Osteoarthritis¶
Chapter 383 | Part 11: Immune-Mediated, Inflammatory, and Rheumatologic Disorders
KEY CLINICAL POINTS¶
- Osteoarthritis (OA) is the most common form of arthritis, characterized by joint cartilage degradation and subchondral bone changes, leading to pain, stiffness, and functional disability.
- Prevalence increases with age, affecting ~12% of adults ≥ 60 years in the U.S. for knee OA and ~6% for hip OA, with women more commonly affected than men.
- Key risk factors include aging, obesity, joint malalignment, prior joint injury, and genetic predisposition (e.g., GDF5 gene variants).
- Management emphasizes weight loss, physical therapy, exercise, and pharmacologic agents (NSAIDs, acetaminophen), with intraarticular injections for localized pain relief.
- Diagnosis relies on clinical symptoms and imaging (X-ray for structural changes, MRI for early cartilage damage), though radiographic findings may not correlate directly with pain severity.
1. DEFINITION & OVERVIEW¶
Osteoarthritis (OA) is a degenerative joint disease characterized by progressive cartilage loss, subchondral bone sclerosis, osteophyte formation, and synovial inflammation. It is a multifactorial condition involving mechanical stress, genetic predisposition, and inflammatory pathways. OA is distinct from inflammatory arthritis, with pain primarily driven by structural changes rather than systemic inflammation.
Table 383-1: Pharmacologic Treatment for Osteoarthritis¶
| TREATMENT | MAXIMAL DOSAGE | COMMENTS |
|---|---|---|
| Oral NSAIDs and COX-2 inhibitors | Naproxen 375–500 mg bid | Take with food. Increased risk of myocardial infarction and stroke. High rates of gastrointestinal side effects, including ulcers and bleeding. Patients at high risk should also take proton pump inhibitors or misoprostol. |
| Salsalate 1500 mg bid | ||
| Ibuprofen 600–800 mg qid/tid | ||
| Celecoxib 100–200 mg qd | An increase in gastrointestinal side effects or bleeding when taken with acetylsalicylic acid. Can also cause edema and renal insufficiency. | |
| Acetaminophen | Up to 2 g/d | Of limited efficacy; conditionally recommended for knee pain. |
| TREATMENT | MAXIMAL DOSAGE | COMMENTS |
|---|---|---|
| Opiates | Common side effects include dizziness, sedation, nausea, vomiting, dry mouth, constipation, urinary retention, and pruritus. Addiction risk. Less efficacious than oral NSAIDs. | |
| Topical NSAIDs | Rub onto hands/knees | Few systemic side effects. |
| Diclofenac Na 1% gel | 4 g qid | Skin irritation common. |
| Capsaicin | 0.025–0.075% cream tid/qid | Can irritate mucous membranes. |
| Intraarticular Injections | Glucocorticoids, Hyaluronic Acid, and Other Products | Mild to moderate pain at injection site. Controversy exists regarding efficacy. Repeated injections may cause minor cartilage loss. |
| Hyaluronans | Varies from 3 to 5 weekly injections. Mild to moderate pain at injection site. | |
| Steroids | Various weekly injections. Controversy exists regarding efficacy. | |
| Other Classes of Drugs and Nutraceuticals | Duloxetine (U.S. FDA approved for OA) may be particularly efficacious when knee pain is part of a syndrome of widespread pain. | |
| Biologic agents and disease-modifying agents | Used for rheumatoid arthritis; trials for OA have mostly been negative, except for two randomized trials for hand OA (prednisolone and methotrexate). |
1.1 Pathophysiology¶
OA results from a combination of mechanical stress, joint injury, and biological factors. Key mechanisms include: (1) cartilage degradation via matrix metalloproteinases (MMPs) and ADAMTS-5, (2) subchondral bone remodeling, (3) synovial inflammation, and (4) neurovascular invasion leading to pain. Cartilage loss and focal stress increase susceptibility to further damage.
1.2 Joint Failure Mechanisms¶
OA is considered joint failure, where all joint structures (cartilage, bone, synovium) undergo pathological changes. Cartilage loss, osteophyte formation, and synovitis contribute to pain and disability. Mechanical stress and aging exacerbate these changes by reducing cartilage resilience and joint protector function.
2. EPIDEMIOLOGY¶
OA is the most common form of arthritis, with prevalence increasing sharply with age. It affects ~12% of adults ≥ 60 years in the U.S. for knee OA and ~6% for hip OA. Women are more commonly affected than men, especially in middle-aged and elderly populations. Obesity is a major risk factor, with a 3.5-fold increased risk of knee OA after major knee injury. Global prevalence is rising due to aging populations and increasing obesity rates.
2.1 Demographics¶
OA is rare in individuals <40 years old but becomes highly prevalent in those >60 years. In the U.S., ~12% of adults ≥ 60 have symptomatic knee OA, and ~6% have hip OA. Women are more commonly affected than men, particularly in middle-aged and elderly populations. In China, hip OA is rare, while knee OA is a major cause of disability in rural areas.
2.2 Risk Factors¶
Key risk factors include: (1) aging, (2) obesity (3–6x body weight transmitted across the knee), (3) joint malalignment (varus/valgus), (4) prior joint injury, (5) genetic predisposition (e.g., GDF5 variants), and (6) repetitive joint use (occupational or recreational).
3. ETIOLOGY & PATHOPHYSIOLOGY¶
OA results from a combination of mechanical stress, joint injury, and biological factors. Key mechanisms include: (1) cartilage degradation via MMPs and ADAMTS-5, (2) subchondral bone remodeling, (3) synovial inflammation, and (4) neurovascular invasion leading to pain. Cartilage loss and focal stress increase susceptibility to further damage. Joint protectors (muscles, ligaments, synovium) fail with aging, exacerbating mechanical stress.
3.1 Joint Protective Mechanisms¶
Joint protectors include muscles, ligaments, synovial fluid, and sensory nerves. These structures provide mechanical stability, reduce friction, and modulate pain through mechanoreceptors. Failure of these mechanisms (e.g., muscle weakness, ligament rupture) increases OA risk.
3.2 Inflammatory Pathways¶
Local inflammation accelerates OA progression by releasing cytokines (e.g., IL-1 β , TNF- α ) and matrix-degrading enzymes (MMPs, ADAMTS-5). Synovial inflammation, cartilage damage, and bone remodeling contribute to pain and structural changes. Neurovascular invasion from cartilage leads to nociceptive innervation.
4. CLINICAL FEATURES¶
OA presents with joint pain, stiffness, and functional limitation. Pain is typically activity-related, worsening with weight-bearing or joint use. Morning stiffness is brief (<30 min). In advanced stages, pain may be constant and nocturnal. Commonly affected joints include knees, hips, hands (distal/proximal interphalangeal joints, thumb base), and spine. Complications include joint deformity, bone marrow edema, and chronic pain due to central sensitization.
4.1 Symptomatology¶
Pain is the primary symptom, often localized to weight-bearing joints (knees, hips) or specific hand joints. Stiffness is prominent but brief. In severe cases, joint deformity (e.g., Heberden’s nodes in hands) and bone marrow edema may occur. Pain may become constant and interfere with daily activities.
4.2 Complications¶
Chronic pain, joint deformity, and functional disability are major complications. Central sensitization may lead to allodynia and hyperalgesia. In severe cases, joint destruction and osteophyte formation may require surgical intervention.
5. DIFFERENTIAL DIAGNOSIS¶
OA must be differentiated from inflammatory arthritis (e.g., rheumatoid arthritis), gout, pseudogout, and other degenerative conditions. Key distinguishing features include: (1) absence of systemic inflammation in OA, (2) radiographic evidence of osteophytes in OA vs. joint space narrowing in rheumatoid arthritis, and (3) synovial fluid analysis (e.g., urate crystals in gout vs. no crystals in OA).
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis is based on clinical symptoms and imaging. X-rays show osteophytes, joint space narrowing, and subchondral sclerosis. MRI detects early cartilage loss and bone marrow edema. Synovial fluid analysis may reveal crystals in gout/pseudogout but not in OA. Radiographs are not always indicative of pain severity, and MRI findings may not correlate with clinical symptoms.
6.1 Imaging¶
X-rays are used to assess structural changes (osteophytes, joint space narrowing). MRI provides detailed visualization of cartilage, menisci, and bone marrow edema. Synovial fluid analysis is critical for differentiating OA from inflammatory or crystal-induced arthropathies.
6.2 Diagnostic Criteria¶
Symptomatic OA is diagnosed based on clinical features (joint pain, stiffness) and imaging findings (osteophytes, joint space narrowing). Radiographic evidence is common but not always correlated with pain severity. MRI is more sensitive for early cartilage damage.
7. MANAGEMENT & TREATMENT¶
Management of OA includes non-pharmacologic and pharmacologic approaches. Weight loss, exercise, and physical therapy are foundational. Pharmacologic options include NSAIDs, acetaminophen, and opioids for pain relief. Intraarticular injections (glucocorticoids, hyaluronic acid) may provide temporary relief. Surgical intervention is reserved for severe cases with structural damage.
7.1 Non-Pharmacologic Therapy¶
Weight loss ( ≥ 10% of body weight) reduces cartilage loss and pain. Exercise (aerobic, resistance training) improves joint function and strength. Physical modalities (braces, splints, orthotics) help unload joints. Patient education and self-management strategies are critical for long-term adherence.
7.2 Pharmacologic Therapy¶
NSAIDs are first-line for moderate-to-severe pain, with caution for GI and cardiovascular risks. Acetaminophen is used for mild symptoms. Opioids are reserved for severe cases due to addiction risks. Topical NSAIDs and capsaicin may be used for localized pain. Intraarticular injections (glucocorticoids, hyaluronic acid) provide temporary relief.
7.3 Surgical Options¶
Surgical intervention is considered for severe structural damage or refractory pain. Options include arthroscopy, osteotomy, and joint replacement. Correcting malalignment (varus/valgus) may alleviate pain in knees, though long-term outcomes vary.
8. PROGNOSIS & COMPLICATIONS¶
OA is a progressive disease with variable outcomes. Early intervention (weight loss, exercise) can slow disease progression. Complications include chronic pain, joint deformity, and functional disability. Central sensitization may lead to persistent pain even after structural damage resolves. Long-term use of NSAIDs increases cardiovascular and GI risks.
8.1 Prognosis¶
Prognosis depends on severity, comorbidities, and adherence to management. Mild OA may be managed with lifestyle changes, while severe cases may require surgery. Weight loss and exercise significantly improve outcomes.
8.2 Complications¶
Chronic pain, joint deformity, and functional disability are major complications. Long-term NSAID use increases cardiovascular and gastrointestinal risks. Central sensitization may lead to persistent pain and reduced quality of life.
9. SPECIAL CONSIDERATIONS¶
OA management in special populations requires tailored approaches. In elderly patients, fall prevention and joint protection are critical. Obesity necessitates weight loss and metabolic control. In pregnant women, NSAIDs and opioids are avoided due to fetal risks. Physical therapy and low-impact exercise are preferred. Genetic factors (e.g., GDF5 variants) may influence treatment response.
9.1 Pregnancy¶
NSAIDs and opioids are contraindicated in pregnancy. Acetaminophen is preferred for pain relief. Physical therapy and weight management are emphasized to reduce joint stress.
9.2 Pediatrics¶
Congenital joint abnormalities (e.g., dysplasia, Legg-Perthes disease) increase OA risk in childhood. Early intervention with bracing or surgery may prevent progression.
9.3 Elderly¶
Aging reduces joint protector function, increasing OA risk. Weight loss, low-impact exercise, and fall prevention are critical. NSAID use requires careful monitoring for GI and cardiovascular risks.
10. KEY POINTS & CLINICAL PEARLS¶
- OA is the most common arthritis, with prevalence increasing with age and obesity. 2. Management prioritizes weight loss, exercise, and non-pharmacologic interventions. 3. NSAIDs are first-line for pain, but long-term use carries cardiovascular and GI risks. 4. Intraarticular injections provide temporary relief but should be used cautiously. 5. Early diagnosis and intervention improve outcomes, while chronic pain may require addressing central sensitization.