Establishing Design Criteria For Anterior Cruciate Ligament Reconstruction

Download or read book Establishing Design Criteria for Anterior Cruciate Ligament Reconstruction written by Rebecca J. Nesbitt and published by . This book was released on 2015 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt: The anterior cruciate ligament (ACL) plays a complex role in knee stability. Injury to this structure can cause abnormal joint kinematics and loadings which may lead to the early onset of osteoarthritis (OA) and joint degeneration. While surgeons are able to restore joint laxity in the short to medium term, long term OA development is currently not prevented in patients who have undergone surgical repair. In order to slow or stop the progression of OA following ACL injury, we hypothesize that reconstruction techniques must achieve a greater degree of native ligament functionality. The principles of Functional Tissue Engineering state that a ligament's functionality may be defined as its in vivo loading characteristics. While this information remains impossible to measure directly in human patients in vivo, in vitro testing can serve as an alternative as long as the following conditions are met: 1) Loads are measured in 6 degrees-of-freedom (DOFs); 2) Loads are measured during activities of daily living (ADLs); 3) Loads are measured within a realistic environment, which may include knees sustaining injury to structures influencing ACL functionality. Due to the invasive nature of in vivo load sensing, researchers have turned to robotics to simulate ADLs kinematics on biological tissue. This technique allows open access to the joint to measure contact forces and 6 DOF ligament loads throughout physiologic motion paths, fulfilling the first 2 requirements for in vitro testing. By using an animal model, specimen-specific kinematics may be collected and applied to the same tissue, overcoming several limitations of cadaveric testing, including specimen quality and kinematic mis-matches. It also allows for consideration of biologic effects and controlled testing of various knee pathologies, fulfilling the 3rd requirement for in vitro testing. Because of these advantages, this work utilized robotics in combination with the sheep knee model to study in vivo ACL loading, which may then serve as design criteria for new and novel repair techniques. Studies were designed to address two specific aims. The first focused on assessing the biomechanical relationships between activity and the corresponding demands placed on the ACL. Results showed that, while a strong link exists between activity and the corresponding knee kinematics, the knee dynamics follow a more complex pattern with inter-relationships between multiple DOFs. Overall, ACL functional demands were most variable during phases of the activities when the knee was less weight bearing, yet still engaged. Specifically, inclined gait placed higher demands on the ACL during hoof strike while declined gait place higher demands on the ACL during push off. Both of these time points corresponded to instances of lower compression levels within each ADL. This is also consistent with the timing of non-contact ACL tears, where most injuries occur during the transition from uncompressed to compressed knee states -- such as landing. The second aim focused on assessing biomechanical relationship between ACL demands and concomitant knee injury. Medial meniscus (MM) injury increased ACL forces during the transitions between swing and stance in response to significant increases in anterior translation. Dual (MM and MCL) injury produced no increases, yet both MM and Dual groups developed significant OA within the medial compartment. MCL injury produced increased ACL force during mid stance in response to increased overall joint laxity but no increase in OA. Results of the this study are the first to relate ADLs and injury of surrounding structures to resulting knee biomechanics and ACL function and provide preliminary data for defining design requirements for future ACL reconstruction techniques.