The anterior cruciate ligament (ACL) provides a complex role to knee stability. Traumatic injury to this structure causes abnormal joint kinematics which poses significant socioeconomic problems. Lost joint stability is linked to long-term degenerative joint disease. In an attempt to restore the functional role of the ACL, reconstruction is performed. Unfortunately, current reconstruction methods have limitations and fail to reduce the likelihood of early onset osteoarthritis.
Advances in technology have allowed researches an opportunity to better assess normal function, injury, and repair. Specifically, the use of robotic technology has made it possible to study the ACL during activities of daily living (ADLs). With the robot, we can convert in vivo kinematic data into reproducible simulated in vivo motions. During kinematic simulations, three-dimensional (3D) joint kinetics can be measured, allowing for assessment of normal and ACL-deficient knees, as well as examining limitations of current reconstruction methods. Ideally this would be performed in the human knee, but there are limitations which make this challenging. The goal of the research presented was to develop the porcine knee as a biomechanical model of the human knee to study different aspects of ACL reconstruction.
The human ACL is critical to anterior knee stability, so a viable model should function similarly. We found that the porcine knee is also an ACL dependent joint. It accounted for 80%-125% of the anterior force during gait, suggesting the porcine model as a candidate for studying ACL function and different repair techniques. We then examined the viability of two prototype ACL graft materials compared to the current “gold standard” bone-patellar tendon-bone (BPTB) graft. We found that the Hybrid graft, a reconstructed porcine dermis matrix with a polymer core, performed the best. It initially restored the anterior force of the native ACL knee, and mimicked the rate of force loss during long-term cyclic testing of the native ACL knee in all degrees-of-freedom (DOFs). However, all grafted knees failed to match the initial forces in other DOFs, and each altered the load sharing of primary and secondary contributions. Additionally, all grafted knees showed a significant increase in the restraining role of the medial collateral ligament, suggesting a failure to restore the normal function of the native ACL knee.
To be clinically relevant, correlations need to be developed between the porcine and human knees. For this, we examined human cadaveric knees. The value in this study was developing a testing methodology for human cadaveric knees using simulated in vivo ADLs. While improvements need to be made to reduce inter-specimen variability, simulating in vivo human gait provided promising prospects. We have begun to develop a database of kinematics and kinetics for the porcine knee, and have established a foundation to use it as a biomechanical screening tool to study ACL reconstruction. Ultimately, defining repair criteria will support development of methods and materials to better restore lost function after ACL reconstruction. The next steps are to optimize human cadaveric testing methodologies in order to fully understand the biomechanical relationships between porcine and human knees.