Evaluation of Epiphyses in the Skeletally Immature Knee Using Magnetic Resonance Imaging

Abstract

Background: Questions have been raised concerning the height of the tibial epiphysis as an important factor related to the safety of intra-articular anterior cruciate ligament (ACL) reconstruction in skeletally immature knees. However, normal values for this parameter have yet to be established on cross-sectional magnetic resonance imaging (MRI). Purpose: To determine normal values for the height of the tibial epiphysis and width of the lateral femoral condylar epiphysis in children and adolescents by use of MRI. 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 August 2007 to July 2011. The height of the tibial epiphysis was determined on the sagittal T1-weighted image best containing the ACL footplate. Lateral femoral condylar width was recorded on coronal proton-density-weighted images. The intraclass correlation coefficient (ICC) was calculated to determine interobserver agreement. Knees were stratified by age into 2 groups based on potential risk of iatrogenic growth plate injury: Group 1 consisted of boys younger than 13 years (range, 7-12 years) and girls younger than 12 years (range, 10-11 years); group 2 consisted of boys between the ages of 13 and 16 years and girls between the ages of 12 and 14 years. Each cohort was further stratified by sex. Results: Group 1 consisted of 17 boys (mean age, 10.4 years) and 5 girls (mean age, 10.8 years), and group 2 contained 23 boys (mean age, 14.4 years) and 14 girls (mean age, 13.7 years). There was a total of 59 knees. No difference was found for average tibial epiphyseal height between group 1 (15.26 ± 1.25 mm) and group 2 (15.01 ± 2.14 mm). However, there was a statistically significant difference related to sex in each cohort: boys versus girls in group 1 (15.63 ± 1.15 mm vs 14.00 ± 0.62 mm, respectively; P = .007) and boys versus girls in group 2 (16.00 ± 1.88 mm vs 13.40 ± 1.47 mm, respectively; P = .0001). The average femoral condylar width for both cohorts was greater than 28 mm where femoral tunnel location would be expected. The ICC was strong (>0.7) at tibial and femoral locations where tunnel placement would be expected. Conclusion: The average height of the tibial epiphysis in both children and adolescents is 15 mm. Girls had shorter tibial epiphyses than boys, but further studies are necessary to determine whether this difference is clinically relevant. Lateral femoral condylar width in children and adolescents can be expected to be greater than 28 mm.