Ankle Ultrasound: Procedure, Preparation, Benefits, and Limitations

How Do You Do an Ankle Ultrasound?

An ankle ultrasound is a non-invasive diagnostic imaging procedure that uses high-frequency sound waves to create real-time images of the soft tissues, ligaments, tendons, and muscles around the ankle joint. It is performed by a trained sonographer or physician who guides a handheld transducer over the ankle, allowing for dynamic assessment and immediate visualization of structures.

What is an Ankle Ultrasound?

An ankle ultrasound, also known as sonography, is an imaging technique that utilizes sound waves, beyond the range of human hearing, to produce dynamic images of internal body structures. Unlike X-rays or CT scans, it does not use ionizing radiation, making it a safe option for repeated assessments. For the ankle, ultrasound is particularly valuable because it excels at visualizing soft tissues—ligaments, tendons, muscles, and nerves—which are frequently involved in ankle injuries and conditions. Its real-time nature allows for dynamic assessment, meaning the structures can be observed as the ankle moves or bears weight, providing insights into function and stability that static imaging cannot.

Why is an Ankle Ultrasound Performed?

An ankle ultrasound is a versatile diagnostic tool employed to investigate a wide range of conditions affecting the ankle joint and surrounding structures. Common indications include:

• Ligament Injuries: To assess the integrity of ankle ligaments, especially after sprains (e.g., anterior talofibular ligament - ATFL, calcaneofibular ligament - CFL, deltoid ligament complex). It can differentiate between partial tears and complete ruptures.
• Tendon Pathologies: Evaluation of tendonitis (inflammation), tenosynovitis (inflammation of the tendon sheath), and tears of various tendons such as the Achilles tendon, tibialis posterior tendon, peroneal tendons, and flexor hallucis longus.
• Muscle Strains: Identification of muscle fiber tears, hematomas, or other injuries to the muscles of the lower leg and foot.
• Fluid Collections: Detection of joint effusions (fluid within the joint), bursitis (inflammation of bursae), ganglia, or other cysts.
• Nerve Entrapment: Assessment for compression or irritation of nerves, such as in tarsal tunnel syndrome affecting the posterior tibial nerve.
• Foreign Bodies: Localization of foreign objects (e.g., splinters, glass) that may not be visible on X-rays.
• Dynamic Assessment: To evaluate ankle stability under stress, such as assessing ligament laxity during specific movements.
• Guidance for Procedures: To guide injections (e.g., corticosteroids, platelet-rich plasma) into specific joints, tendons, or soft tissues, or for aspiration of fluid.
• Monitoring: To track the healing progress of injuries or the response to treatment.

Preparing for an Ankle Ultrasound

Preparation for an ankle ultrasound is generally minimal and straightforward:

• No Dietary Restrictions: You can eat and drink normally before the procedure.
• Comfortable Clothing: Wear loose, comfortable clothing that allows easy access to your ankle. You may be asked to change into a gown.
• Medication Review: Inform your doctor or the sonographer about any medications you are taking, especially blood thinners, if there's a possibility of a guided injection being performed during the ultrasound.
• Remove Jewelry: You will need to remove any jewelry around the ankle area.
• Questions: Feel free to ask any questions you have before the procedure begins.

The Ankle Ultrasound Procedure: A Step-by-Step Guide

The ankle ultrasound procedure is typically performed in a dedicated imaging room or clinic setting. Here’s a breakdown of what generally occurs:

• Patient Positioning: You will be positioned on an examination table, often lying on your back (supine), on your stomach (prone), or sometimes sitting, depending on the specific structures being examined. The goal is to provide optimal access and comfort for the sonographer.
• Gel Application: A warm, water-based gel will be applied to the skin over the ankle area. This gel helps the transducer make full contact with the skin and eliminates air pockets, which could interfere with the sound waves.
• Transducer Selection: The sonographer will select a high-frequency linear array transducer, which is ideal for visualizing superficial structures like those in the ankle with high resolution.
• Anatomical Zones & Scanning Planes: The sonographer will systematically scan different anatomical regions of the ankle, using both longitudinal (along the length of a structure) and transverse (across the width of a structure) scanning planes to obtain comprehensive views.
  • Anterior Ankle: The transducer is placed over the front of the ankle to examine the tibialis anterior tendon, extensor digitorum and hallucis longus tendons, the anterior talofibular ligament (ATFL), anterior tibiotalar ligament (part of the deltoid), and neurovascular structures. Dynamic scans may involve dorsiflexion and plantarflexion.
  • Medial Ankle: The transducer is moved to the inner side of the ankle to visualize the deltoid ligament complex (tibionavicular, tibiocalcaneal, posterior tibiotalar), the tibialis posterior tendon, flexor digitorum longus, and flexor hallucis longus tendons, often within the tarsal tunnel, along with the posterior tibial neurovascular bundle.
  • Lateral Ankle: The outer side of the ankle is scanned to assess the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), posterior talofibular ligament (PTFL), and the peroneal tendons (peroneus longus and brevis) as they course behind the lateral malleolus. Stress views may be performed to assess ligament stability.
  • Posterior Ankle: The back of the ankle is examined, focusing on the Achilles tendon (its insertion, body, and musculotendinous junction), the plantaris tendon, and the deeper posterior talofibular ligament. The fat pad of Kager and the flexor hallucis longus tendon can also be visualized here.
• Dynamic Assessment: Throughout the scan, you may be asked to move your foot and ankle in various directions (e.g., dorsiflexion, plantarflexion, inversion, eversion) or to gently bear weight. This allows the sonographer to observe how tissues and ligaments behave under stress, which is crucial for diagnosing instability or impingement.
• Real-time Interpretation: The sonographer will continuously interpret the images displayed on the monitor, looking for signs of inflammation, fluid, tears, thickening, swelling, or other abnormalities. Measurements of tendon thickness or fluid collections may be taken.

What to Expect During and After the Ultrasound

• Duration: A typical ankle ultrasound takes between 20 to 45 minutes, depending on the complexity of the case and the number of structures requiring evaluation.
• Comfort Level: The procedure is generally painless. You might feel slight pressure from the transducer, and the gel may feel cool initially. If a specific area is tender, inform the sonographer.
• After the Procedure: The gel will be wiped off your skin. There are no restrictions on your activity after an ultrasound. You can immediately resume your normal daily routine.
• Results: In many cases, the sonographer or supervising physician may provide some immediate preliminary findings. However, a formal report will be prepared by a radiologist or specialist physician, which will then be sent to your referring doctor. Your doctor will then discuss the detailed results and next steps with you.

Benefits and Limitations of Ankle Ultrasound

Benefits

• Real-time and Dynamic: Allows for evaluation of structures during movement, providing functional insights.
• No Radiation: Safe for all patients, including pregnant individuals, and can be repeated as needed.
• Cost-Effective and Portable: Generally less expensive than MRI or CT and can be performed at the bedside or in various clinical settings.
• Excellent Soft Tissue Visualization: Highly effective for tendons, ligaments, muscles, and nerves.
• Guided Procedures: Ideal for precise needle guidance during aspirations or injections.
• Patient Interaction: Direct communication with the sonographer can help pinpoint areas of pain.

Limitations

• Operator-Dependent: The quality and accuracy of the examination heavily rely on the skill and experience of the sonographer.
• Limited Bone Penetration: Sound waves cannot penetrate bone effectively, so conditions within the bone or behind dense bone are poorly visualized.
• Limited Field of View: Ultrasound images show a smaller area at a time compared to MRI, requiring the sonographer to mentally reconstruct the anatomy.
• Interference: Gas (e.g., in the bowel) or obesity can sometimes limit image quality.
• Artifacts: Certain image artifacts can sometimes mimic pathology or obscure true pathology.

Who Performs an Ankle Ultrasound?

Ankle ultrasounds are typically performed by highly trained medical professionals who specialize in diagnostic imaging:

• Registered Diagnostic Medical Sonographers (RDMS): These are technologists specifically trained in performing ultrasound examinations.
• Radiologists: Physicians who specialize in interpreting medical images. They often supervise sonographers and may perform complex or interventional ultrasound procedures.
• Sports Medicine Physicians and Orthopedic Surgeons: Increasingly, these specialists are training in point-of-care ultrasound (POCUS) to aid in immediate diagnosis and guide procedures in their clinics.
• Physical Therapists: In some jurisdictions and with appropriate specialized training, physical therapists may use ultrasound for diagnostic purposes or to guide rehabilitation.

The expertise of the individual performing and interpreting the ultrasound is paramount to ensuring an accurate diagnosis and appropriate management plan.