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Fri, Aug 26

Speaker:  Megan Schroeder

Title: Surgical and intrinsic factors contributing to cartilage degeneration following ACL-reconstruction.

Abstract:  Following injury to the anterior cruciate ligament (ACL) of the knee, surgical reconstruction is often indicated for patients seeking a return to high levels of physical activity. Despite short-term success in restoring stability and improving function, this procedure does not offer protection against early-onset joint degeneration and the development of osteoarthritis in this population. Secondary to the initial trauma, this outcome may in part be mediated by increased or abnormal contact stresses in the joint post-reconstruction, which may be attributable to both surgical (graft type, tensioning level, attachment site), and patient-specific (joint geometry, muscle activation patterns) parameters. In this study, we sought to explore the influence of such factors on patellofemoral and tibiofemoral cartilage contact patterns post-reconstruction.
Advisor: Dr. Dhaher

Speaker: Joshua Peng

Title: Characterization and detection of mode transitions for implementation in a powered transfemoral prosthesis.

Abstract: Studies investigating stability during stair negotiation with able-bodied subjects have shown that the most common time for missteps and falls occur when a person is transitioning to and from stairs.  Stair negotiation is a particularly difficult task for transfemoral (above-knee) amputees due to limited stair ambulation modes and transitioning capability.  The most advanced prosthetic knees on the market do not assist amputees in performing continuous (without stopping), automatic (without manual input), and natural (replicating able-bodied gait patterns) transitions. The first objective of this project is to characterize kinematic, kinetic, and electromyographic (EMG) patterns in anticipation of and during transitions from level walking to stair ascent/descent.  We hypothesize that able-bodied subjects exhibit distinct gait mechanics during transition strides when compared to level walking and that they will -modify gait mechanics in anticipation of stair walking to achieve adequate foot clearance to step up (stair ascent) or step down (stair descent).  Our second objective is to differentiate transition strides from level walking and stair ascent/descent strides in order to detect the onset of a transition.  Preliminary data suggests that stronger activation of the biceps femoris precedes toe off during the transition stride from level walking to stair ascent.  Studies on electromechanical delay (EMD) in skeletal muscle have revealed that the onset of force generation and movement occur about 50ms after neuromuscular activation.  Thus, we hypothesize that the inclusion of EMG signals (to kinematic and kinetic data) will allow earlier and more accurate detection of transitions.  Our final objective will involve estimating knee impedance parameters (stiffness, damping, and equilibrium angle) from knee torque and knee angle data to control a powered knee prosthesis to perform continuous, automatic, and natural transitions between level walking and stair ascent/descent modes.
Advisors: Drs Kuiken, Hargrove and Brown