Neural Constraints Affect the Ability to Generate Hip Abduction Torques When Combined With Hip Extension or Ankle Plantarflexion in Chronic Hemiparetic Stroke

Abstract

Stroke lesions interrupt descending corticofugal fibers that provide the volitional control of the upper and lower extremities. Despite the evident manifestation of movement impairments post-stroke during standing and gait, neural constraints in the ability to generate joint torque combinations in the lower extremities are not yet well determined. Twelve chronic hemiparetic participants and 8 age-matched control individuals participated in the present study. In an isometric setup, participants were instructed to combine submaximal hip extension or ankle plantarflexion torques with maximal hip abduction torques. Statistical analyses were run using linear mixed effects models. Results for the protocol combining hip extension and abduction indicate that participants post-stroke have severe limitations in the amount of hip abduction torque they can generate, dependent upon hip extension torque magnitude. These effects are manifested in the paretic extremity by the appearance of hip adduction torques instead of hip abduction at higher levels of hip extension. In the non-paretic extremity, significant reductions of hip abduction were also observed. In contrast, healthy control individuals were capable of combining varied levels of hip extension with maximal hip abduction. When combining ankle plantarflexion and hip abduction, only the paretic extremity showed reductions in the ability to generate hip abduction torques at increased levels of ankle plantarflexion. Our results provide insight into the neural mechanisms controlling the lower extremity post-stroke, supporting previously hypothesized increased reliance on postural brainstem motor pathways. These pathways have a greater dominance in the control of proximal joints (hip) compared to distal joints (ankle) and lead to synergistic activation of musculature due to their diffuse, bilateral connections at multiple spinal cord levels. We measured, for the first time, bilateral constraints in hip extension/abduction coupling in hemiparetic stroke, again in agreement with the expected increased reliance on bilateral brainstem motor pathways. Understanding of these neural constraints in the post-stroke lower extremities is key in the development of more effective rehabilitation interventions that target abnormal joint torque coupling patterns.

Biomechanical Control of Paretic Lower Limb During Imposed Weight Transfer in Individuals Post-Stroke

“…For able-bodied individuals, the hip loading/unloading mechanism and control of ankle joint motion are primary mechanisms for COP movement control (29). After stroke, de cits in hip (14,63,64) and ankle (65) frontal plane movement control have been observed. This is consistent with our ndings that hip abduction angular displacement and velocity were reduced and COP medial-lateral stabilization was delayed in participants with stroke.…”

Biomechanical Control of Paretic Lower Limb During Imposed Weight Transfer in Individuals Post-Stroke

“…the primary mechanisms for COP movement control (29). After stroke, de cits in hip (14,63,64) and ankle (65) frontal plane movement control have been observed. This is consistent with our ndings that hip abduction angular displacement and velocity were reduced and COP medial-lateral stabilization was delayed in participants with stroke.…”

A Method to Quantify Multi-Degree-of-Freedom Lower Limb Isometric Joint Torques in Children with Hemiplegia

“…The MultiLEIT, engineered by Sánchez, Stienen, and colleagues at Northwestern University, is a rigid structure comprised of two 6-DOF load cells which feed into a static mechanical model to simultaneously measure hip, knee, and ankle joint isometric torques across one leg [9]. Initially designed for adult stroke studies [4], [5], [9], the MultiLEIT has been further modified for use in the pediatric population ( Fig. 1).…”

“…Peripheral effects of this injury include motor deficits such as weakness and abnormal joint torque coupling patterns in the upper extremity [1]- [2]. It is hypothesized that lower extremity movement in this population may also be influenced by abnormal joint torque patterns, such as the coupling between hip extension and adduction reported following stroke in adulthood [3]- [5]. The hip is a critical joint for static and dynamic stability, but quantifying strength and motor coordination patterns are challenging using commercially available tools.…”

“…This paper will focus on the use of a multijoint lower extremity isometric torque (MultiLEIT) device [9] to quantify weakness and abnormal joint torque coupling patterns at the hip in children with hemiplegia. Indeed, prior studies have used this device to quantify extensor coupling patterns in the paretic lower limb of adults following hemiparetic stroke [4]- [5]. We will detail the modifications made to adapt the MultiLEIT for the pediatric population as well as describe changes to the lower limb mechanical model to account for the presence of atypical hip bony geometry reported in children with hemiplegia [10]- [13].…”