The effect of lower extremity selective voluntary motor control on interjoint coordination during gait in children with spastic diplegic cerebral palsy

Abstract

Damage to motor tracts in the periventricular white matter is a primary etiology in spastic diplegic cerebral palsy (CP). These tracts are responsible for the production of selective voluntary motor control (SVMC). Lower extremity motor control has been suggested as being an important predictor of improvement following interventions. While there are multiple impairments in spastic CP, the inability to perform purposeful voluntary movement is a critical factor in determining functional ability that merits investigation. The purpose of this study was to examine the relationship between SVMC ability and hip and knee coordination during the swing phase of gait in participants with spastic CP. Gait analysis and SVMC assessments were conducted for 15 participants with CP. Relative phase analysis was used to calculate the minimum relative phase (MRP) angle during swing; a measurement of interjoint coordination between the hip and the knee. SVMC ability was measured using the Selective Control Assessment of the Lower Extremity (SCALE) tool. Significant correlations were found between SCALE scores and both MRP values (p < 0.0001) and duration of out-of-phase movement (p < 0.005) during swing. These findings supported our hypothesis that SVMC ability is related to a patient's ability to move in an uncoupled pattern during the swing phase of gait (i.e., extending the knee while flexing the hip). An understanding of influence of SVMC on swing phase gait mechanics may help establish appropriate goals for interventions, in particular hamstring lengthenings.

Introduction

Damage to motor tracts in the periventricular white matter is a primary etiology in spastic diplegic cerebral palsy (CP) [1]. These tracts, including the corticospinal tracts, are responsible for the production of selective voluntary motor control (SVMC). On clinical examination, patients with impaired or absent SVMC may exhibit reduced speed of movement, mirror movements or abnormal reciprocal muscle activation [2]. In addition, they are often unable to move the hip, knee and ankle joints independently of one another relying on closely coupled flexion and extension patterns to varying degrees [3]. Historically, pathological coupled joint flexion or coupled joint extension movements observed for patients with upper motor neuron lesions have been described as flexor or extensor synergy patterns [4]. These patterns normally occur during kicking in the young infant but decoupling patterns emerge as more skilled and complex movements are developed [5], [6]. Children with CP who have reduced ability to develop the selective motor control necessary for skilled movements may develop movement strategies that retain primitive coupled patterns to various degrees. Preliminary evidence suggests that SVMC ability may be an important factor affecting functional movement tasks [7], [8] and may be predictive of improvement following interventions [9]. Despite these clinical findings, the role of SVMC has not been explored as a factor that can affect biomechanics during walking in children with CP.

Inadequate peak knee extension during the swing phase of gait is an identified problem in patients with CP [10], [11], [12]. This finding has been related to spastic hamstrings [10], [12], [13], static hamstring contractures [11], [13] and premature firing of the hamstrings [14]. Hamstring lengthenings are frequently performed to improve swing phase extension by increasing the muscle length and, thereby, decreasing the effect of spasticity. Although terminal knee extension may improve following lengthening, improvements are not consistent across participants, and peak knee extension does not typically approach normative values. Thometz et al. [15] analyzed gait in patients undergoing hamstring lengthenings and found that average knee position at initial contact improved from 49° to 30° of flexion, in contrast to a position between 0° and 10° flexion in individuals without disability [16]. Others have reported similar findings in knee position at initial contact following hamstring lengthenings [13], [17], [18]. Baumann et al. [13] reported that passive knee range of motion assessed using a goniometer improved to a much greater extent than that observed during swing, indicating that not all of the increased muscle length was utilized during walking.

Knee extension appears to improve to a greater extent during stance, as opposed to swing, following hamstring lengthenings [13], [18]. Variation in SVMC impairment may explain these findings. During stance, the hip and the knee normally extend (appropriate coupling), while during swing, the hip normally flexes while the knee extends (uncoupled movement). During terminal swing, co-activity of the hamstrings and quadriceps, concurrent with hip flexor recruitment, normally occurs. Thometz et al. [15] identified a subset of patients with hamstring activity but diminished or absent quadriceps activity during terminal swing. This abnormal recruitment pattern suggests inappropriate flexor coupling. Patients with poor SVMC may be unable to dissociate hip and knee recruitment resulting in reduced knee extension during terminal swing regardless of hamstring length.

While there are multiple impairments in spastic CP, the inability to perform purposeful voluntary movement is a critical factor in determining functional ability that merits investigation. We have developed a clinical tool entitled “Selective Control Assessment of the Lower Extremity” (SCALE), an objective tool to quantify lower extremity SVMC in patients with spastic CP. The content validity and preliminary inter-rater reliability have been examined, and publications are in progress [19]. The purpose of this study was to examine the relationship between SCALE scores and interjoint coordination of the hip and knee during the swing phase of gait in participants with spastic CP. We hypothesized that SVMC ability measured using this tool is related to a patient's ability to move in an uncoupled pattern during swing.