Summary

This study validates the adolescent porcine stifle joint as a model for ACL research, addressing challenges in adolescent biomechanics. Cyclic tensile tests on 20 porcine joints reveal strain patterns consistent with clinical ACL failures, underscoring the model's reliability and contributing to improved understanding and treatment of ACL injuries in adolescents.

Abstract

Introduction

The rising incidence of anterior cruciate ligament (ACL) injuries, particularly in adolescents, is a significant concern. This research aims to validate the adolescent porcine stifle joint as an appropriate model for ACL studies, addressing the challenges of studying ACL biomechanics in this demographic due to the scarcity of cadaveric specimens. By leveraging existing and emerging material characterization techniques, this study endeavors to provide a viable solution to these challenges, contributing to improved understanding and treatment of ACL injuries in adolescents.

Methods

For this study, 20 adolescent porcine stifle joints were meticulously prepared. All non-ACL ligaments were removed, and a small osteotomy of the medial condyle of the femur was performed to expose the ACL, ensuring optimal viewing and accurate results. Each sample underwent cyclic tensile testing for 100 cycles, with 10 samples subjected to 300N and 10 samples to 600N, both well below the mean ultimate load of 1266±250N. The displacement rate was maintained at 2.00mm/s throughout the testing. Force and displacement were recorded using an MTS System tensile loading machine. To enhance tissue registration for Digital Image Correlation (DIC), the ACLs were painted white and covered with an irregular speckled pattern in black. The first and final cycles of each test were isolated to assess the progression of damage within the ACL. Testing was recorded with a commercial off-the-shelf Android smartphone, and the footage was processed using HitFilm. The images were subsequently analyzed using MATLAB and Ncorr DIC software to determine strain and displacement patterns.

Results

During the cyclic tensile tests, tension was increased to the set point and then reversed to zero, not necessarily returning to the original starting position. Initial cycles at 300N required a displacement of 4.16±1.45mm, while those at 600N required 8.17±2.14mm. In the final cycles, the 300N group exhibited a displacement of 2.65±1.70mm, while the 600N group showed a displacement of 7.30±6.92mm. These results highlight the behavior of the entire ACL during cyclic loading. The highest relative localized yy-strain along the loading axis was 0.208±0.204 for the first cycle at 300N and 0.364±0.097 for the final cycle. At 600N, the yy-strain increased from 1.013±0.609 in the first cycle to 1.509±1.382 in the final cycle. The strain data consistently indicated that the highest strain occurred in the anteromedial bundle of the ACL, near the midline, a finding consistent with previous clinical observations of ACL failure.

SIGNIFICANCE/CLINICAL RELEVANCE: The continued validation of DIC against clinically expected behavior for high-strain biological tissues can significantly enhance material characterization techniques in medical applications. This study’s findings underscore the potential of the adolescent porcine stifle joint as a reliable model for ACL research, contributing to better understanding and treatment of ACL injuries, particularly in adolescent populations.