Root Origin
- Spinal nerve roots: L2, L3, L4
- Plexus: Lumbar plexus (forms within the psoas major, posterior to the femoral nerve)
- Type: Mixed (motor and sensory)
Course
- Lumbar plexus. The nerve forms within the psoas major from the anterior divisions of L2, L3, and L4 ventral rami — in contrast to the femoral nerve, which forms from the posterior divisions of the same roots.
- Pelvic wall. The nerve emerges from the medial border of the psoas major (the femoral nerve exits laterally). It descends along the lateral pelvic wall, crossing the sacroiliac joint and running along the obturator internus.
- Obturator canal. The nerve enters the obturator canal — a short tunnel in the superior part of the obturator foramen formed by the obturator groove of the pubic bone, roofed by the obturator membrane. The obturator artery and vein accompany it.
- Medial thigh. After exiting the obturator canal, the nerve divides into anterior and posterior branches, separated by the adductor brevis muscle.
- Anterior branch. Passes superficial to the adductor brevis (between pectineus/adductor longus anteriorly and adductor brevis posteriorly). Supplies the adductor longus, adductor brevis, gracilis, and occasionally the pectineus. Gives off a cutaneous branch to the medial thigh.
- Posterior branch. Passes deep to the adductor brevis (between adductor brevis anteriorly and adductor magnus posteriorly). Supplies the obturator externus and the adductor portion of the adductor magnus. Sends an articular branch to the posterior knee joint.
Motor Distribution
Anterior Branch
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/adductor-longus | Hip adduction, flexion, medial rotation | Most anterior of the adductors; the palpable tendon at the pubic tubercle |
| anatomy/muscles/adductor-brevis | Hip adduction, flexion | Lies deep to adductor longus; the dividing landmark between anterior and posterior branches |
| anatomy/muscles/gracilis | Hip adduction, knee flexion, medial rotation of tibia | The only adductor that crosses the knee; part of the pes anserine group |
| anatomy/muscles/pectineus | Hip adduction, flexion | Dual innervation from femoral and obturator — damage to one nerve alone may not completely weaken it |
Posterior Branch
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/obturator-externus | Hip external rotation | Deep muscle; wraps behind the femoral neck to insert on the trochanteric fossa |
| anatomy/muscles/adductor-magnus (adductor portion) | Hip adduction | Only the adductor (anterior) portion; the hamstring (posterior) portion is supplied by the sciatic nerve (tibial division) |
Sensory Distribution
- Cutaneous branch to the medial thigh. The anterior branch gives off a small cutaneous branch supplying a variable patch of skin on the medial thigh, usually in the mid-medial region. The sensory territory is inconsistent between individuals and often overlaps with the femoral nerve's medial cutaneous branch of the thigh.
- Articular branch to the knee. The posterior branch sends a branch to the posterior knee joint capsule — the basis for referred hip pain to the knee. A patient with hip pathology (OA, AVN) may present with medial knee pain via this pathway.
- Clinical significance: The obturator nerve's cutaneous territory is small and variable, making sensory testing unreliable for diagnosis. Motor testing (adductor weakness) is more informative than sensory testing for this nerve.
Entrapment Sites
1. Obturator Canal
- Location: The obturator canal in the superior obturator foramen
- Structure: The canal can be narrowed by obturator hernia, pelvic fractures, osteophytes, or soft tissue masses. In athletes, the fascial borders of the canal can compress the nerve during repetitive adduction loading.
- Condition: Obturator nerve entrapment / obturator neuropathy
- Presentation: Medial thigh pain exacerbated by exercise, especially activities involving adduction (running, kicking, skating). Adductor weakness — the patient may report the leg "sliding out" during pivoting activities. Pain may radiate to the medial knee (via the articular branch). The exercise-related pattern distinguishes it from acute groin strain — the pain builds during activity and subsides with rest, then recurs at a predictable exertion level.
- MT relevance: Obturator neuropathy is rare but should be considered in athletes with chronic medial thigh pain that does not respond to adductor strain treatment. If adductor flexibility improves but exercise-related medial thigh pain persists, the problem may be neural rather than muscular.
2. Pelvic Compression
- Location: Along the pelvic wall, between the psoas and the obturator canal
- Structure: Pelvic tumors, endometriosis, pregnancy (fetal head compression), or post-surgical scarring can compress the nerve along its pelvic course
- Presentation: Adductor weakness and medial thigh pain without an exercise-related pattern — symptoms are constant or progressive. In pregnancy, onset in the third trimester with adductor weakness that resolves postpartum.
- MT relevance: Non-exercise-related progressive adductor weakness with medial thigh pain requires medical workup to rule out pelvic pathology.
Clinical Tests
| Test | Procedure | Positive Finding | What It Tells You |
|---|---|---|---|
| Resisted hip adduction | Patient supine with hip slightly abducted. Apply resistance to the medial side of the knee as the patient adducts. | Weakness compared to the opposite side. | Adductor motor function via the obturator nerve. Bilateral comparison is essential. |
| Adductor squeeze test | Patient supine with knees flexed to 45 degrees, feet on the table. Place your fist between the knees and ask the patient to squeeze. | Pain in the medial thigh or groin during the squeeze, or weakness compared to expected. | Tests adductor function under load. Pain suggests adductor pathology (strain, tendinopathy) or obturator nerve irritation. Weakness without pain favors nerve over muscle. |
| Medial thigh sensation | Light touch along the medial thigh. | Decreased sensation — but the territory is variable and often overlaps with femoral cutaneous branches. | Obturator sensory territory. Unreliable in isolation — the cutaneous supply is inconsistent. More useful as a supporting finding alongside motor weakness. |
Clinical Notes
- Hip pathology refers to the knee via the obturator nerve. The obturator nerve sends an articular branch to the posterior knee joint. This is why patients with hip osteoarthritis, avascular necrosis, or hip fracture sometimes present with medial knee pain as their chief complaint — the brain misinterprets the hip afferent signal as coming from the knee. Always examine the hip when a patient has unexplained medial knee pain, especially in older adults.
- Obturator neuropathy versus adductor strain — the athletic differential. Both produce medial thigh pain with exercise. Adductor strain: acute onset with a specific injury mechanism, point tenderness at the musculotendinous junction or pubic attachment, pain with passive stretch (abduction). Obturator neuropathy: insidious onset, exercise-dependent pain at a predictable exertion level, adductor weakness on testing, and pain that does not improve with standard strain rehabilitation.
- Pregnancy-related obturator palsy is usually temporary. The fetal head can compress the obturator nerve against the pelvic wall during late pregnancy or labor. The patient develops adductor weakness postpartum. Recovery is expected over weeks to months as the nerve regenerates. Reassure the patient and avoid aggressive adductor strengthening until motor recovery begins.
- The obturator nerve is the "forgotten" nerve of the lumbar plexus. While the femoral nerve gets attention for quadriceps control and the lateral femoral cutaneous nerve for meralgia paresthetica, the obturator nerve is rarely considered in differential diagnosis. In chronic medial thigh pain that does not respond to adductor treatment, hip assessment, or imaging, the obturator nerve deserves consideration.
Related Nerves
- anatomy/nerves/femoral-nerve — L2-L4. Shares identical root levels but from different divisions (posterior for femoral, anterior for obturator). Supplies the opposite thigh compartment — anterior (femoral) versus medial (obturator). A lumbar plexus lesion or L3-L4 radiculopathy affects both.
- anatomy/nerves/saphenous-nerve — L3-L4 (via femoral). The saphenous nerve's medial knee sensory territory borders the obturator's medial thigh territory. Both contribute to medial lower extremity sensation from the lumbar plexus.
- anatomy/nerves/sciatic-nerve — L4-S3. The sciatic nerve (tibial division) innervates the hamstring portion of adductor magnus — the only adductor not supplied by the obturator nerve. This dual innervation of adductor magnus is a frequent exam question.
Key Takeaways
- Primary motor supply to the hip adductors, passing through the obturator foramen — entrapment produces exercise-related medial thigh pain and adductor weakness that mimics groin strain.
- The articular branch to the knee explains why hip pathology (OA, AVN) can present as medial knee pain — always examine the hip in unexplained medial knee pain.
- Shares L2-L4 roots with the femoral nerve but supplies the opposite compartment — lumbar plexus lesions affect both, producing combined anterior and medial thigh dysfunction.
- Sensory territory on the medial thigh is small and variable — motor testing (adductor strength) is more reliable than sensory testing for diagnosis.