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Not All ‘Ankle Sprains’ Are Ankle Ligament Injuries

December 1, 2012

xrayWith the recent emphasis on exercise and a healthy lifestyle in Singapore, an ever-increasing number of people are participating in sports on both recreational and competitive levels. Ankle injuries or sprains are one of the most common injuries sustained while playing sports of any kind.

Popular sports in Singapore include soccer, netball, basketball, tennis, athletics and water sports; these are all associated with a high incidence of ankle injuries. It is no wonder that ankle injuries are a very common reason for visits to the emergency department and the outpatient clinic. Doctors that frequently treat these injuries include general practitioners, emergency physicians, medical officers in the armed forces, as well as orthopaedic specialists and sports physicians.

The majority of ankle injuries are simple sprains of the ankle ligaments and are not serious. These recover quickly with a short period of rest, ice, compression and elevation—commonly known as ‘RICE’ therapy. Physicians would usually be familiar with and on the lookout for either an ankle ligament injury or a frank ankle fracture. However, there are also a significant number of patients who actually injure their foot when they sustain a twisting injury to their ‘ankle’.

The purpose of this article is to increase awareness and also to highlight some of the atypical injuries that can be sustained from a seemingly simple ‘ankle sprain’.

Commonly Injured Structures

The most commonly injured structure is the anterior talofibular ligament (ATFL) of the ankle. It is part of the ankle lateral ligamentous complex. In more severe injuries, ankle fractures, which usually involve the lateral malleolus and occur due to a supination external rotation mechanism, may result.

Atypical Injuries

Commonly overlooked injuries include peroneal tendon injuries, fifth metatarsal fractures and LisFranc injuries of the foot. These are not all encompassing but will be the focus of this article. Although these are atypical injuries and occur less frequently than an ATFL injury, they may cause long-term morbidity if not detected and treated appropriately. They may be overlooked if not assessed for and are also not always appreciated on a standard series of ankle X-rays.

Peroneal Tendon Injuries

Injuries of the peroneal tendons are, strictly speaking, not injuries of the foot, but they are described here as they commonly occur after an ‘ankle sprain’, and are frequently not diagnosed initially. Either a tear of the peroneus brevis tendon or a dislocation of both the peroneal tendons from the retromalleolar groove, posterior to the lateral malleolus, may occur.

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Figure 1. The lateral aspect of the ankle is seen. Note the swelling mapped out by the dotted line, which is posterior to the lateral malleolus. This is typical for peroneal tendon pathology.

Peroneal tendon injuries are easily misdiagnosed as ATFL tears due to the similar mechanism of injury as well as tenderness and ecchymosis over the lateral aspect of the ankle. On clinical assessment, it is important to differentiate between tenderness and swelling over the anterolateral aspect of the lateral malleolus in an ATFL injury and symptoms posterior to the lateral malleolus in peroneal tendon pathology [Figure 1]. In certain cases of peroneal tendon dislocations, the patient may also describe a ‘snap’ and be able to voluntarily demonstrate dislocation of the peroneal tendons on dorsiflexion and eversion. If the clinician suspects peroneal tendon injury, a focused ultrasound assessment or a MRI scan would be more useful than an X-ray.

It is important to differentiate peroneal tendon injuries from ATFL tears as they typically may not respond well to conservative treatment. Tears of the peroneus brevis are usually longitudinal split tears, and many will require surgical treatment for debridement or repair (tubularisation) of the tendon [Figures 2 and 3]. Peroneal tendon dislocations also may require surgical reconstruction of the peroneal retinaculum or deepening of the retromalleolar groove.

It is important to differentiate peroneal tendon injuries from ATFL tears as they typically may not respond well to conservative treatment. Tears of the peroneus brevis are usually longitudinal split tears, and many will require surgical treatment for debridement or repair (tubularisation) of the tendon [Figures 2 and 3]. Peroneal tendon dislocations also may require surgical reconstruction of the peroneal retinaculum or deepening of the retromalleolar groove.

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Figure 2. An intra-operative photograph of both peroneal tendons is shown. The peroneus brevis tendon is retracted with a hemostat (superiorly) and the forceps are pointing to the peroneus longus tendon (inferiorly). A split tear in the middle of the peroneus brevis is seen.

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Figure 3. The forceps has been inserted into the split tear to better demonstrate the extent of the tear.

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Figure 4. The foot X-rays of a 17-year-old girl who twisted her foot after falling off a bicycle. Note the fracture of the fifth metatarsal base.

Fifth Metatarsal Fractures

Fifth metatarsal fractures are the most common injury in the foot following an inversion injury. These most frequently involve the fifth metatarsal base, and may be viewed as an extension of peroneal brevis injuries since the peroneus brevis tendon extends and attaches to the fifth metatarsal base [Figure 4]. Spiral fractures of the fifth metatarsal shaft may also occur although this pattern of injury is less common [Figure 5].

Patients usually complain of pain and localised tenderness over the fifth metatarsal bone. These injuries can be treated with a period of immobilisation in a cast or cast boot for undisplaced fractures. In displaced fractures, surgical fixation may be required.

LisFranc Injuries

These refer to injuries of the LisFranc complex, including the tarsometatarsal joints and the LisFranc ligament, which attaches to the plantar aspect of the medial cuneiform and the second metatarsal base. These are important injuries as they are associated with a significant rate of post-traumatic arthritis of the tarsometatarsal joints and late deformity with loss of the foot arch.

LisFranc injuries may occur by direct or indirect mechanisms. The type of LisFranc injury that most are familiar with would be a severe type associated with a direct crushing injury to the foot. In such cases, the diagnosis is usually not in doubt. However, when a smaller force is imparted, such as from an indirect twisting injury from sports, an injury to the LisFranc complex may be subtle and not easily appreciated both clinically and even on routine X-rays of the foot.

A patient with a LisFranc injury would complain of pain over the dorsum of the midfoot. The amount of swelling can be variable. A useful clinical sign would be the presence of plantar bruising or ecchymosis, which occurs due to the plantar location of the LisFranc ligament. This can however take some time to appear, and may not be present soon after the injury.

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Figure 5. Spiral fractures of the fifth metatarsal can also occur after a twisting injury. The pre-operative (left) and post-operative (right) X-rays of a patient are shown here.

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Figure 6. This is a weight-bearing X-ray of a young lady who twisted her foot during a netball game. Note the subtle widening between the first and second metatarsal bases and the

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Figure 7. An intra-operative photograph of the same patient in Figure 6. Note the disruption and widening of the LisFranc complex as described in Figure 6.

If a LisFranc injury is suspected, the best radiological investigation would be dorsoplantar (anteroposterior) X-rays of both feet taken in a weight-bearing position. Subtle injuries are best appreciated by comparing the intermetatarsal space between the bases of the first and second metatarsals on the injured side and the contralateral normal foot [Figures 6 and 7]. It is also important to trace a smooth line along the medial border of the second metatarsal along the medial border of the intermediate cuneiform. A line drawn along the medial border of the fourth metatarsal should also line up with the medial border of the cuboid. An increase in the intermetatarsal space or a break in either of the two lines described would indicate a LisFranc injury. With few exceptions, LisFranc injuries require surgical reduction and fixation for a good result. This underlines the importance of detecting these injuries early.

Conclusion

When assessing a patient with an ‘ankle sprain’, it is important to assess for pathology besides that of an ATFL injury. If bony tenderness exists, an ankle X-ray is needed to assess for an ankle fracture. Peroneal tendon injuries as well as foot injuries involving fractures of the fifth metatarsal and LisFranc injuries must also be excluded.

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