The protocol was registered on the PROSPERO international prospective register of systematic reviews, registration number CRD42020182487. The systematic review will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and guidelines [27, 28].
The PICOS (Population, Intervention, Comparison, Outcome, Study Design) framework will be used as a template for defining eligibility criteria for literature search . Characteristics for clinical studies are as follow:
Research involving animal and human models (clinical studies as well as in vitro research) will be considered for review, without exclusion relating to sex or age. Basic science studies must include human cells isolated from a living model. Studies meeting eligibility criteria will apply to acute orthopedic musculoskeletal injury, chronic orthopedic musculoskeletal conditions, or an artificial disease model. Articles will be excluded if they do not relate to orthopedic intervention.
Research meeting inclusion criteria will involve the use of mesenchymal stem cells and/or connective tissue obtained from Wharton’s Jelly. Studies will be excluded if Wharton’s Jelly is not the experimental examined cell type. Studies involving umbilical derived stem cells will be excluded unless the study specifies the use of Wharton’s Jelly. Studies will be excluded if they report the use of Wharton’s Jelly derived mesenchymal stem cells in combination with other cell populations.
Comparators considered will include placebos, non-injury models, acute injury models, non-injury models, and gold standard treatments for orthopedic injury.
For basic scientific research, studies relating to human musculoskeletal injury via histological or biochemical measures will be included. For clinical research, studies pertaining to human or animal orthopedic musculoskeletal injury via histological and/or biochemical measures and functional scores (pain, activity, quality of life, etc.) will be included.
Observational studies (cohort, cross-sectional and case-controlled prospective or retrospective studies) or randomized controlled trials comparing outcomes of connective tissue derived from Wharton’s Jelly with control, experimental therapy, or gold standard treatment at any follow up period will be included. Systematic reviews will only be examined to identify further studies for inclusion, and results of meta-analysis will not be included in the analysis. With regard to publication year, all studies published to date will be included.
A systematic search will be conducted in PubMed, ScienceDirect and Google Scholar databases of English, Italian, French, Spanish and Portuguese language articles published before May 2020. Secondary searching of reference lists of key articles and reviews will be undertaken to identify any additional studies potentially missed in electronic search.
The search and selection process will be based on the PRISMA checklist and flow diagram based on the eligibility and inclusion criteria previously outlined. A web-based reference software system (RefWorks) will be used for data management.
The study selection process will be performed independently by two reviewers. Screening of abstracts will be performed, and full text articles will be retrieved and uploaded to the reference software. A thorough secondary screening will be performed independently by two reviewers. The secondary screening of the full text articles will eliminate studies that do not meet inclusion criteria.
Data extraction from articles that meet inclusion criteria will be performed by two independent reviewers. Data extracted and synthesized will include authors, publication year, study design, group controls, group interventions, outcome measurement, and outcome assessment. Customized forms will be used in the data extraction and collection process. The primary authors will be contacted via email for any information necessitating clarification.
Relevant items of population, problem, intervention, comparison, and outcome will be extracted and included. For basic scientific research, relevant histological and/or biochemical measures will be included. For clinical research, all histological measures, biochemical measures and functional scores will be included.
Risk of bias
Multiple tools will be used to assess the risk of bias for included studies. The Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) risk of bias tool will be applied to animal studies . Ten domains will be addressed related to selection bias, performance bias, detection bias, attrition bias, reporting bias, and other biases. The Risk Of Bias In Non-randomized Studies of Interventions (ROBINS-I) tool will be used to assess observational and quasi-randomized studies . Seven domains will be utilized to assess risk including: confounding, participant selection bias, classification bias, deviation bias, bias due to missing data, outcome measurement bias, and bias in selection of reported results. Studies will be judged to have no information or a low, moderate, serious, or critical risk of bias. For randomized control trials, the Risk of Bias 2 (RoB 2) tool will be used to establish risk of bias . Five domains including biases arising from the randomization process, due to deviations from intended interventions, due to missing outcome data, in measurement of the outcome, and in selection of the reported result will be analyzed. Overall risk of bias will be determined to be low, some concerns, or high. All included studies will be independently scored by two reviewers, and consensus reached by discussion.
Data synthesis and meta-analysis
Data synthesis and meta-analysis will be performed separately for clinical and pre-clinical studies, following the guidelines published by Hooijmans et al . Given the sparsity of homogenous research, a qualitative analysis of common outcome variables will be conducted. Subgroups chosen for analysis will include cells derived from Wharton’s Jelly versus experimental therapy and/or control. Results of meta-analyses extracted data will be summarized in tables and narrative interpretation provided, with emphasis on outcome measures.