Katz, JAMA 2021 - Diagnosis and Treatment of Hip and Knee Osteoarthritis - Article Summary

Diagnosis and Treatment of Hip and Knee Osteoarthritis

Katz, Loeser, et al.·JAMA·2021·2,126 citations·Hip & Knee

This 2021 JAMA narrative review by Katz, Arant, and Loeser synthesizes epidemiology, pathophysiology, diagnosis, and treatment of hip and knee OA. It draws primarily on OARSI 2018 guideline meta-analyses to quantify treatment effect sizes using standardized mean differences. The review covers the full spectrum from clinical diagnosis to total joint replacement outcomes and emerging disease-modifying therapies.

Key Findings

One-third of people over 75 have symptomatic radiographic knee OA, and the lifetime risk is nearly double in obese patients (19.7% vs 10.9%). OA carries a 20% excess age-adjusted mortality driven by reduced physical activity — this is why functional restoration matters beyond pain control.
Bony enlargement on knee exam is highly specific (95%) but only 55% sensitive; it rules in OA when present. Knee pain combined with radiographic osteophyte has a likelihood ratio of 11.9. One of the strongest diagnostic combinations in clinical medicine. For the hip, osteophytes on X-ray are 89% sensitive and 90% specific, and combined with hip pain yield an LR of 8.9.
The Kellgren-Lawrence grading system classifies OA radiographically on a 0-4 scale:
- Grade 0: no pathologic findings
- Grade 1: questionable osteophytes
- Grade 2: definite osteophytes
- Grade 3: definite joint space narrowing
- Grade 4: advanced joint space narrowing
- Knee films must be taken weight-bearing to accurately assess joint space.
Treatment effect sizes (SMD vs placebo, 4-12 week trials):
- Structured exercise. 0.52 (knee), 0.34 (hip). Highest value non-drug option
- Mind-body (tai chi/yoga): 0.63 (knee)
- Oral NSAIDs: 0.28 (knee), 0.33 (hip)
- Duloxetine: 0.39 (knee)
- Intra-articular corticosteroids: 0.41 (knee), 1.65 (hip)
- Opioids: ~0.20 for both joints, with falls, somnolence, and addiction risk
- Acetaminophen: 0.05 for knee (essentially no effect)
Intra-articular corticosteroids provide no greater pain relief than placebo after 3 months and may be inferior to physical therapy at 1 year. Some studies suggest potential deleterious effects on cartilage. Use them for monoarticular flares, not as a long-term strategy.
Total joint replacement delivers durable results: ~90% of THR and ~80% of TKR recipients report little to no residual pain. Revision rates are under 10% for TKR and approximately 20% for THR at 20 years. In an RCT vs rigorous PT, TKR improved KOOS by 35 points vs 17 points (difference 17 points; 95% CI 10.4-23.8).
Black and Hispanic patients are ~25% less likely to receive TKR than non-Hispanic White patients even after adjusting for age and socioeconomic status. They also face higher rates of mortality after THR and joint infection after TKR. A disparity driven by offer rates, implicit bias, and patient-level factors the paper explicitly identifies.

Board PearlExercise (SMD 0.52), NSAIDs (SMD 0.33), and total joint replacement (~90% pain relief) are the evidence-based pillars of OA management; opioids add toxicity with minimal benefit (SMD 0.20).

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