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WBCT & MRI Study Sheds Light on Flat Foot Degeneration

Some degree of subtalar joint subluxation, as well as sinus tarsi impingement, was found in approximately 70 percent of patients with flexible adult acquired flat foot (AAFD) in a recent imaging study using MRI and weight bearing CT (WBCT) imaging.

Investigators used the imaging to assess which soft tissue structures demonstrating MRI signs of degeneration would correlate and influence more positive findings of bone collapse.

The study results were on display in the poster section of the AAOS Annual Meeting  and summarized by the AAOS Daily News.

Investiagators obtained MRI and WBCT imaging for 55 patients. Patients were evaluated for markers of arch collapse including increased valgus alignment of the hindfoot and forefoot abduction. Subfibular impingement was found in only 9 percent of patients.

“The significant and isolated influence of pronounced degeneration of the ligaments as positive indicators of more severe collapse of the bony architecture in AAFD patients, represented by subtalar joint subluxation and subfibular impingement, must be considered essential findings,” Dr. Cesar de Cesar Netto, a coauthor of the study, told AAOS News Daily. “Since we don’t really know which structures degenerate first in AAFD, our results point toward an increased importance of the ligamentous structures in the development and progression of the pathology, with the degeneration of the PTT potentially representing a late finding and only the tip of the ice berg.

The CurveBeam pedCAT is the only weight bearing CT imaging system with a field of view large enough to capture a bilateral foot and ankle scan. Flat foot degeneration is often a bilateral condition.

Demehri: WBCT Preferable Over MRI for Syndesmosis

demehriInjury to the syndesmosis often requires advanced imaging. Up until recently, the most common advanced imaging modality to evaluate this injury has been magnetic resonance imaging (MRI). Dr. Shadpour Demehri, MD, Associate Professor, Russell Morgan Department of Radiology, Johns Hopkins University, discussed the current imaging standards and the evolving role of weight bearing cone beam CT (WBCT) in a presentation he delivered to the WBCT International Study Group in July 2018.

In reviewing recent literature, Dr. Demehri explaind that MRI can reliably and accurately detect syndesmotic injury. There does not appear to be any difference between 3T and 1.5T MRI technologies, and further, there is no advantage to using contrast (MRA) when evaluating the syndesmosis. The biggest limitation of MRI studies is the lack of information regarding the significance of anatomic derangement and biomechanical instability. This limitation is where WBCT technology has emerged as a new tool for evaluation.

Dr. Demehri and his colleges conducted a study of asymptomatic patients to create an atlas of diastasis, rotation, translation, and ankle mortise measurements and range of normals. During this study, they were able to make three conclusions. First, defined syndesmotic measurements can be reliably performed on WBCT. Second, except for medial clear space, syndesmotic measurements did not vary with normal weight bearing. Finally, under physiological load, the relationship between the distal tibia and fibula remains unchanged in the presence of an intact syndesmosis.

The biggest limitation of MRI studies is the lack of information regarding the significance of anatomic derangement and biomechanical instability. This limitation is where weight bearing cone beam CT technology has emerged as a new tool for evaluation.

Considering the conclusions drawn from this initial study, Dr. Shadpour Demehri decided to further evaluate weight bearing versus non weight bearing studies in symptomatic patients. He explains that images were gathered in natural, weight bearing stance to allow for evaluation of comparative anatomy. If apparent syndesmotic injury was evident on plain x-rays or exam, those subjects were removed from the study. This allowed them to evaluate subtle injury more critically and assess the efficacy of typical patients sent for advanced imaging. The findings of this study revealed that in patients with prior ankle injuries, syndesmotic measurements using WBCT are feasible, reproducible, and had moderate to perfect level of agreement between observers. Values of syndesmotic measurements were significantly different between weight-bearing and non-weight bearing images.

As much of the radiology field continues to evolve with technology, Dr. Demehri sees great potential for the utilization of WBCT technology. He hopes to further investigate the role of automated measurements as well as automated bone segmentation and anatomical landmark localization. He believes that using these semi-automated techniques will allow measurements to be obtained using pre-defined anatomic landmarks. Ultimately, this will significantly improve workflow, intra-observer reliability, and level of agreement between radiology readers.

Watch Dr. Demehri’s full presentation here: