Overview
An adult skeleton has 206 bones, divided into the axial skeleton (skull, vertebral column, ribs and sternum) and the appendicular skeleton (shoulder girdle, arms, pelvic girdle and legs). Bones meet at joints, which are held together by ligaments and cushioned by cartilage.
Bone is living tissue. Osteoblasts build new bone, osteoclasts break it down, and osteocytes maintain it. This constant remodeling is driven by mechanical load and by hormones such as parathyroid hormone (PTH), calcitonin, vitamin D and estrogen.
Main functions
- Support and shape for the body
- Protection of the brain, spinal cord, heart and lungs
- Movement, as levers for skeletal muscles
- Mineral storage, mainly calcium and phosphate
- Blood cell formation (hematopoiesis) in red bone marrow
- Energy storage as fat in yellow bone marrow
Key structures
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Skull
The bony case of the head: 8 cranial bones protect the brain and 14 facial bones shape the face.
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Vertebral column (spine)
33 vertebrae stacked in five regions that protect the spinal cord and carry the weight of the upper body.
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Rib cage (thoracic cage)
12 pairs of ribs, the sternum and the thoracic vertebrae form a flexible cage around the heart and lungs.
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Pelvis (hip bones and sacrum)
The ring of the two hip bones, sacrum and coccyx that transfers body weight to the legs and protects pelvic organs.
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Femur
The thigh bone: the longest and strongest bone in the body.
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Humerus
The upper arm bone, from the shoulder to the elbow.
How bone keeps calcium in balance
When blood calcium falls, the parathyroid glands release PTH. PTH activates osteoclasts to release calcium from bone, increases calcium reabsorption in the kidneys and activates vitamin D, which increases calcium absorption from the gut.
When blood calcium rises, the thyroid releases calcitonin, which slows osteoclasts so more calcium stays in bone. Estrogen also protects bone, which is why bone loss speeds up after menopause.
Nursing assessment
- Inspect posture, gait, spinal curves (kyphosis, scoliosis, lordosis) and symmetry of limbs.
- Palpate joints for warmth, swelling, tenderness and crepitus.
- Assess range of motion actively and passively; never force a painful joint.
- For any fracture or cast, check the 6 Ps: pain, pallor, pulselessness, paresthesia, paralysis and poikilothermia (coolness).
- Screen fall risk: history of falls, medications, vision, footwear and home hazards.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Osteoporosis | Loss of bone density so bones break easily | Often silent until a fracture; loss of height, kyphosis, vertebral or hip fractures | Fall prevention, weight-bearing exercise, calcium and vitamin D, teach bisphosphonate administration (upright for 30 minutes, full glass of water, empty stomach) |
| Fracture | Break in the continuity of a bone | Pain, deformity, swelling, crepitus, loss of function | Immobilize, elevate, neurovascular checks, watch for compartment syndrome and fat embolism |
| Compartment syndrome | Rising pressure inside a closed muscle compartment cuts off circulation | Pain out of proportion that is not relieved by opioids, pain on passive stretch, paresthesia | Emergency: notify the provider, loosen dressings or bivalve the cast, keep the limb at heart level (do not elevate) |
| Osteoarthritis | Wear of joint cartilage | Joint pain worse with activity and relieved by rest, short morning stiffness, Heberden's nodes | Pain control, weight management, assistive devices, joint protection |
| Rheumatoid arthritis | Autoimmune inflammation of the synovium | Symmetric joint swelling, morning stiffness longer than 1 hour, fatigue, deformities | Medication teaching (DMARDs, infection risk), energy conservation, warm compresses for stiffness |
| Osteomyelitis | Bone infection, often after open fracture or surgery | Bone pain, fever, warmth, drainage | Long-term IV antibiotics, wound care, monitor drug levels and labs |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| Total serum calcium | 9.0–10.5 mg/dL | Low with hypoparathyroidism and vitamin D deficiency; high with bone metastases and hyperparathyroidism |
| Phosphorus | 3.0–4.5 mg/dL | Moves opposite to calcium |
| Alkaline phosphatase (ALP) | 30–120 U/L | Rises with bone healing, Paget's disease and bone tumors |
| Vitamin D (25-OH) | 30–100 ng/mL | Low levels contribute to osteomalacia and osteoporosis |
| Bone density (DXA) T-score | −1.0 or higher is normal | −1 to −2.5 osteopenia; −2.5 or lower osteoporosis |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- Pain that does not respond to opioids after a fracture or cast is compartment syndrome until proven otherwise.
- Take oral bisphosphonates first thing in the morning with water only, and stay upright for 30 minutes to prevent esophagitis.
- Fat embolism usually appears 24–72 hours after a long-bone fracture: sudden dyspnea, confusion and petechiae on the chest.
Practice questions
8 NCLEX-style questions on the skeletal system. Pick an answer to see the rationale.
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A client has a new cast on the lower leg and reports severe pain that is not relieved by the prescribed opioid. What is the nurse's priority action?
Show the answer and rationale
Answer B: Notify the provider immediately. Pain unrelieved by opioids suggests compartment syndrome, a surgical emergency. Elevating above the heart would further reduce perfusion; the limb should stay at heart level.
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Which instruction is correct for a client starting oral alendronate?
Show the answer and rationale
Answer C: Take it on waking with a full glass of water and stay upright for 30 minutes. Bisphosphonates are poorly absorbed with food or other drinks and can cause esophagitis, so they are taken with plain water on an empty stomach while staying upright.
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Which hormone raises blood calcium by stimulating osteoclasts?
Show the answer and rationale
Answer B: Parathyroid hormone. PTH releases calcium from bone (osteoclast activity), increases renal calcium reabsorption and activates vitamin D. Calcitonin lowers blood calcium.
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Two days after a femur fracture, a client becomes confused and short of breath, with petechiae on the chest. The nurse suspects:
Show the answer and rationale
Answer A: Fat embolism syndrome. The classic triad of fat embolism is respiratory distress, altered mental status and petechiae, typically 24–72 hours after a long-bone fracture.
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A nurse counts intercostal spaces to locate the second intercostal space. Which landmark is used?
Show the answer and rationale
Answer C: Sternal angle (angle of Louis). The sternal angle sits at the level of the second rib; the space just below it is the second intercostal space.
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Which finding is typical of a hip fracture?
Show the answer and rationale
Answer B: Shortened leg with external rotation. Muscle pull on the fractured femur shortens the leg and rotates it outward.
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Which morning stiffness pattern points to rheumatoid arthritis rather than osteoarthritis?
Show the answer and rationale
Answer B: Stiffness lasting more than 1 hour, in symmetric joints. Rheumatoid arthritis causes prolonged morning stiffness in symmetric joints. Osteoarthritis stiffness is brief and pain worsens with use.
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At which level is a lumbar puncture usually performed in adults?
Show the answer and rationale
Answer C: L3–L4 or L4–L5. The adult spinal cord ends around L1–L2, so the needle is placed below it at L3–L4 or L4–L5 to avoid cord injury.