This study provides a novel comparison of male and female knee positions at the time of an ACL injury that may offer information to improve injury prevention strategies.

Background: The in vivo mechanics of the anterior cruciate ligament (ACL) and its bundles during dynamic activities are not completely understood. An improved understanding of how the ACL stabilizes the knee is likely to aid in the identification and prevention of injurious maneuvers. Purpose/Hypothesis: The purpose was to measure in vivo ACL strain during a single-legged jump through use of magnetic resonance imaging (MRI) and high-speed biplanar radiography. We hypothesized that ACL strain would increase with the knee near extension, and a peak in ACL strain would occur just before landing from the jump, potentially due to quadriceps contraction in anticipation of landing. Study Design: Descriptive laboratory study. Methods: Models of the femur, tibia, and ACL attachment sites of 8 male participants were generated from MRI scans through use of solid modeling. High-speed biplanar radiographs were obtained from these participants as they performed a single-legged jump. The bone models were registered to the biplanar radiographs, thereby reproducing the in vivo positions of the joint throughout the jump. ACL and bundle elongations were defined as the centroid to centroid distances between attachment sites for each knee position. ACL strain was defined as ACL length normalized to its length measured in the position of the knee at the time of MRI. Results: Peaks in ACL strain were observed before toe-off and 55 ± 35 milliseconds before initial ground contact. These peaks were associated with the knee positioned at low flexion angles. Mean ACL strain was inversely related to mean flexion angle (rho = −0.73, P < .001), such that ACL strain generally increased with knee extension throughout the jumping motion. ACL bundle lengths were significantly (rho > 0.85, P < .001) correlated with overall ACL length. Conclusion: These findings provide insight into how landing in extension can increase the risk of ACL injury. Specifically, this study shows that peak ACL strain can occur just before landing from a single-legged jump. Thus, when an individual lands on an extended knee, the ACL is relatively taut, which may make it particularly vulnerable to injury, especially in the presence of a movement perturbation or unanticipated change in landing strategy. Clinical Relevance: This study provides a novel measurement of dynamic ACL strain during an athletic maneuver and lends insight into how landing in extension can increase the likelihood of ACL failure.

Understanding in vivo joint mechanics during dynamic activity is crucial for revealing mechanisms of injury and disease development. To this end, laboratories have utilized computed tomography (CT) to create 3-dimensional (3D) models of bone, which are then registered to high-speed biplanar radiographic data captured during movement in order to measure in vivo joint kinematics. In the present study, we describe a system for measuring dynamic joint mechanics using 3D surface models of the joint created from magnetic resonance imaging (MRI) registered to high-speed biplanar radiographs using a novel automatic registration algorithm. The use of MRI allows for modeling of both bony and soft tissue structures. Specifically, the attachment site footprints of the anterior cruciate ligament (ACL) on the femur and tibia can be modeled, allowing for measurement of dynamic ACL deformation. In the present study, we demonstrate the precision of this system by tracking the motion of a cadaveric porcine knee joint. We then utilize this system to quantify in vivo ACL deformation during gait in four healthy volunteers.

Cerebral Palsy (CP) refers to a heterogeneous group of permanent but non-progressive movement disorders caused by injury to the developing fetal or infant brain (Bax et al., 2005). Because of its serious long-term consequences, effective interventions that can help improve motor function, independence, and quality of life are critically needed. Our ongoing longitudinal clinical trial to treat children with CP is specifically designed to meet this challenge. To maximize the potential for functional improvement, all children in this trial received autologous cord blood transfusions (with order randomized with a placebo administration over 2 years) in conjunction with more standard physical and occupational therapies. As a part of this trial, magnetic resonance imaging (MRI) is used to improve our understanding of how these interventions affect brain development, and to develop biomarkers of treatment efficacy. In this report, diffusion tensor imaging (DTI) and subsequent brain connectome analyses were performed in a subset of children enrolled in the clinical trial (n = 17), who all exhibited positive but varying degrees of functional improvement over the first 2-year period of the study. Strong correlations between increases in white matter (WM) connectivity and functional improvement were demonstrated; however no significant relationships between either of these factors with the age of the child at time of enrollment were identified. Thus, our data indicate that increases in brain connectivity reflect improved functional abilities in children with CP. In future work, this potential biomarker can be used to help differentiate the underlying mechanisms of functional improvement, as well as to identify treatments that can best facilitate functional improvement upon un-blinding of the timing of autologous cord blood transfusions at the completion of this study.