EBQ:Ottawa Ankle Rule Study

incomplete Journal Club Article

Stiell I. et al.. "Decision rules for the use of radiography in acute ankle injuries. Refinement and prospective validation.". JAMA. 1993. 269(9):1127-32.
PubMed Full text PDF

Clinical Question

Can a clinical decision rule be used to aid in the efficient use of radiography in acute ankle injuries?

Conclusion

The Ottawa Ankle Rule is a highly sensitive decision rule used to determine the need for radiography in patients with acute ankle injuries.

Major Points

Ankle Rules

Ankle x-ray needed if pain near the maleoli AND

Inability to bear weight immediately and in the ED (4 steps)

OR

Tenderness at posterior edge or tip of lateral malleolus

OR

Tenderness at posterior edge or tip of medial malleolus

Rule had 100% sensitivity and 49% specificity for identifying 50 clinically significant malleolar zone fractures in the prospective validation study.

Foot Rules

Foot x-ray series needed if pain in the midfoot AND

Inability to bear weight both immediately and in the ED (4 steps)

OR

Tenderness at the navicular

OR

Tenderness at the base of the 5th metatarsal

Rule had 100% sensitivity and and 79% specificity for identifying 19 clinically significant midfoot fractures in the prospective validation study.

Study Design

• Conducted in 2 stages in 2 Canadian EDs
• Both prospective cohort studies
• In the first stage, each patient was evaluated for 15 clinical variables before radiographs--standard ankle series for patients with pain in malleolar zone vs. standard foot series for patients with pain in the midfoot zone. Decision rule derived using statistical means. Variables not independently useful in the original stage were excluded from the decision rule in the second stage.
• In the second stage, each patient was evaluated for 6 clinical variables before radiographs.
• In both studies, a subset of patients were also assessed by second EM physician independently.
• Clinically significant fracture seen in ankle or foot radiographic series was the primary outcome, defined as bone fragments greater than 3 mm in breadth.
• All radiographic series were interpreted by qualified radiologists who were blinded to the data collection sheets.

Population

Patient Demographics

Similar characteristics in stage 1 (refinement) vs. stage 2 (validation)

• Mean age: 35 vs. 36
• Male gender: 52% vs. 52%
• Pt at Ottawa Clinic: 60% vs. 64%
• Twisting mechanism: 84% vs. 86%
• Clinically significant fractures: 16% vs. 15%
• Clinically insignificant fractures: 6% vs. 7%
• Ankle rediographs performed: 85% vs. 85%
• Foot radiographs performed: 39% vs. 35%

Inclusion Criteria

• Patients who presented to the emergency department with pain or tenderness 2/2 to blunt ankle trauma due to any mechanism of trauma
• Ankle defined as area commonly involved in twisting injuries
  • Malleolar zone
    • Distal 6 cm of tibia, fibula, talus
  • Midfoot zone
    • Navicular bone, cuboid, cuneiforms, anterior process of calcaneus, base of 5th metatarsal
• 1 of 21 designated EM physicians had to be on duty

Exclusion Criteria

• Age <18 years old
• Pregnant
• Isolated injuries of the skin
• Referred from outside hospital with radiographs
• Injury occurred >10 days previously
• Returned for reassessment of the same injury

Outcomes

First stage (validation and refinement of original rules): n=1032 enrolled and assessed
Second stage (validation of refined rules): n=453 enrolled and assessed

Primary Outcome

First stage (refinement): 121 (12%) clinically significant malleolar zone fractures and 49 (5%) clinically significant midfoot zone fractures identified

Performance of the Ottawa Decision Rule in the second stage (validation) cohort

Ankle Decision Rule	Fracture	No Fracture
Rule Positive	50	205
Rule Negative	0	198

Sensitivity 100% (95% CI 93% to 100%)
Specificity 49% (95% CI 44% to 54%)

Foot Decision Rule	Fracture	No Fracture
Rule Positive	19	90
Rule Negative	0	344

Sensitivity 100% (95% CI 83% to 100%)
Specificity 79% (95% CI 75% to 83%)

Funding

Grant from Emergency Health Services Branch of Ontario Ministry of Health, Toronto