Snowboarder's Ankle

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Original Editor - Puja Gaikwad

Top Contributors - Puja Gaikwad and Kim Jackson  

Introduction

In recent times snowboarding has increased in popularity dramatically, with this increase in popularity comes an increase in a distinct ankle injury which has been aptly termed ‘snowboarder’s ankle’. Snowboarding is a popular winter sport that includes riding a single board down a ski slope or on a half-pipe snow ramp. Snowboarder's Ankle is the common term for a fracture of the lateral process of the Talus (LPF), often overlooked initially and misdiagnosed as a severe ankle sprain. The term snowboarder’s ankle comes from this fracture being 15x more likely amongst snowboarding associated ankle injuries than any other ankle injuries. Ankles are involved in 12-17% of snowboarding-related injuries. A fracture to the lateral process of the talus in snowboarders can account for one-third of ankle fractures in this population. Various types of snowboard equipment, rider stance, and snowboarding activity tend to result in several types of injury. Soft boots give the snowboarder nearly twice the risk of ankle injury compared with hard boots. Sideways motion, soft (non-hard shell) boots, and being strapped to the board are all factors that influence the higher rate.

Anatomy

The talus is one of seven articulating foot bones that are situated between the tibia and fibula of the lower leg and the metatarsal bones of the midfoot. The talus constitutes the lower part of the ankle joint and articulates with the medial malleolus of the tibia and the lateral malleolus of the fibula. The ankle joint permits dorsiflexion and plantarflexion of the foot. The underneath aspect of the talus articulates with the calcaneus forming a subtalar joint. This joint enables inversion and eversion of the foot. The talus also articulates navicular bone allowing for subtle movements of the midfoot that play a vital role when walking on uneven ground. The lateral process of the talus is a wedge-shaped projection of the talar body. The top of the lateral process articulates with the fibula and makes a part of the lateral gutter of the ankle joint. The bottom of the lateral process forms the anterior part of the posterior subtalar joint. As the lateral process is involved in both the ankle and subtalar joints, it is significant in almost all foot movements.

Mechanism of Injury

The mechanism of injury is likely that the injured ankle was the leading foot at the time of the fall. Recent research indicates that forced ankle joint dorsiflexion, eversion, and external rotation of the tibia causes the lateral process of talus (LPT) to shear away as it compresses against the calcaneus. Dorsiflexion causes the Talus to become locked in place by the surrounding bones, the ankle roll outwards then causes that specific small area (LPT) to be compressed in between the calcaneus and the lateral malleolus of the fibula with sufficient force applied, the Talus will fracture, causing Snowboarder’s Ankle.  It can occur during a landing from an aerial maneuver or a jump, especially when the landing has been over-rotated.

Causes

The cause of the prevalence of the fracture of the Talus bone in snowboarders continues to be debated. In all likelihood, the probable cause is the convergence of both the biomechanics and equipment required for the sport. There is the unnatural sideways biomechanical motion of snowboarding. This is coupled with boots that are strapped to the board, which offer no prompt release upon falling. And then there are the boots which are different from the rigid boots worn in downhill skiing. Snowboarders’ boots are softer and suppler, providing for those thrilling jumps and amazing acrobatics. The more flexible construction of snowboarding boots also indicates that they are less protective on those hard landings from high up causing higher rates of foot and ankle injuries, including snowboarder’s ankle. Whenever there is sufficient force to break a bone, there is possible damage to ligaments and tendons as well.

Classification

Snowboarder's ankle injuries are classified by the degree of severity.

According to Hawkins,

• Non-articular type I fracture is an articular process chip fracture of the talus with no extension into the talofibular joint.
• Type II fracture is a single large fragment continuing from the talofibular joint to the subtalar joint.
• Type III fracture is a comminuted fracture of the whole lateral process.

The new classification includes two types according to whether the LPT is an isolated fracture or not based on CT scan.

Type I is an isolated fracture. This type is into three subtypes, the same as the McCrory-Bladin classification:

• Ia: chip fracture without the inclusion of the talofibular joint
• Ib: simple fracture with involvement of the talofibular joint.
• Ic: multiple fragment fracture with joint involvement.

Type II is a lateral process fracture in combination with other fractures of the ipsilateral talus, regardless of whether the fractures involve the articular surface or not. This type is divided into five subtypes:

• IIa: lateral process fracture with talar head fracture.
• IIb: lateral process fracture with a talar neck fracture
• IIc: lateral process fracture with extension into the remainder of the talar body.
• IId: lateral process fracture with talar posterior process fracture.
• IIe lateral process fracture combined with any two or more other fractures of the ipsilateral talus.

Clinical Features

A snowboarder’s ankle has a similar presentation to that of a badly sprained ankle which is why it is important to monitor symptoms if an ankle injury occurs on the slopes. A history of an ankle sprain while snowboarding when the foot and ankle are fixed in stiff boots and strapped to the board whilst twisting the ankles to change direction should certainly arouse suspicion. A huge 33-41% of these injuries are reported to be missed on initial inspection and just diagnosed as a bad sprain as X-rays in this area are often hard to distinguish.

Symptoms of this injury may include:

• Extreme tenderness and sensitivity to pressure around the back of the ankle. Tenderness is localized to a region about 1cm inferior to the tip of the lateral malleolus. Although often mimicking a lateral ankle sprain it may be difficult to specifically elicit this site.
• Swelling to the area.
• Ecchymosis
• There is normally difficulty in walking and an inability to bear weight.

The warning signs for a snowboarder's ankle injury involves inflammation and chronic pain. Those who sprained their ankles many times before and complain about persistent pain and swelling are also possible candidates for this specific type of ankle injury.

Investigation

It may be possible to identify the fracture on a plain x-ray, but the fracture line is often quite subtle and difficult to see due to overlapping bony structures. Both lateral (ankle at 90 degrees) and ankle mortice views are recommended for a routine investigation. Ultrasound can be useful for the detection of cortical disruption and ankle joint space effusion; However, follow-up CT or MRI is often used to visualize the fracture line more clearly and provide information to thoroughly understand the extent of the injury. A CT scan should be considered when these symptoms occur for a long period of time because the scan will provide accurate detail if there is a suspected fracture.