Pittsburgh Knee Rules

What are the Pittsburgh Knee Rules?

The Pittsburgh Knee Rules are a clinical decision tool used to determine whether radiography is necessary for patients with acute knee injuries. They were developed to reduce unnecessary radiographs while maintaining high sensitivity for detecting clinically significant knee fractures.

Clinical Significance

Knee injuries are common in emergency departments and primary care settings. While most acute knee injuries do not involve fractures, radiographs are often ordered to rule out bony injuries. The Pittsburgh Knee Rules provide an evidence-based approach to identify patients who are unlikely to have a fracture, potentially reducing unnecessary imaging, radiation exposure, healthcare costs, and time spent in clinical settings.

The Rules

According to the Pittsburgh Knee Rules, a knee X-ray is only necessary if:

• The patient is younger than 12 years or older than 50 years, OR
• The patient is unable to walk four weight-bearing steps in the emergency department (regardless of limping)

Performance Characteristics

Comparison with Other Decision Rules

Several clinical decision rules exist for knee injuries, including:

• Ottawa Knee Rules: More widely used and validated. They recommend radiography if any of the following are present:
  • Age ≥55 years
  • Isolated tenderness of the patella
  • Tenderness at the head of the fibula
  • Inability to flex to 90 degrees
  • Inability to bear weight both immediately and in the emergency department (four steps)
• Pittsburgh Knee Rules: Simpler but still highly sensitive. They focus on age and ability to bear weight.

The Ottawa Knee Rules have been more extensively validated across different populations and settings, but the Pittsburgh Knee Rules offer a simpler alternative with comparable sensitivity for detecting fractures.

Limitations

• Not validated in children under 12 years of age
• May not be applicable to patients with altered mental status, intoxication, or distracting injuries
• Does not address non-fracture pathologies such as ligamentous injuries or meniscal tears
• Clinical judgment should always supersede decision rules when there is high suspicion for fracture
• Less extensively validated than the Ottawa Knee Rules

References

1. Seaberg DC, Yealy DM, Lukens T, Auble T, Mathias S. Multicenter comparison of two clinical decision rules for the use of radiography in acute, high-risk knee injuries. Ann Emerg Med. 1998;32(1):8-13.
2. Cheung TC, Tank Y, Breederveld RS, Tuinebreijer WE, de Lange-de Klerk ES, Derksen RJ. Diagnostic accuracy and reproducibility of the Ottawa Knee Rule vs the Pittsburgh Decision Rule. Am J Emerg Med. 2013;31(4):641-645.
3. Beutel BG, Trehan SK, Shalvoy RM, Mello MJ. The Ottawa knee rule: examining use in an academic emergency department. West J Emerg Med. 2012;13(4):366-372.