Anatomy

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Chapter 2

Anatomy

section 1 Introduction

I OVERVIEW

A Osteology: The human skeleton has 206 bones: axial skeleton (80) and appendicular skeleton (126)

B Arthrology: Joints are commonly classified into three types on the basis of their freedom of movement

C Myology: classification based on the arrangement of muscle fibers

D Nerves

1. Peripheral nerves

2. Autonomic nerves

E Vessels: arteries, veins, and lymphatic vessels

section 2 Upper Extremity

Table 2-3 summarizes upper extremity innervation. Table 2-4 summarizes standard surgical approaches to the upper extremity.

Table 2-3

Summary of Upper Extremity Innervation

Nerves Muscles Innervated
Musculocutaneous (lateral cord) Coracobrachialis, biceps, brachialis
Axillary (posterior cord) Deltoid, teres minor
Radial (posterior cord) Triceps, brachioradialis, extensor carpi radialis longus and brevis
Posterior interosseous Supinator, extensor carpi ulnaris, extensor digitorum, extensor digiti minimi, abductor pollicis longus, extensor pollicis longus and brevis, extensor indicis proprius
Median (medial and lateral cord) Pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, abductor pollicis brevis, supinator head of flexor pollicis brevis, opponens pollicis, first and second lumbrical muscles
Anterior interosseous Flexor digitorum profundus (first and second), flexor pollicis longus, pronator quadratus
Ulnar (medial cord) Flexor carpi ulnaris, flexor digitorum profundus (third and fourth), palmaris brevis, abductor digiti minimi, opponens digiti minimi, flexor digiti minimi, third and fourth lumbrical muscles, interossei, adductor pollicis, deep head of flexor pollicis brevis

I SHOULDER

A Osteology

1. Scapula

image Spans the second through seventh ribs and serves as an attachment for 17 muscles and four ligaments

image Glenoid is retroverted approximately 5 degrees.

image Scapular spine: separates supraspinatus from infraspinatus.

image Coracoid: Attachments to the coracoid include the coracoacromial ligament, coracoclavicular ligaments (conoid and trapezoid [lateral]), conjoined tendon (coracobrachialis and short head of biceps), and pectoralis minor.

image Acromion

image Suprascapular notch has the superior transverse scapular ligament separating the suprascapular artery (superior) from the suprascapular nerve (inferior).

image Spinoglenoid notch has both the artery and nerve inferior to the inferior transverse scapular ligament; long-term nerve compression at the spinoglenoid notch (i.e., ganglion; assume labral disease) results in infraspinatus atrophy.

2. Clavicle

B Arthrology: one major articulation (glenohumeral joint) and several minor articulations (sternoclavicular, acromioclavicular, scapulothoracic joints)

1. Glenohumeral joint (Figure 2-1): Spheroidal, ball and socket, with the greatest joint range of motion; motion is at the expense of stability with static and dynamic restraints.

image Static restraints include the articular anatomy, glenoid labrum, negative pressure, capsule, and ligaments.

image Dynamic restraints include the rotator cuff and biceps tendon, and scapulothoracic motion is restrained.

image Important glenohumeral stabilizers summarized in Table 2-5

Table 2-5

Glenohumeral Stabilizers

Structure Function
Coracohumeral ligament Primary restraint in inferior translation of the adducted arm and to external rotation
Glenoid labrum Increases surface area, static stabilizer
Superior glenohumeral ligament Primary restraint in external rotation of the adducted or slightly abducted arm
Primary restraint in inferior translation of the adducted arm
Middle glenohumeral ligament (absent up to 30% of shoulders) Primary stabilizer in anterior translation, with the arm abducted to 45 degrees
Inferior glenohumeral ligament complex Primary stabilizer for anterior and inferior translation in abduction

2. Sternoclavicular joint:

3. Acromioclavicular joint:

image Plane/gliding joint with a fibrocartilaginous disc

image Ligaments (Figure 2-2):

image When the arm is maximally elevated, about 5 to 8 degrees of rotation is possible at the acromioclavicular joint, although the clavicle rotates approximately 40 to 50 degrees.

4. Scapulothoracic joint:

5. Intrinsic ligaments of the scapula:

C Muscles (Figure 2-3)

1. Muscles connecting the upper limb to the vertebral column: trapezius, latissimus, both rhomboid muscles, and levator scapulae

2. Muscles connecting the upper limb to the thoracic wall: both pectoralis muscles, subclavius, and serratus anterior

3. Muscles acting on the shoulder joint itself: deltoid, teres major, and the four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis)

image The rotator cuff muscles depress and stabilize the humeral head against the glenoid; all attach to the greater tuberosity except the subscapularis, which has a lesser tuberosity insertion (shoulder internal rotator).

image The shoulder internal rotators (pectoralis major, latissimus dorsi, teres major, and subscapularis) are stronger than the external rotators (teres minor and infraspinatus), which is why posterior shoulder dislocations are more common than anterior dislocations after electrical shock and seizures.

image Table 2-6 presents the specific characteristics of these muscles, and Figure 2-4 and Table 2-7 describe the four layers of shoulder musculature.

Table 2-7

Shoulder-Supporting Anatomic Layers

Layer Structures
I Deltoid; pectoralis major; trapezius
II Clavipectoral fascia; conjoined tendon, short head of biceps, and coracobrachialis
III Deep layer of subdeltoid bursa; rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis [SITS])
IV Glenohumeral joint capsule; coracohumeral ligament

D Nerves

1. Anatomy of brachial plexus (Figure 2-5)

image The brachial plexus is formed from the ventral primary rami of C5 to T1 and lies under the clavicle between the scalenus anterior and scalenus medius.

image Dorsal rami of C5 to T1 innervate the dorsal neck musculature and skin.

image Brachial plexus consists of roots, trunks, divisions, cords, and branches (mnemonic: “Ron Taylor drinks cold beer”).

image Five roots (C5 to T1, although contributions from C4 and T2 can be small)

image Three trunks (upper, middle, lower)

image Six divisions (two from each trunk)

image Three cords (named because of their anatomic relationship to the axillary artery: posterior, lateral, and medial); the termination of each cord is shown in Table 2-8

Table 2-8

Brachial Plexus Cord Terminations

Cord Termination
Lateral Musculocutaneous nerve*
Lateral pectoral nerve
Posterior Radial and axillary nerve*
Upper and lower subscapular nerve
Thoracodorsal nerve
Medial Ulnar nerve*
Medial pectoral nerve
Medial brachial cutaneous nerve
Medial antebrachial cutaneous nerve
Medial and lateral Median nerve*

*Major branches.

image Multiple branches: four preclavicular branches (from roots and upper trunk):

2. Muscle innervation: innervation of all rotator cuff muscles derived from C5 and C6 of the brachial plexus (Table 2-9; see also Table 2-3)

3. Brachial plexus injury

image Preganglionic brachial plexus lesions

image Postganglionic brachial plexus injuries

image Obstetric brachial plexus palsy (Table 2-10)

image Injury to the spinal accessory nerve (cranial nerve XI)

image Injury to the long thoracic nerve (C5 to C7)

E Vessels

1. Subclavian artery

2. Axillary artery (Table 2-11, Figure 2-6)

F Surgical approaches to the shoulder (Table 2-12; see Table 2-4):

Table 2-12

Surgical Approaches to the Shoulder

Approach Interval Structures at Risk
Anterior (Henry’s) Deltoid (axillary nerve) and pectoralis major (medial and lateral pectoral nerve) Axillary nerve limits inferior exposure; place arm in adduction and external rotation
Musculocutaneous nerve: avoid vigorous retraction and medial dissection to the conjoined tendon/coracobrachialis
Lateral Deltoid splitting (axillary nerve) Avoid deltoid split >5 cm below acromion, to avoid damaging axillary nerve
Posterior Infraspinatus (suprascapular nerve) and teres minor (axillary nerve) Dissection inferior to the teres minor puts quadrangular space structures at risk: axillary nerve and posterior humeral circumflex artery
Avoid excessive medial retraction on infraspinatus, which can injure suprascapular nerve

1. Anterior (Henry’s) approach (Figure 2-7)

image Interval: deltoid (axillary nerve) and the pectoralis major (medial and lateral pectoral nerves)

image Dissection:

image Risks:

2. Lateral approach

3. Posterior approach (Figure 2-8)

G Arthroscopy (discussed in Chapter 4, Sports Medicine)

II ARM

A Osteology: humerus

1. Humeral head:

2. Anatomic neck, directly below the humeral head, serves as an attachment for the shoulder capsule.

3. Surgical neck is lower and is more often involved in fractures.

4. Greater tuberosity is lateral to the humeral head.

5. Lesser tuberosity, located anteriorly, has only one muscular insertion: the last rotator cuff muscle, the subscapularis.

6. Bicipital groove (for the tendon of the long head of the biceps brachii) is a bony groove between the two tuberosities.

7. Humeral shaft has a posterior spiral groove (for the radial nerve) adjacent to the deltoid tuberosity and approximately 13 cm above the articular surface of the trochlea.

8. Distally, the humerus flares into medial and lateral epicondyles.

B Arthrology

1. Joints

image Elbow is composed of a hinge joint (the humeroulnar articulation) and a pivot joint (the humeroradial articulation) (Table 2-13).

Table 2-13

Elbow Joint Articulations

Articulation Components
Humeroulnar Trochlea and trochlear notch
Humeroradial Capitulum and radial head
Proximal radioulnar Radial notch and radial head

image Axis of rotation for the elbow is centered through the trochlea and capitellum and passes through a point anteroinferior on the medial epicondyle.

image Elbow joint has capsuloligamentous tissues (Figure 2-9) that are a key source of testable material.

2. Ligaments (Table 2-14)

Table 2-14image

Elbow Ligaments

Ligament Components Comments
Medial collateral Anterior bundle of MCL (ulnar collateral); posterior bundle; transverse bundle (Cooper ligament) Anterior bundle (strongest of all elbow ligaments): anterior band taut from 60 degrees of flexion to full extension, posterior band taut from 60-120 degrees of flexion
Lateral collateral LUCL; annular ligament; quadrate (annular ligament to radial neck) and oblique cord Deficiency of LUCL results in posterolateral rotator instability

LUCL, lateral ulnar collateral ligament; MCL, medial collateral ligament.

image The medial collateral ligament (MCL) (anterior, posterior, and transverse bundles) arises from the anteroinferior portion of the medial humeral epicondyle and provides stability in valgus stress.

image The lateral or radial collateral ligament (annular, radial, and ulnar parts) originates on the lateral humeral epicondyle near the axis of elbow rotation.

C Muscles: four muscles of the arm controlling elbow motion (Table 2-15)

Table 2-15

Muscles of the Arm

image

1. Flexors (biceps, brachialis, and brachioradialis); the brachialis attaches to the coronoid at 11 mm distal to the tip

2. Extensors (triceps); also helps form borders for three important spaces (Figure 2-10 and Table 2-16)

D Nerves

1. Anatomy

image Four major nerves traverse the arm; two give off branches to arm musculature, and two innervate the distal musculature (Figure 2-11). Most of the cutaneous innervation of the arm arises directly from the brachial plexus.

image Musculocutaneous nerve (lateral cord):

image Radial nerve (posterior cord):

image Median nerve (medial and lateral cords):

image Ulnar nerve (medial cord):

image Cutaneous nerves:

2. Compressive neuropathies (Table 2-17)

Table 2-17

Nerve Compression Syndromes of the Arm and Forearm

Syndrome Nerve Involved Sites of Compression
Pronator Median Supracondylar process of humerus and ligament of Struthers
Lacertus fibrosis (bicipital aponeurosis)
Pronator teres
Arch of flexor digitorum superficialis
AIN AIN of median Deep head of pronator teres
Flexor digitorum superficialis
Aberrant vessels
Accessory muscles (i.e., Gantzer’s muscles)
Cubital tunnel Ulnar Arcade of Struthers
Medial intermuscular septum
Medial epicondyle
Cubital tunnel
Proximal edge of flexor carpi ulnaris (Osborne fascia)
Deep flexor pronator aponeurosis
PIN
Radial tunnel		 PIN of radial Fibrous bands
Recurrent leash of Henry
Extensor carpi radialis brevis
Arcade of Frohse (proximal edge of superficial head of supinator)
Supinator distal margin
Superficial radial nerve Superficial radial Between the brachioradialis and extensor carpi radialis longus

AIN, anterior interosseous nerve; PIN, posterior interosseous nerve.

3. Muscle innervation (see Table 2-3)

E Vessels

F Surgical approaches to the humerus. (Table 2-18)

Table 2-18

Surgical Approaches to the Humerus

Approach Interval Structures at Risk
Anterolateral—proximal Proximal—deltoid (axillary nerve) and pectoralis major (medial and lateral pectoral nerve)
Distal—brachialis (radial and musculocutaneous nerve)		 Radial nerve; axillary nerve; anterior humeral circumflex artery
Posterior Triceps (radial nerve); lateral and long heads Radial nerve; deep brachial artery
Anterolateral—distal Brachialis (musculocutaneous and radial nerve) and brachioradialis (radial nerve) Radial nerve
Lateral Triceps (radial nerve) and brachioradialis (radial nerve) Radial nerve with proximal extension

1. Anterolateral approach to the humerus (Figure 2-13)

2. Posterior approach to the humerus (Figure 2-14)

G Surgical approaches to the elbow (Table 2-19)

1. Posterior approach to the elbow (Figure 2-15)

2. Medial approach to the elbow (Figure 2-16)

3. Lateral or posterolateral (Kocher’s) approach to the elbow (Figure 2-17)

4. Proximal extension of lateral approach

H Arthroscopy: portals for elbow arthroscopy

I Cross-sectional anatomy of shoulder and arm (Figure 2-18)

III FOREARM

A Osteology: includes the ulna and radius, which articulate with the humerus (principally the ulna) and carpi (principally the radius)

B Arthrology: proximally includes the elbow joint (discussed earlier) and distally includes the wrist

1. Distal radioulnar articulation (most stable in supination)

2. Radiocarpal joint

3. Triangular fibrocartilage complex (Figure 2-19): originates from the most ulnar portion of the radius and extends into the caput ulnae and the wrist aspect of the ulna to the base of the fifth metacarpal; includes the components listed in Table 2-20

Table 2-20

Components of the Triangular Fibrocartilage Complex

Component Origin Insertion
Dorsal and volar radioulnar ligament Ulnar radius Caput ulnae
Articular disc Radius/ulna Triquetrum
Prestyloid recess Disc Meniscus homolog
Meniscus homolog Ulna/disc Triquetrum/ulnar collateral ligament
Ulnar collateral ligament Ulna Fifth metacarpal

C Muscles (Figure 2-20 and Table 2-21): arranged according to both location and function

D Nerves

1. Anatomy: nerves of upper arm continue into the forearm (Figure 2-21, Table 2-22)

Table 2-22

Neuroanatomic Relationships in the Forearm

Nerve Relationships
Radial Between brachialis and brachioradialis
Posterior interosseous Splits supinator
Superficial radial Between brachioradialis and extensor carpi radialis longus
Median Medial to brachial artery at elbow
Anterior interosseous Splits pronator teres and runs between flexor digitorum superficialis and flexor digitorum profundus
Between flexor pollicis longus and flexor digitorum profundus
Ulnar Between flexor carpi ulnaris and flexor digitorum profundus

image Radial nerve

image Median nerve

image Ulnar nerve

image Cutaneous nerves (see Figure 2-12)

2. Compressive neuropathies of the forearm (see Table 2-17)

3. Innervation of the forearm (Table 2-23)

E Vessels (see Figure 2-11)

1. Brachial artery

image Enters cubital fossa (bordered by the two epicondyles, the brachioradialis, and the pronator teres and overlying the brachialis and supinator)

image Then divides at the level of the radial neck into the radial and ulnar arteries (Table 2-24)

Table 2-24

Vascular Anatomic Relationships in the Forearm

Artery Relationships
Radial On pronator teres deep to brachioradialis
Enters wrist between brachioradialis and flexor carpi radialis
Ulnar Proximally between FDS and FDP
Distally on FDP between flexor carpi ulnaris and FDS

FDP, flexor digitorum profundus; FDS, flexor digitorum superficialis.

2. Radial artery

3. Ulnar artery: larger of the two branches

F Surgical approaches to the forearm (Table 2-25)

Table 2-25

Surgical Approaches to the Forearm

Approach Interval Structures at Risk
Anterior (Henry’s) Brachioradialis (radial nerve) and pronator teres (median nerve)
Distally: flexor carpi radialis (median nerve)		 Ligate leash of Henry (radial artery branches)
Superficial branch of radial nerve
Dorsal posterior (Thompson’s) Extensor carpi radialis brevis (radial nerve) and extensor digitorum communis (PIN)
Distally: extensor pollicis longus		 PIN: avoid excessive retraction of supinator
Ulnar Extensor carpi ulnaris (PIN) and flexor carpi ulnaris (ulnar nerve)  

PIN, posterior interosseous nerve.

1. Anterior (Henry’s) approach (Figure 2-22)

image Interval: between the brachioradialis (radial nerve) and pronator teres or FCR distally (median nerve)

image Dissection:

image Risks:

2. Dorsal (posterior; Thompson’s) approach (Figure 2-23)

3. Exposure of the ulna

G Cross-sectional diagrams of proximal forearm (Figure 2-24), mid-forearm (Figure 2-25), and distal forearm (Figure 2-26)

IV WRIST AND HAND*

A Osteology

1. Carpal bones

image Ossification begins at the capitate (usually present at 1 year of age) and proceeds in a counterclockwise direction, according to posteroanterior radiographs of the right hand.

image Hamate is the second carpus to ossify (by ages 1 to 2 years).

image Triquetrum (by age 3 years)

image Lunate (by ages 4 to 5 years)

image Scaphoid (by age 5 years)

image Trapezium (by age 6 years)

image Trapezoid (by age 7 years)

image Pisiform, which is a large sesamoid bone, is the last to ossify (by age 9 years).

image Several key features are important to recognize in the individual carpal bones (Table 2-26).

Table 2-26

Carpal Features

Carpal Bone Distinctive Features Number of Articulations
Scaphoid Tubercle (TCL, APB), distal vascular supply 5
Lunate Half-moon–shaped 5
Triquetrum Pyramid-shaped 3
Pisiform Spheroidal (TCL, FCU) 1
Trapezium FCR groove, tubercle (opponens, APB, flexor pollicis brevis, TCL) 4
Trapezoid Wedge-shaped 4
Capitate Largest bone, central location 7
Hamate Hook (TCL) 5

APB, abductor pollicis brevis; FCR, flexor carpi radialis; FCU, flexor carpi ulnaris; TCL, transverse carpal ligament.

2. Metacarpals

3. Phalanges

B Arthrology

1. Radiocarpal (wrist) joint

image The wrist is an ellipsoid joint and made up of the distal radius, scaphoid, lunate, triquetrum, and ligamentous structures (Table 2-28).

Table 2-28

Radiocarpal Wrist Ligaments

Structure Attachments Distinctive Features
Articular capsule Surrounds joint Reinforced by volar and dorsal radiocarpal ligament
Volar (radiocarpal ligament) Radius, ulna, scaphoid, lunate, triquetrum, capitate Oblique ulnar, strong
Dorsal radiocarpal ligament Radius, scaphoid, lunate, triquetrum Oblique radial, weak
Ulnar collateral ligament Ulna, triquetrum, pisiform, transverse carpal ligament Fan-shaped, two fascicles
Radial collateral ligament Radius, scaphoid, trapezium, transverse carpal ligament Radial artery adjacent

image The palmar/volar radiocarpal ligament is the strongest supporting structure, although it has a weak area on the radial side (the space of Poirier) that lends less support to the scaphoid, lunate, and trapezoid (Figure 2-27).

2. Intercarpal joints

image Proximal row

image Pisiform articulation

image Distal row

image Midcarpal joint

3. Carpometacarpal (CMC) joints

4. Metacarpophalangeal joints

5. Interphalangeal joints

6. Other important structures

image Extensor retinaculum

image This structure covers the dorsum of the wrist and contains six synovial sheaths (Figure 2-28).

image

Figure 2-28 Extensor compartments of the wrist (1 to 6). See Table 2-29. APL, abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; EDC, extensor digitorum communis; EDM, extensor digiti minimi; EPB, extensor pollicis brevis; EPL, extensor pollicis longus. (Modified from Miller MD, et al: Orthopaedic surgical approaches, Philadelphia, 2008, Saunders, Figure HW-6.)

image Orientation of the extensor tendons at the wrist is a key testable item (Table 2-29).

Table 2-29

Dorsal Wrist Compartments

Compartment Contents Pathologic Condition
I Abductor pollicis longus, extensor pollicis brevis De Quervain’s tenosynovitis
II Extensor carpi radialis longus, brevis Extensor tendinitis (intersection syndrome)
III Extensor pollicis longus Rupture at Lister’s tubercle (after wrist fractures)
Drummer’s tendinitis of the wrist
IV Extensor digitorum communis, extensor indicis proprius Extensor tenosynovitis
V Extensor digiti minimi Rupture (rheumatoid arthritis: Vaughn-Jackson syndrome)
VI Extensor carpi ulnaris Snapping at ulnar styloid

image The first dorsal compartment contains the APL and the EPB.

image The EPB tendon is ulnar to the APL tendon (the APL frequently has multiple tendon slips, which should be addressed during release for de Quervain’s tenosynovitis).

image In the second dorsal compartment, the ECRL tendon is radial to the ECRB tendon. Thus, the EPL tendon is ulnar to the ECRB tendon at the wrist level.

image The anatomic snuffbox is bordered by tendons of the first and third dorsal wrist compartments; the EPB tendon serves as the radial snuffbox border, and the EPL tendon serves as the ulnar border.

image The posterior interosseous nerve is contained within the floor of the fourth dorsal wrist compartment.

image Transverse carpal ligament (TCL)

image This is one component of the flexor retinaculum, which serves as the roof of the carpal tunnel (Figure 2-29).

image It is attached medially to the pisiform and the hook of the hamate and laterally to the tuberosity of the scaphoid and the ridge of the trapezium.

image Carpal tunnel decreases in volume with wrist flexion.

image This tunnel contains the median nerve and nine tendons (one FPL, four FDS, and four FDP).

image In the tunnel, the FDS tendons of the middle and ring fingers are volar to the tendons of the index and small fingers.

image The flexor retinaculum also forms the floor of Guyon’s canal, which is bordered as well by the hook of the hamate and the pisiform and is covered by the volar carpal ligament; the ulnar nerve can become entrapped in this canal (Figure 2-30).

image Triangular fibrocartilage complex

image Intrinsic apparatus (Table 2-30)

Table 2-30image

Intrinsic Apparatus

Structure Attachments Significance
Sagittal bands Covers MCP joint Allows MCP extension
Transverse (sagittal) Volar plate fibers Allows MCP flexion (interossei)
Lateral bands Covers PIP joint Allows PIP extension (lumbrical muscles)
Oblique retinacular ligament (Landsmeer) A4 pulley, terminal tendon Allows DIP extension (passive)

A4, annular 4; DIP, distal interphalangeal; MCP, metacarpophalangeal; PIP, proximal interphalangeal.

image Flexor sheath (Figure 2-32)

C Muscles (Table 2-31); origins and insertions (Figure 2-33)

D Nerves (Figure 2-34)

1. Anatomy

image Median nerve

image Ulnar nerve

image Sensation to the thumb

2. Innervation of the wrist and hand (Table 2-32)

Table 2-32

Innervation of the Wrist and Hand

Nerve Muscles Innervated
Median (medial and lateral cord) Abductor pollicis brevis, superficial head of flexor pollicis brevis, opponens pollicis, first and second lumbrical muscles
Ulnar (medial cord) Abductor digiti minimi, opponens digiti minimi, flexor digiti minimi, third and fourth lumbrical muscles, interossei, adductor pollicis, deep head of flexor pollicis brevis

E Vessels (see Figure 2-34)

F Surgical approaches to the wrist and hand (Table 2-33)

Table 2-33

Surgical Approaches to the Wrist

Approach Interval Structures at Risk
Dorsal wrist Third (extensor pollicis longus) and fourth (extensor digitorum communis) compartments Transection of the innervation of the posterior interosseous nerve to the wrist capsule can be performed
Volar wrist Flexor carpi radialis Palmar cutaneous branch of median nerve
Volar scaphoid Flexor carpi radialis and radial artery Radial artery
Dorsolateral scaphoid First and third compartments Superficial radial nerve and radial artery

1. Dorsal approach to the wrist (Figure 2-35)

2. Carpal tunnel release (Figure 2-36)

3. Volar (Russé’s) approach to the scaphoid

4. Dorsolateral approach to the scaphoid

5. Volar approach to the flexor tendons (Bunnell’s)

6. Midlateral approach to the digits

G Arthroscopy

section 3 Spine

I SPINE

A Osteology

1. Thirty-three vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 4 fused coccygeal

image Normal curves are cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis.

image Vertebral bodies generally increase in width in a craniocaudad direction, with the exception of T1 to T3.

image Important spine topographic landmarks are listed in Table 2-34.

Table 2-34image

Spine Vertebral Bodies

Topographic Landmark Spinal Level
Mandible C2-C3
Hyoid cartilage C3
Thyroid cartilage C4-C5
Cricoid cartilage C6
Vertebra prominens C7
Scapular spine T3
Distal tip of scapula T7
Iliac crest L4-L5

2. Cervical spine

image The atlas (C1) has no vertebral body and no spinous process.

image Highest percentage of neck flexion and extension occurs at the occiput-C1 articulation (50% of the total).

image Axis (C2) develops from five ossification centers, with an initial cartilaginous junction between the dens and vertebral body (subdental synchondrosis) that fuses at 7 years of age.

image Atlantoaxial articulation is responsible for the majority of neck rotation; 50% of total rotation occurs at the C1-C2 articulation.

image Atlantoaxial joint is diarthrodial.

image C2 to C7 vertebrae have foramina in each transverse process and bifid spinous processes (except for the C7 nonbifid posterior spinous process [vertebral prominens]).

image The vertebral artery travels in the transverse foramina of C6 to C1.

image Carotid (Chassaignac’s) tubercle is found at C6.

image The diameter of the cervical spine canal is normally 17 mm, and the cervical cord may become compromised when the diameter is reduced to less than 13 mm.

3. Thoracic spine

4. Lumbar spine

5. Sacrum

6. Coccyx

B Arthrology

1. Spinal ligaments

image Anterior longitudinal ligament (ALL)

image Posterior longitudinal ligament

image Ligamentum flavum

image Supraspinous, interspinous, and intertransverse ligaments

1. Spine stability (Denis model): the three-column system (Table 2-35)

Table 2-35

Denis Model of Spine Columns

Column Composition
Anterior Anterior longitudinal ligament, anterior two thirds of annulus and vertebral body
Middle Posterior third of body and annulus, posterior longitudinal ligament
Posterior Pedicles, facets and facet capsules, spinous processes, posterior ligaments that include interspinous and supraspinous ligaments, ligamentum flavum

2. Specialized ligaments

image Atlanto-occipital joint

image Atlantoaxial joint

image The transverse ligament is the major stabilizer of the atlantoaxial joint.

image This articulation is further stabilized by the apical ligament (longitudinal), which, together with the transverse axial ligament, composes the cruciate ligament.

image In addition, a pair of alar (“check”) ligaments runs obliquely from the tip of the dens to the occiput (Figure 2-37).

image An atlanto-dens interval of more than 7 to 10 mm or a posterior space of less than 13 mm is a relative contraindication to elective orthopaedic surgery, and the spine should be stabilized first.

image Common measurements in C1-C2 disorders are covered in Figure 8-2.

image Iliolumbar ligament

4. Facet (apophyseal) joints

image The orientation of the facets of the spine dictates the plane of motion at each relative level.

image Facet orientation varies with the spinal level (Table 2-36).

Table 2-36

Orientation of Spine Facets

Spinal Level Orientation of Sagittal Facet Orientation of Coronal Facet
Cervical 35 Degrees at C2, increasing to 55 degrees at C7 Neutral, 0 degrees
Thoracic 60 Degrees at T1, increasing to 70 degrees at T12 20 Degrees posterior
Lumbar 137 Degrees at L1, decreasing to 118 degrees at L5 45 Degrees anterior

image In the cervical spine, the superior articular facet is anterior and inferior to the inferior articular process of the vertebra above; the nerve roots exit near the superior articulating process.

image In the lumbar spine, the superior articular facet is anterior and lateral to the inferior articular facet.

5. Intervertebral discs

C Muscles (Table 2-37)

Table 2-37

Spinal Muscle Relationships

Muscle Relationships
Longus capitis Anterior to longus colli
Posterior to sympathetic chain
Longus colli Anterior to vertebral artery
Posterior to longus capitis

1. Neck: functional classification (anterior and posterior regions)

image Anterior neck region

image This region contains the superficial platysma muscle (cranial nerve VII innervated), stylohyoid and digastric muscles (cranial nerve VII innervated) above the hyoid, and “strap” muscles below the hyoid.

image Strap muscles include the sternohyoid and omohyoid in the superficial layer and the thyrohyoid and sternohyoid in the deep layer; all are innervated by the ansa cervicalis (C1 to C3).

image The sternocleidomastoid muscle (cranial nerve XI and ansa) runs obliquely across the neck, rotating the head to the contralateral side.

image The anterior triangle (borders: sternocleidomastoid, midline of the neck, and lower border of the mandible) is the largest area.

image Three smaller triangles are as follows:

image Posterior neck region

2. Back

D Nerves

1. Spinal cord

image General anatomy

image The spinal cord extends from the brainstem to the inferior border of L1, where it terminates as the conus medullaris.

image A small filum terminale continues distal with the surrounding nerve roots contained within a common dural sac (cauda equina) to its termination in the coccyx.

image The spinal cord is enclosed within the bony spinal canal with variable amounts of space (greatest in the upper cervical spine).

image The cord also varies in diameter (widest at the origin of the plexuses).

image In cross-section, the cord is observed to have both geographic and functional boundaries (Figure 2-38). It is divided in the midline anteriorly by a fissure and posteriorly by the sulcus.

image Functional anatomy: The functions of the ascending (sensory) and descending (motor) tracts are summarized in Table 2-38.

Table 2-38

Spinal Cord Tracts

image

image The posterior funiculi (dorsal columns) are located dorsally and receive ascending fibers, which deliver deep tactile, proprioceptive, and vibratory sensations.

image The lateral spinothalamic tract transmits sensations of pain and temperature.

image Descending in the lateral corticospinal tract are fibers that transmit instructions for voluntary muscle contraction.

image The ventral (anterior) spinothalamic tract transmits light tactile sensation.

image Ventral (anterior) corticospinal tract delivers cortical messages of voluntary contraction.

image Deficits associated with patterns of incomplete spinal cord injury are predictable from the anatomy of the ascending and descending tracts.

image The prognosis with incomplete spinal cord injury is unaffected by the presence or absence of the bulbocavernosus reflex.

image Incomplete spinal cord injury patterns are summarized in Table 2-39.

Table 2-39

Patterns of Incomplete Spinal Cord Injury

Pattern of Injury Functional Deficit Recovery
Central (most common) Upper extremity affected more than lower extremity, usually quadriparetic with sacral sparing; flaccid paralysis of upper extremity and spastic paralysis of lower extremity 75%
Anterior Complete motor deficit 10% (worst prognosis)
Brown-Séquard Unilateral cord injury with ipsilateral motor deficit, contralateral pain, and temperature deficit (two levels below injury) >90% recovery

image Spinal cord injury distal to the conus medullaris may permanently interrupt the bulbocavernosus reflex.

2. Nerve roots (Figure 2-39)

image There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

image Within the subarachnoid space, the dorsal root (and ganglia) and ventral roots converge to form the spinal nerve.

image After exiting the foramen, the spinal nerve gives off dorsal primary rami, which supply the muscles and skin of the neck and back regions.

image Innervation of structures within the spinal canal—including the periosteum, meninges, vascular structures, and articular connective tissue—is from the sinuvertebral nerve.

image Ventral rami supply the anteromedial trunk and limbs.

image With the exception of the thoracic nerves, the ventral rami are grouped in plexuses before delivering sensorimotor functions to a general region.

image In the cervical spine, the numbered nerve exits at a level above the pedicle of the corresponding vertebral level (e.g., the C2 nerve exits at the level of vertebrae C1 to C2).

image In the lumbar spine, the nerve root traverses the respective disc space above the named vertebral body and exits the respective foramen under the pedicle (Figure 2-40).

image Herniated discs usually impinge on the traversing nerve root and facet joint.

image The L5 nerve root is relatively fixed to the anterior sacral ala and can be damaged by sacral fractures and errant, anteriorly placed iliosacral screws.

image Key testable neurologic levels are listed in Table 2-40.

Table 2-40image

Key Testable Neurologic Levels

Neurologic Level Representative Muscle Reflex
C5 Deltoid Biceps
C6 Wrist extension Brachioradialis
C7 Wrist flexion Triceps
C8 Finger flexion  
T1 Interossei  
L4 Tibialis anterior Patellar
L5 Toe extensors  
S1 Peroneal Achilles

image Nerve root compression: A summary of the findings of nerve root compression is highlighted in Chapter 8, Spine (Tables 8-2 [cervical] and 8-7 [lumbar]). Dermatomes are key testable items (see Figure 2-12).

3. Sympathetic chain

image Cervical sympathetic chain posterior and medial to the carotid sheath

image Three ganglia of cervical sympathetic chain: superior, middle, and inferior (Table 2-41)

Table 2-41

Cervical Sympathetic Ganglia

Ganglion Location Comments
Superior C2-C3 Largest
Middle C6 Variable
Inferior C7-T1 Stellate

image Sympathetic ganglia: 11 in the thoracic region, 4 in the lumbar region, and 4 in the sacral region

E Vessels

1. Spinal blood supply from segmental arteries

2. Vertebral artery (a branch of the subclavian artery)

3. Artery of Adamkiewicz (great anterior medullary artery)

4. Spinal cord arterial supply

5. Venous drainage of the vertebral bodies

F Surgical approaches to the spine (Table 2-42, Figure 2-41)

Table 2-42

Surgical Approaches to the Spine

Approach Interval Structures at Risk
Anterior cervical Carotid sheath and the trachea Recurrent laryngeal nerve
Sympathetic ganglion
Posterior cervical Midline approach between paracervical muscle Vertebral artery
Anterior thoracic Transverse between ribs two levels above surgical site Intercostal neurovascular bundle; to avoid, dissect over top of rib
Posterior thoracolumbar Midline approach over spinous processes Posterior primary rami and segmental vessels; protect nerve root
Anterior lumbar (transperitoneal) Between segmentally innervated rectus abdominis Presacral plexus of parasympathetic nerve

1. Anterior approach to the cervical spine

image Incision: transverse and based on the desired level (e.g., for C5, the carotid triangle should be entered)

image Dissection

image Risks: Injury to the recurrent laryngeal nerve with right-sided approaches (paralysis is identified by a hoarse, scratchy voice caused by unilateral vocal cord paralysis, visualized with direct laryngoscopy).

2. Posterior approach to the cervical spine

3. Anterior (transthoracic) approach to the thoracic spine

4. Posterior approach to the thoracolumbar spine

image Incision: straight, midline, over the spinous processes and carried down through the thoracolumbar fascia

image Dissection:

image Risks: injury to the posterior primary rami (near the facet joints) and segmental vessels (anterior to the plane connecting the transverse processes)

5. Anterior approach to the lumbar spine (transperitoneal)

6. Anterolateral approach to the lumbar spine (retroperitoneal)

image Incision: oblique, centered over the twelfth rib to the lateral border of the rectus abdominis muscle

image Dissection:

image Risks: injury to the sympathetic chain (medial to the psoas and lateral to the vertebral body) and ureters (between the peritoneum and psoas fascia)

7. Anatomy important in placement of halo pins

image The optimal position for the placement of anterolateral halo pins is approximately 1 cm superior to the orbital rim in the outer two thirds of the orbit below the equator of the skull (Figure 2-42).

image With this pin position, the temporal fossa and temporalis muscle are situated laterally, and the supraorbital nerve, supratrochlear nerve, and frontal sinus are situated medially.

image The supraorbital nerve is lateral to the supratrochlear nerve, which lies anterior to the frontal sinus.

image The most commonly injured cranial nerve with halo traction is the abducens (cranial nerve VI); injury is recognized from the loss of lateral gaze.

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