Since the ankle complex serves as the transition from the “leg” to the foot, significant forces are placed through these structures, resulting in frequent injuries. The talus sits between the medial and lateral malleoli within what is described as the ankle mortise. The orientation of the mortise (lateral malleolus more distal and posterior than the medial) dictates the motion of plantar flexion to have an inversion component, while dorsiflexion includes eversion. As the lower extremity internally rotates during ambulation and the foot must be able to be placed onto the surface, the next inferior linkage to the foot provides a mechanism for dissipation of rotation (subtalar joint) while enabling the foot to adapt to uneven surfaces (serving as a mobile adaptor). It is obvious that a variety of ligamentous structures are required to control the bony structures and to interface with the muscular units permitting normal function. The osseous-ligamentous structures are shown in Figure 17-1A, B, respectively, in medial and lateral orientations. These relationships have been described at length by Inman.1 It is interesting to note how Inman used models to explain the intricate interrelationships and how the ankle must be viewed as a part of the overall complex. This can be perceived as enabling the lower extremity to perform required “functional” tasks while permitting the foot to transfer weight-bearing loads. Unfortunately, the large loads and unique triplanar action of these structures do predispose them to injury.
Ankle ligaments. (A) Medial view. (B) Lateral view.
The initial views are the traditional anteroposterior (AP) and lateral following the 90° rule (Figures 17-2 and 17-3). When the orientation of the talar dome in the mortise is in question, a mortise view is performed (Figure 17-4). Some clinicians prefer what is described as an oblique view, which is somewhat more effective in delineating malleolar relationships (Figure 17-5). Clinicians will typically see an “ankle series” including an AP, lateral, and either the mortise or oblique. It is very interesting to note that the routine use of the ankle series has come under question as a set of manual palpations and clinical observations appear to be sufficient to rule out fractures when applied by therapists or surgeons.2
A normal-appearing AP view radiograph of the ankle. Note the slight overlap of the tibia and fibula at the distal articulation.
A normal-appearing lateral view radiograph of the ankle. Apparent in this view is not only the general osseous alignment, but also the joint space of the talocrural joint.