Background: Early recognition of syndesmotic instability is critical for optimizing clinical outcome. Injuries causing a more subtle instability, however, can be difficult to diagnose. The purpose of this study was to evaluate both distal tibiofibular articulations using weightbearing computed tomography (CT) in patients with known syndesmotic instability, thereafter comparing findings between the injured and uninjured sides. We also aimed to define the range of normal measurement variation among patients without syndesmotic injury. Methods: Patients with unilateral syndesmotic instability requiring operative fixation ( n = 12) underwent preoperative bilateral ankle weightbearing CT. A separate cohort of patients without ankle injury who also underwent bilateral ankle weightbearing CT were included as comparative controls ( n = 24). For each weightbearing CT, a series of 7 axial plane tibiofibular joint measurements, including 1 angular measurement, were utilized to evaluate parameters of the syndesmotic anatomy at a level 1 cm above the tibial plafond. Values were recorded by 2 independent observers to assess for interobserver reliability. Results: Among those with unilateral syndesmotic instability, values differed between the injured and uninjured sides in 4 of the 7 measurements performed including the syndesmotic area: direct anterior, middle, and posterior differences, and sagittal translation ( P < .001, < .001, < .001, and < .001, respectively). In the control population without ankle injury, no differences were identified between any of the bilateral measurements ( P value range, .172-.961). Conclusion: This study highlights the ability of weightbearing CT to effectively differentiate syndesmotic diastasis among patients with surgically confirmed syndesmotic instability from those without syndesmotic instability. It underscores the substantial utility and importance of using the contralateral, uninjured side as a valid internal control whenever the need for confirming potential syndesmotic instability arises. Prospective studies are necessary to fully understand the accuracy of weightbearing CT in diagnosing occult syndesmotic instability among patients for whom the diagnosis remains in question. Level of Evidence: Level III, comparative diagnostic study.

Background: Computed tomography (CT) imaging has traditionally been considered the gold standard for evaluation of syndesmostic reduction, but there is no uniformly accepted method to assess reduction. The aim of this study was to evaluate the intra- and interobserver reliability of published measurement techniques for evaluation of syndesmotic reduction on weightbearing CT scan (WBCT) in hopes of determining which method is best. Methods: Medical records were reviewed to identify patients who underwent operative stabilization of unilateral syndesmotic injuries. Exclusion criteria included patients younger than 18 years, ipsilateral fractures extending to the tibial plafond, any contralateral ankle fracture or syndesmotic injury, and body mass index greater than 40 kg/m2. Twenty eligible patients underwent WBCT evaluation of both ankles at an average of 3 years after syndesmotic fixation. The anatomic accuracy of syndesmotic reduction was evaluated by 2 observers using axial CT images at a level 1 cm proximal to the tibial plafond using 9 previously published radiological measurement techniques. Inter- and intraobserver reliability were assessed for each evaluation method. Results: The syndesmotic area calculation showed the highest interobserver reliability (0.96), the highest intraobserver reliability for observer 2 (0.97), and the second highest intraobserver reliability for observer 1 (0.92). Fibular rotation had the second highest interobserver reliability in our results (0.84), with intraobserver reliability of 0.91 and 0.8 for first and second observers, respectively. The intraobserver reliability of the side-by-side method was 0.49 and 0.24 for the first and second observers, respectively, and the interobserver reliability was 0.26. Conclusion: Qualitatively assessing syndesmotic reduction via side-by-side comparison with the uninjured ankle had the least intra- and interobserver reliability and should not be relied on to determine syndesmotic reduction quality. In contradistinction, syndesmotic area calculation demonstrated the highest reliability when evaluating syndesmotic reduction, followed by fibular rotation. Given that syndesmotic area measurement techniques are not readily available on standard image viewers, technologically updating image viewers to allow such calculation would make this approach more accessible in clinical practice. Level of Evidence: Level IV, case series.

Category: Ankle, Ankle Arthritis, Trauma Introduction/Purpose: End-stage ankle arthritis is frequently treated with tibiotalar or tibio-talar-calcaneal (TTC) arthrodesis, whose sequelae include adjacent joint arthritis presumptively due to the increased stress inherent to the loss of a motion segment. The loss of ankle motion may also stress the distal tibia, and individual case reports exist describing tibial stress fracture after ankle arthrodesis. These case reports do not describe operative treatment however. The purpose of this study is to report a case series of patients who presented with a stress fracture of the tibia after ankle arthrodesis, a subsegment of whom failed nonoperative management, highlighting related risk factors and treatment strategies. Methods: The medical records at two large academic medical centers were reviewed retrospectively, from 1990 to 2017 at the first center and from 2013 to 2017 at the second center, to identify patients who had undergone ankle arthrodesis. Any patient who subsequently developed a stress fracture of the tibia, confirmed clinically and/or radiographically, was included in the subsequent analysis. Patients with a history of stress fracture prior to arthrodesis or with non-tibia stress fractures were excluded. Patient demographics were collected alongside surgical technique, duration of postoperative non-weight bearing status, presence of medical co-morbidities including osteoporosis and tobacco use, location of tibial stress fracture, and treatment strategy. Results: Twelve patients out of 988 (1.2%) developed tibial stress fracture. Seven patients underwent isolated ankle arthrodesis, four underwent ankle arthrodesis subsequent to subtalar fusion with a resultant ankle nonunion in two requiring revision TTC nailing, and one underwent primary TTC arthrodesis. Four patients had fibular osteotomy, and four had the lateral malleolus resected. The stress fracture was at the level of fibular osteotomy in two patients, and at the proximal end of existing or removed implant in six patients. All patients were treated initially with immobilization and activity modification except for one who had fracture displacement and underwent immediate plate fixation, and three who failed to improve with nonoperative treatment required fixation (two intramedullary nails, one plate). Conclusion: Tibial stress fractures can occur after an isolated ankle arthrodesis but is likely potentiated in the setting of previously or concomitantly fused subtalar joint. Transition points are especially at risk, either at the proximal end of an implant or at the proximal extent of a fibular osteotomy. Critically, stress fractures may present many years after ankle arthrodesis, with an average of four years in this series. In our series one third of patients necessitated surgical management, underscoring the importance of accurate diagnosis. Ultimately patients appear to do well with surgical repair even if they fail initial nonoperative treatment.