Impaired proactive and reactive grip force control in chronic hemiparetic patients

Dynamic bimanual force control in chronic stroke: contribution of non-paretic and paretic hands

Dynamic force modulation is critical for performing skilled bimanual tasks. Unilateral motor impairments after stroke contribute to asymmetric hand function. Here, we investigate the impact of stroke on dynamic bimanual force control and compare the contribution of each hand to a bimanual task. Thirteen chronic stroke and thirteen healthy control participants performed bimanual, isometric finger flexion during visually guided, force tracking of a trapezoidal trajectory with force increment and decrement phases. We quantified the accuracy and variability of total force from both hands. Individual hand contribution was quantified with the proportion of force contributed to total force and force variability of each hand. The total force output was 53.10% less accurate and 56% more variable in the stroke compared with the control group. The variability of total force was 91.10% greater in force decrement than increment phase. In stroke group, the proportion of force and force variability contributed by each hand differed across the two phases. During force decrement, the proportion of force contributed by the non-paretic hand reduced and force variability of the non-paretic hand increased, compared with the increment phase. The control group showed no differences in each hand's contribution across the two force phases. In conclusion, dynamic bimanual force modulation is impaired after stroke, with greater deficits in force decrement than force increment. The non-paretic and paretic hands adapt differentially to dynamic bimanual task constraints. During force decrement, the non-paretic hand preferentially assumes force modulation, while the paretic hand produces steady force to meet the force requirements.

Referent control of anticipatory grip force during reaching in stroke: an experimental and modeling study

To evaluate normal and impaired control of anticipatory grip force (GF) modulation, we compared GF production during horizontal arm movements in healthy and post-stroke subjects, and, based on a physiologically feasible dynamic model, determined referent control variables underlying the GF-arm motion coordination in each group. 63% of 13 healthy and 48% of 13 stroke subjects produced low sustained initial force (< 10 N) and increased GF prior to arm movement. Movement-related GF increases were higher during fast compared to self-paced arm extension movements only in the healthy group. Differences in the patterns of anticipatory GF increases before the arm movement onset between groups occurred during fast extension arm movement only. In the stroke group, longer delays between the onset of GF change and elbow motion were related to clinical upper limb deficits. Simulations showed that GFs could emerge from the difference between the actual and the referent hand aperture (R_a) specified by the CNS. Similarly, arm movement could result from changes in the referent elbow position (R_e) and could be affected by the co-activation (C) command. A subgroup of stroke subjects, who increased GF before arm movement, could specify different patterns of the referent variables while reproducing the healthy typical pattern of GF-arm coordination. Stroke subjects, who increased GF after arm movement onset, also used different referent strategies than controls. Thus, altered anticipatory GF behavior in stroke subjects may be explained by deficits in referent control.

Increased center of pressure trajectory of the finger during precision grip task in stroke patients

The aim of this study was to assess the spatial stability of stroke patients while holding a freely movable object. Twenty-two acute stroke patients with mild hand impairment performed a grip and lift task using the thumb and index finger. The displacement of the center of pressure (COP) trajectory, the grip force (GF) and several clinical parameters were monitored. Although the GF was not different between paretic and nonparetic hands, the COP trajectory of the paretic index finger was increased. Moreover, the COP trajectories of the thumb and index finger in hemorrhagic patients were longer than those in ischemic patients. These discrepancies between kinetic parameters suggest that different aspects of grip force control may be considered in patients with mild stroke.

Recovery of Grasp versus Reach in People with Hemiparesis Poststroke

Background and Objective. The authors recently found that grasping was not relatively more disrupted than reaching in people with acute hemiparesis. They now extend this work to the recovery of reach versus grasp.

Methods. Hemiparetic subjects were tested acutely, after 90 days, and then after 1 year poststroke, and a control group was evaluated once. Using kinematic techniques, subjects were studied performing reach and reach-to-grasp movements. The authors quantified 3 characteristics of performance for each movement: speed, accuracy, and efficiency, where an efficient movement was defined as a movement directly to the target without extraneous or abnormally circuitous movements. To evaluate the relative deficits and recovery in reach versus grasp, performance measures were converted to z scores using control group means and standard deviations.

Results. The authors’ results showed that, starting with small deficits in speed acutely, both reach speed and grasp speed improved over time. Deficits in accuracy were greater in the reach than the grasp acutely, and these deficits lessened such that by the 90-day time point, the relative accuracy of the 2 movements was the same. In contrast, deficits in efficiency were greater in the grasp than the reach acutely, and grasp efficiency did not recover. The majority of recovery in reaching and grasping occurred by the 90-day time point, with little change occurring between the 90-day and 1-year time points.

Conclusions. The authors hypothesize that, in chronic hemiparesis, purposeful movements requiring distal control may be more impaired than purposeful movements requiring proximal control, not because of the initial lesion, but because, over the course of recovery, spared components of the descending motor systems may be able to compensate for the accuracy deficits in reaching (proximal control) but not the efficiency deficits in grasping (distal muscular control).

Should we think about wrist extensor after flexor tendon repair?

OBJECTIVE

To evaluate the activity of wrist extensor muscle, correlating with wrist motion during gripping after flexor tendon repair.

DESIGN

Cross-sectional clinical measurement study.

SETTING

Laboratory for biomechanics and rehabilitation.

SUBJECTS

A total of 11 patients submitted to rehabilitation by early passive motion of the fingers with wrist flexion position were evaluated after 8 weeks of fingers flexor tendon repair and 11 healthy volunteers, all ranging from 20 to 37 years of age.

INTERVENTION

Volunteers performed an isometric standardized gripping task.

MAIN MEASURES

We used electrogoniometry to analyze wrist range of motion and surface electromyography, considering 100% maximum voluntary contraction to represent the amplitude of electromyographic activity of the extensor carpi radialis and flexor digitorum superficialis.

RESULTS

Patients with flexor tendon repair showed co-activation deficit between wrist extensor (extensor carpi radialis) and flexor finger muscles (flexor digitorum superficialis) during gripping in the intermediate phase of rehabilitation, despite some recovering mobility for wrist extension (p ≤ 0.05). A moderate correlation between range of motion and extensor carpi radialis was present only for injured group (r = 0.32). Total active motion score, which represents finger active excursion, was regular or poor in 65% of cases, all with nerve repair associated.

CONCLUSION

Wrist extensors have an important synergist role at handgrip, although some imbalance can be present after flexor tendon repair. These preliminary findings suggest that emphasis could be directed to add synergistic wrist motion in rehabilitation protocols after flexor tendon repair. Future studies with early active rehabilitation are necessary.

Reorganization of multi-muscle and joint withdrawal reflex during arm movements in post-stroke hemiparetic patients

OBJECTIVES

To investigate the behavior of the nociceptive withdrawal reflex (NWR) in the upper limb during reaching and grasping movements in post-stroke hemiparetic patients.

METHODS

Eight patients with chronic stroke and moderate motor deficits were included. An optoelectronic motion analysis system integrated with a surface EMG machine was used to record the kinematic and EMG data. The NWR was evoked through a painful electrical stimulation of the index finger during a movement which consisted of reaching out, picking up a cylinder, and returning it to the starting position.

RESULTS

We found that: (i) the NWR is extensively rearranged in hemiparetic patients, who were found to present different kinematic and EMG reflex patterns with respect to controls; (ii) patients partially lose the ability to modulate the reflex in the different movement phases; (iii) the impairment of the reflex modulation occurs at single-muscle, single-joint and multi-joint level.

CONCLUSIONS

Patients with chronic and mild-moderate post-stroke motor deficits lose the ability to modulate the NWR dynamically according to the movement variables at individual as well as at multi-muscle and joint levels.

SIGNIFICANCE

The central nervous system is unable to use the NWR substrate dynamically and flexibly in order to select the muscle synergies needed to govern the spatio-temporal interaction among joints.

Dexterity is impaired at both hands following unilateral subcortical middle cerebral artery stroke

Dexterity was investigated in right-handed subjects in the subacute phase of a first unilateral subcortical middle cerebral artery stroke affecting the left or right hemisphere and right-handed healthy subjects. Dexterity was quantified at both hands by kinematic recordings of finger and hand tapping, a reach-to-grasp movement, quantitative analysis of grip forces in a grasp-lift task and clinical rating scales. Stroke subjects exhibited significant deficits in timing and coordination of tapping movements at both the contralesional and ipsilesional hands, irrespective of the hemisphere affected. Likely for the reach-to-grasp and grasp-lift movements a bilateral impairment was found in stroke subjects. In particular, slowing of hand transport towards the object, deficient timing and scaling of grasp formation, discoordination between grip and lift forces and inefficient scaling of grip forces were observed. The severity of impairment was independent of the hemisphere affected and evident for both the reach (involving more proximal muscles of the arm) and grasp (involving more distal muscles of the arm and hand) components of the task. Strong correlations were found between clinical scores of hand function and loss of sensibility with the deficits in timing, coordination and efficiency of movement of the contralesional and ipsilesional hand. These data provide evidence that dexterity is impaired at both hands after subcortical middle cerebral artery stroke.

Action-perception dissociation; preserved reactive grip force despite tactile extinction due to cortical stroke

Sensory extinction following stroke, manifests as a bias in spatial attention towards ipsilesional spatial locations, which arises when stimuli from other locations compete for pathologically limited attentional resources. In the tactile domain, extinction results in a failure to verbally report tactile stimuli applied to a contralesional body part when they are timed to coincide with ipsilesional tactile contact. While it is typical for research in this area to focus on the verbal report of sensory stimuli as a measure of conscious awareness, work in visual extinction has shown that when contralesional stimuli fail to reach conscious awareness, they may still contribute to the control of actions. We describe the case of a woman with tactile extinction who failed to verbally report contralesional tactile input associated with perturbations to bimanual grasp. Despite this, the same stimulus was sufficient to drive reflexive grip force responses.

The nature of hand motor impairment after stroke and its treatment

Hand motor impairments may be viewed as 1) a deficit in motor execution, resulting from weakness, spasticity, and abnormal muscle synergies, and/or 2) a deficit in higher-order processes, such as motor planning and motor learning, which lead to poorly formed sensorimotor associations that lead to impaired motor control. Although weakness and spasticity impede motor execution, strengthening and tone reduction represent simplistic solutions to the deficit in motor control after stroke. Deficits in hand motor control are better appreciated by examining the coordination of fingertip forces and movements during natural movements, and suggest that impairments in motor learning and planning are fundamental impediments to motor recovery following stroke. However, despite an explosion in the number of therapeutic protocols based on the principles of motor learning, little is known about the types of motor learning impairment that occur after stroke and how lesion location may influence motor relearning.

Impaired Discrimination of Surface Friction Contributes to Pinch Grip Deficit After Stroke

Background. Impaired sensation and force production could both contribute to handgrip limitation after stroke. Clinically, training is usually directed to motor impairment rather than sensory impairment despite the prevalence of sensory deficit and the importance of sensory input for grip control. Objective. The aim of this study was to investigate if sensory deficits contribute to pinch grip dysfunction beyond that attributable to motor deficits poststroke. Methods. The study enlisted 45 stroke participants and 45 healthy controls matched for age, gender, and hand dominance. Ability to differentiate surface friction (Friction Discrimination Test [FDT]), match object weight (Weight Matching Test [WMT]), produce grip force to track a visual target (Visually Guided Pinch Test [VGPT]), and perform a Pinch-Grip Lift-and-Hold Test (PGLHT) was quantified relative to normative performance, as defined by matched controls. The relationship between sensory ability (FDT, WMT) and altered PGLHT performance adjusted for motor ability (VGPT) after stroke was then examined using multivariate regression. Results. Deficits in FDT, WMT, and VGPT ability were present in at least half of the stroke sample and were largely independent across the variables. Poorer friction discrimination was significantly associated with longer latencies of grip-lift ( r = .34; P = .03) and grip force dysregulation ( r= .34; P= .03) after the impact of VGPT was statistically removed from PGLHT ability. However, performance on WMT did not relate to either PGLHT deficit. Conclusion. The findings indicate that impaired friction discrimination ability contributes to altered timing and force adjustment during PGLHT poststroke.

Grip force regulation during pinch grip lifts under somatosensory guidance: comparison between people with stroke and healthy controls

OBJECTIVES

To compare the timing and grip force application in a pinch grip task performed under somatosensory guidance in stroke and matched controls and to identify characteristics of impaired grip force regulation after stroke.

DESIGN

Matched-pairs control group.

SETTING

University research laboratory.

PARTICIPANTS

Forty-five people with stroke who could pick up a pen lid using a pinch grip and actively participated in rehabilitation and 45 adults without neurologic conditions or musculoskeletal or skin impairments affecting the hand, matched for age, sex, and hand dominance.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Timing and magnitude of grip forces applied during pinch grip lift and hold.

RESULTS

Prolonged time to grip and lift objects, and excessive grip force prior to commencing the lift occurred in approximately half of the contralesional (involved) hands of people with stroke. Fluctuating irregular forces and reduced adaptation of the grip safety margin were also observed. Excessive safety margins were not predominant after stroke. Extreme slowing and disorganized sequencing of the grip and lifting forces and difficulty maintaining a stable grip characterized severe dysfunction.

CONCLUSIONS

Delayed grip formulation and variable grip force application are key characteristics of grip dysfunction after stroke.

Impaired anticipatory control of fingertip forces in patients with a pure motor or sensorimotor lacunar syndrome

We examined planning and execution of precision grasp in eight right-handed patients with a right pure motor or sensorimotor lacunar syndrome after a subcortical stroke and eight age-matched controls as they grasped and lifted an instrumented object whose weight could be varied without altering its visual appearance. Grip (normal) and load (tangential) forces at the fingertip-object interface were measured and the grip force rate (GFR) and load force rate (LFR) were derived. Planning of precision grasp was assessed by measurement of anticipatory scaling of peak GFR and peak LFR to object weight. Execution of precision grasp was assessed by measurement of both the timing and efficiency of grip-load force coordination: the pre-load phase duration (PLD) and the load phase duration (LPD) measured timing, whereas the grip force at load force onset (GFO) and the grip force at lift-off (GFL) measured efficiency. Subjects lifted a light and heavy object five times first with the RIGHT hand, then with the LEFT hand, and then once more with the RIGHT AFTER LEFT hand. Patients with stroke did not scale the peak LFR or peak GFR to object weight with the RIGHT hand even with repeated attempts; however, they scaled the peak LFR to object weight on the first lift with the RIGHT AFTER LEFT hand (P = 0.01). Patients also prolonged the PLD and LPD and produced excessive GFO and GFL for RIGHT hand lifts, but decreased the GFL for the heavy object (P = 0.016) with the RIGHT AFTER LEFT hand. Correlation of precision grasp variables from lifts with the RIGHT hand with clinical measures showed that anticipatory scaling of peak LFR and peak GFR did not correlate with clinical measures of hand function, whereas the PLD did (r = 0.88, P = 0.004). The results suggest that patients with right hemiparesis from a subcortical lesion of the corticospinal tract have a higher-order motor planning deficit. This planning deficit is dissociable from deficits in motor execution, is not captured by routine clinical assessment, and is correctable by transfer of information from the unaffected hemisphere. A rehabilitation strategy that involves practice with the left hand prior to practice with the right hand may improve planning of grasping behaviour in patients with right hemiparesis.

Deficits in grasp versus reach during acute hemiparesis

We studied how acute hemiparesis affects the ability to perform purposeful movements of proximal versus distal upper extremity segments. Given the gradient of corticospinal input to the spinal motoneuron pools, we postulated that movement performance requiring distal segment control (grasping) should be more impaired than movement performance requiring proximal segment control (reaching) in people with hemiparesis. We tested subjects with acute hemiparesis and control subjects performing reach and reach-to-grasp movements. Three characteristics of movement performance were quantified for each movement: speed, accuracy, and efficiency. For the reach, we calculated peak wrist velocity, endpoint error, and reach path ratio. For the grasp, we calculated peak aperture rate, aperture at touch, and aperture path ratio. To evaluate the relative deficits in reaching versus grasping, performance measures were converted to z-scores using control group means and standard deviations. For both the movements, movement times were longer and performance was more variable in the hemiparetic group compared to the control group. Hemiparetic z-scores indicated that relative deficits in movement speed were small in the two movements, with deficits in grasp being slightly greater than deficits in reach. Relative deficits in accuracy showed a trend for being larger in the reach compared to the grasp, but this difference did not reach statistical significance. In contrast, relative deficits in efficiency were larger in the grasp compared to the reach, with reaching efficiency near the range of normal performance. When considering data across all three movement characteristics, the ability to perform a purposeful movement with the distal segments was not clearly more disrupted than the ability to perform a purposeful movement with the proximal segments in people with acute hemiparesis.

Support-specific modulation of grip force in individuals with hemiparesis

OBJECTIVE

To investigate whether use of auxiliary sensory input will result in modulated grip force.

DESIGN

Case-control study.

SETTING

Free-standing acute inpatient rehabilitation hospital.

PARTICIPANTS

Six people with unilateral hemiparesis due to unilateral stroke and 6 control subjects without neurologic disorders.

INTERVENTIONS

Seated subjects lifted and transported the same object under 3 different conditions: with no support, with the target arm positioned on a freely moving skateboard, and with a finger from the subject's contralateral hand lightly touching the wrist of the target arm.

MAIN OUTCOME MEASURES

Peak grip force and temporal coupling between the grip force and lift-off of the object.

RESULTS

All subjects were able to better regulate grip force when provided with additional sensory input. Light finger touch resulted in decreased grip force, as did skateboard use ( P <.05). Subjects with hemiparesis showed 2 times longer latency between grip-force application and lift-off of the object ( P <.05).

CONCLUSIONS

Statistically significant grip-force reduction was noted with both support aids. These findings could have implications in clinical and rehabilitative areas.

Evaluation of upper-limb spasticity after stroke: A clinical and neurophysiologic study

OBJECTIVES

To assess upper-limb spasticity after stroke by means of clinical and instrumental tools and to identify possible variables influencing the clinical pattern.

DESIGN

Descriptive measurement study of a consecutive sample of patients with upper-limb spasticity after stroke.

SETTING

Neurorehabilitation hospital.

PARTICIPANTS

Sixty-five poststroke hemiplegic patients.

INTERVENTIONS

Not applicable. Main outcome measures Upper-limb spasticity, as assessed clinically (Modified Ashworth Scale [MAS], articular goniometry) and neurophysiologically (maximum H-reflex [Hmax], maximum M response [Mmax], Hmax/Mmax ratio).

RESULTS

Poorer MAS scores were associated with lower passive range of motion (PROM) values at the wrist ( P =.01) and elbow ( P =.002). The flexor carpi radialis Hmax/Mmax ratio correlated directly with MAS scores at the wrist ( P =.005) and correlated inversely with PROM. The presence of pain in the fingers, wrist, and elbow was significantly associated only with lower PROM values at the wrist.

CONCLUSIONS

Upper-limb spasticity is involved in the development of articular PROM limitation after a stroke. Pain appears to be related to PROM reduction as well, but the exact causal relationship between these 2 factors is still unclear. The MAS and the Hmax/Mmax ratio correlated when evaluating poststroke spasticity; they characterize 2 different aspects of spasticity, clinical and neurophysiologic, respectively, and they could be used as an integrated approach to study and follow poststroke patients.

Effect of human grip strategy on force control in precision tasks

Alternate grip strategies are often used for object manipulation in individuals with sensorimotor deficits. To determine the effect of grip type on force control, ten healthy adult subjects were asked to grip and lift a small manipulandum using a traditional precision grip (lateral pinch), a pinch grip with the fingers oriented downwards (downward pinch) and a "key grip" between the thumb and the side of the index finger. The sequence of grip type and hand used was varied randomly after every ten lifts. Each of the three grips resulted in different levels of force, with the key grip strategy resulting in the greatest grip force and the downward pinch grip using the least amount of grip force to lift the device. Cross-correlation analysis revealed that the ability to scale accurately the rate of grip force and load force changes was lowest in the downward pinch grip. This was also associated with a more variable time-shift between the two forces, indicating that the precise anticipatory control when lifting an object is diminished in this grip strategy. There was a difference between hands across all grips, with the left non-dominant hand using greater grip force during the lift but not the hold phase. Further, in contrast with the right hand, the left hand did not reduce grip force during the lift or the hold phase over the ten lifts, suggesting that the non-dominant hand did not quickly learn to optimise grip force. These findings suggest that the alternate grip strategies used by patients with limited fine motor control, such as following stroke, may partly explain the disruption of force control during object manipulation.

Grip force control during object manipulation in cerebral stroke

OBJECTIVE

To analyze impairments of manipulative grip force control in patients with chronic cerebral stroke and relate deficits to more elementary aspects of force and grip control.

METHODS

Nineteen chronic stroke patients with fine motor deficits after unilateral cerebral lesions were examined when performing 3 manipulative tasks consisting of stationary holding, transport, and vertical cyclic movements of an instrumented object. Technical sensors measured the grip force used to stabilize the object in the hand and the object accelerations, from which the dynamic loads were calculated.

RESULTS

Many patients produced exaggerated grip forces with their affected hand in all types of manipulations. The amount of finger displacement in a grip perturbation task emerged as a highly sensitive measure for predicting the force increases. Measures of grip strength and maximum speed of force changes could not account for the impairments with comparable accuracy. In addition to force economy, the precision of the coupling between grip and load forces was impaired. However, no temporal delays were typically observed between the grip and load force profiles during cyclic movements.

CONCLUSIONS

Impaired sensibility and sensorimotor processing, evident by delayed reactions in the perturbation task, lead to an excessive increase of the safety margin between the actual grip force and the minimum force necessary to prevent object slipping. In addition to grip force scaling, cortical sensorimotor areas are responsible for smoothly and precisely adjusting grip forces to loads according to predictions about movement-induced loads and sensory experiences. However, the basic feedforward mechanism of grip force control by internal models appears to be preserved, and thus may not be a cortical but rather a subcortical or cerebellar function, as has been suggested previously.

Toward a physiological understanding of human dexterity

Dexterity, defined as the skillful manipulation of the hands, is now amenable to physiological investigation. Two topics are discussed here: grasping (i.e., hand-object coupling) and bimanual coordination. Dexterity depends on powerful, distributed neural networks and is particularly vulnerable to brain lesions. A knowledge of physiological mechanisms is needed to deal with these neurological problems.

Neurological problems affecting hand dexterity

The first objective of this review is to summarize how grip force and load force (holding and transporting forces) are coordinated. Usually, the two forces vary in parallel, thereby resulting in a constant force ratio. Departures from this rule have been observed, however, depending on dynamic task constraints. The second objective is to summarize some of the pathophysiology of grasping in movement disorders. By means of a drawer-pulling task, regulation of grip force was analyzed when pulling was perturbed either by self-induced or externally applied load disturbances. Normal subjects automatically increased grip force in anticipation to the expected load. In the same situation, hemiparetic patients failed to generate proactive grip force and frequent slips were observed. Cerebellar patients were shown to adopt a 'default' strategy in producing high grip force output when the drawer had to be pulled up to its mechanical stop. This differed from the more flexible normal mode of raising grip force in accord with the pulling speed. In patients with Huntington's Chorea, grip/load force coordination differed from that of normal subjects, as expressed in an overscaled grip force. This might be a secondary, less flexible 'default' strategy to overcome the failure in adapting grip force to upcoming disturbances. Writer's cramp patients overscaled grip force in both the dominant and non-dominant hand, and grip force further increased when hand muscles were vibrated, suggesting an abnormal sensorimotor integration. The results illustrate the degrading consequences of cortical and subcortical pathology on manual dexterity, which is sometimes partly compensated for by new, less flexible default strategies.