Contents · 12 sections
- 1. Pelvic muscles
- 2. Anterior compartment of the thigh
- 3. Medial compartment of the thigh
- 4. Posterior compartment of the thigh (hamstrings)
- 5. Anterior compartment of the leg
- 6. Lateral compartment of the leg
- 7. Posterior compartment of the leg
- 8. Innervation: main nerves
- 9. Key clinical tests
- 10. Neuropathies and entrapments
- 11. Lower limb myopathies
- 12. FAQ
In a nutshell. Lower limb muscles are divided into groups by function and innervation. Hip: gluteal muscles (L4-S2, extension/abduction), iliopsoas (L1-L3 + femoral nerve, flexion). Thigh: anterior (quadriceps — L2-L4, femoral nerve, knee extension), posterior (biceps femoris, semitendinosus, semimembranosus — L5-S2, sciatic nerve, knee flexion), medial (adductors — L2-L4, obturator nerve). Leg: anterior (L4-L5, dorsiflexion, deep fibular nerve), posterior (S1-S2, plantarflexion, tibial nerve). Clinically: piriformis syndrome, tunnel neuropathies, Trendelenburg sign in m. gluteus medius weakness.
1. Pelvic muscles
Internal group
- Iliopsoas (m. iliopsoas): iliacus + psoas major; hip flexion; innervation — femoral nerve and direct branches of L1-L3.
- Psoas minor — vestigial.
External group (gluteal region)
- Gluteus maximus (m. gluteus maximus) — extension, external rotation; inferior gluteal nerve (L5-S2).
- Gluteus medius (m. gluteus medius) — abduction, pelvic stabilization during gait; superior gluteal nerve (L4-S1). Weakness → Trendelenburg sign.
- Gluteus minimus (m. gluteus minimus) — abduction, internal rotation.
- Piriformis (m. piriformis) — external rotation; passes through the greater sciatic foramen; may compress the sciatic nerve (piriformis syndrome).
- Tensor fasciae latae (m. tensor fasciae latae) — abduction, flexion; superior gluteal nerve.
2. Anterior compartment of the thigh
- Quadriceps femoris (m. quadriceps femoris): rectus femoris + 3 vastus muscles (lateralis, medialis, intermedius). Knee extension; rectus femoris also assists in hip flexion.
- Sartorius (m. sartorius) — hip and knee flexion + external rotation; the longest muscle.
- Innervation — femoral nerve (L2-L4).
- Knee-jerk reflex — test for L3-L4 segments.
3. Medial compartment of the thigh
- Pectineus (m. pectineus) — adduction + flexion; femoral nerve, occasionally obturator nerve.
- Gracilis (m. gracilis) — adduction; obturator nerve.
- Adductor longus (m. adductor longus).
- Adductor brevis (m. adductor brevis).
- Adductor magnus (m. adductor magnus) — mixed innervation: obturator nerve + branch of the sciatic nerve.
- Group innervation — obturator nerve (L2-L4).
4. Posterior compartment of the thigh (hamstrings)
- Biceps femoris (m. biceps femoris) — long and short heads; knee flexion, external rotation of the leg when the knee is flexed.
- Semitendinosus (m. semitendinosus).
- Semimembranosus (m. semimembranosus).
- Function: hip extension, knee flexion.
- Innervation — tibial component of the sciatic nerve (L5-S2); short head of biceps femoris — common fibular nerve.
5. Anterior compartment of the leg
- Tibialis anterior (m. tibialis anterior) — dorsiflexion, foot inversion. Key marker for L4-L5.
- Extensor hallucis longus (m. extensor hallucis longus) — L5 test.
- Extensor digitorum longus (m. extensor digitorum longus).
- Fibularis tertius (m. peroneus tertius).
- Innervation — deep fibular nerve (L4-S1).
- Paresis in L5 lesion — steppage gait (foot drop).
6. Lateral compartment of the leg
- Fibularis longus (m. peroneus longus).
- Fibularis brevis (m. peroneus brevis).
- Function: foot eversion, plantarflexion.
- Innervation — superficial fibular nerve (L5-S1).
- Superficial fibular nerve — sensation of the dorsum of the foot (except the 1st interdigital cleft, which is supplied by the deep fibular nerve).
7. Posterior compartment of the leg
- Superficial layer:
- — Gastrocnemius (m. gastrocnemius) — medial and lateral heads, crosses the knee joint.
- — Soleus (m. soleus) — deep to gastrocnemius, does not cross the knee joint.
- — Plantaris (m. plantaris) — vestigial.
- Deep layer:
- — Popliteus (m. popliteus) — "unlocks" the knee at the start of flexion.
- — Flexor digitorum longus (m. flexor digitorum longus).
- — Flexor hallucis longus (m. flexor hallucis longus).
- — Tibialis posterior (m. tibialis posterior) — inversion and plantarflexion.
- Innervation — tibial nerve (S1-S2).
- Achilles reflex — S1 test.
8. Innervation: main nerves
| Nerve | Segments | Zone |
|---|---|---|
| Femoral | L2-L4 | Anterior compartment of thigh + iliopsoas |
| Obturator | L2-L4 | Medial compartment of thigh |
| Sciatic (main) | L4-S3 | Posterior compartment of thigh + leg + foot |
| Tibial (from sciatic) | L4-S3 | Posterior compartment of leg + sole |
| Common fibular | L4-S2 | Short head of m. biceps; divides into deep and superficial |
| Deep fibular | L4-S1 | Anterior compartment of leg |
| Superficial fibular | L5-S1 | Lateral compartment of leg |
| Superior gluteal | L4-S1 | Gluteus medius, minimus, TFL |
| Inferior gluteal | L5-S2 | Gluteus maximus |
9. Key clinical tests
- Trendelenburg sign — pelvis drops on the opposite side when standing on one leg; lesion of gluteus medius or superior gluteal nerve (L5).
- Gower's sign — "climbs up his own body" when rising from a lying position; proximal myopathy (Duchenne).
- Lasegue's test — straight leg raise, pain up to 60° — L5/S1 radiculopathy.
- Wasserman's test — prone position, straight leg raise → pain in L3-L4.
- Patrick's (FABER) test — flexion-abduction-external rotation; pain in coxarthrosis or sacroiliitis.
- Meniscal tear tests: McMurray, Apley.
10. Neuropathies and entrapments
- Lateral femoral cutaneous nerve (meralgia paresthetica) — entrapment beneath the inguinal ligament; burning and paresthesia on the anterolateral thigh.
- Common fibular nerve — compression at the fibular head level; foot drop.
- Piriformis syndrome — compression of the sciatic nerve; pain in the buttock radiating to the leg.
- Tarsal tunnel syndrome — tibial nerve behind the medial malleolus; paresthesia in the sole.
- Femoral nerve (hematoma in m. iliopsoas in anticoagulated patients) — quadriceps weakness, ↓ knee reflex.
11. Lower extremity myopathies
- Duchenne and Becker muscular dystrophies — proximal muscle weakness; calf pseudohypertrophy.
- Landouzy-Dejerine — facioscapulohumeral, affects legs as it progresses.
- Myositis (polymyositis/dermatomyositis) — symmetrical weakness, ↑ CK.
- Statins and other drugs → drug-induced myopathy.
- Compartment syndrome (Volkmann's ischemic contracture equivalent in the leg) — in open/closed fractures; urgent fasciotomy.
12. FAQ
Why does L5 lesion cause a "slapping gait"?
The L5 nerve root innervates the anterior leg muscles (m. tibialis anterior, m. extensor hallucis longus) — their weakness → inability to dorsiflex → foot "slaps" when walking.
How to differentiate sciatic nerve entrapment at the L5/S1 level from the piriformis level?
L5/S1 radiculopathy — back pain with radiation, positive Lasegue's test, often with ↓ reflexes and objective deficit in the leg. Piriformis syndrome — pain in the buttock, ↑ with prolonged sitting, positive FAIR test (flexion-adduction-internal rotation).
Why is the quadriceps the main knee extensor?
All 4 heads converge into a common tendon attaching to the tibial tuberosity via the patella (quadriceps tendon — patellar ligament). Powerful lever and large cross-sectional area.
Why is a meniscal tear a common injury?
The menisci are medial (C-shaped, rigidly fixed) and lateral (O-shaped, more mobile). Twisting movements with a loaded foot cause asymmetric pressure → tear (more commonly medial). Diagnosis — MRI; treatment — arthroscopic meniscectomy or repair.
How does Trendelenburg's test detect pathology?
Patient stands on one leg → normally the pelvis rises on the opposite side (working m. gluteus medius of the stance leg). In case of muscle weakness (or L5 lesion), the pelvis drops — positive sign. Important: it is recommended to check both sides.
See also: Dermatomes and myotomes · Disc herniation · Knee osteoarthritis · Lumbosacral plexus · Anatomy Catalog