5.3 Bones, Muscles & Nerves of the Hand, Arm, Foot & Lower Leg

Bones, Muscles & Nerves of the Hand, Arm, Foot & Lower Leg

A thorough mastery of the musculoskeletal and neurovascular anatomy of the extremities is vital for practicing nail technicians. Every manicure, pedicure, and massage service directly manipulates the bones, tendons, muscles, nerves, and blood vessels of the hands, forearms, feet, and lower legs. Technicians must understand where these structures reside to deliver safe, therapeutic, and comfortable treatments, maintain proper ergonomic posture, and avoid causing acute injury or triggering severe medical complications in vulnerable clients.

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1. Skeletal System of the Upper Extremity: Hand, Wrist & Forearm

The skeletal framework of the human hand and wrist comprises 27 individual bones, supported proximally by the two bones of the forearm:

                    [SKELETAL ANATOMY OF UPPER EXTREMITY]
                                      │
           ┌──────────────────────────┼──────────────────────────┐
           ▼                          ▼                          ▼
     [FOREARM BONES]            [WRIST BONES]              [HAND BONES]
     - Radius (Thumb side)      - 8 Carpals in 2 rows      - 5 Metacarpals (Palm)
     - Ulna (Pinky side)        - Proximal: Scaphoid,      - 14 Phalanges (Digits)
       (Forms elbow joint)        Lunate, Triquetrum,        * Thumb: 2 phalanges
                                  Pisiform                   * Fingers: 3 phalanges
                                - Distal: Trapezium,           each (Proximal, Middle,
                                  Trapezoid, Capitate,         Distal)
                                  Hamate

The Forearm: Radius and Ulna

• The Radius: The lateral bone of the forearm, situated on the thumb side. The radius is shorter than the ulna; its disc-shaped head articulates with the capitulum of the humerus, allowing the radius to rotate completely around the ulna during pronation and supination movements of the hand.
• The Ulna: The medial bone of the forearm, situated on the little finger (pinky) side. The ulna is longer than the radius and forms the main hinge joint of the elbow with the humerus via its prominent proximal projection, the olecranon process (the elbow bone).

The Wrist: The Eight Carpals

The wrist (carpus) is composed of eight small, irregular bones firmly bound together by tough ligaments. These bones are arranged into two horizontal rows of four:

1. Proximal Row (lateral to medial):
   • Scaphoid (Navicular): Boat-shaped bone articulating with the radius.
   • Lunate: Crescent moon-shaped bone.
   • Triquetrum (Triangular): Pyramidal bone.
   • Pisiform: Small, pea-shaped sesamoid bone resting on the anterior surface of the triquetrum, easily palpated on the palmar-pinky corner of the wrist.
2. Distal Row (lateral to medial):
   • Trapezium: Irregular bone articulating with the base of the thumb metacarpal.
   • Trapezoid: Wedge-shaped bone.
   • Capitate: The largest carpal bone, occupying the central position.
   • Hamate: Hook-shaped bone featuring a prominent palmar hook process.

The Palm: Metacarpals & Digits: Phalanges

• Metacarpals (5 Bones): The framework of the palm consists of five cylindrical metacarpal bones numbered Roman numerals I through V, beginning with the thumb (Metacarpal I) and ending with the little finger (Metacarpal V). The rounded distal heads of the metacarpals form the visible knuckles.
• Phalanges (14 Bones): The digits contain 14 phalangeal bones (singular: phalanx):
  • The thumb (pollex) has only two phalanges: proximal and distal.
  • The other four fingers each contain three phalanges: proximal, middle, and distal.

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2. Skeletal System of the Lower Extremity: Foot, Ankle & Lower Leg

The human foot and ankle contain 26 individual bones, supported by the two long bones of the lower leg and the knee joint:

                    [SKELETAL ANATOMY OF LOWER EXTREMITY]
                                      │
           ┌──────────────────────────┼──────────────────────────┐
           ▼                          ▼                          ▼
     [LOWER LEG & KNEE]         [ANKLE & HEEL]             [FOOT & TOES]
     - Tibia (Medial shin)      - 7 Tarsals:               - 5 Metatarsals (Instep)
     - Fibula (Lateral)           * Calcaneus (Heel)       - 14 Phalanges (Toes)
     - Patella (Kneecap)          * Talus (Ankle)            * Great toe: 2 phalanges
                                  * Navicular, Cuboid,       * Other toes: 3 phalanges
                                    3 Cuneiforms               each

Lower Leg and Knee: Tibia, Fibula, Patella

• Tibia: The shinbone; it is the larger, medial, primary weight-bearing bone of the lower leg. Its prominent distal medial projection forms the inner ankle bone (medial malleolus).
• Fibula: The slender, lateral bone of the lower leg running parallel to the tibia. The fibula does not bear body weight; it functions primarily as an attachment site for muscles. Its distal lateral expansion forms the outer ankle bone (lateral malleolus).
• Patella: The kneecap; a large, triangular sesamoid bone embedded within the quadriceps tendon that shields and protects the anterior surface of the knee joint.

The Ankle and Heel: The Seven Tarsals

The tarsus consists of seven irregular tarsal bones forming the ankle, heel, and rear instep:

• Calcaneus: The heel bone; it is the largest and strongest bone of the foot. It transmits body weight to the ground and serves as the insertion point for the massive Achilles tendon.
• Talus: The second-largest tarsal bone; it sits directly on top of the calcaneus and articulates superiorly with the tibia and fibula to form the ankle joint (talocrural joint).
• Navicular, Cuboid, and Three Cuneiforms: The boat-shaped navicular, cube-shaped cuboid, and medial, intermediate, and lateral cuneiform bones articulate with the metatarsals to create the dynamic arches of the foot.

Instep and Toes: Metatarsals & Phalanges

• Metatarsals (5 Bones): Five long bones forming the midfoot, instep, and ball of the foot, numbered I (great toe) through V (pinky toe).
• Phalanges (14 Bones): Like the hand, the toes contain 14 phalangeal bones:
  • The great toe (hallux) contains two phalanges: proximal and distal.
  • The other four toes each contain three phalanges: proximal, middle, and distal.

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3. Muscular System: Forearm, Hand, Lower Leg & Foot

Muscles produce movement by contracting (shortening), pulling on tendons attached to bones across joints. The muscles relevant to nail services are divided into extrinsic muscles (located in the forearm or lower leg) and intrinsic muscles (located entirely within the hand or foot).

Muscles of the Forearm and Hand

Muscles of the Lower Leg and Foot

• Gastrocnemius: The prominent superficial muscle of the posterior calf. It has two heads originating on the femur and attaches to the calcaneus via the Achilles tendon. It produces plantar flexion (pointing the toes downward) and flexes the leg at the knee.
• Soleus: A broad, flat muscle lying directly beneath the gastrocnemius. Working with the gastrocnemius, it powerfully plantar flexes the foot during standing and walking.
• Tibialis Anterior: Located on the anterior lateral surface of the shinbone. It acts to dorsiflex the foot (pulling the toes upward toward the shin) and inverts the foot.
• Peroneus Longus & Brevis (Fibularis Muscles): Situated on the lateral compartment of the lower leg. They evert the foot (turn the sole outward) and assist in plantar flexion.
• Extensor Digitorum Longus & Flexor Digitorum Longus: Muscles that extend (straighten) and flex (curl) the toes, respectively.

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4. Neurovascular Systems: Nerves and Arterial Blood Supply

Safe massage and implement handling require knowledge of where principal nerves and arteries course through the extremities.

Innervation and Circulation of the Upper Extremity

• Median Nerve: A major branch of the brachial plexus traveling down the anterior forearm. It passes through the narrow carpal tunnel beneath the transverse carpal ligament into the palm. It supplies sensory and motor innervation to the thumb, index finger, middle finger, and the radial half of the ring finger. Repetitive wrist bending and sustained pressure in nail technicians can compress this nerve, causing Carpal Tunnel Syndrome (numbness, tingling, and weakness).
• Ulnar Nerve: Courses along the medial (pinky) side of the forearm, passing posterior to the medial epicondyle of the humerus ("funny bone"). It innervates the little finger and the medial half of the ring finger, as well as the intrinsic hypothenar muscles.
• Radial Nerve: Supplies sensory branches to the back (dorsum) of the hand, dorsal surface of the thumb, and index/middle fingers, and motor innervation to the extensor muscles of the wrist and forearm.
• Digital Nerves: Terminal sensory branches coursing along both the lateral and medial borders of each finger, supplying sensation to the fingertip and natural nail unit.
• Arterial Supply: The brachial artery divides at the elbow into the radial artery (lateral, thumb side; primary pulse point at the wrist) and ulnar artery (medial, pinky side). These two vessels converge in the palm to form the superficial and deep palmar arterial arches, which give off the digital arteries supplying the nail unit.

Innervation and Circulation of the Lower Extremity

• Tibial Nerve: A major branch of the sciatic nerve traveling down the posterior calf. It passes behind the medial malleolus of the ankle, dividing into the medial and lateral plantar nerves that innervate the sole of the foot.
• Common Peroneal (Fibular) Nerve: Wraps around the neck of the fibula below the knee, dividing into the superficial peroneal nerve (supplying lateral leg and top of foot) and deep peroneal nerve (supplying anterior leg muscles and the web space between great and second toes).
• Arterial Supply: The popliteal artery behind the knee divides into the anterior tibial artery (traveling down the anterior leg and becoming the dorsalis pedis artery on top of the foot) and the posterior tibial artery (traveling behind the medial malleolus to supply the sole via plantar arteries).

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5. Clinical Application: Massage Protocols, Ergonomics & Safety Precautions

Massage of the hands, arms, feet, and lower legs is one of the most rewarding components of a salon service, but it requires strict anatomical awareness and regulatory adherence.

Scope of Practice and Permitted Manipulations

Under Minnesota cosmetology law, massage performed by a licensed nail technician must be strictly cosmetic and relaxing—never deep-tissue, rehabilitative, or clinical therapy. Permitted service boundaries extend from the fingertips to the elbow on the upper extremity, and from the toes to the knee on the lower extremity.

• Effleurage: Smooth, continuous, rhythmic stroking motions executed with the cushions of the palms or thumbs. Effleurage is used to begin and end the massage, distribute lubricants, warm tissues, and induce systemic relaxation.
• Petrissage: Gentle kneading, rolling, squeezing, and lifting of muscle tissue. Applied primarily to the fleshy muscular bellies of the forearm and the calf.
• Prohibited Aggressive Movements: Vigorous friction, sharp pinching, deep joint popping, or aggressive percussive tapping (tapotement) are contraindicated in cosmetic manicures and pedicures.

Dangerous Pressure Points to Avoid

• Bony Prominences: Technicians must never apply heavy, crushing pressure over superficial bones, including the radial styloid process and pisiform at the wrist, the patella at the knee, the tibial crest (shinbone), and the medial and lateral malleoli of the ankle.
• Posterior Medial Malleolus: The depression immediately behind the inner ankle bone houses the posterior tibial artery and tibial nerve close to the surface. Heavy circular pressure here can compress these structures, causing acute pain or paresthesia.
• The Carpal Tunnel: Avoid deep thumb pressure into the central proximal palm of the wrist, which compresses the median nerve.

Medical Contraindications: When to Modify or Refuse Massage

• Varicose Veins: Severely dilated, tortuous superficial veins on the lower legs are extremely fragile. Massage over varicose veins is strictly contraindicated as mechanical pressure can rupture vessel walls or induce phlebitis.
• Diabetes Mellitus & Diabetic Neuropathy: Diabetic clients often suffer from peripheral neuropathy (loss of sensory nerve function) and peripheral artery disease (poor circulation). They cannot accurately feel pain, temperature, or heavy pressure, and minor tissue damage heals very slowly. In diabetic clients, massage must be extremely light, gentle, and superficial, or omitted entirely with physician guidance.
• Severe Arthritis & Joint Inflammation: Never vigorously twist, pull, or hyperextend digits displaying osteoarthritic nodules (Heberden's nodes) or acute rheumatoid swelling.