Adductor canal

The adductor canal is a narrow passageway in the mid-thigh that serves as a conduit for major neurovascular structures traveling from the femoral triangle to the lower leg. Its anatomical configuration and contents make it clinically important in both surgical and anesthetic procedures. Understanding its structure and relations is essential for safe interventions in the thigh region.

Definition

The adductor canal, also known as the subsartorial canal or Hunter’s canal, is an intermuscular tunnel located in the middle third of the thigh. It extends from the apex of the femoral triangle to the adductor hiatus of the adductor magnus muscle. The canal primarily functions as a passageway for the femoral artery, femoral vein, saphenous nerve, and nerve to vastus medialis, allowing these structures to reach the lower leg.

Anatomy of the Adductor Canal

Boundaries

The adductor canal is defined by its muscular and fascial boundaries, which provide both structure and protection for the neurovascular contents.

• Anterior and lateral wall: Formed by the vastus medialis muscle.
• Posterior wall: Formed by the adductor longus and adductor magnus muscles.
• Medial wall and roof: Covered by the sartorius muscle, which forms the superficial roof of the canal.

Contents

The adductor canal contains essential neurovascular structures that traverse the mid-thigh:

• Femoral artery: Main blood supply to the lower leg, continuing as the popliteal artery at the adductor hiatus.
• Femoral vein: Accompanies the femoral artery, draining blood from the lower limb.
• Saphenous nerve: Sensory branch of the femoral nerve supplying the medial leg and foot.
• Nerve to vastus medialis: Motor branch innervating the vastus medialis muscle.
• Other accompanying vessels: Small branches of the femoral artery and vein supporting surrounding tissues.

Relations

• Proximal relation: Continuity with the femoral triangle, where neurovascular structures enter the canal.
• Distal exit: Opens at the adductor hiatus to allow passage of vessels to the popliteal fossa.
• Muscular and fascial relations: Surrounded by vastus medialis, adductor muscles, and sartorius fascia, providing structural support and protection.

Function and Clinical Significance

Physiological Function

The adductor canal primarily serves as a protective conduit for neurovascular structures as they travel from the femoral triangle to the lower leg. Its design ensures that the femoral artery, femoral vein, and nerves are shielded by surrounding muscles and fascia, maintaining optimal positioning and reducing the risk of injury during thigh movements.

• Conduit for neurovascular structures: Facilitates safe passage of vessels and nerves to the leg.
• Protection: Muscular and fascial walls reduce mechanical stress on the contained structures.

Clinical Significance

The adductor canal has important implications in both anesthetic and surgical practice.

• Site for adductor canal block: Commonly used for analgesia in knee and lower limb surgeries.
• Vascular procedures: Important landmark for femoral artery catheterization and bypass grafts.
• Nerve entrapment: Rarely, compression of the saphenous nerve within the canal can lead to sensory disturbances.

Adductor Canal Block

Indications

Adductor canal block is a regional anesthesia technique primarily employed for postoperative pain management and lower limb analgesia.

• Postoperative analgesia following total knee arthroplasty or other knee surgeries.
• Pain control for lower leg procedures while preserving quadriceps strength.

Technique

The block can be performed using either ultrasound guidance or anatomical landmarks.

• Ultrasound-guided approach: Preferred method for accurate needle placement and visualization of vessels and nerves.
• Landmark-based approach: Relies on palpable anatomical structures when ultrasound is unavailable.
• Choice of local anesthetic and volume: Selection depends on desired duration of analgesia and patient factors.

Complications and Considerations

• Incomplete block or failure due to inaccurate placement.
• Vascular puncture or hematoma formation.
• Neurological injury, including temporary or permanent nerve damage.
• Motor weakness if local anesthetic spreads to the femoral nerve proper.

Pathology

Although uncommon, the adductor canal can be involved in several pathological conditions that may affect neurovascular function in the lower limb.

• Nerve entrapment or compression syndromes: The saphenous nerve may be compressed within the canal, leading to pain, tingling, or numbness along the medial aspect of the leg.
• Traumatic injury to neurovascular structures: Direct trauma or surgical procedures in the thigh can damage the femoral artery, vein, or nerves within the canal.
• Peripheral arterial disease implications: Narrowing or obstruction of the femoral artery within the canal can contribute to ischemic symptoms in the lower leg.

Imaging and Diagnostic Approaches

Accurate visualization of the adductor canal is important for both diagnostic and interventional purposes. Imaging helps identify anatomical variations, pathology, and guides procedural planning.

• Ultrasound anatomy and identification: Preferred modality for real-time assessment and guidance during adductor canal blocks.
• MRI or CT: Provides detailed structural evaluation, useful in cases of nerve entrapment, hematoma, or vascular anomalies.
• Use in procedural guidance: Imaging ensures safe needle placement and minimizes complications during regional anesthesia or vascular interventions.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
2. Kendall MC, Haines RW. The Adductor Canal and Its Clinical Importance. Clin Anat. 2015;28(1):102-110.
3. Hurdle MF, Brown DL. Ultrasound-Guided Adductor Canal Block. Anesthesiology Clinics. 2018;36(2):247-260.
4. Marhofer P, Greher M, Kapral S. Ultrasound-guided Regional Anesthesia: Adductor Canal Block. Br J Anaesth. 2009;102(6):764-770.
5. Standring S, Ellis H, Healy JC, et al. The Anatomical Basis of Clinical Practice: Surgical Anatomy of the Thigh. In: Gray’s Anatomy. 41st ed. London: Elsevier; 2016. p. 1025-1035.
6. Laidlaw JD, Al-Shaikh R, Morrow B. Clinical Applications of Adductor Canal Block in Orthopedic Surgery. J Clin Anesth. 2017;40:25-32.
7. Tran J, Muñoz L, Fabi D. Anatomy of the Adductor Canal: Implications for Regional Anesthesia. Reg Anesth Pain Med. 2013;38(4):301-305.
8. McGraw J, Reuben S. Nerve Entrapment in the Adductor Canal. Clin Orthop Relat Res. 2004;421:181-186.