In-vivo range of motion of the subtalar joint using computed tomography

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Abstract

Understanding in vivo subtalar joint kinematics is important for evaluation of subtalar joint instability, the design of a subtalar prosthesis and for analysing surgical procedures of the ankle and hindfoot. No accurate data are available on the normal range of subtalar joint motion. The purpose of this study was to introduce a method that enables the quantification of the extremes of the range of motion of the subtalar joint in a loaded state using multidetector computed tomography (CT) imaging. In 20 subjects, an external load was applied to a footplate and forced the otherwise unconstrained foot in eight extreme positions. These extreme positions were foot dorsiflexion, plantarflexion, eversion, inversion and four extreme positions in between the before mentioned positions. CT images were acquired in a neutral foot position and each extreme position separately. After bone segmentation and contour matching of the CT data sets, the helical axes were determined for the motion of the calcaneus relative to the talus between four pairs of opposite extreme foot positions. The helical axis was represented in a coordinate system based on the geometric principal axes of the subjects’ talus. The greatest relative motion between the calcaneus and the talus was calculated for foot motion from extreme eversion to extreme inversion (mean rotation about the helical axis of 37.3±5.9°, mean translation of 2.3±1.1 mm). A consistent pattern of range of subtalar joint motion was found for motion of the foot with a considerable eversion and inversion component.

Introduction

The subtalar joint has an important role in the complex hindfoot motion during gait (Close, 1967; Huson, 1991; Lapidus, 1955). Subtalar joint instability has received increasing attention in the literature as a cause of hindfoot instability. No consensus exists regarding the diagnostic criteria for subtalar joint instability (Budny, 2004; Sijbrandij, 2001). One of the underlying causes is the lack of a standard method for accurately measuring subtalar joint motion. In addition, there are no clear reference values of normal subtalar joint motion. For the evaluation of subtalar joint instability accurate knowledge of the reference values of subtalar joint motion is necessary. Currently, for end-stage osteoarthritis of the subtalar joint unresponsive to conservative treatment the only operative option is a subtalar arthrodesis. Fournol reported a series of 100 implanted prostheses to replace subtalar arthrodesis for post-traumatic osteoarthritis (Fournol, 1999). Over 50% of the patients had unsatisfactory results, mostly because of failure of the prosthesis. Better outcomes are expected with an improved design of the subtalar prosthesis. For this development, kinematic data of the subtalar joint are essential. In addition, an accurate quantitative data set of subtalar joint motion is required for the validation of biomechanical computer models of the ankle joint complex and for studying the kinematic effects of ankle and hindfoot surgery.

The lack of external landmarks of the talus in combination with the subtalar joint geometry has made the subtalar joint kinematics difficult to investigate in living subjects. In vivo studies on subtalar kinematics used camera registration techniques of external surface markers attached to the skin during stance and walking. It is obvious that this technique cannot accurately measure rotations and translations of the bones of the subtalar joint (Cornwall, 1999; Kadaba, 1990; Kepple, 1990; Moseley, 1996; Tranberg, 1998). The invasive roentgen stereophotogrammetric analysis (RSA) has been considered an accurate technique for studying bone-to-bone motion in vivo and was used by numerous authors to study ankle and foot kinematics (Benink, 1985; van Langelaan, 1983; Lundberg, 1989). It is however a cumbersome method and also has the risk of infection and damaging the joint cartilage due to malpositioning of the bone markers. More recently, computed tomography (CT) and magnetic resonance imaging (MRI) techniques were used to study the ankle and subtalar joint motion in cadaveric specimens and living subjects (Metz-Schimmerl, 1994; Ringleb, 2003; Sheehan, 2007; Siegler, 2005; Udupa, 1998). None of these studies reported on the extremes of the range of motion of the subtalar joint in vivo. The purpose of this study was to introduce an accurate method that enables the quantification of the extremes of bone-to-bone motion in a loaded state using multidetector CT imaging. The method was applied to acquire a reference data set of the normal extremes of subtalar joint motion in a group of volunteers.

Section snippets

Subjects and methods

The study was approved by the Medical Ethical Committee of our hospital. Twenty healthy volunteers (10 males, 10 females) signed informed consent prior to participation. The mean age in this group was 26.3 years, ranging from 22 to 35 years. None of the volunteers had any ankle/foot complaints, nor had a history of ankle/foot trauma or underwent surgery of the lower extremities. Physical examination of the ankle and hindfoot was performed to check for any abnormalities. Each subject was

Results

The position of the calcaneus relative to the fixed talus in the eight extreme foot positions for one subject is shown in Fig. 3(A, B). Two consistent extreme positions of the calcaneus relative to the talus were observed, i.e. extreme eversion and extreme inversion, irrespective of the combination with plantarfexion or dorsiflexion of the foot. The helical axes that represented the range of motion of the subtalar joint between two opposite extreme foot positions, were consistent in the group

Discussion

The extremes of the range of motion of the calcaneus relative to the talus in a loaded state in healthy subjects using a multidetector CT scanner were studied. For extreme positions of the foot with a considerable eversion and inversion component, the helical axis parameters for the subtalar joint were consistent between the subjects in our series. We found the helical axis of the right-sided subtalar joint running from postero-lateral-inferior to antero-medial-superior. This finding is in

Conflict of interest statement

The authors have no conflicts of interest to report.

Acknowledgements

Mr. M. Poulus and Ms. M.A. de Graaf (Department of Radiology, University Hospital AMC, Amsterdam, the Netherlands) are thanked for the assistance with acquiring CT images.

Mr. P. Broekhuijsen and colleagues (The Department for Medical Technical Development (M.T.O.), University Hospital AMC, Amsterdam, the Netherlands) are thanked for development of the footplate for CT scanning.

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