Mechanical and Microstructural Properties of Pediatric Anterior Cruciate Ligaments and Autograft Tendons Used for Reconstruction

BACKGROUND: Over the past several decades, there has been a steady increase in pediatric anterior cruciate ligament (ACL) tears, particularly in young female basketball and soccer players. Because allograft tissue for pediatric ACL reconstruction (ACLR) has shown high rates of failure, autograft tissue may be the best option for ACLR in this population. However, differences in the structure and mechanical behavior of these tissues are not clear. PURPOSE: To characterize the mechanical and microstructural properties in pediatric ACLs and autograft tissues using a rare cadaveric cohort (mean age, 9.2 years). STUDY DESIGN: Descriptive laboratory study. METHODS: ACLs, patellar tendons, quadriceps tendons, semitendinosus tendons, and iliotibial bands (ITBs) were harvested from 5 fresh-frozen pediatric knee specimens (3 male, 2 female) and subjected to a tensile loading protocol. A subset of contralateral tissues was analyzed using bright-field, polarized light, and transmission electron microscopy. RESULTS: Patellar tendons exhibited values for ultimate stress (5.2 ± 3.1 MPa), ultimate strain (35.3% ± 12.5%), and the Young modulus (27.0 ± 8.8 MPa) that were most similar to the ACLs (5.2 ± 2.2 MPa, 31.4% ± 9.9%, and 23.6 ± 15.5 MPa, respectively). Semitendinosus tendons and ITBs were stronger but less compliant than the quadriceps or patellar tendons. ITBs exhibited crimp wavelengths (27.0 ± 2.9 μm) and collagen fibril diameters (67.5 ± 19.5 nm) that were most similar to the ACLs (24.4 ± 3.2 μm and 65.3 ± 19.9 nm, respectively). CONCLUSION: The mechanical properties of the patellar tendon were almost identical to those of the ACL. The ITB exhibited increased strength and a similar microstructure to the native ACL. These findings are not entirely congruent with studies examining adult tissues. CLINICAL RELEVANCE: These results can be used to inform further clinical research. In particular, they justify a further examination of the biomechanical and microstructural properties of the ITB in the context of its role as an autograft tissue in pediatric ACL reconstruction.