Orthopaedic Nurses Certification Exam

This chapter covers the orthopaedic history and physical examination, the neurovascular assessment that underpins so many priority questions, and the imaging studies and laboratory tests used to diagnose musculoskeletal conditions. On the ONC exam, assessment content appears as expected findings, findings to report, and the nursing responsibilities before and after diagnostic procedures.

A focused orthopaedic history explores the chief complaint (pain, stiffness, swelling, weakness, deformity, loss of function), the mechanism of injury for trauma, and the onset, location, duration, character, aggravating and relieving factors, and timing of symptoms. Morning stiffness lasting more than an hour suggests inflammatory arthritis, whereas brief stiffness under about 30 minutes that worsens with use suggests osteoarthritis. Night pain or pain at rest raises concern for infection or tumor. The nurse also asks about function (dressing, bathing, stairs, work), past fractures and surgeries, medications (especially corticosteroids, anticoagulants, bisphosphonates and herbal supplements), smoking, alcohol, nutrition, occupation, hobbies, falls, home environment and support systems.

Inspection compares both sides for symmetry, alignment, deformity, swelling, muscle atrophy, skin color, wounds, and posture. Palpation assesses warmth, tenderness, crepitus, effusion and muscle tone. Always examine the unaffected side first so the patient knows what to expect and you have a baseline.

Range of motion (ROM) is assessed actively (the patient moves the joint) and passively (the examiner moves it). Active ROM less than passive ROM suggests weakness or pain, as with a rotator cuff tear, while equal loss of both suggests a mechanical block such as arthritis or adhesive capsulitis. ROM is measured in degrees with a goniometer, which is centered over the joint axis with its arms aligned along the bones. Normal knee motion runs from 0 degrees (full extension) to about 135 degrees of flexion, and functional goals after total knee arthroplasty are commonly full extension and at least 90 to 110 degrees of flexion. Terms the exam expects you to know include flexion, extension, hyperextension, abduction (away from midline), adduction (toward midline), internal and external rotation, pronation and supination of the forearm, inversion and eversion of the foot, and dorsiflexion and plantar flexion of the ankle.

Manual Muscle Strength Grades

Exam Tip: Grade 3 is the threshold of antigravity strength. A patient who can lift the leg off the bed but cannot resist any pressure is grade 3, and a new drop from baseline strength after spine surgery is a finding to report promptly.

Common abnormal gaits include the antalgic gait (shortened stance on the painful leg), the Trendelenburg gait (pelvis drops on the opposite side because of hip abductor weakness), steppage gait (high stepping because of foot drop from peroneal nerve or L5 injury), and the shuffling, festinating gait of Parkinson disease.

Special tests are named on the exam mainly as expected findings. Key examples: Lachman and anterior drawer tests for anterior cruciate ligament tears; McMurray test for meniscal tears; Phalen and Tinel signs for carpal tunnel syndrome; Thompson test (absent plantar flexion with calf squeeze) for Achilles rupture; straight-leg raise for lumbar radiculopathy; Ortolani and Barlow maneuvers for infant hip dysplasia; Adams forward bend test for scoliosis; and the Finkelstein test for de Quervain tenosynovitis. Each is covered in detail in the condition sections.

Neurovascular (NV) checks are the single most tested orthopaedic assessment skill. They are performed distal to every injury, cast, splint, traction device, or surgical site, compared with the unaffected limb, and repeated frequently in the first 24 to 72 hours (often every hour at first, then every 2 to 4 hours per protocol). The assessment includes color, temperature, capillary refill, pulses, swelling, sensation, movement and pain.

The 6 Ps of Neurovascular Compromise

Some sources list 5 Ps (pain, pallor, pulselessness, paresthesia, paralysis) and add poikilothermia or pressure as the sixth. Capillary refill should be less than about 2 to 3 seconds; prolonged refill indicates impaired perfusion. Swelling is assessed by circumference and tightness of dressings or casts.

Sensation and Motor Testing by Peripheral Nerve

Memory Aid: For the hand, think "rock, paper, scissors, OK." Rock (fist) tests the median nerve, paper (spreading fingers) tests the ulnar nerve, a thumbs-up or wrist extension tests the radial nerve, and an OK sign tests the anterior interosseous branch of the median nerve.

Clinical Scenario: Four hours after application of a long leg cast, a patient reports numbness over the top of the foot and cannot dorsiflex the ankle. The nurse recognizes peroneal nerve compression, a classic risk where the nerve wraps around the fibular head. The nurse checks that nothing is pressing on the lateral knee, notifies the provider immediately, and anticipates bivalving or windowing the cast, because nerve compression can cause permanent foot drop.

Common Orthopaedic Imaging and Nursing Responsibilities

MRI safety screening is a priority teaching and assessment point. Before MRI, the nurse screens for implanted devices (pacemakers and defibrillators, neurostimulators, cochlear implants, insulin or pain pumps, aneurysm clips), metal fragments (especially in the eyes, as in welders or metal workers), medication patches with metallic backing, and pregnancy. Most joint replacements, plates and screws are MRI-conditional, but the device must be verified. External fixators often contain ferromagnetic parts and require specific clearance.

Common Trap: Joint replacement hardware does not automatically prohibit MRI, but a cardiac device or retained metal in the eye may. When a question asks which history item to report before MRI, choose the implanted electronic device or metal fragment over a remote joint replacement.

Arthrocentesis is aspiration of synovial fluid with a needle, used for diagnosis (infection, crystals, inflammation) and to relieve a tense effusion; corticosteroid may be injected at the same time. Normal synovial fluid is clear, straw-colored and viscous. Cloudy, purulent fluid with a very high white cell count suggests septic arthritis; needle-shaped, negatively birefringent crystals indicate gout, and rhomboid, positively birefringent crystals indicate calcium pyrophosphate deposition (pseudogout). Blood suggests trauma such as a ligament tear or fracture into the joint. After the procedure, the nurse applies a compression dressing, ice, and teaches the patient to rest the joint briefly and to report fever, increasing redness, warmth or pain, which could indicate infection.

Key Musculoskeletal Laboratory Tests

Exam Tip: A markedly elevated CK with dark, tea-colored urine after a crush injury or prolonged immobilization on the floor indicates rhabdomyolysis. The nursing priority is aggressive IV fluid to protect the kidneys and close monitoring of urine output and potassium.

Compare the affected limb with the unaffected one and document a baseline for every assessment.

Muscle strength is graded 0 to 5; grade 3 means movement against gravity without resistance.

Neurovascular checks cover the 6 Ps and capillary refill; know sensory and motor tests for the peroneal, tibial, radial, median and ulnar nerves.

Before MRI, screen for implanted electronic devices, metal fragments and pregnancy.

Match labs to conditions: CK for muscle injury, alkaline phosphatase for bone formation, anti-CCP for RA, HLA-B27 for spondyloarthropathy, CRP to trend infection.