Osteoarthritis

Osteoarthritis – High-Yield Study Guide for Medical Students

Definition

Osteoarthritis (OA) is a chronic, progressive joint disorder characterized by degeneration of articular cartilage, remodeling of subchondral bone, formation of osteophytes, and varying degrees of synovial inflammation, leading to pain, stiffness, and functional limitation. It is a non-inflammatory, degenerative arthritis classically described as “wear-and-tear,” although biochemical and inflammatory processes also contribute.

Epidemiology

Osteoarthritis is the most common form of arthritis and a leading cause of disability in older adults worldwide.

• Prevalence: Increases with age; highly prevalent in individuals >65 years.
• Sex: Slight female predominance, especially for knee OA, particularly after menopause.
• Common joints: Knees, hips, cervical and lumbar spine (facet joints), first carpometacarpal (CMC) joint of the thumb, and distal (DIP) and proximal (PIP) interphalangeal joints of the fingers.
• Risk factors: Age, female sex, obesity, prior joint injury, occupational or sports-related joint overuse, genetics, malalignment, and joint congenital abnormalities.

Pathophysiology

OA is not simply mechanical “wear-and-tear” but a whole-joint disease involving cartilage, subchondral bone, synovium, ligaments, and periarticular muscles.

• Cartilage degeneration: Chondrocytes respond to biomechanical and biochemical stress by increasing production of matrix-degrading enzymes (e.g., MMPs, ADAMTS), resulting in loss of type II collagen and proteoglycans. Cartilage becomes thinner, softer, and fissured.
• Subchondral bone changes: Increased bone turnover and sclerosis, with formation of subchondral cysts. Altered load distribution contributes to pain and further cartilage damage.
• Osteophyte formation: Bony outgrowths at joint margins develop as a reparative response to instability and cartilage loss, contributing to stiffness and restricted movement.
• Synovial involvement: Low-grade synovitis occurs due to release of cartilage breakdown products into the joint, driving pain and intermittent effusions.
• Biomechanics: Malalignment (e.g., genu varum or valgum) and muscle weakness, especially of quadriceps around the knee, increase focal joint loading and accelerate degeneration.

Clinical Presentation

OA typically presents with chronic, gradually progressive joint pain and functional limitation.

• Pain:
  • Mechanical pain: Worse with activity and weight-bearing, relieved by rest in early disease.
  • Late-stage pain may occur at rest and at night.
  • Deep, aching pain, often poorly localized to the affected joint.
• Stiffness:
  • Short-duration morning stiffness (<30 minutes), improving with gentle movement.
  • Gelling phenomenon: Stiffness after periods of inactivity.
• Functional impairment:
  • Difficulty with activities such as climbing stairs, walking long distances, grasping objects, or rising from a chair.
  • Reduced range of motion and joint instability in advanced disease.
• Physical examination findings:
  • Bony enlargement of joints (e.g., Heberden nodes at DIP, Bouchard nodes at PIP, enlarged knee or hip).
  • Crepitus on active or passive movement.
  • Joint-line tenderness, usually without marked warmth or erythema.
  • Decreased range of motion, especially in weight-bearing joints such as hips and knees.
  • Malalignment (varus/valgus deformity) and joint instability in advanced disease.
  • Effusions may be present but are usually mild and non-inflammatory.

Diagnosis

Diagnosis of osteoarthritis is primarily clinical, supported by imaging when needed to rule out alternative diagnoses or for preoperative planning.

Clinical Diagnosis

Typical OA is suspected in an older adult with chronic, mechanical joint pain, short-lived morning stiffness, and characteristic exam findings (bony enlargement, crepitus, reduced ROM) in commonly affected joints.

• Key features:
  • Age >45 years.
  • Activity-related joint pain.
  • Morning stiffness <30 minutes.
  • Functional limitation in activities involving the affected joint.
• Distinguish from inflammatory arthritis (e.g., rheumatoid arthritis):
  • Inflammatory arthritis tends to have prolonged morning stiffness (>1 hour), systemic symptoms, and more pronounced joint swelling and warmth.
  • RA usually involves MCP and wrist joints, whereas OA classically affects DIP, PIP, and first CMC joints.

Imaging

Plain radiographs are the standard imaging modality for OA and correlate variably with symptoms.

• Classic radiographic features (often summarized as “LOSS”):
  • Loss of joint space (asymmetric, typically in the weight-bearing compartment).
  • Osteophyte formation at joint margins.
  • Subchondral sclerosis (increased bone density beneath cartilage).
  • Subchondral cysts.
• Radiographic severity can be graded (e.g., Kellgren–Lawrence grading) but does not always correlate with pain intensity.
• Imaging is indicated when diagnosis is uncertain, atypical features are present, or surgery is being considered.

Laboratory Tests

There are no specific laboratory markers for OA.

• Routine inflammatory markers (ESR, CRP) are usually normal or only mildly elevated.
• Serologic tests for rheumatoid factor (RF), anti-CCP, and ANA are negative in primary OA and are used to exclude inflammatory or autoimmune arthritis.
• Joint aspiration and synovial fluid analysis may be considered in the presence of acute effusion or suspicion of crystal arthropathy or septic arthritis; OA synovial fluid is typically non-inflammatory (low WBC count).

Management

Management of osteoarthritis focuses on symptom control, preservation or improvement of function, and slowing progression. Treatment is multimodal, combining non-pharmacologic, pharmacologic, and procedural/surgical approaches.

Non-Pharmacologic Management

Non-pharmacologic strategies are the foundation of OA treatment and should be implemented for all patients.

• Patient education:
  • Explain the chronic nature of OA, modifiable risk factors, and the role of exercise and weight management.
  • Set realistic expectations and emphasize self-management.
• Exercise and physical therapy:
  • Low-impact aerobic exercise such as walking, cycling, or aquatic therapy to improve endurance and reduce pain.
  • Strengthening exercises (e.g., quadriceps strengthening for knee OA) to stabilize joints and reduce load.
  • Range-of-motion and flexibility exercises to maintain joint mobility.
• Weight loss:
  • For overweight or obese patients, a target of at least 5–10% weight reduction can significantly decrease knee and hip pain.
• Assistive devices and joint protection:
  • Cane used in the hand opposite the affected hip or knee to offload joint.
  • Knee braces, orthotics, or shoe inserts to correct malalignment and reduce pain.
  • Adaptive devices for hand OA (e.g., jar openers, modified grips).
• Activity modification:
  • Avoid high-impact activities such as running or jumping if they exacerbate symptoms.
  • Break tasks into shorter periods with rest breaks to reduce joint stress.

Pharmacologic Management

Pharmacologic therapy is used for symptom relief and should be combined with non-pharmacologic measures. Choice of agent depends on pain severity, comorbidities, and affected joints.

• Topical therapies (particularly for knee and hand OA):
  • Topical NSAIDs (e.g., diclofenac gel) are first-line for localized OA, especially in older adults, due to lower systemic adverse effects.
  • Topical capsaicin may be considered for hand or knee OA, with the caveat of local burning sensations.
• Oral NSAIDs:
  • Effective for short- and intermediate-term management of OA pain (e.g., ibuprofen, naproxen, celecoxib).
  • Use the lowest effective dose for the shortest possible duration and consider GI, renal, and cardiovascular risk.
  • Consider proton pump inhibitor co-therapy in high GI risk patients.
• Acetaminophen (paracetamol):
  • Previously first-line but now recognized as less effective than NSAIDs for OA pain.
  • May still be used for mild pain or when NSAIDs are contraindicated, within safe dosage limits (taking into account liver function).
• Intra-articular therapies:
  • Corticosteroid injections can provide short-term relief (weeks to a few months) in patients with moderate to severe pain, particularly in knee and hip OA.
  • Frequency should be limited (often no more than 3–4 times per year in a given joint) due to potential cartilage effects.
  • Hyaluronic acid injections are used in some settings for knee OA; evidence is mixed and guidelines vary in recommendations.
• Other medications:
  • Duloxetine (an SNRI) can be useful for chronic musculoskeletal pain, including OA, especially when central sensitization or concomitant mood disorders are present.
  • Opioids are generally not recommended except in exceptional circumstances (severe pain, contraindications to other therapies, or preoperative bridging) and then used at the lowest effective dose for the shortest duration.
  • Glucosamine and chondroitin supplements have inconsistent data; many guidelines do not routinely recommend them, though some patients report benefit.

Procedural and Surgical Management

Procedures are considered when conservative therapy fails and pain or functional limitations are significant.

• Arthroplasty (joint replacement):
  • Total knee or hip arthroplasty is highly effective for end-stage OA with severe pain and disability.
  • Indications include advanced radiographic OA, refractory pain, and significant impairment in activities of daily living.
• Osteotomy:
  • Realignment procedures (e.g., high tibial osteotomy) may be considered in younger, active patients with unicompartmental OA and malalignment.
• Arthroscopic procedures:
  • Routine arthroscopic debridement or lavage for OA is generally not recommended as it has limited benefit in degenerative disease without mechanical derangements (e.g., locked meniscus).

Key Clinical Pearls for Exams

• Pattern of joint involvement is crucial for differentiating OA from inflammatory arthritides on exams:
  • OA: DIP (Heberden nodes), PIP (Bouchard nodes), first CMC, knees, hips, spine.
  • RA: MCP, PIP, wrists; sparing of DIP; symmetric involvement.
• Morning stiffness duration:
  • OA: brief morning stiffness (<30 minutes), worse with use.
  • Inflammatory arthritis: prolonged stiffness (>1 hour), improves with use.
• Radiographic “LOSS” mnemonic for OA:
  • Loss of joint space (asymmetric).
  • Osteophytes.
  • Subchondral sclerosis.
  • Subchondral cysts.
• Non-pharmacologic therapy (exercise, weight loss, physical therapy) is first-line and should be emphasized on exams as foundational.
• Topical NSAIDs are preferred over oral NSAIDs as initial pharmacologic therapy in older adults with localized OA due to lower systemic adverse effects.
• Synovial fluid in OA is non-inflammatory (low leukocyte count) compared with RA or crystal arthropathies.
• Joint replacement is indicated for end-stage OA with severe pain and functional limitation despite maximal conservative therapy.

Summary

Osteoarthritis is a highly prevalent degenerative joint disease characterized by cartilage loss, subchondral bone remodeling, osteophyte formation, and mild synovitis. Clinically, it presents with mechanical joint pain, short-duration morning stiffness, and functional limitation in commonly affected joints such as knees, hips, hands, and spine. Diagnosis is primarily clinical, supported by radiographic features (LOSS). Management is multimodal, with non-pharmacologic strategies as the cornerstone and pharmacologic agents and surgical interventions tailored to symptom severity and functional impact. Recognizing typical patterns, distinguishing OA from inflammatory arthritides, and understanding stepwise management are high-yield for examinations and clinical practice.