SLR - March 2018 - Chandana Halaharvi

Flexible Adult Acquired Flatfoot Deformity: Comparison Between Weightbearing and Nonweightbearing Measurements Using Cone-Bean Computed Tomography

Reference: De Cesar Netto C, Schon LC, Thawait GK,  da Fonseca LF, Chinanuvathana A, Zbijewski WB, Siewerdsen JH, Demehri S. Flexible Adult Acquired Flatfoot Deformity: Comparison Between Weightbearing and Nonweightbearing Measurements Using Cone-Bean Computed Tomography The Journal of Bone and Joint Surgery 2017 sept 20; 99 (18).

Scientific Literature Review

Reviewed By: Chandana Halaharvi, DPM
Residency Program: Grant Medical Center, Columbus, OH

Podiatric Relevance: Adult acquired flatfoot deformity (AAFD) is a common, multifaceted deformity that is progressive in nature. AAFD is a triplane deformity that involves four stages of severity with the first two stages being flexible in nature. The standard protocol is a weightbearing (WB) radiograph to assess the severity of the deformity which provides a two-dimensional image. With the advent of WB computed tomography (WBCT), we can now obtain three-dimensional imaging, which allows a better understanding of this complex deformity. This study reviewed a series of 20 patients with AAFD comparing measurements of WB and nonweightbearing (NWB) CT images.  

Methods: This is a level II prospective cohort study of patients who were diagnosed with a symptomatic flexible adult acquired flatfoot deformity. A cone-beam CT extremity scanner was used to assess scans. All participants received two consecutive scans of the symptomatic foot, one NWB and one WB. Each scan was then reviewed by two surgeons and one radiologist in a randomized and blinded manner. The images were assessed and compared to standard average values in each plane. In the axial plane, the talus-first metatarsal angle and talonavicular coverage angle. In the coronal plane, the forefoot arch angle, navicular-to-skin distance, navicular-to-floor distance, medial cuneiform-to-skin distance, medial cuneiform-to-floor distance, calcaneofibular distance and three angles of the subtalar horizontal angle were assessed. In the sagittal plane, the talus-first metatarsal angle, navicular-to-skin distance, navicular-to-floor distance, cuboid-to-skin distance, cuboid-to-floor, medial cuneiform-to-floor distance, and calcaneal inclination angles were measured.

Results: There was a significant difference between the average values of the aforementioned angles and measurements except for the calcaneal inclination angles. In the axial plane, there was a mean increase in both the talar head uncoverage and talus-first metatarsal angle on WB. In the coronal plane, the WB measurements were decreased in regard to the forefoot arch angle, navicular-to-skin distance, navicular-to-floor distance, medial cuneiform-to-skin distance, medial cuneiform-to-floor distance, calcaneofibular distance with an increase in measurement to the subtalar horizontal angles.

Conclusions: The measurements in the axial plane were less reliable than the other planes. In contrast to other studies, there was a low interobserver reliability for the talus-first metatarsal angle in both sagittal and axial planes. This is an important negative finding as this is used as a standard measurement for grading AAFD. Although there were differences in measurements, they were not statistically significant. There were several limitations to this study, including a lack of a control group, no prospective sample size calculation, a small sample size and measurement errors. The cone-beam CT scanner acquires three-dimensional images; however, it is still a challenge to obtain a plane with all osseous structures to perform the necessary measurements. This article provided a quantitative method in assessing AAFD. This study suggests that the most reliable way to correlate the measurements is to compare with the patient’s symptoms and obtain multiple measurements in various planes. Further studies are needed to explore the role of a WBCT to diagnose AAFD and assess postoperative correction of the deformity. 

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