Root Origin
- Spinal nerve roots: L3, L4 (via the femoral nerve)
- Plexus: Lumbar plexus (through the femoral nerve)
- Type: Sensory only (pure sensory nerve — no motor function)
Course
- Femoral triangle. The saphenous nerve arises from the posterior division of the femoral nerve in the femoral triangle, just below the inguinal ligament. It begins its course lateral to the femoral artery.
- Adductor canal (Hunter's canal). The nerve enters the adductor canal — a fascial tunnel in the mid-thigh bounded by the vastus medialis (anterolaterally), adductor longus and adductor magnus (posteromedially), and sartorius (roof/anteromedially). It travels through the canal with the femoral artery and vein. The nerve exits the canal by piercing the subsartorial fascia (the fascial roof deep to the sartorius) — this is the primary entrapment site.
- Medial knee. After exiting the adductor canal, the nerve becomes subcutaneous at the medial knee, emerging between the sartorius and gracilis tendons. It gives off the infrapatellar branch, which crosses anteriorly to supply the skin over the anterior knee and the medial patellar region.
- Medial leg. The nerve descends the medial leg alongside the great saphenous vein — the two structures are closely bound together (relevant during varicose vein surgery). It runs superficially along the medial tibial border.
- Medial ankle and foot. The nerve continues distally to supply the medial ankle, passing anterior to the medial malleolus. It terminates at the medial foot, reaching approximately the first metatarsophalangeal joint.
Motor Distribution
- None. The saphenous nerve is a purely sensory nerve. It has no motor branches.
Sensory Distribution
- Infrapatellar branch. Exits at the medial knee and crosses anteriorly to supply the anterior and medial knee — the skin over the patella and the medial patellar region. This branch is commonly damaged during knee surgery (medial arthroscopy portals, medial knee incisions, ACL reconstruction with hamstring tendon graft).
- Main trunk territory. Medial leg from the knee to the ankle, following the course of the great saphenous vein. The territory extends from the medial tibial condyle to the medial malleolus.
- Terminal branches. Medial ankle and medial foot, reaching to approximately the first metatarsophalangeal joint.
- Clinical significance: The saphenous nerve is the ONLY nerve below the knee from the lumbar plexus — everything else below the knee is sciatic (sacral plexus). Medial leg numbness with normal motor function throughout the lower extremity is saphenous nerve territory. If the patient has medial leg numbness plus quadriceps weakness, the lesion is higher — at the femoral nerve or L3-L4 root.
Entrapment Sites
1. Adductor Canal (Hunter's Canal)
- Location: Mid-medial thigh, where the nerve exits the adductor canal by piercing the subsartorial fascia
- Structure: The subsartorial fascia (vastoadductor membrane) can compress the nerve as it exits the canal. Compression can also occur from the overlying sartorius or from the vasto-adductor membrane at the distal end of the canal.
- Presentation: Medial knee and medial leg pain or burning, often worsened by prolonged standing or walking. Pain may extend from the medial knee down the medial leg. No motor weakness (pure sensory nerve). Can mimic medial meniscus pathology, pes anserine bursitis, or medial compartment OA.
- MT relevance: Saphenous nerve entrapment in the adductor canal is an underdiagnosed cause of medial knee pain. If medial knee pain does not respond to standard meniscal or pes anserine treatment and there is no mechanical locking or joint line tenderness, consider the saphenous nerve. Adductor canal release — soft tissue work along the vastus medialis-sartorius interval — can reduce compression.
2. Infrapatellar Branch (Surgical Injury)
- Location: Medial knee, where the infrapatellar branch crosses anteriorly over the medial tibial condyle
- Structure: The infrapatellar branch is superficial and crosses directly over the area where medial knee incisions are made. It is damaged in up to 50-70% of knee arthroscopies using a medial portal and in hamstring tendon harvest for ACL reconstruction.
- Presentation: Numbness or dysesthesia (altered, unpleasant sensation) over the anteromedial knee following knee surgery. The area of numbness is typically a palm-sized patch below and medial to the patella. Not painful — but patients find it annoying and notice it when kneeling.
- MT relevance: Post-surgical medial knee numbness is extremely common and usually permanent. It does not indicate ongoing pathology and does not require treatment. Reassure the patient. When working the medial knee post-operatively, be aware that the area may have altered sensation — the patient may not give accurate feedback about pressure depth.
Clinical Tests
| Test | Procedure | Positive Finding | What It Tells You |
|---|---|---|---|
| Medial leg sensation | Light touch and pinprick along the medial leg from knee to ankle, comparing to the opposite side and to adjacent territories (anterior leg, posterior leg). | Decreased or altered sensation confined to the medial leg — the strip along the medial tibial border. | Saphenous nerve territory. If motor function is intact and numbness is confined to this strip, the saphenous nerve is the source. |
| Tinel's at the adductor canal | Palpate the medial thigh at the transition between the vastus medialis and sartorius (approximately mid-thigh). Tap firmly over this area. | Tingling or burning radiating down the medial leg. | Nerve irritability at the adductor canal exit point. Localizes the compression to the canal. |
| Adductor canal compression test | Apply sustained pressure over the adductor canal (medial mid-thigh, at the vastus medialis-sartorius interval) for 30 seconds. | Reproduction of medial knee or medial leg symptoms. | Saphenous nerve compression in the canal. Analogous to Durkan's test for CTS — sustained compression reproduces the symptoms. |
Clinical Notes
- The medial knee pain mimicker. Saphenous nerve entrapment produces medial knee pain that is routinely misdiagnosed as medial meniscus pathology, pes anserine bursitis, or medial compartment osteoarthritis. The key differentiator: there is no joint line tenderness, no mechanical locking, no effusion, and no pain with valgus stress. The pain is superficial and burning rather than deep and mechanical. McMurray's test is negative. If medial knee pain has a burning quality and standard treatments fail, palpate the adductor canal.
- Great saphenous vein surgery puts the nerve at risk. The saphenous nerve and great saphenous vein are intimate companions along the medial leg. Varicose vein stripping or ablation can damage the nerve, producing medial leg numbness or painful neuropathy. Endovenous laser treatment below the knee carries the highest risk because the vein and nerve are closest at this level.
- Post-surgical numbness is expected, not pathological. After medial knee surgery (arthroscopy, ACL reconstruction with hamstring graft, TKA with medial approach), medial knee numbness from infrapatellar branch damage is so common that it should be mentioned in pre-operative counseling. The numbness is rarely functionally significant, but patients who are not warned about it become anxious.
- Running and cycling can aggravate the adductor canal. Repetitive knee flexion-extension with the adductors under tension (long-distance running, cycling with narrow saddle position) can irritate the saphenous nerve in the canal. Runners with medial knee pain that starts after a certain distance and has a burning quality should be assessed for saphenous nerve compression — this is not always a runner's knee or meniscal problem.
Related Nerves
- anatomy/nerves/femoral-nerve — The saphenous nerve's parent trunk. A femoral nerve lesion produces quadriceps weakness PLUS saphenous territory numbness. Isolated saphenous symptoms (numbness without quad weakness) localizes the lesion to the adductor canal or below — the motor branches have already exited.
- anatomy/nerves/obturator-nerve — L2-L4. Sensory territory on the medial thigh (proximal to the knee) borders the saphenous territory (medial knee and below). Both are lumbar plexus derivatives sharing L3-L4 roots.
- anatomy/nerves/tibial-nerve — The tibial nerve's medial plantar branch supplies the medial sole. The saphenous nerve supplies the medial ankle but stops at approximately the first MTP joint. The boundary between the two is at the medial foot.
Key Takeaways
- The only nerve below the knee from the lumbar plexus — medial leg numbness with intact motor function is saphenous territory, not sciatic.
- Adductor canal entrapment is an underdiagnosed cause of medial knee pain that mimics meniscal and pes anserine pathology — look for burning quality, no joint line tenderness, and negative McMurray's.
- The infrapatellar branch is damaged in up to 50-70% of medial knee surgeries — post-surgical medial knee numbness is expected and benign.
- Travels with the great saphenous vein — varicose vein procedures below the knee risk nerve injury.