Orthopaedic Nurses Certification Exam

Pain (about 35 to 45 scored questions) and complications (about 31 to 41) together make up more than half of the exam, and most of that content draws on the principles in Chapters 1.3 and 1.4: multimodal analgesia, opioid safety, venous thromboembolism, compartment syndrome, fat embolism, infection and delirium. Self-care teaching and activity questions lean on the assessment, rehabilitation and assistive-device principles in Chapters 1.2 and 1.5. Master this section first, and the condition sections that follow become a matter of applying familiar rules to new situations.

This chapter reviews the structure and function of bone, cartilage, tendons, ligaments and joints, explains how each tissue heals, and identifies the patient factors that slow healing. The exam rarely asks pure anatomy; instead it expects you to apply these facts, for example by recognizing why a smoker with diabetes is at high risk for nonunion or why a tendon repair must be protected for weeks.

Bone is a living, vascular connective tissue that provides support, protects organs, allows movement through muscle attachment, stores calcium and phosphorus, and houses hematopoietic marrow. Cortical (compact) bone forms the dense outer shell and makes up most of the skeleton's mass; it is organized into osteons (Haversian systems) around central canals carrying vessels and nerves. Cancellous (trabecular or spongy) bone is a lattice found in vertebral bodies, the pelvis, and the ends of long bones. Because cancellous bone has a much higher turnover rate, it is affected first by osteoporosis, which is why vertebral, distal radius and hip fractures are classic fragility fractures.

A long bone has a diaphysis (shaft), metaphyses (flared regions), and epiphyses (ends). In children the physis (growth plate) lies between the epiphysis and metaphysis and is the weakest point of the immature skeleton, which explains why pediatric injuries often involve the growth plate rather than ligaments. The periosteum is a vascular, pain-sensitive membrane covering bone; it supplies osteoprogenitor cells for healing and is the reason bone injuries hurt so intensely.

Three cell types maintain bone. Osteoblasts build bone matrix (osteoid) and later mineralize it; they produce alkaline phosphatase, so the enzyme rises when bone formation is active, as in healing fractures, Paget disease, osteomalacia and growing children. Osteoclasts resorb bone and are the target of antiresorptive drugs such as bisphosphonates and denosumab.

Bone Cells and Their Roles

Bone is constantly remodeled: osteoclasts resorb old bone and osteoblasts replace it. Wolff's law states that bone adapts to the loads placed on it, which is why weight-bearing exercise strengthens bone and immobility, bed rest and spaceflight weaken it. Remodeling is regulated by parathyroid hormone (PTH), which raises serum calcium by increasing bone resorption, renal calcium reabsorption and activation of vitamin D; by calcitriol (active vitamin D), which increases intestinal absorption of calcium and phosphate; by calcitonin, which modestly inhibits osteoclasts; and by estrogen and testosterone, which protect bone. Loss of estrogen at menopause accelerates resorption and is the main driver of postmenopausal osteoporosis. Long-term corticosteroids, by contrast, suppress osteoblasts and are the most common cause of secondary osteoporosis.

Exam Tip: When a question links immobility with bone, think in both directions. Immobility causes bone loss and can raise urinary calcium, increasing the risk of renal calculi, while early weight bearing (when ordered) stimulates healing and preserves bone density.

Fracture healing follows a predictable sequence. Knowing the stages helps you explain to patients why pain and swelling are worst early, why immobilization lasts weeks, and why x-rays may not show healing even when the patient feels better.

Stages of Fracture Healing

Healing time varies with age, bone, fracture type and health. Children heal fastest; an adult long-bone fracture commonly needs about 6 to 12 weeks for clinical union, and the tibia, scaphoid and femoral neck are notorious for slow healing because of limited blood supply. Primary (direct) healing occurs when rigid internal fixation compresses fragments with no gap and produces little visible callus, while secondary (indirect) healing with callus occurs with casts, intramedullary nails and external fixation.

Memory Aid: "Hematoma, soft, hard, shape" summarizes the four stages: hematoma, soft callus, hard callus, remodeling (shaping).

Articular (hyaline) cartilage covers joint surfaces and allows near-frictionless movement. It is avascular and aneural, receiving nutrition from synovial fluid as the joint moves and is loaded. Because it has no blood supply, damaged articular cartilage has very limited ability to repair itself; defects that do heal fill with weaker fibrocartilage. This explains both the progressive nature of osteoarthritis and the value of motion (including continuous passive motion after some cartilage procedures) for cartilage nutrition. Fibrocartilage forms the menisci, intervertebral discs and labrum. The outer third of the meniscus (the red zone) has a blood supply and can be repaired, whereas inner tears often require partial meniscectomy.

Tendons connect muscle to bone, and ligaments connect bone to bone. Both are dense collagen structures with relatively poor blood supply, so they heal slowly through inflammatory, proliferative and remodeling phases that last months. A repaired tendon is weakest during the first several weeks, when the repair depends on sutures rather than new collagen. This is why rotator cuff and Achilles repairs require protected motion, slings or boots, and strict avoidance of active loading until the surgeon advances the protocol.

Common Trap: Patients often feel well within two or three weeks after a tendon repair and want to resume lifting. The correct teaching is that the absence of pain does not mean the repair is strong; re-rupture risk is highest when patients advance activity on their own.

Joints are classified by movement. Synarthroses (such as skull sutures) are immovable, amphiarthroses (such as the pubic symphysis and intervertebral joints) are slightly movable, and diarthroses (synovial joints) are freely movable. Synovial joints have a fibrous capsule lined by synovium that secretes lubricating synovial fluid. Types include ball-and-socket (hip, shoulder), hinge (elbow, interphalangeal joints, the knee functionally), pivot (atlantoaxial joint, proximal radioulnar joint), condyloid (wrist), saddle (thumb carpometacarpal joint) and gliding (intercarpal joints).

The exam frequently asks which patient factor most threatens bone or wound healing, or which teaching point best supports fusion or union. The major factors are summarized in the following table.

Factors That Impair Musculoskeletal Healing

Clinical Scenario: A 58-year-old man is 6 weeks after a posterior lumbar fusion and asks whether he can start using nicotine gum instead of cigarettes. The nurse should explain that nicotine itself, not only smoke, constricts blood vessels and impairs bone formation, and encourage him to discuss nicotine-free cessation options with the surgeon, because nicotine in any form raises the risk of fusion failure (pseudarthrosis).

Exam Tip: When asked which factor in a history poses the greatest risk to fracture union or spinal fusion, smoking or nicotine use is usually the best answer unless a more acute problem (such as active infection) is present.

Cancellous bone turns over fastest, so osteoporosis shows first in the spine, wrist and hip.

Osteoblasts build bone and raise alkaline phosphatase; osteoclasts resorb bone and are targeted by antiresorptive drugs.

Fracture healing moves through hematoma, soft callus, hard callus and remodeling over weeks to months.

Articular cartilage is avascular and heals poorly; tendon and ligament repairs remain weak for weeks and need protection.

Smoking and nicotine, diabetes, corticosteroids, prolonged NSAIDs and malnutrition all delay healing.