Degenerative changes are associated with severity of anterior cruciate ligament injury within the skeletally immature joint

Abstract

Pediatric anterior cruciate ligament (ACL) injuries are a major problem in the pediatric and adolescent populations. Approximately one-quarter of these injuries only extend through only part of the tissue cross-section. Yet, there is very limited data to inform clinical treatments for pediatric partial ACL tears. In particular, understanding how injury severity impacts long-term degenerative changes in the joint is unknown. In this study, we leverage a skeletally immature preclinical porcine model to evaluate joint biomechanics, tissue remodeling, and degeneration after partial (isolated anteromedial (AM) or posterolateral (PL) bundle) or complete (full thickness) ACL injury. Six months after injury, joint laxity increases were minimal for PL bundle injury, minor for AM bundle injury, and major for ACL injury. In both partial injury cases, the remaining bundle remodeled through an increase in CSA to attempt to restore ACL function and stabilize the knee joint. Joint degeneration (evaluated by cartilage T1 relaxation, macroscopic cartilage degeneration, and meniscal hypertrophy) was minimal after PL bundle injury, moderate after AM bundle injury, and substantial after ACL injury. Further analysis with subjects grouped by Lachman grade (indicating the extent of joint destabilization) indicated that degeneration was associated with the extent of biomechanical destabilization, irrespective of the injury type. These findings point to the importance of considering the results of joint laxity exams when creating treatment plans for young patients with significant growth remaining, particularly those with partial ACL injuries.

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

“…Like humans, the porcine stifle joint becomes unstable with complete loss of ACL function 51 . Recent work has also examined the impact of partial ACL injuries created via arthroscopy under multiple loading conditions 57 . Arthrotomy and arthroscopy can also be used for ACL repair and reconstruction procedures as reported previously in the literature 64,65 .…”

“…51 Recent work has also examined the impact of partial ACL injuries created via arthroscopy under multiple loading conditions. 57 Arthrotomy and arthroscopy can also be used for ACL repair and reconstruction procedures as reported previously in the literature. 64,65 Arthrotomy may be more appropriate for specific procedures, including those involving biologics in which a fluid environment may not be desired at the time of implantation.…”

“…allow easy creation of complete or partial ACL injuries (Figure 5B). 57 Such approaches can be used to assess the impact of ACL injury. Like humans, the porcine stifle joint becomes unstable with complete loss of ACL function 51 .…”

“…synovial fluid from the joint on a longitudinal or endpoint basis in pigs, 54,55 as in human studies. 56 In addition to clinically-relevant measures, the size of the porcine joint also lends itself to valuable terminal analyses, including multiple degree-of-freedom joint-and tissue-level biomechanics 49,57 as well as multi-tissue imaging, histological, biochemical, and transcriptional analyses. 55,57,58 Mechanically, tissue properties such as load to failure and stiffness are similar between humans and pigs, while small animal models exhibit much lower mechanical properties.…”

“…F I G U R E 5 Arthroscopic procedures (A) to create partial and complete ACL injuries 6,57 (B) and reconstruction using soft tissue grafts (C). ACL, anterior cruciate ligament.…”