Biomechanics of the natural, arthritic, and replaced human ankle joint

Abstract

The human ankle joint complex plays a fundamental role in gait and other activities of daily living. At the same time, it is a very complicated anatomical system but the large literature of experimental and modelling studies has not fully described the coupled joint motion, position and orientation of the joint axis of rotation, stress and strain in the ligaments and their role in guiding and stabilizing joint motion, conformity and congruence of the articular surfaces, patterns of contact at the articular surfaces, patterns of rolling and sliding at the joint surfaces, and muscle lever arm lengths.The present review article addresses these issues as described in the literature, reporting the most recent relevant findings.

Figure 1

Diagrams of natural anatomy. Diagrammatic representation of the main bones, joints and anatomical structures. The location of the calcaneofibular (CaFi) and the tibiocalcaneal (TiCa) ligaments, important for following descriptions, is depicted.

Figure 2

4-bar-linkage model, single fibre ligaments. Diagrammatic sketches of the single-degree-of-freedom mechanism in the sagittal plane as predicted by the geometrical the 4-bar-linkage model. The geometrical arrangement of the passive structures is shown in three joint positions: at 20° plantarflexion (left), neutral (central) and 10° dorsiflexion (right). The kinematics is guided by the isometric rotation of the CaFi and TiCa ligaments (solid bold). The articular surfaces (the arcs nearly in contact), the line contact, i.e. the common normal CN at the single contact point, the other ankle ligaments (buckled segments), and the instantaneous centre of rotation IC (empty circle) are also depicted.

Figure 3

4-bar-linkage model, with fibre recruitment. Diagram similar of Figure 2, but with the model representation of ligament fibres as array of line segments; the pattern of fibre recruitment over flexion is depicted by the buckling of the ligament fibres.

Figure 4

Diagram of a 3D model. Diagram of a three-dimensional geometrical model for ankle joint mobility.

Figure 5

Mechanism of the three rockers of the foot. Mechanism of the three rockers of the foot-to-shank motion; about the heel first, the ankle second, and the first metatarsophalangeal joint third; the corresponding pattern of dorsi- plantar-flexion is plotted over the gait cycle in level walking is also shown.

Figure 6

‘Elica podalica’. A graphical representation for the concept of ‘elica podalica’, originally rearrangement after Paparella Treccia 1978 [35].

Figure 7

Standard gait analysis. A picture taken in the gait analysis laboratory of the authors during data collection for level walking; a patient implanted with TAR is shown. The marker-set is typical of a pelvis plus lower limb motion analysis according to Leardini et al. [38], with three markers only on the foot, considered as a single rigid body, as well as the shank, thigh and pelvis.

Figure 8

Marker-set for multisegment foot tracking. Marker-set for the multi-segment model of foot tracking by Leardini et al. [39]. It includes those three foot markers as in Figure 7.

Figure 9

Diagram at the 3D mechanical model of the replaced ankle. Three-dimensional mechanical model of a replaced ankle in joint neutral position. Tibial (above), meniscal (in between) and talar (below) components are exactly aligned and fully congruent. Arrangement of the five-fibre ligament model is also shown.

Figure 10

The 2-part ankle prostheses. Picture collection of the main current 2-part TAR prostheses.

Figure 11

The 3-part ankle prostheses. Picture collection of the main current 3-part TAR prostheses.

Figure 12

Diagram for sagittal mobility with the BOX ankle. Diagram for sagittal mobility of an ankle replaced with the BOX prosthesis. The geometrical arrangement of the passive structures are shown at the extremes of the flexion arc: in maximum plantarflexion (left), and maximum dorsiflexion (right). The kinematics is guided by the isometric rotation of the CaFi and TiCa ligaments (solid bold). The articular surfaces (the arcs in nearly contact), the other ankle ligaments (buckled segments), and the instantaneous centre of rotation IC (empty circle) are also depicted. With respect to Figures 1 and 2, the course of the three main muscle-tendon units and the pulleys (full circles) representing the extensor retinaculum bands for force redirection are also depicted. The bi-concave meniscal bearing (dots area, in between) is required to slide forwards on both components during dorsiflexion and backwards during plantarflexion so that the bones roll as well as slide upon each other. During this motion backward and forward, full congruity is maintained at the two articulating surfaces. The rolling element of the relative motion is manifested by the sliding of the bearing on the tibial component. The axis of dorsi-plantarflexion passes through IC and moves forwards and proximally during dorsiflexion, backwards and distally during plantarflexion.