Susan V. Duff

Fingertip forces during object manipulation in children with hemiplegic cerebral palsy. I: anticipatory scaling.

Previous studies of grasping and object manipulation in children with cerebral palsy (CP) have suggested a dichotomy in the ability to use anticipatory control (planning) of the fingertip force output, depending on the type of sensory information (tactile or proprioceptive) on which it is based. The present study further explores this issue by testing the ability of 15 children with hemiplegic CP aged between 8 and 14 years to scale the fingertip force output in advance during the lifting of small objects whose weight and surface texture are varied. The results indicate that children with hemiplegia can use anticipatory control based on both the weight and texture of the object, but require a greater number of trials than age‐matched children without CP (control children) before they can do so. We suggest that the initial lack of anticipatory control results from an indistinct internal representation of the objects physical properties due to disturbed sensory mechanisms, which may have direct implications for therapeutic intervention.

Relation between clinical measures and fine manipulative control in children with hemiplegic cerebral palsy

The present investigation examines the relation between various clinical measures and the performance of a functional precision grip‐lift task. Fifteen children with hemiplegic cerebral palsy (CP), aged 8 to 14 years, and 15 age‐matched control children grasped and lifted an object whose surface texture was varied while their fingertip forces were recorded. The force coordination was compared with tactile sensibility, grip strength, manual dexterity, and spasticity using correlational and regression analyses. The findings highlight the importance of tactile sensibility in this task. However, the manner in which sensibility was related varied for the sensory adaptation of fingertip forces, the anticipatory scaling of the force increase, and the smooth transitions between the temporal phases comprising the grip‐lift task. The findings also indicate that spasticity affects some measures of the task, but not others, suggesting that the relation between spasticity and motor performance may not be absolute. The results further suggest that the impairments in grasping in children with hemiplegic CP are largely but not exclusively due to disturbed sensory mechanisms which may have direct implications for therapeutic intervention.

Fingertip forces during object manipulation in children with hemiplegic cerebral palsy. II: Bilateral coordination

The present study examines the coordination of fingertip forces during object manipulation in both the involved and non‐involved hand of 14 children with hemiplegic cerebral palsy (CP) aged between 8 and 14 years. While no impairment could be observed in the non‐involved hand, subtle deficits in the sequencing of the grip–lift movement were observed in all children tested in this hand. However, they were able to scale the fingertip force output of the non‐involved hand in advance (use anticipatory control) based on the objects weight. In the second experiment in this paper, we tested whether the anticipatory control can be generalized across hands. The results indicate that sensory information from the non‐involved hand can be used for anticipatory scaling of isometric force increase during subsequent lifts with the contralateral involved hand. These findings suggest that the initial lack of anticipatory control usually observed in the involved hand of children with hemiplegic CP is likely to be based on disturbed sensory input.

The Graded Redefined Assessment of Strength Sensibility and Prehension: reliability and validity.

With the advent of new interventions targeted at both acute and chronic spinal cord injury (SCI), it is critical that techniques and protocols are developed that reliably evaluate changes in upper limb impairment/function. The Graded Redefined Assessment of Strength Sensibility and Prehension (GRASSP) protocol, which includes five subtests, is a quantitative clinical upper limb impairment measure designed for use in acute and chronic cervical SCI. The objectives of this study were to: (1) establish the inter-rater and test-retest reliability, and (2) establish the construct and concurrent validity with the International Standards of Neurological Classification of Spinal Cord Injury (ISNCSCI), Spinal Cord Independence Measure II (SCIM), and the Capabilities of Upper Extremity Questionnaire (CUE). The study protocol included repeated administration of the GRASSP to a cross-section of individuals with tetraplegia who were neurologically stable (n=72). ISNCSCI, CUE, and SCIM assessments were also administered. Two assessors examined the individuals over a 7-day period. Reliability was tested with intra-class correlation coefficients; construct validity was established with agreement/discordance analysis between the GRASSP and ISNCSCI sensory and motor items; and concurrent validity was tested with Spearman correlation coefficients. Inter-rater and test-retest reliability for all subtests within the GRASSP were above the hypothesized value of 0.80 (0.84-0.96 and 0.86-0.98, respectively). The GRASSP is about 50% more sensitive (construct validity) than the ISNCSCI when defining sensory and motor integrity of the upper limb; the subtests showed concurrence with the SCIM, SCIM self-care subscale, and CUE. The strongest concurrence to impairment was with self-perception of function (CUE) (0.57-0.83, p<0.0001). The GRASSP was found to demonstrate reliability, construct validity, and concurrent validity for use as a standardized upper limb impairment measure for individuals with tetraplegia.

Applying principles of motor learning and control to upper extremity rehabilitation

The purpose of this article is to provide a brief review of the principles of motor control and learning. Different models of motor control from historical to contemporary are presented with emphasis on the Systems model. Concepts of motor learning including skill acquisition, measurement of learning, and methods to promote skill acquisition by examining the many facets of practice scheduling and use of feedback are provided. A fictional client case is introduced and threaded throughout the article to facilitate understanding of these concepts and how they can be applied to clinical practice.

Does motor lateralization have implications for stroke rehabilitation

Recent findings on motor lateralization have revealed consistent differences in the control strategies of the dominant and nondominant hemisphere/limb systems that could have implications for hemiplegic stroke patients. Studies in stroke patients have demonstrated deficiencies in the ipsilesional arm that reflect these distinctions; patients with right-hemisphere damage tend to show deficits in positional accuracy, and patients with left-hemisphere damage show deficits in trajectory control. Such deficits have been shown to impede functional performance; yet patients with severe dominant-side hemiplegia must often use the nondominant arm as the primary manipulator for activities of daily living. Nevertheless, the nondominant arm may not spontaneously become efficient as a dominant manipulator, as indicated by the persistence of deficits in chronic stroke patients. More research is necessary to determine whether motor therapy can facilitate a more effective transition of this arm from a nondominant to a dominant controller.

Object release under varying task constraints in children with hemiplegic cerebral palsy

Considerable attention has been given in recent years to fingertip force coordination during grasping and lifting small objects in children with cerebral palsy (CP). However, little is known about the childrens ability to replace and release an object from grasp. The present study examined the coordination of fingertip forces during replacement and release of an object from grasp under varying task constraints in the involved hand of 15 children (10 males, five females, age range 7 to 14 years) with hemiplegic CP and in the non‐dominant hand of 15 age‐matched, typically‐developing children (seven males, eight females). Participants released an object, instrumented with force transducers and held with a precision grip, onto a stable surface and onto an unstable surface (requiring higher accuracy) at self‐paced and fast‐as‐possible speeds. Temporal and force measures were recorded and the dependent measures were tested using analyses of variance. Results showed that force coordination was impaired in children with hemiplegia, resulting in prolonged and uncoordinated replacement and release of the object (p<0.05). Differences between controls and children with hemiplegia were greater when speed and accuracy constraints were imposed (i.e. task performance was affected by these constraints to a greater extent in the children with CP, p<0.05). Impairments in temporal coordination of object release were also observed in the non‐involved hand under all conditions (p<0.05). These results provide additional information about impaired hand function in children with hemiplegic CP. Clinical implications of these findings are discussed.

THE IMPACT OF LEFT HEMISPHERE STROKE ON FORCE CONTROL WITH FAMILIAR AND NOVEL OBJECTS: NEUROANATOMIC SUBSTRATES AND RELATIONSHIP TO APRAXIA

Fingertip force scaling for lifting objects frequently occurs in anticipation of finger contact. An ongoing question concerns the types of memories that are used to inform predictive control. Object-specific information such as weight may be stored and retrieved when previously encountered objects are lifted again. Alternatively, visual size and shape cues may provide estimates of object density each time objects are encountered. We reasoned that differences in performance with familiar versus novel objects would provide support for the former possibility. Anticipatory force production with both familiar and novel objects was assessed in six left hemisphere stroke patients, two of whom exhibited deficient actions with familiar objects (ideomotor apraxia; IMA), along with five control subjects. In contrast to healthy controls and stroke participants without IMA, participants with IMA displayed poor anticipatory scaling with familiar objects. However, like the other groups, IMA participants learned to differentiate fingertip forces with repeated lifts of both familiar and novel objects. Finally, there was a significant correlation between damage to the inferior parietal and superior and middle temporal lobes and impaired anticipatory control for familiar objects. These data support the hypotheses that anticipatory control during lifts of familiar objects in IMA patients are based on object-specific memories and that the ventro-dorsal stream is involved in the long-term storage of internal models used for anticipatory scaling during object manipulation.

Enhancing Prehension in Infants and Children: Fostering Neuromotor Strategies.

SUMMARY Learning to reach for and manipulate objects requires considerable neuromotor control and flexibility. Through environmental and object exploration individual neuromotor strategies expand, and prehensile skills improve, as infants and children overcome constraints. Infants and children with prehensile deficits often have difficulty exploring objects and the environment, thus, may not sufficiently develop the strategies needed to expand their prehensile skills. This article reviews neuromotor factors that influence prehension development, discusses limitations to prehensile function and provides guidelines that can be used to examine and enhance prehensile behaviors in infants and young children based on a task-oriented approach addressing impairments, motor strategies and function.

Innovative evaluation of dexterity in pediatrics.

STUDY DESIGN Review paper. INTRODUCTION Hand dexterity is multifaceted and essential to the performance of daily tasks. Timed performance and precision demands are the most common features of quantitative dexterity testing. Measurement concepts such as rate of completion, in-hand manipulation and dynamic force control of instabilities are being integrated into assessment tools for the pediatric population. PURPOSE To review measurement concepts inherent in pediatric dexterity testing and introduce concepts that are infrequently measured or novel as exemplified with two assessment tools. METHODS Measurement concepts included in common assessment tools are introduced first. We then describe seldom measured and novel concepts embedded in two instruments; the Functional Dexterity Test (FDT) and the Strength-Dexterity (SD) Test. DISCUSSION The inclusion of novel yet informative tools and measurement concepts in our assessments could aid our understanding of atypical dexterity, and potentially contribute to the design of targeted therapy programs.