Current Concepts in Clinical Research: Anterior Cruciate Ligament Outcome Instruments

ACL OUTCOME INSTRUMENTS

WESTERN ONTARIO AND MCMASTER UNIVERSITIES OSTEOARTHRITIS INDEX (WOMAC LK 3.0)

The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC LK 3.0) was developed in 1982 and is a widely used, disease-specific instrument recommended for the evaluation of treatment effects in patients with hip and knee osteoarthritis.¹¹ Available in more than 80 languages, it is a self-administered, generic health status questionnaire developed to assess pain, function, and stiffness in daily living, taking respondents between 3 to 7.5 minutes for completion.¹² Using visual analog scales, the 24 items probe the 3 subscales: pain (5 items), stiffness (2 items), and functional difficulty (17 items). Scores are calculated for each dimension, and the total score is normalized to a 100-point scale, with 0 indicating severe symptoms and 100 indicating no symptoms and higher function. The WOMAC score can also be calculated from the Knee Injury and Osteoarthritis Outcome Score (KOOS). The WOMAC questionnaire is well recognized for its good validity, reliability, and responsiveness, and is the most commonly used outcome measure for osteoarthritis.^13-15 Considering its focus on older patients with osteoarthritis, it may not be appropriate for use in a young and active population.

KNEE INJURY AND OSTEOARTHRITIS OUTCOME SCORE (KOOS)

The KOOS is a knee-specific questionnaire developed as an extension of the WOMAC to evaluate the functional status and QOL of patients with any type of knee injury who are at an increased risk of developing osteoarthritis.¹⁶ The patient-based questionnaire is available in over 30 languages and covers both the short- and long-term consequences of an injury of the knee causing traumatic damage to cartilage, ligaments, and menisci. The KOOS is 42 items graded on a 5-point Likert scale, covering 5 subscales: pain (9 items), symptoms (7 items), function in activities of daily living (17 items), function in sports/recreation (5 items), and knee-related QOL (4 items). The questionnaire is self-administered and takes about 10 minutes to complete. Scores are calculated for each dimension, and the total score is transformed to a 0 to 100 scale, with 0 representing severe knee problems and 100 representing no knee problems and better outcome. An advantage of the KOOS is that it evaluates both knee injuries and osteoarthritis; therefore, it is arguably more suitable for evaluating patients over the long-term. The KOOS has been validated for several orthopedic interventions, including ACL reconstruction and rehabilitation^16,17 as well as meniscectomy¹⁸ and total knee replacement.¹⁹ Population-based reference data for the adult population according to age and gender have also been established.²⁰ The KOOS is increasingly utilized in clinical studies on ACL reconstruction.^21-25 The questions of the WOMAC were retained so that a WOMAC score might be calculated separately and compared with the KOOS score.²⁶

PATIENT-REPORTED OUTCOMES INFORMATION SYSTEM (PROMIS)

Since 2004, The National Institutes of Health (NIH) has funded the development of the Patient-Reported Outcome Measurement Information System (PROMIS), a set of flexible tools that reliably and validly measure PROs. The PROMIS consists of a library of question banks that has been developed and operated by a network of National Institutes of Health-funded research sites and coordinating centers and covers many different health domains including pain, fatigue, anxiety, depression, social functioning, physical functioning, and sleep. PROMIS items are developed using Item Response Theory (IRT), wherein the answer to any individual item has a known mathematical probability of predicting the test taker’s overall measurement of the specific trait being tested. This is commonly administered using computer-adaptive testing (CAT), which presents to the test taker an initial item, scores the response to that item, and from the response then presents the most informative second item, and so forth until a predefined level of precision is reached. Because the items are individually validated, they can be used alone or in any combination, a feature that distinguishes the PROMIS from traditional fixed-length PRO instruments that require the completion of an instrument in its entirety to be valid.²⁷ In recent years, orthopedic research has been published with PROMIS physical function (PF) scores as primary outcome measures.^28-30 The PF item bank includes 124 items measuring upper extremity, lower extremity, central and instrumental activities of daily living. PF can be completed as a short form (SF) with a set number of questions or utilizing CAT and evaluates self-reported function and physical activity. An advantage is its ease of use and potential to minimize test burden with very few questions, often as little as 4 items, as compared to other traditional PROMs.³¹

Previously published work has demonstrated that, in patients undergoing meniscal surgery, the PROMIS PF CAT maintains construct validity and correlates well with currently used knee outcome instruments, including KOOS.²⁸ Work by the same group looking at the performance of the PROMIS PF CAT in patients indicated for ACL reconstruction shows that the PROMIS PF CAT correlates well with other PRO instruments for patients with ACL injuries, (SF-36 PF [r = 0.82, P < 0.01], KOOS Sport [r = 0.70, P < 0.01], KOOS ADL [r = 0.74, P < 0.01]), does not have floor or ceiling effects in this relatively young and healthy population, and has a low test burden.^32,33 Papuga and colleagues³³ also compared the International Knee Documentation Committee (IKDC) and PROMIS PF CAT on 106 subjects after ACL reconstruction and found good correlation.

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