Ankle Injuries: Understanding Syndesmosis Injuries and High Ankle Sprains

What is the difference between a syndesmosis injury and a high ankle sprain?

A syndesmosis injury is a broader term referring to damage to the strong fibrous joint connecting the tibia and fibula bones in the lower leg, while a high ankle sprain is the specific and most common type of syndesmosis injury, involving a sprain of the ligaments that stabilize this joint.

Understanding the Ankle Joint

The ankle is a complex hinge joint primarily formed by three bones: the tibia (shin bone), the fibula (smaller lower leg bone), and the talus (a foot bone). While the talocrural joint (where the tibia and fibula articulate with the talus) allows for plantarflexion and dorsiflexion, the stability of the entire ankle complex relies heavily on the integrity of the ligaments connecting the tibia and fibula themselves.

What is the Ankle Syndesmosis?

The ankle syndesmosis refers to the strong fibrous joint located just above the ankle joint, where the distal (lower) ends of the tibia and fibula meet. Unlike typical synovial joints that allow for significant movement, the syndesmosis is a fibrous joint, meaning the bones are held together by tough connective tissue with very little movement designed for stability.

Key structures comprising the ankle syndesmosis include:

• Anterior Inferior Tibiofibular Ligament (AITFL): Located at the front.
• Posterior Inferior Tibiofibular Ligament (PITFL): Located at the back.
• Interosseous Membrane (IOM): A strong sheet of connective tissue running between the tibia and fibula along their entire length.
• Transverse Tibiofibular Ligament (TTFL): A deep band of the PITFL.

The primary role of the syndesmosis is to maintain the stability of the distal tibiofibular joint, preventing excessive separation (diastasis) of the tibia and fibula. This stability is crucial for the proper articulation of the talus within the ankle mortise during weight-bearing and movement.

What is a High Ankle Sprain?

A high ankle sprain is a specific injury that involves the stretching or tearing of the ligaments that form the ankle syndesmosis. It is termed "high" because the injury occurs above the ankle joint itself, differentiating it from the more common lateral ankle sprains which affect the ligaments on the outside of the ankle (e.g., anterior talofibular ligament).

High ankle sprains typically occur due to a mechanism involving forced external rotation of the foot (foot turns outward) and/or excessive dorsiflexion (toes pointing upward) while the foot is planted. This motion forces the talus up into the ankle mortise, widening the space between the tibia and fibula and stressing the syndesmotic ligaments. Common scenarios include:

• Contact sports (e.g., football, hockey) where players fall with their foot externally rotated.
• Skiing, where the boot fixes the lower leg while the foot twists.
• Landing awkwardly from a jump.

When these ligaments are stretched or torn, the stability of the syndesmosis is compromised, leading to pain, swelling, and difficulty bearing weight.

Key Differences: Syndesmosis Injury vs. High Ankle Sprain

The distinction between "syndesmosis injury" and "high ankle sprain" is primarily one of scope and specificity:

• Syndesmosis Injury (Broad Term): This refers to any damage to the syndesmotic complex. While a high ankle sprain is the most common type, a syndesmosis injury could theoretically also encompass a more severe injury like a complete rupture with significant diastasis (separation of the tibia and fibula), or even an associated fracture of the tibia or fibula (e.g., a Maisonneuve fracture, which involves a proximal fibular fracture due to syndesmotic disruption).
• High Ankle Sprain (Specific Injury): This specifically refers to the ligamentous sprain of the syndesmosis, ranging from a mild stretch to a complete tear, but without significant bony involvement or gross instability (though some instability may be present). It is a type of syndesmosis injury.

In essence, all high ankle sprains are syndesmosis injuries, but not all syndesmosis injuries are classified solely as high ankle sprains (especially if a fracture or severe instability is present). In clinical practice, the terms are often used interchangeably to refer to the ligamentous injury.

Symptoms and Diagnosis

Recognizing a high ankle sprain (syndesmosis injury) is crucial for appropriate management, as it often requires a longer recovery period than typical ankle sprains.

Common Symptoms

• Pain above the ankle: Pain is typically located higher up the leg, just above the ankle joint, often felt anteriorly (front) or anterolaterally (front and side) between the tibia and fibula.
• Pain with external rotation: Significant increase in pain when the foot is externally rotated or dorsiflexed.
• Difficulty with weight-bearing: Patients often experience more difficulty putting weight on the affected leg compared to lateral ankle sprains.
• Swelling and bruising: May be present, though sometimes less pronounced than with lateral sprains.
• Pain with squeezing: The "squeeze test" (compressing the tibia and fibula together above the injury site) often elicits pain, indicating syndesmotic involvement.

Diagnostic Process

Diagnosis typically involves:

• Detailed history: Understanding the mechanism of injury (e.g., forced external rotation, dorsiflexion).
• Physical examination: Palpation for tenderness, performing specific tests like the "squeeze test" and "external rotation test" to assess syndesmotic integrity.
• Imaging:
  • X-rays: Used to rule out fractures and assess for tibiofibular diastasis (widening of the syndesmosis). Specific views (e.g., stress views) may be taken to evaluate stability under load.
  • MRI: Often considered the gold standard for visualizing soft tissue injuries, including the syndesmotic ligaments and interosseous membrane. It can help grade the severity of the sprain and identify concomitant injuries.
  • CT scan: May be used in cases of suspected bony involvement or complex fractures.

Treatment and Rehabilitation

Treatment for syndesmosis injuries (high ankle sprains) depends heavily on the severity of the sprain and the degree of instability.

Acute Management

• RICE protocol: Rest, Ice, Compression, and Elevation.
• Immobilization: Often, a walking boot or cast is used to immobilize the ankle and prevent further stress on the healing ligaments. Non-weight-bearing or partial weight-bearing may be prescribed initially.
• Pain management: NSAIDs or other analgesics.

Rehabilitation Phases

Rehabilitation is typically longer and more cautious than for lateral ankle sprains due to the critical role of the syndesmosis in ankle stability.

1. Protection Phase: Focus on pain reduction, swelling control, and protecting the healing ligaments. Gentle range of motion exercises (avoiding external rotation and excessive dorsiflexion) may begin.
2. Controlled Motion & Strengthening Phase: As pain subsides and healing progresses, introduce progressive weight-bearing (if cleared by a physician), gentle strengthening exercises for the ankle and lower leg, and balance training.
3. Return to Activity Phase: Gradual return to sport-specific movements, agility drills, and plyometrics. Emphasis on proprioception and dynamic stability. This phase is carefully monitored, often requiring clearance from a physical therapist and physician.

Surgical Intervention

In cases of severe syndesmosis injury with significant instability (diastasis) that does not reduce with conservative measures, or if there's an associated fracture, surgical intervention may be necessary. This typically involves using screws or a "tightrope" device to stabilize the tibia and fibula, allowing the ligaments to heal in a stable position.

Prevention Strategies

While not all syndesmosis injuries can be prevented, certain strategies can help reduce risk:

• Proper footwear: Ensure shoes provide adequate ankle support.
• Strength and conditioning: Strengthen the muscles around the ankle and lower leg (e.g., calf muscles, tibialis anterior) to improve dynamic stability.
• Proprioceptive training: Balance exercises (e.g., single-leg stands, wobble board) can improve the body's awareness of ankle position, reducing the likelihood of awkward landings.
• Technique correction: In sports, coaching proper landing and cutting techniques can minimize risky ankle positions.
• Taping or bracing: Athletes with a history of ankle injuries may benefit from taping or bracing for additional support during high-risk activities.

Conclusion

Understanding the difference between a syndesmosis injury and a high ankle sprain clarifies that the latter is a specific, common form of the former. Both terms point to damage to the crucial ligamentous complex that stabilizes the lower leg bones above the ankle joint. Due to their vital role in ankle stability, these injuries demand a precise diagnosis, often involving advanced imaging, and a more conservative, prolonged rehabilitation approach compared to common lateral ankle sprains to ensure full recovery and prevent chronic instability.