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CHAPTER 64 • Ankle Fractures

consisting of the tibial plafond (ceiling) superiorly, and the medial malleolus medially. A dorsal projection of the tibia, the posterior malleolus, serves to enlarge this confluent area. The lateral articulation of the talus is with the distal fibula. Each of these articular surfaces shares in load distribution during weight bearing, with the fibula, for example, taking 1/6th of the load. 370 The medial malleolus is both shorter and more anterior, and thus the axis of the joint is in 15 degrees of external rota- tion. The tibial and fibular articular surfaces together comprise the mortise in which the talus sits (Fig. 64-2). The relationship between the tibia and fibula centers on the syndesmosis where the fibula lies in the incisura of the lateral aspect of the tibia, and is stabilized by the anterior-inferior tibiofibular ligament (AITFL), the posterior inferior tibiofibu- lar ligament (PITFL), and the interosseous ligament which is confluent with the interosseous membrane above (Fig. 64-3). The AITFL arises from a prominence of the anterolateral tibia known as the tubercle of Chaput (which may be avulsed, typi- cally in children’s ankle injuries), and inserts onto an equivalent prominence on the fibula: The tubercle of Wagstaffe. The PITFL arises from Volkmann’s tubercle of the posterior malleolus. It is extremely strong and in trimalleolar fractures the fragment usu- ally remains solidly attached to the fibula via this ligament. This relationship can be exploited surgically: Reduction of the distal fibula usually assists in reduction of the posterior malleolus, and conversely stabilization of the posterior malleolus will often restore stability to a fractured fibula. 253 The talus itself is remarkable for three reasons. Its surface is 70% covered in articular cartilage, it has no direct ligamentous attachments for muscle action and it has a tenuous retrograde vascular supply. The body of the talus is geometrically com- plex and describes a frustum, a cone with its apex removed, lying transversely in the mortise, being broader anteriorly and narrower posteriorly. This complex shape prevents the medial and lateral facets of the talus, and their relationships with their respective malleoli, from being seen on any single radiographic projection and this can result in considerable uncertainty when attempting to measure joint spaces unless all three views are obtained (see below). As a result of its frustral shape, the talus is compressed within the mortise of the ankle in dorsiflexion (the position of heel strike), causing the fibula to rotate externally, and is most stable in this position. In plantarflexion (at toe off) the talus is held less rigidly, allowing physiologic external rota- tion and inversion. 248 Osseous stability of the ankle increases with axial loading, when the congruency of the articular sur- faces provides very substantial stability even after division of all ligamentous restraints. 356 The superior surface of the talus (the talar dome), conforms closely to the plafond of the tibia, and the contact area between the two surfaces decreases markedly with displacement of the talus. Ramsey and Hamilton’s 315 famous study reported a decrease in contact area of 42% after just 1 mm of lateral talar displacement, an effect confirmed by other authors. 221,261 Although this study has been criticized, 402 and the precise rela- tionship between displacement, contact area, and contact pres- sure remain contentious, 80,186,379 it is widely accepted that loss of congruence of the mortise leads to altered biomechanical loading and is principally responsible for the poor outcomes

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Figure 64-1.  The changing epidemiology of ankle fractures. Data from Kannus et al. 179

Although ankle fractures are not associated with systemic low bone mineral density per se, 146,354 the microarchitecture of the trabecular bone in the distal tibia of elderly patients with ankle fractures is abnormal and depleted, and bone stiffness is reduced, compared with uninjured controls, 354 suggesting that these injuries should be considered to be true osteoporotic fractures. Specific risk factors for sustaining ankle fractures have been investigated. Hasselman et al. 146 undertook a prospective study of 9,704 women over the age of 65 and found that ankle frac- tures were more common in the obese and those with a history of multiple falls. Further evidence for obesity as a risk factor comes from the international GLOW study of 60,393 women. They found that obese women over the age of 55 years were significantly more likely to sustain an ankle fracture than non- obese women. 69 Moreover, Margolis et al. 235 found that patients with a greater percentage increase in weight since the age of 25 were also significantly more likely to sustain an ankle frac- ture. Obesity also predisposes to more severe injury. Spaine and Bollen 352 found that patients with an unstable ankle fracture were far more likely to be obese (29%) than patients with stable ankle fractures (4%). Alcohol use also appears to be a risk factor and Jensen et al. 170 reported that 29% of patients in their series were found to have consumed alcohol in the 4 hours preceding fracture.

PATHOANATOMY, APPLIED ANATOMY, AND BIOMECHANICS RELATING TO ANKLE FRACTURES

The surgical anatomy of the ankle joint has been well described in detail elsewhere. 159 The joint functions as a mortise with the body of the talus articulating with a confluent area of the tibia