Hypertonia in Patients With Cerebral Palsy

Cerebral palsy (CP) affects 0.25% of newborn babies in the U.S. alone each year. Hypertonia (increased joint resistance to externally imposed motion) is a common symptom that limits function in this patient population. It may originate in spasticity, dystonia or rigidity or may be a combination of all these factors. Surgical, rehabilitation and pharmacotherapeutic methods are used to improve functional outcome in patients with cerebral palsy. These treatments are not always effective, and the amount of improvement is difficult to predict. The choice of treatment is based on clinical tests that are not objective, especially in children, and they do not allow for differentiation between various causes of increased joint resistance. As a result, ineffective treatments are offered to patients with different types of movement disorders. The complex torque devices used in research facilities to quantify the resistance of a joint cannot be easily applied in clinical settings. In previous studies, a portable measurement method was developed based on a hand-held force transducer, which allowed for the quantification of biomechanical and bioelectrical characteristics of resistance of a knee joint at different velocities. Using this method, we found different types of hypertonia that had not been previously reported in patients with cerebral palsy. It is not clear to what degree hypertonia restricts an ability to execute selected functional tasks, due in part to the considerable variability in patients with CP. If this variability could be decreased, the relationship between restricted ability and the different types of hypertonia would be easier to determine. Strong arguments exist to consider different pathophysiologies in these different types of hypertonia.

The aim of this non-invasive study is to sub-classify patients with CP based on the type of knee hypertonia, and to determine if the classification is valid during the functional tasks of walking. When validated, it can serve as a predictive model for the relationship between the clinical evaluation at bedside and functional outcome.

To classify hypertonia, the resistance of a knee joint at different velocities in knee flexion and extension and the maximum activation of stretched and shortened muscles are measured with a hand-held force transducer, an electrogoniometer, and surface electrodes in 100 patients with CP. The strength of velocity-dependent hypertonia during passive stretch and position, and/or velocity thresholds will be calculated. The knee extension and flexion muscles will be classified bilaterally as normal, or as one of the four types based on the pattern of activation of stretched muscles. To determine the impact of other impairments on the function, the maximum isometric knee flexion and extension strength and the monosynaptic reflexes of the rectus femoris muscle will be measured.

At the functional level, we will evaluate knee motion during walking. To determine the impact of hypertonia on function, the Spearman R correlation will be used to analyze data in patients within the same class. To determine if the classification holds during walking, the Cronbach's alpha coefficient will be calculated. The significance of differences will be tested at the level of significance alpha less than or equal to 0.05.

It is expected that as a result of this study, better criteria for classifying patients into predictable categories correlated to specific therapeutic responses will be established. In the future, the improvement of differential diagnoses with quantitative methods will increase the effectiveness of treatment by customizing the needs of each patient.