Standing Reactive Postural Responses of Lower Limbs With and Without Self-Balance Assistance in Individuals With Spinal Cord Injury Receiving Epidural Stimulation.

Spinal cord epidural stimulation can promote the recovery of motor function in individuals with severe spinal cord injury (SCI) by enabling the spinal circuitry to interpret sensory information and generate related neuromuscular responses. This approach enables the spinal cord to generate lower limb extension patterns during weight bearing, allowing individuals with SCI to achieve upright standing. We have shown that the human spinal cord can generate some standing postural responses during self-initiated body weight shifting. In this study, we investigated the ability of individuals with motor complete SCI receiving epidural stimulation to generate standing reactive postural responses after external perturbations were applied at the trunk. A cable-driven robotic device was used to provide constant assistance for pelvic control and to deliver precise trunk perturbations while participants used their hands to grasp onto handlebars for self-balance support (hands-on) as well as when participants were without support (free-hands). Five individuals with motor complete SCI receiving lumbosacral spinal cord epidural stimulation parameters specific for standing (Stand-scES) participated in this study. Trunk perturbations (average magnitude: 17 ± 3% body weight) were delivered randomly in the four cardinal directions. Participants attempted to control each perturbation such that upright standing was maintained and no additional external assistance was needed. Lower limb postural responses were generally more frequent, larger in magnitude, and appropriately modulated during the free-hands condition. This was associated with trunk displacement and lower limb loading modulation that were larger in the free-hands condition. Further, we observed discernible lower limb muscle synergies that were similar between the two perturbed standing conditions. These findings suggest that the human spinal circuitry involved in postural control retains the ability to generate meaningful lower limb postural responses after SCI when its excitability is properly modulated. Moreover, lower limb postural responses appear enhanced by a standing environment without upper limb stabilization that promotes afferent inputs associated with a larger modulation of ground reaction forces and trunk kinematics. These findings should be considered when developing future experimental frameworks aimed at studying upright postural control and activity-based recovery training protocols aimed at promoting neural plasticity and sensory-motor recovery.

Robotic upright stand trainer (RobUST) and postural control in individuals with spinal cord injury.

CONTEXT/OBJECTIVE: Assessed feasibility and potential effectiveness of using a novel robotic upright stand trainer (RobUST) to deliver postural perturbations or provide assistance-as-needed at the trunk while individuals with spinal cord injury (SCI) performed stable standing and self-initiated trunk movements. These tasks were assessed with research participants' hands on handlebars for self-balance assistance (hands on) and with hands off (free hands). DESIGN: Proof of concept study. PARTICIPANTS: Four individuals with motor complete (n = 3) or incomplete (n = 1) SCI who were not able to achieve independent standing and presented a neurological lesion level ranging from cervical 4 to thoracic 2. OUTCOME MEASURES: Ground reaction forces, trunk displacement, and electromyography activity of trunk and lower limb muscles. RESULTS: Research participants received continuous pelvic assistance via RobUST, and manual trainer assistance at the knees to maintain standing. Participants were able to attempt all tasks. Free hands trunk perturbations resulted in greater load bearing-related sensory information (73% ipsilateral vertical loading), trunk displacement (57%), and muscle activation compared to hands on. Similarly, free hands stable standing with RobUST assistance-as-needed resulted in 8.5% larger bodyweight bearing, 112% larger trunk movement velocity, and higher trunk muscles activation compared to standing with hands on. Self-initiated trunk movements controlled by hands on showed 116% greater trunk displacement, 10% greater vertical ground reaction force, and greater ankle muscle activation compared to free hands. CONCLUSION: RobUST established a safe and challenging standing environment for individuals with SCI and has the potential to improve training paradigms and assessments of standing postural control.

Reduced step length reduces knee joint contact forces during running following anterior cruciate ligament reconstruction but does not alter inter-limb asymmetry.

BACKGROUND: Anterior cruciate ligament reconstruction is associated with early onset knee osteoarthritis. Running is a typical activity following this surgery, but elevated knee joint contact forces are thought to contribute to osteoarthritis degenerative processes. It is therefore clinically relevant to identify interventions to reduce contact forces during running among individuals after anterior cruciate ligament reconstruction. The primary purpose of this study was to evaluate the effect of reducing step length during running on patellofemoral and tibiofemoral joint contact forces among people with a history of anterior cruciate ligament reconstruction. Inter limb knee joint contact force differences during running were also examined. METHODS: 18 individuals at an average of 54.8months after unilateral anterior cruciate ligament reconstruction ran in 3 step length conditions (preferred, -5%, -10%). Bilateral patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, loading rate, impulse, and impulse per kilometer were evaluated between step length conditions and limbs using separate 2 factor analyses of variance. FINDINGS: Reducing step length 5% decreased patellofemoral, tibiofemoral, and medial tibiofemoral compartment peak force, impulse, and impulse per kilometer bilaterally. A 10% step length reduction further decreased peak forces and force impulses, but did not further reduce force impulses per kilometer. Tibiofemoral joint impulse, impulse per kilometer, and patellofemoral joint loading rate were lower in the previously injured limb compared to the contralateral limb. INTERPRETATION: Running with a shorter step length is a feasible clinical intervention to reduce knee joint contact forces during running among people with a history of anterior cruciate ligament reconstruction.

Independent effects of step length and foot strike pattern on tibiofemoral joint forces during running.

The purpose of this study was to examine the effects of step length and foot strike pattern along with their interaction on tibiofemoral joint (TFJ) and medial compartment TFJ kinetics during running. Nineteen participants ran with a rear foot strike pattern at their preferred speed using a short (-10%), preferred, and long (+10%) step length. These step length conditions were then repeated using a forefoot strike pattern. Regardless of foot strike pattern, a 10% shorter step length resulted in decreased peak contact force, force impulse per step, force impulse per kilometre, and average loading rate at the TFJ and medial compartment, while a 10% increased step length had the opposite effects (all P < 0.05). A forefoot strike pattern significantly lowered TFJ and medial compartment TFJ average loading rates compared with a rear foot strike pattern (both <0.05) but did not change TFJ or medial compartment peak force, force impulse per step, or force impulse per km. The combination of a shorter step length and forefoot strike pattern produced the greatest reduction in peak medial compartment contact force (P < 0.05). Knowledge of these running modification effects may be relevant to the management or prevention of TFJ injury or pathology among runners.