New anatomical reference systems for the bones of the foot and ankle complex: definitions and exploitation on clinical conditions

Abstract

Background A complete definition of anatomical reference systems (ARS) for all bones of the foot and ankle complex is lacking. Using a morphological approach, we propose new ARS for these bones with the aim of being highly repeatable, consistent among individuals, clinically interpretable, and also suited for a sound kinematic description. Methods Three specimens from healthy donors and three patients with flat feet were scanned in weight-bearing CT. The foot bones were segmented and ARS defined according to the proposed approach. To assess repeatability, intra class coefficients (ICC) were computed both intra- and inter-operator. Consistency was evaluated as the mean of the standard deviations of the ARS position and orientation, both within normal and flat feet. Clinical interpretability was evaluated by providing a quantification of the curvature variation in the medial-longitudinal and transverse arches and computing the Djiann-Annonier angle for normal and flat feet from these new ARS axes. To test the capability to also provide a sound description of the foot kinematics, the alignment between mean helical axes (MHA) and ARS axes was quantified. Results ICC was 0.99 both inter- and intra-operator. Rotational consistency was 4.7 ± 3.5 ° and 6.2 ± 4.4° for the normal and flat feet, respectively; translational consistency was 4.4 ± 4.0 mm and 5.4 ± 2.9 mm for the normal and flat feet, respectively. In both these cases, the consistency was better than what was achieved by using principal axes of inertia. Curvature variation in the arches were well described and the measurements of the Djiann-Annoier angles from both normal and flat feet matched corresponding clinical observations. The angle between tibio-talar MHA and ARS mediolateral axis in the talus was 12.3 ± 6.0, while the angle between talo-calcaneal MHA and ARS anteroposterior axis in the calcaneus was 17.2 ± 5.6, suggesting good capability to represent joint kinematics. Conclusions The proposed ARS definitions are robust and provide a solid base for the 3-dimensional description of posture and motion of the foot and ankle complex from medical imaging.

Unique shape variations of hind and midfoot bones in flatfoot subjects—A statistical shape modeling approach

“…With fast-growing developments in foot assessment, such as weightbearing cone beam computed tomography (WBCT), there could a combination of these SSM techniques, qualitative and quantitative, incorporated into this technology to maximize its potential (Conconi et al, 2021;Krähenbühl et al, 2020).…”

“…The descriptions of what is seen in each mode of variation are qualitative, however heat‐mapping has been added for a more quantifiable approach and to relate our findings to other research (Krähenbühl et al, 2020). Standardization and further quantification of the methodology would be beneficial, and there has been increasing research to further quantify SSMs through the addition of 3D joint space and alignment measurements from detailed frameworks (Carrara et al, 2021; Conconi et al, 2021). While these studies have low subject numbers, which limits generalizing the results, further research on larger population samples would provide even more decision‐making power to SSMs by giving more 3D metrics that could describe joint space and alignment.…”

“…While these studies have low subject numbers, which limits generalizing the results, further research on larger population samples would provide even more decision‐making power to SSMs by giving more 3D metrics that could describe joint space and alignment. With fast‐growing developments in foot assessment, such as weight‐bearing cone beam computed tomography (WBCT), there could a combination of these SSM techniques, qualitative and quantitative, incorporated into this technology to maximize its potential (Conconi et al, 2021; Krähenbühl et al, 2020).…”

Foot kinematics as a function of ground orientation and weightbearing

“…Representation of the different bone reference systems: ARS defined according to, 33 (A, B); TPRS used in the previous literature, 24–27 (C, D). Single pointed arrows denote x axes; double pointed arrows denote y axes; triple pointed arrows denote z axes.…”

“…The full range of foot dorsi/plantar flexion and pronation/supination is considered, both in weightbearing and nonweightbearing conditions to show the effect of loads on the foot kinematics and posture. Foot bone kinematics is reconstructed in vitro from a series of computed tomography (CT) scans both with and without a vertical load insisting on the ankle, by resorting to ARS optimized for the foot kinematics description 33 . To frame the results of the present analysis with respect to the previous literature, at the same time enlightening the impact of the chosen ARS, bone kinematics and ROM will be quantified with respect to the neutral foot posture, expressing our findings also in terms of the most commonly choice of reference systems adopted so far in the literature 24–27 …”