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Ankle Syndesmotic Injury

Zalavras, Charalampos MD, PhD; Thordarson, David MD

Author Information
Journal of the American Academy of Orthopaedic Surgeons: June 2007 - Volume 15 - Issue 6 - p 330-339
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Abstract

Ankle injuries may involve the distal tibiofibular syndesmosis and can be associated with a variable degree of trauma to the soft-tissue and/or osseous structures that play an important role in ankle joint stability. Syndesmotic injury may occur solely as a soft-tissue injury or in association with ankle fracture. Even though the injury is common, however, diagnosis of syndesmotic injury may not be straightforward, and optimal management remains controversial.

Anatomy of the Syndesmosis

The distal tibiofibular syndesmosis consists of the anterior-inferior tibiofibular ligament (AITFL), interosseous ligament (IOL), interosseous membrane, posterior-inferior tibiofibular ligament (PITFL), and inferior transverse ligament (ITL) (Figure 1).

Figure 1
Figure 1:
Anterior, posterior, and lateral views of select ligaments of the distal tibiofibular syndesmosis: the anterior-inferior tibiofibular ligament (AITFL); the posterior-inferior tibiofibular ligament (PITFL), of which the inferior transverse ligament (ITL) is part; and the interosseous ligament (IOL), which represents the thickened distal part of the interosseous membrane. The arrows indicate the respective location and point to the cross-sectional view. (Reproduced with permission from Hamilton CC: Traumatic Disorders of the Ankle. New York, NY: Springer-Verlag, 1984.)

The AITFL originates from the anterolateral (Chaput's) tubercle of the tibia and inserts on the anterior (Wagstaffe's) tubercle of the fibula. The IOL represents the thickened distal part of the interosseous membrane. The PITFL originates from the posterior (Volkmann's) tubercle of the tibia and inserts to the posterior part of the lateral malleolus. The fibrocartilaginous ITL forms the distal part of the PITFL.

Mechanism of Injury

The mechanism of syndesmotic injury involves an external rotation force applied to the foot relative to the tibia. The injury may be purely ligamentous, or there may be associated fracture. Associated fractures include pronation-external rotation ankle fracture (Weber type C), supination-external rotation ankle fracture (Weber type B), and fracture of the proximal fibula (Maisonneuve).

Diagnosis

Physical Examination

Diagnosis of syndesmotic injury is based on careful clinical and radiographic evaluation. In the absence of fracture, symptoms include ankle pain and tenderness directly over the anterior aspect of the syndesmosis, with minimal tenderness over the anterior talofibular or calcaneofibular ligaments. The squeeze test and the external rotation test may be useful for diagnosing purely ligamentous syndesmotic injuries. In the squeeze test,1 compression of the fibula to the tibia above the midpoint of the calf causes separation of the two bones distally2 and pain at the area of the syndesmosis. In the external rotation test, pain over the syndesmosis is elicited with external rotation of the foot while the leg is stabilized with the knee flexed at 90°.

Radiographic Evaluation

Radiographic evaluation should include three views of the ankle joint (anteroposterior [AP], mortise, lateral) as well as two views of the entire length of the tibia and fibula (AP, lateral). Radiographs are evaluated for the presence of ankle fracture and proximal fibula fracture (Figure 2), as well as for disruption of the normal relationship between the distal tibia and distal fibula, which is indicative of syndesmotic injury. The following radiographic parameters have been proposed as indications of syndesmotic injury: increased tibiofibular clear space, decreased tibiofibular overlap, and increased medial clear space3–5 (Figure 3).

Figure 2
Figure 2:
Fracture of the proximal fibula indicative of syndesmotic injury. Anteroposterior (A) and lateral (B) radiographic evaluation of the entire length of the fibula is essential to avoid missing a Maisonneuve fracture and the associated syndesmotic injury.
Figure 3
Figure 3:
Normal syndesmotic relationships include a tibiofibular clear space (open arrows) <6 mm in both the anteroposterior and mortise views, as well as a tibiofibular overlap (solid arrows) >6 mm or >42% of the width of the fibula on the anteroposterior view, or >1 mm on the mortise view. The overlap is measured 1 cm proximal to the plafond. (Reproduced from Stephen D: Ankle and foot injuries, in Kellam JF, Fischer TJ, Tornetta P III, Bosse MJ, Harris MB [eds]: Orthopaedic Knowledge Update: Trauma 2. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2000, p 210.)

Tibiofibular clear space is the distance between the medial border of the fibula and the lateral border of the posterior tibia as it extends into the incisura fibularis. The tibiofibular clear space is measured 1 cm proximal to the plafond and should be <6 mm in both the AP and mortise views3 (Figure 3).

Tibiofibular overlap is the overlap of the lateral malleolus and the anterior tibial tubercle measured 1 cm proximal to the plafond. In the AP view, the overlap should be >6 mm or >42% of the width of the fibula, whereas in the mortise view it should be >1 mm3 (Figure 3).

Medial clear space is the distance between the lateral border of the medial malleolus and the medial border of the talus, measured at the level of the talar dome. In the mortise view with the ankle in neutral position, the medial clear space should be equal to or less than the superior clear space between the talar dome and the tibial plafond.5 An increase in the medial clear space indicates a deltoid ligament injury.

Increased tibiofibular clear space is considered the most reliable indicator of syndesmotic injury.3,4 Pneumaticos et al4 demonstrated that the width of the tibiofibular clear space does not change significantly within an arc from 5° of external rotation to 25° of internal rotation and therefore is not dependent on variations in positioning of the extremity relative to the x-ray beam. In contrast, tibiofibular overlap and medial clear space progressively decrease with internal rotation.

Evidence of syndesmotic injury may not be apparent on static injury radiographs. Stress (external rotation) radiographs may be useful for diagnosing latent syndesmotic injury and for establishing an indication for surgery. Edwards and DeLee6 used stress radiographs to diagnose syndesmotic injuries without fracture and classified ankle diastasis as frank (evident on initial radiographs) or latent (apparent only on stress radiographs). The commonly used stress mortise view shows lateral displacement of the fibula, whereas a stress lateral view shows posterior displacement. Cadaveric studies demonstrate that diastasis of the syndesmosis occurs primarily with posterior displacement of the fibula relative to the tibia.7,8 In both studies, fibular movement was greater in the sagittal than in the coronal plane.7,8

Other Diagnostic Modalities

Advanced techniques for diagnosis of syndesmotic injury include computed tomography (CT), magnetic resonance imaging (MRI), and arthroscopy. CT is able to detect minor (2- to 3-mm) syndesmotic diastasis not apparent on plain radiographs.9 MRI is highly sensitive and specific for the diagnosis of syndesmotic injury.10,11 Oae et al11 evaluated 58 patients with distal fibula fracture or ankle sprain with preoperative MRI and ankle arthroscopy. MRI had a sensitivity of 100% and specificity of 93% for diagnosis of AITFL rupture, using ankle arthroscopy as the benchmark.11 The clinical significance of these diagnostic modalities in the evaluation and management of syndesmotic injury remains unclear.

Nielson et al12 prospectively evaluated 70 patients with ankle fracture, using MRI to determine the role of radiographic measurements in the diagnosis of syndesmosis injury. Increased medial clear space (>4 mm) correlated with rupture of the deltoid and tibiofibular ligaments; however, normal tibiofibular overlap and clear space measurements did not preclude syndesmotic injury. This finding underscores the importance of clinical history, physical examination, and intraoperative stress testing to determine stability of the syndesmosis.

Associated Fracture Location

High fibula fracture has traditionally been associated with syndesmotic disruption. Although such a fracture should alert the treating surgeon to the potential for ankle mortise instability, not all high fibula fractures are associated with ankle syndesmosis instability. A proximal fibula fracture may occur with an external rotation injury that produces an incomplete syndesmotic injury and spares the posterior syndesmosis and the deep deltoid. In a clinical study of nine patients with high fibula fractures, eight of whom were treated nonsurgically, a satisfactory outcome was achieved in eight patients at mean follow-up of 26 months.13 A proximal fracture also may occur from direct trauma to the lateral side of the leg, causing a fracture of the fibula without distal instability.14

Effect of Syndesmotic Injury on Ankle Stability

Cadaveric experiments have demonstrated that the distal tibiofibular syndesmosis plays a secondary role in ankle joint stability, whereas the deltoid ligament is a primary stabilizer. Boden et al15 transected the syndesmosis, then sequentially divided the interosseous membrane in 1.5-cm increments in two groups of cadavers: one with intact medial structures and one with sectioned deltoid ligament and anteromedial capsule. The group with intact medial structures, simulating a rigidly fixed medial malleolus fracture, demonstrated minimal widening of the syndesmosis under load (1.4 mm), even with sectioning of the interosseous membrane to 15 cm proximal to the ankle. In contrast, the group with a sectioned deltoid ligament demonstrated progressive widening of the syndesmosis (from 0.5 to 4.5 mm) with disruption of the interosseous membrane (from 1.5 to 15 cm proximal to the ankle). Sectioning of the interosseous membrane from 3 to 4.5 cm proximal to the ankle resulted in a large increase in widening of the syndesmosis (from 1.0 to 1.7 mm).15

Michelson and Waldman16 reported that a fibular fracture 4 cm proximal to the plafond and syndesmotic disruption up to 6 cm did not alter coupled motion of the talus in the absence of deltoid injury. However, when the deep deltoid was cut, the ankle dislocated at 20° to 30° of plantar flexion.16

The posterior tibiofibular ligament is attached to the posterior malleolar fragment; thus, fracture of the posterior malleolus indicates increased instability. The key factor determining the need for intervention, however, is the status of the deep deltoid ligament. Therefore, disruption of the distal tibiofibular syndesmosis is not in itself an important factor for ankle instability; however, the coexistence of deltoid injury critically changes ankle motion and destabilizes the ankle joint.

Preoperative stress radiographs may be beneficial in the diagnosis of deltoid incompetence in the patient with an intact medial malleolus. In the patient with an isolated fibula fracture, the presence of medial tenderness, ecchymosis, and swelling has been considered an indicator of deep deltoid ligament injury and helps differentiate stable Weber type B supination-external rotation injury (which can be managed nonsurgically) from unstable injury (which requires surgical management). Recent studies have demonstrated that clinical examination cannot accurately diagnose deltoid injury;17 stress radiographs are encouraged to assess ankle stability and determine the need for surgical intervention.18–20

Indications for Syndesmosis Fixation

Boden et al15 attempted to clarify the indications for syndesmosis fixation based on their experimental data. They suggested that stabilization of the syndesmosis is unnecessary in a stable fibula fracture (regardless of location) associated with a rigidly fixed medial malleolus fracture, and in a fixed fibula fracture within 3 to 4.5 cm of the ankle joint in association with a deltoid tear.

These guidelines were evaluated in a prospective clinical study by Yamaguchi et al.21 Of 21 patients with a Weber type C ankle fracture, only the 3 who sustained a fibula fracture more than 4.5 cm proximal to the ankle joint associated with a deltoid tear underwent syndesmosis fixation. The remaining 18 patients did not demonstrate syndesmosis widening >1 mm at final follow-up (1 to 3 years). The authors concluded that syndesmosis fixation is indicated only for a fibula fracture located at least 4.5 cm above the ankle joint in the presence of a deltoid ligament tear.21 This recommendation is based on two assumptions: first, that fixation of a medial malleolar fracture is equivalent to an intact deltoid, and second, that the interosseous membrane tear is limited to the level of the fibula fracture.

Fixation of a Medial Malleolar Fracture

Tornetta20 challenged the notion that injury to the medial side of the ankle will involve in a mutually exclusive way either the osseous (medial malleolus fracture) or the ligamentous (deltoid) structures. In 27 patients with bimalleolar fracture, anatomic reduction and internal fixation of the medial malleolus was done, after which the ankle was evaluated under stress to assess the medial clear space and the presence of talar subluxation. In 26% of fractures (7/27), the stress radiograph demonstrated medial clear space >4 mm and talar subluxation >1 mm, indicating that deltoid incompetence was present in conjunction with fracture of the medial malleolus.20 The size of the medial malleolar fragment was the most important variable in predicting deltoid competence. The deltoid ligament was spared in supramalleolar fractures, whereas the deltoid was incompetent in fractures of the anterior malleolus (Figure 4).

Figure 4
Figure 4:
Bimalleolar fracture showing osseous and ligamentous disruption on the medial side. (Reproduced with permission from Tornetta P III: Competence of the deltoid ligament in bimalleolar ankle fractures after medial malleolar fixation. J Bone Joint Surg Am 2000;82:843-848.)

Injury to the medial side may be a combination of osseous and ligamentous disruption. Anterior colliculus fracture can be fixed when it is noncomminuted and large enough (approximately 1 cm × 1 cm) to accommodate a screw, but fixation of the medial malleolus fracture does not necessarily restore competence of the deltoid ligament or stability of the ankle joint.

Yamaguchi et al,21 however, imply that although stability may not be completely restored by fixation of the medial malleolus because of concomitant deltoid injury, the degree of stability established may be enough for clinical purposes.

Interosseous Membrane Tear

Nielson et al22 prospectively evaluated the MRI scans of patients with ankle fracture to assess the integrity of the interosseous membrane. The authors found that 30 of 73 ankle fractures were associated with interosseous membrane tears. In 10 of these 30 fractures (33%), the level of the interosseous membrane tear did not correspond to the level of the fractured fibula. In 7 of 30 fractures (23%), the tear extended more proximally than the level of the fibula fracture.22

The interosseous membrane tear may extend proximal to the level of the fibula fracture, and it may not be possible to judge the stability of the syndesmosis by the location of the fibula fracture. A low fibula fracture (Weber type B) does not exclude the need for syndesmosis fixation18,23 (Figure 5, A); syndesmotic instability has been described with low fibula fracture. In a recent series of 51 ankle fractures managed with syndesmotic fixation, 15 (30%) were Weber type B fractures, whereas 36 (70%) were Weber type C fractures.24 This study did not have a control group, however, so the fact that syndesmosis screws were used does not mean that they were necessary for a satisfactory clinical result.

Figure 5 A,
Figure 5 A,:
Anteroposterior radiograph demonstrating Weber type B supination-external rotation ankle fracture associated with disruption of the syndesmosis. B, Syndesmosis fixation with a single 4.5-mm screw.

Intraoperative Assessment

Intraoperative assessment of syndesmotic stability is based on the Cotton test25 and imaging evaluation. The Cotton test involves placing a bone hook or key elevator on the fibula and applying a distraction force in an attempt to separate the fibula from the tibia. A 3- to 4-mm lateral shift of the talus indicates syndesmotic instability. Under imaging, applying external rotation stress on the ankle joint may demonstrate increased tibiofibular clear space, decreased tibiofibular overlap, and increased medial clear space. Our preferred method is to obtain a fluoroscopic external rotation stress mortise view for evaluating the medial clear space; this view is the easiest to interpret.

A recent study by Jenkinson et al19 prospectively investigated the predictive value of the biomechanical criteria for syndesmosis fixation described by Boden et al.15 The authors compared static preoperative radiographs with intraoperative fluoroscopic stress testing in external rotation ankle fractures. Intraoperative fluoroscopy detected syndesmotic instability that was not predicted by biomechanical criteria in 4 of 7 (57%) pronation-external rotation injuries, and in 10 of 30 (33%) supination-external rotation injuries.19 Overall, unpredicted syndesmotic instability was intraoperatively demonstrated in 37% of fractures. The degree of instability after rigid bimalleolar fixation was small (mean difference, 1.9 mm of tibiofibular clear space between the injured and the contralateral ankle), and relevance of this residual instability to adverse clinical outcome was not demonstrated.19

Routine intraoperative testing is necessary for detection of syndesmotic instability, and the decision whether to perform syndesmosis fixation must be individualized to each patient. In our opinion, fixation of the syndesmosis is indicated whenever intraoperative evidence of syndesmotic diastasis is present after rigid fixation of medial malleolus and fibula fractures. However, the clinically relevant degree of syndesmotic instability has not been established.

Management

With syndesmotic injury, the goal of management is to restore and maintain the normal tibiofibular relationship to allow healing of the ligamentous structures of the syndesmosis.

Syndesmotic Injury Without Fracture

Syndesmotic injury may occur in the absence of fracture (syndesmotic or high ankle sprain). Hopkinson et al1 reported that syndesmotic sprain accounted for approximately 1% of ankle sprains (15/1,344) sustained by cadets at the United States Military Academy. Syndesmotic injuries have also been reported in athletes.26,27

Edwards and DeLee6 classified acute syndesmotic sprain into three categories: sprain without diastasis, sprain with frank diastasis (evident on initial radiographs), and sprain with latent diastasis (normal initial radiograph but instability apparent on stress radiographs).

Syndesmotic sprain usually is not associated with diastasis or instability. In the absence of syndesmotic diastasis or instability, the patient can be treated nonsurgically. Nonsurgical management begins with rest, ice, compression, and elevation. Subsequently, a non-weight-bearing cast is used for 2 to 3 weeks, after which time the patient is allowed to progressively bear weight as tolerated using a walking boot. In the series by Hopkinson et al,1 13 of 15 syndesmotic injuries were managed nonsurgically, whereas 2 injuries associated with ankle instability were treated surgically. The recovery time for patients with syndesmotic sprain was considerably longer compared with patients with severe nonsyndesmotic ankle sprain (55 versus 28 days). In the 10 syndesmotic injuries evaluated at a mean 20-month follow-up, no ankle was unstable. Interosseous calcification was observed in 9 of 10 ankles.1

Syndesmotic sprain occasionally may be associated with ankle instability. Edwards and DeLee6 reported on six patients with syndesmotic instability without fracture. Diastasis was evident on routine radiographs, and all patients underwent syndesmotic screw fixation. When initial radiographs are negative and clinical examination is suggestive of syndesmosis injury, stress radiographs may be useful for diagnosing a latent diastasis. In the series by Hopkinson et al,1 one of seven patients with syndesmotic injury demonstrated latent instability on stress radiographs; this patient underwent transfixation of the syndesmosis. Other authors have proposed nonsurgical management of syndesmotic sprain with latent diastasis with a non-weightbearing cast for 4 to 6 weeks, provided that anatomic reduction of the fibula can be achieved and maintained.27

Syndesmotic Injury Associated With Fracture

Restoration of the proper tibiofibular relationship involves regaining fibular length and reestablishing correct rotation and position of the fibula relative to the tibia. Accurate restoration of fibula length, which is necessary to avoid talar subluxation, is achieved with open anatomic reduction and stable fixation of the fibula fracture in external-rotation type ankle fracture. When the fibula fracture is located in the middle or proximal one third of the diaphysis, length and rotation may be restored indirectly. Michelson et al28 evaluated 26 ankle fractures on CT. Internal rotation of the proximal fibula relative to the tibia occurred in 19 of these fractures. However, a subsequent CT evaluation of externalrotation type ankle fractures showed internal rotation of the proximal fibula in 1 of 26 ankles and demonstrated that the distal fibular fragment rotates externally relative to the proximal fibular fragment.29 As such, the reverse movement (internal rotation of the distal fibular fragment) should be used to assist reduction of the fibula in the proper location against the tibia, into the fibular notch.

When the fibula fracture is treated indirectly, proper length and rotation are assessed by intraoperative imaging of the involved ankle joint. In the mortise view, attention should be paid to restoration of the medial clear space, tibiofibular overlap, and tibiofibular clear space. The dense subchondral bone of the distal tibia should be at the same level as a small spike seen on the fibula, resulting in an unbroken Shenton's line of the ankle.30 The lateral view should also be evaluated to ensure the proper position of the fibula relative to the tibia in the sagittal plane.

Syndesmosis Fixation

The optimal method of syndesmosis fixation remains to be determined. Controversies surround implant selection (ie, size of screws, number of cortices engaged, composition of implants), position of the ankle joint during syndesmosis fixation, postoperative weight-bearing status, and the need and timing for implant removal.

Screw Size

Both 3.5- and 4.5-mm screws have been used for syndesmotic fixation. In a cadaveric study,31 their biomechanical properties were found to be similar. The larger head of the 4.5-mm screw may facilitate screw removal in the clinic, but it may cause patient discomfort (Figure 5, B).

Number of Cortices

Syndesmotic screw fixation may involve a total of three or four cortices of the fibula and tibia. A cadaveric study using a 4.5-mm screw engaging four cortices demonstrated decreased tibiotalar external rotation.32 Engaging three cortices may allow greater physiologic motion, which more commonly leads to hardware loosening rather than to failure.33,34 Engaging four cortices improves syndesmosis stability, but it is unclear whether it results in any difference in clinical outcome.

In a prospective randomized study, Hoiness and Stromsoe35 compared fixation of the syndesmosis with two tricortical 3.5-mm screws (n = 34) with fixation with one quadricortical 4.5-mm screw (n = 30). No differences in pain, ankle dorsiflexion, and function were observed at 1 year. However, in this study, the number of cortices was not the only variable of the fixation technique that differed between groups.

Screw Composition

Metal screws traditionally have been used for syndesmosis fixation. However, they require removal to restore the biomechanics of the syndesmosis; when left in place, they may break or loosen. Bioabsorbable screws have been proposed as an alternative because they eliminate the need for removal.36–38 Hydrolysis and degradation of the bioabsorbable implant will gradually reduce its strength39 and lead to failure of the implant sometime after initiation of weight bearing, which is believed to restore normal motion of the syndesmosis.36

Thordarson et al37 compared a 4.5-mm polylactide bioabsorbable screw with a stainless steel screw of the same size in a cadaveric model of syndesmotic injury. No differences in load to failure and stiffness were noted between the two groups.

In a subsequent randomized clinical trial, Thordarson et al38 tested the hypothesis that syndesmosis fixation with a polylactide screw, which retains 80% of its tensile strength at 4 weeks, is equivalent to stainless screw fixation. Seventeen patients were randomized to bioabsorbable syndesmotic screw fixation and 15 to stainless steel screw fixation. At a mean 11-month follow-up, there was no medial clear space widening or loss of syndesmosis reduction in any patient, and there was no difference in subjective complaints or range of motion of the ankle joint between the two groups. Bioabsorbable screw fixation did not result in osteolysis or inflammatory reactions.38

In a prospective clinical study, Hovis et al36 evaluated the use of polylevolactic acid bioabsorbable screws for fixation of the syndesmosis. None of the 23 patients available for long-term follow-up (mean, 34 months) demonstrated medial clear space widening, loss of syndesmosis reduction, osteolysis, or inflammatory reactions. Recent cadaveric40 and clinical studies41 found no differences between bioabsorbable and metallic screws.

Surgical Technique

Syndesmotic screws should be inserted parallel to the ankle joint in the coronal plane. A screw that is not parallel to the joint may either shorten or lengthen the fibula. A cadaveric study indicated that placement of a syndesmotic screw at a distance of 2 cm proximal to the ankle joint resulted in less syndesmotic widening compared with a screw placed at 3.5 cm proximal to the joint.42 A clinical study, however, found no difference in outcome in patients who had a syndesmotic screw placed 2 cm proximal to the joint versus 3 to 5 cm proximal.43 In the transverse plane, the screw should follow a 25° to 30° oblique direction from posterolateral to anteromedial because the fibula is located posterior to the tibia (Figure 6). The screw that is not directed anteriorly may miss the tibia.

Figure 6
Figure 6:
Proper placement of a syndesmotic screw. In the transverse plane, the screw should follow a 25° to 30° oblique direction from posterolateral to anteromedial. (Reproduced with permission from Carr J: Malleolar fractures and soft tissue injuries of the ankle, in Browner BD, Jupiter JB, Levine AM, Trafton PG [eds]: Skeletal Trauma, ed 3. Philadelphia, PA: WB Saunders, 2003, vol 2, p 2309.)

During syndesmotic screw insertion, reduction should be held with a clamp to avoid shifting of the drill holes. Each screw should be fully threaded and not inserted in lag fashion. The drill should be centered on the fibula to avoid fracturing the bone.

It has been proposed that the ankle joint should be in a position of maximum dorsiflexion during screw insertion. This recommendation is based on the anatomy of the talar dome, which is trapezoidal in shape, with the posterior part of the talus 2.5 mm narrower than the anterior part. This anatomic fact creates the concern that syndesmotic screw fixation with the ankle in plantar flexion may limit dorsiflexion, since the wider anterior part of the talar dome must be accommodated in the mortise, which may lead to overtightening of the syndesmosis, with adverse mechanical consequences.32

However, Tornetta et al44 demonstrated in a cadaveric study that syndesmotic compression with the ankle in plantar flexion does not limit dorsiflexion and maximal dorsiflexion of the ankle during fixation of the syndesmosis is not necessary to avoid loss of dorsiflexion. This observation may facilitate management because dorsiflexion recreates the deforming force of external rotation and may contribute to malreduction of an unstable syndesmosis. In this study, however, the authors used an unloaded method of testing to assess resultant range of motion;44 thus, the optimal position of the ankle during screw insertion remains controversial.

In the presence of a bony avulsion of the insertion of a syndesmotic ligament, open reduction and internal fixation with a screw can be performed, provided the bony fragment is large enough. This bony fragment will most commonly be the bony insertion of the AITFL on the tibia (ie, Chaput's tubercle). With good fixation, syndesmotic transfixation may not be necessary.

Authors' Preferred Method

We use one syndesmotic screw when simultaneously fixing an associated fibula fracture. For the middle or proximal shaft fibula fracture that is not stabilized, we prefer to use two syndesmotic screws (Figure 7). The degree of instability and the size of the fibula should be considered when selecting screw size and determining the number of cortices to be engaged. In the presence of minimal instability and in a fibula of small size, we use a 3.5-mm screw, engaging three cortices. We prefer a 4.5-mm screw through four cortices in the presence of increased instability in the fibula of larger dimensions. We currently use metallic screws because of difficulty in acquiring bioabsorbable ones.

Figure 7
Figure 7:
Syndesmosis fixation with two screws in the presence of a proximal third (Maissonneuve) fracture of the fibula that was not stabilized.

Postoperative Management

Controversy exists regarding postoperative weight-bearing status and the need for screw removal. A commonly used postoperative regimen includes no weight bearing until screw removal, at a minimum of 12 weeks, to allow enough time for healing of the disrupted syndesmotic ligaments. Recurrence of syndesmotic diastasis following early screw removal has been described.9,45

Alternatively, weight bearing can be initiated with the syndesmotic screw(s) in place. In such instances, the patient should be warned that screw loosening and/or breakage may occur.

We prefer to keep the patient non-weight-bearing for 6 weeks, after which the patient begins weight bearing in a short leg walking cast for 2 weeks, followed by use of a soft ankle brace for 4 weeks. At 12 weeks, we remove the syndesmotic screws.

Outcomes

Failure to diagnose and stabilize syndesmotic disruption adversely affects outcome.24,46–49 Pettrone et al48 evaluated subjective patient response, objective clinical outcome, and radiographic results of 146 ankle fractures with a minimum 1-year follow-up using a scoring system ranging from 0 to 12 points (12 being the best possible outcome). The authors reported that preoperative syndesmotic instability (demonstrated by abnormal tibiofibular overlap or clear space on AP radiograph) was not a predictive indicator of the final result. Patients with syndesmotic instability evident on injury radiographs had a score of 8.38, compared with 8.96 in patients with stable syndesmosis. The difference was not significant. However, postoperative syndesmotic instability significantly compromised the final outcome (8.11 versus 8.96 points, P = 0.03).48

Leeds and Ehrlich47 studied the results of 34 ankle fractures at a mean 4-year follow-up and concluded that adequate reduction of the syndesmosis had a marked effect on the clinical outcome and incidence of ankle arthrosis. Chissell and Jones49 reviewed 43 Weber type C ankle fractures at a mean 4.5-year follow-up. Nonanatomic reduction of the syndesmosis was present in 44% of patients with fair or poor outcome (7/16), compared with 22% of patients with excellent or good outcome (5/23).49

Weening and Bhandari24 reviewed the functional outcome of 39 patients with syndesmotic screw fixation at a mean 18-month follow-up. Overall, patients achieved functional status similar to that of US population norms, as assessed by the functional index of the Short Musculoskeletal Functional Assessment questionnaire (range, 0-100, with 0 as the best score). Reduction of the syndesmosis was the only significant predictive factor for functional outcome. Patients with a reduced syndesmosis had a mean score of 10.2 versus a score of 17 in patients with a nonreduced syndesmosis (P = 0.04).24 Associated ankle dislocation showed a trend toward decreased function. Patient age, number of cortices, presence of medial malleolar fracture, and screw removal were not significantly associated with functional outcome.

Summary

Injury to the distal tibiofibular syndesmosis occurs secondary to an external rotation force and may be associated with ankle fracture. The concomitant presence of deltoid injury is an important factor leading to instability of the ankle joint. Radiographs may demonstrate signs of syndesmotic injury, such as increased tibiofibular clear space, decreased tibiofibular overlap, and increased medial clear space. However, the diagnosis may not be straightforward.

Preoperative determination of the need for syndesmosis fixation based on predetermined criteria may not be accurate. Routine intraoperative stress testing is recommended for detection of syndesmotic instability. Intraoperative evidence of syndesmotic diastasis after rigid fixation of the medial malleolus and fibula fractures warrants syndesmosis fixation. The proper tibiofibular relationship should be restored and maintained by screw fixation until healing of the syndesmotic ligaments is achieved.

Satisfactory clinical outcome is associated with adequate reduction and stabilization of the syndesmosis. Controversies still surround the size of screws, number of cortices engaged, composition of implants, the position of the ankle joint during syndesmosis fixation, postoperative weight-bearing status, and the need for and timing of implant removal. Overall, there is no evidence strongly supporting one technique over the other, which may mean that each technique can be effective when applied properly.

References

Evidence-based Medicine: Level I/II prospective randomized studies are noted in references 21, 35, 38, and 47. The remaining references are level III/IV case-control, cohort studies or expert opinion (references 25-27, and 34).

Citation numbers printed in bold type indicate references published within the past 5 years.

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