The ACL injury response: A collagen-based analysis.
BACKGROUND
Anterior cruciate ligament (ACL) injuries do not effectively heal. Tendon graft tissue after reconstruction shows rapid tissue turnover and 'ligamentization.' It is unknown whether native torn ACL tissue undergoes significant collagen turnover after injury or is arrested by the intraarticular environment. It is also unknown whether injury mechanism or chronicity affect torn ligament tissue turnover.


METHODS
Thirty-three mid-substance ACL biopsies were obtained during primary arthroscopic ACL reconstruction (n=31; nine contact injuries, 22 non-contact injuries, 22 males, 11 females; mean age 28.5 years; median injury to surgery time 12 weeks), or from cadavers as uninjured ACL (n=2). As a marker for collagen turnover, immature collagen cross-link content was determined by ninhydrin reagent assays. The immature cross-link content was assessed against injury mechanism, patient age, and injury to surgery time. Histochemical analysis was conducted on two uninjured ACL cadaveric controls, a four-week-old ACL tear, and a four-year-old ACL tear.


RESULTS
Contact and non-contact groups were not demographically different with respect to sex, patient age, injury to surgery time, and activity involvement prior to injury, which ranged from basketball to logging. Collagen crosslink content was very low across all samples, suggesting high tissue turnover between injury and surgery regardless of injury mechanism (non-contact: 1.68ng/mol, CI 0.48-2.89; contact: 1.50ng/mol, CI 0.14-2.86; p=0.842).


CONCLUSIONS
Collagen turnover occurs rapidly after ACL injury regardless of contact or non-contact mechanism. Robust tissue turnover starts within the first several weeks after injury and persists to some extent throughout the life of the torn ACL.
College of Medicine, The Ohio State University, United States; Orthopaedics, The Ohio State University Wexner Medical Center, United States.
Joshua S
JS
Everhart
College of Medicine, The Ohio State University, United States.
John H
JH
Sojka
Orthopaedics, The Ohio State University Wexner Medical Center, United States.
Christopher C
CC
Kaeding
Orthopaedics, The Ohio State University Wexner Medical Center, United States.
Alicia L
AL
Bertone
Orthopaedics, The Ohio State University Wexner Medical Center, United States. Electronic address: David.flanigan@osumc.edu.
David C
DC
Flanigan
D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology*; D000070598:Anterior Cruciate Ligament Injuries / Q000209:etiology / Q000601:surgery; D059549:Anterior Cruciate Ligament Reconstruction; D001265:Athletic Injuries; D001706:Biopsy; D016022:Case-Control Studies; D003094:Collagen / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018919:Neovascularization, Physiologic; D055815:Young Adult
D003094:Collagen
ACL injury; Biopsy; Collagen turnover; Contact injury; Non-contact injury