Elsevier

Gait & Posture

Volume 36, Issue 3, July 2012, Pages 389-393
Gait & Posture

Correlation between anatomic foot and ankle movement measured with MRI and with a motion analysis system

https://doi.org/10.1016/j.gaitpost.2012.03.023Get rights and content

Abstract

Several studies have attempted to measure how well external markers track internal bone movement using pins drilled into the foot, but this is too invasive for the pediatric population. This study investigated how well a six segment foot model (6SFM) using external markers was able to measure bone movement in the foot compared to MRI measurements. The foot was moved into different positions using a plastic foot jig and measurements were taken with both systems. The aims were to: (1) Look at the correlation between movement tracked with an Electronic Motion Tracking System (EMTS) and by measurements derived from MRI images, specifically the principal intercept angles (PIAs) which are the angles of intersection between principal axes of inertia of bone volumes. (2) To see how well external motion measured by the 6SFM could predict PIAs. Four bone pairs had their movement tracked: Tibia–Calcaneus, Calcaneus–Cuboid, Navicular–1st Metatarsal, and 1st Metatarsal–Hallux. The results showed moderate correlation between measured PIAs and those predicted at the Tibia–Calcaneus, Navicular–1st Metatarsal, and 1st Metatarsal–Hallux joints. Moderate to high correlation was found between the PIA and movement in a single anatomic plane for all four joints at several positions. The 6SFM using the EMTS allows reliable tracking of 3D rotations in the pediatric foot, except at the Calcaneus–Cuboid joint.

Highlights

► The six segment foot model can be correlated using MRI to underlying bone motion at three different joints in the foot at several positions. ► Underlying bone motion at the Calcaneus–Cuboid joint may not be reliably tracked with the six segment foot model. ► The six segment foot model can be used in the pediatric population.

Introduction

MR imaging has been used previously to quantify bone movement in the foot when the foot is moved into different positions [1], [2], [3], [4], [5], [6]. These studies involve placing the foot in different positions, imaging the foot, identifying bones in the foot, and rendering 3D bone volumes. Embedded coordinate systems were defined for the different bones using either anatomically defined axes, principal axes of inertia rendered from the bone volumes using Principal Component Analysis, or some combination of the two. In most studies the motion between the bones was defined using Euler angle rotations between the coordinate systems [1], [2], [3], [4], [6]. A few studies have looked at the angle of intersection of the principal axes of pairs of bones and in one case the intersection angles have been used in an attempt to identify foot deformities [5], [6], [7]. Using the principal intercept angle (PIA), which is the angle of intersection between principal axes of inertia of bones, avoids the problem of choosing an order of rotation, which some studies do with little justification, and the problem of gimbal lock, which occurs when second axis rotation approaches 90° [2], [5], [8], [9].

The 3D motion of bones in the foot or segments of the foot has been measured using many different marker configurations [10], [11], [12], [13], [14], [15], [16], [17], [18]. Multi-segment foot models have placed external markers on various anatomical landmarks to track bone motion or motion of a particular grouping of bones, i.e. a foot segment. While the multi-segment foot models have given consistent results, a persistent question is how well the models’ external markers track actual bone motion.

Several studies have attempted to quantify how closely external marker movement follows underlying bone movement in the foot by inserting pins into the bones [19], [20]. The studies results showed varying levels of agreement between the external markers and the bone pins depending on the pair of bones examined and the plane of motion. While drilling pins into the foot may get rid of skin movement artifacts, bone pins are unsuitable pediatric use. This study investigated how well a six segment foot model (6SFM) using external markers was able to track bone movement compared to measurements taken by an MRI [10], [11]. The MRI derived measurement PIA was used to compare bone movement to the external 6SFM measurements. The foot was moved into different positions from a starting position or “neutral” position using a plastic foot jig and measurements using both systems were taken. The study aimed to determine the correlation between 6SFM movement measured in a single anatomic plane and the PIA and to determine how motion measured in all 3 dimensions by the 6SFM could predict the PIA.

Section snippets

Subjects and the testing positions

Ten feet from five subjects, between the ages of ten and fifteen, without a history of foot pathology had their feet measured in duplicate positions with an MRI machine (1.5 T GE HealthCare 1.5 T LX 12) and an Electronic Motion Tracking System (EMTS). The EMTS was composed of StarTrak hardware (Polhemus, VT) and 6D Research™ software (Skill Technologies, VT). A commercially available plastic foot jig (CHAMCO™, Cocoa, Fl) was used to situate and hold the foot in the different positions when

Correlation between measured PIA and motion in a single anatomic plane

The Tibia–Calcaneus joint had three positions where there was a significant correlation between the 1st PIA and motion in a single anatomic plane (|r| = 0.69–0.8) (Table 2). For the external positions the mean 1st PIAs increased along with the mean 6SFM measurements in all 3 dimensions (Fig. 2).

The Navicular–1st Metatarsal joint had one position where there was a significant correlation between the 1st PIA and motion in two anatomic planes. The absolute correlation values ranged from r = 0.66 to

Discussion

For all the joints, except the Calcaneus–Cuboid, the 3D motion measured by the 6SFM had a moderate to high correlation to the 1st and 2nd PIA (r = 0.78–0.88) at several testing positions. This indicates that our 6SFM is able to measure rotations in the medial ray of the foot. The lack of high correlation between motion in a single anatomic plane and the 1st or 2nd PIA at all the positions for all the joints might be explained by the foot's multi-planar motion. When the foot is moving in all three

Conflict of interest statement

All of the authors have stated that they have no conflict of interest.

Acknowledgements

We would like to thank the NIDRR grant (H133G060155) for the support of this study. We appreciate the assistance given with the MRI measurements by Ms. Bessette at the radiology department in the Children's Hospital of Wisconsin. We would like to extend our thanks to Mr. Verber for helping with the 3DVIEWNIX MRI measurement software and to Ms. Epps our research coordinator.

References (29)

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