Lower limb fascial compartments

Overview of Lower Limb Fascia - The Body's Stockings

• Superficial Fascia (Subcutaneous Tissue): Lies deep to the skin, containing fat, cutaneous nerves, superficial veins (Great & Small Saphenous), and lymphatics.
• Deep Fascia: A strong, stocking-like layer covering limb muscles.
  • Fascia Lata in the thigh; continuous with the Crural Fascia in the leg.
  • Forms intermuscular septa that attach to bone, creating distinct neurovascular compartments (anterior, posterior, medial).
  • Thickened laterally to form the Iliotibial (IT) Tract.

⭐ The deep fascia is inelastic; this property is vital for the musculovenous pump, but it also contributes to the pathophysiology of compartment syndrome, where swelling can compress neurovascular structures.

Thigh Fascial Compartments - Upper Leg Powerhouses

• Anterior Compartment (Extensors)

  • Muscles: Quadriceps femoris, Sartorius, Iliopsoas.
  • Action: Extends leg at the knee; flexes thigh at the hip.
  • Innervation: Femoral nerve.

• Medial Compartment (Adductors)

  • Muscles: Adductor (longus, brevis, magnus), Gracilis, Pectineus.
  • Action: Adducts the thigh.
  • Innervation: Obturator nerve.

• Posterior Compartment (Flexors)

  • Muscles: Hamstrings (Biceps femoris, Semitendinosus, Semimembranosus).
  • Action: Flexes leg at the knee; extends thigh.
  • Innervation: Sciatic nerve (tibial division, except short head of biceps femoris).

⭐ Compartment Syndrome: The anterior compartment is the most common site for chronic exertional compartment syndrome in the thigh due to its tight fascial enclosure.

Leg Fascial Compartments - Lower Leg Movers

• Anterior Compartment

  • Muscles: Tibialis anterior, Extensor hallucis longus, Extensor digitorum longus.
  • Innervation: Deep peroneal (fibular) nerve.
  • Function: Dorsiflexion, foot inversion.

• Lateral Compartment

  • Muscles: Peroneus (fibularis) longus & brevis.
  • Innervation: Superficial peroneal (fibular) nerve.
  • Function: Eversion, plantarflexion.

• Superficial Posterior Compartment

  • Muscles: Gastrocnemius, Soleus, Plantaris.
  • Innervation: Tibial nerve.
  • Function: Plantarflexion.

• Deep Posterior Compartment

  • Muscles: Tibialis posterior, Flexor hallucis longus, Flexor digitorum longus.
  • Innervation: Tibial nerve.
  • Function: Plantarflexion, foot inversion.
  • 📌 Mnemonic: Tom, Dick, ANd Harry (medial malleolus).

⭐ The anterior compartment is the most common site for acute compartment syndrome. Presents with pain out of proportion to injury and paresthesias. The deep peroneal nerve is most vulnerable.

Compartment Syndrome - Anatomy Under Pressure

Increased pressure within a fascial compartment compromises circulation and neuromuscular function. Most common in the anterior compartment of the leg after a tibial fracture.

• Pathophysiology: Swelling → ↑ compartment pressure → venous outflow obstruction → ↓ arteriolar inflow → ischemia.
• Clinical Signs (The 6 P's):
  • 📌 Pain out of proportion to injury (earliest sign)
  • Paresthesias (early sign)
  • Pallor
  • Paralysis (late sign)
  • Pulselessness (very late sign)
  • Poikilothermia (coolness)
• Diagnosis: Compartment pressure > 30 mmHg.

⭐ Irreversible muscle and nerve damage begins after 4-6 hours of ischemia. Prompt fasciotomy is the only definitive treatment.

High‑Yield Points - ⚡ Biggest Takeaways

• Compartment syndrome: A surgical emergency from ↑ intracompartmental pressure, leading to neurovascular compromise.
• Anterior thigh: Quadriceps, innervated by the femoral nerve.
• Medial thigh: Adductors, innervated by the obturator nerve.
• Posterior thigh: Hamstrings, innervated by the sciatic nerve.
• Anterior leg: Dorsiflexors; injury to the deep fibular nerve causes foot drop.
• Lateral leg: Evertors, innervated by the superficial fibular nerve.
• Posterior leg: Plantarflexors, innervated by the tibial nerve.