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BDS 1st Year Anatomy - Board Exam Answers (Kathmandu University)

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QUESTION 1: Describe the Root Value, Course, and Clinical Importance of the Sciatic Nerve [5 Marks]

Root Value

• L4, L5, S1, S2, S3
• Posterior divisions of L4-S2 form the common fibular part
• Anterior divisions of L4-S3 form the tibial part

Mnemonic for root value: "L4 L5 S1 S2 S3" → "Lucky Lovers Sometimes See Stars"

Course

• Exits the pelvis through the greater sciatic foramen, inferior to the piriformis muscle
• Lies deep to gluteus maximus, halfway between the ischial tuberosity and greater trochanter
• Crosses posterior to obturator internus, gemelli, and quadratus femoris

• Descends in the midline, under cover of biceps femoris
• Gives branches to all muscles of the posterior compartment of the thigh (hamstrings + part of adductor magnus from ischium)
• Divides into its two terminal branches at the apex of the popliteal fossa (or variable levels higher up):
  • Tibial nerve (L4-S3)
  • Common fibular nerve (L4-S2)

Structures Innervated

• All posterior thigh muscles (biceps femoris, semitendinosus, semimembranosus)
• Ischial part of adductor magnus
• All muscles of the leg and foot (via its terminal branches)
• Skin on the lateral leg and the sole + lateral foot

Clinical Importance

1. Sciatica - compression at L4/L5 or S1 disc causes pain radiating down the posterior thigh and leg
2. Intramuscular injections - always given in the upper outer quadrant of the buttock to avoid the sciatic nerve
3. Hip dislocation - posterior dislocation can stretch or damage the sciatic nerve, causing foot drop (injury to fibular component)
4. Piriformis syndrome - nerve compressed by an abnormal piriformis muscle, mimicking sciatica
5. Hamstring injury - avulsion of ischial tuberosity can involve the sciatic nerve

Mnemonic for course: "PIG-QB-TP" Piriformis (below it) → Ischial tuberosity midpoint → Gluteus maximus deep surface → Quadratus femoris → Biceps femoris (under) → Terminal division → Popliteal fossa

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QUESTION 2: Explain the Boundaries, Contents, and Applied Anatomy of the Popliteal Fossa [5 Marks]

Introduction

Boundaries

Mnemonic for upper borders: "Semi-Semi on the Medial, Bicep on the Lateral" For the floor from top to bottom: "Femur, Capsule, Pop" = FCP

Contents

1. Posterior cutaneous nerve of the thigh (in the roof)
2. Small (short) saphenous vein (in the roof - drains into popliteal vein here)
3. Tibial nerve (most superficial of the deep structures)
4. Common fibular nerve (exits laterally along biceps femoris)
5. Popliteal vein (middle)
6. Popliteal artery (deepest - continuation of femoral artery after passing through adductor hiatus)
7. Popliteal lymph nodes (alongside vessels)
8. Fat (fills the space)

Mnemonic for depth (superficial → deep): "The Very Popliteal Artery Lies Flat" Or remember: "Nerve-Vein-Artery" from back to front (same principle as femoral triangle but reversed)

Applied Anatomy

1. Baker's cyst (Popliteal cyst) - synovial fluid herniates through the posterior capsule into the fossa; presents as a swelling behind the knee
2. Popliteal artery aneurysm - the artery can dilate (>7 mm); risk of distal limb ischemia from thromboembolism
3. Common fibular nerve injury - most common nerve injury in the region; occurs at the neck of fibula; causes foot drop (loss of dorsiflexion and eversion)
4. Popliteal pulse - palpated by deep pressure at the midline; pulse here is important in peripheral vascular disease assessment
5. Popliteal lymph node enlargement - drains the knee and lateral leg; enlarged nodes may indicate infection or malignancy

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QUESTION 3: Mention the Boundaries, Contents, and Applied Anatomy of the Femoral Triangle [5 Marks]

Introduction

Boundaries

Mnemonic for borders: "I Like Silk" = Inguinal ligament, adductor Longus, Sartorius

Contents

Mnemonic: "NAVY" from lateral to medial - Nerve, Artery, Vein, Y-lymphatics

• Lateral: femoral artery
• Middle: femoral vein
• Medial: femoral canal (lymphatics) - site of femoral hernia

Applied Anatomy

1. Femoral hernia - loop of intestine enters the femoral canal (medial compartment of femoral sheath); more common in women; presents below and lateral to pubic tubercle
2. Femoral pulse - palpated just below the inguinal ligament at the mid-inguinal point (midpoint between ASIS and pubic symphysis); used in resuscitation and cardiac catheterization
3. Femoral artery catheterization - the femoral artery is a common access site for coronary angiography
4. Femoral vein thrombosis - DVT can start here; risk of pulmonary embolism
5. Femoral nerve block - used for anesthesia in knee and hip surgery
6. Enlarged femoral lymph nodes - can be due to infection, lymphoma, or lower limb/perineal cancer

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SHORT NOTES (5 Marks Each)

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Short Note 1: Great Saphenous Vein

• Origin: Dorsal venous arch of the foot (medial side), drains the medial aspect of the dorsum
• Course: Ascends in front of the medial malleolus, along the medial surface of the leg and thigh
• Termination: Passes through the saphenous opening (fossa ovalis) in the deep fascia to join the femoral vein in the femoral triangle, approximately 3.5 cm below and lateral to the pubic tubercle
• Tributaries joining at the saphenofemoral junction: superficial epigastric, superficial circumflex iliac, superficial external pudendal veins (the three "superficial" veins)
• Valves: Contains 10-20 valves; important for preventing reflux

1. Varicose veins - incompetent valves cause dilation and tortuosity
2. Coronary artery bypass graft (CABG) - harvested and used as bypass conduit
3. Cutdown access - at medial malleolus in emergencies when IV access is difficult
4. Long saphenous venous stripping - surgical treatment for varicose veins

Mnemonic: "GSV = Goes Steadily Veinward medially" - it runs up the medial side all the way from foot to femoral triangle

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Short Note 2: Arches of the Foot

1. Medial Longitudinal Arch (MLA) - highest and most important

• Bones: Calcaneus → Talus → Navicular → 3 Cuneiforms → Medial 3 metatarsals
• Keystone: Talus
• Maintained by: Plantar calcaneonavicular (spring) ligament, plantar fascia, tibialis posterior, flexor hallucis longus, intrinsic muscles

2. Lateral Longitudinal Arch (LLA) - lower and flatter

• Bones: Calcaneus → Cuboid → Lateral 2 metatarsals
• Keystone: Cuboid
• Maintained by: Long and short plantar ligaments, peroneus longus

3. Transverse Arch

• Bones: Bases of metatarsals + cuneiforms + cuboid (at the level of tarsometatarsal joints)
• Keystone: Middle cuneiform / 2nd metatarsal base

• Pes planus (flat foot) - loss of MLA; causes pain and fatigue
• Pes cavus (high arch) - excessively high MLA; associated with neurological disorders
• Plantar fasciitis - inflammation of plantar fascia which supports MLA

Mnemonic: "3 arches = MML" = Medial longitudinal, lateral longitudinal, Middle transverse (at Metatarsals)

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Short Note 3: Claw Hand

• Cause: Damage to the ulnar nerve (predominantly) - causes inability to flex at MCP due to lost lumbricals
• For all 4 fingers: Combined median + ulnar nerve injury produces "all finger" claw
• For ring and little fingers only: Ulnar nerve injury produces "partial claw"

• Lumbricals (especially 3rd and 4th via ulnar nerve) normally flex MCP and extend IP joints
• When lost, extensor digitorum hyperextends at MCP; FDP/FDS flexes the IP joints unopposed

Mnemonic: "Claw = MCP Extended, IP Flexed" → MEIF → "My Exam Is Foul"

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Short Note 4: Femoral Sheath

• A funnel-shaped sleeve of fascia in the femoral triangle surrounding the proximal femoral vessels
• Derived from: transversalis fascia (anteriorly) + iliac fascia (posteriorly)
• Extends about 3-4 cm below the inguinal ligament
• Three compartments (from lateral to medial):
  1. Lateral: Femoral artery
  2. Middle: Femoral vein
  3. Medial: Femoral canal (lymphatics + fat + lymph node of Cloquet/Rosenmüller)
• Femoral nerve is NOT in the femoral sheath (it is lateral to it)
• The femoral canal opens superiorly into the abdomen through the femoral ring (bounded by: inguinal ligament anteriorly, femoral vein laterally, lacunar ligament medially, pectineal ligament posteriorly)

Mnemonic: "FANN" = Femoral sheath from lateral to medial: Femoral Artery, Femoral veiN, femoral caNal (No Nerve)

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Short Note 5: Hunter's Canal (Adductor Canal)

• Location: Middle third of the medial thigh, deep to sartorius
• Shape: Triangular in cross-section
• Boundaries:
  • Anterior: Sartorius muscle (roof) + vastoadductor membrane
  • Medial wall: Adductor longus (below), adductor magnus (below)
  • Lateral wall: Vastus medialis
• Extends from: Apex of femoral triangle → adductor hiatus in adductor magnus
• Contents:
  • Femoral artery
  • Femoral vein (posterior to artery in the canal)
  • Saphenous nerve (branch of femoral nerve - exits through the roof)
  • Nerve to vastus medialis
  • (Lymphatics)

Mnemonic for contents: "FAVS" = Femoral Artery, femoral Vein, Saphenous nerve, nerve to Vastus medialis

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Short Note 6: Angle of Louis (Sternal Angle)

• The sternal angle (of Louis) is the junction between the manubrium and the body of the sternum (manubriosternal joint)
• It is a secondary cartilaginous joint (symphysis) - slightly mobile
• It forms a visible and palpable transverse ridge on the anterior chest wall

1. Articulation of the 2nd costal cartilage with the sternum (starting point for rib counting)
2. Bifurcation of the trachea into right and left main bronchi (T4-T5 level)
3. Aortic arch begins and ends
4. Azygos vein draining into the superior vena cava
5. Upper border of the pericardium
6. T4-T5 vertebral level
7. Division between the superior and inferior mediastinum

Mnemonic: "ABCDEF at the Angle of Louis" A = Aortic arch starts/ends B = Bifurcation of trachea C = 2nd Costal cartilage D = Division of mediastinum E = sEcond rib (rib counting starts here) F = T4-T5 level (Fourth-Fifth)

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DOUBLE NERVE SUPPLY (Short Note / Viva Concept)

Mnemonic: "ABPP gets Double Power" Adductor magnus, Biceps femoris, Pectineus, Pectoralis major

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CLINICAL CORNER: Bursae of the Knee

• Locking (full extension): Achieved by medial rotation of the femur on the tibia (or lateral rotation of tibia on femur) - the quadriceps femoris is responsible for maintaining the locked position
• Unlocking: Initiated by the popliteus muscle, which laterally rotates the femur or medially rotates the tibia to "unlock" the knee and allow flexion

Mnemonic: "Pop goes the Lock" - Popliteus Pops open (unlocks) the locked knee

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SUMMARY MNEMONIC SHEET

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