Reliability and validity of pendulum test measures of spasticity obtained with the Polhemus tracking system from patients with chronic stroke

Abstract

Background: Spasticity is a common impairment accompanying stroke. Spasticity of the quadriceps femoris muscle can be quantified using the pendulum test. The measurement properties of pendular kinematics captured using a magnetic tracking system has not been studied among patients who have experienced a stroke. Therefore, this study describes the test-retest reliability and known groups and convergent validity of the pendulum test measures obtained with the Polhemus tracking system.

Methods: Eight patients with chronic stroke underwent pendulum tests with their affected and unaffected lower limbs, with and without the addition of a 2.2 kg cuff weight at the ankle, using the Polhemus magnetic tracking system. Also measured bilaterally were knee resting angles, Ashworth scores (grades 0-4) of quadriceps femoris muscles, patellar tendon (knee jerk) reflexes (grades 0-4), and isometric knee extension force.

Results: Three measures obtained from pendular traces of the affected side were reliable (intraclass correlation coefficient > or = .844). Known groups validity was confirmed by demonstration of a significant difference in the measurements between sides. Convergent validity was supported by correlations > or = .57 between pendulum test measures and other measures reflective of spasticity.

Conclusion: Pendulum test measures obtained with the Polhemus tracking system from the affected side of patients with stroke have good test-retest reliability and both known groups and convergent validity.

Figure 1

Line drawing illustrating pendulum test performed with subject supine and leg swinging freely with motion sensors attached and weight secured at ankle.

Figure 2

Representative pendulum test tracing with angle of first reversal identified (large trace) and area under curve highlighted (small insert).

Figure 3

Pendulum test traces from all subjects. Those on the left are from the unaffected side while those on the right are from the affected side. Blue dashed lines represent traces obtained without weights whereas red solid lines represent traces obtained with weights.