Ankle Sprains, Lateral

Christopher A. Gee, MD, MPH, FACEP, CAQSM

BASICS

DESCRIPTION

Lateral ankle sprains are the most common injury sustained by athletes (1) and comprise approximately 14% of all sports-related injuries (2).
Over 80% of sprains are due to an inversion type of mechanism that injures the lateral ankle ligaments.
Whereas the medial side of the ankle has the broad, strong deltoid ligament as a restraint, the lateral side of the ankle has three smaller ligaments that act as the static restraint system.
Primary static restraints to ankle inversion:
- Anterior talofibular ligament (ATFL): passes from the tip of the fibula to the lateral talar neck; taut in plantar flexion; injured most commonly
- Calcaneofibular ligament (CFL): passes inferior and posterior from the tip of the fibula to the lateral calcaneus; usually injured with the ATFL
- Posterior talofibular ligament (PTFL): passes posteriorly from the fibula to the talus; injured less often
These ligaments are injured in a sequential pattern as extreme inversion and plantarflexion forces are placed on the ankle. The ATFL is injured first (isolated ATFL injuries occur in approximately 2/3 of injuries). After the small ATFL is injured, the CFL then is stressed and injured, followed by the PTFL. The ankle joint capsule is also sprained during an inversion injury. Given this pattern, isolated CFL injuries are uncommon.
Increasing inversion force leads to more damage to lateral ligaments and capsule.
Bony support of the distal fibula assists the deltoid ligament in restricting eversion stress to the ankle.
The smaller medial malleolus provides less protection and allows inversion stress to injure the lateral ankle ligaments more easily.
Ankle sprain grading:
- Grade 1: stretch or partial tearing of ligaments but no gross laxity
- Grade 2: partial tear of ligaments with increased laxity of ankle but still firm end point
- Grade 3: complete rupture of ligaments; gross laxity of ankle with no end point

EPIDEMIOLOGY

Incidence

Very common injury in athletes and the general population, with around 23,000 cases every day (3)

ETIOLOGY AND PATHOPHYSIOLOGY

Lateral ankle sprains occur when the ankle is stressed with extreme inversion and plantarflexion forces that overcome the static restraints (ligaments, capsule). Spraining and tearing of the ligaments leads to pain, swelling, and varying degrees of disability.

RISK FACTORS

Athletes (especially those involved in sports with jumping near other players and quick “cutting” motions, i.e., basketball, soccer, football) (4)
Dancers
Congenital tarsal coalition (allows less “give” in the foot and results in more stress to ankle)
Prior ankle injury (Previously injured or stretched ligaments provide less overall stability.) (5)