Summary

Physeal-sparing techniques revealed a superior ability to restore initial joint stability compared to the complete transphyseal technique in an early adolescent porcine joint, with less transfer of anterior force from the reconstructed ACL graft to the MCL.

Abstract

Introduction

The incidence of pediatric anterior cruciate ligament (ACL) injuries has been increasing [1]. Current pediatric ACL reconstruction (ACLR) techniques include complete transphyseal, partial transphyseal, and physeal-sparing [2]. Patient age is a major factor in technique selection; however, in the pre-adolescent/early adolescent age range (11-13 years old) all three techniques are commonly used [3]. Surgical technique has been found more associated with the surgeon’s fellowship training rather than the joint and ACL function [3]. Animal models have shown age-specific joint function during growth [4]. Thus, it is essential to compare ACLR techniques for specific ages using age-specific models. Therefore, the current work aims to compare initial joint stability and function following complete transphyseal, partial transphyseal, and physeal-sparing ACLR within an early adolescent porcine model.

Methods

A total of 18 deep digital flexor tendons and 18 hindlimbs were collected from early adolescent (4.5 months old) pigs. The specimens were divided into three groups (n=6 each) with different pediatric ACLR techniques: complete transphyseal, partial transphyseal, and physeal-sparing. A 6-degree-of-freedom robotic testing system with a universal force-moment sensor was used to test joint function (Kuka, simVITRO). An 80 N anterior-posterior (AP) load, a 120 N compression, and a 4 N·m varus-valgus (VV) torque were applied to the intact and ACL-transected (ACLT) joint at 60° of flexion. ACL reconstruction was then performed, using a porcine flexor tendon allograft. The same AP, compression, and VV loads were applied following ACLR. AP tibial translation (APTT) under applied AP load, anterior tibial translation (ATT) under applied compression, and VV rotation under applied VV torques were calculated for intact, ACLT, and ACLR states. Tissue forces were calculated using the principle of superposition. One-way ANOVA with Tukey’s HSD was utilized to compare joint laxity between different states as well as tissue force contribution between different surgical techniques. Significance was set at 0.05.

Results

ACLT resulted in destabilization in the joint under all loading conditions. ATT under compression was restored to intact state (4.5 mm) after ACLR with partial transphyseal (4.9 mm) and physeal-sparing (2.9 mm), but not complete transphyseal technique (9.6 mm, P=0.01). Under varus-valgus torque, VV rotation was restored to intact state after all techniques, with no statistical differences in the changes of VV rotation across techniques. The increase of APTT under AP drawer slightly differed by 3.2 mm between complete transphyseal and physeal-sparing technique (P=0.056). Following complete transphyseal ACLR, the MCL had a greater anterior load contribution (55%) compared to physeal-sparing (28%). The changes in forces taken by other soft tissues were similar under compression and varus-valgus rotation.

Conclusion

Physeal-sparing techniques revealed a superior ability to restore initial joint stability compared to the complete transphyseal technique in an early adolescent porcine joint, with less transfer of anterior force from the reconstructed ACL graft to the MCL. Identifying the impact of different pediatric ACLR techniques within age-appropriate joints can lead to a better understanding of operative treatments for ACL injuries in young patients. Future in-vivo work will compare the long-term degenerative outcomes following different pediatric ACLR techniques.


ACKNOWLEDGEMENTS
We would like to thank the NC State College of Veterinary Medicine and Laboratory Animal Resources for their contribution to this work. Funding provided by NIH (R01 AR071985).