An ankle sprain is one of the most common musculoskeletal injuries, occurring when the strong bands of tissue that support the ankle joint are stretched or torn. These tissues, called ligaments, connect bones to one another, preventing excessive movement and providing stability. A sprain happens when a sudden force pushes the ankle joint beyond its normal range of motion, compromising the integrity of these stabilizing ligaments. Understanding the specific location and mechanism of the injury is the first step in classifying the different types of ankle sprains.
Lateral Ankle Sprains
Lateral ankle sprains affect the ligaments on the outside of the foot and are the most frequent type, accounting for approximately 85% of all ankle injuries. The mechanism of injury is typically an inversion motion, commonly referred to as “rolling the ankle,” which forces the sole of the foot inward. This often occurs when the foot is pointed downward, such as during a misstep or an awkward landing.
Three main ligaments form the lateral ligament complex and are usually injured in a sequential pattern. The Anterior Talofibular Ligament (ATFL) is the weakest and most commonly injured, stretched first during inversion. If the force continues, the injury may extend to the Calcaneofibular Ligament (CFL), which runs from the fibula to the heel bone. The Posterior Talofibular Ligament (PTFL) is the strongest and is rarely involved unless the injury is very severe.
Medial Ankle Sprains
Medial ankle sprains affect the ligaments on the inner side of the ankle and are significantly less common than lateral sprains. This lower occurrence rate is attributed to the inherent strength of the Deltoid Ligament complex, a thick, fan-shaped group of ligaments that stabilize the inside of the joint. Injuries to this complex occur from an eversion mechanism, where the foot is forcefully rolled outward.
Because the Deltoid Ligament is robust, the force required to sprain it is substantial. Eversion injuries often result in a fracture of the outer ankle bone (fibula) before the ligament itself tears. Consequently, an isolated Deltoid Ligament sprain is rare; it is often seen in conjunction with other severe injuries.
High Ankle Sprains
A high ankle sprain, medically known as a syndesmotic sprain, is a distinct and often more severe injury category. Unlike lateral or medial sprains, a high ankle sprain involves the ligaments connecting the tibia and the fibula, the two long bones of the lower leg. These ligaments form the syndesmosis, a fibrous joint located just above the ankle joint.
The injury is called “high” because it occurs above the main ankle joint, in the area where the tibia and fibula meet. The most common mechanism is a forceful external rotation of the foot, often combined with the foot being driven upward (dorsiflexion). This action forces the lower leg bones apart, tearing the syndesmotic ligaments. Because these ligaments are essential for maintaining the stability of the ankle joint, recovery typically takes a considerably longer time than recovery from a lateral sprain.
Grading Sprain Severity
Medical professionals classify the severity of an ankle sprain using a universal three-part grading system. This system is based on the extent of the ligament damage and the resulting functional instability of the ankle joint. Understanding the grade is important for guiding the appropriate treatment and determining the expected recovery timeline.
A Grade I sprain is the mildest form, involving a simple stretching of the ligament fibers with only microscopic tearing. The ankle joint remains stable, and the patient experiences mild pain, swelling, and tenderness. Patients are often able to bear weight with minimal difficulty, and this level of injury generally requires the shortest recovery time.
A Grade II sprain indicates a significant injury with a partial tearing of the ligament fibers. This moderate damage results in increased pain, swelling, and bruising. The joint may exhibit mild to moderate instability upon examination, and walking is often painful, requiring a more structured rehabilitation period.
The most severe injury is a Grade III sprain, which involves a complete rupture of one or more ligaments. This results in significant pain, substantial swelling, and profound instability of the joint, often making it impossible to bear weight. A complete tear may necessitate the use of a cast or boot for immobilization, and in some cases, surgical consultation may be required to repair the torn ligament and restore joint stability.