PubMed Health⌕ Search

Biomedical subjects

Garth R Johnson

Publications and source records attributed to Garth R Johnson.

7 recordsLinked to original sources
PubMed2006

The construct validity of a spasticity measurement device for clinical practice: an alternative to the Ashworth scales.

INTRODUCTION: Spasticity is a significant cause of disability in people with an upper motor neurone lesion, but there is a paucity of appropriate outcome measures to evaluate this phenomenon. The aim was to test the construct validity of a clinically relevant, non-invasive measure of spasticity. METHODS: A cross-section study design in which participants with elbow flexor spasticity and capable of providing written informed consent were recruited. RESULTS: Fourteen stroke patients participated (six female and eight male). Median age was 61 years and the median time post stroke was 48 months. Six patients had a MAS grading of '1+', three a grade of '2' and five a grade of '3'. The velocity of the brisk stretch was significantly higher than that of the slow stretch (p < 0.05: median difference, 34 degrees /s: IQR, 20 - 46). Flexor muscle activity during the brisk stretch was significantly higher than that of the slow stretch (p < 0.05: median difference, 2.0 microV; IQR, 0.4 - 8.4). In contrast the RPE was not significantly different between the slow and the fast stretches (p > 0.1: median difference, 0.07 N/deg; IQR, - 0.09 - 0.16). There were no patterns of association between the MAS, elbow flexor muscle activity and RPE. Other important observations, in some patients, were: continuous background muscle activation consistent with descriptions of spastic dystonia; muscle activity at the slow velocity stretch; muscle activation patterns consistent with the clasp-knife phenomenon. CONCLUSIONS: The measurement system was capable of measuring spasticity as defined by Lance (1980; In: Lance et al., editors. Spasticity: disordered motor control. Chicago, IL: Year Book. p 185 - 204). In addition, it enabled various other clinical phenomena associated with spasticity to be measured. Assessing spasticity by measuring changes in resistance to passive movement only may not be sufficient, as the latter is influenced by many factors of which spasticity may only be one. Further work is now required to investigate repeatability and sensitivity.

Biomechanical Phenomena↗
PubMed2005

Distal ligamentous restraints of the first metatarsal. An in vitro biomechanical study.

BACKGROUND: Hypermobility or instability of the first metatarsal is associated with increased hallux valgus deformity and greater risk of recurrence after surgery. The objective of this in vitro study was to determine the ranges of movement, under directional loading, of the normal first metatarsal and the effect of the longitudinal plantar aponeurosis and the transverse tie-bar ligamentous system. METHODS: A model has been developed to quantify the influence of the first intermetatarsal ligament and plantar aponeurosis on movements of the first metatarsal. All muscular structures controlling movements of the first ray in cadaver feet were detached and static ligament structures retained for study. Using a specially designed test system, a static load was applied to the metatarsal to produce flexion, extension, abduction or adduction moments. The first intermetatarsal ligament and the plantar aponeurosis were detached sequentially and a movement map of the first metatarsal in the frontal plane was obtained using the Isotrak II magnetic measuring system. RESULTS: The first intermetatarsal ligament was shown to be an important stabiliser of the first metatarsal in all directions. The plantar aponeurosis was shown to be a secondary stabiliser resisting medial and dorsal rotation of the metatarsal after division of the first intermetatarsal ligament. INTERPRETATION: Recognition of the importance of the plantar aponeurosis and the first intermetatarsal ligament in the normal foot has implications for our understanding of hallux valgus.

Biomechanical Phenomena↗
PubMed2005

The activity in the three regions of the trapezius under controlled loading conditions--an experimental and modelling study.

BACKGROUND: There is a degree of conflict in the literature regarding the biomechanical role of the three regions of trapezius. It is suggested that some of this may result from a lack of experiments using a well defined loading regime. OBJECTIVES: To study the activity of the three regions of trapezius under controlled load in order to gain further insight into its role in shoulder biomechanics. DESIGN: The emg activity of the three regions of trapezius was studied on five subjects using a specially designed test system which allowed the application of either a uniaxial shrug force or a pure couple in the coronal plane. METHODS: Test rigs were designed and constructed to measure isometric loads applied by shoulder shrugging and isometric pure moments produced in coronal plane abduction and adduction. Surface emg of the three regions of trapezius was performed simultaneously with loading. RESULTS: The activity of upper trapezius was always present but changed little with the type of loading. Middle trapezius was dominant during both shrug and abduction whereas the lower fibres predominated during adduction. CONCLUSIONS: The use of a test system applying defined loading at the shoulder allows the detail analysis of trapezius muscle activity. The reproducible technique can be extended to other shoulder muscles. RELEVANCE: The biomechanics of the shoulder calls for detailed analysis of the activity of all the interacting muscles. This paper describes a techniques which allows study of muscle activity under carefully defined loading.

Adult↗
PubMed2004

A study of the external forces and moments at the shoulder and elbow while performing every day tasks.

OBJECTIVES: To establish a database of upper limb kinematics and kinetics to support the development of a biomechanical model of the shoulder and elbow. DESIGN: Ten unimpaired subjects were studied when performing 10 different tasks of every day living. BACKGROUND: The development of biomechanical models of the upper limb to support the design of total joint replacements requires data on the commonly performed activities. Unlike the lower limb, this involves the selection of the tasks believed to be the most common. METHODS: Kinematic data were collected using four video cameras to track the movements of reflective markers attached to the upper limb and trunk. The rigid body kinematics was then analysed and the external forces and moments at the shoulder and elbow were calculated using inverse dynamics. RESULTS: The greatest ranges of motion at the shoulder occurred during reaching and lifting tasks as did the greatest shoulder moment (14.3 Nm flexion). The greatest elbow flexion occurred while reaching the back of the head but the greatest moment (5.8 Nm) occurred while lifting a block to head height. CONCLUSIONS: A database of ranges of motion and external forces and moments has been established to support the development of biomechanical models of the upper limb. RELEVANCE: The development of biomechanical models to support the design of upper limb joint replacements requires detailed knowledge of the types and magnitudes of forces and moments at the joints.

Activities of Daily Living↗
PubMed2003

A biomechanical investigation into the validity of the modified Ashworth Scale as a measure of elbow spasticity.

OBJECTIVE: To investigate the criterion validity of the modified Ashworth Scale. POPULATION: Volunteers from a stroke population admitted to a district general hospital stroke unit diagnosed with a first ever stroke less than 26 weeks previously. OUTCOME MEASURES: Resistance to passive movement about the elbow was simultaneously quantified (biomechanically) and graded (modified Ashworth Scale). Passive range of movement and peak instantaneous velocity during passive movement were also measured. ANALYSIS: Criterion validity was investigated as convergent construct validity (using the Spearman's correlation coefficient) and concurrent validity (using analysis of variance). RESULTS: One hundred measurements were taken on 63 subjects. Correlation between the modified Ashworth Scale and resistance to passive movement was 0.511. Resistance to passive movement and velocity showed significant differences between the modified Ashworth score of '0' and a modified Ashworth score greater than '0' (p < 0.01). There were no significant differences between MAS '1', '1+' and '2'. Resistance to passive movement in the impaired arm was significantly higher than in the nonimpaired arm (p < 0.01). CONCLUSION: The modified Ashworth Scale does not provide a valid measure of spasticity at lower grades but it may provide a measure of resistance to passive movement.

Biomechanical Phenomena↗
PubMed2002

Are we underestimating the clinical efficacy of botulinum toxin (type A)? Quantifying changes in spasticity, strength and upper limb function after injections of Botox to the elbow flexors in a unilateral stroke population.

OBJECTIVE: To quantify the clinical efficacy of botulinum toxin type A in treating elbow flexor spasticity in a unilateral stroke population. LOCATION: A spasticity clinic at a regional neurological rehabilitation centre. STUDY DESIGN: A convenience sample longitudinal study. Fourteen subjects with elbow flexor spasticity secondary to a stroke were recruited. Two repeated measures, one before and another four weeks after treatment, were taken to quantify clinical efficacy. OUTCOME MEASURES: Elbow flexor spasticity was simultaneously rated with the modified Ashworth scale (MAS) and quantified by measuring the surface EMG from the flexors using a custom-built device. Strength at the elbow (isometric), grip strength and upper limb function (Action Research Arm test) were also assessed. TREATMENT: Injections of botulinum toxin type A (Botox) to the m.biceps brachii (mean dose 70 U), m.brachioradialis (mean dose 56.5 U) and m.flexor digitorum longus (mean dose 83.3 U). RESULTS: Following treatment, spasticity (as measured by flexor EMG activity) reduced but the MAS was unable to detect this improvement. In some subjects, isometric flexor strength at the elbow as well as grip strength increased. This was contrary to the expected weakening following treatment with botulinum toxin type A and suggests an optimization of motor control. CONCLUSION: Treatment with Botox reduces spasticity but does not necessarily cause a reduction in the force generating capabilities at the joint. The improvement in strength may have contributed to the improvements in upper limb function. The MAS is an inappropriate measure of spasticity.

Adult↗