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Ankle sprains

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Ankle sprains are among the most common musculoskeletal injuries. Patients typically describe an episode where they “roll their ankle” to one side (often inward, a so called  “inversion” sprain (see figureFigure 1) and thereby tear the ligaments on the outside (lateral) ankle.  This is contrasted with a less common "eversion" sprain where the foot rolls to the outside and the medial (deltoid) ligament is torn.  Patients with sprained ankles can have significant pain and swelling. There is usually a limp, but unlike an ankle fracture, a sprained ankle usually will tolerate some weight-bearing. Although the phrase “it’s just a sprain” may suggest that this is always a minor injury, ankle sprains can in some cases lead to significant impairment , at least in the short termif other additional structures are injured. Expeditious treatment –directed to limiting swelling and regaining motion –helps ensure the best possible recovery.

FigureFigure1: ankle inversion, the typical mechanism of injury of an ankle sprain

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The ankle joint is composed of the articulation of the tibia and fibula with the talus, though although there are soft tissue connections between the long bones and the navicular and calcaneus as well.  The tibia and fibula are held together by the tibial-fibular ligament and interosseous membrane; these two bones connect with the talus by forming a mortise (inverted “U”) into which the talus fits (Figure 2).  
  

Figure 2: the talus (T) sits in an inverted U known as the mortise. The appropriate distance between the tibia (Tib) and fibula (Fib), and with that, the fit between those bones and the talus, is maintained by the syndesmosis (shown in red).

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  1. the talo-fibular ligaments (anterior and posterior) on the lateral side of the ankle joint (Figure 3)
  2. the calcaneo-fibular ligament on the lateral side of the ankle joint (Figure 3), andand 
  3. the deltoid ligament on the medial side (Figure 4).

 

Figure 3: the lateral ligaments of the ankle. The talo-fibular ligaments (anterior and posterior) are shown in yellow, and the calcaneo-fibular ligament is in red. The pink lines represent the tibio-fibular ligaments of the syndesmosis. (Redrawn from http://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/Ankle.PNG/375px-Ankle.PNG)

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The posterior talo-fibular ligament (PTFL) runs from the fibula into the calcaneoustalus, posterior to the calcaneo-fibular ligament. The PTFL  stabilizes the ankle joint and the subtalar joint. Injuries to the PTFL are rare, unless there is an ankle dislocation or subluxation.

Figure 4: The deltoid ligament on the medial ankle, outlined in yellow (and shaped like a Delta). Within this ligament, there is a connection between the tibia and the navicular (blue), talus (red) and calcaneus (green). Credit/blame: JB original

The deltoid ligament is a strong fan-shaped band of connective tissue on the inside of the ankle. It runs from the medial malleolus to the talus and calcaneous. The deeper branch of the ligament is securely fastened in the talus, while the more superficial, broader aspect runs into the calcaneous. This ligament is extremely strong and stabilizes the inside of the ankle. Tears of this ligament are most common when the ankle undergoes an unstable ankle fracture. Like the anterior talo-fibular ligament, the deltoid is rarely torn completely but rather becomes stretched (deformed) when stressed.

The anterior inferior tibial tibio-fibular ligament is the one injured in a so-called “high ankle sprain”.  This ligament is positioned on the anterolateral aspect of the ankle and helps stabilize the mortise. Injuries to this ligament occur when the foot is stuck on the ground and rotated inwardly. A high ankle sprain can be very painful and lead to scar formation. This scar can cause irritation to the outside of the ankle joint–a condition known as anterior-lateral ankle impingement.

The interosseous membrane is composed of strong fibrous tissue and runs along the tibia and fibula, and keeps the two bones moving as one unit. It can be torn in certain patterns of ankle fractures, in which the tibia and fibula have to be torn apart.

Collectively, the tibial tibio-fibular ligament and the interosseous membrane are called the syndesmosis

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Physical examination of the acutely injured ankle will reveal swelling over the outer aspect of the ankle. There will be tenderness over the outer front (anterolateral) aspect of the ankle (see figureFigure 5).

Figure 5: Clinical photo of a lateral ankle sprain (Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Ankle-Sprain-Figure-2.jpg)

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This test is performed twice (Figure 6A and 6B): once with the foot in full plantar flexion, to test the ATFL, and then again in dorsiflexion to assess the CFL.  The examiner assesses the amount of translation of the foot relative to the shin and also the “quality of the end point” (ie, if a firm stop –a rope snapping to attention–is encountered), using the contralateral limb as a control.

Figures 6A and 6BThe drawer test is performed with the patient sitting on an exam table, with knees flexed and the foot dangling over the edge of the table. The examiner grasps and stabilizes the shin in one hand  and applies anterior force to the heel with the other hand. 

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So-called "high ankle sprains" , namely, are injuries to the syndesomosis between the syndesomosis 0the ligaments between the tibia and fibula ("high") above the joint,. High ankle sprains are less common than regular ankle sprains, but when they occur they are often more debilitating. They occur from a twisting injury to the ankle when the foot is planted on the ground. These injuries often occur in a sporting event, where there is a sudden change of direction, and an excessive applied force, such as being tackled while playing football.  Pain located on the anterior aspect of the ankle is the main symptom.  However, a high ankle sprain can also occur in combination with a conventional ankle sprain and therefore medial or lateral pain (and not quite localized to the anterior aspect of the joint) can be present as well.

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X-rays should be obtained if there is bony tenderness on the posterior aspect of either malleoli or an inability to bear weight (Ottawa Ankle Rules). The x-rays should include the foot if there is tenderness on either the 5th metatarsal or the navicular.  X-rays of the knee joint are needed if an ankle fracture is detected on the initial film or if there is widening of the mortise (to exclude a proximal fibular fracture, which can be seen in combination with ankle injuries).

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Particular attention should be paid to ensure that the ankle joint mortise is symmetrical: the space between the talus and tibia medially should match the space laterally (Figure 7).

 

Figure 7: The talus should sit squarely in the mortise and the amount of space (arrows) should be uniform on all sides. 

Stress x-rays –imaging the ankle while the heel is pushed towards one side while the leg is pushed in the opposite direction – may be used to assess instability in chronic cases. These films are not used acutelyshould be used cautiously with acute injuries. Stress x-rays should be compared to the opposite ankle.  

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“Figure of Eight” exercises are particularly helpful for regaining range of motion and proprioception. Patients should be instructed to imagine that the tip of their big toe is a pen and to then “draw” a figure of eight with the toe slowly, repeating the motion for 30-60 seconds.   In the alternatives, patients can “sign” their names in script. It is important that the motion follow a deliberate pattern –and not random waving of the foot–as thoughtful motion helps improve proprioception as well.

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Risk factors for ankle sprains include a high arched foot (cavus foot), ligamentous laxity leading to increased inversion, participating in high risk activities (ex. basketball, soccer, volleyball), and a history of previous ankle sprains.

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