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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 Figure 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 rare cases lead to significant impairment if other additional structures are injured. Expeditious treatment –directed to limiting swelling and regaining motion –helps ensure the best possible recovery.

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Structure and function

The ankle joint is composed of per se comprises the articulation of the tibia and fibula with the talus, although there are soft tissue connections between the long these 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).  
  

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The talus in turn acts as a “ball joint” that is connect connected to the calcaneous  (via the so-called subtalar joint) as well as the navicular.

The ligaments of the ankle, beyond the important (and at times overlooked) syndesmotic ligaments between the tibia and fibula above the joint, include:

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The anterior talo-fibular ligament (ATFL) is the ankle ligament that is most often sprained. The ATFL courses from the fibula to the neck of the talus and stabilized stabilizes the ankle joint against inversion. The ATFL itself is very broad, more like a sheet than a rope.  When it is sprained, it tends to become stretched out (that is, undergoes plastic deformation with microscopic or macroscopic tearing).  This stretching out may lead to symptomatic ankle instability.

The calcaneo-fibular ligament (CFL) starts at the tip of the fibula and runs along the outside of the ankle and into the calcaneous. It is more rope-like than the ATFL, and less susceptible (though not immune) to damage, although it can be injured during a severe ankle sprain.

The posterior talo-fibular ligament (PTFL) runs from the fibula into the talus, 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.

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The deltoid ligament is a strong fan-shaped band of connective tissue on the inside medial 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 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 heal with irritating scar formation–a condition known as anterior-lateral ankle impingement.

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

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

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A sprained ankle may often have associated redness due to the increased blood flow to this area (as shown). Without a history of an injury, this skin appearance may suggest cellulitis (infection of the skin) but with the appropriate history, it is not a worrisome finding at all.

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 Figure 5).

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

It is important to palpate the base of the 5th metatarsal, the navicular and the Lisfranc joint for tenderness, as the same mechanism that creates an ankle sprain can lead to other injuries there as well.

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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 6B: The 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" are injuries to the syndesomosis 0the ligaments , which lies between the tibia and fibula ("high") above the joint.

High ankle sprains are less common than regular medial or lateral 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 are produced by a sudden change of direction , and due to an excessive externally applied force, such as being tackled while playing footballas may be seen from a tackle in a football game.  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.

The “squeeze test”, namely compressing (squeezing) the tibia and fibula together approximately four inches above the ankle joint, can be used to detect a high ankle sprain. This test will tend to reproduce focal symptoms in patients who have had a high ankle sprain. The external rotation test, namely, holding the foot in dorsiflexion and then externally rotating it, will also reproduce focal symptoms when high ankle sprain is present.

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X-rays must be examined to exclude not only fracture but diastasis, namely, increased distances an increased distance between the tibia and fibula (suggesting ligament damage).  implying damage to the syndesmosis

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).

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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 –namely, 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 should be used cautiously only with great caution in the acute injuries. Stress x-rays should be compared to the opposite ankle.  setting as the procedure may displace otherwise non-displaced injuries.

Although there is typically no role for MRI in acute ankle sprains, an MRI may be indicated in cases of chronic pain after a sprain. An MRI could detect a talar osteochondral injury or extra-articular sources of pain such as tendonitis or scarring of the restraining ligaments.  Approximately 10% of severe ankle sprains may have associated injuries to the articular surface of the talus.  An MRI may also help demonstrate an injury to the syndesmosis in an initially missed high ankle sprain.

 

Epidemiology

According to Waterman et al (PMID: 20926721), emergency department data suggest an incidence rate of 2.15 ankle sprain per 1000 person-years in the United States, with a peak incidence rate more than triple that for teen agers between fifteen and nineteen years of age. The overall incidence rate by gender is about the same, though younger males and older females have higher rates than their female and male counterparts respectively. Nearly half of all ankle sprains seen were related to athletic activity.

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The initial treatment of an ankle sprain is known by the mnemonic RICE. RICE is used to limit swelling, as too much swelling can significantly increase the patient's ultimate recovery time.

  • Rest and Activity Modification 
  • Ice should be applied, but not continuously. A regimen of 10 minutes on and 10 minutes off done repeatedly. Ice helps limit the blood flow to the injured ankle. Normally increasing the blood flow to an area is a good thing. However, after an ankle sprain excessive local blood flow leads to too much swelling during the acute phase of the injury
  • Compression: Compression helps decrease the swelling (which if present could limit motion and cause pain).
  • Elevation also helps decrease the swelling. Note that to will minimize the risk of thermal injury to the skin.  
  • Compression. This should be tight enough to decrease swelling but loose enough to allow the foot to be perfused.
  • Elevation. To be maximally effective,  the foot should be held higher than the thigh, to allow gravity to help drain the edema. Propping the foot in a stool or pillow is not apt to help drain fluid but may help enforce rest and inactivity.

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Proprioception is the ability of the brain to sense the position of a joint (ex. ankle) and control its movement relative to the rest of the body.  Note that nerves within the ligament mediate proprioception and therefore this sense can be easily affected with out of kilter following a ligament injury.  Patients with ostensibly normal seeminglynormal ankles on examination (no swelling, no tenderness, no laxity) may still feel unstable if proprioception has not returned to normal. Proprioception deficits are likely to lead to re-injury, as deficient joint can more easily be placed in an extreme position before the brain reacts and attempts to stabilize the joint with muscle action. 

“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 deliberate motion helps improve proprioception as well.

Proprioception can also be improved by having the patient stand on one foot with eyes closed.  Once this is mastered, standing on one foot on a soft surface (such as a pillow or bed) with eyes closed and head moving side to side can further improve proprioception.

The course of rehabilitation Rehabilitation after an ankle sprain can often be followed completed with a home program, though trained physical therapists may be beneficial in providing initial instruction and ensuring compliancedefining the program.

Surgery is not rarely indicated for the treatment of acute ankle sprains per se.  On the other hand, patients who have recurrent ankle sprains may be candidates for an ankle ligament stabilization procedure to treat their recurrent instability. (Note that many patients can compensate for torn ligaments with muscular action, and thus the state of the ligament in isolation --as opposed to the patient's functional status–is not itself an indication for surgery.) 

Most people with sprained ankles fully recover. Even if the ligaments are permanently deformed, the muscles crossing the ankle joint can provide sufficient dynamic stability.  That said, because this is ankle sprains are such a common injuryinjuries, even a low rate of complications imply a (coupled with a high incidence) may produce a significant number of people with suboptimal poor outcomes.

Risk factors and prevention

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