Accuracy and reliability of single camera measurements of ankle clonus and quadriceps hyperreflexia

In people with stroke, spinal cord injury, multiple sclerosis, and other upper motorneuron lesions, ankle clonus and quadriceps spasms may limit self-care and mobility tasks. The ankle clonus drop test, which measures the plantar flexor reflex threshold angle (PFRTA), and the pendulum test, which measures the quadriceps reflex threshold angle (QRTA), provide valid and reproducible measurements of ankle clonus and quadriceps hyperreflexia. However, measuring the PFRTA and QRTA requires high fidelity motion capture systems that are limited to laboratory settings by cost and complexity. The aim of this study was to evaluate a simple, single-camera based method of measuring ankle clonus and quadriceps spasticity in clinical settings. With synchronous 3-D inertial motion capture to provide a high fidelity reference, we used a smartphone camera and green stickers to measure the PFRTA and QRTA of 14 individuals with ankle clonus or quadriceps hyperreflexia in one or both legs. This resulted in test sessions on 22 impaired legs with four repetitions of each test on each leg conducted by a student physical therapist and an experienced physical therapist. We hypothesized that the smartphone camera measurements would provide clinically useful outcome measures for assessing ankle clonus and quadriceps spasticity. To assess accuracy of the camera-measurements, we computed the bias and limits of agreement between the camera and the inertial motion capture measurements. For reliability, we computed intra-rater and inter-sensor reliability coefficients in addition to the minimum detectable change. The smartphone PFRTA biases were smaller than 0.2° and the QRTA biases smaller than 1.2°. The limits of agreement for the PFRTA were ±4.66°/ ±7.49° (student/expert), and for the QRTA were ±4.40°/±4.67°. Reliability was similar between the camera and inertial measurements of tests by both rater types: intra-rater reliability ranged from 0.85-0.90 for the PFRTA and ranged from 0.96-0.98 for the QRTA. The inter-sensor reliability when measuring the PFRTA and QRTA was 0.97 and 0.99. The minimum detectable change for the PFRTA ranged from 7.10°-8.70°, while for the QRTA ranged from 7.65°-8.27°. Based on prior research, the limits of agreement and minimum detectable change were sufficiently low for purposes of interindividual, repeatable measurement. These data show that student and experienced physical therapists using ubiquitous existing hardware such as a smartphone can produce accurate, reliable assessments of ankle clonus and quadriceps hyperreflexia in a clinical environment.