Abstract
Background:
While ACL reconstruction (ACLR) in skeletally immature patients was traditionally delayed until physeal closure, the development of techniques that avoid physeal disturbance have allowed surgical intervention with minimization of growth compromise. Previous reports have shown excellent patient outcomes and functional stability with low re-tear rates at short and mid-term follow-up in one of the most widely used physeal-sparing techniques, the combined extra-articular/intra-articular modified-MacIntosh ACL reconstruction with Iliotibial band autograph (ACLR-ITB). However, there is a lack of evidence regarding the kinematic performance of the reconstruction, which has been referred to as ‘non-anatomic’, as well as the effect of time on function and effectiveness. This component of a single-site, prospective, cross-sectional study of ACLR-ITB patients at different times following their reconstruction, between 1 and 20 years post-operatively, was designed to compare the sports performance-based features of the ACLR-ITB knee to the contralateral, uninjured contralateral knee, including strength, dynamic balance, and functional hop testing, as well as patient-reported functional outcome measures and activity scores. The primary hypothesis is that similar function will be found, between the ACLR-ITB and Non-ACL of individuals, and that the degree of similarity will be maintained with increasing age, growth, and/or time from reconstruction.
Methods:
Patients who underwent an ACLR-ITB between 1-20 years prior to study initiation were identified from the surgical database of three high-volume surgeons at a tertiary care pediatric hospital. Exclusion criteria were major injury or surgery on the contralateral knee at any time point, or on the ACLR-ITB knee since the time of reconstruction. The resulting study cohort of 40 subjects participated in a single day of testing at a specialized sports injury prevention center. Evaluation consisted of isometric and isokinetic strength (quadriceps, hamstring, hip abductor, hamstring: quadriceps ratio), dynamic Y-balance, and single leg hop testing, with the limb symmetry index (LSI) tabulated to allow for comparisons between knees. Patient-reported functional outcomes and activity level were recorded by Pedi-IKDC and HSS-Pedi FABS questionnaires, respectively. For the comparisons between knees, the LSI values minus 100 were compared to 0 using the Wilcoxon signed rank test. Additionally, equivalence analysis using two one-sided paired t-tests was applied to further support comparison of the two limbs. The LSI-100 measures were tested to examine equivalency between the two limbs using a margin of equivalence of 8 (a difference less than 8 was not considered clinically important). The magnitude of the relationship between test results and time was assessed using Pearson correlation coefficients (r).
Results:
The 40 study subjects had a mean age of 10.6 years (range 6-14) at time of reconstruction and 18.0 years (range: 9-30) at time of testing. Time between ACLR and time of testing ranged from 1-17 years with 8 patients beyond 10 years (Table 1). Completed Pedi-IKDC and HSS-Pedi FABS resulted in mean scores of 96 (range: 79-100) and 22 (range 0-30), respectively. The outlier subject who reported an athletic activity level of ‘0’ attributed the low score to a busy career in construction. Mean LSI for the single leg hop was 99.2% (p=0.727) and 98.4% (p=0.045) for dynamic Y-balance. Of the isometric and isokinetic strength tests, the three major muscle groups (hip abductors (LSI: 97.9%, p=0.207), quadriceps (LSI: 97.9%, p=0.260) hamstring (LSI: 102.6%, p=0.264)) showed no significant differences. Hamstring to quadriceps ratio for both limbs showed a mean value of 0.5. The equivalence analysis of LSI minus 100 confirmed equivalency, that the measures for the two limbs are close enough so that the reconstructed limb cannot be considered superior or inferior to the native limb (all p<0.05). No correlation between scores and time from reconstruction was observed, other than an expectable decline in HSS-Pedi FABS activity scores (r=-0.37, p=0.018) and improvement in hip abductor LSI (r=0.36, p=0.027) with increasing time from surgery.
Conclusion / Significance:
Similar to other long-term follow-up studies following ACLR, the current study demonstrated expectably decreasing activity with increasing patient age and time from ACLR-ITB. However, mean activity scores and functional outcome measures in this cohort are superior to age-based normative values, with outcome scores showing no decline in excellent knee function over time, up to 17 years following ACLR-ITB. Moreover, strength and functional hop testing show no clinically significant differences between the uninjured and reconstructed knees after at least 1 year, regardless of time from reconstruction. Equivalence in the measures between the two knees was shown for all LSI measures. The reported ‘non-anatomic’ features of the ACLR-ITB procedure do not appear to translate into clinically meaningful limitations in knee performance and function, which remain absent over time.
Tables and figures:
Distribution of follow-up for patients who underwent the Primary Iliotibial Band ACLR during skeletal immaturity