Muscle weakness: Are our clinical beliefs correct?

SUMMARY

Objective: To investigate strength impairments following stroke: in particular the differences in impairments between proximal and distal muscle actions; flexor and extensor actions; upper and lower limb actions; and ‘hemiplegic and ‘non-hemiplegic’ sides.

Design: Retrospective analysis of clinical data collection.

Setting: In-patient rehabilitation unit, USA.

Patients: Patients admitted between January 1994 and August 1997 within 6 weeks of their first stroke, with no comorbidities and able to follow simple commands. Of 114 admitted patients, 48 met the inclusion criteria and 31 were assessed at both admission and discharge. Average age was 63.8 + 11.6 years; average time from onset of stroke to first assessment (admission) was 9.6 + 5.8 days; average time from onset to second assessment (discharge) was 25.9 + 13.5 days.

Main outcome measures: Static strength measured using a digital hand-held dynamometer, using standardised testing positions, from shoulder abductors, elbow flexors, elbow extensors, wrist extensors, hip flexors, knee flexors, knee extensors and ankle dorsiflexors, bilaterally.

Main results: Muscle strength was expressed as a percentage of normal muscle strength. Mean muscle strength for the patients was less than normal for all actions bilaterally. (At admission: between 20-34% of normal on the hemiplegic side and between 60-90% on the non-hemiplegic side. At discharge: between 29-45% on the hemiplegic side and between 65-89% on the non-hemiplegic side). On both sides distal muscle strength was less impaired than proximal muscle strength. Elbow extension was significantly less impaired than elbow flexion on both sides. On the hemiplegic side there were few differences between the strength impairments in the upper and lower limb; on the non-hemiplegic side the upper limb had less strength impairments than the lower limb.

Conclusions: The results don’t support the often historically held beliefs that proximal muscle strength is less impaired than distal muscle strength, and that elbow flexors are less impaired than elbow extensors.

DEBATE: WHAT DO WE THINK OF IT?

Introduction: Do we know the key aim of the study? And why/how this was formed?

The authors clearly lay out what the common "historical consensus" is regarding patterns of muscle strength impairment following stroke. They point out that these historical beliefs are not always supported by research. This forms a sound argument for carrying out this study.

This is reported as a retrospective review of clinical data. Retrospective analysis can be problematic due to inconsistencies and potential bias in the assessment and recording of data. However this study does have the strength that all the assessments were carried out by a single assessor, and that a documented standardised assessment protocol was used. Nevertheless the assessor was one of the principal investigators and may have held beliefs regarding muscle strength impairments which could have led to the introduction of bias. Furthermore, the assessor was not blinded to the results of the first assessment at the time of the second assessment, which could also have introduced bias.

The authors identify that key limitations of this study are the inability to generalise from the study sample to larger populations, and the fact that the measurements were largely all taken in the first month following stroke and are not therefore representative of longer term changes in muscle strength.

The mean muscle strength, and this expressed as a percentage of the normal, are provided and substantial details are given in the statistical analyses carried out. For anyone who has long been exposed to the widespread ‘historical perspectives’ of muscle strength impairment it is definitely worthwhile taking time to explore this data.

The results of this study do not support the often widespread clinical beliefs that proximal muscles will be less impaired than distal, and elbow extensors will be less impaired than elbow flexors. Although this is a relatively small scale study, these results do have clinical implications. These results emphasise the importance of not holding onto clinical beliefs when they are not supported by evidence.