Hand Anatomy/ Embryology

Question 1

What tissues comprise the limb bud?

Answer 1

Mesenchyme covered by ectoderm. The limbs grow by proliferation of mesenchyme.

Question 2

Which genes regulate patterning in limb development?

Answer 2

Homeobox-containing (HOX ) genes.

Question 3

When do the limb buds first appear?

Answer 3

Toward the end of the fourth week of development, at which time a group of mesenchymal cells in the lateral
mesoderm are activated. The buds are visible by day 26 to day 27.

Question 4

When is the critical period for upper limb development?

Answer 4

Twenty-four to thirty-six days after fertilization.

Question 5

When are finger buds visible?

Answer 5

The end of week 6.

Question 6

When does ossification occur?

Answer 6

Between weeks 8 and 12, ossification of the cartilaginous framework occurs. Epiphyses gradually ossify until the
termination of puberty.

Question 7

What are the last bones to ossify within their cartilaginous framework?

Answer 7

The carpal bones in which ossification begins during the first year of life.

Question 8

Does sensory or motor innervation occur first?

Answer 8

Sensory axons enter the limb after motor axons and use these for guidance.

Question 9

When is nervous system myelination completed?

Answer 9

Around 2 years of age.

Question 10

What is responsible for proximodistal development?

Answer 10

The apical ectodermal ridge (AER), which expresses endogenous fibroblast growth factors.

Question 11

What is responsible for radioulnar development?

Answer 11

The zone of polarizing activity, found in the posterior margin of the limb bud, and activated by fibroblast growth
factors from the AER that cause Sonic hedgehog (SHH) gene expression.

Question 12

What is responsible for dorsoventral development?

Answer 12

Expression of WNT7 and engrailed-1 (EN1) from the dorsal and the ventral epidermis, respectively.

Question 13

What process is responsible for syndactyly occurrence?

Answer 13

Apoptosis, likely mediated by bone morphogenic proteins signaling TGF-􏰁.

Question 14

How common is syndactyly and which digits are most commonly affected?

Answer 14

Occurs in one in 2,200 births, most commonly affecting the webspace between the middle and ring fingers.

Question 15

Which arteries supply the limb buds?

Answer 15

Dorsal intersegmental arteries arising from the aorta.

Question 16

Outline the American Society for Surgery of the Hand classification of congenital deformities of the hand.

Answer 16

The original classification scheme was proposed by Swanson:
i. Failure of formation
ii. Failure of differentiation
iii. Duplication iv. Overgrowth
v. Undergrowth
vi. Constriction band syndromes
vii. Generalized anomalies and syndromes

Question 17

What is the anatomic snuffbox?

Answer 17

The area bounded by the tendons of the abductor pollicis longus and extensor pollicis brevis anteriorly and the tendon of the extendor pollicis longus posteriorly. The floor is formed by the scaphoid and trapezium, and it is a frequent site of tenderness after scaphoid fracture

Question 18

Where is the metacarpophalangeal (MCP) joint relative to the MCP palmar flexion crease?

Answer 18

Proximal.

Question 19

What is the “fixed unit” of the hand?

Answer 19

The distal carpal row and second and third metacarpals.

Question 20

What is a felon?

Answer 20

A subcutaneous abscess of the distal digital pulp. It involves the septal compartments and causes compartment
syndrome of the distal phalangeal pulp. If the pad is not involved, then it is an “apical infection” instead.

Question 21

What is the normal value for moving two-point discrimination of the fingertip?

Answer 21

2 to 3 mm, with best discrimination occurring in individuals in their 20s and in ulnar sided digits. A score of 7 out of 10 correct answers determines the value of two-point discrimination.

Question 22

What is the perionychium? Paronychium? Hyponychium? Eponychium? Lunula?

Answer 22

The perionychium includes the nail bed, nail fold, eponychium, paronychium, and hyponychium. The paronychium is the skin on either side of the nail bed. The hyponychium is skin distal to the nail bed. The eponychium is the skin proximal to the nail that covers the nail fold. The white arc in the proximal nail is the lunula and is the distal extent of the germinal matrix. Distal to this is the sterile matrix

Question 23

Which tissues contribute to nail growth?

Answer 23

The germinal matrix produces approximately 90% of the nail, while the sterile matrix adds a thin layer of cells
underneath the nail to ensure its adherence.

Question 24

What is a paronychia?

Answer 24

Acute paronychia is infection of the paronychial tissues.

Question 25

How long does a nail take to grow?

Answer 25

Approximately 6 months.

Question 26

Name the median innervated intrinsic muscles of the hand.

Answer 26

The intrinsic muscles of the hand are innervated by the ulnar nerve, except the radial two lumbricals, opponens pollicis, abductor pollicis brevis, and superficial head of the flexor pollicis brevis

Question 27

What are the functions of the palmar and dorsal interossei?

Answer 27

The interossei originate from the metacarpal shafts and form the lateral bands, aiding in the function of the lumbrical muscles. In addition, the Palmar interossei ADduct the fingers and the Dorsal interossei ABduct the fingers

Question 28

Name the thenar muscles. What order are they in?

Answer 28

Superficial to deep, they are: abductor pollicis brevis flexor pollicis brevis opponens pollicis adductor pollicis

Question 29

Name the hypothenar muscles.

Answer 29

Palmaris brevis Abductor digiti minimi Flexor digiti minimi brevis r Opponens digiti minimi

Question 30

Name the muscles of the mobile wad.

Answer 30

Brachioradialis, extensor carpi radialis brevis, extensor carpi radialis longus.

Question 31

How can you test for extensor pollicis longus (EPL) function?

Answer 31

Ask the patient to rest their hand palm down on a table and lift the thumb—only the EPL can move lift the thumb dorsal to the plane of the palm.

Question 32

What are Cleland’s and Grayson’s ligaments?

Answer 32

Cleland’s ligaments connect the digital fascia to the sides of the phalanges and are not involved in Dupuytren disease. They lie dorsal to the neurovascular bundle. Grayson’s ligaments connect the tendon sheath to the digital fascia and are often involved in Dupuytren disease. They lie volar to the neurovascular bundle.

Question 33

What are natatory ligaments?

Answer 33

This is another name for the superficial transverse metacarpal ligaments and these help to create the webspaces. These coalesce distally with the spiral bands and may be involved in Dupuytren’s disease.

Question 34

What are the boundaries and contents of the carpal tunnel?

Answer 34

1. Roof: transverse carpal ligament 4. Ulnar border: pisiform and hamate 2. Floor: carpal bones 5. Contents: the median nerve and nine tendons 3. Radial border: scaphoid and trapezium (flexor digitorum superficialis [FDS], flexor digitorum profundus [FDP], and flexor pollicis longus [FPL])

Question 35

What are the boundaries and contents of Guyon’s canal?

Answer 35

1. Roof: volar carpal ligament and pisohamate ligament 2. Floor: transverse carpal ligament 3. Ulnar wall: pisiform 4. Contents: ulnar nerve and artery

Question 36

What is the oblique retinacular ligament?

Answer 36

A ligament running between the flexor tendon sheath at the proximal phalanx and the terminal extensor tendon, linking flexion and extension between the interphalangeal joints.

Question 37

What is the transverse retinacular ligament?

Answer 37

They are ligaments that span the edge of the flexor tendon sheath to the conjoined lateral bands, preventing dorsal shift of the lateral bands, and thus preventing a swan neck deformity

Question 38

What are the pulleys? What do they do? How many pulleys are there? Which pulleys are the most important?

Answer 38

Thickened areas of the synovial sheath. They prevent bowstringing of the flexor tendons. There are five annular and four cruciate pulleys in each of the fingers and two annular and one oblique pulley in the thumb. A2, A4, and the oblique pulleys are essential to prevent bowstringing

Question 39

What is a boutonniere deformity?

Answer 39

PIP hyperflexion with DIP hyperextension, which may be caused by extensor mechanism injury, synovitis, or iatrogenic causes.

Question 40

What is a swan neck deformity?

Answer 40

PIP joint hyperextension with DIP joint flexion, which may be due to multiple potential causes including FDS loss, synovitis, mallet deformity, or iatrogenic causes.

Question 41

Name the seven potential spaces and two bursae in the hand.

Answer 41

1. thenar space 2. midpalmar space 3. hypothenar space 4. interdigital webspace 5. dorsal subcutaneous space 6. dorsal subaponeurotic space 7. Parona’s space In addition to the above, the radial and ulnar bursae.

Question 42

What is a collar button abscess?

Answer 42

A webspace abscess in which infection tracks both volarly and dorsally. These infections usually start on the volar surface but dense attachments of the palmar fascia to the skin limit the volar extension causing it to track dorsally forming an hourglass shape.

Question 43

What is a horseshoe abscess and why does it occur?

Answer 43

This is an abscess formed by communication or rupture between the ulnar and the radial bursae of the hand through Parona’s space (region between FPL, FDP, and pronator quadratus).

Question 44

What is the ultimate result of an untreated compartment syndrome?

Answer 44

Decreased capillary perfusion pressure leads to tissue necrosis and ultimately may result in a Volkmann’s contracture.

Question 45

What are Kanavel’s signs?

Answer 45

These are used to diagnose infectious tenosynovitis: 1. Pain and tenderness along the course of the tendon 2. Flexed resting posture 3. Uniform and symmetric swelling 4. Pain on passive extension

Question 46

What is the safe position for splinting the hand and why?

Answer 46

The intrinsic plus or safe position: the metacarpophalangeal joints are flexed to 60◦ to 70◦, the interphalangeal joints are fully extended, the wrist is at 10◦ less than maximal extension, and the thumb is abducted. Owing to the nature of the cam of the joint, the collateral ligaments of the metacarpophalangeal joints are maximally stretched when the joint is fully flexed and of the interphalangeal joints are maximally stretched when the joint is fully extended

Question 47

Which is the most mobile carpometacarpal (CMC) joint?

Answer 47

The first CMC joint.

Question 53

Where are the epiphyses in the bones of the hand?

Answer 53

Proximally on all phalanges and the thumb metacarpal, and distally on the other metacarpals.

Question 53

What extensor compartments is Lister’s tubercle between?

Answer 53

The second and third extensor compartments.

Question 53

What is a Seymour fracture?

Answer 53

A juxtaepiphyseal fracture of the terminal phalanx of the finger. The terminal tendon is attached to the proximal epiphyseal fragment, and the profundus tendon, attached to the distal fragment, causes it to flex.

Question 53

What is an extra octave fracture?

Answer 53

A Salter–Harris 2 fracture of the proximal phalanx of the small finger with ulnar angulation of the small finger.

Question 53

What is a jersey finger fracture?

Answer 53

Traumatic avulsion of the flexor digitorum profundus tendon.

Question 53

What is a boxer’s fracture?

Answer 53

Metacarpal neck fractures of the ulnar digits.

Question 53

Name the types of mallet injuries.

Answer 53

Type I : closed with tendon rupture Type II: laceration Type III: abrasion with tissue loss Type IV: with fracture

Question 54

What is a Stener lesion?

Answer 54

This occurs in ulnar collateral ligament injury in the thumb when the adductor aponeurosis interposes between the distally avulsed ligament and its insertion into the base of the proximal phalanx

Question 55

What are the origins and insertions of the lumbrical muscles? What is their function?

Answer 55

Originate from the flexor digitorum profundus tendons and insert into the radial aspect of the extensor mechanism distal to the metacarpophalangeal joint. They help flex the metacarpophalangeal joint and extend the interphalangeal joint.

Question 56

What prevents profundus tendons from retracting fully when cut?

Answer 56

They may be tethered by the lumbricals, vinculae, and adjacent tendons (with which they share a muscle belly).

Question 57

How are the flexor tendons arranged in the carpal tunnel?

Answer 57

The FDP tendons lie on the floor side by side. The FDS tendons to the ring and middle fingers are superficial to the index and small fingers. FPL lies radially.

Question 58

How often is the palmaris longus tendon present?

Answer 58

Between 7% and 20% of people do not have a palmaris longus.

Question 59

What is Camper’s chiasm?

Answer 59

This is where the FDS slips that have bifurcated (to allow passage of the FDP tendon) come back together and rejoin on the volar surface of the middle phalanx. Proximal to this location, the profundus tendon is deep to the superficialis tendon.

Question 60

How is the FDP to the index finger unique?

Answer 60

It has an independent muscle belly.

Question 61

How do flexor tendons receive nutrition?

Answer 61

They receive nutrition through the parietal paratenon, bony insertions, muscle bellies, and the longitudinal vincular system on the dorsal aspect of the tendon—including the vinculum brevis superficialis, vinculum brevis profundus, vinculum longum superficialis, and vinculum longum profundus

Question 62

What are the flexor tendon zones

Answer 62

Zone 1: distal to FDS insertion Zone 2: from the A1 pulley to FDS insertion Zone 3: from the distal edge of the carpal ligament to the proximal edge of the A1 pulley Zone 4: the carpal tunnel Zone 5: proximal to the carpal tunnel

Question 63

Name the insertions of the extrinsic extensors.

Answer 63

The base of the proximal, middle, and distal phalanges.

Question 64

Name the extensor tendon zones

Answer 64

Zone I: distal interphalangeal joint Zone II: middle phalanx Zone III: proximal interphalangeal joint (metacarpophalangeal joint in thumb) Zone IV: proximal phalanx (metacarpal in thumb) Zone V: metacarpophalangeal joint (carpometacarpal join in thumb) Zone VI: metacarpal Zone VII: dorsal retinaculum/carpal bones Zone VIII: distal forearm Zone IX: mid and proximal forearm

Question 65

How many dorsal extensor compartments are there at the wrist? What are their contents?

Answer 65

1. APL, EPB 2. ECRL, ECRB 3. EPL 4. EDC, EIP 5. EDM 6. ECU

Question 66

Which digits have their own unique extensor tendons? Where are these located?

Answer 66

The index and small fingers each have proprius tendons (EIP and EDM) that typically lie both ulnar and volar to their EDC tendons. The EIP tendon typically has a more distal muscle belly than its EDC counterpart.

Question 67

What is a juncturae tendinae?

Answer 67

Connections between the common extensor tendons that prevent independent finger extension.

Question 68

What is the primary metacarpophalangeal joint extensor?

Answer 68

The extrinsic system, while the intrinsic system is its primary flexor.

Question 69

Name the vascular arches in the hand.

Answer 69

1. Superficial palmar arch (anastomosis between the ulnar artery and the superficial branch of the radial artery). 2. Deep palmar arch (extension of the radial artery after giving off the princeps pollicis artery). 3. Dorsal carpal arch (anastomosis of the radial and ulnar dorsal carpal branches).

Question 70

Where do digital arteries originate?

Answer 70

Common digital arteries originate from the superficial palmar arch.

Question 71

How can radioulnar anastomosis be tested?

Answer 71

An Allen’s test is used—the ulnar and radial arteries are occluded by the examiner, blood is removed from the hand by making a fist, and each artery is released in turn to test patency.

Question 72

Why may an upper arm tourniquet not sufficiently prevent bleeding in the hand?

Answer 72

Blood may be shunted via nutrient vessels present in the humerus. A tourniquet should be placed as high as possible to avoid this.

Question 73

What is the dominant vascular supply to the hand?

Answer 73

Most commonly the ulnar artery—66% ulnar artery, 30% radial artery, and 4% persistent median artery.

Question 74

Which are the dominant proper digital arteries for each digit?

Answer 74

1. thumb and index: ulnar digital artery 2. middle and ring: codominance 3. small finger: radial digital artery

Question 75

Name the draining lymphatic beds of the arm.

Answer 75

Axillary, supraclavicular, and infraclavicular.

Question 76

Between which musculotendinous structures is the radial artery located at the wrist and distal forearm?

Answer 76

Between the brachioradialis and the flexor carpi radialis.

Question 77

Between which musculotendinous structures is the posterior interosseous artery located in the forearm?

Answer 77

Between extensor carpi ulnaris and extensor digiti minimi.

Question 78

Where does the motor branch of the median nerve arise within the carpal tunnel?

Answer 78

Around half are extraligamentous, approximately 30% subligamentous, and approximately 20% transligamentous.

Question 79

Where is the palmar branch of the median nerve found?

Answer 79

This sensory nerve arises approximately 6 cm proximal to the transverse carpal ligament between FCR and palmaris longus and running distally along on radial aspect of the carpal tunnel. Overly radial placement of a carpal tunnel release incision may cause injury to this nerve.

Question 80

What does the anterior interosseous nerve supply? What does the posterior interosseous nerve supply?

Answer 80

The anterior is a branch of the median nerve supplies FPL, FDS to middle/long fingers, and pronator quadratus. The posterior is a branch of the radial nerve and supplies ECRB, EDC, EDM, ECU, supinator, APL, EPL, EPB, and EIP.

Question 81

Which nerve supplies the flexors of the hand and wrist?

Answer 81

The median nerve supplies all flexors except the flexor carpi ulnaris and flexor digitorum profundus to the ring and small fingers (which are supplied by the ulnar nerve).

Question 82

Are digital nerves dorsal or volar to digital arteries?

Answer 82

Volar.

Question 83

List the Sunderland classification of nerve injuries.

Answer 83

Grade I is a neurapraxia (the axon is preserved with altered conduction). Grade II is an axonotmesis (the axonal integrity is disrupted). Grade III is neurotmesis (disruption of supporting structures) with preservation of the perineurium. Grade IV is neurotmesis with preservation of the epineurium. Grade V is complete transaction of the nerve trunk. Grade VI (MacKinnon modification) is a mixed injury.

Question 84

What is a Riche–Cannieu anastomosis?

Answer 84

An communication between the deep branch of the ulnar nerve and the recurrent motor branch of the median nerve in the palm.

Question 85

What is a Martin–Gruber anastomosis?

Answer 85

An communication of motor fibers from the median to ulnar nerve in the forearm.

Question 86

Name the possible sites of ulnar nerve compression in ulnar nerve entrapment.

Answer 86

These include the following: 1. intermuscular septum (arcade of Struthers, medial septum, medial head of triceps) 2. medial epicondyle 3. epicondylar groove 4. cubital tunnel (between the heads of the flexor carpi ulnaris) 5. flexor–pronator aponeurosis 6. Guyon’s canal

Question 87

Name the possible sites of median nerve compression in pronator syndrome.

Answer 87

These include the following: 1. bicipital aponeurosis 2. ligament of Struthers 3. between the heads of pronator teres

Question 88

What is the difference between de Quervain and intersection syndromes?

Answer 88

De Quervain syndrome is a stenosing tenosynovitis of the first extensor compartment with pain felt at the wrist, whereas intersection syndrome is caused by the tendons of the first extensor compartment crossing over those of the second compartment and pain is felt proximal to the wrist joint.