Authors’ Disclosure Statement: The authors report no actual or potential conflict of interest in relation to this article.
Dr. Day and Dr. Hancock are Orthopedic Surgery Residents; Dr. Glass is a Statistician; and Dr. Bollier is Congdon Professor in Orthopedic Surgery, Sports Medicine Fellowship Director, and Team Physician, Department of Orthopedics and Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, Iowa.
Address correspondence to: Matthew J. Bollier, MD, University of Iowa Hospitals and Clinics, Department of Orthopedics and Rehabilitation, 200 Hawkins Drive, Iowa City, IA 52242 (tel, 319-467-8324; fax, 319-356-8999; email, matthew-bollier@uiowa.edu).
Am J Orthop. 2018;47(5). Copyright Frontline Medical Communications Inc. 2018. All rights reserved.
Molly Day, MD, ATC Kyle Hancock, MD Natalie Glass, PhD Matthew Bollier, MD . Current Concepts in Clinical Research: Anterior Cruciate Ligament Outcome Instruments. Am J Orthop.
May 4, 2018
References
PATIENT-REPORTED OUTCOME INSTRUMENTS
Recently, there has been a transition to increased use of PRO instruments rather than clinician-based postoperative assessment, largely due to the increasing emphasis on patient satisfaction in determining the value of an orthopedic intervention.4 PRO instruments are widely used to capture the patient’s perception of general health, quality of life (QOL), daily function, and pain. PRO instruments offer the benefit of allowing patients to subjectively assess their knee function during daily living and sports activities, conveying to the provider the impact of ACL reconstruction on physical, psychological, and social aspects of everyday activities. Furthermore, patient satisfaction has been shown to closely follow outcome scores related to symptoms and function.5 A multitude of specific knee-related PRO instruments have been developed and validated to measure outcomes after ACL reconstruction for both research and clinical purposes (Table).
Table. ACL Outcome Measures
Outcome Measure
Condition/Intervention
Measures
Internal Consistency (Cronbach’s a)
Test-Retest Reliability
Minimal Clinically Important Difference
Ref
AAOS Sports Knee Scale
Many Knee
Stiffness, swelling, pain/function, locking/catching, giving way, limitation of activity, pain with activity
0.86-0.95
0.68-0.96
Unknown
59, 60
ACL-QOL
Chronic ACL deficiency
Physical complaints, work, recreation and sports competition, lifestyle, social and emotional functioning
Lower extremity function, central body function, activities of daily living
0.98
0.96-0.99
30, 31
WOMAC
Hip/knee OA
Physical function, pain, stiffness
0.81-0.95
0.80-0.92
12% baseline score or 6% max score; 9-12 points
13, 14
Abbreviations: AAOS, American Academy of Orthopaedic Surgeons; ACL, anterior cruciate ligament; ACL-QOL, anterior cruciate ligament quality of life score; CAT, computer-adapting testing; IKDC, International Knee Documentation Committee; KOOS, Knee Injury and Osteoarthritis Outcome Score; OA, osteoarthritis; PF, physical function; PROMIS, Patient-Reported Outcome Measurement Information System; Ref, references; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.
MEASUREMENT PROPERTIES
In general, clinicians and investigators should use health-related outcome measures with established reliability, validity, patient relevance, and responsiveness for assessing the specific condition.6
Reliability refers to the degree to which a measurement score is free from random error, reflecting how consistent or reproducible the instrument is when administered under the same testing conditions. Internal consistency, test-retest reliability, and measurement error are measures of reliability. Internal consistency is tested after a single administration and assesses how well items within a scale measure a single underlying dimension, represented using item-total correlation coefficients and Cronbach’s alpha. A Cronbach’s alpha of 0.70 to 0.95 is generally defined as good.7 Test-retest reliability is designed to appraise variation over time in stable patients and is represented using the intraclass correlation coefficient (ICC).8 An ICC >0.7 is considered acceptable; >0.8, good; and >0.9, excellent.9 An aspect of accuracy is whether the scoring system measures the full range of the disease or complaints. The incidence of minimum (floor) and maximum (ceiling) scores can be calculated for outcome scores. An instrument with low floor and ceiling effects, below 10% to 15%, is more inconclusive and can be more reliably used to measure patients at the high and low end of the scoring system.10
Validity is the ability of an outcome instrument to measure what it is intended to measure. Establishing validity is complex and requires evaluation of several facets, including content validity, construct validity, and criterion validity. Content validity is a relatively subjective judgment explaining the ability of an instrument to assess the critical features of the problem. Construct validity evaluates whether the questionnaire measures what it intends to measure, and is often assessed by correlating scores form one instrument to those from other proven instruments that are already accepted as valid. Finally, criterion validity assesses the correlation between the score and a previously established “gold standard” instrument.
Responsiveness is the ability of the instrument to detect a change or identify improvement or worsening of a clinical condition over time. Most frequently, the effect size (observed change/standard deviation of baseline scores) and standardized response mean (observed change/standard deviation of change) are used as measures of responsiveness. The minimal clinically important difference of an outcome measure is the smallest change in an outcome score that corresponds to a change in patient condition.
