ONC® Certification cheat sheet

Compartment syndrome hallmark: pain out of proportion to injury, worse with passive stretch; pain and paresthesia are early, pulselessness and paralysis are late and unreliable.

Normal compartment pressure is roughly 0-8 mmHg; delta pressure (diastolic BP minus compartment pressure) below 30 mmHg supports fasciotomy in the at-risk limb.

Fat embolism syndrome triad: hypoxemia, petechial rash, neurologic change; typically 24-72 hours after long-bone fracture, often with falling platelets.

Osteomyelitis: Staphylococcus aureus is the most common pathogen; chronic infection requires bone biopsy for culture rather than sinus-tract swab.

Avascular necrosis risk sites: femoral head, scaphoid proximal pole, talar body, lunate; risk rises with displaced fractures and corticosteroid or alcohol exposure.

Traction rule: skeletal traction is applied through a pin in bone; skin traction is limited to low weights (commonly about 2.3-4.5 kg) to protect skin integrity.

Hip fracture: shortened, externally rotated leg suggests displaced femoral neck or intertrochanteric fracture; shortening with internal rotation suggests posterior hip dislocation.

Bone healing phases: hematoma/inflammation (days), soft callus, hard callus, remodeling (months to years); smoking and NSAIDs impair union.

Neurovascular checks (5 P's plus capillary refill) are documented hourly after fracture reduction, cast application, or surgery; compare with the unaffected limb.

Cast care: window a cast for wound checks, never pad a tight cast, and bivalve or split a cast if swelling threatens circulation.

Osteoarthritis: joint-space narrowing, subchondral sclerosis, osteophytes, and cysts; pain worsens with use and eases with rest.

Rheumatoid arthritis: symmetric small-joint synovitis, morning stiffness over 1 hour, anti-CCP and rheumatoid factor; cervical spine instability requires caution with intubation.

Osteoporosis diagnosis: T-score of -2.5 or lower on DXA; a fragility fracture of hip or spine establishes the diagnosis regardless of T-score.

Total hip arthroplasty precautions (posterior approach): avoid hip flexion beyond 90 degrees, adduction past midline, and internal rotation; abductor pillow or wedge used in bed.

Total knee arthroplasty: continuous passive motion and early ambulation reduce stiffness; monitor for DVT, peroneal nerve palsy, and wound drainage.

DVT prophylaxis after major orthopaedic surgery: mechanical plus pharmacologic agents (low-molecular-weight heparin, aspirin, or direct oral anticoagulants per protocol) and early mobilization.

Acute osteomyelitis in children: fever, point tenderness, refusal to bear weight; blood cultures positive in roughly half of cases, and MRI is the imaging of choice.

Septic arthritis: joint aspiration shows elevated white count (often over 50,000/mm3) with neutrophil predominance; drainage and IV antibiotics are urgent.

Open fracture: tetanus status, antibiotic within 1 hour, and urgent irrigation and debridement; Gustilo grading guides fixation and coverage.

Amputation: wrap with distal-to-proximal figure-eight bandage; avoid elevation of an ischemic limb and monitor for phantom pain versus residual limb infection.

Scoliosis: Adams forward bend test screens for rotational deformity; curves of 25-40 degrees in a growing child may be braced to limit progression.

Spinal fusion: log-roll technique, assess bowel function for ileus, and monitor neurologic status; ileus is common after anterior approaches.

Osteogenesis imperfecta: blue sclera, recurrent fractures, hearing loss; handle with care and avoid forceful limb manipulation.

Paget disease of bone: elevated alkaline phosphatase with normal calcium and phosphorus; bone pain, bowing, and risk of pathologic fracture or osteosarcoma.

Pain assessment in the cognitively impaired older adult: use PAINAD or similar observational tool; behavior change and guarding may be the only indicators.

Multimodal analgesia after orthopaedic surgery: scheduled acetaminophen and NSAIDs where appropriate, opioids for breakthrough, plus regional blocks to reduce opioid load.

Opioid adverse effects to monitor: respiratory depression (sedation precedes it), constipation (prophylactic bowel regimen), pruritus, and nausea.

Regional anesthesia: monitor for local anesthetic systemic toxicity (tinnitus, metallic taste, seizures) and for compartment syndrome masked by a dense block.

Delirium after hip fracture: risk factors include age over 70, dementia, and untreated pain; prevention includes orientation, hydration, and early mobilization.

Pressure injury staging: stage 1 non-blanchable erythema; stage 2 partial-thickness loss; stage 3 full-thickness loss; stage 4 exposed bone, tendon, or muscle.

Falls prevention after orthopaedic injury: bed low and locked, call light within reach, non-skid footwear, and assist to ambulate rather than discouraging mobility.

Fat embolism versus DVT: fat embolism presents with respiratory and neurologic signs plus petechiae within 72 hours; DVT presents with unilateral calf pain and swelling.

Pulmonary embolism after arthroplasty: sudden dyspnea, tachycardia, and hypoxemia; heparin-induced thrombocytopenia must be excluded before starting heparin.

Rhabdomyolysis: dark urine, elevated creatine kinase, hyperkalemia; treat with aggressive IV fluids and monitor for acute kidney injury and arrhythmia.

Hypercalcemia of immobility: occurs with prolonged bed rest; signs include fatigue, confusion, constipation, and polyuria; hydration and mobilization are treatment.

Bone tumor red flags: night pain unrelieved by rest, palpable mass, and pathologic fracture; osteosarcoma often occurs around the knee in adolescents.

Metastatic bone disease: breast, prostate, and lung are most common primary sites; pathologic fracture risk is assessed with Mirels scoring.

Cauda equina syndrome: saddle anesthesia, bowel or bladder dysfunction, and bilateral leg weakness require emergency MRI and surgical referral.

Skeletal pin sites: clean daily with prescribed solution, keep dry, and report loosening, drainage, or redness; do not routinely use antibiotic ointment unless ordered.

External fixation: assess alignment, pin integrity, and neurovascular status; ring fixators allow gradual correction and require pin-tract care teaching.

Ilizarov principles: distraction osteogenesis requires a latency of several days, distraction about 1 mm per day in divided increments, and consolidation.

Amputation stump shaping: rigid or elastic dressing controls edema; check for hematoma and infection; begin range of motion and strengthening early.

Prosthetic fitting: residual limb volume stabilizes over weeks to months; a shrinking limb requires sock changes and socket refitting.

Arthroscopy: assess for joint effusion and neurovascular status; cryotherapy and elevation reduce swelling; weight-bearing is per surgeon protocol.

Joint replacement infection: persistent pain, effusion, and elevated ESR/CRP suggest periprosthetic joint infection; aspiration for culture is diagnostic.

Calcium and vitamin D: adults generally need 1,000-1,200 mg calcium daily and 800-1,000 IU vitamin D; dietary intake is preferred over supplements.

Weight-bearing and resistance exercise preserve bone density; swimming and cycling are not weight-bearing and do not stimulate bone formation as strongly.

Bone mineral density: DXA reports T-score (versus young adult) and Z-score (versus age-matched); Z-score below -2.0 warrants evaluation for secondary causes.

Osteoporosis medications: bisphosphonates require upright posture for 30 minutes and adequate calcium; denosumab requires adherence because rebound fractures occur after missed doses.

Fracture risk tools: FRAX estimates 10-year major osteoporotic and hip fracture probability; treatment thresholds are commonly 20 percent major and 3 percent hip.

Osteoporosis in men: evaluate for hypogonadism, alcohol use, glucocorticoids, and hyperparathyroidism; do not assume bone loss is age-related alone.

Vertebral compression fracture: sudden back pain, height loss, and kyphosis; treat pain, consider bracing, and assess for falls risk and further fracture prevention.

Splinting: immobilize one joint above and one below the injury; check distal pulses, sensation, and motor function before and after application.

Traction types: Buck traction is skin traction for hip fractures; Russell traction is a sling-and-pulley system; balanced suspension allows limited movement.

Cast complications: compartment syndrome, pressure necrosis, nerve palsy, and cast saw burns; report burning, numbness, or unrelieved pain promptly.

Nerve injuries to monitor: radial nerve with humeral shaft fracture (wrist drop), peroneal nerve with knee or fibular injury (foot drop), ulnar nerve at the elbow.

Fat embolus prevention: early fracture fixation and careful handling of long-bone fractures reduce embolic load.

Crutch fitting: hand grips at wrist level with elbows flexed 15-30 degrees; three-point gait for non-weight-bearing, and stairs lead with the good leg going up.

Walker and cane use: cane held in the hand opposite the affected limb; walker advanced first, then the weaker leg, then the stronger leg.

Pediatric bone: open growth plates make Salter-Harris classification relevant; type I through V injuries have increasing risk of growth disturbance.

Child abuse red flags: fractures in non-mobile infants, metaphyseal corner fractures, and injuries inconsistent with the stated mechanism.

Developmental dysplasia of the hip: Ortolani and Barlow maneuvers in infants, asymmetric thigh folds, and limited abduction; ultrasound is used before ossification.

Clubfoot (talipes equinovarus): Ponseti method uses serial casting with Achilles tenotomy in many cases; adherence to bracing prevents relapse.

Legg-Calve-Perthes: avascular necrosis of the femoral head in children aged 4-8; presents with limp and groin or knee pain.

Slipped capital femoral epiphysis: obese adolescent with hip or knee pain and limited internal rotation; requires surgical pinning and non-weight-bearing until treated.

Juvenile idiopathic arthritis: chronic joint swelling for at least 6 weeks; uveitis screening by ophthalmology is required because eye disease is often asymptomatic.

Wound assessment after orthopaedic surgery: document drainage amount and character; serosanguineous drainage is expected early, purulent drainage is not.

Negative pressure wound therapy: improves granulation in open wounds; contraindicated over exposed vessels, malignancy, or untreated osteomyelitis.

Antibiotic prophylaxis timing: give within 60 minutes before incision (within 120 minutes for vancomycin or fluoroquinolones) and redose for long procedures.

Surgical site infection: occurs typically within 30 days (up to 90 days for implants); fever, wound erythema, and increasing pain warrant evaluation.

Sterile technique for pin and wound care: perform hand hygiene, use clean or sterile supplies per protocol, and avoid cross-contamination between sites.

Nutrition for wound healing: protein, vitamin C, and zinc support healing; malnutrition and uncontrolled diabetes increase infection and dehiscence risk.

Documentation of neurovascular status includes color, temperature, capillary refill, pulses, sensation, and motor function, each compared with the contralateral limb.

Osteoarthritis pain management follows a stepped approach: exercise and weight management, then topical or oral NSAIDs, then intra-articular injections, then arthroplasty.

Weight loss of about 10 percent of body weight reduces knee osteoarthritis pain and improves function.

Intra-articular corticosteroid provides short-term relief (weeks); repeated injections over months may accelerate cartilage loss.

Hyaluronic acid injections have modest and inconsistent benefit; guidelines vary and many do not recommend routine use.

Opioids for chronic musculoskeletal pain: reassess benefit, use the lowest effective dose, and monitor for falls, constipation, and sedation in older adults.

Total joint replacement readiness: failure of conservative care, night pain, and functional limitation are key indications; uncontrolled infection and poor rehabilitation potential are contraindications.

Enhanced recovery after surgery: preoperative education, carbohydrate loading, opioid-sparing anesthesia, and early mobilization shorten length of stay.

Upper extremity fracture care: assess radial and ulnar pulses, capillary refill, and median, ulnar, and radial nerve function; document before and after splinting.

Shoulder dislocation: anterior dislocation is most common; axillary nerve injury is assessed by deltoid strength and sensation over the lateral shoulder.

Rotator cuff tear: weakness with abduction and positive drop arm or empty can test; night pain and overhead difficulty are common.

Carpal tunnel syndrome: median nerve distribution numbness, positive Phalen and Tinel tests; night splinting and ergonomic change are first-line.

Distal radius fracture: watch for median nerve symptoms and complex regional pain syndrome; elevation and finger range of motion reduce edema.

Scaphoid fracture: tenderness in the anatomic snuffbox; risk of nonunion and avascular necrosis means immobilization and repeat imaging even with normal initial x-ray.

Elbow dislocation: assess brachial artery and ulnar nerve; reduce promptly and check for associated fractures.

Spinal cord injury: immobilize the spine, maintain mean arterial pressure (often 85-90 mmHg or higher per protocol) to support cord perfusion, and log-roll for transfers.

Neurogenic shock: hypotension with bradycardia from loss of sympathetic tone; treat with fluids and vasopressors, not just Trendelenburg.

Autonomic dysreflexia: occurs with injuries at T6 or above; hypertension, pounding headache, and bradycardia are triggered by bladder or bowel distension; sit up and relieve the stimulus.

Spinal precautions: maintain cervical alignment with a rigid collar and log-roll; assess motor and sensory levels using a standardized scale.

Bowel and bladder management after spinal cord injury: intermittent catheterization and a scheduled bowel program prevent distension and autonomic dysreflexia.

Pressure injury risk after spinal cord injury is high because sensation and mobility are impaired; reposition every 2 hours and inspect skin under devices.

Deep vein thrombosis risk is elevated with paralysis; use mechanical prophylaxis and anticoagulation as prescribed.

Sports injury: RICE (rest, ice, compression, elevation) is initial care for soft-tissue injury; ice for 15-20 minutes with a barrier to protect skin.

Anterior cruciate ligament tear: audible pop, immediate effusion, and instability; the Lachman test is most sensitive.

Concussion: remove from play, no same-day return, and follow graduated return-to-sport protocol after symptom resolution.

Meniscal tear: joint-line tenderness and mechanical symptoms such as locking or catching; MRI confirms when surgery is considered.

Achilles tendon rupture: positive Thompson test and inability to plantarflex; urgent orthopaedic referral is required.

Ankle sprain: the anterior talofibular ligament is most commonly injured; the Ottawa ankle rules guide when x-ray is needed.

Stress fracture: focal bone tenderness and pain with activity that eases with rest; early imaging may be normal, and MRI is more sensitive than x-ray.

Rehabilitation after fracture: begin isometric exercises and unaffected joint range of motion early; progress to active and resistive exercise as healing allows.

Weight-bearing status: non-weight-bearing, toe-touch, partial, weight-bearing as tolerated, and full; clarify the order because misinterpretation risks fixation failure.

Continuous passive motion after knee arthroplasty increases early flexion but does not replace active therapy; ambulation and quadriceps exercises are essential.

Transfer training: use a gait belt for safety, lock wheelchair brakes, and teach the patient to bear weight on the stronger side when standing.

Home safety after orthopaedic surgery: remove throw rugs, install grab bars, and use raised toilet seats after hip replacement.

Pain and function outcomes are improved by preoperative education and realistic goal setting; document baseline function.

Return to work and driving: driving is typically restricted while on opioids or after lower-extremity surgery; follow surgeon guidance.

Immobilization complications: disuse osteoporosis, muscle atrophy, joint contracture, and pressure injury; early mobilization and range of motion reduce risk.

Constipation after orthopaedic surgery: caused by immobility, opioids, and dehydration; use a bowel regimen and encourage fluids and fiber.

Urinary retention after spinal or regional anesthesia: monitor for bladder distension and use intermittent catheterization as ordered.

Anemia after major orthopaedic surgery: blood loss can exceed 1-2 liters with hip or knee arthroplasty; monitor hemoglobin and transfusion thresholds.

Hypothermia in the operating room and after surgery: active warming reduces surgical site infection and cardiac events.

Glycemic control after orthopaedic surgery: hyperglycemia increases infection risk; monitor glucose and follow the insulin protocol.

Smoking cessation before elective arthroplasty reduces wound complications and improves bone healing; offer cessation support.

Medication safety: anticoagulants after arthroplasty require monitoring for bleeding, and neuraxial anesthesia timing rules apply to heparin and direct oral anticoagulants.

Corticosteroid use: long-term use increases osteoporosis, infection, and poor wound healing; taper rather than stop abruptly.

Methotrexate for rheumatoid arthritis: weekly dosing only; folic acid supplementation and monitoring of liver and blood counts are required.

Biologic therapy for rheumatoid arthritis: screen for latent tuberculosis before starting; hold for active infection.

Gout: monosodium urate crystals are negatively birefringent; treat acute flares with NSAIDs, colchicine, or corticosteroids, and lower urate with allopurinol after the flare.

Antibiotic bone penetration: chronic osteomyelitis often needs prolonged IV therapy guided by culture and sometimes surgical debridement.

Analgesic safety in older adults: avoid meperidine and use caution with NSAIDs because of renal, gastrointestinal, and cardiovascular risk.

Fracture description: include bone, location, pattern (transverse, oblique, spiral, comminuted), displacement, angulation, and whether it is open or closed.

Salter-Harris classification: I through physis, II through physis and metaphysis, III through physis and epiphysis, IV through both, V crush injury.

Healing time: upper extremity fractures typically 4-6 weeks; lower extremity fractures 8-12 weeks; healing is longer in adults and with open fractures.

Hardware: plates and screws provide rigid fixation; intramedullary nails share load; external fixators span contaminated or unstable zones.

Removal of hardware is not routine unless it causes pain, infection, or limits growth; discuss with the surgeon.

Nonunion versus delayed union: nonunion shows no healing over months and requires intervention; delayed union heals slowly but progresses.

Pathologic fracture: occurs through bone weakened by tumor, cyst, or osteoporosis; evaluate the underlying cause.

Osteoarthritis versus rheumatoid arthritis: osteoarthritis affects weight-bearing joints asymmetrically with bony nodes; rheumatoid arthritis affects small joints symmetrically with soft swelling.

Seronegative spondyloarthropathies: ankylosing spondylitis causes sacroiliitis and morning back pain improved by exercise; HLA-B27 is associated.

Systemic lupus erythematosus: joint pain without erosions is common; monitor for renal and hematologic involvement.

Fibromyalgia: widespread pain with tender points and normal inflammatory markers; treatment is exercise, sleep hygiene, and selected medications.

Osteoporosis versus osteomalacia: osteoporosis has normal calcium, phosphorus, and alkaline phosphatase; osteomalacia has low calcium and phosphorus with elevated alkaline phosphatase.

Bone infection versus tumor: infection has fever and elevated inflammatory markers; tumor pain is often nocturnal and unrelieved by rest.

Referral triggers: neurovascular compromise, open fracture, suspected infection, and cauda equina symptoms require urgent orthopaedic evaluation.