The ankle joint is simply not a hinged joint that gives uniplanar motion, but the complex anatomy of the ankle joint permits triplanar motion (1,2). The talus rests within the framework of the distal tibia and fibula (Fig. 109.1). The tibia and fibula are held together by the syndesmotic ligaments that comprise the anterior and posterior inferior tibiofibular ligaments, interosseous ligament, and the inferior transverse ligament. The syndesmotic ligaments permit the distal fibula to rotate approximately 12 degrees relative to the tibia (3). The talar dome and distal tibial plafond create a congruent and stable articular joint that is able to withstand four times the body weight during the stance phase of gait. The talar dome is wider anteriorly than posteriorly and has a central indentation that separates two crests (4). Posteriorly, the distal tibia has a shallow groove for the flexor hallucis longus tendon. The lateral surface of the tibia includes the fibular notch, which articulates with the fibula. Superior to the notch is the interosseous tibiofibular ligament. The tubercle at the anterior border of the fibular notch, tubercle of Tillaux-Chaput, and the posterior malleolus, at the posterior border of the fibular notch, assist to stabilize the posterior ankle joint (5,6,7,8,9,10 and 11). The posterior inferior tibiofibular ligament originates from the posterior tubercle laterally on the posterior tibial surface. The posterior inferior transverse ligament also originates from the posterior tubercle. Lateral talar rotation in the transverse plane may injure the posterior tubercle. Loading of a plantarflexed talus may cause fracture of the posterior malleolus (Volkmann fracture) due to excessive tension to the posterior ligaments (5,11,12). The anterior inferior tibiofibular ligament starts 5 mm above the articular surface and descends obliquely between the tibia and fibula (13). It proceeds anteriorly to the syndesmosis to the anterior aspect of the lateral malleolus and assists in stabilizing the hindfoot to the forefoot during push-off in gait (14). The talus has medial and lateral articular surfaces that articulate with its respective malleoli.

Medially, the distal tibia extends into the medial malleolus that consists of the anterior and posterior colliculi. The deep deltoid ligament originates in the intercollicular groove between the colliculi (15,16). The deep deltoid ligament has an intermediate and posterior component (Fig. 109.2). The posterior component originates from the intercollicular groove and posterior colliculus. The deep deltoid ligament inserts just distal to the medial talar surface on the central and posterior aspects. The superficial deltoid originates from the anterior colliculus and attaches to the anterior talar neck, the navicular tuberosity, spring ligament, and the sustentaculum tali of the calcaneus (16,17 and 18). Talar external rotation is prevented by the deep deltoid ligament, and hindfoot eversion is prevented by the superficial deltoid ligament (19). Excessive plantarflexion and eversion of the foot may cause rupture of the superficial deltoid at the anterior colliculus (5,17). Anterior colliculus fractures contribute 15% to 20% of medial malleolar ankle fractures (20,21,22,23 and 24). Similarly, excessive dorsiflexion stresses the posterior deep deltoid at the posterior colliculus. Fracture patterns may vary due to the deltoid ligament complex (22,23). Direct varus inversion of the ankle forces the talus against the medial malleolus, which may cause a vertical supracollicular fracture pattern (25,26,27,28 and 29).

The distal fibula includes the origin of the three lateral ankle ligaments. The medial surface of the distal fibula presents an articular facet placed anteriorly for the lateral surface of the body of the talus. Posterior to the articular fossa is the malleolar fossa, which is a rough depression for the origin of the posterior talofibular ligament and inferior transverse ligament. The anterior border of the lateral malleolus is the origin of the anterior talofibular and the calcaneofibular ligaments. The posterior border of the lateral malleolus presents a shallow groove, called lateral malleolus sulcus, which permits the passage of the peroneal tendons. The apex of the lateral malleolus is rounded and may contribute to the origin of the calcaneofibular ligament. The anterior talofibular ligament restricts foot anterior displacement, internal rotation, and talar inversion and is the weakest of the lateral ankle ligaments (14,30,31 and 32). The calcaneofibular ligament, deep to the peroneal tendons, helps to stabilize the subtalar joint and restricts inversion (30,31,32,33 and 34). The posterior talofibular ligament restricts foot posterior displacement and is the strongest lateral ankle ligament (32).

Understanding the mechanism of injury allows physicians to categorize the fracture patterns, communicate the injury, evaluate the severity of the bone and soft tissue damage, and determine the treatment approach.

The mechanism of most ankle fractures is the result of the body weight and momentum compressing and rotating the tibia and fibula in relationship to the talus. The talus is fixed against the ground, while the tibia and fibula are moving to create the fracture dislocation. Vertical gravity, transverse movement, and the torsional force of the tibia and fibula against the fixed talus exceed the structural integrity of the ankle ligaments and bone. The description of these movements is very confusing in the literature. Some articles describe the movement of the tibia to the talus, and others describe the movement of the talus against the tibia. Most authors have presented the mechanism in terms of describing the motion of the talus with respect to the tibiofibular mortise. To quote William Hamilton in his book, Traumatic Disorders of the Ankle, “this custom will be observed in this text.”

The position of the ankle joint, the position of the knee, and the movement of the body determine the pathomechanics of the osseous and soft tissue damage. The combination of gravity, anterior movement, lateral movement, or posterior movement can predict the injury. A straight perpendicular gravity fall with the knee fully extended and locked will produce a vertebra compression fracture and a joint depression calcaneal fracture. An anterior movement with the knee fully extended will produce a tendo Achilles rupture or an anterior tibial axial compression or pilon fracture. A posterior movement will produce a hip fracture or low back injury. A forced ankle dorsiflexion movement with the knee flexed will produce a talar neck fracture. A lateral transverse fall will produce a supination or pronation subtalar joint dislocation. The focus of this chapter is the more common ankle malleolar fractures.

Two classifications have prevailed and are commonly used today. They provide insight into the diagnosis of occult soft tissue injuries. They are the Lauge-Hansen classification and the Danis-Weber classification.

Although not the first classification system to correlate ankle fractures to the mechanism of injury, Lauge-Hansen classification system has been widely accepted as the primary classification system in evaluating ankle fracture patterns (35,36,37,38,39,40,41 and 42). The classification is simple; only four types accurately describe over 95% of all ankle fractures.

Lauge-Hansen fracture patterns and observations were made based on cadaveric models. Injuries were classified with a two-word description: first by the foot position (supination or pronation) and second by direction of the talus in relation to the tibia and fibula (abduction, adduction, or eversion). The original work was done in a laboratory setting. It is the rotation of the talus that supplies the forces necessary to injure the bony and ligamentous structures (43). The classification system breaks down each fracture pattern into a sequential series of events based on the severity of injury (44). Two basic concepts make this classification useful. First, a soft tissue injury and a bone injury cannot occur during the same stage. If there is tension on a ligament, either the ligament will tear or the ligament will remain intact and avulse a piece of bone, but both ligament and the bone cannot be damaged. Second, the injury cannot skip a stage. In the sequence of an injury, as each stage happens, either the ligament is torn or the bone is fractured. If the radiographs do not show a fracture, then the soft tissue injury must have occurred at that stage. These two concepts allow accurate evaluation of soft tissue damage based on radiographic evaluation and assist in the surgical decision making. There are four types of fibular fractures:

All of these are unique to the classification and sequence stage. These are called hallmark fractures. There are two types of tibial fractures: (a) vertical and (b) transverse. The vertical fracture is unique and a hallmark fracture. The transverse fracture is either an avulsion of the deltoid ligament or a “knock-off” fracture by the rotating talus and is common to three classification stages. Simply identifying these osseous hallmarks fractures on an x-ray will identify the exact mechanism and stage of accompanying soft tissue injury in both a Lauge-Hansen and Danis-Weber classification. The Lauge-Hansen classification identifies fibula fractures, tibia fractures, and ligament damage. The Danis-Weber classification identifies only fibular fractures and ligament damage. The hallmark fractures are underlined in Table 109.1.

As such, the supination-adduction type refers to inverting the foot and ankle on a supinated foot. The pronation-abduction type refers to everting the foot and ankle on a pronated foot. The pronation-eversion type refers to internally rotating the leg on a pronated fixed foot. The supination-eversion type refers to internally rotating the leg on a supinated fixed foot.
Ankle dislocations and open fractures are commonly seen in the latter stages of these fracture patterns (6,45). Although this system illustrates the mechanism of injury and the method to reduce fracture dislocations, the reliability of the Lauge-Hansen classification system has been noted to vary on the observer (41,46,47 and 48).