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 (LPT), 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 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 1 fracture is an articular process chip fracture of the talus with no extension into the talofibular joint.
• Type 2 fracture is a single large fragment continuing from the talofibular joint to the subtalar joint.
• Type 3 fracture is a comminuted fracture of the whole lateral process.

The new classification includes two types according to whether the LTPF 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:

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

Type Il 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:

• lla: 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.
• lld: lateral process fracture with talar posterior process fracture.
• Ile lateral process fracture combined with any two or more other fractures of the ipsilateral talus.