Three-dimensional printing technology has existed for more than 30 years, but has only recently garnered increased attention among scientists, engineers, and the public . The rise of 3D technology is attributed to the availability of lower‐cost printers and breakthroughs in techniques and processing. In the current study we established the feasibility of 3D printing the TRI-HFT. We found that all objects of the TRI-HFT could be easily printed except for the triangular sponge and the paper. The discrepancy in dimensions of the paper and sponge are limitations associated with 3D printing process. However, it is important to note that the “paper” and “sponge” created using the 3D technology have the look and design of the original objects and that the modifications are a trade-off that needed to be accepted to make the test universally accessible and reproducible. The sponge required a new design where it will have the properties of the “sponge” but is now shaped as a square instead of a triangle. Today the TRI-HFT can be 3D printed for ~ Canadian $ 500. This cost will decline as 3D printers become cheaper. For reference, the 3D printers costed ~ £175,000 – £250,000 in the 1990’s and currently that price has decreased 10-fold with high end 3D printers costing ~ £10,000 – £35,000.
In our convenience sample of 9 individuals with chronic stroke we found that the 3D printed TRI-HFT had high inter and intra-rater reliability and moderately strong construct validity when compared to the CMSA and FMA. As seen from the results however it was not possible to rate the 9 rectangular blocks with different weight and textures from the video assessments. These are now modified (numbered) to have a clear indication of which block is being manipulated and this indicator can be seen clearly on video recordings allowing for grading from a video assessment.
Construct (Convergent) validity of the test was assessed as there are no outcome measures identified as a gold standard for measurement of upper extremity function in the activity or body structure and function domain of the ICF . The object manipulation component of the 3D TRI-HFT showed a strong correlation with the CMSA-Arm whereas there was a moderately strong correlation between 3D TRI-HFT and CMSA-Hand and the 3D TRI-HFT and FMA-Hand. Although the scoring system was initially developed with the spinal cord population in mind, the granular scoring system allows one to capture function equally effectively in stroke population as well. Moreover, the test measures function from proximal to distal and allows the assessor to differentiate between use of physiological versus compensatory grasping patterns. Since most of the study participants had severe upper extremity impairment, distal function was severely compromised and subtle differences went undetected by both the CMSA- hand and the FMA-hand. The 3D TRI-HFT however not only successfully captured arm function as seen by the strong relationship between 3D TRI-HFT and CMSA-Arm but also captured the subtle changes in hand function.
We found no statistically significant relationship between CAHAI and 3D TRI-HFT. This is not surprising given that CAHAI is designed to measure bilateral upper extremity function, whereas 3D TRI-HFT is designed to measure unilateral upper extremity function. In CAHAI, participants can score points by using the non-paretic hand to stabilize the object to assist the paretic hand in grasping an object. Participants can also hold objects with both hands to reduce the gravitational load and use the paretic hand as the supporting hand while the non-paretic hand performs the accurate arm motions, supinations, and dextrous fine motor skills. Conversely, the 3D TRI-HFT isolates the portions of each task that can be performed unimanually.
We found no statistically significant relationship between the rod, instrumented cylinder and instrumented credit card of the 3D TRI-HFT with any of the other measures. The rod in the TRI-HFT is aimed at measuring the participant’s ability to withstand eccentric forces about the shoulder joint, the instrumented cylinder and the instrumented credit card are both objective measures and they measure torque and grip strength in Nm and N, respectively using a dynamometer. The scores on these measures are influenced by the strength of the upper extremity muscles and neither the CMSA nor the FMA take into account strength of the muscles but are focused on synergies and movement isolation.
Existing upper extremity measures like the ARAT and the Fugl Meyer Scale commonly used in clinical and research settings fail to meet the demands of these environments, which experience shortages in time and personnel resources. The 3D TRI-HFT takes approximately ~ 11 min to be administered on the affected upper extremity and is cost effective. Another consideration is around importance of the findings of the current assessment tools to patients and their care givers. Stroke survivors identified the outcomes of ‘Independence, freedom and autonomy’, ‘Difficulty (with routine tasks)’ and ‘Everyday tasks’ as their three most important outcomes . The objects used in the 3D TRI-HFT are objects commonly used in activities of daily living. Besides, the scoring system measures the ability to manipulate these objects as they would be manipulated during activities of daily living and hence the score on the TRI-HFT provides an objective measure of patient’s independence with these tasks. A recent review conducted by Duncan Miller et al., quoted that though there are a 144 upper extremity outcome measures being used in individuals with stroke  none of these assessments measure what is important to stroke survivors, their carers and clinicians .There are various other review articles in literature that have looked at existing measures and most have concluded that there is no consensus amongst clinicians regarding best practices related to use of outcome measures or that existing tools are not sensitive to change in function and do not capture outcomes that are important to stroke survivors, carers and clinicians [3, 19, 30–32].
The 3D printed version of the TRI-HFT was pursued to fill this is gap in literature and because 3D printing technology is becoming increasing accessible and affordable and it ensures standardization and reproducibility of the outcome assessment tool. As far as we know the TRI-HFT is the first upper extremity measure that can be 3D printed, and hence can be accessed from anywhere in the world. This is important for clinicians and researchers as it gives them easy access to a reliable and valid tool. Further, the objects used in the test are day to day objects that can also be used as therapy tools by clinicians. From a researcher perspective, having an outcome assessment tool that is easy to manufacture in-house is important to reduce dependencies on high-cost manufacturing and out of country equipment orders. In a review conducted by Galeoto G et al., the authors concluded that a universal, validated outcome measure is needed to allow comparisons across practice and recommended that future researchers use a common set of outcome assessments .
There are certain limitations to the study like the small sample size, homogenous study sample with very limited upper extremity function and lack of gold standard outcome measures for this population which prevented a more critical comparison of the 3D TRI-HFT. Nonetheless, this test could be easily 3D printed and was found to be reliable and valid. Future studies will look at expanding the psychometric testing to the acute and sub-acute stroke population as well as those with higher levels of upper extremity function.