Introduction

One of the main causes of disability, after a spinal cord injury (SCI), is the complete or partial loss of hand and arm function [1, 2], which severely limits participation in the activities of daily living (ADL) as well as independence and quality of life [3]. Numerous scientific studies have shown that during rehabilitation, people with tetraplegia consider the recovery of hand and arm function to be a priority over not just the recovery of sexual, bowel, and bladder function but also trunk stability and walking movements [4,5,6]. Therefore, accurate measurement and assessment of upper limb function must be a critical part of the treatment and rehabilitation offered after SCI [7].

During rehabilitation, many evaluation scales can be used for the assessment of the hand and arm, including basic functions, such as moving objects. Such assessments include grasp and release tests [8,9,10,11,12,13,14] as well as more complex functions, such as getting dressed and using the toilet [15,16,17]. Some of the tools available for upper limb evaluation in people with SCI are the capabilities of upper extremity test (CUE-T), graded redefined assessment of strength, sensibility and prehension (GRASSP), Van Lieshout test (VLT). All of them show good psychometric properties and methodological qualities. However, these assessments are based on ordinal scales with rather subjective rating criteria. Among the available scales, the Jebsen–Taylor hand function test (JTHFT) is one of the most widely used non-diagnosis-specific assessment tools due to its simplicity and convenience [18]. Furthermore, the JTHFT allows to measure objectively the performance of standardized tasks. It evaluates broad aspects of those hand functions commonly used during everyday activities, and it can be administered in a short time using readily available materials. The test was designed in 1969 by Jebsen et al. as a performance-based measure for assessing manual dexterity using seven timed subtests related to functional tasks, including writing, simulated page turning, lifting small objects, simulated feeding, stacking, moving light objects, and moving heavy objects [19].

The JTHFT is very versatile when it comes to the assessment of upper limb function, which is why it is so widely used worldwide [20,21,22,23]. The advantage of having a measurement tool that can be used with different diagnostic groups is exemplified in the opportunity to test the same treatment in different populations and register improvement with comparable outcomes. The Italian version of the tool (JTHFT-IT) was initially validated in a healthy population [19]; it was subsequently tested in a sample with different disorders affecting the upper limbs, including rheumatoid arthritis [23] and hemiparesis [24]. Studies concerning other pathologies, such as cerebral palsy [25, 26], are currently underway, however, an assessment of the psychometric properties of the test has not yet been performed on people with SCI. Populations that present different diseases affecting upper limb function get different results with a test such as JTHFT. Studying the psychometric properties of this test for each population is essential in order to determine whether it is a valid tool for evaluating that particular sample. The study of psychometric properties of the JTHFT in Italian individuals with SCI not only will allow to compare outcomes of various studies internationally, but it is also useful for testing the effectiveness of the same treatment in various diseases. Finally, by using the same assessment tool, it can be defined which treatment is more effective.

Therefore, the aim of the present study was to evaluate the internal consistency, concurrent validity, and construct validity of the JTHFT-IT in an Italian SCI population with tetraplegia.

Methods

Participants

The study sample was recruited in Italy in 2019. The following inclusion/exclusion criteria were applied to all those interested in participating: (1) being assigned a level of A–D on the American Spinal Cord Injury Association Impairment Scale (AIS); (2) having had a cSCI (C2–C7 level, International Standards for Neurological Classification of SCI - ISNCSCI); (3) being older than age 18; and (4) being able to communicate in Italian well enough to understand instructions and perform the relevant activities. In addition, exclusion criteria consisted in having comorbidities that affected the functionality of the upper limb and having severe cognitive or psychiatric disability, which were determined by clinical screening. Those individuals interested in taking part in the study were informed about its purpose and methods, and their interest was recorded. Included participants signed the informed consent.

Procedures

The JTHFT-IT [19] was administered by three clinicians trained in its administration. The clinicians followed the manual (two occupational therapists and one physical therapist) and independently tested different participants from the population, all of whom had been previously screened for recruitment according to the inclusion/exclusion criteria. Once the participants were enrolled, the clinicians collected their demographic and clinical variables. The testing session included the administration of the JTHFT-IT, the Jamar dynamometer, which showed good reliability properties with a Spearman Rho correlation coefficient of 0.82 [27, 28], and the administration of the “gold standard” Van Lieshout Test Short Version in Italian (VLT-SV-IT) [9, 10] to all the participants, by the same trained rater who followed VLT-SV-IT manual.

Instruments

The JTHFT-IT comprises seven unilateral items administered using standardized procedures and verbal instructions. The tasks are performed first with the left(non-dominant) hand and then with the right hand. The functional tasks include: writing a 24-letter sentence; reading a third-grade level sentence; turning 3 in ×5 in (7.62 cm × 12.7 cm) cards during simulated page turning; picking up small common objects such as pennies, paper clips, and bottle caps and placing them in a container; stacking checkers; simulated feeding; and moving both light cans and heavier (1 lb–0.45 kg) cans. The subtests are scored by recording the number of seconds required to complete each task. The literature reports that item 1 is more difficult than the others, which means that individuals take longer to complete it than other items. For this reason, a total JTHFT score is not recommended, as it would not allow clinicians to register an improvement in fine movements [20]. The maximum execution time for the seven items is 14 min since the maximum execution time for each item is 120 s. Requiring additional time to complete the test is related to decreased hand function. In the Italian cross-cultural adaptation [20], in item 3, “Lifting small objects,” US pennies were replaced with European 2 cent coins; in item 6, “Lifting large and lightweight objects,” standard empty cans (No. 303) were replaced by empty cans measuring weight 62 g, circumference 22 cm, diameter 7.5 cm, and height 10.5 cm; in item 7, “Lifting large and heavy objects,” standard full cans (No. 303) were replaced by empty cans measuring weight 463 g, circumference 22 cm, diameter 7.5 cm, and height 10.5 cm. A stopwatch is used to time the completion of each task. Normative data from the scoring system are available for both the left and the right hands [20].

Consistent with previous studies in which the JTHFT-IT was validated in other populations [20, 24, 25], the instrument used in this study to assess the participants’ grip strength (kg) was the Jamar J00105 [19, 29], a dynamometer that calculates the strength of the flexor muscles of the hand. When the grip is measured, the participant’s arm should be at their side, with the elbow flexed at approximately 90 degrees and the forearm neutral. The wrist should be neutral, and there should be no more than 30 degrees of extension or 15 degrees of ulnar deviation. When ready, the participant is encouraged to squeeze the dynamometer with maximum isometric effort, which should be maintained for about 5 s. In addition, according to the scientific literature, instrumented strength testing has shown more reliable results than manual muscle testing (MMT) in people with SCI [29, 30].

The VLT-SV-IT [4] comprises 10 items out of the 19 items used in the complete version. It specifically evaluates the recovery of function of the arm and hand associated with ADL in people with tetraplegia. It is useful in establishing treatment and rehabilitative goals and state at the time of evaluation, providing information about how the tasks are to be carried out. The time needed to administer the tool is short (~25 min), with a total score ranging from 0 to 50. Among the evaluation scales used for the assessment of the hand and arm, the VLT-SV-IT [31] is considered the “gold standard” because in recent years, the VLT-SV-IT has been frequently considered as one of the most valuable tools for assessing hand function in cervical SCI (cSCI) [32,33,34], psychometric properties are significant, Cronbach’s alpha is 0.95 (left hand and right hand) and the intraclass correlation coefficient for test–retest reliability is 0.90 for the right hand, the left hand, and the total score. In Italy, since 2014, the Italian National Coordination of Professional Operators in Spinal Units in the functional hand rehabilitation’s protocol has indicated the VLT-SV-IT as one of the reference tools [35]. The VLT-SV-IT has also been indicated as a reference outcome measure in the Italian medicine, physics, and rehabilitation’s guidelines [36]. The VLT-SV-IT was chosen for this study because, compared with the other tests, it provides detailed information about how the tasks of the test should be carried out, which might make it more useful in establishing treatment goals [37].

Data analyses

All the statistical analyses performed in this study were carried out using the Statistical Package for the Social Sciences (SPSS) version 23.0.

The internal consistency and validity of the JTHFT-IT were assessed following the consensus-based standards for the selection of health status measurement instruments (COSMIN) checklist [31]. The internal consistency was examined using Cronbach’s alpha (α) to assess the interrelatedness of the items and the homogeneity of the scale. The α coefficient is considered sufficient at 0.70 to indicate the satisfactory homogeneity of all the items within a scale [29]. The α values were calculated separately for the left and right hands in order to record any differences.

Concurrent validity was evaluated using Pearson’s coefficient to compare JTHFT with the Jamar dynamometer measuring handgrip strength; construct validity was evaluated by using Pearson’s coefficient to compare JTHFT with VLT-SV-IT measuring other features of the upper limb. There is no cut-off score for Pearson’s correlation coefficient to determine the existence of construct validity. The linear correlation between the two scales can only be considered low, medium, or high. It is usually sufficient that there are medium or high correlations between items. The following values were considered when interpreting the results: 0 indicated no linear relationship; +1/−1 indicated a perfect linear positive/negative relationship; a value between 0 and 0.3 (or between 0 and −0.3) indicated a weak linear positive (negative) relationship through a shaky linear rule; values ranging from 0.3 to 0.7 (or −0.3 to −0.7) indicated a moderate positive (negative) linear relationship; and values between 0.7 and 1.0 (or −0.7 and −1.0) indicated a strong positive (negative) linear relationship through a firm linear rule.

Any p values less than or equal to 0.05 were considered statistically significant.

Results

Fifty-two inpatients at two spinal units met the inclusion criteria and agreed to participate; four of these were left-handed and were dropped in order to maintain consistency in the analysis. The demographic and clinical characteristics of the 48 right-handed participants are summarized in Table 1, all participants’ handedness was the same pre-injury and post-injury. The internal consistency of the JTHFT-IT showed Cronbach’s α values of 0.94 for the left hand and 0.96 for the right hand. This tool has, therefore, proved to have high values of internal consistency and high intercorrelation of items. Table 2 reports the results for the left and right hand in the total population taken as a sample.

Table 1 Demographic and clinical characteristics of the 48 participants in the reliability study JTHF-IT in people with tetraplegia.
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Table 2 Item-total analysis: Cronbach’s alpha for each item in the reliability study JTHFT-IT in people with tetraplegia.
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Pearson’s coefficient showed significant correlations for both concurrent validity (dynamometer) and construct validity (VLT-SV-IT). As shown in Tables 3 and 4, some items of the JTHFT-IT were correlated to the VLT-SV-IT; there were more correlations for the dominant right hand than the left hand. Values of correlation between JTHFT-IT and VLT-SV items are reported in Table 3 for the left hand and Table 4 for the right hand.

Table 3 Gold-standard analysis: Pearson’s correlation coefficient between the JTHFT-IT and the VLT-SV-IT, left-non-dominant-hand.
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Table 4 Gold-standard analysis: Pearson’s correlation coefficient between the JTHFT-IT and the VLT-SV-IT, right-dominant-hand.
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Discussion

The aim of this study was to evaluate the psychometric properties of the JTHFT-IT in a population with tetraplegia. The results showed that the JTHFT-IT has good internal consistency and is a valid instrument for use with this population. To evaluate the consistency of the scale, Cronbach’s α coefficient was used, and it reported a high rate of internal consistency for both the left (0.94) and right (0.96) hands. For both the left and the right hands, there is one item (handwriting) that, if deleted, would raise the alpha; but this would be a such a minimal raising that the authors decided that all items are important in assessing the functionality of the upper limb. Compared to precedent-setting studies in which the JTHFT-IT was administered in populations with rheumatoid arthritis [24] and hemiparesis [25], the evaluation of the weights of the items (item-total) showed that item 1 (writing a 24-letter sentence) was related to the other items. This is probably due to the fact that writing is a particularly common activity in both tetraplegia rehabilitation and in everyday life in comparison with the other activities from the JTHFT-IT, such as turning over a 3″ × 5″ card or stacking checkers. However, in this study, the item-total correlation for writing with the left hand, as well as ‘moving 1 lb cans’, was very low; this could be due to hand dominance, no items were deleted.

Pearson’s correlation was calculated to define the validity of the test. It showed an association between the JTHFT-IT and the dynamometer and indicated a moderate-to-strong relationship, as shown in previous studies [20, 24]. Pearson’s correlation also associated the JTHFT-IT with the VLT-SV-IT [4], which indicated the good construct validity of the test for both the left and the right hands. From the correlation analysis of JTHFT-IT and the VLT-SV, several statistically significant correlations resulted showing that as the execution time of the JTHFT-IT activities increased, the VLT-SV-IT scores decreased (better performance of the relevant task). However, the familywise alpha should be set to a significance level of 0.0003 for true significance. The law of probability would suggest that some of them are false positives; this could be the case with “Turning over a 3″ × 5″ card” and “Thumb opening.” Almost all the items of the JTHFT-IT were correlated to the VLT-SV-IT with an inversely proportional relationship, which means that as the execution time of the activity (JTHFT-IT) increased, performance in execution deteriorated (VLT-SV-IT).

Therefore, the study showed that the JTHFT-IT is a valid tool for the population with SCI because it allows data to be collected that can be compared with those obtained from the general population or from other pathologies [20, 24, 25]. Given the good psychometric properties shown, it is advisable to use it as an additional assessment tool in the evaluation of the upper limb for people with tetraplegia, in association with the other tests already in use. Compared to other scales and tools, the JTHFT is a timed diagnostic test that uses time as a parameter, allowing for more information regarding aspects of those hand functions commonly used in everyday activities, not only in the initial assessment but also in the follow-ups. Thus, it can integrate the already existing tools.

Although the Italian version of the instrument was used, this study is intended to be a starting point for the international use of the JTHFT, already validated in many languages, for the population with tetraplegia.

Although no test used in isolation can provide a realistic assessment of hand function, it is important to consider the potential usefulness of the JTHFT as part of a battery of tests [34, 35]. The JTHFT-IT seems highly suitable for use in assessments in clinical contexts, as the materials used in the test can easily be purchased, and it takes a maximum of 14 min to complete. The instructions for the test are straightforward and simple, and gaining expertise in administering the test is not time-consuming. Moreover, the JTHFT-IT concerns the potential to evaluate movements related to ADL, which makes it an ideal tool for use in a rehabilitation program for people with tetraplegia. Specifically, it can be used to evaluate the person at baseline, to register improvements, and as an outcome measure. Finally, since plenty of assessment tools are described in the literature, it is extremely important to determine which tools have the best characteristics and which have been used internationally to the greatest extent. Having specific information regarding the tools’ reliability among different categories of patients will allow researchers and clinicians to choose the right tool from among the multitude of available tools. The JTHFT is one of the few tests that, starting from generic activities, has been studied over the years in many clinical conditions. Using this tool, the authors managed to obtain important information regarding the functionality of the upper limb in different pathologies, which could be used and compared in further studies.

Limitations of the study

This study had a number of limitations. Consistent with previous studies [20, 24, 25], the participants’ grip strength was tested using a Jamar dynamometer; however, since JTHFT assesses fine hand use, the use of a pinch gauge could also have generated interesting results. The relatively small sample of participants with tetraplegia represents another limitation, as the main differences between the different injury levels and AIS scale ranges could not be examined, moreover, by limiting the study to right-handed subjects only, the scope and relevance of this type of evaluation test are limited. Further study could consider the level and completeness of the lesion crossed. Moreover, all participants were right-handers; this did not allow stratification for hand dominance, and future studies should consider this element. Furthermore, it was not possible to evaluate the inter-rater reliability of the tool in the population with SCI [19, 21,22,23, 29].

Furthermore, although in Italy the VLT is considered a gold standard tool for the evaluation of upper limb in people with SCI, this test is not widely used outside of a few European countries, therefore, future studies should consider the use of different outcome measures. Another limitation is represented by the lack of the upper limb motor scores, which implies missing a comprehensive picture of participants, in fact they were a sample of convenience with no available data to describe their upper limb strength or hand function.

Finally, we agree with the authors of previous studies that the JTHFT itself has certain limitations [38,39,40,41]. The score for the test does not reflect the different compensation mechanisms available for positioning the upper limb, moreover there is a lack of an accurate assessment of finger opening. Thus, prior to starting the test, it is important to provide appropriate instructions as well as to ask participant not to change their strategy while being tested. In clinical trials that use the JTHFT score as an end point, participants should be asked not to change strategies during follow-up evaluations [42]. Furthermore, based on clinical experience, individuals with moderate-to-sever functional impairment are often not testable with the JTHFT as the tasks are too difficult for people with limited hand function.

Conclusion

In conclusion, despite the limitation and the need of a study of the sensitivity to change and of the minimally detectable difference, the findings of this study suggest that the JTHFT-IT is a useful tool for assessing the functioning of the hand and the harm during ADL among people with tetraplegia. The JTHFT is very versatile for the assessment of upper limb function, and it allows evaluating individuals both during the rehabilitation phase, in order to determine any functional limitations and/or recovery, and in follow-ups, in order to evaluate the effectiveness of the functional hand over time.