Reliability of hand-held dynamometry in children with spastic diplegia

Investigators : Ms Jodi Crompton, Prof Mary Galea, Dr Bev Phillips

Hand-held dynamometry has been used to assess strength in children with spastic cerebral palsy (CP). However until recently, there has been no information as to its reliability in this population, despite its extensive use over the last 15 years as an outcome tool in intervention studies.   Consequently, it has been difficult to interpret changes in muscle strength, measured using a hand-held dynamometer, following these interventions.  

This study investigated the reliability of hand-held dynamometry when measuring isometric muscle strength in lower limbs of children with spastic Cerebral Palsy.   Twenty-three children with cerebral palsy (spastic diplegia, GMFCS levels I-III) were tested on two occasions, one week apart. Isometric strength of six muscle groups was measured (Fig. 1), based on those test positions previously reported.

Within-session ICC values were higher than 0.90 for most tests and were comparable to those reported in previous studies that have measured strength in children/adolescents with CP using more sophisticated isokinetic machines. In addition, strength tended to be higher in the less impaired limb than in the more impaired limb.

Only some muscle groups that were tested had demonstrated acceptable between-session reliability (ICC>0.70).   These muscle tests were relatively stable with the difference (CV ME ) in strength values between repeated testing sessions ranging from 13% to 27%.

The between-session reliability for the other muscle tests was questionable. The measurement errors for these muscle tests were relatively high (36% - 53%).

From this study, there are several clinical implications and recommendations regarding the testing of isometric muscle strength with a hand-held dynamometer in children with CP. Most importantly, that changes in strength should therefore be determined for each separate muscle group and limb, as the measurement error was different for each muscle test and across more and less impaired limbs.

Figure 1 . Measurement of knee extensor strength using the hand-held dynamometer

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