Articular contact at the tibiotalar joint in passive flexion

Abstract

The knowledge of the contact areas at the tibiotalar articulating surfaces during passive flexion is fundamental for the understanding of ankle joint mobility. Traditional contact area reports are limited by the invasive measuring techniques used and by the complicated loading conditions applied.

In the present study, passive flexion tests were performed on three anatomical preparations from lower leg amputation. Roentgen Stereophotogrammetric Analysis was used to accurately reconstruct the position of the tibia and the talus at a number of unconstrained flexion positions. A large number of points was collected on the surface of the tibial mortise and on the trochlea tali by a 3-D digitiser. Articular surfaces were modelled by thin plate splines approximating these points. Relative positions of these surfaces in all the flexion positions were obtained from corresponding bone position data. A distance threshold was chosen to define contact areas.

A consistent pattern of contact was found on the articulating surfaces. The area moved anteriorly on both articular surfaces with dorsiflexion. The average position of the contact area centroid along the tibial mortise at maximum plantarflexion and at maximum dorsiflexion was respectively 58% posterior and 40% anterior of the entire antero-posterior length. For increasing dorsiflexion, the contact area moved from medial to lateral in all the specimens.

Introduction

It has been recently observed that the tibiotalar joint is not fully conforming and that the mutual action of articular contact and ligament isometric rotation guides the physiological mobility of this joint (Leardini et al., 1999a, Leardini et al., 1999b, Leardini et al., 2000). Patterns of articular contact in unloaded conditions provide important insight in this respect, since currently only bone relative positions and ligament shape and orientation have been investigated (Leardini et al., 1999a, Leardini et al., 1999b; O’Connor et al., 1998). Prosthetic design and ligament reconstruction techniques for the human ankle joint would greatly benefit from this knowledge, as it has been for the knee (Henche et al., 1981; Benjamin et al., 1998; Iwaki et al., 2000; Wilson et al., 1998; Wu et al., 2000).

For the contact at the tibiotalar joint, many experimental studies have been reported in the literature (Beaudoin et al., 1991; Bertsch et al., 2001; Calhoun et al., 1994; Clarke et al., 1991; Curtis et al., 1992; Driscoll et al., 1994; Earll et al., 1996; Friedman et al., 2001; Hartford et al., 1995; Kimizuka et al., 1980; Macko et al., 1991; Michelson et al., 2001; Pereira et al., 1996; Ramsey and Hamilton, 1976; Steffensmeier et al., 1996; Tarr et al., 1985; Thordarson et al., 1997; Ting et al., 1987), particularly looking at the effect of joint flexion position, joint loading, and integrity of the ligaments. Most of these are limited by the invasive measuring devices, i.e. pressure-sensitive films, cartilage staining techniques, and by the loading conditions of the tested specimens. Rare data describe contact on the tibial mortise (TiM) (Kura et al., 1998), and no studies have been carried out in passive flexion, the only condition where mobility is prescribed only by the articular surfaces and the ligaments (O’Connor et al., 1998; Leardini et al., 1999a).

In the present study, a novel measurement technique, combining Roentgen Stereophotogrammetric Analysis (RSA), 3-D digitisation and surface mathematical modelling, is utilised to calculate position and size of the contact areas on both the TiM and the trochlea tali (TTa) in several joint positions along passive flexion (Leardini et al., 1999a). The issue to be investigated was that, during unloaded flexion of the tibiotalar joint, a consistent motion of the contact area occurs at both surfaces.