Use of the Knee Injury and Osteoarthritis Outcomes Survey (KOOS) in a Normal US Population

OBJECTIVES: Patient-reported outcome instruments are frequently used for assessing clinical outcomes after injury and surgery. Previously reported normative data for the Knee Injury and Osteoarthritis Outcome Survey (KOOS) instrument is limited to a narrow subset of ages and has not accounted for a history of knee injury. METHODS: The KOOS was administered to 1000 patients or accompanying family members who presented to an outpatient orthopaedic clinic in a suburban metropolitan city for an orthopaedic issue unrelated to their knee in July 2014. Participants were eligible if they self-reported a medical history negative for ankle, knee, or hip surgery. KOOS scale means, standard deviations, medians, ranges, interquartile ranges, and percentiles were calculated by sex, age range, laterality, and history of knee injury in the past year. Non-parametric statistical analysis was used to evaluate differences in KOOS scale scores between five age ranges and between those with or without a history of knee injury. RESULTS: There were 402 males and 598 females in the final study cohort. Males scored lower on the Symptoms scale compared to other scales (median score = 96.4 for Symptoms; median score = 100 for all other scales) in all age cohorts except ages 56-64. Females also reported lower scores in the Symptoms scale. Median Symptoms score for females in each of the age groups from 18-55 years old was 96.4, and median score for the 56-64 year old cohort was 92.9. Median scores for Pain and Knee-related Quality of Life scales were lower in the 56-64 year old female cohort (97.2 and 93.8 respectively). CONCLUSION: Normative values for KOOS scale scores at all age ranges suggest a high level of functioning among participants with no history of knee injury in the past year. Symptoms, Pain, and Knee-related Quality of Life scales showed the greatest variability in KOOS scores for patients, particularly in the youngest and oldest cohorts. This study can aid surgeons in counseling patients and in developing expectations after treatment of injuries.