Bassett's Ligament: Anatomy, Impingement Syndrome, Diagnosis, and Treatment

What is Bassett's ligament?

Bassett's ligament is an accessory fascicle of the anterior inferior tibiofibular ligament (AITFL) located in the anterolateral aspect of the ankle joint, an anatomical variant that can lead to anterolateral ankle impingement syndrome.

Understanding Bassett's Ligament: An Overview

Named after Dr. Frank H. Bassett, who first described it in detail, Bassett's ligament is not a universal anatomical structure but rather an accessory band found in a significant percentage of the population. While many accessory ligaments exist without consequence, Bassett's ligament holds particular clinical relevance due to its potential to cause pain and dysfunction within the ankle joint. Its presence can be a contributing factor to chronic ankle pain, especially in individuals with a history of ankle sprains or those engaging in activities requiring repetitive ankle movements.

Anatomy and Location

Bassett's ligament is anatomically described as an anomalous or accessory fascicle of the anterior inferior tibiofibular ligament (AITFL), which is a crucial component of the ankle syndesmosis.

• Origin: It typically originates from the distal aspect of the fibula, just anterior to the main body of the AITFL.
• Insertion: It then courses obliquely downwards and medially to insert onto the lateral aspect of the talus, often near the anterior process.
• Relationship to Syndesmosis: Its close proximity to the normal syndesmotic ligaments (AITFL, PITFL, interosseous ligament) means it lies within the joint capsule, positioned anterior to the fibula and lateral malleolus. This specific location places it directly in the path of impingement during certain ankle movements.

While its exact prevalence varies in studies, it is considered a relatively common anatomical variant, though its symptomatic presentation is less frequent.

Function and Biomechanics

Unlike the primary ligaments of the ankle, which are essential for stability, Bassett's ligament is generally not considered to have a significant positive biomechanical function in ankle stability. In fact, its very presence can be detrimental.

• Impingement Mechanism: During ankle dorsiflexion (pointing the toes upwards towards the shin) and inversion (turning the sole of the foot inwards), the normal anatomical structures within the ankle joint cavity can be compressed. When Bassett's ligament is present, particularly if it is thickened or inflamed, it can get "pinched" or impinged between the talus and the distal fibula.
• Chronic Irritation: This repetitive impingement can lead to chronic irritation, inflammation (synovitis), and hypertrophy (thickening) of the ligament itself and the surrounding synovial tissue. Over time, this can result in fibrous changes or even chondromalacia (cartilage damage) on the opposing bone surfaces.

Clinical Significance and Associated Conditions

The primary clinical significance of Bassett's ligament lies in its association with anterolateral ankle impingement syndrome.

• Anterolateral Impingement Syndrome: This is a condition characterized by chronic pain and tenderness in the front and outer aspect of the ankle. When Bassett's ligament is the cause, it often presents as:
  • Persistent pain: Especially during activities involving ankle dorsiflexion, such as squatting, running uphill, or landing from a jump.
  • Clicking or catching sensation: As the ligament gets caught between the bones.
  • Tenderness: Palpation over the anterolateral ankle joint line.
  • Swelling: Localized swelling may be present.
• Post-Traumatic Origin: While an anatomical variant, its symptomatic presentation often follows an ankle sprain. The initial injury can cause inflammation and swelling, leading to the ligament becoming entrapped and subsequently hypertrophied, creating a cycle of impingement.
• Differential Diagnosis: Symptoms of Bassett's ligament impingement can mimic other ankle pathologies, such as osteochondral lesions of the talus, syndesmotic injuries, or other forms of soft tissue impingement, making accurate diagnosis crucial.

Diagnosis of Bassett's Ligament Impingement

Diagnosing symptomatic Bassett's ligament impingement requires a comprehensive approach, combining clinical assessment with imaging studies.

• Clinical Examination:
  • Patient History: A detailed history of ankle pain, especially in the anterolateral region, exacerbated by dorsiflexion and activity, and often following an ankle sprain.
  • Physical Examination: Localized tenderness to palpation over the anterolateral ankle joint line. Pain and possibly a "positive impingement sign" (pain reproduced with forced dorsiflexion and eversion/inversion).
• Imaging Studies:
  • X-rays: Primarily used to rule out bony abnormalities, fractures, or osteophytes (bone spurs) that could also cause impingement.
  • Magnetic Resonance Imaging (MRI): Often the most valuable imaging modality for soft tissue assessment. An MRI can visualize a thickened or inflamed Bassett's ligament and associated synovitis, although its definitive identification can sometimes be challenging due to its small size and variable appearance.
  • Ultrasound: Dynamic ultrasound can sometimes identify the ligament and demonstrate its impingement during ankle movement.
• Diagnostic Injection: A local anesthetic injection into the suspected area of impingement can provide temporary pain relief, helping to confirm the source of pain.
• Arthroscopy: An ankle arthroscopy (minimally invasive surgery using a small camera) is considered the gold standard for definitive diagnosis. It allows direct visualization of the ligament and its impingement within the joint.

Treatment Approaches

Treatment for symptomatic Bassett's ligament impingement typically follows a stepwise approach, starting with conservative measures and progressing to surgical intervention if necessary.

Conservative Management

• Rest and Activity Modification: Avoiding activities that exacerbate pain, particularly those involving extreme dorsiflexion.
• Ice and Compression: To reduce inflammation and swelling.
• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): To manage pain and inflammation.
• Physical Therapy:
  • Range of Motion Exercises: To maintain and improve ankle mobility without causing impingement.
  • Strengthening Exercises: For the muscles surrounding the ankle to improve stability.
  • Proprioceptive Training: To enhance balance and neuromuscular control.
  • Gait Training: To optimize walking and running mechanics.
• Corticosteroid Injections: In some cases, a corticosteroid injection into the affected area may provide temporary relief from inflammation and pain.

Surgical Intervention

• Arthroscopic Resection: If conservative measures fail to provide adequate relief after several months, surgical intervention is often considered. Ankle arthroscopy is the preferred method.
  • Procedure: A small incision is made, and a camera is inserted into the joint. The surgeon identifies the impinging Bassett's ligament and carefully resects (removes) the hypertrophied portion using specialized instruments. Any associated inflamed synovium is also debrided.
  • Benefits: Minimally invasive, allows for direct visualization and treatment of the impingement, and typically results in a good prognosis for pain relief and return to activity.
  • Rehabilitation: Post-surgical rehabilitation focuses on pain control, restoring range of motion, strengthening, and gradual return to activity.

Key Takeaway

Bassett's ligament is an important anatomical variant that, when symptomatic, is a common cause of anterolateral ankle impingement syndrome. Understanding its anatomy, biomechanical implications, and clinical presentation is crucial for accurate diagnosis. While conservative measures are the initial approach, arthroscopic resection offers an effective solution for individuals experiencing persistent pain and functional limitations due to impingement by this accessory ligament. Early and accurate diagnosis, followed by a tailored treatment plan, is key to restoring ankle function and alleviating chronic pain.