Malleolar Fractures and Soft Tissue Injuries of the Ankle

Incidence

Approximately 10% of all fractures are ankle fractures, making it the second most common lower extremity fracture. In modern Western societies, the incidence of ankle fractures is between 122 and 184 ankle fractures per 100,000 persons. The incidence of ankle fractures follows a bimodal distribution with peaks for men 15 to 35 and women 55 and older. Nearly half of all ankle fracture are due to a ground-level or low-level fall. Athletic injuries account for approximately 36% of ankle fractures, and high-energy motor vehicle accidents and falls from height are responsible for 15%. One percent of ankle fractures are due to direct trauma.

The incidence of ankle fractures has increased over the past half century, especially in older women. Bengnér et al. found that the incidence of ankle fractures in Malmö, Sweden, increased by 165% from 65 per 100,000 persons in 1950–1952 to 107 per 100,000 persons in 1980–1982. Similarly, Kannus and colleagues reported similar findings in Finland where the incidence of ankle fractures rose 163% from 57 per 100,000 persons in 1970 to 150 per 100,000 persons in 2000. In both of those studies, the incidence of ankle fractures was highest in women during the seventh decade of life. Thus it is important for the orthopaedic surgeon to be comfortable with the management of ankle fractures and especially with geriatric ankle fractures.

Bony Anatomy

Ankle anatomy has been thoroughly reviewed by several investigators. Distally, the tibial shaft flares and the bone changes from triangular cortical to metaphyseal and cancellous ( Fig. 66.1 ). In the young, active adult, the distal tibia may be exceptionally dense. The medial border of the tibia is subcutaneous along its entire length, especially at the medial malleolar flare, which makes the soft tissues particularly at risk for injuries that have significant displacement such as ankle fractures with lateral talus subluxation. The anteromedial aspect of the distal tibia is notable for the prominent medial malleolus, which carries the medial articular surface of the ankle mortise. It is smaller than the lateral malleolus and can be separated into an anterior colliculus, covered laterally with articular cartilage, and a posterior colliculus. The deltoid ligament connects the tibia to the talus. Deltoid ligament anatomy will be discussed later in the chapter.

The articular surface of the distal tibia is concave, apex proximal in the sagittal plane, with the anterior and, especially, posterior lips projecting more distally. The posterior lip of the plafond is the anchorage for the posterior part of the inferior tibiofibular syndesmotic ligaments. It does not limit movement of the talus as the medial and lateral malleoli do. However, the posterior portion is frequently injured along with the lateral and medial malleoli, becoming the “third malleolus,” less commonly called a Volkmann fragment. This injury is the basis for the term trimalleolar fracture.

Laterally, the distal tibia is indented by a shallow groove or incisura for the fibula ( Fig. 66.2 ). This groove is formed by a larger anterior tubercle (Chaput or Tillaux-Chaput) and a significantly smaller posterior tubercle. Regarding ankle fractures, occasionally the Tillaux-Chaput tubercle can be fractured from the pull of the anterior inferior tibiofibular ligament or it can be considered the anterolateral fragment of a distal tibia articular (pilon) fracture.

Moving more laterally, the distal fibula forms the lateral malleolus. The lateral malleolus nearly circumferentially serves as the origin or insertion of ligaments imparting stability to the ankle joint and the distal tibiofibular relationship (discussed in the next section). Additionally, the lateral malleolus serves to keep the talus congruent in the ankle mortise. In the setting of a lateral malleolus fracture, the talus can translate laterally. This is important because a 1-mm lateral shift produces a 42% decrease in joint contact area. It is presumed that increased joint pressure, caused by the same amount of force through a smaller area, results in degenerative changes of the articular cartilage.

Ligamentous Anatomy

Syndesmosis

The syndesmosis unites the distal tibia and fibula and is composed of four distinct ligaments ( Fig. 66.3 ):

• 1.

  Anterior inferior tibiofibular ligament (AITFL)

  • The AITFL runs obliquely slightly distally from the anterolateral tubercle of the tibia (Chaput tubercle) to the anterior portion of the lateral malleolus, where its fibular attachment is occasionally referred to as the Wagstaffe tubercle.

  • The Wagstaffe tubercle or Chaput tubercle can be fractured by the pull of the AITFL. These fractures should undergo internal fixation to restore stability to the syndesmosis.

  • Recognized to be the major contributor to resisting external rotation.

  • Contributes 35% (strongest) of the syndesmosis’ ability to resist lateral fibular translation.

• 2.

  Posterior inferior tibiofibular ligament (PITFL)

  • The PITFL runs obliquely distally from the posterior tubercle (Volkmann or third or posterior malleolus) to the posterior portion of the lateral malleolus.

  • Strongest restraint to internal rotation.

  • It is distinguished from a similar connection between the tibia and the fibula that lies just distally and is called the inferior transverse tibiofibular ligament that can often be seen during arthroscopic surgery .

• 3.

  Interosseous ligament (IOL)

  • The IOL is the distal aspect of the interosseous membrane between the tibia and fibula.

  • Acts as a spring, allowing for separation between the medial and lateral malleolus during dorsiflexion at the talocrural joint.

• 4.

  Inferior transverse ligament (ITL)

Syndesmosis Importance

During neutral weight bearing, there is little or no widening of the syndesmosis. It is believed that supraphysiologic external rotation moments, such as those seen with ankle fractures, are the most common mode of failure for the distal tibiofibular syndesmosis. If the syndesmotic ligaments fail and the fibular malleolus displaces laterally, the talus follows it and loses its normal relationship with the weight-bearing surface of the tibial plafond. This lateral talar shift can occur despite an apparently intact deltoid ligament. This is a very important point. Although syndesmosis and deltoid injuries do occur concomitantly, it is important to understand that they can occur without one another.

Lateral Ankle Ligaments

The lateral collateral ligament complex is made up of three portions ( Fig. 66.4 ). The anterior talofibular ligament (ATFL) is directed anteromedially to the lateral neck of the talus. The bulky and stout posterior talofibular ligament (PTFL) is posteromedially attached to the posterior process of the talus. The middle part of the ankle's lateral collateral ligament complex is the calcaneofibular ligament (CFL). It runs obliquely posteriorly and distally deep to the peroneal tendons, more or less perpendicularly across the posterior facet of the subtalar joint, and attaches to the calcaneus just posterior to the proximal extent of its peroneal tubercle.

Relevant Tendinous Anatomy

On the lateral side of the ankle, the peroneus brevis and peroneus longus tendons (the latter more posteriorly) course around the posterior surface of the lateral malleolus ( Fig. 66.5 ). They are tethered there by the superior peroneal retinaculum, which, with its fibrocartilaginous attachment, may be avulsed from the fibula, permitting anterior dislocation of the tendons. Such a dislocation is not prevented by the more anteriorly located inferior peroneal retinaculum, a prolongation of the inferior extensor retinaculum. The peroneal tendons are superficial to the CFL.

On the medial side of the ankle, the posterior tibial tendon is the most important tendinous structure. It is in direct contact with the posterior border of the tibia and courses under the medial malleolus, deep to the flexor retinaculum and parallel but posterior to the superficial deltoid ligament. Posterior tibial tendon laceration can occur with medial malleolus fractures or it can be injured with screw placement for medial malleolus fractures. The surgeon should identify it whenever possible.

Biomechanics

Patient Presentation: Polytrauma

As noted previously, most other injuries take precedence over definitive treatment of the ankle aside from a pulseless foot resulting from an ankle fracture-dislocation. Evaluation with as much history as possible, a brief physical examination, and application of a well-padded splint with provisional reduction of dislocation with gross deformity and vascular compromise may be all that can be done for some time. Adequate radiographs are necessary for definitive diagnosis and treatment. If life- or limb-threatening injuries require urgent attention, radiographs of the ankle should be deferred until the earliest appropriate time and can be obtained in the operating room. Although operative treatment of an open wound should be accomplished as soon as possible, fracture fixation may be deferred.

History

The mechanism of injury is important in providing clues about the nature of the fracture and how it will “behave” with treatment.

• High-energy fractures (motor vehicle crash or fall from height) are likely to have complex fracture patterns and associated soft tissue damage.

• Conversely, a severely displaced trimalleolar fracture with a simple twisting mechanism may indicate osteoporosis.

• Patients who are unsure of how they were injured or who walked on the injury for days before coming to the emergency department (ED) typically have diabetic neuropathy or schizophrenia.

Systemic illness clearly has an impact on overall management and often on local treatment choice as well. Smokers have a higher risk of problems with wound and fracture healing. Diabetes places the patient at a much higher risk of complications with any type of treatment.

Physical Examination

Physical examination of the injured ankle is conducted according to injury severity. A brief inspection may reveal severe deformity or an open wound. It is necessary to identify all elements of the injury and to proceed rapidly with the treatment required to reduce a dislocation in a pulseless foot, relieve tension on overlying soft tissues, or decontaminate and appropriately treat an open wound.

The ankle should be inspected circumferentially for open or impending wounds; crushed, abraded, or swollen areas; and bone deformity. Pallor may suggest ischemia. Any open wound in the setting of a fracture, even a small one, should be considered an open fracture and a methylene blue challenge should be performed.

Without adequate perfusion, the foot cannot survive. Therefore it is crucial to recognize ischemia. Except in the case of a mangled foot and ankle, it is unusual for an ankle-level arterial injury to be limb threatening, probably because three arteries cross the region. Thus if the foot is ischemic, the surgeon must look for a more proximal arterial lesion.

Marked deformity, usually resulting from a dislocation, fracture-dislocation, or severely displaced fracture, poses a threat to the local perfusion of skin stretched over bony prominences. It promotes local swelling and may also interfere with distal blood circulation. Therefore provisional reduction to improve local perfusion and prevent further injury calls for immediate attention. Application of a very well-padded splint should follow. Although not always successful, an attempted manipulation in the ED often yields at least some improvement and is an appropriate part of applying a splint. It is better to return exposed and contaminated bone to the wound than to splint it in a position of excessive deformity. Because urgent operative wound care must soon follow, the benefits of correcting a deformity outweigh the theoretical risks of introducing additional contamination into an already dirty wound.

Even without ischemia, the vascular examination must include palpation of the posterior tibial and dorsalis pedis pulses. Swelling or deformity may interfere with this. A Doppler device can help identify the pulses. A decision must be made about the adequacy of perfusion, both before and after any treatment, with measures rapidly taken to identify and correct the cause of ischemia.

The nerves that cross the ankle are assessed in each of their sensory areas. The sural nerve supplies the lateral heel and lateral border of the foot. The sole of the foot is innervated by the medial and lateral plantar nerves, which are branches of the tibial nerve. The medial border of the foot is innervated by the saphenous nerve. The medial heel is supplied by the medial calcaneal branch. The dorsal web space between the great and second toes is the territory of the deep peroneal nerve. This nerve gives motor branches to the short extensors on the dorsum of the foot. Their contraction can be palpated locally if swelling is not excessive. The superficial peroneal nerve provides sensation for the majority of the dorsum of the foot.

Range of motion and function of the tendons crossing the ankle may be difficult to assess in the acute fracture or fracture-dislocation. An attempt to check initially must be made and then reviewed as a more thorough examination becomes tolerable.

It is essential to realize that ankle pain may be the complaint of a patient with a developing calf compartment syndrome (see Video 66.1 ). The pain of compartment syndrome is severe and poorly responsive to immobilization or narcotics. Impaired distal motor and sensory function may be the early manifestation of such a problem, which should suggest a careful search for calf tenderness, induration, and stretch-induced pain within involved muscle groups. When doubt exists, measurement of calf compartment pressures may be diagnostic.

Each of the traversing structures reviewed previously must be checked for tenderness. Each bony prominence should be assessed as well. The entire fibula must be palpated because standard ankle radiographs do not demonstrate the occasional fracture of the upper fibula associated with disruption of the ankle joint (Maisonneuve fracture).

It is important to check other regional structures that might be injured in association with the ankle or that might lead the patient to complain of ankle symptoms in spite of the tibiotalar joint not being directly involved. In particular, fractures of the anterior process of the calcaneus, the lateral process of the talus, or the base of the fifth metatarsal may be missed, as might a fracture elsewhere in the calcaneus or talus, a fracture of the navicular, or osteoligamentous injuries of the midfoot (e.g., a tarsometatarsal dislocation; see Chapter 67 ). Any findings suggesting foot abnormalities should lead to a request for additional radiographic projections of the foot, because routine ankle radiographs poorly demonstrate foot abnormalities.

Routine Imaging

Localized malleolar tenderness and inability to bear weight are the best indications to obtain ankle radiographs. Protocols exist to guide whether or not to obtain ankle radiographs after injury, but clinical acumen must be employed.

Routine studies for the ankle must include anterior-posterior (AP), lateral, and internally rotated mortise views. The mortise view is a true AP radiograph of the ankle joint in a plane parallel to its intermalleolar empirical axis. The traditional AP view, in the anatomic coronal plane, may provide additional evaluation of the medial aspect. The distal tibia, medial malleolus, fibula, and posterior malleolus should be carefully inspected for a fracture. If an ankle fracture is identified, radiographs of the knee and foot should be obtained (joint above and below). If proximal leg tenderness is present or direct trauma has occurred (such as being struck by the bumper of a car), full-length views of the fibula are essential to evaluate for proximal fibula fracture (Maisonneuve injury).

Ligamentous Assessment and Preoperative External Rotation Stress Radiographs

In addition to fracture, the normal radiographic relationship of the tibia, fibula, and talus must be assessed to determine whether there is ligamentous injury. These radiographic relationships are as follows and should be assessed on the AP radiograph :

• 1.

  The tibiofibular clear space is defined as the space between the medial border of the fibula and lateral border of the tibia, 1 cm proximal to the plafond, and should be less than 6 mm on AP and mortise radiographs.

• 2.

  The tibiofibular overlap is also measured 1 cm proximal to the plafond and is the amount of overlap of the anterior tibial tubercle (Chaput-Tillaux) onto the fibula. On an AP view, it should be greater than 6 mm or greater than 42% of the width of the fibula and greater than 1 mm on the mortise.

Although the aforementioned radiographic values may be obviously abnormal, sometimes there is uncertainty and an external rotation stress radiograph is needed. A preoperative stress radiograph is mandatory in isolated fibula fractures that occur above the joint line (supination-external rotation or Weber B, discussed later).

• The external rotation stress radiograph is necessary to determine whether the ankle mortise is unstable in two locations: the deltoid ligament in addition to the obvious lateral malleolus fracture on routine, nonstress radiographs ( Fig. 66.10 ).

  

• Again, the purpose of a stress radiograph is primarily to assess the competency of the deltoid ligament and not the syndesmosis complex, as is sometimes thought, although syndesmosis widening can be seen.

• The fracture classification will be discussed later in this chapter, but supination-external rotation type-II injuries involve a fracture of the lateral malleolus without an injury to the medial structures and can be treated nonoperatively.

However, supination-external rotation type-IV injuries involve a lateral malleolus fracture and a medial malleolus fracture or deltoid ligament injury (supination-external rotation type-IV equivalent fracture) and are treated operatively because the mortise is unstable in two locations and can lead to lateral talus translation. Even a 1-mm lateral shift of the talus significantly decreases ankle joint contact area and increases contact forces by 42%.

There has been extensive literature discussing the methods of external rotation stress testing the ankle joint. Regardless of the method for performing the test, the authors consider a positive stress test to have a medial clear space of 4 mm or more, with that value being at least 1 mm greater than the superior tibiotalar space. There are three methods of performing this test:

• 1.

  Manual stress test. The tibia is rotated internally to bring the malleoli into a plane parallel with the film. The talus is then pulled laterally or externally rotated and is held in this position while the radiograph is exposed. A control view of the other side is helpful.

• 2.

  Gravity stress test. The patient is placed in the lateral decubitus position with the fractured side down but hanging off the end of a radiographic examination table. The foot is allowed to externally rotate from the force of gravity and an AP radiograph is taken.

• 3.

  Weight-bearing stress radiograph. It is used less frequently because of pain with weight bearing immediately after ankle fracture. It is simply a weight-bearing AP radiograph. The authors do not routinely use this stress test as it is not as reliable.

Gill and colleagues performed manual stress and gravity stress tests in 25 patients with isolated distal oblique fibula fractures. They found no significant difference in medial clear space widening between the two tests. Similarly, in a prospective study of consecutive isolated oblique fibula fractures starting at the level of the tibia plafond, LeBa et al. found no statistical difference between the manual and gravity stress tests. The authors of this chapter perform the gravity stress test on all isolated fibula fractures starting at the tibia plafond and extending proximally in an oblique direction that do not have obvious medial clear space widening.

Other Studies

Computed tomography (CT) can be even more informative, as it provides a cross-sectional view of the joint that clarifies the relationship of the fibula to the tibia, as well as the fit of the talus within the mortise, plafond involvement, and the status of soft tissue structures. The authors find that CT can be very helpful identifying the size of posterior malleolus fractures. CT scanners with multiple detector row arrays allow reduced scan times, increased resolution, and improved reconstructions in multiple planes, including three-dimensional (3-D) reconstructions. The extent and location of articular surface involvement are obvious, and planning of surgical approaches is facilitated, particularly for the posterior malleolus. In fact, the authors routinely get a CT scan for all displaced posterior malleolus fractures because CT scans can accurately determine the size and location of posterior malleolar fractures. Regular radiographs underestimate the size of the latter lesion ( Fig. 66.11 ). Transaxial views of the syndesmosis reveal the reduction of the fibula in the incisura and the presence of loose bodies. There is evidence that helical CT and 3-D reconstructions provide excellent imaging of the ligaments and cartilage surface.

Magnetic resonance imaging (MRI) is not as valuable in the acute ankle fracture because of traumatic edema. In fact, Nortunen et al. used MRI to assess injury to the deep deltoid ligament in the setting of supination-external rotation (discussed later) injuries. They found that interobserver reliability was higher with a radiographic stress test than MRI assessment of the deep deltoid and concluded no additional value of obtaining the MRI for treatment decision making. However, it can be useful in the setting of syndesmosis disruption. Park et al. assessed the utility of MRI for syndesmotic instability in unstable ankle fractures. In patients who had preoperative MRI and intraoperative stress testing, they found that a PITFL tear on MRI was the most predictive (74% sensitivity, 78% specificity, 54% positive predictive value) of intraoperative syndesmosis injury. Although the MRI may add diagnostic value, the cost-to-benefit ratio must be considered. The authors do not routinely obtain MRIs on ankle fractures.