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Through a grant funded by the OCPM Foundation, KSU was able to acquire a CurveBeam pedCAT weight-bearing CT scanner. This unit utilizes cone-beam technology to yield low dose scans of either one or both feet, and to date, is the only one of its kind in Northeast Ohio. Part and parcel with this process, three potentially ground breaking research projects were proposed, all dealing with controversial topics in podiatric pre-operative evaluation. In the short time since, another seven research topics have been developed.
A team of KSUCPM researchers has completed the first project, which focused on the evaluation of hallux valgus deformity in the coronal plane of the foot. The team was comprised of CPM faculty members Jill Kawalec, PhD, Larry Osher, DPM, and Duane Ehredt, DPM, along with CPM students Kelsi Nutter (class of 2019) and Joseph Fleck (class of 2018).
In the evaluation of hallux valgus deformities, podiatric physicians routinely use weight-bearing radiographs to assess the magnitude of the deformity as an essential step in planning surgical correction. Unfortunately, there are a number of well-known issues associated with conventional foot radiographs. These include geometric distortion(s), unreliable measurements made between different observers, limited imaging in the coronal plane, and marked differences between weight-bearing and non-weight-bearing images. CT scanning allows cross-sectional imaging (slices) of the anatomical parts in all three planes of the foot without typical radiographic distortion. In addition, CT scanners effectively allow for three-dimensional reconstruction of the foot.
Hallux valgus is considered to be a triplane deformity. The sesamoids commonly displace from their normal alignment in patients with this deformity. In the recent medical literature, evidence suggests that the magnitude of this displacement can be determined by the coronal plane sesamoid rotation angle. The current x-ray imaging standard for the coronal plane is the sesamoid (forefoot) axial study, which requires the foot to be placed in an “affected” (supinated, semi-weight-bearing) position. Using the weight-bearing CT scanner, this research study was designed to determine the effect of different weight-bearing foot positions on the coronal plane sesamoid rotation angle as compared with standard sesamoid axial studies. All subjects with bunion deformities underwent both standard radiographic forefoot axial studies and weight-bearing CT studies in two extreme weight-bearing positions of the foot: maximum subtalar joint pronation and supination. The sesamoid rotation angle was then determined on all studies by all five investigators.
Recently, arguments have been brought forth advocating for the surgical correction of the coronal plane component as part of the bunion repair (e.g. Lapidus procedure). However, if the sesamoids significantly vary their position with differing weight-bearing foot attitudes, then the utility of the radiographic sesamoid axial study must be questioned. Our data did, in fact, demonstrate significant differences in the rotation angle between the two extreme weight-bearing positions. In particular, sesamoid
rotation angles were significantly higher in the pronated foot position. Moreover, sesamoid rotation angles from the weight-bearing CT supinated position, which simulates the position of the forefoot axial study, correlated with those values.
These results strongly suggest that the current imaging standard for evaluating the coronal plane degree of sesamoid rotation significantly underestimates this value. From a surgical point of view, these results suggest that weight-bearing CT scan determination with the foot in a non-affected weight-bearing position should replace forefoot axial studies as the accepted imaging standard.
Special thank you to the exclusive research sponsor of this study, OCPM Foundation!