The calcaneofibular ligament (CFL) is a band of tissue on the outer side of the ankle and a frequent site of injury following common ankle sprains. It is a key element of the ankle’s lateral ligament complex, working alongside two other ligaments to provide stability to the joint. The CFL prevents excessive motion, and its injury can lead to a feeling of the ankle “giving way.”
Location and Stabilizing Function
The calcaneofibular ligament runs obliquely, connecting the fibula (the smaller bone of the lower leg) to the calcaneus (the heel bone). It originates from the tip of the lateral malleolus, the bony prominence on the outside of the ankle, and extends downward and backward to attach to the heel bone. This roughly cylindrical ligament crosses two separate joints: the talocrural joint (the main ankle joint) and the subtalar joint, which sits just below it.
The CFL’s primary responsibility is to resist excessive inversion, the motion of turning the sole of the foot inward. It acts as a primary restraint against inversion when the ankle is in a neutral or dorsiflexed (toes pointed up) position. The ligament also provides stabilization to the subtalar joint, helping to limit the tilting of the talus bone. This support keeps the ankle joint complex aligned and stable during movement.
Mechanism of Injury
Injury to the calcaneofibular ligament most commonly occurs during an acute lateral ankle sprain. The specific action that damages the ligament is a sudden, forceful combination of inversion and plantar flexion (pointing the toes downward). During this motion, the ligaments on the outer side of the ankle are stretched beyond their capacity, leading to tearing or spraining.
The anterior talofibular ligament (ATFL) is typically the first and most frequently injured ligament in this scenario, as it is under the most strain during plantar flexion. A more severe ankle sprain, often classified as a higher-grade injury, involves a complete tear of the ATFL and a simultaneous tear or significant stretch of the CFL. While an isolated injury to the CFL is rare, it can occur if the inversion force happens when the foot is in a neutral or dorsiflexed position. The CFL is inherently strong, having a higher failure load than the ATFL, which is why it is usually injured only in substantial sprains.
Diagnosis and Acute Management
A medical professional diagnoses a CFL injury through a detailed medical history and physical examination. Tenderness along the course of the ligament is a strong indicator of injury, often accompanied by swelling and bruising on the outer ankle. Specific tests assess the ligament’s integrity, such as the Talar Tilt Test, which evaluates the degree of side-to-side ankle laxity when the foot is inverted.
Excessive gapping or movement during this test suggests a significant tear of the CFL. X-rays are used to rule out an associated fracture, an important first step in the acute phase. Initial treatment focuses on conservative management, often summarized by the RICE protocol: Rest, Ice, Compression, and Elevation. This phase aims to control the inflammatory response and pain, typically lasting for the first four to five days after the injury. For a significant sprain, the ankle may be immobilized using a brace or walking boot to protect the healing ligament during the early weeks.
Rehabilitation and Long-Term Recovery
Following the initial acute phase, rehabilitation is necessary for restoring full ankle function and preventing chronic instability. The process begins with gentle exercises to regain the full range of motion, followed by strengthening activities. A major focus is placed on strengthening the peroneal muscles, which run along the outside of the lower leg, because they act as dynamic stabilizers to resist inversion.
Proprioception, the body’s sense of joint position, is often impaired after a CFL sprain and must be retrained. This is accomplished through balance exercises, such as standing on one leg or using specialized balance boards, to improve neuromuscular control around the ankle. The recovery timeline for a significant CFL sprain can vary, with the remodeling and strengthening phase potentially lasting several months. A gradual return to sport-specific activities occurs over a period of 10 to 12 weeks or longer, depending on the injury’s severity. Consistent adherence to a supervised physical therapy program ensures a stable and lasting recovery.