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1. Describe the organization of neurovasculature in the cubital fossa.

The cubital fossa is a triangular-shaped depression on the anterior portion of the elbow region, and can be thought of as a transition from the arm to the forearm.

It is bounded medially by the proximal attachment of the flexor muscles of the anterior forearm, and laterally by the proximal attachment of the extensor muscles of the posterior forearm. 

There are numerous important structures located in this region.

Superficial

Superficially, there are superficial veins including the cephalic v., basilic v., and whichever variation of shunting vein - most typically median cubital v., although it should be noted that there is considerable variation in this area. Due to the prominence and relative ease of accessibility, the cubital fossa is a common site of venipuncture (for intravenous injections, sampling & transfusions of blood).

Intermediate

The biceps tendon can easily be palpated in the cubital fossa as it descends to attach to the radial tuberosity. It will send a flattened band of aponeurosis (bicipital aponeurosis) to span most of the cubital fossa deep to the superficial veins. This aponeurosis serves as an additional layer of protection for the deeper structures of the cubital fossa. In particular, its presence during venipuncture helps prevent access to the brachial a.

Deep

The terminal portion of the brachial artery is located within the cubital fossa, as are its terminal branches: the radial & ulnar aa.

The median n. is located either just deep to the brachial a. or just medial to the artery.

The radial n. is located along the lateral border of the cubital fossa, typically deep to the extensor muscles of the forearm - and is not as visible during dissection without retraction of the muscles.

2. Identify the major joints in the wrist region. Explain what types of movement occur at these joints and other pertinent clinical information.

The major joint of the wrist region is the radiocarpal (wrist) joint.The distal radio-ulnar joint is located just proximal to the wrist joint, and with the proximal radio-ulnar joint will facilitate pronation and supination. Intercarpal joints are plane-type synovial joints located between carpal bones. They produce very slight gliding motions that can increase the overall range of movement of the wrist joint.

Radiocarpal (Wrist) Joint

The radiocarpal (wrist) joint involves the articulation of the distal end of radius and proximal row of carpal bones (excluding the pisiform), and is a synovial, condyloid joint.

As a condyloid joint, the radiocarpal (wrist) is capable of:

• Flexion/Extension

• Abduction (radial deviation) & Adduction (ulnar deviation)

• Circumduction

Clinical Consideration

• FOOSH (Falling On an Out-Stretched Hand) or direct trauma are common causes of a fracture to the distal radius (Colles’ fracture)

  • One of most common fracture of the upper extremity

  • Will greatly affect actions at wrist joint

3. Identify the major joints in the hand region. Explain what types of movement occur at these joints.

Carpometacarpal (CMC) Joints 

• Articulations: distal row of carpals and metacarpals

• Synovial joint type: all are plane type, except for the 1st CMC (of thumb) which is a saddle type

• Movements:

  • CMC joint 1 (of thumb): flexion/extension; abduction/adduction; circumduction

• Part of complex movements that will lead to opposition of thumb

• CMC joints 2-5: comparatively slight gliding movements

Metacarpophalangeal (MP; MCP) Joints

• Articulations: metacarpals & proximal phalanges

• Synovial joint type: condyloid

• Movements: Flexion/extension; abduction/adduction; circumduction

  • 1st MCP only really flexes and extends, but is typically still classified as condyloid

Interphalangeal (IP) Joints

• Synovial joint type: Hinge

• Movements: flexion/extension

• Two main types:

  • Proximal interphalangeal (PIP) joints: between proximal and intermediate phalanges 2-5

  • Distal interphalangeal (DIP) joints: between intermediate and distal phalanges 2-5

  • 1st digit does not have an intermediate phalange - so there is a single interphalangeal joint.

4. Identify the major muscles, innervation, and actions of the anterior compartment of the forearm.

The anterior (sometimes referred to as flexor/pronator) compartment of the forearm is organized into three layers, largely with superficial muscles acting on more proximal joints (wrist, i.e. radiocarpal, and radio-ulnar joints) and deeper muscles acting upon the more distal joints (metacarpophalangeal [MP] and interphalangeal [PIP & DIP]). Flexion of the wrist, MP, and PIP & DIP joints are primary actions of the anterior compartment, dependent on muscle, as well as pronation of the radio-ulnar joints.

The median n. innervates the majority of muscles in the anterior compartment, with a small contributions from the ulnar n.

Superficial Layer of Muscle

• The superficial layer is composed of 4 muscles: pronator teres, flexor carpi radialis (FCR), palmaris longus, and flexor carpi ulnaris (FCU).

• When looking at an anterior view of the superficial forearm, you actually see some of the ‘posterior’ muscles on the lateral third, with the superficial anterior/flexor muscles on the other 2/3rds of the anteriomedial surface.

Notable Attachments

• These muscles share a proximal attachment via a common flexor tendon on the medial epicondyle of the humerus.

Actions

• Flexor carpi radialis m. (FCR) and flexor carpi ulnaris m. (FCU)are the primary flexors of the radiocarpal (wrist) joint.

• Flexor carpi radialis m. abducts the wrist (radial deviation), whereas the flexor carpi ulnaris m. adducts the wrist (ulnar deviation).

• The pronator teres m. pronates the radio-ulnar joints, particularly when speed and/or power is needed in this action.

Unique innervation

• Flexor carpi ulnaris (FCU) is the only muscle of the anterior compartment fully innervated by the ulnar n.

Intermediate Layer of Muscle

• The intermediate layer consists of the flexor digitorum superficialis (FDS).

Notable Attachments

• A portion of the muscle shares a proximal attachment with the superficial muscles on the medial epicondyle of the humerus.

• The FDS divides into 4 long tendons that traverse the carpal tunnel and distally attach on the intermediate phalanges 2-5.

Actions

• The FDS can affect any joint that it crosses (wrist, CMC, MP), but its primary actions are flexion of the proximal interphalangeal joints (PIPs) of digits 2-5.

Deep Layer of Muscle

• This layer consists of 3 muscles: flexor digitorum profundus (FDP), flexor pollicis longus (FPL), and pronator quadratus.

Notable Attachments

• Distally, the FDP divides into 4 long tendons that traverse the carpal tunnel and distally attach on the distal phalanges 2-5.

  • The flexor pollicis longus’ (FPL) tendon also traverses the carpal tunnel and distally attaches on the distal phalanx 1.

Actions

• The FDP and FPL can affect any joint that they cross (wrist, CMC, MP, PIP), but their primary actions are in flexion of the distal interphalangeal joints 2-5 (FDP) and flexion of the 1st interphalangeal joint (FPL).

• The pronator quadratus is typically the prime mover in pronation of the radio-ulnar joints.

Unique Innervation

• The flexor digitorum profundus muscle is innervated by 2 nerves. The lateral half is innervated by the median n. with the medial half innervated by the ulnar n. You can test the integrity of these nerves in one muscle!

5. Identify the major muscles, innervation, actions, and clinical considerations regarding the posterior compartment of the forearm.

The posterior compartment of the forearm is conceptualized in 2 layers: superficial and deep. Both layers are innervated by the radial n. and its branches.

Superficial Layer of Muscle

• Consists of 6 muscles: brachioradialis, extensor carpi radialis longus & brevis, extensor digitorum, extensor digiti minimi, & extensor carpi ulnaris.

Notable Attachments

• 4 of these muscles have a proximal attachment (via a common extensor tendon) on the lateral epicondyle of the humerus. The other two attach just proximal to the lateral epicondyle.

  • Clinical consideration: with repetitive use of these superficial extensor muscles, this can lead to microtears in the common extensor tendon or periosteum of the lateral epicondyle - leading to lateral epicondylitis (‘tennis elbow’)

• The extensor digitorum tendons flatten distally to create the extensor expansions on the posterior (dorsal) portions and sides of the digits 2-5, specifically the metacarpals and proximal phalanges - causing extension of the interphalangeal joints.

  • Other muscle tendons will attach on these extensor expansions.

Actions

• Brachioradialis m. is unique in that it is NOT an extensor m., its belly is mostly located on the anterior surface of the forearm, and its distal tendon does not reach the wrist. However, like the other muscles, it is innervated by the radial n.

  • This muscle is typically synergistic in flexion of the elbow joint

• There are two extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB)

  • These muscles will extend the radiocarpal (wrist) joint and with the flexor carpi radialis abduct the wrist joint (radial deviation).

• Extensor carpi ulnaris m. will extend the wrist joint and with flexor carpi ulnaris adduct the wrist joint (ulnar deviation)

• Extensor digitorum mm. are the primary extensors of digits 2-5.

Deep Layer of Muscle

• 5 muscles: supinator m., abductor pollicis longus m., extensor pollicis longus & brevis mm., & extensor indicis m.

  • The pollicis muscles in this layer are often referred to as ‘outcropping muscles,’ meaning that while deep for the majority of forearm, they will become superficial near the wrist.

  • 3 of the 5 muscles only affect actions at the 1st digit.

Actions

• The supinator m. is the prime mover for supination of the radio-ulnar joints in slow, unopposed movement.

• The primary action of abductor pollicis longus m. is abduction of 1st digit at the 1st carpometacarpal (CMC) joint.

• The extensor pollicis longus & brevis mm. cause extension of the 1st digit throughout the various joints in the hand.

6. List the boundaries of the ‘anatomical snuff box,’ and describe the contents and clinical considerations.

The ‘anatomical snuff box’ is a depression on the posterolateral side of the wrist. It is most obvious when the first digit (thumb) is in almost complete extension (thumb jutting out laterally; ‘hitchhiker’s thumb’).

It is bounded medially and laterally by the long pollicis tendons (EPL, EPB, APL).

• Floor: primarily the scaphoid & trapezium (carpal bones)

Contents include:

• Radial a.: a radial pulse can be felt here (not the most typical place for radial pulse)

• Cutaneous branch of the radial n.

• Potentially the cephalic v.

Clinical Consideration: Scaphoid fracture

• The scaphoid is the most commonly fractured carpal bone, which can be caused by FOOSH or direct trauma.

• Initial imaging may not clearly show a fracture, but will become noticeable on future images due to a higher likelihood of avascular necrosis due to a tenuous blood supply in this region

7. Describe the structures that form and lie within the carpal tunnel and how they are affected by carpal tunnel syndrome.

The carpal tunnel is located in the anterior wrist region, and is formed by:

• Floor (and walls): carpal bones

• Roof: transverse carpal ligament (flexor retinaculum)

• Contents:

  • Long flexor tendons (flexor digitorum superficialis, flexor digitorum profundus, & flexor pollicis longus mm.)

    • Tendon sheaths surrounding tendons

      • Recall that tendon sheaths are elongated bursa-like structures

  • Median n.

    • The cutaneous branch that supplies skin of palm branches just proximal to the carpal tunnel

Carpal Tunnel Syndrome

Carpal tunnel syndrome is most commonly caused by inflammation of the tendon sheaths (a form of bursitis). This often will result in the compression of the median n. in the carpal tunnel, affecting branches that come off within or distal to the carpal tunnel, which can present as:

• Typically issues with cutaneous sensation (paresthesia or anesthesia) of lateral digits 

• Loss of strength and/or coordination of 1st digit, particularly with opposition, affecting innervation of muscles of thenar compartment (potentially leading to atrophy)

8. Describe the arrangement and compartments of the hand, and differentiate between extrinsic and intrinsic hand muscles.

The hand is the most distal with the wrist at the junction of the forearm and hand. The digits are numbered 1 to 5 with the thumb (lateral) as digit 1 and the little finger (medial) as digit 5. 

The extrinsic muscles of the hand include the long tendons from muscles that have muscle bellies in the forearm (both flexor and extensor mm.). These muscles very much play a role in the actions of the hand joints, but have proximal attachments and a muscle belly located at a distance away from the hand.

The intrinsic muscles of the hand have attachments (both proximal & distal) entirely in the hand and will affect actions of the hand joints.

The palmar surface has a central concavity separating two eminences:

• thenar eminence: larger & lateral

• hypothenar eminence: smaller & medial

Deep fascia is thinner over the eminences, but much thicker over the central compartment. The fascia over the central portion of the palm forms the palmar aponeurosis.

The palmar portion of the hand is divided into 5 compartments: thenar, hypothenar, adductor, central (lumbricals), and interosseous compartments.

Thenar Compartment

• Most lateral compartment of the hand on the palmar side and is located at the base of the thumb

• 3 intrinsic muscles & 1 extrinsic tendon

  • Muscles will play a role in abduction, flexion, and opposition of the 1st digit

• Innervation: recurrent br. of median n.

Hypothenar Compartment

• Most medial compartment of the hand on the palmar side and is located at the base of the 5th digit

• 3 intrinsic muscles that will play a role in abduction, flexion and opposition of the 5th digit

• Innervation: ulnar n. branches

Adductor Compartment

• 1 large intrinsic adductor muscle - affects adduction of 1st digit

• Innervation: ulnar n. branches

Central Compartment

• The tendons of the flexor digitorum (superficialis & profundus) muscles are dominant in this region

• Lumbricals: 4 ‘worm-like’ muscles with proximal attachments on the flexor digitorum profundus tendons and distal attachments on the extensor expansions of digits 2-5

  • Flex metacarpophalangeal joints (2-5); extend interphalangeal joints (2-5)

  • Innervated by both median n. branches (lateral 2 lumbricals) & ulnar n. branches (medial 2 lumbricals)

Interosseous Compartment

• Deepest compartment

• Dorsal interossei (4) and palmar interossei (3)

  • Similar actions as lumbricals

  • Dorsal interossei ABduct digits; Palmar interossei ADduct digits

    • DAB & PAD

  • Innervated by ulnar n. branches