The added value of kinematic evaluation of the timed finger-to-nose test in persons post-stroke

Abstract

Background: Upper limb coordination in persons post-stroke may be estimated by the commonly used Finger-to-Nose Test (FNT), which is also part of the Fugl-Meyer Assessment. The total movement time (TMT) is used as a clinical outcome measure, while kinematic evaluation also enables an objective quantification of movement quality and motor performance. Our aims were to kinematically characterize FNT performance in persons post-stroke and controls and to investigate the construct validity of the test in persons with varying levels of impairment post-stroke.

Methods: A three-dimensional motion capture system recorded body movements during performance of the FNT in 33 persons post-stroke who had mild or moderate upper limb motor impairments (Fugl-Meyer scores of 50-62 or 32-49, respectively), and 41 non-disabled controls. TMT and kinematic variables of the hand (pointing time, peak speed, time to peak speed, number of movement units, path ratio, and pointing accuracy), elbow/shoulder joints (range of motion, interjoint coordination), and scapular/trunk movement were calculated. Our analysis focused on the pointing phase (knee to nose movement of the FNT). Independent t or Mann-Whitney U tests and effect sizes were used to analyze group differences. Sub-group analyses based on movement time and stroke severity were performed. Within the stroke group, simple and multiple linear regression were used to identify relationships between TMT to kinematic variables.

Results: The stroke group had significant slower TMT (mean difference 2.6 s, d = 1.33) than the control group, and six other kinematic variables showed significant group differences. At matched speeds, the stroke group had lower accuracy and excessive scapular and trunk movements compared to controls. Pointing time and elbow flexion during the pointing phase were most related to stroke severity. For the stroke group, the number of movement units during the pointing phase showed the strongest association with the TMT, and explained 60% of the TMT variance.

Conclusions: The timed FNT discriminates between persons with mild and moderate upper limb impairments. However, kinematic analysis to address construct validity highlights differences in pointing movement post-stroke that are not captured in the timed FNT.

Keywords: Arm; Hand; Kinematic assessment; Stroke; Validity.

Fig. 1

Marker set up, events and normalized phases of the Finger-to-Nose test. A) The unfilled marker was positioned on the dorsal side of the head, and the markers with a center dot were positioned on the trunk. Three markers (placed on nose, right and left medial epicondyles) were removed after recording a static trial for modelling purpose. Left hand shows the start position (Knee touch) and right hand shows the end position (Nose touch) for the pointing phase. B) Normalized phases of the Finger-to-Nose-Test based on the time derivative of distance (a negative value denotes that the finger moves towards the nose, and a positive value denotes that the finger moves from the nose). Note that the end of the pointing phase is also the event ‘Nose touch’. Likewise, the end of the return phase is when the hand reaches the knee, for the event ‘Knee Touch’. For detailed definitions of the events a–d, see Methods

Fig. 2

Examples of movement paths and velocity profiles from the stroke group and the control group. Movement paths from the pointing phase of the markers of the index finger and the acromion in the sagittal plane, and velocity profiles with marked movement units of one person post-stroke (left panel) and one control person (right panel). The arrow indicates the direction of the movement

Fig. 3

Histograms of variable error and acromion displacement from time-matched subgroup data. Mean and 95% confidence interval for (a) variable error (mm) and (b) acromion displacement (mm) during the Finger-to-Nose test. Data from 22 controls (dark bars) are compared with data from 22 persons post-stroke (light bars)

Fig. 4

Histograms of pointing time and elbow flexion from stroke subgroup data. Mean and 95% confidence interval) for (a) pointing time (s) and (b) elbow flexion (deg) during the knee to nose movement of the Finger-to-Nose-Test. Data from 23 persons post-stroke with mild impairments (dark bars) and ten persons post-stroke with moderate impairments (light bars) are compared with data from the control group (horizontal lines indicate mean and 95% confidence interval)