title: T2* relaxometry and volume predict semi-quantitative histological scoring of an ACL bridge-enhanced primary repair in a porcine model.
abstract: Magnetic resonance imaging (MRI) variables, such as T2* and volume, can predict the healing ligament structural properties. How these MR variables relate to semi-quantitative histology of the healing ACL is yet unknown. We hypothesized that T2* and volume would predict the histological scoring of a healing ACL. Yucatan minipigs underwent ACL transection and received bridge-enhanced ACL repair or no treatment. The surgical legs were harvested after 52 weeks and imaged using a high resolution 2-echo sequence. For each ligament, the volume and median T2* values were determined. The ACL specimens were then histologically analyzed using the advanced Ligament Maturity Index (LMI). The T2* of the healing ligaments significantly predicted the total LMI score as well as the cell, collagen and vessel sub-scores; R(2)  = 0.78, 0.67, 0.65, and 0.60, respectively (p ≤ 0.001). The ligament volume also predicted the total LMI score, cell, and collagen sub-scores; R(2)  = 0.39, 0.33, 0.37, and 0.60, respectively (p ≤ 0.001). A lower ligament T2* or a higher volume was associated with higher histological scores of the healing ligaments. This study provides a critical step in the development of a non-invasive method to evaluate ligament healing on a microscopic scale.
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University/Rhode Island Hospital, Suite 404, 1 Hoppin Street, Providence, Rhode Island.|School of Engineering, Brown University, Providence, Rhode Island.
authors.forename: Alison M
authors.initials: AM
authors.lastname: Biercevicz
authors.affiliation: Department of Orthopaedic Surgery, Children's Hospital Boston, Boston, Massachusetts.
authors.forename: Benedikt L
authors.initials: BL
authors.lastname: Proffen
authors.affiliation: Department of Orthopaedic Surgery, Children's Hospital Boston, Boston, Massachusetts.
authors.forename: Martha M
authors.initials: MM
authors.lastname: Murray
authors.affiliation: Department of Neuroscience, Division of Biology and Medicine, Brown University, Providence, Rhode Island.
authors.forename: Edward G
authors.initials: EG
authors.lastname: Walsh
authors.affiliation: Department of Orthopaedics, Warren Alpert Medical School, Brown University/Rhode Island Hospital, Suite 404, 1 Hoppin Street, Providence, Rhode Island.|School of Engineering, Brown University, Providence, Rhode Island.
authors.forename: Braden C
authors.initials: BC
authors.lastname: Fleming
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D013552:Swine; D013556:Swine, Miniature; D014945:Wound Healing
keywords: ACL; MRI; healing; histology; ligament