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This study focuses on the application of new experimental techniques (robotic/UFS testing system), analytical tools (FEA), and physical models to the investigation of lumbar functional spinal unit structural properties.

The current study investigated the efficacy of virtual reality (VR) assisted visual feedback for improving control of voluntary movements of the cervical spine during performance of active range-of-motion maneuvers. Active range-of-motion was assessed in 10 asymptomatic volunteers, both without and with VR-assisted visual feedback of overall cervical spine rotations. 8 of the 12 secondary rotations were significantly lower (p < 0.01) with VR feedback than the corresponding secondary rotations without VR feedback. No statistically significant differences were found between the primary rotations attained without VR and with VR feedback. These results support the use of VR-based visual feedback for enabling control of in-vivo cervical spine kinematics.

The PCL consists of two primary bundles, the anterolateral (AL) and posteromedial (PM). The AL bundle is larger, stiffer, and has a higher ultimate load (Harner, 1995), and has been the focus of PCL replacement surgery (Clancy, 1983). However, clinical outcomes of PCL reconstruction have been unsatisfactory (Lipscomb, 1993); which has led to the question of the advancement of a double bundle procedure in hopes to more accurately reproduce the PCL (Clancy, 1998). It was therefore the objective of this study to evaluate the biomechanics of a double bundle PCL reconstruction (PCL-2), and compare these results with those obtained for the intact knee as well as a single bundle PCL reconstruction (PCL-1). To study this, a robotic/universal force-moment sensor (UFS) testing system which measures the multiple degree of freedom (DOF) knee kinematics determines the in situ force in the ligaments (or replacement grafts) in response to external loading conditions was utilized. The hypothesis was that PCL-2 would improve knee kinematics and in situ forces to those of the intact knee throughout the range of knee flexion as compared to PCL-1.

Numerical modeling of the human knee joint has been pursued by various researchers [1,2]. Several knee joint models have been reported to simulate the kinematic and dynamic response of the knee joint to external loads, which to various degrees are representative of those found in the knee’s daily function. However, experimental validation of these models has been scarcely documented. Typical validation procedures should include a comparison of computational results from numerical simulations, to those from experimental tests performed on actual human joint specimens. The loading conditions must be carefully controlled and reproduced from one testing approach to another for acceptable comparison of the knee joint responses.

Previous studies, using imaging techniques[4] and mathematical models, have predicted that loads up to 90% of body weight are transmitted across the glenohumeral (GH) joint at 90° of abduction[2, 3]. However, in comparison to weight-bearing joints like the hip and knee, there is little quantitative data describing 3-D reaction forces generated at the GH joint during active motion. This information is important to our understanding of GH joint function in both normal and pathological conditions. It can also provide an experimental validation for computational models of the GH joint.

Clinical outcomes of reconstructive surgery for injuries to the posterior cruciate ligament (PCL) of the knee have been unsatisfactory, with persistent instability predisposing patients to early degenerative joint disease [Clancy, 1983]. One explanation for these outcomes has been the high incidence (up to 60%) of associated injuries to the posterolateral structures (PLS), which include the lateral collateral ligament (LCL) and popliteus complex. Combined PCL/PLS injuries are particularly debilitating because restraints to both posterior tibial translation and external rotation are lost [Grood, 1988]. Further, PLS injuries are difficult to reconstruct due to its complex anatomy; thus, often only the PCL is reconstructed when combined injuries occur.

In-vivo biomechanical studies of cervical spine movements are useful for defining “kinematic envelopes” of motion. Data are readily available on the ranges-of-motion of the cervical spine in flexion/extension, left/right lateral bending, and left/right axial rotation [1]. There is increasing evidence that “combined movements” may also be of clinical importance [2,3,4]. In this study, we tested the hypothesis that axial rotation limits active flexion/extension of the cervical spine. We used a specially developed measurement system featuring a 3-D magnetic tracking device with virtual reality technology that enables subjects to perform combined movements that would otherwise be difficult to achieve.