In Situ Joint Stiffness Increases During Skeletal Growth but Decreases Following Partial and Complete Anterior Cruciate Ligament Injury

Abstract

Partial and complete anterior cruciate ligament (ACL) injuries occur in both pediatric and adult populations and can result in loss of joint stability and function. The sigmoidal shape of knee joint function (load-translation curve) under applied loads includes a low-load region (described by slack length) followed by a high-load region (described by stiffness). However, the impact of age and injury on these parameters is not fully understood. The current objective was to measure the effects of age and injury on the shape of joint function in a porcine model. In response to an applied anterior–posterior tibial load, in situ slack did not change (p > 0.05), despite sevenfold increases in joint size with increasing age. Joint stiffness increased from an average of 10 N/mm in early youth to 47 N/mm in late adolescence (p < 0.05). In situ ACL stiffness increased similarly, and changes in in situ joint stiffness and ACL stiffness were highly correlated across ages. With complete ACL injury, in situ slack length increased by twofold to fourfold and in situ stiffness decreased threefold to fourfold across ages (p < 0.05). Partial ACL injury resulted in less dramatic, but statistically significant, increases in joint slack and significant decreases in in situ joint stiffness in the adolescent age groups (p < 0.05). This work furthers our understanding of the interaction between joint biomechanics and ACL function throughout growth and the impact of ACL injury in the skeletally immature joint.

Sex-Specific Function and Morphology of the Anterior Cruciate Ligament During Skeletal Growth in a Porcine Model

“…Biomechanical testing was performed using a robotic testing system (KR300 R2500, KRC4, Kuka, Shelby Charter Township, MI, USA) equipped with a universal force-moment sensor (Omega160 IP65, ATI Industrial Automation, Apex, NC, USA), as previously described. 23; 24 Systems were integrated and controlled using the simVitro software knee module (Cleveland Clinic, Cleveland, OH, USA). Stifle joints were thawed at room temperature to be prepared for robotic testing.…”

“…To assess sub-maximal joint behavior, in situ joint slack and stiffness were calculated using Matlab, as previously described. 24; 34 Biphasic curves consisting of an exponential region and a linear region were fitted to the anterior and posterior portions each force-translation curve. Anterior and posterior engagement points were determined as the points of maximum curvature.…”

“…Data from female specimens has been previously reported. [22][23][24] was not certified by peer review) is the author/funder. All rights reserved.…”

“…Our group and others have used the porcine model to study the skeletally immature ACL [22][23][24][25][26][27] and sex-specific ACL behavior. 28; 29 The porcine model is widely used for musculoskeletal applications 30 and is a good model to study function of the mature ACL.…”

Age‐ and sex‐specific differences in ACL and ACL bundle size during adolescent growth

“…21 Interestingly, the kinematic response to applied loads following partial and complete ACL injuries also varies with age, with instability due to loss of the AM bundle function at adolescent but not preadolescent ages in the porcine model. 22 These functional changes occur alongside a shift in the relative CSA of the porcine AM and PL bundles during growth, suggesting that an initial key to understanding functional changes in the multibundle ACL may be characterizing changes in the structure of the AM and PL bundles during pediatric human growth. 20 As such, the objective of this study was to compare age-specific changes in the length and CSA of the AM and PL bundles of the ACL during growth in human patients.…”