Most patients with knee injury have soft tissue damage to ligaments, tendon or meniscus; while these may be serious, radiography does not significantly help in diagnosis and may be unnecessary. A decision rule can be used in adults to reduce the number of unnecessary radiographic examinations of the knee. This could lead to important health savings without jeopardizing patient care.

Decision Rule: A knee radiograph is only performed if at least one of the following is true:

(1) age of patient is 55 years or older

(2) tenderness is present at the head of the fibula

(3) isolated tenderness of the patella (no other bone tenderness other than patella)

(4) inability to flex the knee to 90°

(5) inability to bear weight both immediately and in the emergency department using the 4 step test



• 4 step test: unable to transfer weight onto each lower limb twice, regardless of limping


Patients were instructed to return for reassessment if any of the following occurred:

(1) pain did not get better

(2) ability to walk did not improve

(3) requires use of crutches, splint or other assistance to walk

(4) unable to return to normal occupational activities


The decision rule should not be applied in patients:

(1)  < 18 years of age

(2) with intoxication due to drugs or alcohol

(3) with paraplegia or decreased limb sensation

(4) with multiple painful injuries or head injury


Performance: sensitive but not specific:

• sensitivity of 100% for detecting clinically important fractures

• specificity of 49%

• negative predictive value is 100%; positive predictive value 11%

• reduction in radiographic examinations estimated at 28%

• no patient dissatisfaction

• reduced waiting times and cost

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