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Year : 2021  |  Volume : 4  |  Issue : 1  |  Page : 34-39

Reliability of peg restrained intrinsic muscle evaluator for measurement of intrinsic hand muscle strength in adults with tetraplegia

1 Department of Physical Medicine and Rehabilitation, McGovern Medical School, University of Texas Health Science Center at Houston, The NeuroRecovery Research Center, TIRR Memorial Hermann, Houston, TX, USA
2 Department of Neurosurgery, Houston Methodist Neurological Institute, Houston, TX, USA

Date of Submission29-Jul-2020
Date of Decision30-Sep-2020
Date of Acceptance09-Oct-2020
Date of Web Publication22-Feb-2021

Correspondence Address:
Dr. Nuray Yozbatiran
TIRR Memorial Hermann, 1333 Moursund St, Room 315, Houston, TX, 77030
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jisprm.jisprm_27_20

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Background: The manual muscle test (MMT) is the traditional method to assess the intrinsic hand muscle test. However, this test is qualitative and subjective. A device capable of rapidly measuring motor output along a linear scale may be of value in the evaluation of hand recovery from any neurological impairment. Objective: To demonstrate inter-rater reliability of the Peg Restrained Intrinsic Muscle Evaluator (PRIME) device for measuring intrinsic hand muscle strength in adults with impaired hand functions. Methods: 16 subjects (2 female, 14 male, mean age=47±15 years) with cervical spinal cord injury were enrolled. Intrinsic hand muscle strength of adults were performed by two-tester with use of PRIME device and manual muscle testing, within the same session. Inter-tester correlation was tested by Pearson's correlation and Intraclass correlation coefficient (ICC). Results: Intraclass correlation coefficients for hypothenar, first dorsal interosseous, abductor pollicis brevis and opponence pollicis muscles ranged from 0.7 to 0.8 with hypothenar muscle test being lowest ICC=0.7 and thumb opposition highest, ICC=0.81. Conclusion: Results from this study suggest that PRIME device demonstrates good reliability within testers for quantified measuring of intrinsic hand muscle strength. Further use of PRIME in clinic will aid in diagnostics, medical decision making and evaluation of rehabilitation progress in patients with cervical spinal cord injury.

Keywords: hand, intrinsic muscle, strength, tetraplegia

How to cite this article:
Yozbatiran N, Russell MB, Korupolu R, Grossman R, Toups E, Francisco GE. Reliability of peg restrained intrinsic muscle evaluator for measurement of intrinsic hand muscle strength in adults with tetraplegia. J Int Soc Phys Rehabil Med 2021;4:34-9

How to cite this URL:
Yozbatiran N, Russell MB, Korupolu R, Grossman R, Toups E, Francisco GE. Reliability of peg restrained intrinsic muscle evaluator for measurement of intrinsic hand muscle strength in adults with tetraplegia. J Int Soc Phys Rehabil Med [serial online] 2021 [cited 2022 May 20];4:34-9. Available from: https://www.jisprm.org/text.asp?2021/4/1/34/309891

  Introduction Top

Cervical spinal cord injury (SCI) may result in a wide range of abnormalities in hand motor function.[1],[2],[3] A number of standardized tests have been available to measure the hand functions for monitoring recovery, assessing therapeutic interventions and predicting prognosis. However, each scale has its limitations. Some require special skills to administer and some lack in sensitivity to quantify small motor deficits or detect small changes after rehabilitative interventions.

To date, one of the most commonly used traditional method of hand muscle strength testing is the manual muscle test (MMT). The MMT was developed by Lovett and first described by Wright in 1912[4] is a qualitative and subjective method. Muscle strength is graded based on muscle performance in relation to the magnitude of manual resistance applied by the examiner. Perceived amount of resistance is graded by using the Medical Research Council (MRC) 6-point scale from 0 (no contraction) to 5 (full power).[5] However the scores can be affected by variables extrinsic to the individual tested. Such variables include the experience of examiners with MMT to discern subtle changes in muscle strength (in particular between grades 4 and 5), and the relative size and strength of the examiner compared to the subject. This inherent subjectivity of manual muscle testing often leads clinicians and researchers to seek for quantified, reliable techniques.

Therefore, there is a need for objective, reliable and sufficiently sensitive technique for measurement of purely intrinsic muscle strength in current clinical practice. In this context, several devices are introduced as an alternative objective measurement of hand muscle strength.[6],[7],[8],[9] However, these devices require extensive clinician involvement and force participants into contorted positions that lead to high interobserver error ranging from 37% to 52% and present poor sensitivity.[7],[8]

A device capable of rapidly measuring motor output along a linear scale may be of value in the evaluation of hand recovery from any neurological impairment. People with cervical-level SCI reported regaining of arm and hand functions will significantly improve their independence level in daily living activities and ultimately improve quality of life.[10] In this context, evaluation of capabilities of remaining hand function is of particular importance in planning surgical reconstruction of hand functions (i.e., tendons transfers)[11],[12] evaluation of neuroprosthetics,[13] functional electrical stimulation[14] activity-based interventions[15],[16] as well as screening of prognosis.[17]

A novel device, the peg restrained intrinsic muscle evaluator (PRIME) has the potential to overcome these shortcomings and quantitatively measure intrinsic muscle strength. PRIME is specifically designed to isolate specific intrinsic muscles or functional muscle groups using a peg restraint mechanism.[18]

The goal of the present study was to evaluate inter-rater reliability of the PRIME in measuring hand intrinsic muscle strength in adults with cervical SCI.

  Materials and Methods Top

Study participants

Sixteen subjects (2 female, 14 male) ranging from age 24 to 65 (mean age = 48 ± 14 years) with cervical SCI were enrolled from a convenience sample at an outpatient rehabilitation clinic. Inclusion criteria were; age at least 18 years; diagnosis of a complete or incomplete cervical lesion as defined by the American Spinal Injury Association classification; no previous central or peripheral nervous system insult interfering with the interpretation of the results; no significant trauma to forearm or hand and no condition (e.g., severe arthritis, extreme shoulder pain) that would interfere with valid administration of the measures or with interpreting motor testing. Participants who could not provide informed consent; had orthopedic limitations of either upper extremity that would affect performance on the study were excluded.

The study was approved by the Committee for the Protection of Human Subjects of the University. All participants gave written consent before participation.

Testing device

The PRIME was developed as a portable testing device and is composed of three major components: a foldable pegboard, a force transducer, and a hand-held dynamometer [Figure 1].
Figure 1: The pegs (1) enable isolation of intrinsic hand muscles and minimize recruitment from extrinsic muscles. The force sensor (2) within the FTE delivers high accuracy. The bolt (3) operates so that the FTE can rotate freely and move up or down the vertical axis to accommodate a wide range of hand sizes and morphologies. The PDA and custom software (4) delivers powerful sampling, portability and data export

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The pegboard base and corresponding pegs act as a restrain mechanism that allows for the isolation of specific intrinsic hand muscles and minimizes contributing forces from other muscles. Second, the force transducer enclosure (FTE) is a black plastic module that holds the force sensor, amplification circuitry and a battery source. Within the FTE is an amplification circuitry, a battery and a load cell (LCL-010; Omega Engineering, Inc., Stamford, CT) rated to 4.5 kg with a resolution of 0.25%. The FTE can rotate 360° and lock automatically at any vertical position. An adjustable hook and loop strap is used to interface the force sensor with the patient's individual finger. Lastly, the digital display unit utilizes National Instrument's portable data acquisition technology and a Bluetooth Module. The custom software on the digital display unit displays applied force on a dial and automatically determines peak force at the completion of a test. In addition, the digital display unit enables patient data storage and the export of a data file to facilitate further analysis. The design of the PRIME device enabled testing of a wide range of hand sizes and morphologies. Five finger movements were tested; thumb opposition (opponens pollicis), thumb palmar abduction (abductor pollicis brevis), index finger abduction (first dorsal interosseous), little finger abduction (abductor digiti minimi) and II-V finger flexion (lumbricals).

Testing protocol

Testers: In order to standardize testing procedure and minimize inter-tester variance, testers were trained prior to performing and recording of actual data.

Testing procedure

The nature and procedure of PRIME testing was explained and demonstrated [Figure 2]. Participants were allowed to perform one test trial. During the PRIME testing, the device was placed on a height adjusted table in front of the participants while they were seated in an upright position comfortably in their chair. The hand being tested was placed on the pegboard in a predetermined position. The tester placed the loop strap around the finger and adjusted the length to eliminate slack. Pegs were placed in the pegholes in a standardized manner (e.g., along the forearm, wrist, hand and fingers) to ensure that the force measured comes only from the desired muscle, without compensatory help from other muscle/tendon units. A direct line of pull was required to eliminate off-axis loading. Therefore the FTE was positioned perpendicular to the force being measured. The subjects were instructed to “pull as hard as possible.” An isometric peak force was automatically calculated and stored. Tests were repeated three times and average score was recorded for analysis.
Figure 2: Position and peg placement for muscles of interest (a) Thumb opposition, (b) Thumb abduction, (c) Index finger abduction, (d) Little finger abduction, (e) II-V finger flexion

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Testing of thumb opposition

The subject's hand was placed on the pegboard with the forearm in mid-position. The back of the hand faces the FTE. The loop was placed around the thumb at proximal phalanx, and the height of the FTE was adjusted to the level of thumb. Pegs were placed on medial and lateral side of the wrist, palm and dorsum of the hand and distal to metacarpophalangeal joints of four fingers. The subject is instructed to move thumb away from the palm towards the little finger.

Testing of thumb palmar abduction: The subject's forearm and hand was placed as above (thumb opposition) testing position. The loop was placed around the thumb at interphalangeal joint and the height of the FTE was adjusted to the level of thumb. Pegs were placed on medial and lateral side of the wrist, palm and dorsum of the hand and distal to metacarpophalangeal joints of four fingers. The subject is instructed to move thumb away from the palm in a perpendicular direction.

Testing of index finger abduction

The subject's hand was placed on the pegboard with the forearm in pronation. The loop was placed around proximal phalanx of index finger, and the height of the FTE was adjusted to the level of index finger. Pegs were placed on radial and ulnar side of the wrist, medial side of thumb and middle finger. The subject is instructed to move index finger toward thumb.

Testing of little finger abduction: The subject's hand was placed on the pegboard with the forearm in pronation. The loop was placed around proximal phalanx of little finger, and the height of the FTE was adjusted to the level of little finger. Pegs were placed on radial and ulnar side of the wrist, medial side of index finger, lateral side of ring finger distal phalanx. The subject is instructed to move little finger away from the ring finger.

Testing of finger flexion (II-V)

The subject's hand was placed on the pegboard with the forearm in mid-position. The loop was placed around proximal phalanx of all four fingers (II-V) and the height of the FTE was adjusted to the level of middle finger. Pegs were placed on palmar and dorsal side of the hand, and on both medial and lateral side of forearm. The subject is instructed to move fingers away from the FTE toward palm.

Manual muscle testing

MRC grading system was used to manually test and grade the strength of five specific muscle groups.[5] MRC use a scale between 0 and 5 to differentiate 5 = muscle contraction against full resistance, 4 = strength reduced, but contraction can still move joint against resistance, 3 = active movement against gravity, ty, 2 = active movement with gravity eliminated, 1 = trace of contraction or fasciculations are observed, and 0 = no muscle contraction/movement.

All tests were performed on the same day by two different testers. Subjects were given sufficient rest breaks in order to eliminate fatigue from repeated testing.

Data analysis

Mean and standard deviation values were calculated for descriptive data from each measurement. Inter-rater reliability was determined using the intraclass correlation coefficients (ICC) and associated 95% confidence intervals for all data (PRIME and MMT).

Convergent validity was analyzed by using Pearson correlation coefficient, in order to evaluate the relationship between PRIME and MMT scores. Mann–Whitney U test was used to compare to PRIME and MMT values between two testers.

All calculations were completed using IBM SPSS Statistics 23 (IBM Corp. Released 2015. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp.) and a p value less than 0.05 was considered as statistically significant.

  Results Top

Data from 16 subjects (2 female, 14 male; average age 48 ± 14, range:) with cervical SCI are presented in this study.

Strength of specific muscle groups of 16 subjects, evaluated with PRIME device and MMT are presented on [Table 1] and [Table 2]. There was no significant difference between Examiner 1 and Examiner 2 average scores for selected group of manual muscel testing and PRIME scores (P > 0.05). Also the grip and pinch scores demonstrated no statistically signficinat difference (P > 0.05). Representative data from a single subject to demonstrate repeatability of the test scores by examiner 1 and examiner 2 are shown in [Figure 3].
Table 1: Intrinsic hand muscle strength with peg restrained intrinsic muscle evaluator (kgf)

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Table 2: Intrinsic hand muscle strength with manual muscle testing

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Figure 3: Representative data from Examiner 1 and Examiner 2 for intrinsic hand muscle strenght testing with peg restrained intrinsic muscle evaluator device. Each muscle testing is performed three times

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Some of the participants who tested as Grade “0” on MMT, were actually tested to have some degree of muscle force when measured with PRIME. For example both examiners were able to record force readings for thumb oppositon, MMT = 0, PRIME = 0–0.3 kgf (examiner 1), 0.2 kgf (examiner 2); thumb palmar abduction, MMT = 0, PRIME = 0–0.1 kgf (examiner 1), 0.1–0.5 kgf (examiner 2); lumbricals, MMT = 0, PRIME = 0–0.0 kgf (examiner 1), 0.4 kgf (examiner 2); index finger, MMT = 0, PRIME = 0–0.0 kgf (examiner 1), 0.1 kgf (examiner 2), little finger, MMT = 0, PRIME = 0–1.2 kgf (examiner 1), 0.9 kgf (examiner 2).

Inter-examiner reliability for PRIME has shown highest for index finger abduction (0.87) whereas the highest score for MMT was revealed as thumb opposition (0.96). Thumb opposition exhibited highest correlation with PRIME testing and little finger abduction for MMT. The ICC was lowest for little finger abduction and finger flexion in PRIME testing whereas thumb opposition exhibited lowest score for MMT [Table 3].
Table 3: Pearson correlation and intraclass correlation coefficient for peg restrained intrinsic muscle evaluator and manual muscle test intertester

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  Discussion Top

This article describes a new method of a quantified measure of hand intrinsic muscle strength in people with cervical SCI.

PRIME device was successfully administered in all participants and results have shown that the device was capable to detect finger muscle forces regardless of the level (C3–C7) and degree of impairment (complete paralysis vs. some preserved motor functions).

One of the interesting finding in this study was the ability of PRIME to detect muscle force, even though these muscles were reported as Grade “0” according to MMT. From a clinical point of view, even smallest change in muscle force is significant in tracking recovery and regeneration process. For example a change from “0” to “1” on MMT within 1-month postinjury has shown to be a predictor of recovering to grade ≥3/5 by 12 month postinjury.[19] However, a device that is capable to differentiate a muscle force from absolute “0” on a ratio scale has potential to provide reliable information about muscle activity than a subjective method that relies solely on examiner's subjective assessment of palpable muscle activity (MMT). Therefore objective measurements should be an integral part of carefully planned rehabilitation programs to identify patient-tailored physical therapy or occupational therapy programs, medications and planning of surgical interventions. Serial and accurate assessment of intrinsic hand muscle strength is also needed to track the progress or deterioration of motor recovery after injury. Normative values stratified by age and gender can influence gross hand strength and therefore imperative for comparison.[20]

The results of this research demonstrate in a group of adults with impaired hand functions, the inter-tester reliability of the PRIME tested on five hand muscles, is highly reliable. However, compared to MMT it requires precise protocol with standardized instructions to achieve high reliability scores. Compared to hand-held myometers PRIME device provides a standardized peg placement that (a) Restrains hand and wrist movement (b) Isolates individual intrinsic muscles or muscle groups related to a specific movement, (c) Reduces contribution of extrinsic muscles. This design feature allows more precise testing protocol and decreases the risk of variations in serial testing, while hand-held myometers are highly dependent on counterforce by the tester and angle of force generation.

The PRIME device has been successfully tested in pediatric population. Xu et al.[18] enrolled 119 children and adolescents between 4 and 16 years to establish normative values and determine inter-and intra-rater reliability. Gender and age were significant predictors of strength. The authors reported that mean index and small finger abduction strength was significantly lower than the thumb abduction and opposition in both genders. Similarly, we found small finger abduction and index finger flexion strength lowest among other muscles. While the ICC coefficients ranged from 0.85 to 0.94 for inter-rater reliability, in Xu et al.,[18] study, our findings demonstrated an ICC range between 0.70 and 0.81.

Jacquemin et al.,[21] analyzed hand intrinsic muscle strength (thumb opposition, index finger abduction, and little finger abduction) to identify thresholds for serial change in strength that can be useful in monitoring neurologic recovery, either indicator of clinical improvement or decline in patients with SCI. They used a handheld digital myometer and demonstrated good inter-rater reliability between healthy volunteers and patients with SCI.

According to the testers the testing method was simple, fast and adequate to quantify muscle strength. Participants had no difficulty in following instructions (no more than minimal verbal communication was required).

One of the limitations of our study is small sample size. Lack of normative data from healthy adults is another limitation. Because test performance can be influenced by many intrinsic and extrinsic factors, normative data adjusted to gender, age and hand dominance is important to adequately interpret patient's score on muscle strength. Additionally, normative data from healthy adults is particularly critical in serial evaluation of hand functions and for comparison between various conditions affecting hand muscle strength. Furthermore, these values will be valuable for clinical decision-making process, and to quantify and guide rehabilitative progress. Finally, specific positioning of hand and fingers are limiting this testing procedure to participants who don't exhibit severe muscle tone or joint contracture. Further research is recommended to define normative values, determine the inter-and intra-tester reliability of PRIME device in healthy adults, and its usability to assess intrinsic hand muscle strength in relatively larger sample of patients with neurological and/or orthopedic impairment.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Dolbow DR, Gorgey AS, Recio AC, Stiens SA, Curry AC, Sadowsky CL, et al. Activity-based restorative therapies after spinal cord injury: Inter-institutional conceptions and perceptions. Aging Dis 2015;6:254-61.  Back to cited text no. 16
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Wu L, Marino RJ, Herbison GJ, Ditunno JF Jr. Recovery of zero-grade muscles in the zone of partial preservation in motor complete quadriplegia. Arch Phys Med Rehabil 1992;73:40-3.  Back to cited text no. 19
McGee C, Hoehn A, Hoenshell C, McIlrath S, Sterling H, Swan H. Age- and gender-stratified adult myometric reference values of isometric intrinsic hand strength. J Hand Ther 2020;33:402-1000.  Back to cited text no. 20
Jacquemin GL, Burns SP, Little JW. Measuring hand intrinsic muscle strength: Normal values and interrater reliability. J Spinal Cord Med 2004;27:460-7.  Back to cited text no. 21


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]


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