Applied Anatomy and Clinical Correlations

LL Nerve Injuries - Nerve Wrecks

• Sciatic (L4-S3): Post. hip dislocation/IM inj. → Hamstrings, all below-knee muscles affected (foot drop, flail foot). Sensory: post. thigh, leg, foot (spares saphenous).
• Common Peroneal (L4-S2): Fibular neck #/cast. → Foot drop (steppage gait), eversion loss. Sensory: ant-lat leg, dorsum foot.

  ⭐ Common peroneal nerve is the most commonly injured nerve in the lower limb, especially vulnerable as it winds around the neck of the fibula.

• Tibial (L4-S3): Popliteal fossa/tarsal tunnel. → Plantarflex/inversion loss (no tiptoe). Sensory: sole.
• Femoral (L2-L4): Pelvic #/iatrogenic. → Quadriceps weak (↓ knee ext., ↓ patellar reflex). Sensory: ant. thigh, med. leg/foot.
• Obturator (L2-L4): Ant. hip dislocation/pelvic surgery. → Adduction loss. Sensory: med. thigh.

LL Vascular Issues - Flow Failures

• Acute Limb Ischemia (ALI)

  • Causes: Embolism (e.g., AF), thrombosis (e.g., atherosclerosis), trauma.
  • Symptoms: 📌 6 P's (Pain, Pallor, Paresthesia, Pulselessness, Paralysis, Poikilothermia).
  • Management: Urgent revascularization (embolectomy, bypass, thrombolysis).

  ⭐ The 6 P's (Pain, Pallor, Paresthesia, Pulselessness, Paralysis, Poikilothermia) are classical signs of acute limb ischemia, often seen in compartment syndrome or arterial occlusion.

• Compartment Syndrome

  • Patho: ↑ Pressure in fascial compartment → ↓ tissue perfusion → ischemia.
  • Signs: Severe pain (out of proportion), tense limb, paresthesia. Pulses may be present initially.
  • Dx: Compartment pressure > 30 mmHg or ΔP (Diastolic BP - Compartment Pressure) < 20-30 mmHg.
  • Tx: Emergency fasciotomy.

• Peripheral Artery Disease (PAD) / Chronic Limb-Threatening Ischemia (CLTI)

  • Cause: Atherosclerosis.
  • Symptoms: Intermittent claudication, rest pain, ischemic ulcers, gangrene.
  • Dx: Ankle-Brachial Index (ABI) < 0.9 (severe < 0.4).
  • Tx: Risk factor modification, exercise, antiplatelets, revascularization.

LL Fractures & Dislocations - Break Points

• Hip Region:
  • Femoral Neck: Intracapsular (↑AVN risk with displacement) vs. Extracapsular. Garden classification for intracapsular.
  • Intertrochanteric/Subtrochanteric.
  • Posterior Hip Dislocation: Sciatic nerve injury; dashboard injury.
• Femur Shaft: High energy trauma; risk of fat embolism, compartment syndrome.
• Knee Region:
  • Patellar Fracture: Direct blow or forceful quadriceps contraction.
  • Tibial Plateau Fracture: Axial load with valgus/varus stress.
  • Knee Dislocation: ⚠️ High risk of popliteal artery injury!
• Tibia/Fibula:
  • Shaft Fractures: Open fractures common; compartment syndrome risk.
  • Ankle Fractures: Pott's (malleolar), Maisonneuve (proximal fibula # + medial ankle injury).
• Foot:
  • Calcaneus: Fall from height; associated spinal injuries.
  • Talus: Neck fractures (↑AVN risk).
  • Lisfranc Fracture-Dislocation: Midfoot injury.
  • Jones Fracture: Base of 5th metatarsal (watershed area).

⭐ Avascular necrosis (AVN) of the femoral head is a major complication of displaced intracapsular fractures of the neck of femur due to disruption of the main blood supply from retinacular arteries (medial circumflex femoral artery branches).

LL Joint Pathologies & Gait - Joint Jam

• Osteoarthritis (OA): Degenerative. Hip/knee. Osteophytes, ↓joint space.
• Rheumatoid Arthritis (RA): Autoimmune. Symmetrical. Pannus, erosions.
• Gout: Urate crystals. Podagra (1st MTP). Tophi.
• Septic Arthritis: Infection. Fever, ↑WBC. Emergency.

High‑Yield Points - ⚡ Biggest Takeaways

• Trendelenburg gait indicates superior gluteal nerve injury, affecting gluteus medius/minimus.
• Foot drop results from common peroneal nerve damage, typically at the fibular neck.
• Femoral hernias are medial to the femoral vein and carry a high strangulation risk.
• The "unhappy triad" involves injury to the ACL, MCL, and medial meniscus.
• Achilles tendon rupture often presents with a positive Thompson test and sudden pain.
• Anterior compartment syndrome is the most common in the leg, requiring urgent fasciotomy.
• Meralgia Paresthetica: Entrapment of lateral femoral cutaneous nerve causes anterolateral thigh burning pain/paresthesia.