What Role Does Weight-Bearing Computed Tomography Play In Assessment of Progressive Collapsing Foot Deformity?

The answer to the question posed in this blog title may depend upon whether the assessment is clinical or primarily research-based, at least for now. Conventional plain film radiographs remain the most predominant modality for assessment of progressive collapsing foot deformity, mainly from a practical standpoint, as far as availability and cost-effectiveness. Not only are these views crucial for a comprehensive evaluation of the deformity for surgical preparation, but they also provide important data points for procedure selections. Importantly, these views must be taken weight-bearing and include foot (anteroposterior, medial oblique, and lateral), ankle (anteroposterior, mortise, and lateral), and axial calcaneal views.
 
As our understanding of progressive collapsing foot deformity (PFCD) continues to expand, such as the recent change in nomenclature from adult-acquired flatfoot or posterior tibial tendon dysfunction (PTTD), research into other imaging modalities has emerged and demonstrated benefits over conventional imaging.¹ Specifically, weight-bearing computed tomography (WBCT) has shown sensitivity in a comparative study by Lintz and associates to evaluate diagnostic accuracy of conventional 2D-imaging and the 3D-imaging measurements provided from WBCT.² The investigators found that the simultaneous use of both modalities led to the highest diagnostic accuracy of the deformity with 100 percent specificity.
 
By comparison, magnetic resonance imaging (MRI) is a valuable tool to assess 3D pathology involving both soft tissue and osseous structures. These findings guide the surgeon in deciding joint-sparing procedures. As an example, the tibialis posterior tendon can be associated with PCFD with findings of edema within the tendon, demonstrating degenerative changes that may indicate the need for an augmentative tendon transfer. Additional MRI findings can show an attenuated spring or deltoid ligament, peroneal tendon impingement under the distal fibular tip, and degenerative changes to the subchondral plate under the articular surfaces.³ All of these findings impact surgical procedure selection and inclusion.
 
Interestingly, de Cesar Netto and associates combined and assessed the results of WBCT and MRI finding significant correlations between critical WBCT markers of peritalar subluxation with MRI soft tissue injury.⁴ Significantly, tibialis posterior tendon degeneration was associated with sinus tarsi impingement, spring ligament degeneration with subtalar subluxation, and talocalcaneal interosseous ligament involvement with subfibular impingement.⁴
 
The primary advantage of utilizing WBCT include the ability to limit positioning errors with the patient and X-ray beam. Additional advantages, discussed by Lôbo and associates, include but are not limited to: assessing medial arch collapse, hindfoot alignment, peritalar subluxation, posterior subtalar joint valgus, intrinsic talus valgus, and lateral extra-articular bone impingement.⁵ As mentioned earlier, WBCT is able to evaluate such conditions as sinus tarsi and subfibular impingement through its significant association of important WBCT markers and MRI findings. Specifically in the sagittal and coronal WBCT imaging, extra-articular contact between the talus and the calcaneus in the sinus tarsi as well as direct contact between the distal fibula and the calcaneus are the WBCT markers used for sinus tarsi and subfibular impingement.⁴
 
To evaluate WBCT accuracy, Fuller and associates used digitally reconstructed radiographs obtained from WBCT imaging data and compared them to conventional radiographs on the same patients.⁶ After evaluating six radiographic measurements including Meary’s angle, calcaneal pitch, medial cuneiform height, anteroposterior talar-first metatarsal angle, talonavicular coverage, and talar incongruency, the authors found no significant differences between the data obtained from the digitally reconstructed WBCT radiographs and the conventional radiographs. In fact, they found that the medial arch anatomy was more accurately represented in the digital recreation of the radiographs than the conventional radiographs. The study suggested that while this specific modality has not been clinically validated, the long-term future implications could have the potential to completely replace conventional radiographs with WBCT once easily available.⁶
 
Currently, we are far from replacing plain film radiography for the evaluation of PCFD with WBCT. WBCT imaging modality dates back to the mid-2010s in its application to clinical orthopedic use. The scientific research and publications with this modality have grown exponentially with about half of the research dedicated to the foot and ankle. Reasonable critiques of the modality include its cost and amount of time to perform. Others question even if it is necessary, but these critiques are common for any technology before it becomes widely accepted.
 
While WBCT may not be practically available due to its high cost and accessibility, practitioners should be aware of emerging modalities as it pertains to PCFD. The precision and accuracy for evaluating PCFD will likely also improve the evidence-based data with procedure selection.
 
Dr. Husain is the Residency Director of the McLaren Oakland Hospital Podiatric Surgery and Medicine Residency Program in Pontiac, MI. He is a Fellow of the American College of Foot and Ankle Surgeons and a Fellow of the American Society of Podiatric Surgeons. Dr. Husain is also the President of the Michigan Podiatric Medical Association and Chairman of the Michigan Podiatric Residency Consortium.
 
Dr. Putz is a second-year podiatric resident at McLaren Oakland Hospital in Pontiac, MI.
 
References
1.   de Cesar Netto C, Myerson MS, Day J, et al. Consensus for the use of weightbearing CT in the assessment of progressive collapsing foot deformity. Foot Ankle Int. 2020;41(10):1277-82.
2.   Lintz F, Bernasconi A, Li S, et al. Diagnostic accuracy of measurements in progressive collapsing foot deformity using weight bearing computed tomography: A matched case-control study. Foot Ankle Surg. 2022;S1268-7731(22)00001-7.
3.   Lintz F, de Cesar Netto C. Is advanced imaging a must in the assessment of progressive collapsing foot deformity? Foot Ankle Clin. 2021;26(3):427-42.
4.   de Cesar Netto C, Saito GH, Roney A, et al. Combined weightbearing CT and MRI assessment of flexible progressive collapsing foot deformity. Foot Ankle Surg. 2021;27(8):884-891.
5.   Lôbo CFT, Pires EA, Bordalo-Rodrigues M, et al. Imaging of progressive collapsing foot deformity with emphasis on the role of weightbearing cone beam CT. Skeletal Radiol. 2022;51(6):1127-41.
6.   Fuller RM, Kim J, An TW, et al. Assessment of flatfoot deformity using digitally reconstructed radiographs: reliability and comparison to conventional radiographs. Foot Ankle Int. 2022;43(7):983-93.

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