Abstract
Objectives:
Minimum clinically important difference (MCID) is a value that helps identify the patient-reported outcome measure (PROM) change deemed to be clinically meaningful to a patient. Although MCID values and PROMs are being increasingly used in the context of anterior cruciate ligament (ACL) reconstruction (ACLR) to determine treatment success and inform health policies, MCID values are subject to wide variation depending on the methodology used in the calculation. The anchor-based method determines the change in PROM associated with the smallest detectable improvement of another measure that is deemed clinically significant by the patient. The Single Assessment Numeric Evaluation (SANE) is a single-item questionnaire graded on a scale from 0 to 100 that is commonly used by sports surgeons because of its ease in use and responsiveness. SANE score can reliably measure outcomes for ACL injuries and ACLR while decreasing survey burden. A pure anchor-based MCID value has not been reported in the literature. The purpose of this study was to identify ACLR patients at 2-year follow-up that meet a literature-based MCID for SANE in addition to 3 other anchor-based MCIDs calculated by anchoring to three questions from the Knee Injury and Osteoarthritis Outcome Score (KOOS) scale. The secondary aim was to determine if there were differences in baseline or treatment characteristics among patients that achieve the MCID. The hypothesis was that patients would achieve each MCID value at differing rates depending on the anchor.
Methods:
This was a retrospective review conducted within three ambulatory surgery centers. The institutional PROM database was queried for ACLR procedures between 2009 and 2021. Revision procedures, concomitant ligament repairs or reconstructions, and patients lacking SANE or KOOS at baseline or two years were excluded. Demographic, injury, and surgical characteristics were extracted via chart review. Outcomes of interest were SANE and KOOS. SANE is a single-item questionnaire asking, “On a scale of 0 to 100, how would you rate your knee’s function, with 100 being normal?” KOOS is a 42-item valid and reliable measure of knee pathology that assesses 5 areas of knee functioning: symptoms (7 items, KOOS-S), pain (9 items, KOOS-P), activities of daily living (17 items, KOOS-ADL), sports participation (5 items, KOOS-SP), and quality of life (4 items, KOOS-QoL). Each item asks for the degree of symptom burden or performance difficulty and is graded on a 5-point Likert scale from “(1) None” to “(5) Extreme.” As published in the literature, a decrease of 1 point in the Likert scale was deemed the clinically significant anchor improvement to calculate MCIDs. The responses to these items result in a raw score that is then converted to an overall KOOS score from 0 to 100, where an increasing score, in this case, indicates better knee function (ie score of 100 indicates perfect knee function). Three anchor-based MCIDs were calculated as described based on 1 item from the KOOS-SP (SP4: “What difficulty have you experienced the last week turning/twisting on your injured knee?”), 1 item of the KOOS-P (P1: “How often do you experience knee pain?”), and 1 item from the KOOS-QoL (QoL4: “In general, how much difficulty do you have with your knee?”). Patients who met these MCIDs as well as the literature-reported MCID for SANE were identified and reported.
Results:
A total of 273 patients (60.1% female, average age 31.8) were included in the analysis. Average baseline and 2-year SANE were 65.9 and 89.7, respectively. The average 2-year SANE change was +23.18. The anchor-based SANE MCID values for SP4 and QoL4 were 12 and 13, respectively, which were lower than the literature-reported MCID value of 19. In contrast the MCID of 21 for P1 was higher. While 54.6% of patients achieved the literature-reported SANE MCID, significantly more patients attained SP4 (67.4%, p = 0.002) and QoL4 (67.0%, p = 0.003) MCIDs. Significantly less patients achieved the P1 MCID (45.8%, p = 0.039). Overall, 32.6% of patients did not achieve any MCID. When looking at differences among patients that did not meet MCID, patients that met the literature-reported MCID, and patients who met MCID anchored to SP4, P1, or QoL4, there was a significantly higher proportion of females (72.0% vs. 60.6%, p = 0.049), as well as, interestingly, a higher prevalence of American Society of Anesthesiologists (ASA) score 2 (83.1%, p = 0.007) who met MCID. Additionally, the rates of MCID achievement was found to differ by graft type (allograft = 86.8%, bone-patellar tendon-bone autograft = 60.4%, hamstring autograft = 70.9%, p = 0.004).
Conclusions:
This study calculated anchor-based MCIDs for SANE based on a KOOS-SP, KOOS-P, and KOOS-QoL anchor. Compared to the literature-derived MCID for SANE, 2 of these anchors were able to identify a higher percentage of patients reporting clinically meaningful outcomes after ACLR. Still, 32.6% of patients were not identified as having achieved any MCID, which is surprising given the high satisfaction rate reported by ACLR patients. Graft selection, patient sex, and ASA were all found to influence MCID achievement. Determining MCID values and clinically significant outcomes is still not well-understood, but surgeons should be aware of the role that tool selection and patient/injury factors play in changing the way we measure successful outcomes in ACLR.
