SLR - September 2016 - Dunja Delevska

Rotational Dynamics of the Talus in a Normal Tibiotalar Joint as Shown by Weightbearing Computed Tomography

Reference: Lepojärvi, S, Niinimäki, J, Pakarinen, H, Koskela L, Leskelä, HV. Rotational Dynamics of the Talus in a Normal Tibiotalar Joint as Shown by Weightbearing Computed Tomography. J Bone Joint Surg Am, 2016 Apr 6; 98 (7): 568–575

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Reviewed By: Dunja Delevska, DPM
Residency Program: New York Presbyterian – Queens, Flushing, NY

Podiatric Relevance: Understanding the normal dynamics of the talus within the tibiotalar joint is crucial in evaluating patients with trauma to the ankle. Small deviations of the talus from its anatomic position can lead to altered joint mechanics and subsequently posttraumatic arthritis. Conventional radiographs have limited accuracy in evaluating the lateral shift of the talus, and, until recently, computed tomography (CT) scans have been feasible only with the patient in the supine position, therefore unable to evaluate normal physiologic mobility of the joint while weightbearing. This study investigates the rotational dynamics of the talus in the tibiotalar joint using a novel weightbearing cone-beam CT (WBCT) with the patient standing and the ankle under rotational stress.

Methods: WBCT axial images of both tibiotalar joints were acquired on the same day with the ankle in the neutral position, in maximal internal rotation and in maximal external rotation in 32 healthy subjects with excellent functional conditions of the ankles (as evaluated by an orthopedic surgeon). The analysis includes measurements of rotation of the talus, medial clear space, anterior and posterior widths of the tibiotalar joint, translation of the talus and talar tilt.

Results: Increasing age was associated with increasing talar tilt, and the talus was more everted in the external rotation position. Between external and internal rotation of the talus, the mean changes were 10 degrees in talar rotation, 2.0 degrees in talar tilt, 20.2 mm in the medial clear space, 0.9 mm in anterior width, 20.4 mm in posterior width and 2.9 mm in translation of the talus. Statistically significant asymmetry was detected in talar rotation, in internal rotation, in the neutral position and in external rotation.

There was no significant difference between female and male subjects with regard to any of the measurements. Comparison of the paired right and left ankles showed minor intrasubject (i.e., bilateral) asymmetry. All of the WBCT measurements demonstrated good to excellent interobserver and intraobserver reliability.

Conclusions: This study provides clinically applicable information. The neutral position of the talus in relation to the medial malleolus varies and is largely determined by the talar rotation. The tibiotalar joint width was found to vary widely and was the largest in the medial clear space. This could lead to a false-negative diagnosis in patients with a small medial clear space and a false-positive diagnosis in patients with a large medial clear space if, for example, the traditional criterion of 5 mm or more of medial clear space on the mortise radiograph is used to consider an ankle mortise unstable. Also, they identified large intersubject variation in both the static and dynamic measurements, but only minor intrasubject variation, further supporting the evaluation of the patient’s contralateral ankle as an individual roadmap to assess the injured ankle.

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