New horizons in the compression of functional decline.

Population ageing, which has come about through the combination of increases in life expectancy, larger post-war cohorts reaching older age and reductions in fertility, is challenging societies and particularly health and care providers, worldwide. In Europe, the USA and Japan, there have been increases in years spent with disability and dependency. The majority of such research, as well as professional health and social care practice, measures loss of functional capability or need for social care, by aggregate disability scores, based around activities of daily living and instrumental activities of daily living. Although useful for defining whether an individual has passed a threshold, aggregate scores obscure how functional decline unfolds, and therefore where early intervention might improve intrinsic capacity and reverse or slow down decline, or maintain function. We propose a framework, the compression of functional decline (CFD), based on the latest understanding of the hierarchy of age-related functional decline, which has the potential to (i) help people understand how to live better for longer, (ii) allow the various stakeholders to be able to measure, at a population level, whether that is happening and (iii) identify which interventions are most effective at which stages. CFD is coherent with the World Health Organisation's Healthy Ageing model and is more easily understood by stakeholders and older people themselves, than current indicators such as frailty. CFD thus provides a realistic view of age-related functional decline in the context of modifiable behaviour to counter widespread public misconceptions about ageing and inform improvements.

Sensitivity of a biomechanical model of the finger to errors in experimental input.

Biomechanical models of the fingers are used to gain a greater understanding of internal loading. This can help guide the treatment of injuries and pathologies. However, to be valid these models require accurate measurement of body kinematics, external reaction forces and soft tissue architecture. This study aimed to quantify the sensitivity of one such model, to errors in these inputs. Experimental data was collected from a single subject carrying out a simple gripping activity and the experimental data altered to introduce artificial errors. We found that the correlations between errors in measurement of body kinematics and the model outputs could be used to express errors in motion capture data in terms of internal loading. However, these correlations were specific to grip type, therefore, if the grip changed significantly a new analysis would be required. Sensitivity analysis of the muscle and tendon locations indicated which parameters were most important to measure accurately; outputs were most sensitive to changes in the most highly loaded muscle-tendon units, these results were applicable across different hand orientations.

Adaptation of scapula lateral rotation after reverse anatomy shoulder replacement.

Scapula motion is significant for support of the arm and stability of the shoulder. The effect of the humeral elevation on scapular kinematics has been well investigated for normal subjects, but there are limited published studies investigating adaptations after shoulder arthroplasty. Scapula kinematics was measured on 10 shoulders (eight subjects) with a reverse total joint replacement. The measurements were performed using an instrumented palpating technique. Every subject performed three simple tasks: abduction, elevation in scapula plane and forward flexion. Results indicate that, lateral scapula rotation was significantly increased (average of 24.42% over the normal rhythm) but the change was variable. Despite the variability, there is a clear trend correlating humeral performance with increased rotation (R2 0.829). There is clearly an adaptation in lateral scapula rotation in patients with shoulder joint replacement. The reason for this is unclear and may be related to joint pathology or to muscle adaptation following arthroplasty.

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.

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.

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.

A novel four-caster manual vehicle manoeuvring investigation: Higher loading-weights require larger turning spaces.

Patient-hoists, goods-trolleys and other omni-directional manually operated vehicles are ubiquitous. Yet no substantive, empirically based dynamic analysis has been made of these four-caster vehicles despite manual handling concerns. A relationship between loading-weight and turning space is indicated by theoretical analysis which further shows that this effect is represented by only 11 different manoeuvres. A qualitative account of the theory is presented. These 11 manoeuvres were implemented experimentally. A total of 17 subjects selected a maximum comfortable loading-weight for the four-caster vehicle for each of the 11 manoeuvres. Vehicle displacement and handle forces were measured for different centres of zero velocity. The median loading-weight of the manoeuvre with the highest loading-weight selections was 101% greater than the mean loading-weight of the three manoeuvres with the lowest loading-weight selections. The manoeuvre with the highest loading-weight selections required a larger vehicle turning space: one dimension increased by 37% (173 mm) compared with the three lowest loading-weight selection manoeuvres and the other dimension increased by 17% (130 mm) compared with one of the lowest loading-weight selection manoeuvres. Higher loading-weights require larger turning spaces. These results can contribute to building designs which facilitate safe manual manoeuvring of four-caster vehicles.

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.

Musculoskeletal shoulder models: a technical review and proposals for research foci.

Musculoskeletal shoulder models allow non-invasive prediction of parameters that cannot be measured, particularly the loading applied to morphological structures and neurological control. This insight improves treatment and avoidance of pathology and performance evaluation and optimisation. A lack of appropriate validation and knowledge of model parameters' accuracy may cause reduced clinical success for these models. Instrumented implants have recently been used to validate musculoskeletal models, adding important information to the literature. This development along with increasing prevalence of shoulder models necessitates a fresh review of available models and their utility. The practical uses of models are described. Accuracy of model inputs, modelling techniques and model sensitivity is the main technical review undertaken. Collection and comparison of these parameters are vital to understanding disagreement between model outputs. Trends in shoulder modelling are highlighted: validation through instrumented prostheses, increasing openness and strictly constrained, optimised, measured kinematics. Future directions are recommended: validation through focus on model sub-sections, increased subject specificity with imaging techniques determining muscle and body segment parameters and through different scaling and kinematics optimisation approaches.

Comparison of range of motion and function of subjects with reverse anatomy Bayley-Walker shoulder replacement with those of normal subjects.

Patients with rotator cuff tear and degenerative shoulder joint disease commonly experience severe pain and reduced performance during activities of daily living. A popular way to treat these patients is by means of reverse anatomy shoulder prosthesis. Studying the kinematics of subjects with reverse anatomy implant would be useful in order to gain knowledge about functionality of different designs. It is hypothesized that the kinematics of these subjects, in the absence of rotator cuff muscles, differs from that of normal subjects. In this study the upper limb kinematics of 12 subjects with a Bayley-Walker reverse anatomy shoulder prosthesis while performing tasks common in everyday activities and those that represent the range of motion was analyzed and compared to that of 12 normal subjects. Each patient also completed an Oxford Shoulder Score. Substantial reduction in the Bayley-Walker subjects' ranges of motion was observed compared to normal subjects. The mean abduction angle decreased from 109° (±20) for normal subjects to 64° (±25). A similar trend was observed during flexion and axial rotation tasks. Furthermore, the normal group showed less variable ranges of motion performing the standard tasks, whereas for the prosthetic group this varied greatly, which is likely to be dependent on muscle strength. Although the decreased range of motion was prominent, subjects were able to complete most of the tasks by compensating with their elbow and trunk. The most challenging task for Bayley-Walker subjects was lifting an object to head height.

Glenohumeral contact forces in reversed anatomy shoulder replacement.

A major requirement to design an implant is to develop our understanding of the applied internal forces during everyday activities. In the absence of any basic apparatus for measuring forces directly, it is essential to rely on modelling. The major aim of this study was therefore to understand the biomechanical function of subjects with the reversed anatomy Bayley-Walker prosthesis, using an inverse dynamic shoulder model. In this context, the muscle and joint forces of 12 Bayley-Walker subjects were compared to those of 12 normal subjects during 12 activities of daily living. Maximum glenohumeral contact forces for normal and Bayley-Walker subjects were found to be 77% (+/-15) and 137% (+/-21) body weight for lifting a 2kg shopping bag, and the least forces 29% (+/-4) and 67% (+/-8) body weight for reaching to opposite axilla, respectively. For normal subjects, middle deltoid, supraspinatus and infraspinatus were found to be the most active muscles across the subjects and tasks. On the other hand, for implanted subjects with a lack of rotator cuff muscles, the middle deltoid and coracobrachialis muscles were found to be the most active. The biomechanical model can therefore be used in order to gain knowledge about the pathology as well as possible post surgical rehab for subjects with reversed shoulder replacement.

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.

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.