Study guide
Musculoskeletal System: High-Yield PANCE Review
The musculoskeletal system is one of the most heavily weighted PANCE content areas (~8-10% of the exam), spanning traumatic, degenerative, inflammatory, infectious, and neoplastic disorders. This guide targets the highest-yield, most frequently tested board content with current first-line management.
Rheumatologic Arthritides (RA, OA, Gout, Pseudogout)
- ◆Osteoarthritis: asymmetric, weight-bearing joints (knee, hip, DIP=Heberden/PIP=Bouchard nodes); worse with use, brief (<30 min) morning stiffness; radiographs show joint-space narrowing, osteophytes, subchondral sclerosis. First-line (ACR): exercise/weight loss + topical NSAIDs (knee/hand) or oral NSAIDs; acetaminophen weakly recommended.
- ◆Rheumatoid arthritis: symmetric small-joint (MCP, PIP, wrist) polyarthritis, morning stiffness >1 hr, spares DIPs; anti-CCP most specific, RF sensitive; erosions/juxta-articular osteopenia. First-line DMARD = methotrexate (add folic acid; monitor LFTs/CBC).
- ◆Gout: acute monoarthritis, classically 1st MTP (podagra); negatively birefringent needle-shaped urate crystals. Acute flare: NSAIDs, colchicine, or steroids (first-line options). Chronic urate-lowering: allopurinol is first-line for all (including CKD), treat-to-target urate <6 mg/dL, with anti-inflammatory prophylaxis for 3-6 months on initiation.
- ◆Gout ULT timing (ACR 2020 update): do NOT stop urate-lowering therapy during a flare; ULT may even be initiated during a flare as long as anti-inflammatory coverage is given (older 'wait until flare resolves' teaching is outdated).
- ◆Pseudogout (CPPD): positively birefringent rhomboid crystals; chondrocalcinosis on X-ray; often knee/wrist; associated with hemochromatosis, hyperPTH; treat like acute gout (NSAIDs, colchicine, or intra-articular steroids).
- ◆SLE pearls: young women, malar/discoid rash, photosensitivity, serositis, nephritis; ANA sensitive (screen), anti-dsDNA and anti-Smith specific; drug-induced (hydralazine, procainamide, isoniazid) → anti-histone antibodies.
Emergent Orthopedic Injuries
- ◆Compartment syndrome: pain out of proportion, pain with passive stretch (earliest), paresthesia; pulselessness/pallor are LATE. Diagnose clinically or delta pressure <30 mmHg; treat with emergent fasciotomy — do NOT elevate above heart.
- ◆Open fracture: emergency; early IV antibiotics (cefazolin; add gram-negative/aminoglycoside coverage for higher-grade Gustilo III, penicillin for barnyard/fecal contamination), tetanus prophylaxis, urgent irrigation and debridement in OR.
- ◆Scaphoid fracture: FOOSH with anatomic snuffbox tenderness; high AVN/nonunion risk. Thumb spica splint and repeat imaging in 10-14 days even if initial X-ray is negative.
- ◆Hip dislocation (usually posterior): limb shortened, adducted, internally rotated; emergent reduction to reduce femoral head AVN risk.
- ◆Septic joint and cauda equina (see other sections) are can't-miss; also consider neurovascular injury with knee dislocation (popliteal artery — get ABI/CTA).
Bone and Joint Infections
- ◆Septic arthritis: acute monoarthritis with fever; arthrocentesis WBC typically >50,000 (mostly PMNs). Most common overall = S. aureus; sexually active young adults consider disseminated gonococcus (migratory arthritis, tenosynovitis, pustular rash).
- ◆Septic arthritis management: joint drainage/washout PLUS empiric IV antibiotics (vancomycin for MRSA coverage; add ceftriaxone for gonococcal/gram-negative).
- ◆Osteomyelitis: S. aureus most common; MRI most sensitive early imaging; ESR/CRP for monitoring; bone biopsy/culture guides therapy. Diabetic foot and sickle cell (Salmonella) are classic associations.
- ◆Open fractures, prosthetic joints, and IV drug use raise infection risk; probe-to-bone positive in diabetic ulcer supports osteomyelitis.
Spine and Low Back Disorders
- ◆Cauda equina syndrome: saddle anesthesia, urinary retention/overflow incontinence, bilateral leg weakness — emergent MRI and surgical decompression.
- ◆Sciatica/herniated disc: L4-L5 and L5-S1 most common; positive straight-leg raise; imaging only if red flags or persistent >6 weeks. Most acute low back pain resolves with activity as tolerated + NSAIDs (avoid bed rest).
- ◆Red flags prompting imaging: age >50, history of cancer, fever/IVDU (infection), trauma, unexplained weight loss, neurologic deficits, night pain.
- ◆Spinal stenosis: older adults, neurogenic claudication improved by leaning forward/sitting (shopping-cart sign). Ankylosing spondylitis: young men, HLA-B27, inflammatory back pain improving with exercise, bamboo spine.
Pediatric Orthopedics
- ◆Developmental dysplasia of hip: Barlow (dislocatable) and Ortolani (reducible) maneuvers in newborns; ultrasound <4-6 months, X-ray after. Treat with Pavlik harness.
- ◆Legg-Calvé-Perthes: idiopathic femoral head AVN, ages ~4-8, painless limp; vs SCFE: obese adolescent, hip/knee pain with externally rotated leg — urgent non-weight-bearing and surgical pinning.
- ◆Nursemaid elbow (radial head subluxation): axial traction on pronated arm; child holds arm flexed/pronated; reduce by supination-flexion or hyperpronation.
- ◆Osgood-Schlatter: tibial tubercle pain in active adolescents; self-limited with rest/ice. Salter-Harris classification grades physeal (growth plate) fractures (SALTR mnemonic).
- ◆Always consider non-accidental trauma with metaphyseal corner (bucket-handle) fractures, posterior rib fractures, or injuries inconsistent with history.
Bone Metabolism, Tumors, and Soft Tissue
- ◆Osteoporosis: screen women ≥65 (USPSTF, 2024 update specifies central DXA) and higher-risk postmenopausal women <65; T-score ≤ -2.5 = osteoporosis. First-line = bisphosphonates (alendronate) + calcium/vitamin D; take upright, fasting to prevent esophagitis. Very-high-risk patients (severe/multiple fractures) may start with an anabolic (romosozumab, teriparatide/abaloparatide) then transition to a bisphosphonate.
- ◆Osteomalacia/rickets: vitamin D deficiency; low calcium/phosphate, high ALP and PTH; bowing in children. Paget disease: isolated markedly elevated ALP, bone pain/deformity; treat with bisphosphonates.
- ◆Primary malignant bone tumors: osteosarcoma (metaphysis of long bones, Codman triangle/sunburst, adolescents), Ewing sarcoma (diaphysis, onion-skin, children), chondrosarcoma (older adults).
- ◆Common soft-tissue: rotator cuff (supraspinatus) tears/impingement, lateral epicondylitis (tennis elbow), carpal tunnel (median nerve, thenar wasting, Phalen/Tinel), plantar fasciitis (heel pain worst with first morning steps).
- ◆Fibromyalgia: chronic widespread pain, fatigue, nonrestorative sleep, normal labs/imaging; first-line = non-pharmacologic (exercise, patient education, CBT); add duloxetine, milnacipran, or pregabalin if inadequate response.