Make sure to check out an informative session titled, “Weight Bearing CT – Where Are We Going?” led by the WBCT International Study Group (WBCT ISG) President Dr. Martinus Richter Friday, February 1 from 3 pm to 3:10. CurveBeam is a co-sponsor of the WBCT ISG, an independent organization dedicated to WBCT research.
Ankle syndesmosis injury, commonly known as high ankle sprain, is one of the most common cases seen by foot and ankle specialists. An estimated 11% of all ankle injuries and 8.5-18% of all ankle fractures have injury to the syndesmosis. An inaccurate diagnosis can lead to chronic problems or repeat surgeries. Common indications for delayed surgery or reoperation include improper diagnosis, malreduction and inadequate fixation.
The syndesmosis connects the tibia and fibula above the ankle joint. One of the most difficult distinctions to make is whether the injury is isolated to the syndesmosis itself or if it has affected the stability of the ankle joint as well.
Dr. Daniel Guss, MD, MBA, assistant professor of orthopedic surgery at Harvard Medical School, took a deeper look at syndesmosis and how weight bearing CT imaging could improve diagnostic ability in a presentation he delivered to the WBCT International Study Group in July 2018.
Syndesmosis – Variabilities Are Common
The ankle syndesmosis serves two main functional purposes. First, it is designed to maintain the spatial relationship between the tibia and fibula in order to stabilize the ankle mortise throughout weight bearing activity. Second, it allows for flexibility of the ankle mortise in the coronal plane along the talar dome throughout various degrees and dorsiflexion and plantarflexion.
Dr. Guss reminded clinicians that when assessing the functional ability of the syndesmosis, it is important to note that recent studies have shown considerable variability in the concavity of the incisura, bony overlap, and clear space within the ankle mortise from one patient to another. In this regard, comparative anatomy images of the left and right ankle are essential for a thorough evaluation.
During a physical exam, the most common tests for evaluation of syndesmosis injury are external rotation stress test, calf squeeze test, and cross-legged test. By and large, all of these tests give greater indication of injury, but all have low sensitivity and specificity, Dr. Guss said. In addition, a positive test from any of these maneuvers is not considered diagnostic.
Imaging – Need for Contralateral Evaluation
Once history and physical exam have been completed, most clinicians turn to initial standard radiographs for evaluation. Tibia/fibula overlap, tibia/fibular clear space, and medial clear space are most often the areas of focus for more definitive diagnostic information in regard to instability. Most will attempt dynamic stress radiographs with high level of clinical suspicion.
However, Dr. Daniel Guss explained the importance of contralateral evaluation, as there has been great variability in measurements of the syndesmosis using weight bearing CT imaging within the same joint when measured in neutral, maximum external rotation, and maximum internal rotation. There is also evidence of significant syndesmosis measurement difference in weight bearing versus non-weight bearing images of uninjured ankles. This further illustrates the flexibility of the syndesmosis as a support structure.
Finally, if MRI is believed to be necessary, it is important to remember that this modality is very successful at detecting injury, but it does not shed any light on instability as it is a non-weight bearing image, Dr. Guss said.
Case Study – Undetected on X-Ray
Dr. Guss shared a case in which a 20-year-old male fell down a flight of stairs and thought he had sprained his ankle. He went to his college health services and obtained an X-Ray, which was negative for fracture. However, the X-Ray did show subtle calcifications within the syndesmoses.
X-Rays taken four months later at Dr. Guss’s clinic showed heterotopic ossification in the syndesmotic region.
Dr. Guss ordered a pedCAT weight bearing CT so he could assess the HO further. He was able to see the asymmetry under physiologic load at the distal tibio-fibular articulation and also that the HO was forming posterio-laterally.
The patient ultimately underwent an excision of the HO and fixation.
Case Study – Subtle Asymmetry
Dr. Guss shared another case where a Gentleman in his 50’s presented to the ER complaining of right ankle and lower leg pain after slipping on ice. Traditional x-rays were obtained, and he was diagnosed with a Maisonneuve-type injury with proximal fibula fracture and medial ankle sprain.
Upon follow up, the patient had a weight bearing CT scan done of both ankles that allowed for cross-section comparison under physiologic stress. This scan revealed subtle asymmetry and widening between the distal tibia and fibula of the injured right ankle compared to the non-injured left ankle.
Subsequently, this patient went on to have surgical fixation performed despite being told originally that he had simply sprained his ankle.
In conclusion, syndesmosis injury can be easily missed and yet carries long term implications for functional instability and chronic pain. When considering what imaging studies are necessary, it is essential to look at weight bearing and contralateral images to obtain a thorough picture of functional anatomy specific to that patient. As weight bearing CT technology becomes more widely available, this may be the most streamlined way to evaluate bilateral, weight bearing images to diagnose ankle syndesmosis instability.
Daniel J. Cuttica, D.O. will share his experience using weight bearing CT in clinical practice in this webinar titled, “Applications of weight bearing CT in common foot & ankle disorders“. Dr. Cuttica is a foot and ankle surgeon practicing at the Orthopaedic Foot & Ankle Center division of the Centers for Advanced Orthopaedics, in Falls Church, Virginia. He is an Assistant Professor of Clinical Orthopaedic Surgery at Georgetown University School of Medicine, and the author of numerous publications in foot and ankle journals.
Gaining an accurate and complete measurement of the hindfoot alignment of a patient with adult acquired flatfoot deformity (AAFD) is difficult when using traditional clinical assessment. In a paper published in the journal Foot and Ankle Surgery, Dr. Cesar de Cesar Netto, MD, PhD, and his colleagues posit that weight-bearing cone beam computed tomography (CBCT) scanning technology may give a more complete, three-dimensional view of the deformity and its underlying causes.
In the article, “Hindfoot Alignment of Adult Acquired Flatfoot Deformity,” the team studied twenty patients with AAFD, twelve men and eight women. All participants had to undergo a clinical assessment of their hindfoot alignment and got a weight-bearing CBCT scan. After all tests were completed, the team found that the weight-bearing CBCT scans provided far more accurate, reliable and repeatable measurements than those of the clinical assessments, thus making a strong case for the use of cone beam technology in AAFD diagnosis and treatment.
In the video below, Dr. de Cesar Netto describes how WBCT assists in AAFD evaluation. “We have been finding really interesting things while studying the flat foot deformities in the weight bearing CT images, most of them related to coronal plane assessment. But it’s not just that,” Dr. Cesar de Netto says. “We are trying to use the three dimensional environment to find out how the deformity progresses.”
The problem with current practices, according to de Cesar Netto and his colleagues, is that they rely on two systems that make it difficult to obtain universally accepted results. The first is radiographic examinations. These are two-dimensional and cumbersome, with further difficulty added when trying to discern hindfoot alignment due to the complexity of the subtalar joint. Not only that, but these examinations are especially prone to improper positioning which would throw off the results. The other traditional system used for hindfoot alignment measurement is made up of a series of clinical measurements including simple visual evaluation. These measurements have consistently been shown to be inaccurate and highly variable from physician to physician.
Recent advancements in CBCT technology now allow physicians to obtain a three-dimensional, highly detailed view of a patient’s lower extremities. They also allow for a complete picture of both the soft-tissue and bone within the foot, so that no issues go overlooked. Of particular interest to the study at hand was the fact that CBCT allows for scans to be taken of the foot in a natural, weight-bearing state. As AFFD is highly dynamic, analysis of the condition with the effects of a patient’s full body weight can be immensely beneficial when developing a treatment plan.
Leading the way with weight-bearing cone beam technology is CurveBeam. The CurveBeam LineUP is revolutionizing how physicians approach diagnosis and treatment plan development as their technology provides complete views of the lower extremities with high image quality.