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Biomedical subjects

Caroline Stewart

Publications and source records attributed to Caroline Stewart.

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

Development of an instrumented pole test for use as a gait laboratory quality check.

Gait analysis is becoming an increasingly common procedure in the diagnosis of movement disorders. Core equipment includes 3D tracking cameras and force platforms. Important clinical decisions are made with the assistance of gait data, therefore it is essential to have confidence in its quality. Calibration has a major role to play here and this paper describes the development of a daily spot check pole test for use in a gait laboratory. The work develops previous such tests, by the addition of a force transducer, removing the need to assume an idealised force system and allowing amplifier gain ranges to be checked. Repeatability results are presented, along with the response to 14 simulated error modes. The test provides useful data on system performance and is able to identify and diagnose failures. Failure thresholds can be tightened as accuracy improves, particularly in the area of centre of pressure measurement. Spot checks, such as this, along with full calibration tests, will become essential as new standards are introduced into clinical practice.

Biomechanical Phenomena↗
PubMed2006

Musculo-tendon length and lengthening velocity of rectus femoris in stiff knee gait.

Inappropriate activity of M. rectus femoris (RF) during swing is believed to contribute to stiff knee gait in cerebral palsy. This study used musculoskeletal modeling techniques to analyze rectus femoris musculo-tendon (MT) length and lengthening velocity during stiff knee gait in 35 children with diplegic cerebral palsy (CP). Duncan Ely test scores were used to categorize the patients into four groups with increasing levels of rectus femoris spasticity. Knee kinematics confirmed a significant reduction and delay of maximal peak knee flexion during swing in the patient groups compared to reference values. Maximal musculo-tendon length of M. rectus femoris was reduced and occurred prematurely in swing. Musculo-tendon lengthening velocity was significantly reduced and the timing of the maximal lengthening velocity was shifted into stance phase. The present study demonstrates altered dynamic behavior of the M. rectus femoris in stiff knee gait and the results indicate that maximal knee flexion in swing was not a valid reference for the MT length of the M. rectus femoris. Furthermore, in the patient group maximal musculo-tendon lengthening velocity of the muscle related to the stance phase rather than the stance-swing transition.

Acceleration↗
PubMed2004

Estimation of hamstring length at initial contact based on kinematic gait data.

This study proposes a simple estimate of hamstring length at initial contact (LEST) for use when musculoskeletal modelling is not available. The estimate is calculated by using the kinematic curves to measure the excessive flexion (above normal) at the hip and knee at initial contact. The excessive hip flexion is then multiplied by a scaling factor (k) and the excessive knee flexion subtracted from the result. Validation of this estimate was carried out using kinematic gait data from 25 children with cerebral palsy (50 limbs) by comparing the results of the estimate with an equivalent measure derived from musculoskeletal modelling (LTRUE). Very high agreement was found when LTRUE and LEST were compared for the three biarticular hamstring muscles, demonstrated by correlation coefficients of over 0.9. Different k values were tested with a value of 3 giving the best results overall. The estimate is acceptable as a simple 'rule of thumb' for use in clinical practice. It can provide useful additional information to complement the clinical examination and gait assessment results.

Adolescent↗
PubMed2003

The study of muscle action during single support and swing phase of gait: clinical relevance of forward simulation techniques.

Individual muscle function during single stance and swing phase of gait were analyzed using muscle driven forward simulation. The activation of each of 22 muscles in a musculoskeletal model with seven degrees of freedom were excluded from the forward simulation and the resulting changes in joint angles studied. A classification of muscle function during single support and swing phase of gait is presented. Altered joint kinematics due to the absence of individual muscle action is discussed in the light of pathological gait kinematics and clinical decision-making.

Ankle Joint↗
PubMed2003

The complementary role of the plantarflexors, hamstrings and gluteus maximus in the control of stance limb stability during gait.

This paper focuses on the contributions of the gluteus maximus, biceps femoris, gastrocnemius and soleus in maintaining the stability of the stance limb in the sagittal plane during the mid-stance phase of gait. In the absence of any one of these muscles, the potential compensatory changes in muscle activation are explored, the aim being to restore stability to the stance limb. The investigation was carried out by integrating musculoskeletal modelling, forward simulation and optimization techniques. We concluded that maintenance of stance limb stability requires a subtle interplay of muscle activations. Weakness in a single muscle is unlikely to be adequately compensated for by increasing or decreasing the activation of one muscle alone.

Extremities↗
PubMed2002

A comparison of the biomechanical effects of opening and closing wedge varus osteotomies in Perthes' disease.

Varus femoral osteotomy is a commonly employed surgical method of effecting containment in the management of Perthes' disease. This can be achieved by performing either an opening lateral wedge or a closing medial wedge osteotomy. The effects of these two techniques on the biomechanical interrelationships about the involved hip were compared using a three-dimensional computer simulation. Both procedures lead to femoral shortening and reduce the moment capacity of the hip abductors. The shortening effect and consequent leg length discrepancy are greater for the closing wedge osteotomy than for the opening wedge procedure. Pelvic obliquity compensation, likely to be greater for a closing wedge osteotomy, provides a beneficial increase in femoral head coverage but at the cost of a further reduction in the hip abductor moment capacity.

Biomechanical Phenomena↗
PubMed2002

Microgastria-limb reduction anomaly with total amelia.

The Microgastria-limb reduction anomaly is a rare disorder of unknown aetiology in which microgastria is associated with limb defects, along with splenic and other variable congenital abnormalities. In 15 previously reported cases, none have had the most extreme form of amelia. We report the clinical progress of a 3-year-old girl with severe microgastria and total amelia who has been managed conservatively with minimal surgical intervention.

Abnormalities, Multiple↗