44.1 Acute Inflammatory Arthritis & Spondyloarthropathies

ABFM Family Medicine Certification Study Guide Exam

Track your progress as you read

Finished sections get a check mark.

1 Chapter 1: Exam Structure, Blueprint & Clinical Decision-Making

1.1 Exam Blueprint, FMCLA vs. One-Day Exam & Board Scoring 1.2 Clinical Reasoning, Test-Taking Strategy & Ambiguity Management 1.3 Evidence-Based Medicine & Clinical Practice Guidelines in Primary Care

2 Chapter 2: Healthcare Systems, Practice Management & Quality

2.1 Practice Management, Billing, Coding & Documentation 2.2 Quality Improvement, Patient Safety & Diagnostic Stewardship 2.3 Interprofessional Team-Based Care & Care Coordination

3 Chapter 3: Ethics, Law, Biostatistics & Health Equity

3.1 Medical Ethics, Informed Consent & Surrogate Decision-Making 3.2 Biostatistics, Clinical Epidemiology & Diagnostic Test Interpretation 3.3 Social Determinants of Health, Health Equity & Cultural Humility 3.4 Physician Wellness, Burnout Prevention & Professionalism

4 Chapter 4: Lifestyle Counseling & Behavior Change

4.1 Alcohol Use Screening & Brief Intervention 4.2 Illicit Drug & Cannabis Counseling 4.3 Tobacco & Vaping Cessation Counseling

5 Chapter 5: Nutrition, Physical Activity & Chronic Disease Prevention

5.1 Dietary Counseling for Obesity & Chronic Disease Prevention 5.2 Exercise Prescription & Physical Activity Counseling 5.3 Genetic Risk Assessment & Family History Counseling

6 Chapter 6: Routine Adult Immunizations

6.1 ACIP Adult Respiratory Vaccines: Influenza, COVID-19, RSV & Pneumococcal 6.2 ACIP Adult Non-Respiratory Vaccines: Tdap, Shingrix, HPV & Hep B 6.3 Immunizations in Special Populations: Pregnancy, Asplenia & Immunocompromise

7 Chapter 7: Pediatric Health Maintenance & Surveillance

7.1 Newborn Examination & Early Postnatal Care 7.2 Well-Child Care, Developmental Surveillance & Milestones 7.3 Pediatric & Adolescent Screening: Vision, Hearing, Anemia & Lead 7.4 Pediatric Oral Health, Dental Screening & Fluoride

8 Chapter 8: Behavioral Health & Safety Screening

8.1 Primary Care Depression, Anxiety & Behavioral Health Screening 8.2 Domestic Violence, Intimate Partner Violence & Firearm Safety 8.3 Occupational Health & Recreational Safety Counseling

9 Chapter 9: Adult Preventive Screening: Cardiovascular & Metabolic

9.1 Cardiovascular Disease & Hypertension Screening 9.2 Type 2 Diabetes Screening & Prediabetes Risk Stratification 9.3 Abdominal Aortic Aneurysm & Osteoporosis Screening

10 Chapter 10: Adult Cancer Screening: Breast & Gynecologic

10.1 Breast Cancer Screening & Risk-Assessment 10.2 Cervical Cancer Screening & ASCCP Algorithms 10.3 Skin Cancer Clinical Assessment & Counseling

11 Chapter 11: Adult Cancer Screening: Colorectal, Lung & Prostate

11.1 Colorectal Cancer Screening Modalities & Intervals 11.2 Lung Cancer Screening with Low-Dose CT 11.3 Prostate Cancer Screening & Shared Decision-Making

12 Chapter 12: Sexual Health, Infectious Disease Screening & Contraception

12.1 Sexual Health Counseling & Risk-Reduction Strategies 12.2 STI Screening: Chlamydia, Gonorrhea, Syphilis & Trichomoniasis 12.3 Bloodborne Infectious Disease Screening: HIV & Hepatitis C

13 Chapter 13: Reproductive Life Planning, Lactation & Preoperative Care

13.1 Preconception Planning & Comprehensive Contraception Management 13.2 Lactation Support & Breastfeeding Counseling 13.3 Preoperative Medical Evaluation & Pre-Participation Sports Exam

14 Chapter 14: Emergent Cardiovascular Conditions

14.1 Acute Coronary Syndromes & Myocardial Infarction 14.2 Acute Chest Pain Risk Stratification & Triage 14.3 Acute or Critical Valvular Heart Emergencies

15 Chapter 15: Cardiac Arrhythmias, Heart Failure & Hypertensive Crises

15.1 Acute Atrial & Ventricular Arrhythmias 15.2 Acute Decompensated Heart Failure & Cardiogenic Shock 15.3 Hypertensive Emergency & Urgency Management

16 Chapter 16: Vascular & Thromboembolic Emergencies

16.1 Pulmonary Embolism & Deep Vein Thrombosis 16.2 Acute Aortic Syndromes & Peripheral Vascular Emergencies 16.3 Critical Limb Ischemia & Acute Arterial Occlusion

17 Chapter 17: Neurologic Emergencies: Stroke & Altered Consciousness

17.1 Acute Ischemic Stroke & Intracranial Hemorrhage 17.2 Syncope Evaluation & Status Epilepticus 17.3 Acute Delirium, Encephalopathy & Severe Confusion

18 Chapter 18: Neurologic Trauma & Acute Cranial Emergencies

18.1 Concussion, Moderate-to-Severe TBI & Intracranial Injury 18.2 Thunderclap & Acute Severe Secondary Headaches 18.3 Acute Ophthalmologic Emergencies

19 Chapter 19: Acute Abdominal, Pelvic & Gastrointestinal Emergencies

19.1 Acute Abdominal & Pelvic Pain Triage 19.2 Upper & Lower Gastrointestinal Bleeding 19.3 Acute Hepatic Failure, Cholangitis & Severe Jaundice

20 Chapter 20: Acute Pulmonary & Airway Emergencies

20.1 Acute Hypoxic Respiratory Failure & ARDS 20.2 Severe Community-Acquired Pneumonia & Empyema 20.3 Acute Severe Epistaxis & Airway Obstruction

21 Chapter 21: Acute Traumatic Injuries & Wound Care

21.1 Major Trauma Resuscitation & Initial Assessment 21.2 Burn Assessment, Inhalation Injury & Resuscitation 21.3 Laceration Management, Complex Wounds & Animal Bites

22 Chapter 22: Acute Orthopedic & Musculoskeletal Emergencies

22.1 Acute Ambulatory Fractures & Initial Splinting 22.2 Compartment Syndrome & Major Orthopedic Trauma 22.3 Septic Arthritis & Acute Microcrystalline Crises

23 Chapter 23: Severe Infections, Sepsis & Systemic Emergencies

23.1 Sepsis, Septic Shock & Initial Fluid Resuscitation 23.2 Necrotizing Soft Tissue Infections & Severe CNS Infections 23.3 Anaphylaxis Diagnosis, Epinephrine Dosing & Airway Protection

24 Chapter 24: Metabolic, Endocrine & Electrolyte Emergencies

24.1 Diabetic Ketoacidosis & Hyperosmolar Hyperglycemic State 24.2 Critical Electrolyte Emergencies: Dyskalemias & Dysnatremias 24.3 Severe Calcium Abnormalities & Acute Adrenal Crisis

25 Chapter 25: Hematologic, Urologic & Dental Emergencies

25.1 Severe Symptomatic Anemias & Coagulopathic Emergencies 25.2 Testicular Torsion, Priapism & Acute Urinary Retention 25.3 Urgent Odontogenic Infections & Dental Trauma

26 Chapter 26: Psychiatric, Behavioral & Obstetric/Gynecologic Emergencies

26.1 Suicidal Ideation, Acute Agitation & Behavioral Emergencies 26.2 Acute Physical & Sexual Assault Care 26.3 Life-Threatening Vaginal Bleeding & Ectopic Pregnancy 26.4 Environmental Heat Stroke & Severe Hypothermia

27 Chapter 27: Acute Head, Neck & Neurologic Symptoms

27.1 Primary Acute Headaches: Migraine, Tension & Cluster 27.2 Concussion & Minor Closed Head Injury Evaluation 27.3 Transient Ischemic Attack Evaluation & ABCD2 Risk Scoring

28 Chapter 28: Acute Cranial Nerves, Hearing & Sensory Symptoms

28.1 Peripheral Neuropathies: Bell's Palsy, Carpal Tunnel & Radiculopathy 28.2 Acute Tinnitus, Sudden Sensorineural Hearing Loss & Cerumen Impaction 28.3 Acute Dizziness, Benign Paroxysmal Positional Vertigo & Vestibular Neuritis

29 Chapter 29: Acute Upper Respiratory Tract Infections

29.1 Acute Viral Rhinosinusitis vs. Bacterial Rhinosinusitis 29.2 Acute Pharyngitis: Group A Streptococcus & Centor Criteria 29.3 Acute Otitis Media, Otitis Externa & Serous Effusion

30 Chapter 30: Acute Lower Respiratory Infections & Cough

30.1 Influenza, COVID-19 & Viral Respiratory Syndromes 30.2 Acute Bronchitis & Lower Respiratory Tract Infections 30.3 Ambulatory Community-Acquired Pneumonia

31 Chapter 31: Allergic, Nasal & Non-Infectious Pulmonary Conditions

31.1 Allergic Rhinitis & Acute Non-Anaphylactic Allergic Reactions 31.2 Acute Dyspnea in Ambulatory Care 31.3 Interstitial Lung Diseases & Sarcoidosis Presentation

32 Chapter 32: Acute Chest, Cardiac & Vascular Symptoms

32.1 Palpitations Evaluation & Arrhythmia Triage in Primary Care 32.2 Deep Vein Thrombosis & Superficial Thrombophlebitis 32.3 Ambulatory Hypotension & Orthostasis Evaluation

33 Chapter 33: Acute Upper Gastrointestinal Conditions

33.1 Peptic Ulcer Disease & Gastritis 33.2 Dysphagia, Esophagitis & Acute Esophageal Disorders 33.3 Acute Nausea, Vomiting & Foodborne Illness

34 Chapter 34: Acute Lower Gastrointestinal Conditions

34.1 Acute Infectious Diarrhea & Gastroenteritis 34.2 Acute Constipation & Functional Bowel Changes 34.3 Ano-Rectal Disorders: Hemorrhoids, Fissures, Abscesses & Pruritus Ani

35 Chapter 35: Inflammatory, Functional & Malabsorptive GI Disorders

35.1 Acute Flares of Inflammatory Bowel Disease 35.2 Irritable Bowel Syndrome: Diagnosis, Subtyping & Management 35.3 Celiac Disease & Malabsorption Syndromes

36 Chapter 36: Acute Abdominal, Hepatic & Biliary Disorders

36.1 Ambulatory Abdominal & Pelvic Pain Triage 36.2 Acute Cholecystitis, Biliary Colic & Pancreatitis 36.3 Acute Liver Injury & Viral Hepatitis

37 Chapter 37: Acute Abdominal Wall, Hernias & Dental Conditions

37.1 Abdominal Wall, Inguinal & Ventral Hernias 37.2 Acute Dental Pain, Odontogenic Abscess & Aphthous Ulcers 37.3 Acute Edema: Unilateral vs. Bilateral Diagnostic Evaluation

38 Chapter 38: Acute Infectious Dermatoses

38.1 Bacterial Skin Infections: Impetigo, Cellulitis & Cutaneous Abscesses 38.2 Fungal Skin Infections: Tinea Corporis, Cruris, Pedis & Onychomycosis 38.3 Viral Cutaneous Infections: Herpes Simplex, Zoster & Molluscum Contagiosum

39 Chapter 39: Inflammatory, Allergic & Autoimmune Dermatoses

39.1 Atopic Dermatitis, Contact Dermatitis & Eczematous Flares 39.2 Non-Infectious Rashes: Urticaria, Drug Eruptions & Erythema Multiforme 39.3 Cutaneous Malignancies & Premalignant Lesions: AK, BCC, SCC & Melanoma

40 Chapter 40: Acute Shoulder, Elbow & Upper Extremity Injuries

40.1 Rotator Cuff Pathology, Tendinopathy & Shoulder Impingement 40.2 Lateral & Medial Epicondylitis, Olecranon Bursitis & Elbow Sprains 40.3 Wrist & Hand Soft-Tissue Injuries: De Quervain, TFCC & Finger Sprains

41 Chapter 41: Acute Knee, Ankle & Lower Extremity Injuries

41.1 Meniscal Tears, Ligamentous Knee Injuries & Patellofemoral Pain 41.2 Ankle Sprains, Ottawa Ankle Rules & Achilles Tendinopathy 41.3 Plantar Fasciitis, Shin Splints & Overuse Syndromes

42 Chapter 42: Acute Ambulatory Fractures & Dislocations

42.1 Distal Radius, Scaphoid & Common Upper Extremity Fractures 42.2 Metatarsal, Clavicle & Common Lower Extremity Fractures 42.3 Joint Dislocation Management: Nursemaid's Elbow & Shoulder Subluxation

43 Chapter 43: Acute Axial Musculoskeletal Pain & Falls

43.1 Acute Low Back Pain: Red Flags, Strain & Disc Herniation 43.2 Acute Cervical Strain, Whiplash & Axial Neck Pain 43.3 Evaluation of Falls in Ambulatory & Older Patients

44 Chapter 44: Acute Inflammatory Arthropathies & Generalized Pain

44.1 Acute Inflammatory Arthritis & Spondyloarthropathies 44.2 Myalgias, Rhabdomyolysis & Post-Viral Pain Syndromes 44.3 Acute Non-Headache Pain Management Strategies

45 Chapter 45: Acute Renal, Urinary & Genitourinary Conditions

45.1 Uncomplicated UTI, Pyelonephritis & Acute Urethritis 45.2 Hematuria Workup & Glomerulonephritis 45.3 Nephrolithiasis & Acute Urinary Tract Obstruction

46 Chapter 46: Acute Male Genitourinary & Prostatic Conditions

46.1 Acute Prostatitis, Epididymitis & Orchitis 46.2 Acute Scrotal Pain: Torsion vs Appendage, BPH & Male Genital Emergencies 46.3 Acute Urinary Retention & Incontinence Evaluation

47 Chapter 47: Acute Women's Health & Early Pregnancy Care

47.1 Early Pregnancy Diagnosis, Dating & Initial Complications 47.2 Abnormal Uterine Bleeding & Acute Menstrual Disorders 47.3 Premenstrual Syndrome & Premenstrual Dysphoric Disorder

48 Chapter 48: Breast Disorders, STIs & Pediatric Elimination

48.1 Palpable Breast Mass, Mastitis & Nipple Discharge 48.2 Sexually Transmitted Infections: Diagnosis, Staging & CDC Guidelines 48.3 Pediatric Enuresis & Encopresis

49 Chapter 49: Systemic Signs, Metabolic Dysregulation & Miscellaneous Infections

49.1 Acute Fever, Sepsis Screening & FUO in Primary Care 49.2 Acute Hyperglycemia & Symptomatic Hypoglycemia 49.3 Electrolyte Abnormalities: Mild-to-Moderate Disturbances 49.4 Vector-Borne, Tick-Borne & Rickettsial Illnesses

50 Chapter 50: Chronic Cardiovascular Diseases: Hypertension & Ischemia

50.1 Essential Hypertension Management: 2025 AHA/ACC Guideline & JNC Strategies 50.2 Chronic Coronary Artery Disease & Post-MI Secondary Prevention 50.3 Chronic Heart Failure: HFrEF, HFpEF & Quadruple GDMT

51 Chapter 51: Chronic Vascular, Valvular & Dyslipidemic Diseases

51.1 Peripheral Arterial Disease & Claudication 51.2 Chronic Valvular Heart Disease & Murmur Evaluation 51.3 Lipid Disorders & ASCVD Risk-Based Statin Therapy

52 Chapter 52: Chronic Respiratory Diseases: Asthma & COPD

52.1 Chronic Asthma Management: GINA Stepwise SMART Therapy 52.2 Chronic Obstructive Pulmonary Disease: GOLD Recommendations 52.3 Solitary Pulmonary Nodule Evaluation & Fleischner Society Criteria

53 Chapter 53: Chronic Metabolic Diseases: Diabetes Mellitus

53.1 Type 2 Diabetes Management: ADA Pharmacotherapy Algorithms 53.2 Type 1 Diabetes: Basal-Bolus Insulin, CGMs & Diabetic Complications 53.3 Diabetic Microvascular & Macrovascular Disease Surveillance

54 Chapter 54: Obesity, Nutrition & Metabolic Bone Diseases

54.1 Medical & Behavioral Management of Obesity & Incretin Mimetics 54.2 Osteoporosis & Metabolic Bone Disease: DEXA, FRAX & Antiresorptives 54.3 Nutritional Deficiencies: Vitamin D, B12, Iron & Malnutrition

55 Chapter 55: Chronic Endocrine Disorders

55.1 Primary & Subclinical Hypothyroidism, Hyperthyroidism & Nodules 55.2 Adrenal Disorders: Addison's Disease & Cushing's Syndrome 55.3 Hypercalcemia, Hyperparathyroidism & Pituitary Disorders

56 Chapter 56: Chronic Kidney Disease & Venous Disorders

56.1 Chronic Kidney Disease: KDIGO Staging & Renoprotective Therapy 56.2 Chronic Venous Insufficiency, Stasis Dermatitis & Lymphedema 56.3 Chronic Electrolyte & Acid-Base Management in CKD

57 Chapter 57: Chronic Gastrointestinal & Hepatic Diseases

57.1 Gastroesophageal Reflux Disease, Barrett's Esophagus & Dyspepsia 57.2 Chronic Liver Disease: MASLD/NAFLD, Cirrhosis & Portal Hypertension 57.3 Viral Hepatitis B & C: Long-Term Monitoring & DAA Therapy

58 Chapter 58: Colorectal Surveillance & Chronic Pancreaticobiliary Care

58.1 Post-Polypectomy Colorectal Polyp Surveillance Guidelines 58.2 Chronic Pancreatitis & Exocrine Pancreatic Insufficiency 58.3 Chronic Nausea, Gastroparesis & Functional GI Disorders

59 Chapter 59: Chronic Musculoskeletal & Rheumatologic Disorders

59.1 Osteoarthritis: Hip, Knee & Hand Management 59.2 Spinal Conditions: Spinal Stenosis, Spondylolisthesis & Compression Fractures 59.3 Chronic Myopathies & Fibromyalgia Syndrome

60 Chapter 60: Chronic Neurologic & Neurodegenerative Disorders

60.1 Dementia: Alzheimer's, Vascular & Lewy Body Disease 60.2 Parkinson's Disease & Essential Tremor 60.3 Epilepsy: Chronic Antiseizure Medications & Post-Stroke Care

61 Chapter 61: Chronic Peripheral Nerves, Pain & Sensory Disorders

61.1 Diabetic & Chronic Peripheral Neuropathies 61.2 Chronic Pain Syndromes & Chronic Daily Headaches 61.3 Chronic Tinnitus, Presbycusis & Persistent Dizziness

62 Chapter 62: Chronic Psychiatric Disorders

62.1 Major Depressive Disorder & Generalized Anxiety Disorder 62.2 Bipolar Disorder: Maintenance Pharmacotherapy & Lithium Monitoring 62.3 Adult & Pediatric Attention-Deficit/Hyperactivity Disorder

63 Chapter 63: Chronic Behavioral Health & Neurodevelopmental Conditions

63.1 Chronic Behavioral Conditions: PTSD, OCD & Somatization 63.2 Autism Spectrum Disorder & Intellectual Disabilities 63.3 Eating Disorders: Anorexia Nervosa, Bulimia & Binge Eating

64 Chapter 64: Chronic Substance Use Disorders & Tobacco Cessation

64.1 Alcohol Use Disorder: Pharmacotherapy & Relapse Prevention 64.2 Opioid & Stimulant Use Disorders: MOUD & Harm Reduction 64.3 Longitudinal Tobacco Cessation Pharmacotherapy

65 Chapter 65: Chronic Dermatologic Conditions

65.1 Acne Vulgaris, Rosacea & Seborrheic Dermatitis 65.2 Chronic Plaque Psoriasis & Biologic Therapies 65.3 Chronic Eczema, Hidradenitis Suppurativa & Cutaneous Lupus

66 Chapter 66: Chronic Reproductive, Infectious & Geriatric Special Care

66.1 Chronic Menstrual Disorders, Infertility & Sexual Dysfunction 66.2 Menopause Management & Hormone Replacement Therapy 66.3 Chronic HIV Infection Management & Primary Care Integration 66.4 Gender-Affirming Primary Care & Hormone Therapy 66.5 Advance Care Planning, Palliative Care & End-of-Life Symptom Control

67 Chapter 67: Continuity Care: Sleep, Fatigue, Cancer, Pregnancy & the Adult Preventive Visit

67.1 Chronic Insomnia & Obstructive Sleep Apnea 67.2 Chronic Malaise, Fatigue & ME/CFS 67.3 Primary Care During Cancer Treatment & Survivorship 67.4 Routine Prenatal Care & Longitudinal Pregnancy Management 67.5 The Periodic Adult Health Examination & Medicare Annual Wellness Visit

44.1 Acute Inflammatory Arthritis & Spondyloarthropathies

Key Takeaways Explain This Topic AI

Acute monoarthritis is a medical emergency until septic arthritis is excluded via urgent diagnostic arthrocentesis (synovial fluid WBC >50,000/μL with >75-90% PMNs; Gram stain and culture; empiric IV vancomycin plus ceftriaxone and emergent orthopedic drainage).

Gout demonstrates needle-shaped, negatively birefringent monosodium urate crystals (yellow when parallel to polarized light axis, blue when perpendicular), while CPPD (pseudogout) shows rhomboid, weakly positively birefringent crystals (blue when parallel) and chondrocalcinosis on plain radiographs.

First-line acute gout flare therapy includes oral NSAIDs, oral colchicine (1.2 mg then 0.6 mg 1 hour later if within 36 hours of onset), or oral systemic corticosteroids (prednisone 35-40 mg/day for 5-7 days; preferred in CKD or GI bleeding risk); critical board rule: do NOT initiate or discontinue allopurinol during an acute flare, but if already taking allopurinol chronically, continue it unchanged.

CPPD is associated with systemic metabolic disorders (hemochromatosis, primary hyperparathyroidism, hypomagnesemia, hypophosphatasia) and is managed identically to gout flares.

Spondyloarthropathies (HLA-B27 associated) feature enthesitis and axial/peripheral inflammation: Ankylosing Spondylitis (insidious inflammatory back pain improving with exercise, morning stiffness >30 min, syndesmophytes/bamboo spine, anterior uveitis; first-line NSAIDs then TNF inhibitors), Psoriatic Arthritis (dactylitis/sausage digits, DIP arthritis, nail pitting, pencil-in-cup deformity), and Reactive Arthritis (triad of arthritis, urethritis, conjunctivitis/uveitis 1-4 weeks post-Chlamydia or enteric infection).

Last updated: September 2026

Clinical Triage & Differential Diagnosis of Acute Monoarthritis

Acute monoarthritis—defined as acute-onset inflammation, swelling, erythema, and severe pain localized to a single synovial joint developing over hours to a few days—is one of the most common and high-stakes musculoskeletal presentations in primary care and emergency medicine. The primary clinical imperative is to rapidly distinguish between a true infectious emergency (septic arthritis) and crystal-induced arthropathies (gout or pseudogout) , as untreated septic arthritis causes irreversible chondrocyte death, subchondral bone necrosis, and permanent joint destruction within 24 to 48 hours.

The Cardinal Rule of Monoarthritis: Diagnostic Arthrocentesis

Important

URGENT ARTHROCENTESIS MANDATE Every patient presenting with an unexplained acute monoarticular joint effusion or severe joint inflammation must undergo urgent diagnostic arthrocentesis prior to the initiation of antimicrobial therapy, unless an absolute contraindication exists (e.g., severe overlying cellulitis at the puncture site or severe uncorrected coagulopathy with active bleeding).

Clinical examination, plain radiography, and serum inflammatory markers (ESR, CRP, leukocytosis) CANNOT reliably differentiate septic arthritis from an acute crystal flare. Even if a patient has a documented history of chronic gout, crystal deposition and bacterial infection can, and frequently do, coexist in the same joint.

Synovial Fluid Analysis & Classification

Synovial fluid obtained via arthrocentesis should immediately be analyzed for four cardinal parameters: macroscopic appearance/clarity, total leukocyte count with differential, polarized light microscopy for crystals, and microbiological staining (Gram stain) and aerobic/anaerobic bacterial cultures. SYNOVIAL FLUID CLASSIFICATION MATRIX

• Category Clarity & Color WBC Count (/μL) % PMNs Glucose (% Serum) Common Etiologies
• ═══════════════════════════════════════════════════════════════════════════════════════════════════════════
• Normal Transparent, clear <200 <25% ~100% Normal joint

• Non- Transparent, yellow 200 to 2,000 <25% ~100% Osteoarthritis,
• Inflammatory trauma, meniscal tear

• Inflammatory Translucent to 2,000 to 50,000 50% to 50% to 80% Gout, Pseudogout,
• opaque, yellow 80% Rheumatoid arthritis,
• Spondyloarthropathies

• Septic Opaque, turbid, >50,000* >75% to <50% Bacterial infection
• (Infectious) purulent yellow- 90% (often marked drop) (S. aureus, N. gonorrhoeae,
• green Streptococcus spp.)

• Hemorrhagic Opaque, bloody/red 200 to 10,000 Variable ~100% Trauma, ACL rupture,
• coagulopathy, tumor
• ═══════════════════════════════════════════════════════════════════════════════════════════════════════════

Note on WBC Overlap: While a synovial WBC count >50,000/μL is the classical threshold for septic arthritis, bacterial infection (especially low-virulence organisms, partially treated infections, or disseminated gonococcal infection) can present with counts between 20,000 and 50,000/μL. Conversely, severe acute gout flares can occasionally exceed 50,000 to 100,000 WBC/μL. Therefore, Gram stain and culture remain the definitive gold standard.

• Septic Arthritis: Microbiology, Workup & Emergent Management
• 1. Microbiology

Staphylococcus aureus : The most common causative pathogen across all age groups in adults (>50% of non-gonococcal cases). Methicillin-resistant S. aureus (MRSA) accounts for a substantial fraction in patients with healthcare exposure, intravenous drug use (IVDU), indwelling catheters, or chronic skin ulcers.

Streptococcus Species : Streptococcus pneumoniae , Group A streptococci, and Group B streptococci account for 15% to 20% of cases.

Neisseria gonorrhoeae : The leading pathogen in healthy, sexually active adolescents and young adults. Gonococcal arthritis manifests in two distinct clinical syndromes:

Disseminated Gonococcal Infection (DGI) Triad : Migratory asymmetric tenosynovitis (wrists, ankles), dermatitis (painless pustular, petechial, or necrotic papules on distal extremities), and asymmetric polyarthralgias without purulent monoarthritis.

Purulent Gonococcal Monoarthritis : Frank purulent monoarthritis (knee, wrist, ankle) without prominent skin rash.

Clinical Pearl : Synovial fluid cultures are positive in fewer than 25% to 50% of DGI cases because the organism is fastidious. Clinicians must obtain nucleic acid amplification testing (NAAT) from urogenital (cervical, urethral), pharyngeal, and rectal sites, alongside blood cultures.

Gram-Negative Bacilli ( Escherichia coli , Pseudomonas aeruginosa ) : Encountered in older adults with urinary tract infections, immunocompromised hosts, and individuals who use intravenous drugs (where Pseudomonas has a predilection for axial fibrocartilaginous joints: sternoclavicular, sacroiliac, and pubic symphysis).

2. Clinical Presentation & Physical Examination

Acute monoarticular pain, swelling, warmth, and profound functional limitation.

The joint is held in slight flexion (maximizing intracapsular volume).

Exquisite pain with both active AND passive range of motion is a cardinal sign distinguishing true articular pathology from periarticular inflammation (such as prepatellar bursitis or tenosynovitis, where passive motion is relatively preserved).

3. Emergent Treatment Protocol

Urgent Orthopedic Surgical Consultation : Closed needle joint aspiration, arthroscopic debridement, or open arthrotomy (mandatory for hip and shoulder infections, or refractory knee infections) to evacuate pus, decompress intra-articular pressure, and prevent avascular necrosis.

Immediate Empiric Intravenous Antimicrobials (initiated immediately after synovial fluid aspiration):

Standard empiric regimen: Intravenous Vancomycin (15-20 mg/kg IV q8-12h; targeting trough 15-20 mcg/mL) PLUS a third-generation cephalosporin such as Intravenous Ceftriaxone (1-2 g IV q24h) to cover MRSA, Gram-negative bacilli, and N. gonorrhoeae .

In patients with severe beta-lactam anaphylaxis: Vancomycin plus an aminoglycoside (tobramycin) or aztreonam/fluoroquinolone.

Tailor antibiotics based on definitive Gram stain and culture susceptibility data; total antibiotic duration is typically 3 to 4 weeks (minimum 2 weeks intravenous followed by oral step-down for susceptible organisms).

Crystal-Induced Arthropathies: Gout

Gout is the most common inflammatory arthritis in adult males, resulting from the tissue deposition of monosodium urate (MSU) crystals into synovial joints and soft tissues following sustained hyperuricemia (serum urate concentration exceeding the physiologic saturation threshold of approximately 6.8 mg/dL ).

Pathophysiology

Hyperuricemia arises predominantly from renal underexcretion (>90% of patients) due to genetic variants in renal urate transporters (URAT1, GLUT9) or acquired renal impairment, whereas metabolic overproduction accounts for <10% (e.g., myeloproliferative disorders, tumor lysis syndrome, high-purine diets, inborn errors of metabolism). MSU crystals precipitate within the joint space and are phagocytosed by synovial macrophages, activating the intracellular NLRP3 inflammasome complex . This triggers caspase-1-dependent activation and massive secretion of interleukin-1 beta (IL-1β) , recruiting waves of neutrophils that release reactive oxygen species and lysosomal proteases, creating an explosive inflammatory flare.

Polarized Light Microscopy: The Definitive Diagnostic Hallmark POLARIZED MICROSCOPY: GOUT VS. PSEUDOGOUT

• Feature Gout (Monosodium Urate) Pseudogout (CPPD)
• ═════════════════════════════════════════════════════════════════════════════════════════
• Crystal Morphology Needle-shaped or needle-like; Rhomboid-shaped, rod-like,
• sharp pointed ends parallelepiped; blunt ends

• Birefringence STRONGLY NEGATIVE WEAKLY POSITIVE
• birefringence birefringence

• Compensated Color: YELLOW BLUE
• Parallel to Axis ("Yellow Parallel") ("Blue Parallel")

• Compensated Color: BLUE YELLOW
• Perpendicular to Axis ("Blue Perpendicular") ("Yellow Perpendicular")
• ═════════════════════════════════════════════════════════════════════════════════════════

High-Yield Exam Memory Aid : Remember the mnemonic "YENP" : Y ellow is E longated (needle) and N egative when P arallel (Gout). For pseudogout: "PBP" : P seudogout is B lue when P arallel.

Acute Gout Flare Triggers

Dietary Purines : Organ meats (liver, kidneys), red meat, shellfish, sardines, and anchovies.

Alcohol : Beer contains high levels of purines (guanosine) and alcohol metabolizes to lactic acid, which competitively inhibits renal tubular urate secretion. Spirits and wine also increase risk.

High-Fructose Corn Syrup : Fructose phosphorylation in the liver consumes ATP, generating AMP that enters the purine degradation pathway, rapidly elevating uric acid.

Medications : Thiazide and loop diuretics (enhance proximal tubular urate reabsorption), low-dose aspirin (<2 g/day), cyclosporine, tacrolimus, and niacin.

Physiologic Stressors : Surgery, systemic infection, starvation, dehydration, trauma, and rapid fluctuations in serum urate levels (such as commencing urate-lowering therapy).

Clinical Presentation: Podagra

Over 50% of initial acute flares involve the first metatarsophalangeal (MTP) joint (podagra) ; over a lifetime, >80% of gout patients experience podagra. Other common sites include the midfoot, ankle, knee, wrist, and olecranon bursa. Onset is characteristically explosive, often beginning overnight, reaching maximum pain intensity within 12 to 24 hours. The joint displays dusky erythema, dramatic swelling, warmth, and exquisite tenderness (patients describe agony even from a bedsheet resting on the toe), followed by desquamation of overlying skin as inflammation resolves.

Evidence-Based Pharmacotherapy for Acute Gout Flares

Three equally effective first-line pharmacologic classes exist; the selection depends entirely on patient comorbidities:

Oral Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) :

Regimens: Indomethacin (50 mg PO TID) or Naproxen (500 mg PO BID) or Ibuprofen (800 mg PO TID) initiated at maximum doses and tapered over 5 to 7 days after symptom resolution.

Contraindications : Chronic kidney disease (eGFR <60 mL/min), active peptic ulcer disease or GI bleeding, decompensated heart failure, cirrhosis, and concurrent therapeutic anticoagulation.

Oral Colchicine :

Regimen: 1.2 mg PO stat , followed by 0.6 mg PO 1 hour later (total 1.8 mg). A maintenance dose of 0.6 mg once or twice daily may be continued starting 12 hours later until the flare resolves.

Window of Efficacy : Highly effective if started within 24 to 36 hours of symptom onset ; efficacy drops dramatically after 36 hours.

Safety & Interactions : Substrate for CYP3A4 and P-glycoprotein (P-gp). Dose reduction required in renal impairment (eGFR <30 mL/min); contraindicated in combined renal and hepatic failure or with strong CYP3A4 inhibitors (clarithromycin, ketoconazole) due to fatal neuromyopathy.

Oral Systemic Corticosteroids :

Regimen: Prednisone 35 to 40 mg PO daily for 5 to 7 days , then stop (or taper over 7 to 10 days).

Preferred First-Line Choice : Patients with chronic kidney disease (CKD) , heart failure, peptic ulcer disease, or anticoagulation where NSAIDs and colchicine are hazardous.

Intra-articular Corticosteroid Injection : Triamcinolone acetonide (10-40 mg depending on joint size); ideal for an acute flare in 1 or 2 accessible joints once septic arthritis is definitively excluded.

• Caution
• THE CRITICAL BOARD EXAM RULE: ALLOPURINOL MANAGEMENT IN ACUTE FLARES

DO NOT INITIATE allopurinol (or other urate-lowering therapy) during an acute gout flare! Rapidly reducing serum urate promotes crystal dissolution, destabilizing articular tophi and prolonging or intensifying the acute flare. Wait until the acute flare has fully resolved (typically 2 to 4 weeks) before starting urate-lowering therapy.

DO NOT DISCONTINUE allopurinol if the patient is ALREADY taking it chronically at the time of the flare! Abrupt discontinuation causes a rebound spike in serum urate, triggering secondary crystal deposition and worsening the flare. Continue the baseline allopurinol dose unchanged and treat the flare aggressively with NSAIDs, colchicine, or steroids.

• Long-Term Management of Hyperuricemia & Gout Prophylaxis
• Indications for Urate-Lowering Therapy (ULT)

According to American College of Rheumatology (ACR) guidelines, ULT is strongly indicated for patients with:

• >=2 acute gout flares per year
• Presence of tophi on physical examination or imaging

Radiographic evidence of gouty joint damage / erosions (e.g., "punched-out" erosions with overhanging sclerotic margins / Martel sign)

• Gout with concurrent stage 3 or higher chronic kidney disease (CKD eGFR <60 mL/min)
• History of urolithiasis (uric acid nephrolithiasis)
• First-Line Urate-Lowering Therapy: Allopurinol

Mechanism : Xanthine oxidase inhibitor that blocks the sequential conversion of hypoxanthine to xanthine and xanthine to uric acid.

Dosing Strategy : Start at a low dose ( 100 mg PO daily ; or 50 mg daily in CKD stage 3-5 ) to avoid precipitously dropping serum urate. Titrate every 2 to 4 weeks by 100 mg increments based on serial serum urate measurements, up to a maximum dose of 800 mg/day.

Target Serum Urate Level :

Standard target: Serum urate <6.0 mg/dL (below the 6.8 mg/dL solubility threshold to promote crystal dissolution).

Severe tophaceous gout: Serum urate <5.0 mg/dL for accelerated tophus resolution.

HLA-B*5801 Genetic Screening :

Mandatory testing prior to allopurinol initiation in high-risk populations: patients of Southeast Asian descent (Han Chinese, Korean, Thai) and African American descent .

Possession of the HLA-B*5801 allele confers an astronomical risk of Allopurinol Hypersensitivity Syndrome (AHS), characterized by Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), eosinophilia, systemic vasculitis, hepatitis, and acute renal failure with a 25% mortality rate.

Mandatory Flare Prophylaxis During ULT Initiation

When initiating urate-lowering therapy, mobilizing crystals frequently triggers secondary gout flares. Clinicians must co-prescribe prophylactic anti-inflammatory therapy:

First-line prophylaxis : Low-dose oral Colchicine 0.6 mg once or twice daily (0.3 mg daily in CKD), OR low-dose oral NSAID (e.g., naproxen 250 mg PO BID with a PPI).

Duration : Continue prophylaxis for at least 3 to 6 months after achieving the target serum urate level without active flares.

Calcium Pyrophosphate Dihydrate (CPPD) Crystal Deposition Disease (Pseudogout)

CPPD disease results from the precipitation of calcium pyrophosphate dihydrate crystals in articular and fibrocartilaginous structures.

Clinical Presentation

Acute CPPD Crystal Arthritis (Pseudogout) : Acute, self-limiting monoarthritis or oligoarthritis resembling gout. However, unlike gout's predilection for the 1st MTP, pseudogout most commonly involves the knee (>50% of cases) , followed by the wrist, shoulder, ankle, and elbow.

Chronic CPPD Arthropathy : Resembles severe osteoarthritis with prominent joint destruction, but characteristically affects atypical joints (radiocarpal joint, metacarpophalangeal joints) with prominent morning stiffness.

Radiographic Hallmark: Chondrocalcinosis

Plain radiographs demonstrate pathognomonic chondrocalcinosis —punctate and linear radiodense calcifications within hyaline cartilage and fibrocartilage. Classic anatomic sites to image:

Knees : Calcification of the medial and lateral menisci and articular hyaline cartilage.

Wrists : Calcification of the triangular fibrocartilage complex (TFCC).

Pelvis : Calcification of the pubic symphysis.

Systemic Metabolic Associations: High-Yield Screening

CPPD occurring in patients under age 60 mandates laboratory screening for secondary metabolic and endocrine disorders:

Hereditary Hemochromatosis : Iron overload; check serum ferritin and transferrin saturation (>45%). CPPD characteristically produces squaring of bone ends and hook-like osteophytes at the 2nd and 3rd MCP joints.

Primary Hyperparathyroidism : Check serum calcium and intact parathyroid hormone (PTH).

Hypomagnesemia : Low magnesium levels impair pyrophosphatase enzyme activity, accelerating crystal deposition.

Hypophosphatasia : Check serum alkaline phosphatase (characteristically low).

Acute Management

Identical to acute gout flares: oral NSAIDs, low-dose colchicine, oral systemic corticosteroids, or intra-articular corticosteroid injection. Long-term urate-lowering therapies (such as allopurinol) have no efficacy in CPPD .

Spondyloarthropathies (SpA)

The spondyloarthropathies represent a family of interconnected chronic inflammatory rheumatic diseases characterized by genetic association with HLA-B27 , seronegativity for rheumatoid factor (RF) and anti-CCP, prominent axial skeletal involvement (sacroiliitis and spondylitis), asymmetrical peripheral oligoarthritis, enthesitis (inflammation at tendon/ligament insertions into bone), and dactylitis. COMPARISON OF THE SPONDYLOARTHROPATHIES

• Disease Demographics Key Clinical Features Radiographic & Lab Findings
• ═══════════════════════════════════════════════════════════════════════════════════════════════════════════
• Ankylosing Males > Females Insidious inflammatory back pain; Bilateral sacroiliitis;
• Spondylitis (AS) (2-3:1); improves with exercise, not rest; syndesmophytes; "bamboo spine";
• Age 20-30 morning stiffness >30 min; uveitis HLA-B27 positive (>90%)

• Psoriatic Males = Females Dactylitis ("sausage digits"); "Pencil-in-cup" deformity;
• Arthritis (PsA) Age 30-50; DIP joint predilection; nail asymmetric sacroiliitis;
• Psoriasis (85%) pitting; plaque psoriasis HLA-B27 in axial disease (50%)

• Reactive Young adults; Triad: arthritis, urethritis, Asymmetric sacroiliitis;
• Arthritis (Reiter) Post-infection conjunctivitis; keratoderma HLA-B27 positive (65-80%);
• (GU or enteric) blennorrhagica; circinate balanitis sterile synovial fluid
• ═══════════════════════════════════════════════════════════════════════════════════════════════════════════
• 1. Ankylosing Spondylitis (AS)

Inflammatory Back Pain Criteria : Chronic axial pain present for >3 months, age at onset <45 years, insidious onset, improves with physical exercise and activity , does NOT improve with rest , and prominent morning stiffness lasting >30 to 60 minutes with frequent nocturnal awakenings during the second half of the night.

Physical Examination Maneuvers :

Modified Schober Test : Assesses restricted lumbar flexion. Mark the lumbosacral junction (dimples of Venus / L5 level) and a point 10 cm superiorly while standing upright. Have the patient bend fully forward with knees straight. Normal lumbar expansion increases the distance by >=5 cm (to >=15 cm) . An increase of <5 cm (<15 cm total) indicates restricted lumbar mobility.

Chest Expansion : Measured at the 4th intercostal space; expansion <2.5 cm reflects costovertebral and costosternal joint ankylosis.

Occiput-to-Wall Distance : Normally 0 cm; an inability to touch the occiput to the wall while standing against it signifies fixed thoracic kyphosis and loss of cervical extension.

Diagnostic Imaging :

Pelvic plain radiograph: Demonstrates bilateral, symmetric sacroiliitis (blurring of joint margins, sclerosis, erosions, and ankylosis).

Lumbar spine radiograph: Vertebral body squaring, calcification of the annulus fibrosus forming vertically oriented marginal syndesmophytes , and late continuous ossification producing the classic "bamboo spine" .

Pelvic MRI (STIR sequence): Most sensitive early diagnostic tool for non-radiographic axial SpA, detecting subchondral bone marrow edema years before plain radiographic changes emerge.

Extraskeletal Manifestations :

Acute Anterior Uveitis (Iritis) : Most common extraskeletal feature (25% to 30% of patients); presents as acute unilateral eye pain, photophobia, ciliary flush, and blurred vision. Requires urgent ophthalmologic referral and topical glucocorticoid/cycloplegic drops.

Cardiovascular: Aortic root dilation, aortic valve regurgitation, and cardiac conduction defects (AV blocks).

Pulmonary: Apical pulmonary fibrocystic changes and restrictive ventilatory defect from chest wall rigidity.

Treatment Protocol :

First-line: Continuous, scheduled oral NSAIDs (e.g., naproxen, celecoxib) plus structured physical therapy (aerobic exercise and swimming to preserve spinal mobility).

Second-line for active axial disease refractory to NSAIDs: Biologic DMARDs —Tumor Necrosis Factor (TNF) inhibitors (adalimumab, infliximab, etanercept) or Interleukin-17 (IL-17) inhibitors (secukinumab, ixekizumab). Oral systemic corticosteroids are ineffective for axial disease.

2. Psoriatic Arthritis (PsA)

Develops in 15% to 30% of patients with cutaneous psoriasis; cutaneous lesions precede arthritis in 85% of cases.

Cardinal Clinical Hallmarks :

Dactylitis ("Sausage Digits") : Diffuse, uniform inflammatory swelling of an entire digit resulting from concurrent tenosynovitis and synovitis of MCP, PIP, and DIP joints.

Distal Interphalangeal (DIP) Joint Predilection : Characteristic joint involvement that distinguishes PsA from rheumatoid arthritis (which strictly spares the DIP joints).

Psoriatic Nail Dystrophy : Deep punctate nail pitting , onycholysis (separation of nail plate from bed), subungual hyperkeratosis, and "oil-drop" discoloration.

Radiographic "Pencil-in-Cup" Deformity : Severe osteolysis tapering the head of the proximal phalanx ("pencil") fitting into the expanded, hollowed base of the adjacent distal phalanx ("cup").

Treatment : NSAIDs for mild disease; conventional synthetic DMARDs ( Methotrexate ) for peripheral arthritis; TNF inhibitors or IL-17/IL-23 inhibitors for erosive disease, dactylitis, or axial involvement.

3. Reactive Arthritis (Reiter Syndrome)

Pathophysiology : Autoimmune sterile synovitis developing 1 to 4 weeks following an antecedent mucosal genitourinary or gastrointestinal infection in an HLA-B27-positive individual.

Triggering Pathogens :

Genitourinary: Chlamydia trachomatis (most common) or Mycoplasma genitalium .

Gastrointestinal: Enteric Gram-negative bacilli— Campylobacter jejuni , Salmonella enterica , Shigella flexneri , Yersinia enterocolitica , and Clostridioides difficile .

Classic Clinical Triad : Mnemonic "Can't see, can't pee, can't climb a tree" :

Asymmetric Oligoarthritis : Predominantly lower extremities (knees, ankles, subtalar joints, dactylitis).

Non-Gonococcal Urethritis / Cervicitis : Dysuria, mucopurulent discharge, or aseptic sterile pyuria.

Ocular Inflammation : Bilateral sterile conjunctivitis or acute anterior uveitis.

Pathognomonic Mucocutaneous Signs :

Keratoderma Blennorrhagica : Waxy, hyperkeratotic papules and pustules on the palms and soles that coalesce into crusting plaques resembling pustular psoriasis.

Circinate Balanitis : Painless, superficial, serpiginous erythematous erosions on the coronal sulcus or glans penis.

Painless oral aphthous ulcerations.

Treatment Protocol :

First-line: High-dose oral NSAIDs (indomethacin 50 mg PO TID or naproxen 500 mg PO BID).

Antimicrobials: Treat active genitourinary Chlamydia infection with Doxycycline 100 mg PO BID for 7 days (including sexual partners); note that antibiotics do NOT alter or shorten the joint arthritis once established.

Chronic refractory disease: Intra-articular steroid injections or oral Sulfasalazine .

Loading diagram... Clinical Decision Pathway: Acute Monoarthritis Diagnostic Triage