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This section describes patient-based outcomes and clinician-rated outcome measures that are designed to rate an individual’s function objectively and reliably. Although these outcome tools may be sensitive in some patients, subjective complaints such as difficulty with pivoting, cutting, and twisting may be the most sensitive information gained when assessing a patient’s functional abilities. These limitations should be captured using patient-reported outcome measures.


The following measures represent a selection of the wide range of lower extremity scales that are clinically useful. Additional scales are often being investigated and may become readily available to clinicians and researchers, along with their associated reliability data.

Lower Extremity Functional Scale (LEFS)

The LEFS comprises 20 questions relating to a patient’s ability to participate in everyday tasks. It may be used with unilateral and bilateral lower extremity conditions. The patient selects a number from 0 (Extreme Difficulty or Unable to Perform Activity) to 4 (No Difficulty). Scores range from 0 to 80, with higher scores reflecting less disability.1

  • Minimal Detectable Change: 9

  • Minimal Clinically Important Difference: 9

Knee Injury Osteoarthritis and Outcome Score (KOOS)

This patient-rated outcome measure is designed for patients with knee osteoarthritis or injuries associated with the development of osteoarthritis, such as ACL tears and meniscal lesions. The patient responds to 42 items concerning symptoms and disability experienced during the previous week. A normalized score ranging from 0 to 100 is calculated for each of five sub-scales: Pain, Other Symptoms, Activities of Daily Living (ADLs), Sports and Recreation Function, and Knee-Related Quality of Life. Lower scores indicate more symptoms and a more significant impact on the patient’s life. A pediatric version, used in patients aged 9 to 12, and a short form (KOOS-12) is also available at:

  • Minimal Detectable Change (for patients with knee injury):

    • Pain subscale: 6–6.1

    • Other Symptoms subscale: 5–8.5

    • ADL subscale: 7–8

    • Sports and Recreation Function subscale: 6–12

    • Knee-Related Quality of Life subscale: 7

  • Minimal Clinically Important Difference: 8–10. However, this value likely changes based on patient population, intervention, and time since initial injury.2

Foot and Ankle Ability Measure (FAAM)

The patient-rated FAAM consists of 21 items relating to ADLs and an 8-item sports subscale. Patients with leg, foot, and/or ankle disorders respond to the items on a 5-point scale, with lower scores indicative of greater levels of disability.

  • Minimal Detectable Change: 5.7 points (ADLs); 12.3 points (sports subscale)

  • Minimal Clinically Important Difference: 8 points (ADLs); 9 points (sports subscale)3

International Knee Documentation Committee –Subjective Knee Form (IKDC)

Specific to knee injuries, the IKDC is considered an effective general measure for all knee conditions.4 The patient-reported IKDC includes 18 total items (7 for symptoms, ...

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