Abstract
Background:
The minimal clinically important difference (MCID) has been established for adult questionnaires administered after pediatric anterior cruciate ligament reconstruction (ACLR) and medial patellofemoral ligament reconstruction (MPFLR), but the MCID remains unquantified in pediatric-specific patient-reported outcome (PRO) instruments.
Purpose:
To establish MCIDs for the Hospital for Special Surgery Pediatric Functional Activity Brief Scale (HSS Pedi-FABS), Pediatric International Knee Documentation Committee (Pedi-IKDC), and pediatric and parent-proxy Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference (PI), mobility, and physical activity scores in pediatric patients who underwent ACLR and MPFLR.
Study Design:
Cohort study; Level of evidence, 3.
Methods:
The medical records of patients <18 years of age who underwent ACLR or MPFLR with 1 of 2 pediatric orthopaedic surgeons between 2016 and 2023 were retrospectively reviewed. Patient demographic and clinical factors were collected. Preoperative HSS Pedi-FABS, Pedi-IKDC, and pediatric and parent-proxy PROMIS pain interference (PI), physical activity, and mobility questionnaire scores were collected. The MCID was defined as one-half the standard deviation of preoperative scores. The MCIDs were calculated for patients undergoing ACLR and MPFLR.
Results:
In the ACLR group (505 patients; mean age, 14.5 ± 2.0 years), the MCIDs were established for the HSS Pedi-FABS (–5.0); Pedi-IKDC (8.7); pediatric PROMIS PI (–5.2), mobility (2.2), and physical activity (5.6); and parent-proxy PROMIS PI (–4.3), mobility (4.3), and physical activity (5.0) questionnaires. In the MPFLR group (253 patients; mean age, 14.4 ± 2.1 years), the MCIDs were established for the HSS Pedi-FABS (–5.1); Pedi–IKDC (9.1); pediatric PROMIS PI (–5.7), mobility (4.9), and physical activity (5.6); and parent-proxy PROMIS PI (–4.3), mobility (4.5), and physical activity (5.9) questionnaires. Negative MCIDs were reported for activity and pain scores to indicate MCID thresholds for decreased postoperative pain (i.e., pain improvement) and activity levels (i.e., decreased activity levels compared to healthiest and most active condition, absence of full recovery).
Conclusion:
This study establishes novel MCIDs for the HSS Pedi-FABS, Pedi-IKDC, and pediatric and parent-proxy PROMIS PI, physical activity, and mobility questionnaires in pediatric patients undergoing ACLR and MPFLR.
Keywords
The incidence of pediatric knee injuries and subsequent surgeries has considerably increased globally during the past 20 years.10,19,33 Between 2004 and 2014, there was a 2.8-fold increase in anterior cruciate ligament reconstructions (ACLRs) relative to total pediatric orthopaedic operations, owing to a greater exposure of children and adolescents to athletic activity and an increase in the number of available sports. 38 Similar increases in medial patellofemoral ligament reconstruction (MPFLR) to treat patellofemoral instability (PFI) have been observed, given improved functional outcomes with reconstruction compared with repair of the ligament.19,34
Recent paradigm shifts have focused on maximizing patient-centered care after surgical management of the pediatric knee. Patient-reported outcomes (PROs) are an increasingly common and effective modality to quantify mental, physical, and/or social health to evaluate clinical outcomes from a patient's perspective. The minimal clinically important difference (MCID) is the threshold value that reflects the smallest change in a PRO that is clinically meaningful to a patient after surgery. Increasing interest has been placed on defining MCID after orthopaedic surgeries.13,18,22,26,28,29,31 Nwachukwu et al 28 utilized these standards in adult ACLR, showing the predictive value of a general 12-item physical and mental health questionnaire toward return to play and achievement of the MCID on knee-specific questionnaires. In the pediatric population, Maheshwer et al 20 established MCID threshold values in pediatric ACLR for the International Knee Documentation Committee (IKDC) score and Knee injury and Osteoarthritis Outcome Score.
However, there remains a notable paucity of literature on MCID thresholds for pediatric-specific questionnaires for utilization after pediatric ACLR and MPFLR. While some adult questionnaires such as the IKDC questionnaire have been validated in the pediatric population, pediatric orthopaedic patients require pediatric-specific PROs.21,30,40 MCID thresholds have not been established for several pediatric-specific PROs, including the Hospital for Special Surgery Pediatric Functional Activity Brief Scale (HSS Pedi-FABS), Pediatric IKDC (Pedi-IKDC), and both pediatric and parent-proxy Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference (PI), mobility, and physical activity scores. Pediatric-specific MCID thresholds on these questionnaires are critical for accurately contextualizing PRO changes after ACLR and MPFLR in pediatric patients. This study aimed to establish the MCIDs for the HSS Pedi-FABS, Pedi-IKDC, pediatric PROMIS, and parent-proxy PROMIS questionnaires for pediatric patients who underwent primary ACLR or MPFLR.
Methods
Patient Selection
Institutional review board approval was obtained for the study. Pediatric patients (aged <18 years at the time of surgery) from a single urban tertiary care center who underwent ACLR or MPFLR surgery between 2016 to 2023 with 1 of 2 fellowship-trained pediatric orthopaedic surgeons (P.D.F., D.W.G.) were retrospectively identified. Preoperative PROs were collected from the medical record, and patients without a preoperative PRO were excluded. Patient characteristics, including age, sex, date of birth, and comorbid medical conditions, were collected. Surgical history, including date of surgery, type of surgery, laterality, and graft type (eg, autograft vs allograft), was identified. The indications for ACLR in this pediatric population were participation in sports or persistent pain and instability after a period of physical therapy. A lateral extra-articular tenodesis (LET) was generally added for patients with at least 2 of the following: return to contact sports, ligamentous laxity, genu recurvatum or knee hyperextension, and high-grade pivot shift (2+). 3 For patients undergoing MPFLR, the surgical indications were recurrent patellar instability and pain/functional limitation or concomitant osteochondral fragment in the setting of primary dislocation. For patients who underwent MPFLR, the performance of concomitant lateral release or lengthening, chondroplasty, meniscal repair and/or meniscectomy, or guided growth was identified. For patients who underwent ACLR, technique (eg, transphyseal vs all-epiphyseal) and the performance of concomitant LET, chondroplasty, meniscal repair and/or meniscectomy, or guided growth was identified. Several adjunctive procedures were considered exclusion criteria to ensure a more homogeneous cohort for MCID calculation; patients with ACLR who underwent multiligament reconstruction, ACL primary repair, revision ACLR, or an additional osteochondral procedure (e.g., osteochondral fracture fixation and stage 2 matrix-associated autologous chondrocyte implantation) were excluded. Patients with MPFLR who underwent tibial tubercle osteotomy, MPFL primary repair, revision MPFLR, or an additional osteochondral procedure (eg, open reduction internal fixation) were excluded. Patients with syndromic PFI were excluded (Figure 1).
STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) diagram demonstrating the flow of patients receiving ACLR and MPFLR who completed each study questionnaire.
Outcome Measures
PROs collected included the HSS Pedi-FABS, Pedi-IKDC, pediatric PROMIS PI, pediatric PROMIS mobility, and pediatric PROMIS physical activity scores. PROMIS parent proxies for the same scales were obtained for patients aged 5 to 17 years.9,15,17,23,36,39 All PROs were collected preoperatively for routine clinical purposes.
Statistical Analysis
Descriptive statistics are reported for baseline characteristics and surgical history. Continuous variables are reported as mean with standard deviation. In this study, the MCID was calculated as one-half the standard deviation using preoperative scores for each PRO in cohorts undergoing ACLR and MPFLR. Negative MCIDs were reported for the pediatric PROMIS PI and parent-proxy PROMIS PI questionnaires since a lower postoperative score compared with the preoperative score denotes an improvement in pain. A negative MCID was reported for the HSS Pedi-FABS, as this instrument is designed to assess a patient's activity level at their “healthiest and most active condition.” 15 Accordingly, the preoperative HSS Pedi-FABS score reflects the patient's preinjury activity level, rather than their status immediately before surgery. Given that optimal postoperative recovery after ACLR or MPFLR is characterized by a return to, but not an exceedance of, preinjury activity levels, the MCID for the HSS Pedi-FABS represents the threshold beyond which a postoperative decline in activity is considered clinically meaningful. All statistical analyses were performed using RStudio (Version 2023.12.1; Posit).
Results
A total of 505 patients underwent ACLR. The mean age of the cohort was 14.5 ± 2.0 years, and 238 (47.1%) patients were female. A transphyseal technique was utilized in most patients (n = 376; 74.5%), followed by the modified MacIntosh (n = 102; 20.2%) and all-epiphyseal (n = 27; 5.3%) techniques. Clinical characteristics and operative history are detailed in Table 1. The MCIDs for the HSS Pedi-FABS and Pedi-IKDC scores for patients with ACLR were –5.0 and 8.7, respectively (Table 2). The MCIDs for pediatric PROMIS PI, mobility, and physical activity scores were –5.2, 2.2, and 5.6, respectively (Table 2). The MCIDs for the parent-proxy PROMIS PI, mobility, and physical activity scores were –4.3, 4.3, and 5.0, respectively (Table 3).
Demographic and Clinical Characteristics of Patients Who Underwent ACLR and MPFLR a
Data are presented as n (%) or mean ± SD. ACLR, anterior cruciate ligament reconstruction; BTB, bone-tendon-bone; ITB, iliotibial band; LET, lateral extra-articular tenodesis; MPFLR, medial patellofemoral ligament reconstruction.
MCIDs for HSS Pedi-FABS, Pediatric IKDC, and Pediatric PROMIS Questionnaires a
ACLR, anterior cruciate ligament reconstruction; HSS Pedi-FABS, Hospital for Special Surgery Pediatric Functional Activity Brief Scale; MCID, minimal clinically important difference; MPFLR, medial patellofemoral ligament reconstruction; Pedi-IKDC, Pediatric International Knee Documentation Committee; PI, pain interference; PROMIS, Patient-Reported Outcomes Measurement Information System.
The n variable represents the number of patients who answered the specific questionnaire.
MCIDs for PROMIS Parent-Proxy Questionnaires a
ACLR, anterior cruciate ligament reconstruction; MCID, minimal clinically important difference; MPFLR, medial patellofemoral ligament reconstruction; PI, pain interference; PROMIS, Patient-Reported Outcomes Measurement Information System.
The n variable represents the number of parents who answered the specific questionnaire.
A total of 253 patients underwent MPFLR. The mean age was 14.4 ± 2.1 years, and 140 (55.3%) patients were female. Clinical characteristics and operative history are detailed in Table 1. The MCIDs for the HSS Pedi-FABS and Pedi-IKDC scores for patients with MPFLR were –5.1 and 9.1, respectively (Table 2). The MCIDs for the pediatric PROMIS PI, mobility, and physical activity scores were –5.7, 4.9, and 5.6, respectively (Table 2). The MCIDs for the parent-proxy PROMIS PI, mobility, and physical activity scores were –4.3, 4.5, and 5.9, respectively (Table 3).
Discussion
MCID thresholds for PROs are critical for contextualizing patient reported outcomes after surgery, yet they are not defined for many pediatric orthopaedic sports conditions.13,17,20-22,28,31,32 We report the first pediatric-specific MCID thresholds for the HSS Pedi-FABS, Pedi-IKDC, pediatric PROMIS, and parent-proxy PROMIS questionnaires in patients who underwent ACLR and MPFLR.
While MCIDs for patients undergoing ACLR have been extensively studied in adult populations, these thresholds have not been established for pediatric-specific questionnaires.2,5,20,29 Distribution-based MCIDs for the original IKDC questionnaire in patients who underwent ACLR have been reported between 8.7 and 9.5 in adults and 9.6 in pediatric patients.20,29 Our distribution-based MCID for the Pedi-IKDC score (8.7) was similar to the MCID established through the adult IKDC questionnaire. Anchor-based MCIDs for the IKDC questionnaire have been previously reported at substantially higher values between 18.9 and 33.3. 20 Further research on an anchor-based approach for Pedi-IKDC MCID calculation is required. Distribution-based MCIDs for PROMIS questionnaires in adult patients with ACLR have been established for physical function (4.6) and PI (–4.0). 2 Similarly, our distribution-based MCIDs for pediatric PROMIS physical activity and PI were 5.6 and –5.2, respectively. Our MCID for parent-proxy PROMIS PI (–4.3) was also concordant with adult data. We additionally present novel MCIDs for pediatric PROMIS mobility, parent-proxy PROMIS mobility and physical activity, and HSS Pedi-FABS scores, which can be used in future studies on pediatric ACLR. A future area of research should assess MCID achievement of the HSS Pedi-FABS questionnaire in patients undergoing ACLR.
While MCID scores have been established for the IKDC score in adult patients undergoing MPFLR, MCIDs for questionnaires in pediatric patients undergoing MPFLR have not been reported.11,35,41,42 Prior reports of distribution-based MCIDs for adult patients undergoing MPFLR have varied between 1.5 and 12.5.9,11,35,41 Our distribution-based MCID calculation for Pedi-IKDC (9.1) after MPFLR demonstrated a pediatric threshold at the higher bound of the adult range. Furthermore, we report novel distribution-based MCID thresholds for HSS Pedi-FABS and PROMIS pediatric/parent-proxy questionnaires, which can be used in future studies on pediatric MPFLR.
This study has several limitations. First, we only calculated MCID using the distribution-based method as complete anchor questionnaire data were not available in our cohort. No gold-standard method of MCID calculation exists, and several studies have proposed using both distribution and anchor-based estimates in conjunction.4,6-8,12,16,37,43 Future research should assess anchor-based MCID calculations for the pediatric PROs included in this study. Second, while several formulas exist for calculating distribution-based MCIDs, we only reported on the one-half standard deviation approach since it is a highly reliable and reproducible technique.24,25 The one-half standard deviation approach is also the most frequently used technique in orthopaedics and was used in this study to allow standardized reporting and fair comparisons with prior literature.1,14,27 Third, we did not report patient achievement of the MCID due to limited responses on postoperative PROs. This limitation precludes evaluation of whether the calculated MCIDs were actually realized within our cohort. Fourth, the reporting of specific surgical techniques and postoperative rehabilitation protocols was deemed beyond the scope of this study, but could differ across institutions and may influence achievement of MCID postoperatively. Fifth, this study may have a risk of selection bias for the scores collected on preoperative PROs. Nevertheless, our results suggest that MCIDs are largely similar for a given PRO when evaluating patients undergoing either ACLR or MPFLR.
Conclusion
This study establishes novel MCIDs for the HSS Pedi-FABS, Pedi-IKDC, and pediatric and parent-proxy PROMIS PI, physical activity, and mobility questionnaires in pediatric patients undergoing ACLR and MPFLR. This information should be useful for interpreting clinical outcomes research and for conducting power and sample size calculations when designing prospective studies.
Footnotes
Final revision submitted November 11, 2025; accepted November 16, 2025.
One or more of the authors has declared the following potential conflict of interest or source of funding: P.D.F. has received consulting fees from BICMD and publishing royalties from Springer Nature; and holds stock or stock options in OssoVR. D.W.G. has received royalties from Orthopediatrics. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
Ethical approval for this study was obtained from Hospital for Special Surgery, New York, New York, USA.
