# Bio‐Compositional and Microstructural Changes in Rabbit Knee Collateral Ligaments Eight Weeks After Anterior Cruciate Ligament Transection

## TL;DR

This study examines how ACL injury affects the composition and structure of rabbit knee collateral ligaments eight weeks post-injury.

## Contribution

The study reveals novel bio-compositional and microstructural changes in collateral ligaments following ACL injury.

## Key findings

- ACL-transected ligaments showed lower collagen and higher proteoglycan content.
- Collagen fiber matrix became more disorganized with increased crimp angles and lengths.
- Findings highlight structural-function changes in collateral ligaments after ACL injury.

## Abstract

Injury to the anterior cruciate ligament (ACL) is common in young, active individuals. It has the potential to lead to post‐traumatic osteoarthritis. However, the effects of ACL injury on the bio‐composition and microstructure of the knee's collateral ligaments have been poorly explored. In this study, Fourier transform infrared (FTIR) imaging and quantitative polarized light microscopy (qPLM) were used to identify the respective changes in bio‐composition and collagen fiber arrangements of the knee's collateral ligaments. To mimic an ACL trauma, unilateral ACL transection surgery was performed on either the left or right knee of 6 mature New Zealand white rabbits. Lateral and medial collateral ligaments were harvested from the transected and contralateral knees 8 weeks after the ACL transection surgery. At the same time, collateral ligaments of 4 age‐matched, healthy rabbits were collected from the right and left knees. From acquired FTIR images, the relative collagen and proteoglycan contents of the collateral ligaments were estimated and compared between the transected, contralateral, and control knees. The results revealed lower collagen and higher proteoglycan content in ACL‐transected collateral ligaments compared to collateral ligaments of contralateral and control group knees. Additionally, qPLM revealed a more disorganized collagen fiber matrix, accompanied by increased crimp angles and longer crimp lengths following ACL transection. This study provides novel insight into the bio‐compositional and microstructural alterations of collateral ligaments following ACL injury, highlighting the importance of considering the structure‐function properties of collateral ligaments in treatment planning aimed at restoring normal knee joint function after ACL injury.