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Ankle fractures

Description

Fractures of the ankle comprise injuries to the medial +/- lateral malleolus (the distal tibia and fibula respectively), such that the "side" articulations with the talus are disrupted. Typically, injuries to the direct weigh bearing superior articular surface of the ankle joint (ie: lateral to the medial corner of the articulation with the tibia), are considered separately, as "tibial plafond" fractures. Ankle fractures can occur in isolation or with ligament injuries as well although even with the "avulsion type" fractures of medial and lateral malleoli, there is significant injury to the associated connecting ligament. Remember that all fractures should be considered as an extension of a soft tissue injury.

Structure and function

The ankle is a hinge joint composed of the tibia, fibula and talus as well as three ligament complexes: the deltoid (medially, tibia to talus), lateral collateral (connecting the fibula to the talus and calcaneus) and syndesmosis (connecting the tibia and fibula). The connection between the talus and the bones above is via a mortise joint; that is, the talus fits precisely (like a jigsaw puzzle piece) as shown:

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Thus, any disruption of the bones or the ligaments that hold the bones in fixed relation to each other will make the joint unstable. 
The second structure/function consideration is that the perfect fit of the talus with the mortise allows the widest possible surface for load bearing. In these two figures, the normal relationship is shown at left; at the right, there is a fibular fracture that allows the talus to shift laterally. With this shift, there is not only instability of the joint, but the contact area between the tibia and talus is reduced.   Stress  is equal to the force (load) divided by area ( ?=F/A). The reduction in the weight bearing surface area  that occurs with even relatively minor joint subluxation (eg  2mm of lateral talar shift) can thus result in a significant increase in the stress on the remaining articulating surface. This can cause reactive bone formation (following Wolff's Law) and in turn sclerosis of the bone, decreased compliance, and ultimately, post-traumatic arthrosis. This is compounded by any injury that occurred to the hyaline cartilage at the time of injury.

Epidemiology

Most ankle fractures occur in elderly women. Each year, 187 per 100,000 people sustain an ankle fracture (where? USA? global? PLEASE CITE). As such, they are less common than many other fractures. Two thirds of ankle fractures involve one bone; one fourth are bimalleolar, involving both. The remainder are labeled "trimalleolar", involving the posterior malleolus as well.

Clinical presentation

The typical presentation of an ankle fracture is a patient who sustained an acute injury and now no longer can bear full weight on the leg. Swelling and deformity are common as well. In the vast majority of cases the foot and ankle are in a supinated position (heel is inverted) at the time of the injury although often the patient has difficulty in recollecting or describing exactly what happened. It is the rarer injuries that start with foot/ankle in a pronated position (heel everted) that can result in the syndesmotic injuries so it is worth making particular note of this mechanism.

Red flags

Blood on the skin suggests an open fracture. If there is an open fracture antibiotics and tetanus prophylaxis as indicated. A formal irrigation and debridement is usually done in operating room by specialist but cleaning the wound with saline and applying and dressing and splint (with realignment as needed) should not await the arrival of a specialist.

An isolated avulsion type medical maleolar fracture (particularly with  a "non inversion" type mechanism) may have an associated syndesmotic ligament injury

A severe deformity suggests a dislocation or displacement; both place the skin and neurovascular structures at risk. Gentle reduction should be performed once the injury is defined.

Any ankle injury in a patient with open growth plates must be evaluated for a growth plate injury.

Bear in mind that patients who present with what seems to be a severe ankle fracture (injury, pain, inability to bear weight at all) but have normal ankle x-rays may have an injury to the foot, such as a Lisfranc joint disruption or navicular injury. That is, the x-rays are normal only because they were aimed at the wrong body part

Differential diagnosis

The differential diagnosis of ankle fractures includes those conditions that could present like an ankle fracture or, more to the point, may be present in addition to an ankle fracture (and not obvious at first glance). The first point to consider is that some injuries create obligate secondary injuries. Shown in the figure is a simple example: to the left is the bony outline showing a fibular fracture, as would be seen on an xray; to the right, the tear of the deltoid ligament, which logically must be present is shown as well.

At times, bone or ligament damage on the medial side of the ankle joint (eg a fracture of the medial malleolus or rupture of the deltoid ligament) will cause lateral damage that is not seen on the standard ankle x-ray. There, energy coursing up the leg through the syndesmosis and interosseous membrane is present at the proximal fibula, near the knee, a so called "Maisonneuve fracture" as shown below (credit:http://www.wikiradiography.com/page/Maisonneuve+Fracture))

Next, it must be considered that pain near the ankle might be caused by an injury outside the ankle itself, such as in the Lisfranc joint (tarsometatarsal joint); careful examination of where the area of maximal tenderness lies helps identify this injury. A “squeeze test” can be performed “5 cm proximal to the intermalleolar axis” to assess for syndesmotic ligament injury. Ankle fractures are also associated with impaction injury to the talar dome, but because there is nothing that can be done to prevent progression of cartilage damage, were that to occur, there is no particular point in seeking out to discover if there was a cartilage injury as well.

Objective evidence

The so-called Ottawa ankle rules state that if an awake and alert patient can bear weight and has no bony tenderness on examination, ankle radiographs can be omitted as they are almost certain to be negative. All other patients with ankle injuries are required to have AP, lateral and mortise X-rays. These films should be scrutinized not only for the condition of the bones and joint surfaces themselves but their relationships: On the AP view, a tibiofubular overlap of less than 10 mm or a tibiofibular clear space of greater than 5 mm implies syndesmotic ligament injury (PICTURE). On the lateral view, the talus is normally centered directly under the tibia. On the mortise view, the clear space around the talus should be symmetric.

Risk factors and prevention

The primary risk factor for sustaining an ankle fracture is participation in high risk activities, but this applies only to a scant minority of such injuries.  

According to a recent study which assessed bone mineral density,  (PMID:12030550) ankle fracture is not associated with osteoporosis. 

Treatment options

The goal of treatment is to create the proper biological and mechanical environments for optimal healing. That is, the aim is to allow the bones to heal and to restore their normal geometry and relationships. If the fracture is not displaced, a cast may suffice. If there is displacement (either of the bone fragments themselves, or of the mortise architecture) surgical fixation may be needed. Recall that if a lot of side-to-side pressure is needed to hold the bones in place, a cast applying that pressure is apt cause skin abrasion and breakdown.

If non-operative treatment is chosen, serial radiographic monitoring may be needed to ensure that alignment is not lost.

Once the bones have healed, physical therapy to regain motion and proprioceptive function may be needed.

Many patients will need physical therapy after the fracture has united, to regain range of motion and proprioception.

Outcomes

Most ankle fractures heal uneventfully. Full recovery can take months, as rehabilitation to regain functional use and normal range of motion of the ankle cannot begin until the bones have at least started to unite.

Some fractures increase the likelihood of developing arthritis, even with optimal treatment. In those cases, there may have been damage inflicted on to the articular surface leading to chondrocyte death/dysfunction. Needless to say, a poor reduction of the fracture leading to mal-alignment is almost certainly going to promote arthritis, just as failing to tighten the lug nuts on a wheel and having it wobble almost certainly increases wear and tear of the tire. 

Very infrequently, patients with ankle fractures will develop  a complex regional pain syndrome (formerly known as reflex sympathetic dystrophy). This condition may be diagnosed only after some delay, as the initial pain complaints are attributed to the fracture itself.

Holistic medicine

According to a recent study (PMID: 21886001), smokers had six times higher odds of developing a deep infection compared with nonsmokers following surgical treatment of ankle fractures.

Miscellany

A small fleck of bone may be seen on radiographs, just distal to the malleolus: a so-called avlusion fracture. An avlusion fracture is not structurally significant itself but rather serves to inform the viewer that a sprain has been sustained. The avulsed fragment is a sliver of bone that remained attached to the ligament as it was pulled off its insertion site (akin to a bit of paint that comes off the wall when tape is applied and than rapidly pulled off).

Race horses (such as Barbero) are occasionally in the news for "ankle fractures" but their injury is actually to the "fetlock", not the ankle; what appears to be the ankle joint (based on its location above the foot) is actually the metatarsophalangeal joint.

Key terms

  • Deltoid ligament
  • Fibular collateral ligament
  • Lateral malleolus
  • Medial malleolus
  • Mortise 
  • Syndesmosis  

Skills

  • Physical examination of the injured ankle, especially to exclude associated injuries
  • Apply Ottawa ankle rules to identify patients who need radiographs
  • Interpret radiographs to identify fractures and infer ligament injuries; describe the radiographic findings; recognize instability and displacement (criteria for specialist referral!)
  • Provide first line treatment to open fractures (wound management) and dislocations (gross reduction and splinting)
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  1. Apr 08, 2012

    Having read this article a graduating medical student should have a very clear understanding of what they would need to know and do in order to manage such a patient presenting if they came across them at a sporting event, a friend's barbeque  or in the emergency ddepartment of a county hospital. Remember operative management and debridement is going to be done by specialist. Focus on what the intern family practitioner or "off duty doctor" would be expected to do.

  2. May 04, 2012

    Changes are excellent - much clearer and better targeted to medical student and junior doctor. See additional edits in text. Suggest indicate in pictures using arrows to highlight importance of looking for widened medial joint space on mortice view as indication of lateral talar  shift.