Biomedical subjects

Michael H Schwartz

Publications and source records attributed to Michael H Schwartz.

9 recordsLinked to original sources

PubMed2007

An exploration of the function of the triceps surae during normal gait using functional electrical stimulation.

Gastrocnemius and soleus have a common tendon and both are active during stance phase, where they are thought to arrest and control tibial advance. Soleus is associated with the production of an extending moment at the knee. The two-joint gastrocnemius, which crosses the knee joint, will have an additional contribution to the knee flexors. Recent work using induced acceleration analysis (IAA) has demonstrated distinct differences between the actions of gastrocnemius and soleus. This study aims to use gait analysis to provide in vivo examination of these theoretical predictions. Functional electrical stimulation (FES) was chosen to provide a perturbation in muscle force, a close physical analogue to the theoretical predictions of IAA. Five adult male subjects, with no gait problems, participated. Each had gastrocnemius and soleus stimulated at three different timings during normal gait, while 3D gait data were collected. The order of testing was randomised and unstimulated trials were randomly interspersed to act as a control. The results show very different actions for soleus (ankle plantarflexing/knee extending) and gastrocnemius (ankle dorsiflexing/knee flexing) in stance phase. The counterintuitive nature of the action of gastrocnemius suggests that further clinical and biomechanical investigation into this muscle's function is required. The actions of both muscles at the knee confirm published IAA predictions. In vivo evidence such as this gives greater confidence when using model predictions. The approach adopted in this study could eventually be extended to other muscles and patient populations.

Adult↗

PubMed2006

A baseline of dynamic muscle function during gait.

An existing induced acceleration (IA) model was used to create a comprehensive baseline of dynamic muscle function. In this study, 20 control subjects were modelled as three-dimensional linkage systems. Muscle architecture was taken from an existing muscle model. Each subject-specific model was configured with gait data and 36 unit muscle forces were then applied one at a time to each linkage model. After muscle force application, all joint, segment, and centre of mass (COM) accelerations were derived. The results showed that most uni-articular muscles function as expected while some bi-articular muscles function in a paradoxical manner. This indicates that both the local and remote effects of muscles should be considered when assessing dynamic muscle function during gait. The results also agree with previous IA studies, lending support to the validity of IA analysis as a means for understanding dynamic muscle function.

Acceleration↗

PubMed2005

The role of estimating muscle-tendon lengths and velocities of the hamstrings in the evaluation and treatment of crouch gait.

Persons with cerebral palsy frequently walk with excessive knee flexion during terminal swing and stance. This gait abnormality is often attributed to "short" or "spastic" hamstrings that restrict knee extension, and is often treated by hamstrings lengthening surgery. At present, the outcomes of these procedures are inconsistent. This study examined whether analyses of the muscle-tendon lengths and lengthening velocities of patients' hamstrings during walking may be helpful when deciding whether a candidate is likely to benefit from hamstrings surgery. One hundred and fifty-two subjects were cross-classified in a series of multi-way contingency tables based on their pre- and postoperative gait kinematics, muscle-tendon lengths, muscle-tendon velocities, and hamstrings surgeries. The lengths and velocities of the subjects' semimembranosus muscles were estimated by combining kinematic data from gait analysis with a three-dimensional computer model of the lower extremity. Log-linear analysis revealed that the subjects who walked with abnormally "short" or "slow" hamstrings preoperatively, and whose hamstrings did not operate at longer lengths or faster velocities postoperatively, were unlikely to walk with improved knee extension after treatment (p < 0.05). Subjects who did not walk with abnormally short or slow hamstrings preoperatively, and whose hamstrings did operate at longer lengths or faster velocities postoperatively, tended to exhibit unimproved or worsened anterior pelvic tilt after treatment (p < 0.05). Examination of the muscle-tendon lengths and velocities allows individuals who walk with abnormally short or slow hamstrings to be distinguished from those who do not, and thus may help to identify patients who are at risk for unsatisfactory postsurgical changes in knee extension or anterior pelvic tilt.

Adolescent↗

PubMed2005

Do the hamstrings operate at increased muscle-tendon lengths and velocities after surgical lengthening?

Children with crouch gait frequently walk with improved knee extension during the terminal swing and stance phases following hamstrings lengthening surgery; however, the mechanisms responsible for these improvements are unclear. This study tested the hypothesis that surgical lengthening enables the hamstrings of persons with cerebral palsy to operate at longer muscle-tendon lengths or lengthen at faster muscle-tendon velocities during walking. Sixty-nine subjects who had improved knee extension after surgery were retrospectively examined. The muscle-tendon lengths and velocities of the subjects' semimembranosus muscles were estimated by combining kinematic data from gait analysis with a three-dimensional computer model of the lower extremity. Log-linear analyses confirmed that the subjects who walked with abnormally short muscle-tendon lengths and/or slow muscle-tendon velocities preoperatively tended to walk with longer lengths (21 of 29 subjects, p<0.01) or faster velocities (30 of 40 subjects, p<0.01) postoperatively. In these cases, surgical lengthening may have slackened the subjects' tight hamstrings and/or diminished the hamstrings' spastic response to stretch. Other subjects walked with muscle-tendon lengths and velocities that were neither shorter nor slower than normal preoperatively (22 of 69 subjects), and the semimembranosus muscles of most of these subjects did not operate at increased lengths or velocities after surgery; in these cases, the subjects' postsurgical improvements in knee extension may have been unrelated to the hamstrings surgery. Analyses of muscle-tendon lengths and velocities may help to distinguish individuals who have "short" or "spastic" hamstrings from those who do not, and thus may augment conventional methods used to describe patients' neuromusculoskeletal impairments and gait abnormalities.

Adolescent↗

PubMed2005

A new method for estimating joint parameters from motion data.

Joint centers and axes of rotation (joint parameters) are central to all branches of movement analysis. In gait analysis, the standard protocol used to determine hip and knee joint parameters is prone to errors arising from palpation, anthropometric regression equations, and misplaced alignment devices. Several alternative methods have been proposed, but to date none have been shown to be accurate and reliable enough for use in the clinical setting. This article describes a new method for joint parameter estimation. The new method can be summarized as follows: (i) the motions of two adjacent segments spanning a single joint are tracked, (ii) the axis of rotation between every pair of observed segment configurations is computed, (iii) the most likely intersection of all axes (effective joint center) and most likely orientation of the axes (effective joint axis) is found. Initial validation of the method was conducted on a hinged mechanical analog and a single healthy adult subject. For the analog, the center was found to be within 3.8 mm of the geometric center and 2.0 degrees of the geometric axis (standard deviation). For the adult subject, hip centers varied on the order of 1-3 mm, knee centers by 3-9 mm, and knee axes by 2.0 degrees. The results suggest that the new method is an objective, precise, and practical alternative to the standard clinical approach.

Adult↗

PubMed2004

Measurement and management of errors in quantitative gait data.

Gait analysis is a valuable tool in the evaluation of children and adults with movement disorders. The data produced from gait analysis, however, is not necessarily free of errors. The purpose of this study was two-fold: (i) to estimate the errors associated with quantitative gait data; and (ii) to propose a method for incorporating the knowledge of these errors into the clinical interpretation process. An experimental protocol was designed that allowed within-subject, within-observer and between-observer errors to be computed at each point in the gait cycle. The estimates were then used in a practical scheme for detecting significant deviations in joint angles. The results of this study provide a means for managing error, while simultaneously improving the rigor and objectivity of clinical interpretations.

Adult↗

PubMedDate not supplied

Correlation of the Edinburgh Gait Score with the Gillette Gait Index, the Gillette Functional Assessment Questionnaire, and dimensionless speed.

This study examines the correlation of the Edinburgh Gait Score (EGS) with the Gillette Gait Index (GGI; formerly the Normalcy Index), the Gillette Functional Assessment Questionnaire, and speed, all of which are used as measures of gait quality or function. Scores were computed for 58 subjects, all with a diagnosis of cerebral palsy. The correlation of the EGS with all of the other scores was found to be significant, with r2 ranging from 0.26 to 0.79. The strongest correlation was found with the GGI, which may reflect common features in the derivation of both of these scores, although the EGS was derived from observational gait analysis and the GGI from principal component analysis of variables from computerized 3-dimensional gait data. We conclude that the EGS shows good concurrent validity with alternative gait assessment scores.

Adolescent↗

PubMedDate not supplied

Intramuscular psoas lengthening improves dynamic hip function in children with cerebral palsy.

The efficacy of psoas surgery for the treatment of hip flexor dysfunction in cerebral palsy has long been a subject of debate. A retrospective, repeated-measures analysis was performed to examine the effect of psoas surgery based on gait and clinical and functional measures. The results of this study show that intramuscular psoas lengthening over the pelvic brim is a safe and effective way to improve the hip function of independently ambulatory children with cerebral palsy while maintaining hip flexor power. The data also support the use of the multivariate hip flexor index as an overall measure of hip function.

Adolescent↗

PubMedDate not supplied

Comprehensive treatment of ambulatory children with cerebral palsy: an outcome assessment.

A retrospective study was used to evaluate the outcome of treatment of 135 ambulatory children with cerebral palsy. Diplegic subjects were selected from the existing database at the Gillette Children's Specialty Healthcare Motion Analysis Laboratory. All subjects had undergone gait analysis before and after intervention, which included orthopaedic surgery, selective dorsal rhizotomy, or both treatments. Outcome was based on gait pathology, gait efficiency, functional walking ability, and higher-level functional skills. Gait pathology was assessed using 16 clinically relevant kinematic parameters. Gait efficiency was assessed with steady-state oxygen consumption. Walking ability and higher-level functional skills were based on patient report surveys. Improvements were seen in all outcome measures. A significant majority of subjects (79%) improved on a predominance of outcome measures; only 7% of subjects worsened. Within the restrictions of this study design, the results indicate that surgical intervention, guided by preoperative gait analysis, is effective and safe for children with cerebral palsy.

Cerebral Palsy↗