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Ankle sprains

Description

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 rare cases lead to significant impairment. Expeditious treatment –directed to limiting swelling and regaining motion –helps ensure the best possible recovery.

Figure1: ankle inversion, the typical mechanism of injury of an ankle sprain

Structure and function

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

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).

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

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

  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), and 
  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)

The anterior talo-fibular ligament (ATFL) is the ankle ligament often sprained. The ATFL courses from the fibula to the neck of the talus and 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 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.

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.

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 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. 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 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 connects the tibia and fibula. The  interosseous membrane can be torn in certain patterns of ankle fractures, in which the tibia and fibula spread apart, a so-called diastasis.

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

 

Patient Presentation


Ankle Sprains

Patients with ankle sprains typically describe a twisting episode where they invert (or less often, evert) their ankle. Pain, swelling and difficulty ambulating are common.

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).

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. 

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.

With time after the swelling and pain has decreased, laxity can be assessed with an anterior drawer maneuver. (Because there is normal motion between the talus and calcaneus, it is difficult to assess the ligaments with recreated inversion or eversion forces: that is, some “tilt” is normal.) 

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).

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. 

High Ankle Sprains

So-called "high ankle sprains" are injuries to the syndesomosis, which lies between the tibia and fibula ("high") above the joint.

High ankle sprains are less common than 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 are produced by a sudden change of direction due to an externally applied force, as 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 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.

Clinical evidence

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).

X-rays must be examined to exclude not only fracture but diastasis, namely, increased an increased distance between the tibia and fibula 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).

 

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 –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 only with great caution in the acute 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 demonstrate an injury to the syndesmosis.

 

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.

 

Differential diagnosis

The key element in the differential diagnosis of an acute ankle injury is discerning what was injured: which bones may have been broken and which ligaments may have been sprained. Note that combination injuries are not only possible but are common.

Bony tenderness on the anterior process of the calcaneus, base of the 5th metatarsal, or navicular suggests a fracture there.

Tenderness coursing up the lateral aspect of the leg may suggest a peroneal tendon injury.

The squeeze test and external rotation test may detect a high ankle sprain (anterior inferior tibia-fibular ligament injury).

Once the diagnosis of an ankle sprain is made, it can be further refined into a grade:

  •  A grade 1 sprain is defined as one where the ligament is injured but not elongated (and thus not prone to cause instability); 
  • A  grade 2 sprain is a partial tear of the ligament resulting in stretching that may destabilize the joint; and 
  • A grade 3 sprain is a complete tear. Note that instability may be masked by swelling initially.

Red flags

An inability to bear weight or tenderness in the bone (including the medial and lateral malleoli as well as the 5th metatarsal and navicular) signify a need for radiographs (as per the Ottawa Ankle Rules)

Blood on the skin suggests an open fracture

 

Treatment options and outcomes

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  
  • Ice should be applied, but not continuously. A regimen of 10 minutes on and 10 minutes off 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.

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as ibuprofen can be very helpful to decrease pain by decreasing the inflammatory response to the injury. However, there is some evidence that suggest that anti-inflammatories may have an adverse effect on ligament healing.

Once the symptoms associated with the initial ankle sprain has started to improve patients will benefit from physical therapy exercises designed to improve their range of motion, strength and proprioception.

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 out of kilter following a ligament injury.  Patients with seeminglynormal ankles on examination (no swelling, no tenderness, no laxity) may still feel unstable if proprioception has not returned to normal.  

“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 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.

Rehabilitation after an ankle sprain can often be completed with a home program, though trained physical therapists may be beneficial in providing initial instruction defining the program.

Surgery is rarely indicated for the treatment of acute ankle sprains.  On the other hand, patients who have recurrent ankle sprains may be candidates for an ankle ligament stabilization procedure to treat their recurrent instability.  

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 ankle sprains are such a common injuries, even a low rate of complications (coupled with a high incidence) may produce a significant number of people with poor outcomes.

Risk factors and prevention

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.

Rovere et al (PMID: 3132864) studied the effectiveness of taping, wearing a laced stabilizer and high-top or low-top shoes among collegiate football for 6 seasons.  They reported that the combination associated with the fewest injuries overall was low-top shoes and laced ankle stabilizers.

Miscellany

Ankle sprains from playing basketball represent nearly 20% of all ankle sprains in the US. Football  and soccer are the next most implicated sports causing ankle sprains during athletics.

In carpentry, wood can be held together in a so-called mortise and tenon joint: a sliver of one of the pieces of wood (the tenon) is inserted into a slot or hole (the mortise) in the other. By analogy, the talus is the “tenon” of the ankle.

 

Key terms

Ankle sprain, Syndesmosis, mortise, talo-fibular ligament, calcaneo-fibular ligament, deltoid ligament, proprioception

Skills

Recognize an ankle sprain and differentiate between it and other injuries

Apply the Ottawa ankle rules to recognize need for x-rays.

 

 

 

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