What is known from the existing literature about the treatment of Mallet Injury using 3D printed splints? A Scoping Review Protocol

Background Mallet finger injuries are a frequent cause of hospital attendance, being the fifth most common injury in the body. They are therefore a frequent cause of hospital visits. To date, these injuries have primarily been managed using generic splints. As a generic splint provides a generic fit, patients who receive these are not provided with a custom splint experience. As the size and fit of these splints are not bespoke to the patient’s anatomy, patients may not always find the fit comfortable and may find complying with these splints difficult at times. However, an opportunity is developing within healthcare where custom splinting can be obtained for some using Three-D (3D) printing. The rationale for this review is to gain an understanding of the research that has been conducted on 3D printing of mallet injury splints. Objective The objective of this scoping review is to map the current literature on 3D printing associated with mallet finger injury. Methods The Joanna Briggs Institute (JBI) methodology for scoping reviews will be used throughout along with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Two researchers will search the databases that will include CINAHL, Embase, Cochrane, EbscoHost, Medline/Pubmed, Science Direct, Web of Science, and Google Scholar. The search will include a hand search of sources falling outside the chosen databases. Screen titles, abstracts, and full-text articles will be reviewed by two researchers independently using Rayaan software. The data extracted from the literature will first be presented in a tabulated chart followed by a narrative synthesis. Registration The protocol was registered on 6 th September 2023, with the Open Science Framework. Registration DOI: https://doi.org/10.17605/OSF.IO/FSJPK


Introduction
Mallet finger is a common finger injury.It occurs when the distal interphalangeal joint (DIPj) is unable to extend, usually following trauma to the distal phalynx 1 .In soft tissue mallet injuries, the tendon is partially torn or experiences a complete rupture, usually following a low energy trauma 2 .Bony mallet injuries, whereby a large proportion of the articular surface is involved, is associated with extension of the distal joint, following a greater force of energy 3 .Uncomplicated cases of mallet injury are treated with immobilisation of the DIPj, where the joint is held in extension for 6-8 weeks using a splint 4 .The splint must be worn continuously to keep an upward force on the injured finger until the tendon injury or fracture heals.If the splint is removed and the injured finger bends, the extensor tendon can re-rupture, meaning the splinting process needs to be repeated, which can delay healing by a number of weeks 5 .
There are many splint variations available in healthcare facilities, with most studies reporting similar results [6][7][8] .Although no gold standard exists regarding the optimum splint to use for the treatment of mallet injury, many options are available.Some examples include generic Stack splints, aluminum foam splints, dorsal glue splints and custom thermoplastic splints 9 .
A systematic review conducted in 2015 compared custommade finger splints with pre-fabricated splints 10 .They found custom splinting resulted in less skin complications as compared with custom-made splints.Another study conducted in 2022, recommended clinicians should use custom splints to best provide complete immobilisation of the DIPj which is essential to ensure recovery from the injury 11 .Although generic and custom splints are available within some healthcare facilities, they do have documented complications.Examples of these include skin complications, the splint being bulky, not being waterproof and not being well ventilated 12 .
However, the emerging field of 3D printing is showing promising alternatives to generic and hand moulded custom splints.3D printing involves printing materials by reading a digital blueprint and then printing the object layer by layer.The benefits offered by 3D printing include cost effective prototyping, time efficient modelling, the manufacture of complex geometries 13 .Most recently, 3D printing has been adapted to directly treat patients, moving away from its initial application for anatomical modelling to aid in education and planning for procedures 14 .Advances in 3D printing technology and experience have led to increased clinical use, including in personalised healthcare solutions 15 .There is now an opportunity to provide custom care to patients suffering from mallet injury using 3D printing.To progress this concept, it is essential to gain an understanding of the research conducted on this topic thus far.
To date, some reviews have been conducted within the domain of 3D printing splints and orthoses 12,[16][17][18] .The most relevant review to our realm of interest was conducted by Oud in 2021 12 .Their review primarily focused on 3D-printed orthosis for hand conditions secondary to trauma, with a concentration on their effect.They found the literature consisted of low patient numbers and had poor methodological quality.They highlighted there is an opportunity for high-quality controlled trials 12 .
The broad scope and autonomy afforded in Scoping Reviews provide a template to identify the main concepts and themes along with the research gaps associated with 3D printing and mallet splints.As this area is a novel development, the associated literature may lack high quality and homogeneous studies.A preliminary google search uncovered relevant literature available in healthcare journals.To that end, a scoping review was chosen to allow an exploration of the breadth of published literature on the topic of the treatment of mallet injury using 3D-printed splints.A holistic synthesis of the available evidence will be conducted, while locating gaps in the research and highlighting areas for further research focus.

Aim and review question
This scoping review aims to deliver a thorough comprehension of all the research available on the topic of 3D-printing of mallet splints.The JBI methodology for scoping reviews will be utilised to conduct this scoping review 19 .
The Population Concept Context (PCC) framework guided the development of the main research questions as follows:

Amendments from Version 1
• Mallet finger is a common finger injury.It occurs when the distal interphalangeal joint (DIPj) is unable to extend, usually following trauma to the distal phalynx.In soft tissue mallet injuries, the tendon is partially torn or experiences a complete rupture, usually following a low energy trauma.Bony mallet injuries, whereby a large proportion of the articular surface is involved, is associated with extension of the distal joint, following a greater force of injury.
• The text has been updated to: Participants: Eligible studies will include participants of any age with soft tissue and/or bony and/or hyperextension mallet injury due to trauma.
• Gray literature is now removed from the inclusion criteria.
• Details have been added to explain why this paper has studied mallet finger injury.This study contributed towards a PhD for the author, and their area of focus in 3D printing and mallet injuries.
• The eligibility of participants has been updated.Eligible studies will include participants of any age with soft tissue and/or bony and/or hyperextension mallet injury due to trauma.

REVISED
Participants Eligible studies will include participants of any age with soft tissue and/or bony and/or hyperextension mallet injury due to trauma.Both acute and chronic injuries will be included.

Concept
The phenomenon of interest is 3D printing of mallet splints.

Context
As 3D printing of mallet splints is a novel and emerging field, we felt it important to include both clinical and research settings.The preliminary search of the literature identified some studies detailing the design and print of mallet splints not designed for or placed on specific patients with mallet injuries.These studies describe the process and science emerging around 3D printing of mallet splints in the research setting, thus will be included as they will add a further layer of experience to the clinical studies.
The sub-questions underpinning this overarching question include: 1. What techniques and processes (examples being measuring, printing, securing) are most frequently used for 3D printing mallet splints on patients and in research settings?
2. What is the potential for 3D printing of mallet splints in the clinical field/ point of care?

Inclusion criteria
• Studies that report on 3D printing of mallet splints or 3D printing for mallet injury.
• Literature published since 1980.The earliest applications of 3D printing were in the 1980's therefore the search will range from 1980 to end of September 2023 20 .
• Only full-text publications will be included.
• Articles published in English only.

Exclusion criteria
• There are no specific exclusion criteria.

Types of sources
All study methodologies will be considered in this review.Both qualitative and quantitative data will also be included in the review.Text and opinion papers will also be considered for inclusion in this scoping review.

Methods
A preliminary search of Embase, CINAHL, Cochrane, PUBMED (Medline), Google Scholar and JBI Evidence Synthesis was conducted on September 6 th 2023.No past or ongoing scoping reviews on this subject were discovered.
The review was conducted using the JBI methodology guidance for scoping reviews.The protocol was registered on the 6 th of September 2023 with the Open Science Framework.

Search strategy
The search strategy will be created in association with a specialist librarian (MOH).The review will include both published and unpublished literature.The search strategy will be iterative throughout with the first step involving a literature search of the subsequent databases: CINAHL, EMBASE, Science Direct, Cochrane, Web of Science, MEDLINE (Pubmed), and Google Scholar.The search strategy will involve the combining of medical subject headings (MESH) and Boolean Operators.Identified keywords and English language filters will be applied.Each indexed database will include an adapted search strategy.Following this, the reference lists of each included study will be examined.The authors of eligible studies will be contacted as needed for extra material or to clarify any unclear areas in the literature.The published review will include the entire search strategy and results.The search strategy is presented in Table 1.

Study/source of evidence selection
After completing the search, all relevant references will be inserted post-collating into Endnote X8 (Clarivate Analytics, PA, USA).The screening process will be carried out using Rayaan, a web-based literature screening program.Duplicates will then be deleted.Two reviewers (UC and AS) will conduct a pilot test (n=5) by screening the title and abstracts of the search using the set eligibility criteria.Following this, the full manuscript of each chosen literature will be reviewed using the predetermined eligibility criteria.The sources of evidence excluded at full text will be recorded and detailed in this review.A 'snowball' search methodology will be adopted by reviewing the reference lists of the chosen studies to aid in identifying any literature that was not captured in the initial search.Any conflicts in relation to inclusion of specific literature will be discussed, and if not resolved, a third reviewer (NC) will be consulted.All outcomes of the literature search and the process of inclusion and exclusion will be presented clearly in the final paper.

Data extraction
A data extraction tool will be created by the researchers to aid the information extraction process.The extracted data shall provide detail on the participants, concept and context of each paper.The study methodologies utilised, along with all data relevant to the review question, what is known from the existing literature regarding the treatment of mallet injury using 3D-printed splints will be presented.

Database Exact search
Ebscohost mallet AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") EMBASE mallet AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") Scopus mallet (title, abstract, keywords) AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") (title, abstract, keywords) Pubmed mallet AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") Web of Science mallet AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") Science direct mallet (title, abstract, keywords) AND ("additive manufacturing" or "3d printing" or "3-d printing" or "three-dimensional printing") (title, abstract, keywords) Any modifications made to the data extraction tool will be presented clearly in the final review.Again, any conflicts in decisions regarding inclusion and exclusion of data that arise will be discussed and resolved if needed by a third reviewer.If additional information is needed, the relevant authors of the paper will be communicated with to provide clarity or supplementary data.The purpose of the scoping review is to describe current practices relating to the 3D-printing of mallet splints thus a critical appraisal of the methodological quality of each paper is not essential.

Data analysis and presentation
All data will first be introduced in a descriptive manner, using tables and charts to aid the explanation of the results.A narrative summary will also be included.This approach ensures a logical and descriptive summary that conforms with the objective of scoping reviews.The PRISMA-ScR will be used to guide the report 21 .

Ryan Trickett
University Hospital of Wales, Cardiff, UK The authors have acknowledged my queries and responded.I still consider that the protocol as described is narrow in scope, but will provide decisive answers concerning this somewhat niche field.
I also acknowledge that there are as yet no results or conclusions to comment on in this report.
Is the rationale for, and objectives of, the study clearly described?Yes

Are the datasets clearly presented in a useable and accessible format? Yes
Competing Interests: No competing interests were disclosed.

Ryan Trickett
University Hospital of Wales, Cardiff, UK In the introduction the authors discuss mallet finger and avulsion fractures.It is important to be clear that soft tissue mallet fingers and TRUE avulsion fractures are likely very similar injuries in terms of mechanism and outcome -true hyperflexion injuries and usually relatively low energy trauma.
So-called bony mallet fractures, particularly those involving a larger proportion of the articular surface are much more likely to be an alternative mechanism -axial loading associated with EXTENSION of the distal joint -with a greater force of injury.These injuries conversely are often best treated with slight flexion, particularly where there is articular incongruence.All mallet injuries are often clumped together in the literature but should be clearly defined in the introduction and the inclusion criteria should be clear in this regard too.
Participants -soft tissue and/or bony and/or hyperextension injuries (see above)?
Why has September 2023 been chosen as an end date to the searches?
Can the authors be more specific around their searching of the "grey literature"?It is also odd that only "full-text" articles are being included, but grey literature is being included.The 2 statements seem at odds with one another.
Has chronicity of mallet finger been considered in the inclusion criteria?
Why have non-English articles been excluded?This potentially adds a selection bias.
I worry that the search will yield no usable outcomes data and simply demonstrate what we almost certainly know already -that there is an almost complete lack of literature around 3D printing of mallet splints.A quick search using the search strategy -which seems to be somewhat restrictive -shows only 2 relevant articles.
Why was mallet finger chosen specifically for this review?
Perhaps a more useful review could be "3D printing splints for the treatment of closed digital tendon injuries" which could include mallets and Boutonniere's; or an even wider scope to include open tendon injuries?
Is the rationale for, and objectives of, the study clearly described?Yes Is the study design appropriate for the research question?Yes

Are sufficient details of the methods provided to allow replication by others? Partly
Are the datasets clearly presented in a useable and accessible format?Partly Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Hand trauma and surgery I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
is involved, is associated with extension of the distal joint, following a greater force of injury.
Comment 2: Participants -soft tissue and/or bony and/or hyperextension injuries (see above)?
Response 2: Based on your suggestion, this text has been updated to: Participants: Eligible studies will include participants of any age with soft tissue and/or bony and/or hyperextension mallet injury due to trauma.
Comment 3: Why has September 2023 been chosen as an end date to the searches?
Response 3: The plan for the search strategy was based on academic needs.
Comment 4: Can the authors be more specific around their searching of the "grey literature"?It is also odd that only "full-text" articles are being included, but grey literature is being included.The 2 statements seem at odds with one another.
Response 4: Gray literature will be removed from the inclusion criteria.
Comment 5: Has chronicity of mallet finger been considered in the inclusion criteria?
Response 5: This is a helpful suggestion.Both acute and chronic mallet injuries will be included in the criteria.
Comment 6: Why have non-English articles been excluded?This potentially adds a selection bias.
Response 6: Resource constraints within the research team preclude us from translating any literature outside of English.
Comment 7: I worry that the search will yield no usable outcomes data and simply demonstrate what we almost certainly know already -that there is an almost complete lack of literature around 3D printing of mallet splints.A quick search using the search strategywhich seems to be somewhat restrictive -shows only 2 relevant articles.
Response 7: This is a reasonable suggestion, thank you.As this work is contributing toward a PhD for the author, it was deemed important to take the opportunity to delve into any literature related to mallet injury and 3D printing, to give a thorough analysis on which to base the future studies on.
Comment 8: Why was mallet finger chosen specifically for this review?
Response 8: This study contributed towards a PhD for the author, and their area of focus in 3D printing and mallet injuries.
Comment 9: Perhaps a more useful review could be "3D printing splints for the treatment of closed digital tendon injuries" which could include mallets and Boutonniere's; or an even wider scope to include open tendon injuries?
Response 9: This is a reasonable suggestion.The language in participants has been updated to better explain the scope of the inclusion: Participants: Eligible studies will include participants of any age with soft tissue and/or bony and/or hyperextension mallet injury due to trauma.
Competing Interests: No competing interests were disclosed.

1 Reviewer
Expertise: Hand trauma and surgery I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.Version Report 11 July 2024 https://doi.org/10.21956/hrbopenres.15195.r41020© 2024 Trickett R.This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Table 2
displays the initial draft data extraction tool created by two researchers.As is typical for scoping reviews, the data extraction tool will be modified as needed throughout the iterative process of information review and extraction.

the rationale for, and objectives of, the study clearly described? Yes Is the study design appropriate for the research question? Yes Are sufficient details of the methods provided to allow replication by others? Yes Are the datasets clearly presented in a useable and accessible format? Yes Competing Interests:
No competing interests were disclosed.

have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
https://doi.org/10.21956/hrbopenres.15295.r41988© 2024 Trickett R.This is an open access peer review report distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.