Biomedical subjects

Mark F Abel

Publications and source records attributed to Mark F Abel.

12 recordsLinked to original sources

PubMed2006

Center of mass motion and the effects of ankle bracing on metabolic cost during submaximal walking trials.

The goal of this research was to examine the relationship between center of mass (CoM) motion and metabolic cost and to assess secondarily the effects of equinus gait on metabolic cost during walking trials at various velocities. Twelve (n=12) healthy male adults walked in four brace conditions, including fixed equinus, at three different walking speeds. Metabolic measures and 3D kinematic data were collected during each trial. Significant main effects for velocity were observed on both dependent measures, net O2 cost (p<0.001), and CoM vertical excursion (CoMz) (p<0.01). Correlation analysis showed significant positive correlations between net O2 cost and CoMz that were strongest at fast velocities. Further, analysis revealed the cost of walking at a comfortable speed in the equine position was 28% greater than walking in braces without springs or springs in neutral position and 64% greater than walking in shoes alone. CoMz does correlate with metabolic cost as measured by net O2 cost. Also, normal subjects walking in equinus have an increased net O2 cost and increased CoMz when compared to walking with shoes alone or the other brace conditions at all velocities.

Adult↗

PubMed2005

Repeatability of surface EMG during gait in children.

Although mean amplitude and ON-OFF timing of muscle recruitment and electromyography (EMG) activation during gait is achieved by an age of six to eight years in normally developing children, recruitment dynamics illustrated by the shape of the EMG waveform may require continued developmental practice to achieve a stable pattern. Previous analyses have quantified the repeatability of the EMG waveform in adult subjects, but EMG variability for a pediatric population may be significantly different. The goal of this study was to quantify intra-session and inter-session variability in the phasic EMG waveform patterns from the lower limb muscles during self-selected speeds of walking in healthy-normal children for comparison with adult variability in gait EMG. The variance ratio quantifies the repeatability of the integrated EMG waveform shape in a group of normally-developing children. Results reveal that between-session EMG waveform variability were similar in adult and pediatric populations, but within-session variability for the children was approximately twice the published value for adults. Clinical implications of this pediatric EMG variability suggest cautious interpretation of data from limited trial samples or inter-session changes in performance of gait data.

Analysis of Variance↗

PubMed2005

Relationship of spasticity to knee angular velocity and motion during gait in cerebral palsy.

This study investigated the effects of spasticity in the hamstrings and quadriceps muscles on gait parameters including temporal spatial measures, knee position, excursion and angular velocity in 25 children with spastic diplegic cerebral palsy (CP) as compared to 17 age-matched peers. While subjects were instructed to relax, an isokinetic device alternately flexed and extended the left knee at one of the three constant velocities 30 degrees/s, 60 degrees/s and 120 degrees/s, while surface electromyography (EMG) electrodes over the biceps femoris and the rectus femoris recorded muscle activity. Patients then participated in 3D gait analysis at a self-selected speed. Results showed that, those with CP who exhibited heightened stretch responses (spasticity) in both muscles, had significantly slower knee angular velocities during the swing phase of gait as compared to those with and without CP who did not exhibit stretch responses at the joint and the tested speeds. The measured amount (torque) of the resistance to passive flexion or extension was not related to gait parameters in subjects with CP; however, the rate of change in resistance torque per unit angle change (stiffness) at the fastest test speed of 120 degrees/s showed weak to moderate relationships with knee angular velocity and motion during gait. For the subset of seven patients with CP who subsequently underwent a selective dorsal rhizotomy, knee angular extension and flexion velocity increased post-operatively, suggesting some degree of causality between spasticity and movement speed.

Biomechanical Phenomena↗

PubMed2005

Center of mass movement and energy transfer during walking in children with cerebral palsy.

OBJECTIVE: To gain insight into the mechanical inefficiencies of gait patterns used by children with spastic diplegia by analysis of center of mass (COM) movement and energy recovery. DESIGN: Prospective study using between-group measures to analyze differences between children with cerebral palsy (CP) and age-matched controls without CP. SETTING: Assessments were performed in a gait laboratory. PARTICIPANTS: Fifteen children with spastic diplegia and 6 age-matched controls without CP with a mean age of 9.7 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Gait data assessed included temporal-distance factors, COM vertical excursion, work done on the COM, and the percentage of energy transferred and relative phase between the potential and kinetic energy. RESULTS: Children with CP had a 33% smaller energy recovery factor than the controls (P<.001). They also had 60% greater COM vertical excursion (P<.02) and a poorer phasic relation between potential and kinetic energies (P<.02), both of which contributed to greater mechanical work performed (P<.003). CONCLUSIONS: Compared with the age-matched controls without CP, the children with CP were mechanically less efficient in their gait. Interventions that promote heel contact and roll over and greater knee stability to better utilize the kinetic energy of push-off could improve walking efficiency.

Biomechanical Phenomena↗

PubMed2005

Biomechanical changes in gait following selective dorsal rhizotomy.

OBJECT: The purpose of this study was to evaluate the effects of selective dorsal rhizotomy (SDR) on the walking pattern of children with cerebral palsy (CP). The authors hypothesized that SDR would reduce the overactive stretch reflex and result in improved joint positions, greater joint angular velocities and motion, and greater strides. The authors also expected that the changes from the SDR would be reflected in the electrical activities of the muscles. METHODS: Twenty children with CP participated in the study. Ten underwent SDR and 10 who met the inclusion criteria but who did not undergo SDR formed a control group. Gait analysis was performed twice in both groups at comparable time intervals. Within-group (pre- and post-SDR) assessments and between-group (SDR compared with no SDR) assessments were performed. The results indicated that strides increased 1.4 cm on average (p < 0.001), hip and knee excursion increased as a result of greater hip and knee flexion in swing, and ankle dorsiflexion in stance improved. Hip-flexion and knee-extension velocities were increased in swing. Electromyography changes were consistent with these gait changes and support the authors' hypothesis. CONCLUSIONS: By attenuating the stretch response, SDR alters gait mechanics. The effects of SDR include greater strides, joint excursions, and joint angular velocity.

Adolescent↗

PubMed2004

Seated postural control in adolescents with idiopathic scoliosis.

STUDY DESIGN: The center of pressure (COP) path in 14 adolescents with idiopathic scoliosis and 12 age-matched able-bodied adolescents was compared using traditional measures and a two-level decomposition. OBJECTIVES: To investigate whether asymmetries in the spines of children with idiopathic scoliosis are reflected in altered sway patterns in quiet sitting. SUMMARY OF BACKGROUND DATA: Previous studies have studied the sway of children with scoliosis while standing. However, the standing posture is typically controlled at the ankle joint. To date, there are no studies with this population of sitting sway, where the movement is controlled by the trunk muscles. METHODS: Traditional measures of the COP of the trunk were analyzed. The COP was also decomposed into an approximation of the center of mass path and deviations around this path. RESULTS: COP movement in sitting, reflecting the postural control of the spine, was decreased in adolescents with idiopathic scoliosis. Children with scoliosis had symmetric sitting COP trajectories and most measures were similar between the two groups. CONCLUSIONS: The results suggest a control strategy for maintaining a sitting posture that does not change with the development of scoliosis but does adapt by decreasing movement to maintain the trunk in a region where the it can remain "passively" stable.

Adolescent↗

PubMed2003

Pediatric spinal deformities.

Pediatric spinal deformity results from multiple conditions including congenital anomalies, neuromuscular disorders, skeletal dysplasia, and developmental disorders (idiopathic). Pediatric spinal deformities can be progressive and cause pulmonary compromise, neurological deficits, and cardiovascular compromise. The classification and treatment of these disorders have evolved since surgical treatment was popularized when Harrington distraction instrumentation was introduced. The advent of anterior-spine instrumentation systems has challenged the concepts of length of fusion needed to arrest curvature progression. Segmental fixation revolutionized the surgical treatment of these deformities. More recently, pedicle screw-augmented segmental fixation has been introduced and promises once again to shift the standard of surgical therapy. Recent advances in thoracoscopic surgery have made this technique applicable to scoliosis surgery. Not only has surgical treatment progressed but also the classification of different forms of pediatric deformity continues to evolve. Recently, Lenke and associates proposed a new classification for adolescent idiopathic scoliosis. This classification attempts to address some of the shortcomings of the King classification system. In this article the authors review the literature on pediatric spinal deformities and highlight recent insights into classification, treatment, and surgery-related complications.

Adolescent↗

PubMed2003

Spastic velocity threshold constrains functional performance in cerebral palsy.

OBJECTIVES: To evaluate a quantitative, velocity-based assessment of spasticity in the quadriceps and hamstrings muscles of children with cerebral palsy (CP) and to show the effects of spasticity in constraining knee velocities during fast gait. DESIGN: A quantitative comparison of neuromuscular and biomechanical performance in patients with CP and controls without CP. SETTING: Movement analysis laboratory within a university clinical referral center. PARTICIPANTS: A convenience sample of 18 ambulatory patients with CP and 11 control subjects without CP. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Spastic threshold velocity recorded from electromyographic response during passive isovelocity knee movement was compared with knee angular velocity during fast walking, Gross Motor Function Measure (GMFM) scores, and Ashworth Scale score. RESULTS: Patients with measurable spasticity showed slower peak knee angular velocity during walking than patients without spasticity (P<.005). A significant correlation existed between spastic threshold velocity and peak knee angular velocity during fast walking (r=.85, P<.001). Spastic threshold velocity correlated significantly with GMFM (r=.58, P<.05) but not with Ashworth score. CONCLUSIONS: The velocity dependency of spasticity can be measured by electromyograph and dynamometer to determine spastic threshold velocity. Spastic threshold velocity correlated with limitations in joint angular velocity during walking and functional performance.

Adolescent↗

PubMed2002

What does the Ashworth scale really measure and are instrumented measures more valid and precise?

This study aimed to explore the limitations of the Ashworth scale for measuring spasticity. An isokinetic dynamometer to quantify resistance to passive stretch and surface EMG was used to verify if a stretch response occurred and, if so, at what joint angle. The authors sought to determine which components of passive resistance (magnitude, rate of change, onset angle of stretch, or velocity dependence) were most related to Ashworth scores and which were related to motor function in cerebral palsy (CP). Twenty-two individuals with spastic CP (11 males, 11 females; mean age 11.9 years, SD 4.3) and a comparison group of nine children without CP (four males, five females; mean age 11.3 years, SD 2.5) participated in the study. The group with CP included those with a diagnosis of spastic diplegia, hemiplegia, or quadriplegia, distributed across Gross Motor Functional Classification Levels. Procedures included: (1) clinical assessment at the knee joint, (2) functional assessments, and (3) isokinetic assessment of passive resistance torque in hamstrings and quadriceps at three velocities. EMG data were recorded simultaneously to identify stretch responses. Detecting stretch responses using the Ashworth scale compared with instrumented measures showed near complete agreement at extremes of the scale, with marked inconsistencies in mid-range values. Ashworth scores were correlated with instrumented measures, particularly for the quadriceps, with higher correlations to the rate of change in resistance (stiffness) and onset angle of stretch than to peak resistance torque. Those with greater resistance tended to have poorer function with isokinetic relations typically stronger.

Cerebral Palsy↗

PubMed2002

Ankle and knee coupling in patients with spastic diplegia: effects of gastrocnemius-soleus lengthening.

BACKGROUND: Empirical observations of subjects with an equinus gait have suggested that there is coupled motion between the ankle and knee such that, during single-limb stance, the ankle moves into equinus as the knee extends. Since the gastrocnemius-soleus muscle-tendon unit spans both joints, we hypothesized that this muscle-tendon unit may be responsible for the coupling and that lengthening of the gastrocnemius-soleus muscle alone would result in greater ankle dorsiflexion as well as greater knee extension in single-limb stance, effectively uncoupling these joints. The concept that gastrocnemius-soleus lengthening may promote knee extension is counter to the popular notion that crouch gait may result if the hamstrings are not lengthened concomitantly. METHODS: A retrospective review identified thirty-four subjects with specific kinematic characteristics of equinus gait, and their gait was compared with that of normal children. Of the thirty-four subjects, eleven (twenty-two limbs) subsequently underwent isolated midcalf lengthening of the gastrocnemius and soleus muscles with use of a recession technique. Gait analysis including joint kinematics and joint kinetics, electromyography, and physical examination were performed to test the hypothesis. RESULTS: We found that, unlike the normal subjects, the patients with an equinus gait pattern had a positive correlation (r = 0.7) between ankle and knee motion during single-limb stance. As hypothesized, ankle plantar flexion occurred while the knee moved into extension during single-limb stance. Calculations of the lengths of the gastrocnemius-soleus muscle-tendon units showed them to be short throughout the gait cycle (p < 0.0001). After gastrocnemius-soleus recession, peak ankle dorsiflexion (p < 0.001) and peak ankle power (p < 0.001) shifted to occur later in stance than they did in the preoperative gait cycle. Furthermore, the magnitude of peak power increased (p < 0.001) in late stance despite the added length of the gastrocnemius-soleus muscle-tendon unit. The electromyographic amplitude of the gastrocnemius-soleus was reduced during loading (p < 0.02), and this finding, together with the kinetic changes, suggested that muscle tension was reduced. Changes at the knee were less pronounced but included greater knee extension at foot contact (p < 0.01). No increase in the knee flexion angle or extension moment occurred in midstance after the surgery. CONCLUSIONS: Patients with an equinus gait pattern function with a shortened gastrocnemius-soleus muscle-tendon unit, and this results in coupled motion between the ankle and knee during single-limb stance. Lengthening, with use of a recession technique, shifted ankle power generation and dorsiflexion to a later time in stance with no tendency to increase midstance knee flexion. Knee extension did increase at foot contact, but excessive midstance knee flexion persisted and was likely due to concomitant contracture of the hamstrings.

Adolescent↗

PubMedDate not supplied

Responsiveness and uniqueness of the pediatric outcomes data collection instrument compared to the gross motor function measure for measuring orthopaedic and neurosurgical outcomes in cerebral palsy.

The Pediatrics Outcomes Data Collection Instrument (PODCI) is a valid and reliable measure of functional health status in children with acute and chronic musculoskeletal disorders, including cerebral palsy (CP), but its responsiveness has not been documented specifically for this population. The Gross Motor Function Measure (GMFM) and the Pediatric Evaluation of Disability Inventory (PEDI) are the only two instruments validated specifically as evaluative measures for CP, and while widely used, they are limited by a ceiling effect when assessing higher-functioning children. The PEDI is further restricted to children who are 7 years old or less. The goal of this study was to evaluate the responsiveness, and secondarily the uniqueness, of the PODCI compared with the GMFM for evaluating surgical outcomes in CP. Changes in the GMFM and PODCI Parent forms were assessed at two time points in 64 children with spastic CP who underwent muscle-tendon lengthenings (MT; n = 22) or neurosurgical spasticity reduction consisting of either selective dorsal rhizotomy (SDR; n = 18) or intrathecal baclofen pump implantation (ITB; n = 11) or who had no surgery between assessments (n = 13). The GMFM Total score was responsive to change after both MT surgery and SDR, with a nearly equivalent magnitude of change in both groups. However, the PODCI Global Function Scale was responsive to changes only after MT surgery, with improvement in the Sports and Physical Function subscale particularly prominent. No significant changes were noted in the ITB group for either measure.

Adolescent↗

PubMedDate not supplied

Relationships among musculoskeletal impairments and functional health status in ambulatory cerebral palsy.

Orthopedic surgery for patients with cerebral palsy addresses motion impairments, assuming that this will improve motor function. This study evaluates the relationships among clinical impairment measures with standardized assessments of function and disability as an initial step in testing this assumption. A total of 129 ambulatory children and adolescents across six institutions participated in a prospective evaluation that consisted of passive motion and spasticity examination of the lower extremities, three-dimensional gait temporal-spatial and kinematic analysis, and administration of the Gross Motor Function Measure (GMFM) and the Pediatric Outcomes Data Collection Instrument (PODCI). The analysis found that isolated impairment measures of motion and spasticity were only weakly related to motor function in cerebral palsy and even when averaged across multiple joints yielded no more than a fair correlation with functional scores, nor did a combination of impairments emerge that could predict substantial variance in motor function. These findings suggest that caution should be exercised when anticipating functional change through the treatment of isolated impairment and that addressing multiple impairments may be needed to produce appreciable effects.

Adolescent↗