Normal side-to-side variability in knee strength in children is greater when peak torque is lower, which must be considered when evaluating unilateral injuries.
Clinicians should interpret pediatric knee strength asymmetries relative to torque output; extends normative data while leaving prospective validation open.
Isokinetic measurements of knee flexion extension in children and adolescents are a useful means of quantifying strength. In the routine clinical situation with a unilateral problem, evaluation of the affected extremity is usually based on comparisons with the unaffected side. To interpret these results, there must be an appreciation for normal side-to-side differences. Twenty-one normal, healthy children (ages 6-16 years) were evaluated using a Cybex II isokinetic dynamometer at 90 and 240 degrees/sec. In children who were able to generate peak torque values greater than 50 ft-lbs, the side-to-side differences in peak torque averaged 11 +/- 12% (mean +/- SD). A similar amount of variability has been reported with adults. For children with whom peak torque values were less than 50 ft-lbs, the side-to-side differences were much greater (mean = 22 +/- 19%). The stronger leg was equally likely to be on the nondominant side as the dominant side. Side-to-side variability was slightly decreased if the mean of several repetitions was used for comparisons rather than comparing just the single highest peak torque values.
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Henderson et al. (1993) studied this question.
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