Excellent test–retest and inter-rater reliability for Tardieu Scale measurements with inertial sensors in elbow flexors of stroke patients
Introduction
A variety of patients with neurological disorders suffer from spasticity, which is apparent in 38% of the stroke patients and a major source of disability [1], [2]. Spasticity hinders voluntary movements, and prolonged spasticity may lead to pain and severe reduction of joint range of motion (ROM) [3]. These ‘contractures’ and spasticity itself often reduce function of the limbs and complicate patient care [4]. Therefore, adequate management of spasticity is a major challenge in rehabilitation medicine [1].
To evaluate spasticity treatments, like Botulinum toxin therapy, accurate quantification of spasticity is needed [5]. Although several devices to quantify spasticity are available for research purposes, all have to be used in a controlled setting, are complex, time consuming and not easy to use in a clinical setting [6], [7], [8]. In clinical practice there is no universally used measure to quantify spasticity [9]. Rating scales, like the Ashworth Scale (AS) [10] and the Modified Ashworth Scale (MAS) [11], are most often used [12]. However, their validity has been questioned because they focus on grading resistance and do not take the velocity-dependent characteristic of spasticity into account [6], [13]. Moreover, the inter-rater reliability of both scales is poor, and influenced by the experience of the individual rater [14]. Furthermore, because of their ordinal rating, the sensitivity of the scales to detect change is limited.
The Tardieu Scale takes the velocity-dependent characteristic of spasticity into account and is therefore suggested to be a more appropriate measure for spasticity than the AS [13], [15]. It compares the response of the muscle to passive stretch at both slow and fast speeds [16], [17]. At fast stretch an increase in muscle tone reflex is elicited and can be felt as a ‘catch’. The joint angle where this catch is felt, in reference to the angle where muscle stretch is minimal, is called the ‘Angle of Catch’ (AoC; equal to Tardieu's R1). As the severity of spasticity increases, the AoC appears earlier in the passive ROM (Tardieu's R2), and the Tardieu score (passive ROM-AoC) becomes higher [18], [19].
Also, for the Tardieu Scale the rater's experience is of considerable influence and its reliability has been questioned for various patient groups [17], [20]. Mackey et al. found poor test–retest reliability for Tardieu Scale measurements of elbow flexors of children with hemiplegia [21]. Ansari et al. showed that the inter-rater reliability for Tardieu Scale measurements with goniometry of elbow flexors of adult patients with hemiplegia is insufficient [22].
Recently, van den Noort et al. stated that goniometry is an imprecise method to measure the true AoC due to inaccurate repositioning of the joint to the position where the catch was felt [23]. Newly available inertial sensors (IS) can accurately measure orientation in space [24]. Van den Noort et al. showed that IS can measure the angle of catch in calf muscles of children with cerebral palsy, and advised to apply IS instead of goniometry when a precise measurement of the AoC is required [23]. IS are small, portable and easy to use, and if they can quantify spasticity reliable they can be of great value in clinical practice.
The present study examines the test–retest and inter-tester reliability of Tardieu Scale measurements in spastic elbow flexors of stroke patients, based on both goniometry and IS. Because the lower arm does not have to be repositioned for AoC analysis with IS, measurement error was expected to be lower for IS than for goniometry. It was therefore hypothesized that both test–retest and inter-rater reliability would be better for IS than for goniometry.
Section snippets
Participants
A total of 13 stroke patients (mean age 70.2 ± 12.3 years; 7 men), from the stroke department of the Laurens Antonius IJsselmonde nursing home, with spasticity in their elbow flexors (MAS 2–3, quantified by an experienced physiotherapist) participated in this study. Patients with co-morbidity or with serious cognitive problems were excluded from participation. All patients signed informed consent, approved by the nursing home.
Measurements
The testing protocol was based on the dynamic part of the Tardieu Scale
Results
Both physiotherapists extended the elbow in all fast measurements within 1 s and they felt a catch for each participant. Attaching the IS, performing one session and then removing the devices took less than 15 min.
Discussion
As hypothesized, inter-rater reliability was better for IS than for goniometry. Because IS detect the AoC objectively; computer analysis detected the catch instead of the rater himself. Most likely, different raters will use different strategies to locate the catch and reposition the arm, which will influence goniometry results. However, influence of the rater in AoC measurements with IS is minimized and, consequently, inter-rater reliability for IS is better than for goniometry.
The inter-rater
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