A Study of Epiphyses in the Young Prepubescent Knee Using Magnetic Resonance Imaging

BACKGROUND Questions have been raised concerning the safety of intra-articular anterior cruciate ligament (ACL) reconstruction in prepubescent children aged <7 years. However, normal values for the width of the lateral femoral condylar epiphysis and height of the tibial epiphysis have yet to be established through the use of magnetic resonance imaging (MRI). PURPOSE To determine normal values for the width of the lateral femoral condylar epiphysis and height of the tibial epiphysis at the knee in prepubescent children aged <7 years by use of MRI and to compare this age group with an older cohort of prepubescent children aged <10 years. STUDY DESIGN Cross-sectional study; Level of evidence, 3. METHODS An electronic search was conducted for pediatric knee MRI examinations at the authors' institution from March 2003 to March 2013. The total and ossified lateral femoral condylar widths were determined on coronal proton density-weighted images. The total and ossified tibial epiphyseal heights were recorded on the sagittal T1-weighted image best containing the ACL footplate. The intraclass correlation coefficient (ICC) was calculated to determine interobserver agreement. Knees were stratified by age into 2 groups: children between the ages of 3 and 6 years (group 1) and children between the ages of 7 and 9 years (group 2). Each cohort was further stratified by sex. RESULTS Group 1 consisted of 10 children (mean age, 4.3 years) and group 2 consisted of 10 children (mean age, 8.5 years). There were a total of 20 knees. There was a statistically significant difference between groups 1 and 2 for the ossified lateral femoral condylar width where femoral tunnel location would be expected (20.00 ± 4.20 vs 26.27 ± 4.12 mm, respectively; P = .0035) and for total lateral femoral condylar width (25.57 ± 3.47 vs 29.43 ± 4.04 mm, respectively; P = .0339). No difference was found for total tibial epiphyseal height between the 2 groups. However, there was a difference between groups 1 and 2 for ossified tibial epiphyseal height (13.20 ± 1.63 vs 15.27 ± 0.94 mm, respectively; P = .0028). No difference was found for average ossified tibial epiphyseal height or ossified lateral femoral condylar width between boys and girls in the younger or older cohorts. The ICC was strong (>0.7) at femoral and tibial locations where tunnel placement would be expected. CONCLUSION Prepubescent children <7 years old have smaller knee epiphyses than older prepubescent children, and on average, present with an osseous bone stock of 20 mm for lateral femoral condylar width and 13 mm for tibial epiphyseal height. Study results suggest that children aged <7 years possess enough osseous bone stock at the lateral femoral condyle to support transepiphyseal ACL reconstruction. However, future studies will be necessary to determine the safety and effectiveness of this procedure in children aged <7 years. CLINICAL RELEVANCE ACL tears in children are more frequently being recognized by the orthopaedic community. The trend toward increasing participation in competitive and recreational sports has contributed to this phenomenon. Young patients with complete ACL tears and open growth plates often provide a management dilemma for surgeons who wish to perform reconstructive surgery.