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3-Mark SAQ Answers

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1. Deltoid

Deltoid is tested by abduction against resistance. Axillary nerve injury causes "flattening" of shoulder contour.

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2. Biceps Brachii

Rupture of long head tendon produces "Popeye sign" - a distally bulging muscle belly.

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3. Brachioradialis

Brachioradialis is a "border crosser" - it lies in the extensor compartment but acts as a flexor.

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4. Triceps Brachii

Radial nerve injury in the spiral groove (e.g., "Saturday night palsy") preserves elbow extension because the medial head branch arises proximal to the groove.

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5. Gluteus Maximus

Trendelenburg gait occurs with weakness. The gluteus maximus is the largest muscle in the body and the main "climbing" muscle.

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6. Sartorius

Sartorius is the longest muscle in the body. It forms the lateral border of the femoral triangle.

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7. Popliteus

Popliteus is the "key that unlocks the knee" - it initiates knee flexion from the fully extended (screw-home) position.

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8. Hamstrings

All hamstrings cross both hip and knee joints (except short head of biceps femoris). They are commonly strained in athletes.

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9. Rotator Cuff

Supraspinatus is the most commonly torn tendon. A painful arc (60-120°) suggests supraspinatus pathology.

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10. Branches of Axillary Artery

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11. Epithelium

Classification (Table 5.1 - Histology: A Text and Atlas)

• Endothelium - lines blood and lymphatic vessels
• Endocardium - lines heart chambers
• Mesothelium - lines serous body cavities

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12. Arch of Aorta

Three Branches (arising from the superior border):

• All three branches are crossed anteriorly by the left brachiocephalic vein
• The arch is initially anterior, then lateral to the trachea
• The ligamentum arteriosum connects the arch to the pulmonary trunk (remnant of ductus arteriosus)

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Sources: Miller's Review of Orthopaedics 9th Ed; Gray's Anatomy for Students; Histology: A Text and Atlas (Pawlina); Rosen's Emergency Medicine

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7-MARK SAQ Answers

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1. Cubital Fossa

Boundaries

Contents (lateral to medial - mnemonic: "TAN")

• T - Tendon of biceps brachii (most lateral - easily palpable)
• A - Brachial Artery (here it divides into radial and ulnar arteries)
• N - Median Nerve (most medial)

Additional: The radial nerve travels deep to brachioradialis at the lateral margin. The ulnar nerve passes behind the medial epicondyle (NOT in the fossa).

Superficial structures

• Median cubital vein crosses the roof (connects cephalic and basilic veins) - used for venepuncture
• Cephalic and basilic veins are lateral and medial respectively

Clinical significance

• Site of venepuncture and IV cannulation (median cubital vein)
• Brachial artery pulse palpated here; used for blood pressure measurement
• Cubital tunnel syndrome - ulnar nerve compression at medial epicondyle

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2. Popliteal Fossa

Boundaries

Contents (superficial to deep)

1. Popliteal artery (deepest - continuation of femoral artery through adductor hiatus)
2. Popliteal vein (superficial to artery)
3. Tibial nerve (most superficial)
4. Common fibular (peroneal) nerve - along medial border of biceps femoris
5. Popliteal lymph nodes (4-5 nodes) draining deep structures of leg and foot
6. Posterior cutaneous nerve of thigh (in fat above fossa)
7. Small saphenous vein - enters popliteal vein
8. Popliteal fat fills the space

Arrangement from superficial to deep: Nerve (tibial) > Vein > Artery - "NVA from superficial to deep"

Clinical significance

• Popliteal aneurysm - most common peripheral artery aneurysm
• Semimembranosus bursa / Baker's cyst - swelling in medial popliteal fossa, communicates with knee joint in rheumatoid arthritis
• Popliteal artery pulse - felt against popliteal surface of femur with knee flexed

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3. Femoral Triangle

Boundaries

Contents (lateral to medial - mnemonic: "NAVL")

• N - Femoral Nerve (lateral to femoral sheath, NOT inside it)
• A - Femoral Artery (lateral compartment of femoral sheath)
• V - Femoral Vein (intermediate compartment of femoral sheath)
• L - Lymphatics + femoral canal (medial compartment - potential site of femoral hernia)

Femoral Sheath

• Funnel-shaped sleeve of transversalis + iliac fascia
• Contains femoral artery, vein, and lymphatics in 3 separate compartments
• Femoral nerve is outside the sheath
• Most medial compartment = femoral canal; its opening = femoral ring (site of femoral hernia)

Clinical significance

• Femoral pulse: palpable midway between ASIS and pubic symphysis (mid-inguinal point)
• Femoral hernia: contents descend through femoral canal - more common in women
• Femoral artery access for cardiac catheterization and angiography

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4. Arches of the Foot

A. Longitudinal Arch

• Bones: Calcaneus - talus - navicular - 3 cuneiforms - medial 3 metatarsals
• Keystone: Head of talus
• Maintained by: Plantar calcaneonavicular (spring) ligament, tibialis posterior tendon, flexor hallucis longus, plantar aponeurosis

• Bones: Calcaneus - cuboid - lateral 2 metatarsals
• Maintained by: Long and short plantar ligaments, fibularis longus, plantar aponeurosis

B. Transverse Arch

• Runs mediolaterally across the foot
• Highest at the head of talus, disappears near metatarsal heads
• Bones: Bases of metatarsals and cuneiforms and cuboid
• Maintained by: Deep transverse metatarsal ligaments, fibularis longus tendon, tibialis posterior

Support Mechanisms Summary

Clinical significance

• Pes planus (flat foot): Medial arch collapse - spring ligament laxity
• Pes cavus (high arch): Exaggerated medial arch
• Plantar fasciitis: Inflammation of plantar aponeurosis at calcaneal insertion

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5. Classification of Joints

A. Structural Classification

1. Fibrous Joints

• Bones connected by fibrous connective tissue; no joint cavity
• Subdivided into:
  • Sutures - found between skull bones; interlocking bone edges bound by short fibrous tissue; e.g., coronal, sagittal sutures
  • Gomphoses - peg-and-socket; e.g., roots of teeth in alveolar bone
  • Syndesmoses - bones connected by interosseous membrane or ligament; e.g., inferior tibiofibular joint, interosseous membrane of forearm

2. Cartilaginous Joints

• Bones united by cartilage; no joint cavity
• Subdivided into:
  • Primary (synchondroses) - hyaline cartilage; temporary joints in growing bones; e.g., epiphyseal plates, 1st sternocostal joint; immovable
  • Secondary (symphyses) - fibrocartilage; slightly movable; e.g., pubic symphysis, intervertebral discs, manubriosternal joint

3. Synovial Joints

• Have a joint cavity containing synovial fluid; freely movable (diarthroses)
• Features: articular cartilage, joint capsule, synovial membrane, synovial fluid, ligaments (intracapsular/extracapsular), articular discs (in some)

B. Functional Classification

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6. Blood Supply of Long Bones

Sources of Blood Supply

1. Nutrient (Diaphyseal) Artery - Principal Supply

• Single (occasionally 2) artery entering through the nutrient foramen in the diaphysis
• Oblique direction of foramen (directed away from the growing end - "growing end knows")
• Divides into ascending and descending branches in the medullary cavity supplying the inner 2/3 of cortex
• Origin: From main regional artery (e.g., posterior tibial for tibia, brachial for humerus)

2. Epiphyseal Arteries

• Enter through the epiphysis via multiple foramina
• Supply epiphyseal bone and epiphyseal plate
• Derived from periarticular arterial plexus
• Before closure of growth plate, epiphyseal and metaphyseal circulations are separate (important - epiphyseal avascular necrosis can occur if these vessels are damaged)

3. Metaphyseal Arteries

• Branches of periosteal vessels incorporated into metaphysis during bone growth (as the bone widens)
• Supplement the nutrient artery supply at the flared ends of bone

4. Periosteal Arteries

• Supply the outer 1/3 of cortical bone
• A lesser but important supply from branches of periosteal arteries entering via Volkmann's canals
• Important in fracture healing and after disruption of nutrient artery

Venous Drainage

• Exits through nutrient foramina and through the bone tissue of the shaft out via periosteum
• Bone tissue lacks lymphatic vessels; lymphatic drainage only from periosteum

Direction of Flow

• Centrifugal - blood flows from the medullary cavity through Haversian canals (via Volkmann's canals) outward to periosteum

Clinical significance

• Disruption of nutrient artery in fractures leads to avascular necrosis (e.g., femoral head, scaphoid, talus)
• Osteomyelitis in children typically begins in metaphysis (rich slow-flow sinusoidal vessels)
• In adults, the periosteal supply becomes more important after fusion of growth plate

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7. Mediastinum

Boundaries

• Superior: Thoracic inlet (between T1 and manubrium)
• Inferior: Diaphragm
• Anterior: Sternum
• Posterior: Vertebral column (T1-T12)
• Lateral: Mediastinal pleura (right and left)

Divisions

A. Superior Mediastinum

• Thymus (or thymic remnant)
• Arch of aorta and its 3 branches (brachiocephalic trunk, left common carotid, left subclavian)
• Brachiocephalic veins and superior vena cava (upper part)
• Trachea and esophagus
• Thoracic duct (upper part)
• Vagus nerve, phrenic nerve (upper part), cardiac plexus
• Left recurrent laryngeal nerve (hooks around arch of aorta)
• Lymph nodes

B. Inferior Mediastinum (divided into 3 parts by pericardium)

• Thymic lower part (in children) / lymph nodes / fat / sternopericardial ligaments
• Smallest subdivision

• Heart and pericardium
• Ascending aorta and pulmonary trunk (origins)
• Superior vena cava (lower part) and inferior vena cava
• Pulmonary veins (4)
• Phrenic nerves and pericardia-phrenic vessels
• Tracheal bifurcation (carina) and main bronchi

• Descending thoracic aorta
• Esophagus and esophageal plexus (vagal trunks)
• Thoracic duct
• Azygos and hemiazygos veins
• Sympathetic chain and splanchnic nerves
• Posterior mediastinal lymph nodes

Clinical significance

• Mediastinal widening on CXR: suggests aortic aneurysm, lymphoma, or mass
• Mediastinitis: life-threatening after esophageal perforation or cardiac surgery

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8. Right Atrium

External Features

• Sulcus terminalis: A vertical groove on the external surface, running from the right side of the SVC opening to the right side of the IVC opening
• Right auricle: Ear-like conical pouch overlapping the ascending aorta

Internal Features

1. Sinus of Venae Cavae (Smooth part - posterior)

• Embryologically derived from the right horn of sinus venosus
• Smooth thin walls
• Receives:
  • Superior vena cava (SVC) - upper, returns blood from upper body
  • Inferior vena cava (IVC) - lower, returns blood from lower body; has a rudimentary valve (Eustachian valve)
  • Coronary sinus - returns blood from the heart wall; has Thebesian valve

2. Atrium Proper (Rough part - anterior + auricle)

• Walls covered by musculi pectinati (pectinate muscles) - ridges like "teeth of a comb" arising from crista terminalis
• The right auricle is continuous with this part

3. Interatrial Septum

• Separates right from left atrium
• Contains the fossa ovalis - oval depression, remnant of embryonic foramen ovale
• Surrounded by the limbus fossa ovalis (prominent raised border)
• Clinical: Patent foramen ovale (PFO) in ~25% of adults - may allow paradoxical embolism

Openings in the Right Atrium

1. Superior vena cava (no valve)
2. Inferior vena cava (Eustachian valve)
3. Coronary sinus (Thebesian valve)
4. Right atrioventricular orifice (tricuspid valve - 3 leaflets: anterior, posterior, septal)
5. Small foramina of Thebesius (small cardiac veins opening directly)

Blood supply

• Right coronary artery supplies the right atrium and the sinu-atrial (SA) node

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9. Bronchopulmonary Segment

Definition

Structure

• Shaped like an irregular cone, with the apex at the origin of the segmental bronchus and the base projecting onto the pleural surface
• Each segment has its own bronchus, artery (from pulmonary artery), and vein (pulmonary tributaries pass intersegmentally between segments)
• Separated from adjacent segments by connective tissue septa

Number of Segments

Clinical Significance

• Surgical resection: Because each segment has its own blood and air supply, a diseased segment can be removed (segmentectomy) while preserving surrounding healthy lung
• Postural drainage: Each segment can be independently drained by positioning; used in bronchiectasis, CF, lung abscess
• Bronchoscopy: Segmental anatomy guides bronchoscopic localization of lesions
• Pneumonia: Often lobar or segmental in distribution
• Most common site of aspiration pneumonia: right lower lobe (posterior basal segment) in upright patients; right upper lobe (posterior segment) in recumbent position

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10. Sciatic Nerve

Origin

• Arises from the lumbosacral plexus from anterior rami of L4, L5, S1, S2, S3
• Two components run together within a common sheath:
  • Tibial part (anterior divisions of L4-S3)
  • Common fibular part (posterior divisions of L4-S2)

Course

1. In the pelvis: Formed on the anterior surface of piriformis
2. Exit from pelvis: Passes through the greater sciatic foramen, inferior to the piriformis muscle
3. In the gluteal region:
   • Runs deep to gluteus maximus
   • Lies on: obturator internus, gemelli, quadratus femoris muscles
   • Covered by gluteus maximus
   • Accompanied by: posterior cutaneous nerve of thigh, inferior gluteal artery
4. In the posterior thigh:
   • Runs midway between ischial tuberosity and greater trochanter, then descends vertically
   • Lies on adductor magnus, covered by long head of biceps femoris
   • Gives branches to all hamstrings and adductor magnus (ischial head)
5. Division (usually at apex of popliteal fossa, but may divide higher):
   • Tibial nerve (medial terminal branch)
   • Common fibular nerve (lateral terminal branch)

Branches and Innervation

Terminal Branches

• All posterior compartment leg muscles (gastrocnemius, soleus, popliteus, tibialis posterior, FHL, FDL)
• All intrinsic muscles of sole of foot (except extensor digitorum brevis)
• Skin: posterolateral lower leg, lateral ankle, sole of foot

• Short head of biceps femoris (posterior thigh)
• All anterior and lateral compartment leg muscles
• Extensor digitorum brevis (dorsum of foot)
• Skin: lateral leg, dorsum of foot

Clinical significance

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Sources: Gray's Anatomy for Students (Drake et al.); Histology: A Text and Atlas (Pawlina); Grainger & Allison's Diagnostic Radiology; Rosen's Emergency Medicine