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Is there agreement between hand-held dynamometry, instrumented dynamometry and functional strength in children with cerebral palsy?

S REID PHD1, C ELLIOTT PHD 2, T SHILLINGTON MSC PT 2,
J VALENTINE MD 2

1. School of Sport Science, Exercise & Health, University of Western Australia, perth, WA;
2. Department of Paediatric Rehabilitation, Princess Margaret Hospital for Children, Perth, WA, Australia

Background/Objectives: To determine the agreement between lower limb strength as assessed by hand-held dynamometry and instrumented dynamometry and their relationship to functional strength in children with cerebral palsy (CP).

Design: Validation study.

Participants and Setting: A volunteer sample of 19 children with CP (spastic diplegia), aged 5-11 years (m=7.5 SD=1.8), completed the strength assessments at a tertiary setting. The cohort consisted of 9 female and 10 male participants, 14 of the children were classified as GMFCS level II and 5 as level III.

Materials/Methods: Participants completed bilateral strength assessments of their knee flexor and extensor muscle groups. Children performed familiarization trials and warm-ups prior to each assessment. Hand-held muscle testing (Model 01163, Lafayette Instrument Company, IN, USA), was completed in standardized positions [ 1 ], whereby children were required to beat the effort of the experienced assessor. Instrumental strength assessments were completed with the use of a Biodex Dynamometer (System 3, Biodex Medical Systems, Inc. NY). Participants completed three consecutive isometric maximum efforts; followed by three consecutive isokinetic maximum efforts at 60% sec and 90 % sec. Children were provided adequate rest and recovery between trails. The best effort of three trials from each condition was used in the analysis. Children completed a 6-minute walk test on the same day.

Results: The results reveal weak to moderate correlations between hand-held and Biodex isometric muscle testing for the quadriceps (r=0.39) and hamstring muscle groups (r=0.5). When the isometric conditions were compared to the isokinetic conditions, again weak to moderate correlations were found for the quadriceps (r=0.39) and hamstring muscle groups (r=0.48), irrespective of isokinetic speed. However, the two isokinetic tasks were highly correlated for both the quadriceps (r=0.84) and hamstring muscle groups (r=0.87). To assess the relationship between strength and function, the lab based measures were correlated with children’s performance on the 6-minute walk test. Weak to moderate correlations were seen between isometric strength and the 6-minute walk test. However, strong correlations existed between isokinetic strength and the 6-minute walk test for both the quadriceps (r=0.70) and the hamstring muscle groups (r=0.73).

Conclusions/Significance: It appears that there may be little correlation between measures of isometric strength in children with CP. Secondly; it appears that children’s isometric capacity may not relate to their isokinetic nor their functional strength capacity. However, isokinetic measures of strength appear to be highly related to children’s functional capacity as measured via the 6-minute walk test. This data indicate that care should be taken in interpreting measures of isometric strength in relation to the functional capacity of children with CP.

Reference:
1. Wiley ME, Damiamo DL. Lower-extremity strength profiles in spastic cerebral palsy. Dev Med Child Neurol 1998; 40:100-107.

 
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