Adductor Canal (Hunter's Canal / Subsartorial Canal)
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Direct answer
A tunnel beneath sartorius carries the femoral artery from thigh to popliteal fossa: the adductor (Hunter's, subsartorial) canal runs from the apex of the femoral triangle to the adductor hiatus, the tendinous gap in adductor magnus above the knee where the femoral vessels become popliteal. Its roof is sartorius with the vastoadductor membrane, its lateral wall vastus medialis, its floor adductor longus above and adductor magnus below. Inside are the femoral artery, the femoral vein medial to it, the saphenous nerve — entering lateral to the artery, crossing in front, and leaving between sartorius and gracilis — the nerve to vastus medialis above, and lymphatics. John Hunter ligated the femoral artery here for popliteal aneurysm in the 1780s, trusting genicular collaterals — hence the eponym.
What you must remember
- Extent: apex of femoral triangle (where sartorius crosses adductor longus) to the adductor hiatus in adductor magnus, at the junction of the middle and lower thirds of the thigh.
- Boundaries: roof — sartorius and the vastoadductor membrane bridging vastus medialis to the adductors; lateral wall — vastus medialis; floor — adductor longus (upper) then adductor magnus (lower).
- Contents: femoral artery, femoral vein (medial to the artery within the canal), saphenous nerve, nerve to vastus medialis (upper canal only), lymphatics, and occasionally the saphenous branch of the descending genicular artery accompanying the nerve.
- Saphenous nerve trajectory: enters lateral to the artery, crosses in front, then quits the canal between sartorius and gracilis to run subcutaneously with the great saphenous vein.
- Adductor hiatus: the aperture in adductor magnus tendon, roughly a hand's breadth above the knee, converting femoral vessels into popliteal vessels; the saphenous nerve does not pass through it.
- Hunter's ligation: John Hunter tied the femoral artery here for popliteal aneurysm, deliberately placed for the descending genicular and genicular anastomosis to maintain flow — the collateral reasoning of vascular surgery.
- Clinical surface anatomy: the femoral artery here is the target of mid-thigh approaches for embolectomy and bypass — common in Indian practice in young male smokers with Buerger disease.
- Nerve entrapment and block: saphenous nerve entrapment at the canal's roof mimics knee pathology; ultrasound-guided subsartorial blocks anaesthetise the medial leg for vein harvesting and ankle surgery.
Two patients who make the canal memorable
A man on his feet all day develops aching numbness along the medial knee and shin after long saphenous vein stripping. The saphenous nerve left the canal between sartorius and gracilis and travelled with the great saphenous vein below the knee — stripping or harvesting the vein can stretch or cut it, leaving exactly this medial strip of dysaesthesia. The same nerve is the reason anaesthetists perform a subsartorial (adductor canal) block: deposit local anaesthetic in the canal and the saphenous nerve alone is caught, sparing the motor nerves to the quadriceps — patients walk soon after knee surgery.
The second patient is historical but examinable: Hunter's man with a pulsatile popliteal swelling. Ligating the artery at the canal's lower end, below the profunda's branches and above the genicular network, threw the collateral load onto the descending genicular and the genicular anastomosis — The limb survived on that circle of vessels around the knee; every vascular surgeon who ligates or bypasses the superficial femoral artery repeats the same wager.
Where students slip
Students include the femoral nerve among the contents — it never enters; the canal's nerves are the saphenous and the nerve to vastus medialis, and the latter only in the upper part. They forget where the saphenous nerve goes: not through the adductor hiatus with the vessels, but out through the roof between sartorius and gracilis. Inside the canal the artery lies lateral and the vein medial. In Indian prof vivas, "boundaries and contents of the adductor canal with applied anatomy" is the standard five-marker — close with the eponym and the motor-sparing block.
Frequently asked questions
What are the boundaries of the adductor canal?
Roof: sartorius with the vastoadductor membrane; lateral wall: vastus medialis; floor: adductor longus above and adductor magnus below. It runs from the femoral triangle apex to the adductor hiatus.
Where does the femoral artery become the popliteal artery?
At the adductor hiatus, the gap in the adductor magnus tendon roughly a hand's breadth above the knee. The saphenous nerve leaves the canal above this, through the roof.
Why is it called Hunter's canal?
He ligated the femoral artery here for popliteal aneurysm in the 1780s, relying on genicular collaterals. The eponym honours that reasoning.
Which nerve is targeted in an adductor canal block, and why is it preferred?
The saphenous nerve — a sensory nerve, so the block spares quadriceps power unlike a femoral block. It is standard for knee arthroplasty analgesia and saphenous-harvest anaesthesia.
What happens to the saphenous nerve after it leaves the canal?
It emerges between sartorius and gracilis, becomes subcutaneous on the medial side of the knee, and descends with the great saphenous vein, supplying the medial leg and foot arch. Injury here causes medial-leg numbness after vein surgery.