominent and caused discomfort. They concluded that the benefit of using 3.5 mm screws included a less prominent screw head. However, 3.5 mm screws also had inferior fatigue performance in comparison to 4.5 mm screws. The authors noted that the use of K-wires for stabilization of syndesmosis was comparable to a 3.5 mm screw with two oblique K-wires.¹⁰ Interestingly, this study found that increased stiffness and resistance to external rotation occurred with use of two screws with four cortices engaged instead of three cortices engaged with a single syndesmotic screw. Also, other authors have stated that loosening is more likely when screws engage three instead of four cortices.³

We have found in our institution that using two 4.0 mm or 4.5 mm fully threaded cortical screws with quadricortical fixation has given us excellent results, especially in non-adherent patients or patients with osteoporosis. We have found this type of fixation is more beneficial in creating a stable construct, especially in fractures that are comminuted or with complete failure of all of the syndesmotic ligaments. We also recommend this form of fixation in patients who have poor bone quality and these patients often include smokers, those with diabetes and the geriatric population.

Many studies have focused on what size of screw is superior in fixating these injuries.^1-3,10,13,14 A study by Stuart and colleagues determined that the central core or minor root diameter of a 3.5 mm cortical screw is similar to a 4.0 mm cortical screw so biomechanically, both should have similar fatigue strength.¹ A 4.5 mm screw has a larger core diameter and is likely to be superior to either the 3.5 mm or 4.0 mm diameter screw. Their study found that none of the 4.5 mm screws demonstrated radiographic evidence of loosening or backing out. Also, none of the 4.5 mm screws were associated with loss of syndesmotic reduction. This study supports the concept that the larger diameter screw would provide stronger fixation for the syndesmosis.

Moore and colleagues found in their prospective study that either three or four cortices of fixation are sufficient to stabilize the syndesmosis during healing and there was no significant difference between the two groups with regard to loss of reduction.¹⁴ However, there did appear to be a trend toward higher loss of reduction using two 3.5 mm cortical screws traversing three cortices versus two 3.5 mm screws traversing four cortices. There continues to be a debate in the literature as to which device and method are best.

Case Study One: Achieving Stability With Quadricortical Fixation

A 66-year-old male sustained an injury to his right ankle after falling on ice and twisting his right ankle. The patient’s past medical history was unremarkable and he denied smoking. The radiographic examination revealed a trimalleolar ankle fracture of the right ankle with diastasis between the tibia and the lateral malleolus.

In the emergency department, we performed closed reduction of the patient’s right ankle and immobilized it with a posterior splint. His surgery consisted of open reduction with internal fixation of the right ankle. We reduced the fibular fracture and inserted an interfragmentary 3.5 mm cortical screw, first crossing the fracture with subsequent application of a 1/3 tubular plate using 3.5 mm cortical screws. We proceeded to insert a single 4.0 cancellous screw through the plate at the distal aspect of the fibula. Following syndesmotic reduction of the fibula, we inserted two 4.5 mm fully threaded cortical screws from lateral through the fibula into the tibia, achieving quadricortical fixation for the syndesmosis. The posterior malleolar fragment did not have fixation because it comprised only 10 percent of the tibia and had appropriate reduction. Although the deltoid ligament had been torn, we did not repair it.

Postoperatively, the patient wore a non-weightbearing, below-knee cast for two weeks and then wore a controlled ankle motion (CAM) boot, and bore partial weight. At eight weeks, radiographs revealed consolidation of the fibula. He went to physical therapy for four weeks to reduce swelling, increase ankle motion and increase strength and endurance. The patient returned to full activity in an athletic shoe in 12 weeks and was pain-free. We did not remove the syndesmotic screws postoperatively because the patient was asymptomatic and did not want them removed.

We believe the quadricortical fixation with larger diameter bone screws achieved greater stability and less likelihood of hardware loosening. This allowed the patient to remain pain-free and allowed early weightbearing without complications.

Case Study Two: When A Tricortical Screw Fails In A Non-Adherent Patient

A 59-year-old male presented to the emergency department after tripping and twisting his left ankle. His medical history was positive for hypertension, hyperlipidemia and type 2 diabetes. Medications consisted of valsartan (Diovan, Novartis Pharmaceuticals), atorvastatin (Lipitor, Pfizer) and glyburide (Micronase, Pfizer). Radiographic examination revealed a Weber B comminuted fibular fracture and increased medial clear space. The fracture pattern was consistent with a supination external rotation mechanism of injury.

The patient’s surgery consisted of an open reduction internal fixation of the left ankle fracture using a 3.5 mm cortical screw across the fracture, a 1/3 tubular plate attached with 3.5 mm cortical screws and a 4.0 mm cancellous screw distally. After fixation, we noted that fibular motion was greater than expected. Inspection revealed only a tear of the anterior tibiofibular ligament but because of the patient’s diabetes and soft bone, we inserted a single 4.0 mm, fully threaded cortical screw, purchasing three cortices.

Postoperatively, the patient wore a non-weightbearing, below-knee cast for four weeks and then a non-weightbearing CAM boot for an additional four weeks. He was supposed to be non-weightbearing but did walk in his cast and CAM boot. At eight weeks, radiographs revealed loosening and displacement of the syndesmotic screw, lateral shifting of the talus and a loss of syndesmotic reduction. The patient developed an infection in the area in which the head of the syndesmotic screw penetrated through the skin.  

Surgery consisted of removal of the syndesmotic screw and incision and drainage. We noted that the fibular fracture had not healed. We debrided necrotic bone in the fibula at the screw site and obtained a bone biopsy. We packed antibiotic impregnated beads into the surgical site. The bone biopsy confirmed osteomyelitis and the patient received six weeks of IV antibiotics.

At seven weeks, following the incision and drainage procedure, the patient went back to surgery for a revision. We removed all remaining fixation and applied a locking plate to the fibula attached with 2.7 mm locking screws distally and 3.5 mm cortical screws proximally. We reduced the fibula into the fibular notch and inserted two 4.0 mm cortical screws, purchasing all four cortices.

Postoperatively, the patient wore a CAM boot and remained non-weightbearing for six weeks. He bore partial weight for an additional two weeks. Three months after the revision of the ankle surgery, the fracture had completely healed with no evidence of osteomyelitis recurrence and the patient had returned to all of his pre-fracture activities.

This case demonstrates syndesmotic failure in a Weber B fracture stabilized with a single tricortical screw in a non-adherent patient with diabetes and osteoporosis.
 
In Conclusion

Ankle syndesmotic injuries are complex and require accurate reduction and fixation to restore the normal biomechanics of the ankle joint and avoid long-term complications. There continues to be an ongoing debate in the literature on the need for fixation, the position and method of fixation, screw sizes and the number of screws used, how many cortices the screws should engage, and whether and when one should remove the screws. The surgeon should tailor the treatment plan to each patient individually and provide the most stable construct in order to minimize complications. Future randomized controlled trials are warranted to further elucidate proper outcomes.

Dr. Bawa is a second-year podiatric surgical resident at Oakwood Wayne Hospital in Wayne, Mich.

Dr. Fallat is the Program Director of Podiatric Surgical Residency at Oakwood Hospital-Wayne in Wayne, Mich. He is a Fellow of the American College of Foot and Ankle Surgeons.

References

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Editor’s note: For further reading, see “Mastering The Treatment Of High Ankle Sprains” in the January 2011 issue of Podiatry Today or “Mastering The Treatment Of Complex Ankle Sprains” in the March 2011 issue.