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Osteoarthritis (OA)

BASICS

Description

  • Progressive loss of articular cartilage with reactive changes in joint margins and subchondral bone
  • Primary OA: Idiopathic (localized, generalized, erosive)
  • Secondary OA: Posttraumatic, congenital, metabolic, neuropathic, endocrinopathic, or secondary to inflammatory arthritides (RA, gout, pseudogout)
  • Synonyms: Osteoarthrosis, Degenerative Joint Disease (DJD)

EPIDEMIOLOGY

  • Most common joint disease in the US
  • Most frequent in patients >40 years; leading cause of disability in >65 years
  • >30 million affected in the US
  • Predominantly affects weight-bearing joints (hips, knees, spine, hands)
  • Incidence: Hip OA (88/100,000/year), Knee OA (240/100,000/year)
  • Prevalence increases with age

ETIOLOGY & PATHOPHYSIOLOGY

  • Imbalance of chondrocyte activity (degradation > synthesis of collagen matrix)
  • Loss of collagen → altered proteoglycan matrix → degeneration
  • Genetics: Up to 65% genetic contribution, 27% heritability for hip OA, >100 DNA variants identified

RISK FACTORS

  • Age >50 years (hip, knee, shoulder OA)
  • Obesity (BMI >35 kg/m²)
  • Trauma, infection, inflammatory arthritis
  • Female gender (hand/knee OA)
  • Childhood anatomic abnormalities
  • Family history, metabolic/endocrine disease

GENERAL PREVENTION

  • Weight management
  • Regular physical activity
  • Peri-joint muscle strengthening (“prehabbing”)

COMMONLY ASSOCIATED CONDITIONS

  • Obesity
  • History of trauma
  • Rotator cuff tear (shoulder OA)

DIAGNOSIS

History

  • Slowly developing joint pain (aching, burning)
  • Minimal inflammation
  • Absence of systemic symptoms
  • Morning stiffness (<15 min) or after inactivity, relieved by movement
  • Distribution: Distal/proximal interphalangeal joints > thumb CMC > PIP > MCP
  • Worsening with use; improves with rest (early); persistent/rest pain (late)

Physical Exam

  • Bony enlargement, decreased range of motion
  • Mechanical symptoms (clicking, locking) in knees
  • Joint malalignment (genu varum/valgum)
  • Local pain/stiffness; may have effusions in advanced disease

Differential Diagnosis

  • Inflammatory arthritis: RA, spondyloarthropathies
  • Crystalline: Gout, pseudogout
  • Other: Septic arthritis, AVN, fibromyalgia, Lyme, trauma

Diagnostic Tests

  • Labs: Not helpful; rule out other causes if suspected
  • X-ray: Narrowed asymmetric joint space, osteophytes, subchondral sclerosis/cysts (later stages)
  • MRI: Chondral degeneration, meniscal tears, subchondral bone edema (early changes)
  • Aspiration: Not usually required; cell count <500 cells/mm³ (OA); exclude infection/crystals if uncertain

TREATMENT

General Measures

  • Weight management + exercise/physical therapy: Quadriceps strengthening (knee), periscapular/core/abductor work (shoulder/hip), transition to low-impact activity
  • Bracing/orthotics (unicompartmental knee OA, instability)
  • Patient education: Disease course, prognosis, self-management

Medication

First Line

  • Acetaminophen (up to 1,000 mg TID)
  • Topical NSAIDs (gel/cream, especially for hands, elbows, ankles, AC joint)
  • Oral NSAIDs/COX-2 inhibitors (lowest effective dose, short duration; monitor for GI, cardiac, renal side effects)
  • Avoid NSAIDs in patients with: renal disease, CHF, HTN, peptic ulcer, prior NSAID/aspirin allergy
  • Combine with PPI in high-risk patients
  • Nonacetylated salicylates, low-dose ibuprofen

Second Line

  • Topical capsaicin/CBD (lower GI/renal risk)
  • Bracing (medial/lateral unloader for knee OA)
  • TENS, cryotherapy (adjunctive)

Third Line

  • Intra-articular corticosteroid injections (limit ≤3/year per joint)
  • PRP or Bone Marrow Aspirate Concentrate (BMAC): Effective in mild-moderate knee OA (better than hyaluronic acid)
  • Surgery: TKA, THA, TSA, RTSA, TAA, TEA (in advanced, refractory cases)
  • Arthroscopy not routinely recommended unless mechanical symptoms present
  • Osteotomy/UKA for younger patients with unicompartmental disease

Complementary & Alternative Medicine

  • Glucosamine/chondroitin: Mixed evidence; try for ≤6 months
  • TENS, yoga, acupuncture: May benefit some patients

ONGOING CARE

  • Follow-up every 3 months for reassessment; annual X-rays for progression
  • Monitor for NSAID side effects (GI, cardiac, renal); periodic CBC, renal function, stool guaiac
  • Assess functional status and range of motion

DIET

  • Ensure adequate vitamin D and bone health

PATIENT EDUCATION

  • Disease is chronic and progressive, but early intervention slows progression
  • Pain control and functional improvement are main goals

PROGNOSIS

  • Progressive: Early—pain relieved by rest; Late—pain at rest/night
  • Effusions/enlargement common as disease advances
  • Osteophyte formation at joint margins

COMPLICATIONS

  • Leading cause of disability
  • NSAID/aspirin complications: CHF, GI bleeding, renal impairment

ICD-10 Codes

  • M19.239: Secondary OA, unspecified wrist
  • M19.9: OA, unspecified site
  • M19.212: Secondary OA, left shoulder

Clinical Pearls

  • Morning stiffness <15 min is typical.
  • OA commonly affects hips, knees, hands (DIP/PIP).
  • NSAID use ↑ CV risk.
  • Limit intra-articular steroids to ≤2/year/joint.
  • PRP and BMAC preferred for early-stage knee OA over hyaluronic acid.
  • Individualize therapy to pain and activity goals.