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1. Describe the cutaneous innervation of the hand; including primary nerve and spinal cord level.

The median, ulnar, and radial nn. supply the skin of the hand. Cutaneous branches of these nerves provide sensory innervation.

Median n. – a cutaneous branch of the median n. supplies the skin of the palmar surface on the lateral side. Typically it branches into ‘digital branches,’ and supplies the skin of the lateral palm, thumb and lateral 3.5 digits. These branches also supply the nail beds of the thumb and same 3.5 digits.

Ulnar n. – cutaneous branches of the ulnar n. supply the skin on the medial palmar and medial dorsal surfaces of the hand and 1.5 digits.

Radial n. – a cutaneous branch of the radial n. supplies the skin of the dorsum of the hand and lateral 3.5 digits, except for the nail beds (from median n.).

2. Describe the arrangement of compartments and muscles in the hand. Differentiate between extrinsic and intrinsic hand muscles.

Click here to download a PDF of all individual muscle charts for the hand. 

Click here to download a PDF of the comprehensive hand muscles chart.

*Students are only responsible for muscles discussed in the main text of the learning objectives and/or list of structures

The hand is the most distal and the manual part of the upper limb; with the wrist at the junction of the forearm and hand. The digits are numbered 1 to 5 with the thumb (lateral side) as digit 1 and the little finger (medial side) as digit 5. The palmar surface has a central concavity separating two eminences: lateral, the thenar eminence, is larger; medial, the hypothenar eminence, is smaller.

The fascia of the hand is continuous with the antebrachial fascia. The fascia is thin over the thenar and hypothenar eminences, but much thicker over the central compartment. The fascia over the central portion of the palm forms the palmar aponeurosis. If the palmaris longus muscle is present, it inserts into the palmar aponeurosis.

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

• • Thenar compartment: the most lateral compartment of the hand on the palmar side. This compartment is at the base of the thumb. 

    • Muscles:

      • Abductor pollicis brevis m.

      • Flexor pollicis brevis m.

      • Opponens pollicis m.

    • In addition to these intrinsic muscles, the tendon from the flexor pollicis longus m. resides in this compartment.

Hypothenar compartment: the most medial compartment of the hand on the palmar side, this compartment is at the base of the little finger. 

• Muscles:

  • Abductor digiti minimi m.

  • Flexor digiti minimi brevis m.

  • Opponens digiti minimi m.

• Deep adductor and interosseous compartments: contains the muscles of the palm of the hand deep to the central compartment. Tendons are the large adductor pollicis and the interosseous muscles. The adductor pollicis adducts the thumb, the palmar interossei adduct the digits toward midline – the middle (digit 3) finger, and the dorsal interossei abduct the digits away from the midline.

3. Describe the neurovascular supply to the hand.

The sensory innervation is described in a previous learning objective. The motor innervation of the intrinsic hand muscles is primarily from the ulnar nerve; remember that most of the forearm muscles also act on the hand and are innervated as described in the previous sessions.

Most all of the intrinsic hand muscles are innervated by the ulnar n. except the three thenar muscles. The three thenar muscles are innervated by an efferent branch from the median n. – the recurrent branch of median n. This nerve branches from the median after the median n. passes through the carpal tunnel into the hand.

The hand is supplied by an abundance of anastomosing arteries that are derived from the radial and ulnar aa. This collateral supply ensures that the blood reaches the hand regardless of the various positions and pressures it endures. The ulnar a. enters the hand lateral to the ulnar n. It branches into superficial and deep branches to form superficial & deep palmar arches. There is a reliable pulse point as the ulnar passes across the wrist just lateral to the tendon of the flexor carpi ulnaris. The radial a. crosses the wrist at the scaphoid bone and curves onto the dorsal side of the lateral hand. It passes across the floor of the “anatomical snuff box.” The radial a. dives through the muscle tissue between the thumb and first finger to form the deep palmar arch on the palmar side by anastomosing with the deep branch of the ulnar a. Commonly, before the radial artery curves onto the dorsum of the hand, then it gives off a superficial branch that anastomoses with the superficial branch of the ulnar artery to form the superficial palmar arch

4. Describe the carpal tunnel and explain the mechanism and consequences of carpal tunnel syndrome.

The carpal tunnel is formed at the wrist by carpal bones and connective tissue. The carpal bones form a concavity (C-shape with the opening on the ventral side) through which tendons from forearm muscles and the median nerve pass. The concavity is covered (and held in shape) by the transverse carpal ligament (sometimes referred to as flexor retinaculum).

The tendons are wrapped in synovial sheaths which act, like bursae, to reduce friction as the tendons pass through a tight compartment. In the image below, notice the tendon of the flexor pollicis longus adjacent to the median n. on one side and the tendons of the superficial digital flexors on the other side as they pass through the carpal tunnel.

In addition to the tendons of the extrinsic digital flexors passing through the carpal tunnel, the median n. does as well. Note that the ulnar n., and the radial and ulnar aa. and vv. do not pass through the tunnel. If the space of the carpal tunnel is reduced (potentially by inflammation of the synovial sheaths, thickening of the transverse carpal ligament, or other causes (flex and extend your wrist and think about which position creates more or less space)), the median nerve can be compressed. This compression can affect the “downstream” branches of the nerve – so, the cutaneous branches and/or the recurrent branch of the median n. Think about what symptoms one would have if any of these branches of the median nerve were compromised.

5. Describe the main arches of the foot and the ligaments and tendons that support them.

Arches of the foot are important in distributing weight and absorbing shock that occurs in locomotion.

• • Medial longitudinal arch

    • Formed by tarsals (except cuboid) and 1st-3rd metatarsals

    • This is the higher of the two longitudinal arch

    • Head of talus is important component of this arch

    • Plantar calcaneonavicular (spring) ligament: supports head of talus

      • Sustentaculum tali of calcaneus to navicular

    • Long plantar ligament

      • Calcaneus to cuboid

    • Plantar calcaneocuboid (short) ligament

      • Between spring and long plantar ligaments

    • Leg muscle tendons also play an active role in supporting this arch

    • Clinical importance: the medial longitudinal arch is most affected in cases of flatfeet (‘fallen arches’)

• Transverse arch of foot

  • Formed by cuboid, all cuneiforms, and bases of all metatarsals

  • Tendons of tibialis posterior and fibularis longus support this arch

6. Understand the organization of the fascia of the ankle and foot.

In the ankle region, the crural fascia thickens to form retinacula that hold tendons close to the bone, creating a sort of pulley system; so they do not pull away from the bone while muscles contract as tendons cross joints. 

• • superior extensor retinaculum: superior to the ankle, on the anterior aspect of the leg

  • inferior extensor retinaculum: on the anterior aspect of the ankle. It is Y-shaped, extending onto the dorsum of the foot.

  • flexor retinaculum: on the posteromedial aspect of the ankle

The deep fascia of the foot is continuous with the crural fascia of the leg. As in the leg, it divides the foot into muscular compartments, very similar to the muscular compartments of the hand. On the plantar surface, the central portion of the fascia is thick, dense connective tissue with longitudinally arranged fibers and forms the plantar aponeurosis (“plantar fascia”). The plantar fascia holds parts of the foot together and helps support the longitudinal arches of the foot. It arises posteriorly from the calcaneus, courses across the midfoot, and divides into five longitudinal bands distally that course into the digits.

7. Describe the cutaneous innervation of the foot; including primary nerve and spinal cord level.

Cutaneous nerves (most are branches of nerves that innervate lower limb muscles) supply the skin of the foot. In the foot, it is important clinically or diagnostically to associate deficits of sensation with nerves and/or spinal cord levels.

On the plantar surface of the foot, the medial plantar & lateral plantar nn. (branches of tibial n.) provide cutaneous innervation to most of the plantar surface. The lateral edge of the foot, plantar and dorsal surfaces, is from the sural nerve. The skin on the majority of the dorsum of the foot is innervated by the superficial fibular (peroneal) n. with the small patch of skin between the big toe and 2nd digit innervated by the deep fibular (peroneal) n.

The dorsum of the foot is superficial and deep branches of the fibular (peroneal) n.

8. Identify structures entering the foot at the lateral and medial malleoli.

Medial malleolus:

The tendons of the posterior leg, along with the neurovasculature (tibial n. and posterior tibial a.), enter the plantar foot by coursing posterior to the medial malleolus. The tendons are surrounded by synovial sheaths like the tendons in the carpal tunnel and are held down by a retinaculum – a thickened band of the crural fascia that typically holds tendons in place. This location, just posterior to the medial malleolus, is a place to feel the pulse of the posterior tibial a.

Lateral malleolus:

The tendons of the two fibularis (peroneus) muscles travel to the foot from the lateral side of the leg behind or posterior to the lateral malleolus. Like the medial malleolus, there is a retinaculum that holds the tendons down. The tendon of the deeper fibularis muscle (fibularis brevis) travels behind the lateral malleolus and inserts on the base of the fifth metatarsal. In forceful inversion sprains, this tendon can pull on and break the fifth metatarsal bone.