Dynamic motor tracking is sensitive to subacute mTBI.

Effective screening for mild traumatic brain injury (mTBI) is critical to accurate diagnosis, intervention, and improving outcomes. However, detecting mTBI using conventional clinical techniques is difficult, time intensive, and subject to observer bias. We examine the use of a simple visuomotor tracking task as a screening tool for mTBI. Thirty participants, 16 with clinically diagnosed mTBI (mean time since injury: 36.4 ± 20.9 days (95 % confidence interval); median = 20 days) were asked to squeeze a hand dynamometer and vary their grip force to match a visual, variable target force for 3 min. We found that controls outperformed individuals with mTBI; participants with mTBI moved with increased variability, as quantified by the standard deviation of the tracking error. We modeled participants' feedback response-how participants changed their grip force in response to errors in position and velocity-and used model parameters to classify mTBI with a sensitivity of 87 % and a specificity of 93 %, higher than several standard clinical scales. Our findings suggest that visuomotor tracking could be an effective supplement to conventional assessment tools to screen for mTBI and track mTBI symptoms during recovery.

Characterization of compensatory trunk movements during prosthetic upper limb reaching tasks.

OBJECTIVE: To characterize the compensatory movements of the trunk during functional reaching tasks performed by upper limb prosthesis users. DESIGN: Survey. SETTING: Clinical laboratory at a national rehabilitation hospital. PARTICIPANTS: Transhumeral and transradial prosthesis users (n=10) and uninjured control subjects (n=10). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Three-dimensional motion analysis data were collected during simulated reaching tasks, such as donning a cap, placing a nut, and sorting clothes. The metrics were range of motion of the trunk in the 3 anatomical directions and elbow and shoulder path distance. RESULTS: Prosthesis users had significantly larger truncal movements than controls during all 3 reaching tasks in all 3 directions (P≤.03). Shoulder path distance in persons with amputation was larger than in controls in all 3 tasks (P<.01). Elbow path distance in persons with amputation was larger than in controls in the nut and clothes tasks (P≤.02). The subgroup of transradial prosthesis users displayed these abnormal movements despite the presence of an intact elbow. CONCLUSIONS: The altered physiologic structure of the arm caused the individuals to develop a different motor control strategy than an intact arm. Functional limitations, such as the loss of distal degrees of freedom, required persons with amputation to use trunk displacement in place of arm/hand movement. These compensatory movements during reaching tasks may be a cause of prosthesis rejection and, in some cases, may be resolved with proper rehabilitative training. Analysis of compensatory trunk movements may also provide a useful endpoint for evaluating new prosthesis designs.

Feedforward control strategies of subjects with transradial amputation in planar reaching.

The rate of upper-limb amputations is increasing, and the rejection rate of prosthetic devices remains high. People with upper-limb amputation do not fully incorporate prosthetic devices into their activities of daily living. By understanding the reaching behaviors of prosthesis users, researchers can alter prosthetic devices and develop training protocols to improve the acceptance of prosthetic limbs. By observing the reaching characteristics of the nondisabled arms of people with amputation, we can begin to understand how the brain alters its motor commands after amputation. We asked subjects to perform rapid reaching movements to two targets with and without visual feedback. Subjects performed the tasks with both their prosthetic and nondisabled arms. We calculated endpoint error, trajectory error, and variability and compared them with those of nondisabled control subjects. We found no significant abnormalities in the prosthetic limb. However, we found an abnormal leftward trajectory error (in right arms) in the nondisabled arm of prosthetic users in the vision condition. In the no-vision condition, the nondisabled arm displayed abnormal leftward endpoint errors and abnormally higher endpoint variability. In the vision condition, peak velocity was lower and movement duration was longer in both arms of subjects with amputation. These abnormalities may reflect the cortical reorganization associated with limb loss.