Quantification of functional weakness and abnormal synergy patterns in the lower limb of individuals with chronic stroke

Abstract

BackgroundThe presence of abnormal muscle activation patterns is a well documented factor limiting the motor rehabilitation of patients following stroke. These abnormal muscle activation patterns, or synergies, have previously been quantified in the upper limbs. Presented here are the lower limb joint torque patterns measured in a standing position of sixteen chronic hemiparetic stroke subjects and sixteen age matched controls used to examine differences in strength and coordination between the two groups.MethodsWith the trunk stabilized, stroke subjects stood on their unaffected leg while their affected foot was attached to a 6-degree of freedom load cell (JR3, Woodland CA) which recorded forces and torques. The subjects were asked to generate a maximum torque about a given joint (hip abduction/adduction; hip, knee, and ankle flexion/extension) and provided feedback of the torque they generated for that primary joint axis. In parallel, EMG data from eight muscle groups were recorded, and secondary torques generated about the adjacent joints were calculated. Differences in mean primary torque, secondary torque, and EMG data were compared using a single factor ANOVA.ResultsThe stroke group was significantly weaker in six of the eight directions tested. Analysis of the secondary torques showed that the control and stroke subjects used similar strategies to generate maximum torques during seven of the eight joint movements tested. The only time a different strategy was used was during maximal hip abduction exertions where stroke subjects tended to flex instead of extend their hip, which was consistent with the classically defined "flexion synergy." The EMG data of the stroke group was different than the control group in that there was a strong presence of co-contraction of antagonistic muscle groups, especially during ankle flexion and ankle and knee extension.ConclusionThe results of this study indicate that in a standing position stroke subjects are significantly weaker in their affected leg when compared to age-matched controls, yet showed little evidence of the classic lower-limb abnormal synergy patterns previously reported. The findings here suggest that the primary contributor to isometric lower limb motor deficits in chronic stroke subjects is weakness.

Foot placement control and gait instability among people with stroke

“…Unlike in control participants and the low fall risk group, swing limb GM activity was not significantly associated with FP location. The reduced ability of GM activity to cause more lateral FP may be due to the decreased hip abduction strength of many patients with stroke [43] or an inability to appropriately produce independent GM contractions and isolated frontal plane hip torques [43–45]. Within the higher fall risk group, the initial mechanical state of the paretic swing limb also had an altered relationship with its eventual FP location.…”

Evaluation of Abnormal Synergy Patterns Poststroke: Relationship of the Fugl-Meyer Assessment to Hemiparetic Locomotion

“…Alternatively, those with more severe hemiparesis may not be able to activate the BF, SM, and GM during the tasks, but there is no evidence of mass extension and flexor patterns as the theory behind the FM-LE would assert. In analyses of voluntary single-plane motions while in a functionally significant standing position, Neckel et al 33 demonstrated that while individuals poststroke produce reduced torque in 6 of the 8 motions in the paretic leg, they used similar strategies to controls in 7 of the motions. The only evidence of an abnormal synergy pattern producing the desired movement emerged with maximal hip abduction when hip flexor torque was also recorded in the stereotyped “flexor synergy” activity.…”

“…The only evidence of an abnormal synergy pattern producing the desired movement emerged with maximal hip abduction when hip flexor torque was also recorded in the stereotyped “flexor synergy” activity. 33 …”

A Multiple Degree of Freedom Lower Extremity Isometric Device to Simultaneously Quantify Hip, Knee, and Ankle Torques

“…Additionally, studies of isometric lower extremity joint-torque coupling in cerebral palsy quantified stereotypical spontaneous coupling between hip and knee extension 20 . However, findings with regards to the expression of abnormal joint coupling patterns on individuals post-stroke have not been conclusive and have not obtained consistent results; some studies demonstrated spontaneous coupling of hip adduction with hip and knee extension torques 17, 20, 21 , coincident with what is described clinically as an “extension synergy” (coupling of hip extension/adduction with knee extension and ankle plantar-flexion 30 ); in contrast, other studies found weakness in specific DOFs but no stereotypical joint torque coupling patterns across subjects 18, 19 .…”

“…Specifically, studies were performed in recumbent seating 20 or standing 17–19 affecting vestibular and cutaneous input as concluded by Thelen and colleagues 20 . Also, the amount of body weight support provided differed between studies from zero 1, 18, 19 to 100% 17 changing the gravitational contribution to joint torques. Additionally, results could be affected by poorly constrained systems that do not limit movement during maximum torque generation 15, 18, 19 .…”