Review Reports - Research Landscape of Stem Cell Applications in Musculoskeletal Tissue: A Scoping Review

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

Information on stem cell dosage and treatment outcomes is still lacking. Both would be welcome additions, but are apparently not the focus of this work, which in my opinion significantly diminishes its scientific value. That aside, the manuscript has been significantly improved.

Author Response

We thank the reviewer for the time and effort devoted to evaluating our manuscript entitled “Research Landscape of Stem Cell Applications in Orthopedic Tissue: A Scoping Review” (Manuscript ID: cells-4172187). We sincerely appreciate the detailed and constructive comments, which have been invaluable in guiding substantial revisions to improve the clarity, rigor, and presentation of our work.

In response to the reviewers’ comment, we have undertaken extensive revisions to the manuscript. All changes have been clearly highlighted in the revised version, and detailed, point-by-point responses to each comment are provided. The key revisions include the following:

Comments:

Response:

Thank you for your constructive feedback. We completely agree that data on cell dosage and clinical outcomes are vital for translating preclinical findings into practice.

While a detailed quantitative synthesis of these dosage and outcomes fell outside the descriptive scope of this scoping review, we recognize that their absence is a point of concern. To address this and clarify our position, we have made the following updates:

In Section 4.1.6 Biological Rationale Underlying Observed Preclinical Trends (Page 21, Lines 559-562), we expanded a discussion on how the current lack of standardized dosing frameworks and inconsistencies in reporting methodologies (units, schedules, etc.) hinder reliable cross-study comparisons and the assessment of dose-dependent effects. Specifically, we added the following text to highlight the issue of reporting variability:

“Inconsistencies in reported cell dosages hinder direct comparisons between studies. Variations in dosing units, administration schedules, and reporting methodologies limit the ability to assess dose-dependent effects accurately, underscoring the need for standardized dosing frameworks in orthopedic stem cell research.”

In Section 4.3 Limitations, Critical Gaps and Future Considerations (Page 24, Lines 713-719), we have explicitly acknowledged the exclusion of dosage and outcome extraction as a limitation. We explained that the high variability in existing literature makes a meaningful synthesis challenging at this stage, and we have formally suggested this as a priority for future systematic reviews. The following text has been added to clarify our research scope and the rationale behind this decision:

“A notable limitation of this review is that the study was not designed to extract or synthesize stem cell dosages and clinical outcomes. While we recognize their importance for comparative effectiveness, including them would have required a level of stratification that falls outside our descriptive scope. Furthermore, the inconsistent reporting of doses across studies varying in units, schedules, and methods makes any meaningful cross-study comparison challenging. These variables may better be suited in future systematic reviews and meta-analyses that focus specifically on dose-response patterns.”

We believe that these extensive revisions have significantly strengthened the manuscript in terms of transparency, structure, and interpretability, and have improved its overall suitability for the readership of Cells. We respectfully submit the revised manuscript for reconsideration and hope that it will now meet the journal’s standards for further processing.

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

To authors

A review aiming to cover a very extensive field of stem cell application in musculoskeletal tissues. Please note that orthopedics is a discipline and the tissue are not orthopedics but rather muscle, tendon, bone, cartilage, menisci commonly known as musculoskeletal. Besides, it is not only the orthopedic specialist involved in their management (but as well rheumatologist, physiotherapist balneologist, many of them performing stem cell based therapies)

Comments are inserted below

Abstract and introduction

Please note stem cell based therapy can not be regarded as “ recognized” in regenerative medicine but rather represent an intrinsic part of regenerative medicine. R 57, 58 phrase is not accurate. It is true that SOME of musculoskeletal tissue such as cartilage and menisci lack vascularization (menisci in part) but there are musculoskeletal tissues (such as muscle) with very abundant vascular supply. This part of the exposure basically only refers to cartilage and it needs to be presented as such.If authors want to address specifically on cartilage repair this need to be presented in title abstract and introduction clearly and not to mention “orthopedic tissues” in general Either narrow the scope or rewrite this part of introduction to address (as the title all musculoskeletal tissues

Methos.

The authors claim “a scoping review” however there are many exclusion criteria that include SVF, BMAC, exosomes, . These represent a large amount of clinical trials and our practice, In this case the work only addresses isolated cell injection studies, which is a subset of existing work

How are “stem cells defined “ in this work. From the text one can observe authors imply stem cells_mesenchymal stem cells of various tissue origin but this should be stated clearly (as well as in the title and introduction “stem cells” are many and they are of different translational value

Furthermore, authors include clinical trials + observational studies + animal studies but there is no study stratification by level of evidence, nor minimal bias commentary included Without this quality check study conclusions risk becoming frequency counts of low-quality literature.

Search strategy listed in the main text appears insufficiently reproducible since reader is not informed on  l anguage restrictions publication type filters, handling of conference abstracts inclusion or not of clinical trial registries, date /temporal limitations How exactly were disease grouped “for consistency” On which criterion? These should be stated as they can introduce major count bias (for example A vs cartilage degeneration vs chondral defect

How exactly the “study “counting unit” was actually resolved? Do counts represent publications? Experiments? Arms within a trial? Cohorts? Animal models ? Authros state that when multiple variables appeared, they recorded each separately. This could create numbering inflation since a single paper may contribute to multiple entries (if is a clinical study with multiple arms or one paper reporting on animal and clinical trial How were the follow up studies reported? Were the trials that published multiple papers on same cohort merged?

The major procedural flaw this reviewer perceives is, however, merging everything in one single box.

Small animals, large animals, clinical trials . These groups should be treated separately since they infer different strength of the finding, different translational relevance

Results display several inconsistencies (BM-MSCs appear 202 studies, 204 or 195 while OA (again how was OA defined?) appear as 92/87/85

A substantial proportion of the results relies on Sankey diagrams. Although visually informative, these diagrams only display descriptive counts and do not establish causal relationships or analytical hierarchies. In the absence of weighting by sample size or statistical testing, the figures primarily represent visual summaries of frequencies. Their interpretive value should be improved by either quantitative analysis or explicit framing of them as purely descriptive mapping tools.

In this perspective the study clearly overinterpets some purely descriptive data as “research maturity” or “approaching clinical readiness” Since we have no information regarding the trial phase(s) effect of the size of the respective study, regulatory framework and most of all about clinical outcomes such statement is not valid.

Author Response

Comment:

Comments are inserted below

Comment 1: Abstract and introduction

Response 1:

We sincerely thank the Reviewer for this insightful and rigorous comment. We agree that the previous phrasing regarding both the conceptual positioning of stem cell therapy and the physiological characteristics of musculoskeletal tissues required greater precision.

Following the Reviewer’s recommendations, we have opted to maintain the broad scope of the review while refining the text to ensure biological accuracy across musculoskeletal tissues. The following revisions have been made:

Terminology (Abstract, Page 2, lines 28-29): We have replaced the phrase "recognized in" with "represents an intrinsic part of" to accurately define stem cell therapy’s role within regenerative medicine.

Biological Accuracy (Introduction, Page 3, lines 57-67): We have rewritten the section regarding tissue vascularization to improve biological precision and avoid overgeneralization. The text now explicitly distinguishes between avascular tissues and highly vascularized tissues, as follows: “A key challenge in managing musculoskeletal disorders lies in the marked heterogeneity of intrinsic healing capacity among tissues, with bone exhibiting remarkable regenerative capacity, while tendons, ligaments, and cartilage demonstrate poor intrinsic healing capacity [3]. Certain musculoskeletal structures, particularly articular cartilage and the inner regions of the meniscus, exhibit limited vascularization, a well-recognized biological constraint that restricts their intrinsic healing capacity [4]. As a result, these tissues demonstrate limited spontaneous healing following injury [5]. In contrast, other musculoskeletal tissues, such as skeletal muscle, possess abundant vascular supply and a comparatively robust regenerative response [6]. These biological differences partly explain why regenerative strategies, including stem cell-based therapies, have attracted substantial interest across orthopedic and musculoskeletal research.”

Scope and Title Consistency (Title & Introduction, Page 4, lines 108-110): To ensure conceptual clarity and consistency with the breadth of our data synthesis, we have revised the terminology throughout the manuscript, including the title. Specifically, we replaced the phrase “orthopedic tissue” with “musculoskeletal tissue” to more accurately reflect the multi-tissue scope of this review.

In addition, the study objective has been clarified as follows: “Therefore, this scoping review aims to comprehensively map the current research landscape of stem cell applications across musculoskeletal tissue regeneration, including bone, cartilage, tendon, ligament, and skeletal muscle.”

Comment 2:

Response 2:

We appreciate this important observation. We fully agree that SVF, BMAC, exosomes, and related strategies represent major components of contemporary regenerative medicine. However, the exclusion of these approaches was intentional and conceptually driven.

The primary objective of this scoping review was to specifically examine stem cells as therapeutic entities, rather than mixed cellular preparations or cell-free products. Approaches involving mixed cellular preparations (e.g., SVF, MFAT, BMAC) and cell-free products represent biologically distinct intervention categories with differing mechanisms of action. Inclusion of these strategies would have required a broader analytical framework beyond the intended objectives of this review.

This methodological decision has been acknowledged as a limitation in Section 4.3 (Limitations, Critical Gaps, and Future Considerations).

Comment 3:

Response 3:

We appreciate the reviewer’s observation regarding conceptual clarity.

In this scoping review, the term “stem cells” was applied in a broad sense to capture the full landscape of stem cell-based interventions investigated in orthopedic and musculoskeletal contexts. The included studies therefore were not restricted exclusively to mesenchymal stem/stromal cells (MSCs).

While MSCs represent the predominant cell population across both preclinical and clinical literature, our dataset also contained a smaller yet important subset of studies involving other stem cell categories, including pluripotent stem cell-derived populations (e.g., iPSC-derived MSCs, ESC-derived MSCs) and tissue-specific stem/progenitor cells. This distribution is explicitly reflected in our extracted data and summarized in the Results section (Stem Cell Types and Sources).

To address this concern and prevent conceptual ambiguity, we have revised the manuscript to explicitly clarify the scope and definition of stem cells, as follows:

Introduction (Page 3, Lines 92-96):

“Although MSCs represent the most extensively investigated platform in orthopedic regeneration, the present scoping review was not restricted to MSC-based therapies. Instead, this review intentionally adopted a broad stem cell framework encompassing multiple stem cell classes, including pluripotent stem cell-derived populations and tissue-specific stem/progenitor cells captured within predefined eligibility criteria.”

Methods (Page 4, Line 126):

The sentence was revised from:

“…using stem cells as the primary therapeutic agent”

to:

“…using stem cells (including but not limited to MSCs) as the primary therapeutic agent.”

Discussion (Page 19, Lines 484-489):

We added the following clarifying statement:

“While MSCs dominate the identified literature and consequently shape many observable patterns, the review also captured a heterogeneous subset of non-MSC stem cell platforms. These cell classes differ substantially in developmental origin, differentiation behavior, and translational implications. Therefore, interpretations derived from aggregated mapping should not be viewed as MSC-specific conclusions but rather as reflective of the broader stem cell research landscape.”

These revisions ensure conceptual alignment between the definition of stem cells, the study scope, and the interpretation of findings.

Comment 4:

Response 4:

Thank you for this insightful comment. This review was conducted as a scoping review, whose primary objective is evidence mapping rather than evidence appraisal. Consistent with PRISMA-ScR guidance, formal risk-of-bias assessment and evidence hierarchy grading were not performed.

We acknowledge that combining clinical, observational, and preclinical studies without stratified appraisal may influence interpretive framing. To address this concern, we have revised the Methods section (Page 7, Lines 205-208) as follows: “All analyses were conducted descriptively to characterize study designs, stem cell sources, delivery methods, target tissues, and research trends. Given the inclusion of heterogeneous evidence sources, studies were categorized by design type to support context-sensitive interpretation.”

Accordingly, the findings should be interpreted as a descriptive mapping of research patterns rather than frequency-based evidence of effectiveness or quality.

Comment 5:

Search strategy listed in the main text appears insufficiently reproducible since reader is not informed on • l anguage restrictions publication type filters, handling of conference abstracts inclusion or not of clinical trial registries, date /temporal limitations How exactly were disease grouped “for consistency” On which criterion? These should be stated as they can introduce major count bias (for example A vs cartilage degeneration vs chondral defect

Response 5:

Thank you for this valuable comment. We appreciate the suggestion regarding clarification of the search strategy and disease classification criteria.

No language restrictions were applied. Review articles were excluded through publication type filtering. Where available, database-specific filters for clinical trials were applied as appropriate. Conference abstracts were not included, and clinical trial registries were not searched, as this review focused exclusively on published articles. No temporal limitations were imposed, and searches were conducted using the full coverage available within each database.

Studies were categorized according to the disease entities explicitly described by the original authors. No reinterpretation or reclassification of clinical terminology was performed. This approach was adopted to maintain consistency with the source literature and to minimize potential classification bias.

The full search strategy is provided in the Supplementary Materials to ensure transparency and reproducibility.

Comment 6:

Response 6:

Study Counting Unit: The unit of analysis was defined at the publication level. Accordingly, each eligible article was counted once for descriptive analyses.

Handling of Multiple Variables Within Publications: When a single publication reported multiple variables of interest (e.g., different cell types, disease indications, experimental models, or intervention conditions), each variable was extracted and recorded separately. This approach was intentionally adopted to capture methodological heterogeneity rather than to represent the number of unique trials.

Publications and Follow-up Reports: Publications arising from the same clinical trial or experimental cohort, including follow-up reports or secondary analyses, were not merged. Each eligible article was retained as a distinct analytical unit. No assumptions regarding study linkage were imposed in order to maintain methodological transparency. This approach does not influence study counts, as numerical summaries were calculated at the publication level rather than at the extracted-variable level.

Therefore, the following clarification was added to the Methods section (Page 7, Lines 183-192): “The unit of analysis in this scoping review was defined at the publication level, whereby each eligible article was counted once for descriptive analyses. When individual publications reported multiple variables of interest (e.g., different stem cell types, tissue targets, delivery strategies, or experimental models), these variables were extracted and recorded separately to capture methodological heterogeneity. Publications arising from the same clinical trial or experimental cohort, including follow-up reports or secondary analyses, were not merged. Each eligible article was retained as a distinct analytical unit. No assumptions regarding study linkage were imposed in order to maintain methodological transparency. This approach does not influence study counts, as numerical summaries were calculated at the publication level rather than at the extracted-variable level.”

Comment 7:

The major procedural flaw this reviewer perceives is, however, merging everything in one single box.

Small animals, large animals, clinical trials . These groups should be treated separately since they infer different strength of the finding, different translational relevance

Response 7:

Thank you for this important observation. We agree that small animal studies, large animal studies, and clinical investigations represent distinct evidence domains.

In the present review, studies were structurally categorized and analyzed within their respective design classifications (preclinical vs clinical), consistent with the descriptive objective of scoping reviews. In the Results section, findings were presented in separate Preclinical and Clinical domains to preserve interpretive clarity and translational relevance.

To further enhance interpretive clarity, we have explicitly clarified that findings are presented descriptively and do not imply equivalence of evidentiary strength across study designs.

Method section, Page 7, Lines 206-208:

“Given the inclusion of heterogeneous evidence sources, studies were categorized by design type to support context-sensitive interpretation.”

Comment 8:

Results display several inconsistencies (BM-MSCs appear 202 studies, 204 or 195 while OA (again how was OA defined?) appear as 92/87/85

Response 8:

Thank you for this important observation. The apparent numerical differences arise from the data charting and extraction framework employed in this scoping review.

Specifically, data were first extracted into a structured dataset, from which all visualizations, including Sankey diagrams and other graphical summaries, were generated. When individual publications reported multiple entries within a given parameter (e.g., more than one disease indication, target tissue, or stem cell category), each entry was recorded separately during data extraction.

Consequently, a single publication may contribute to more than one analytical category or pathway in Sankey diagrams and related visualizations. Accordingly, values presented in pathway-based figures reflect publication frequencies per extracted variable rather than unique study counts.

Therefore, we added the following clarification to the Methods section (Page 7, Lines 193-198):

“When individual publications reported multiple entries within specific parameters (e.g., multiple disease indications, target tissues, or stem cell types), each entry was recorded separately during data extraction. Consequently, a single publication may contribute to more than one analytical category or visualization pathway. Numerical summaries derived from extracted variables therefore represent publication frequencies per parameter rather than unique study counts.”

And we have added the following clarification to all Sankey visualization captions:

“Values represent publication frequencies across the extracted analytical parameters and do not indicate quantitative evidence of efficacy.”

Regarding osteoarthritis (OA), disease classification was based on the diagnostic terminology explicitly reported by the original authors, without reinterpretation or reclassification. Variations in OA counts across figures therefore reflect differences in analytical parameters rather than inconsistencies in disease definition.

Comment 9:

Response 9:

Thank you for this important observation. We fully agree that Sankey diagrams represent descriptive visualizations rather than analytical or causal models.

Consistent with the scoping review framework, the primary objective of this study was evidence mapping to characterize research patterns, methodological diversity, and variable distributions across the literature. Accordingly, Sankey diagrams were intentionally employed as descriptive mapping tools to visualize relationships between extracted variables.

No causal inference, analytical hierarchy, or statistical weighting was intended or implied. This reflects the inherent descriptive nature of scoping review methodology rather than a methodological limitation of the visualization approach.

Comment 10:

Response 10:

Thank you for this important comment. We agree that terminology implying developmental progression (e.g., “research maturity” or “approaching clinical readiness”) may suggest an interpretive strength beyond the descriptive scope of a scoping review.

Consistent with the evidence-mapping objective of this study, the analyses were designed to characterize research patterns rather than to infer developmental stages, regulatory readiness, or clinical efficacy.

To address this concern, we have revised the manuscript to remove language that could be interpreted as implying evaluative or causal inference. Interpretations are now explicitly framed within a descriptive context aligned with scoping review methodology.

Specifically, the relevant statements were revised in Section 3.4 Summary of key findings, Page 19, Lines 477-480 as follows:

Previous text:

“Research maturity is reflected in temporal trends, with preclinical activity peaking in 2019 and 2022 and clinical output surging between 2020 and 2021. This trajectory marks a methodical evolution from foundational animal research to clinical trials, especially in knee osteoarthritis, where regenerative therapies are approaching clinical readiness.”

Revised text:

“Temporal trends indicate shifts in research activity, with peaks observed in both preclinical and clinical publication periods. These patterns reflect evolving investigative focus and growing research interest across experimental and clinical contexts, particularly in knee osteoarthritis.”

We believe that these extensive revisions have significantly strengthened the manuscript in terms of transparency, structure, and interpretability, and have improved its overall suitability for the readership of Cells. We respectfully submit the revised manuscript for reconsideration and hope that it will now meet the journal’s standards for further processing.

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

Authors have addressed most of the reviewer comments. Even though the quality of the work has not been extensively improved how they claim, readers should ponder on its importance

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

This manuscript entitled "Research Landscape of Stem Cell Applications in Orthopedic Tissue: A Scoping Review"presents an extensive scoping review of stem cell applications in orthopedic and musculoskeletal regeneration, synthesizing data from 500 preclinical and clinical studies in accordance with PRISMA-ScR guidelines. The scope of the review is broad, the database coverage is appropriate, and the visual mapping using Sankey diagrams and heatmaps is a clear strength. The manuscript successfully captures dominant trends such as the prevalence of BM-MSCs, the focus on knee osteoarthritis, and the growing use of perinatal cell sources and large-animal models.

However, the manuscript suffers from significant issues related to conceptual clarity, methodological consistency, redundancy, and scientific depth. While the descriptive mapping is exhaustive, the interpretative and translational insights remain relatively superficial. Several methodological choices (notably the exclusion of biomaterial-assisted delivery and cell-free products) are insufficiently justified in light of current orthopedic regenerative medicine practice. In addition, the Results section is excessively long and repetitive, often restating numerical distributions without advancing biological or clinical interpretation. Substantial revision is required to improve focus, reduce redundancy, and strengthen the critical and translational value of the review.

Major comments

Conceptual positioning and novelty
While the manuscript is comprehensive, its conceptual novelty is limited. The review largely catalogs frequencies and trends without clearly articulating what new understanding emerges beyond confirmation of already well-known patterns (e.g., dominance of BM-MSCs, knee OA focus). The authors should explicitly clarify what this scoping review adds compared to existing systematic or scoping reviews in orthopedic regenerative medicine, particularly in terms of translational guidance, regulatory implications, or strategic gaps.
Justification of exclusion criteria
The exclusion of studies involving biomaterials, scaffolds, hydrogels, and cell-free products (e.g., extracellular vesicles) is a major limitation, given that these approaches dominate contemporary orthopedic tissue engineering. Although this choice is stated, it is not adequately justified. The authors should either (a) provide a stronger rationale explaining why exclusion was necessary and how it affects interpretability, or (b) acknowledge more explicitly that the findings represent only a narrow subset of current regenerative strategies and may not reflect real-world clinical development.
Overly descriptive and repetitive Results section
The Results section (especially Sections 3.2.1–3.2.7) is excessively long and repetitive, with many paragraphs reiterating numerical distributions already evident in figures. This impairs readability and dilutes key messages. The authors should substantially condense the Results by removing repetitive explanations and shifting interpretative statements to the Discussion.
Insufficient biological and mechanistic interpretation
Although MSC biology (e.g., paracrine signaling, immunomodulation) is briefly introduced, the Results and accompanying interpretations do not sufficiently connect observed trends to biological rationale. For example, the frequent use of xenogeneic perinatal MSCs is described but not critically discussed in terms of immune compatibility, translational relevance, or regulatory barriers. Stronger biological interpretation is needed.
Limited critical appraisal of translational relevance
The manuscript maps preclinical and clinical studies together but does not adequately distinguish between exploratory animal research and clinically meaningful translation. The authors should more clearly discuss how current animal model choices, cell sources, and delivery routes align (or fail to align) with realistic clinical implementation and regulatory expectations.
Clinical studies insufficiently highlighted
Despite including clinical trials, the manuscript heavily emphasizes preclinical data. Clinical studies should be more clearly separated, summarized, and critically discussed, particularly regarding indications, cell sources, delivery routes, and study design heterogeneity. As written, the clinical impact of the review is underdeveloped.
Lack of quality or maturity assessment
Although scoping reviews do not require risk-of-bias assessment, some stratification by study phase (e.g., early exploratory vs. late preclinical vs. clinical) or by maturity of evidence would greatly enhance interpretability. Without this, all studies are implicitly weighted equally, which is misleading.

Author Response

This manuscript entitled "Research Landscape of Stem Cell Applications in Orthopedic Tissue: A Scoping Review" presents an extensive scoping review of stem cell applications in orthopedic and musculoskeletal regeneration, synthesizing data from 500 preclinical and clinical studies in accordance with PRISMA-ScR guidelines. The scope of the review is broad, the database coverage is appropriate, and the visual mapping using Sankey diagrams and heatmaps is a clear strength. The manuscript successfully captures dominant trends such as the prevalence of BM-MSCs, the focus on knee osteoarthritis, and the growing use of perinatal cell sources and large-animal models.

Major comments

Comment 1: Conceptual positioning and novelty
While the manuscript is comprehensive, its conceptual novelty is limited. The review largely catalogs frequencies and trends without clearly articulating what new understanding emerges beyond confirmation of already well-known patterns (e.g., dominance of BM-MSCs, knee OA focus). The authors should explicitly clarify what this scoping review adds compared to existing systematic or scoping reviews in orthopedic regenerative medicine, particularly in terms of translational guidance, regulatory implications, or strategic gaps.

Response 1: Thank you for this thoughtful comment. We appreciate the reviewer’s perspective regarding conceptual novelty. The primary objective of our scoping review is to systematically organize and contextualize a large, heterogeneous body of preclinical and clinical evidence in orthopedic and musculoskeletal regenerative medicine.

Beyond confirming well-recognized patterns such as the historical dominance of BM-MSCs and the strong focus on knee osteoarthritis, our analysis offers additional insight by contextualizing these trends across preclinical-to-clinical translation, cell source evolution, and disease-target prioritization over time. Notably, the temporal analyses highlight a clear shift from invasive, patient-specific BM-MSC approaches toward adipose- and perinatal-derived MSCs, reflecting growing interest in scalable, minimally invasive, and off-the-shelf strategies with potential translational and regulatory relevance.

Importantly, this scoping review adds value by integrating donor-recipient context (autologous/allogeneic/xenogeneic), delivery-route mapping, and temporal trend analyses across both preclinical and clinical studies, enabling identification of translational misalignment and strategic gaps. This integrated framework allows identification of strategic gaps, such as the relative saturation of osteoarthritis research compared with underexplored musculoskeletal indications, and discrepancies between preclinical experimentation and clinical implementation.

Therefore, this scoping review provides an evidence-based landscape intended to support strategic decision-making for researchers, clinicians, and stakeholders by clarifying where evidence is concentrated, where translational momentum exists, and where future research efforts may be most impactful.

Comment 2: Justification of exclusion criteria
The exclusion of studies involving biomaterials, scaffolds, hydrogels, and cell-free products (e.g., extracellular vesicles) is a major limitation, given that these approaches dominate contemporary orthopedic tissue engineering. Although this choice is stated, it is not adequately justified. The authors should either (a) provide a stronger rationale explaining why exclusion was necessary and how it affects interpretability, or (b) acknowledge more explicitly that the findings represent only a narrow subset of current regenerative strategies and may not reflect real-world clinical development.

Response 2: Thank you for this insightful comment. We acknowledge that biomaterials, scaffolds, hydrogels, and cell-free products (such as extracellular vesicles) represent major and rapidly growing components of contemporary orthopedic tissue engineering.

In this scoping review, our decision to exclude these approaches was driven by the aim to specifically examine the outcomes and application patterns of stem cells as therapeutic entities in their own right. Different MSC types exhibit distinct biological behaviors and therapeutic capacities, and inclusion of biomaterial-based or cell-free combinatorial strategies would introduce substantial heterogeneity related to material properties, delivery systems, and bioengineering design. Such complexity would make cross-study comparison and high-level mapping less interpretable within the scope of this review.

We therefore acknowledge that the findings presented here represent a focused subset of current regenerative strategies in orthopedic tissue engineering. This limitation has now been more explicitly stated in the Limitations section. At the same time, we believe that isolating cell-based interventions provides a valuable evidence-based overview of translational trends, disease targeting, and clinical adoption pathways that may inform future research planning.

We agree that dedicated reviews focusing on specific organs or indications, integrating biomaterials, scaffolds, hydrogels, and cell-free products, would be highly valuable and represent an important direction for future evidence synthesis.

Comment 3: Overly descriptive and repetitive Results section
The Results section (especially Sections 3.2.1–3.2.7) is excessively long and repetitive, with many paragraphs reiterating numerical distributions already evident in figures. This impairs readability and dilutes key messages. The authors should substantially condense the Results by removing repetitive explanations and shifting interpretative statements to the Discussion.

Response 3: Thank you for this insightful comment. In response, we have substantially revised Sections 3.2.1-3.2.7 and 3.3.1-3.3.5 to reduce redundancy and improve focus by condensing repetitive numerical descriptions and emphasizing cross-domain patterns rather than reiterating raw frequency data.

While absolute numbers are still reported, these are now primarily used to support higher-level interpretation. In particular, Sankey diagrams were intentionally retained to visualize relational trends across stem cell sources, target tissues, and study models. Because Sankey diagrams do not inherently display numerical values, we explicitly report dataset counts in the accompanying text to preserve transparency and interpretability.

We believe this combined approach concise numerical reporting alongside relational visualization better supports integrative understanding without overloading the Results section with repetitive statistics.

Comment 4: Insufficient biological and mechanistic interpretation
Although MSC biology (e.g., paracrine signaling, immunomodulation) is briefly introduced, the Results and accompanying interpretations do not sufficiently connect observed trends to biological rationale. For example, the frequent use of xenogeneic perinatal MSCs is described but not critically discussed in terms of immune compatibility, translational relevance, or regulatory barriers. Stronger biological interpretation is needed.

Response 4: Thank you for this important comment. We agree that stronger biological and mechanistic interpretation is needed. In the revised manuscript, we have expanded the Discussion (Sections 4.1.6-4.1.7) to explicitly link observed preclinical trends to underlying MSC biology, including paracrine signaling and immunomodulatory mechanisms.

In particular, we now critically discuss the frequent use of xenogeneic perinatal MSCs in terms of immune compatibility, transient versus durable therapeutic effects, translational interpretability, and regulatory implications. These additions aim to clarify why certain cell platforms dominate preclinical research while also highlighting biological and translational constraints that may limit direct clinical extrapolation.

Comment 5: Limited critical appraisal of translational relevance
The manuscript maps preclinical and clinical studies together but does not adequately distinguish between exploratory animal research and clinically meaningful translation. The authors should more clearly discuss how current animal model choices, cell sources, and delivery routes align (or fail to align) with realistic clinical implementation and regulatory expectations.

Response 5: Thank you for this important comment. We agree that clearer critical appraisal of translational relevance is necessary. In the revised manuscript, we have substantially expanded the Discussion to more explicitly distinguish exploratory preclinical research from clinically meaningful translation.

Specifically, Sections 4.1.1-4.1.5 now clarify how animal model selection, stem cell sources, and delivery routes are often driven by experimental feasibility and mechanistic exploration, while Sections 4.1.6-4.1.7 critically discuss where these preclinical choices align or fail to align with realistic clinical implementation. We explicitly address translational gaps related to disease model biology, immune context (including xenogeneic transplantation), delivery feasibility, and regulatory expectations such as scalability, product consistency, and clinical practicality.

In addition, the clinical Discussion (Section 4.2) and Limitations (Section 4.3) further emphasize that publication frequency should not be conflated with clinical readiness, and that translational value depends on the degree to which preclinical design approximates real-world clinical and regulatory pathways.

Comment 6: Clinical studies insufficiently highlighted
Despite including clinical trials, the manuscript heavily emphasizes preclinical data. Clinical studies should be more clearly separated, summarized, and critically discussed, particularly regarding indications, cell sources, delivery routes, and study design heterogeneity. As written, the clinical impact of the review is underdeveloped.

Response 6: Thank you for this comment. We agree that clinical studies required clearer separation and more focused discussion. In the revised manuscript, clinical evidence is now treated as a distinct translational tier rather than an extension of preclinical mapping.

Specifically, Section 4.2 has been expanded to systematically summarize and critically discuss clinical studies according to therapeutic indications, stem cell sources, delivery routes, and study design heterogeneity, with emphasis on real-world implementation and interpretive limitations rather than study frequency alone.

We further emphasize that clinical relevance is influenced by trial design and comparators, while recognizing that dosing strategies and follow-up duration remain inconsistently reported and limit cross-study interpretation. Accordingly, publication volume should not be conflated with clinical readiness or efficacy. These considerations are reinforced in Section 4.3, where we explicitly acknowledge limitations related to heterogeneity, the lack of adequately powered comparative trials, and regulatory and logistical barriers that currently constrain the clinical impact of MSC-based orthopedic therapies.

Comment 7: Lack of quality or maturity assessment
Although scoping reviews do not require risk-of-bias assessment, some stratification by study phase (e.g., early exploratory vs. late preclinical vs. clinical) or by maturity of evidence would greatly enhance interpretability. Without this, all studies are implicitly weighted equally, which is misleading.

Response 7: Thank you for this thoughtful comment. We agree that stratification by study phase or maturity of evidence can enhance interpretability in many contexts. However, in this scoping review, our primary objective was to provide an inclusive, panoramic mapping of how stem cells have been explored across orthopedic tissues, rather than to frame the literature along a developmental or translational hierarchy.

Introducing stratification by research phase would shift the conceptual focus of the review from landscape mapping toward implicit evidence weighting, which was not the intended aim of this work. Importantly, our approach does not imply that all studies carry equal scientific or translational weight; rather, it reflects a deliberate choice to capture the full breadth of exploratory and clinical research without privileging specific stages.

To avoid potential misinterpretation, we have acknowledged the absence of evidence-maturity stratification as a limitation of the review (Section 4.3, Limitations). We believe that future focused reviews may benefit from phase-specific or quality-stratified analyses building upon the landscape presented here.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “Research Landscape of Stem Cell Applications in Orthopedic Tissue: …” is actually of moderate interest to the readership of Cells. The authors provide an extensive overview of the literature concerning the use of stem cells in orthopedic applications. Their review focuses on the different types of stem cells, their main sources and target tissues, as well as the organisms used in research. This is clearly the stated aim of the manuscript, and this aim has been fulfilled.

However, readers might also be interested in treatment outcomes, particularly in terms of which stem cell types are most effective for the repair of damaged orthopedic tissues. In addition, information regarding stem cell dosage is lacking. Including such information could significantly increase the relevance and impact of the manuscript.

The article is technically sound; however, some points should be addressed, as outlined below:

If possible, please add information regarding the effectiveness and dosage of the different stem cell types and discuss these aspects.
Page 12, lines 217–225: Decimal places in percentage values are of limited value when n < 100. Please round percentages to whole numbers.
Page 13, Figure 2C: Please increase the size of this diagram, as the categories on the x-axis are barely readable.
There is a high degree of homogeneity in the description of the results. For example, the text describing animal cells is very similar to the text describing human cells. While this is not incorrect, it may impair readability. Consider introducing more variation in wording.

Author Response

The article is technically sound; however, some points should be addressed, as outlined below:

Comment 1: If possible, please add information regarding the effectiveness and dosage of the different stem cell types and discuss these aspects.

Response 1: Thank you for this important comment. We agree that information on treatment effectiveness and stem cell dosage would be valuable and could further enhance the clinical relevance of this topic.

However, the effectiveness of different stem cell types in orthopedic applications is multifactorial and depends not only on the stem cell type itself, but also on several variables, including disease indication, disease severity, treatment protocol, follow-up duration, and concomitant therapies. Consequently, direct comparison or systematic mapping of the “most effective” stem cell types across heterogeneous indications is challenging and may be misleading if interpreted outside a disease-specific context.

With respect to stem cell dosage, we acknowledge that dosage information would be clinically informative. Nevertheless, dosing strategies vary substantially across orthopedic conditions and are often made to specific disease entities and levels of severity. Given the broad scope and heterogeneity of indications included in this scoping review, a detailed synthesis of dosage would be more appropriately addressed in focused, disease-specific systematic reviews rather than in a landscape-level analysis.

To avoid potential misinterpretation, we have explicitly acknowledged the absence of comparative dosing synthesis as a limitation of this scoping review in the Limitations section (Section 4.3).

All available information regarding reported outcomes has been extracted and is presented in the full data tables (as request), allowing readers to extract detailed information according to their specific research or clinical interests. We believe that this approach is consistent with the objectives of a scoping review and provides a useful overview of the current research landscape.

Comment 2: Page 12, lines 217–225: Decimal places in percentage values are of limited value when n < 100. Please round percentages to whole numbers.

Response 2: Thank you for raising this point. We have revised the percentage values in the main text by rounding them to whole numbers, as suggested.

Comment 3: Page 13, Figure 2C: Please increase the size of this diagram, as the categories on the x-axis are barely readable

Response 3: Thank you for pointing this out. We have increased the size of Figure 2C to improve the readability of the x-axis categories in the revised manuscript.

Comment 4: There is a high degree of homogeneity in the description of the results. For example, the text describing animal cells is very similar to the text describing human cells. While this is not incorrect, it may impair readability. Consider introducing more variation in wording.

Response 4: We thank the reviewer for this helpful comment and agree that some wording was repetitive. The manuscript has been revised accordingly, and all changes are tracked in the revised version. While consistency in stem cell nomenclature across preclinical and clinical studies is necessary, we have introduced targeted wording variations to more clearly distinguish preclinical, model-driven results from clinical, practice-oriented findings. The relevant sections of the Results (Section 3.2.1-3.3.5) and Discussion (4.1.1-4.2.4) have also been refined to reduce redundancy and improve clarity as suggested.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

You have successfully addressed the majority of my comments.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript was partially improved. Unfortunately, the article still contains very little relevant information in relation to its length.