Syndesmotic Widening Research Articles

Varus External Rotation Stress Test for Radiographic Detection of Deep Deltoid Ligament Disruption With and Without Syndesmotic Disruption

External rotation stress is used intraoperatively for diagnosing medial ankle and syndesmotic instability in rotational ankle fractures after reduction and fixation of the fibula. However, external rotation includes hindfoot, midfoot, and ankle motion. The purpose of this study was to determine the effect of hindfoot positioning when using the external rotation stress test. Isolated deep deltoid ligament (DDL) instability and combined DDL and syndesmotic instability were modeled. An intact fibula was used as a surrogate for an anatomically fixed fibula fracture. Six cadaver specimens with full-length tib-fib articulations were used. Specimens were fixed into a Taylor Spatial Frame (Smith&Nephew, Memphis, TN) with 4 to 5 points of fixation in the tibia and the foot. Specimens were mounted in ankle and foot neutral position. Metal markers were placed at the medial gutter and syndesmosis. Anteroposterior (AP) and mortise radiographs were obtained in 3 positions: neutral hindfoot, valgus external rotation stress, and varus external rotation stress. For both valgus and varus external rotation stress, the frame was loosened and stressed to a hard end point and then locked. Three modes were studied: intact ligaments, DDL transected, and DDL+ syndesmosis transected. Digital radiographs were used to measure the displacement of the markers. The varus external rotation stress test demonstrated significant widening of the medial gutter in specimens with isolated DDL instability, in both AP (P = .01) and mortise (P = .02) views. Both maneuvers demonstrated significant medial gutter widening with combined DDL and syndesmosis disruption (P ≤ .01), although the varus external rotation stress test produced nearly twice as much displacement (10.7 vs 5.4 mm). Syndesmotic widening was not significant with either maneuver. Varus external rotation stress was more effective than valgus external rotation stress in demonstrating displacement of markers at the medial gutter and on AP and mortise radiographs for both DDL and DDL with syndesmotic instability. These findings may lead to improved clinical detection of rotational ankle instability from combined DDL and syndesmotic disruption, which may affect decision making for using syndesmotic fixation when using intraoperative stress fluoroscopy images. Occult DDL instability may be underdiagnosed, and this may affect future directions of the treatment of rotational ankle fractures and severe sprains.

Using a cervical spine cage to reconstruct malunited fibular fractures

Anatomical reduction and fixation of unstable ankle fractures is necessary to prevent post-traumatic arthritis. Malunion of the distal fibula in unstable ankle fractures can lead to late degenerative changes of the ankle. Late reconstruction of the ankle can improve its function and postpone the need for ankle fusion or replacement. We discuss three patients who presented with fibular malunion. All developed medial gutter opening, syndesmotic widening, and lateral shift and/or talar tilt. Surgery involved an anteromedial approach to clean the medial gutter, an anterolateral approach to clean the syndesmotic interval, elongation of the fibula by six to eight millimetres and stabilisation with a cervical spine cage and a locked plate. After oneyear, all patients had radiologically demonstrated reduction of the talus in the mortise. Improved function was recorded at final follow up. The cage provides several advantages over other fixation methods, including osteoconductive properties, avoiding bone graft donor site morbidity, and the range of sizes allows the surgeon to adjust the amount of elongation. Using spinal cages to treat malunited fibula fractures has several advantages compared to bone graft and good results can be expected.

Comments on Hsu et al.: Surgical treatment of syndesmotic diastasis: emphasis on effect of syndesmotic screw on ankle function

Dear Editor, With great interest we read the article of Hsu et al. entitled “Surgical treatment of syndesmotic diastasis: emphasis on effect of syndesmotic screw on ankle function” [1]. The authors report on screw fixation in patients with syndesmotic diastasis. They describe a syndesmotic diastasis recurrence in six of 52 patients (11.5%) with an average increase in widening of 3.8 mm (range 3–7 mm) diagnosed on anteroposterior radiographs. At 19 months (range 12–36) follow-up they observed no difference in ankle function, as defined by Bray’s scoring system, between patients with and without recurrence of syndesmotic diastasis. We were surprised by their conclusion and would like to make some remarks that we feel should be discussed. Distal tibiofibular syndesmotic injuries occur in over 10% of ankle fractures [2]. Syndesmotic instability is most commonly associated with pronation external rotation, pronation abduction or less frequently with supination external rotation trauma mechanisms. Syndesmotic instability leads to mortise widening and this should be treated with syndesmotic stabilisation to prevent long-term complications. Widening of the ankle mortise leads to increased stress on the articular cartilage. This statement is based on the studies of Ramsey and Hamilton, and later of Lloyd et al. When the talus moves 1 mm laterally, the contact area in the tibiotalar articulation is decreased by 42%. This results in an increase in the stress per unit area on the articular cartilage [3, 4]. Leeds and Ehrlich found a negative correlation between syndesmosis instability and subjective outcome, objective outcome and degenerative changes in the ankle joint at four years follow-up [5]. Pettrone et al. concluded that if the syndesmosis is not adequately reduced the function scores were significantly lower after one to five years follow-up [6]. We think that there are some potential reasons why the authors came to their conclusions. As already stated by the authors, a larger sample size could possibly provide significance. In this series six patients out of a total of 52 sustained recurrence of syndesmotic widening. There are many tests available to evaluate ankle function. The authors have used the Bray’s scoring system. No validity studies or methodological evaluation have been performed proving this system to be adequate for scoring ankle function [7]. The criteria used for recurrence of syndesmotic diastasis are controversial. Beumer et al. stated that no optimal radiographic parameter exists to assess syndesmotic integrity, because all are dependent on the position of rotation. Except for unilateral absence of tibiofibular overlap and the combination of the medial and superior clear space, quantitative measurement of syndesmotic parameters in repeated ankle radiographs may be of little value [8]. The most important cause could be the short follow-up. It is likely that degenerative osteoarthritis was already developing but, in this short follow-up, had not yet resulted in reduced ankle function. It would be interesting to increase the follow-up or check the status of the tibiotalar joint with X-ray images to examine early degenerative pathology. We are of the opinion that recurrent syndesmotic widening leads to long-term degenerative changes. Early treatment is necessary because late repairs give satisfactory but less favourable outcomes in comparison to properly treated acute injuries. It is not easy to regain complete stability by means of these secondary procedures [9]. We agree with the authors that more research is necessary to confirm the reliability and validity of the results presented. We also hope the authors will present the long-term outcome of this series.

Comment 2

The authors describe an alternative method for assessment of the integrity of the distal tibiofibular syndesmosis. In their description of the technique, they highlight the importance of fixation of the fibular fracture prior to performing the test. However, they neglect to mention the importance of fixation of any associated medial malleolar fracture prior to testing syndesmotic stability. Indeed, the images accompanying the note show their test being performed on a bimalleolar fracture with the medial malleolar fracture untouched, but the final image shows medial malleolar fracture fixation and syndesmosis screws present. This is in contrast to conventional teaching. In the majority of bimalleolar fractures, rigid fixation of both medial malleolar and fibular fractures should stabilise the syndesmosis and abolish the need for a syndesmosis screw.1,2 The exception to this is if there is co-existing ligamentous disruption medially or laterally, in which case syndesmotic widening would be observed on testing the syndesmosis after fixation of both medial malleolar and fibular fractures.

Distal Fibula Malunions

Anatomic reduction and fixation of unstable ankle fractures is necessary to prevent posttraumatic arthritis. Malunion of the distal fibula in unstable ankle fractures may lead to progressive talar instability. Ankle fracture malunions often present with concomitant syndesmotic widening, which can cause surgeons to overlook changes in fibula length and rotation. The decision to proceed with surgery should be made only after a careful diagnostic workup and detailed preoperative discussion with the patient. Considerations for surgical management include location and orientation of a corrective osteotomy, use of structural graft, widening of the syndesmosis, assessment of reduction, and the need for medial exposure. Good and excellent clinical results after fibular reconstruction have been reported in 67% to 92% of ankles. Proper patient selection is critical, because ankle malunions can be complicated, with coexisting fibular, syndesmotic, medial, and posterior malleolar malalignment, along with degenerative joint disease. Understanding the indications and surgical technique for revising fibular malunions may obviate a future salvage procedure.

Screw fixation of the syndesmosis: a cadaver model comparing stainless steel and titanium screws and three and four cortical fixation

We assessed syndesmotic set screw strength and fixation capacity during cyclical testing in a cadaver model simulating protected weight bearing. Sixteen fresh frozen legs with artificial syndesmotic injuries and a syndesmotic set screw made of stainless steel or titanium, inserted through three or four cortices, were axially loaded with 800 N for 225,000 cycles in a materials testing machine. The 225,000 cycles equals the number of paces taken by a person walking in a below knee plaster during 9 weeks. Syndesmotic fixation failure was defined as: bone fracture, screw fatigue failure, screw pullout, and/or excessive syndesmotic widening. None of the 14 out of 16 successfully tested legs or screws failed. No difference was found in fixation of the syndesmosis when stainless steel screws were compared to titanium screws through three or four cortices. Mean lateral displacement found after testing was 1.05 mm (S.D. = 0.42). This increase in tibiofibular width exceeds values described in literature for the intact syndesmosis loaded with body weight. Based on this laboratory study it is concluded that the syndesmotic set screw cannot prevent excessive syndesmotic widening when loaded with a load comparable with body weight. Therefore, we advise that patients with a syndesmotic set screw in situ should not bear weight.

Missed fractures on emergency room ankle radiographs: An analysis of 433 patients

The purpose of this study was to review fractures and radiographic abnormalities that are detectable, but often overlooked, on a standard ankle radiographic series. We carried out a retrospective review of 556 consecutive ankle radiographic series obtained between June 1, 1995, and May 31, 1996. From this population, 433 complete ankle radiographic series on patients with suspected trauma were selected. The original radiologist's interpretation was compared to a twostep “gold standard” interpretation, consisting of reinterpretation by a musculoskeletal radiologist with the patient's medical and imaging records at hand, with review of discrepant cases by a consensus panel. Eighteen studies were incorrectly interpreted at the initial reading, yielding an overall error rate of 4.2%. Fifteen of the errors were missed fractures, ankle syndesmotic widening, or incorrect classification of old fractures as acute. The rate for this type of error was 3.5%. The most commonly missed fractures were of the talus (4 patients), followed by fracture of the base of the fifth metatarsal and calcaneal stress fracture (2 cases each); tibiofibular syndesmotic injury was missed in 2 cases. Missed fractures on ankle radiographs most commonly involved bones of the hindfoot, especially the talus. It is important to recognize these uncommon and easily missed fractures, so that a modified search pattern may result in improved accuracy of radiographic interpretation.

Tibiotalar joint dynamics: indications for the syndesmotic screw--a cadaver study.

Pronation-external rotation ankle injuries involve varying degrees of disruption of the syndesmotic ligaments. The loss of ligament support and alteration in the stability of the mortise have been postulated to lead to an increase in joint reactive forces and traumatic arthritis. The purpose of this study was to determine the changes in tibiotalar joint dynamics associated with syndesmotic diastasis as a result of the sequential sectioning of the syndesmotic ligaments to simulate a pronation-external rotation injury. Dissections were conducted on 10 fresh-frozen, knee-disarticulated cadaveric specimens which were then axially loaded in an unconstrained manner. Tibiotalar joint forces were measured at each level of sequential sectioning of the syndesmotic ligaments, the interosseous membrane, and finally the deltoid ligament. Complete disruption of the syndesmosis with the medical structures of the ankle intact resulted in an average syndesmotic widening of 0.24 mm and no significant change in the tibiotalar contact area or the peak pressure. However, deltoid ligament strain increases with sectioning of the syndesmosis. With the addition of deltoid ligament sectioning, there was an average syndesmotic diastasis of 0.73 mm, a 39% reduction in the tibiotalar contact area, and a 42% increase in the peak pressure. In a simulated unconstrained cadaveric model of a pronation-external rotation ankle injury that results in complete disruption of the syndesmosis, if rigid anatomic medial and lateral joint fixation is obtained and the deltoid ligament complex is intact, syndesmotic screw fixation is not required to maintain the integrity of the tibiotalar joint.

Postoperative radiographs as predictors of clinical outcome in unstable ankle fractures.

This study reviews a group of 80 consecutive displaced ankle fractures treated operatively and followed for an average of 3.2 years. Fractures included bone or combined bone and ligamentous injuries in which the initial talar displacement was greater than or equal to 2 mm. The immediate postoperative roentgenograms were examined for several features, which included widening of the syndesmosis, fibular length, talo-crural angle, talar tilt, presence and size of a posterior malleolar fracture, and an abnormality of the medial clear space. Patients were examined at follow-up per Cedell, and their clinical evaluations were correlated with the analysis of radiographic features and demographic data. Good to excellent results were seen in 80% of the cases. The radiographic factors most predictive of a poor outcome were abnormal medial clear space and the presence of a large (greater than 20%) posterior malleolar fracture (p less than 0.05). Fibular shortening, talar tilt, and syndesmotic widening suggested a poor result, but these findings were not statistically significant. Multiple (two or more) radiographic abnormalities correlated with a poor prognosis. Conversely, a perfect radiographic result did not guarantee an excellent clinical outcome. Older patients and those with a delay between injury and surgery greater than 7 days tended to have a poorer result.

A Radiographic Evaluation of the Tibiofibular Syndesmosis

A radiographic evaluation of the normal as well as the progressively widened tibiofibular interval in the area of the syndesmosis was done using 12 fresh cadaver lower extremities. The width of the tibiofibular "clear space" and the amount of tibiofibular overlap was determined on accurately positioned anterior-posterior and mortise radiographs. Based on a 95% confidence interval, measurements obtained for the intact specimens would support the following criteria as consistent with a normal tibiofibular relationship: (1) a tibiofibular "clear space" on the anterior-posterior and mortise views of less than approximately 6 mm; (2) tibiofibular overlap on the anterior-posterior view of greater than approximately 6 mm or 42% of fibular width; (3) tibiofibular overlap on the mortise view of greater than approximately 1 mm. The width of the tibiofibular "clear space" on both anterior-posterior and mortise views appeared to be the most reliable parameter for detecting early syndesmotic widening.