8.2 Bones, Muscles, and Joints of the Arms and Hands

8.2 Bones, Muscles, and Joints of the Arms and Hands

A manicure happens on a skeleton, not on a floating nail plate. If you cannot name the carpals, metacarpals, and phalanges, you cannot explain why a stiff knuckle will not flatten into a soak bowl, why an enhancement levered on a painful DIP joint is a complaint waiting to happen, or why your own forearm flexors scream after a day of tight e-file grip. NIC Domain 2 tests bones, muscles, and joints of the arms and hands at technician level: enough names to read an item, enough function to change the service.

The bones you brace, file, and massage

The humerus is the upper-arm bone from shoulder to elbow. You rarely do nails on the humerus, but you massage toward it, you rest the client's arm along it, and your own humerus sets shoulder height at the table. A client who cannot abduct the arm after a shoulder injury needs the table raised and the arm supported. Do not yank a stiff shoulder to get the hand into your preferred spot. That is an ergonomics decision with a bone under it, the same skeleton Chapter 6 already asked you to protect on your side of the table.

The radius and ulna are the two forearm bones. The radius is on the thumb side. The ulna is on the little-finger side; its proximal end is the point of the elbow you feel as the olecranon. When the palm turns up (supination) and down (pronation) for polish, the radius rotates around the ulna. If a Federal Way client has a rigid wrist from a healed fracture or a plate, that rotation may be limited. Turn the client's whole arm gently. Do not crank the hand.

The wrist is a stack of eight carpal bones. NIC items typically want the number eight, not a memorized Latin roll call. They sit between the forearm and the palm. A fall on an outstretched hand often injures carpals (the scaphoid is famous in emergency rooms). A client with a recent wrist injury, a brace, or a surgical implant does not get a forced wrist extension over the table edge so you can see the thumb from your favorite angle. Support the wrist. Shorten the massage. Skip anything that requires bending the joint past comfort.

The palm is five metacarpals, numbered from the thumb as I through V. You can palpate their shafts on the back of the hand and their heads as the knuckles of the metacarpophalangeal (MCP) joints. An enhancement that is too long and too levered puts extra moment on those joints. That is a product decision with a skeleton under it: a Kirkland coffin set that looks perfect in the photo can still be a week of MCP ache for a client with already-stiff knuckles.

The digits are fourteen phalanges in each hand: the thumb has two (proximal and distal); the other four fingers have three each (proximal, middle, distal). Four times three plus two equals fourteen. A common trap is fifteen, three per digit. The thumb does not have a middle phalanx. Distal phalanges wear the nail plates you polish and enhance. When you hold a finger to file, you are stabilizing phalanges. When you squeeze a distal phalanx to make the polish easier, you can blanch the nail bed and hurt the client.

Count for one hand that NIC likes: 8 carpals + 5 metacarpals + 14 phalanges = 27 bones.

Joints that change the service: DIP, PIP, MCP

Learn three finger joints by name because they appear on exams and because arthritis and implants live there.

The MCP joint is the knuckle at the base of the finger, where the metacarpal meets the proximal phalanx. Rheumatoid patterns often involve MCPs. Ulnar drift, swollen knuckles, and limited fist-making are things you observe, not diseases you name as a diagnosis. You do not force a fist into a bowl. You do not wrench a ring over a hot MCP. You adapt the hold, the soak position, and the enhancement length.

The PIP (proximal interphalangeal) joint is the middle knuckle, between proximal and middle phalanges. It is a hinge. Bony enlargement here is common in aging hands. You do not need a medical eponym. You need to see a bulky, stiff PIP and stop treating the finger like a straight stick you can mash onto a table. File with the angle the joint actually gives you.

The DIP (distal interphalangeal) joint is the last hinge, under the nail plate's proximal half, between middle and distal phalanges. Bony enlargement lives here too. So does a lot of enhancement stress: a long coffin or a thick acrylic on a painful DIP is a lever on an already unhappy hinge. The thumb has an interphalangeal (IP) joint instead of both PIP and DIP, matching its two phalanges.

Implants, pins, and fused joints are not salon emergencies. They are reasons to ask how the client prefers the hand held, to avoid torque, and to skip deep joint massage. A client with a thumb CMC implant may still want polish. She does not want you demonstrating opposition range for fun. Recent surgery, a bulky dressing, or a hot, red joint is a stop: WAC 308-20-110 already bars work on inflamed skin, and RCW 18.16 does not include joint manipulation as manicuring.

Muscles at technician level, not a cadaver list

NIC-style items use action names: flexor, extensor, abductor, adductor. They also expect you to know the thenar and hypothenar pads you actually massage. Do not memorize forty Latin muscle names. Teach the groups that explain massage direction and injury prevention.

Flexors of the forearm sit mainly on the anterior (palm-up) side. They flex the wrist and fingers — close the hand, bend the wrist toward the palm. Clients who type, lift, or grip all day often feel tightness here. Massage of the forearm in a manicure generally moves from the hand toward the elbow, which is also toward the heart, following venous and lymph return. You are not a physical therapist prescribing a protocol. You are not digging into a painful medial elbow because a video said to release the flexors.

Extensors sit mainly on the posterior forearm. They extend the wrist and fingers — open the hand, lift the wrist. When you ask a client to hold the fingers straight for polish, extensors are working. If extension hurts, do not insist on a rigid flat hand. Support the digits so the client is not holding an isometric pose for twenty minutes.

Abductors move a part away from the midline. In the hand, thumb abductors move the thumb away; abductor digiti minimi moves the little finger away. Adductors move a part toward the midline. Adductor pollicis pulls the thumb back toward the palm. Exam items that say which muscle moves the finger away from the hand's midline are testing abductor, not a catalog.

The thenar eminence is the fleshy pad at the base of the thumb. It contains short thumb muscles (flexor, abductor, opponens of the thumb). The hypothenar eminence is the pad on the little-finger side. Both pads are classic manicure massage territory. They are also where a technician with a death-grip e-file builds her own overuse story. Massage them with lotioned, sliding pressure, not a thumb that gouges the client's thenar against the first metacarpal.

Pronation and supination (palm down, palm up) come from forearm rotators. You use them every time you flip a hand to paint. Move the whole forearm. Do not twist only at the carpals.

Circulation and lymph: massage is not medicine

The radial artery runs on the thumb side of the inner wrist, against the radius, lateral to the flexor tendon you feel when the client flexes the wrist. That is the everyday radial pulse. You are not required to chart a pulse like a nurse. You should know the location so you do not grind a deep massage into it, so you understand why a tight bracelet-area grip can be uncomfortable, and so you can recognize that this is a major vessel feeding the hand. The ulnar artery runs the little-finger side of the wrist. They form arches in the palm. Distal fingers can blanch if you squeeze too hard while painting — release the pinch; a white nail bed is not a better polish canvas.

Veins are more superficial, especially on the dorsum of the hand. Elderly skin has a thinner dermis and less subcutaneous fat; veins bruise. Gentle contact is an anatomy decision. A client may mention a blood thinner. You do not diagnose a clotting disorder. You stop treating the hand like a stress ball.

Lymph from the hand and forearm drains toward cubital nodes at the elbow and axillary nodes at the armpit. Edema — visible swelling, pitting, a tight, heavy hand — is a reason to skip vigorous massage. You do not work the fluid out. That can be a medical problem (infection, injury, lymph-node surgery, systemic illness). A client who reports arm swelling after breast surgery is describing a classic caution for aggressive arm massage. Stay on the nails if the skin is intact and the service is appropriate; do not invent a salon lymphedema protocol. Infection, red streaks, or hot swelling is a refuse-and-refer picture, and WAC 308-20-110 already bars work on inflamed skin.

Massage direction toward the heart is the technician-level circulation rule. It matches venous return. It is not a license to use force. Light effleurage on intact skin is a manicure add-on. Deep, painful stripping of a swollen forearm is not.

The same skeleton on your side of the table

Your humerus, radius, ulna, and finger joints take the job. Keep a neutral wrist, not a bent MCP-PIP-DIP stack holding an e-file like a dagger. Support the client's phalanges so your own flexors are not holding a live hand in the air. Keep the work near elbow height so the shoulder is not shrugged for six hours. A Vancouver, WA technician who can name every carpal and still cocks her own wrist into hard extension for every fill is using anatomy only as trivia.

Washington floor pictures

Tacoma RA knuckles. MCP joints are large and tender. Do not force a soak-bowl fist. File each digit at the angle the joint allows. Keep enhancements shorter so the DIP and MCP are not fighting a lever all week.

Seattle scaphoid follow-up. Client is out of a cast, still guarded at the wrist. Support the forearm on the table. Skip deep wrist-circle massage. Polish is in scope; rehab is not.

Yakima thenar grind. A firm massage request is not permission to compress the thenar eminence onto the first metacarpal until the thumb goes numb. Thenar muscles and the thumb's joints sit right there.

Olympia radial pulse. A student practices massage by raking the inner wrist. Relocate. The radial artery is not a trigger point.

Exam sentence: eight carpals, five metacarpals, fourteen phalanges; DIP, PIP, and MCP are the hinges you must not force; thenar and hypothenar, flexors and extensors, abductors and adductors explain massage; skip vigorous work on a swollen limb and do not grind the radial pulse.