Finite element analysis of patient-specific additive-manufactured implants.

Introduction: Bone tumors, characterized by diverse locations and shapes, often necessitate surgical excision followed by custom implant placement to facilitate targeted bone reconstruction. Leveraging additive manufacturing, patient-specific implants can be precisely tailored with complex geometries and desired stiffness, enhancing their suitability for bone ingrowth. Methods: In this work, a finite element model is employed to assess patient-specific lattice implants in femur bones. Our model is validated using experimental data obtained from an animal study (n = 9). Results: The results demonstrate the accuracy of the proposed finite element model in predicting the implant mechanical behavior. The model was used to investigate the influence of reducing the elastic modulus of a solid Ti6Al4V implant by tenfold, revealing that such a reduction had no significant impact on bone behavior under maximum compression and torsion loading. This finding suggests a potential avenue for reducing the endoprosthesis modulus without compromising bone integrity. Discussion: Our research suggests that employing fully lattice implants not only facilitates bone ingrowth but also has the potential to reduce overall implant stiffness. This reduction is crucial in preventing significant bone remodeling associated with stress shielding, a challenge often associated with the high stiffness of fully solid implants. The study highlights the mechanical benefits of utilizing lattice structures in implant design for enhanced patient outcomes.

Predictive Tool Use and Willingness for Surgery in Patients With Knee Osteoarthritis: A Randomized Clinical Trial.

Importance: Despite the increasing number of tools available to predict the outcomes of total knee arthroplasty (TKA), the effect of these predictive tools on patient decision-making remains uncertain. Objective: To assess the effect of an online predictive tool on patient-reported willingness to undergo TKA. Design, Setting, and Participants: This parallel, double-masked, 2-arm randomized clinical trial compared predictive tool use with treatment as usual (TAU). The study was conducted between June 30, 2022, and July 31, 2023. Participants were followed up for 6 months after enrollment. Participants were recruited from a major Australian private health insurance company and from the surgical waiting list for publicly funded TKA at a tertiary hospital. Eligible participants had unilateral knee osteoarthritis, were contemplating TKA, and had previously tried nonsurgical interventions, such as lifestyle modifications, physiotherapy, and pain medications. Intervention: The intervention group was provided access to an online predictive tool at the beginning of the study. This tool offered information regarding the likelihood of improvement in quality of life if patients chose to undergo TKA. The predictions were based on the patient's age, sex, and baseline symptoms. Conversely, the control group received TAU without access to the predictive tool. Main Outcomes and Measures: The primary outcome measure was the reduction in participants' willingness to undergo surgery at 6 months after tool use as measured by binomial logistic regression. Secondary outcome measures included participant treatment preference and the quality of their decision-making process as measured by the Knee Decision Quality Instrument. Results: Of 211 randomized participants (mean [SD] age, 65.8 [8.3] years; 118 female [55.9%]), 105 were allocated to the predictive tool group and 106 to the TAU group. After adjusting for baseline differences in willingness for surgery, the predictive tool did not significantly reduce the primary outcome of willingness for surgery at 6 months (adjusted odds ratio, 0.85; 95% CI, 0.42-1.71; P = .64). Conclusions and Relevance: Despite the absence of treatment effect on willingness for TKA, predictive tools might still enhance health outcomes of patients with knee osteoarthritis. Additional research is needed to optimize the design and implementation of predictive tools, address limitations, and fully understand their effect on the decision-making process in TKA. Trial Registration: ANZCTR.org.au Identifier: ACTRN12622000072718.

Influences on clinical trial participation: Enhancing recruitment through a gender lens - A scoping review.

Background: Suboptimal clinical trial recruitment contributes to research waste. Evidence suggests there may be gender-based differences in willingness to participate in clinical research. Identifying gender-based differences impacting the willingness of trial participation may assist trial recruitment. Objectives: To examine factors that influence the willingness of men and women to participate in clinical trials and to identify modifiable factors that may be targeted to optimise trial participation. Material and methods: Electronic databases were searched with key words relating to 'gender', 'willingness to participate' and 'trial'. Included studies were English language and reported gender-based differences in willingness to participate in clinical trials, or factors that influence a single gender to participate in clinical trials. Studies were excluded if they described the demographic factors of trial participants or if the majority of participants were pregnant. Extracted data were coded, categorized, analysed thematically and interpreted using Arksey and O'Malley's framework. Results: Sixty-three studies were included. Two main themes were identified: trial characteristics and participant characteristics. A number of gender-based differences moderating willingness to participate were observed although only one, 'concern for self' was found to influence actual trial participation rates between genders. Conclusion: The relationship between factors influencing willingness to participate in clinical trials is complex. The influence of gender on willingness to participate, while important, may be moderated by other factors including socioeconomic status, ethnicity and health condition. Exploring factors that influence willingness to participate specific to a study cohort likely offers the most promise to optimise trial recruitment of that cohort.

Radiotherapy versus limb-sparing surgery alone in low-grade soft-tissue sarcoma of the extremity and trunk wall: a systematic review and meta-analysis.

Current guidelines recommend the use of radiotherapy in the management of intermediate and high-grade soft-tissue sarcoma of the extremity and trunk wall. Its use in low-grade sarcoma is less clear. To date there have been no pooled data analyses regarding its role in this context. Its use is not without complications and therefore must be justified. We aim to assess the oncological impact of radiotherapy versus limb-sparing surgery alone in this subset of sarcoma. Medline, EMBASE and Cochrane's databases were searched from 1982 to present. Studies on or having a subgroup analysis of low-grade soft tissue sarcoma, with a radiotherapy and a surgery only arm were included. Outcomes included local recurrence and overall survival. Patients were at least 16 years of age with primary de-novo sarcoma who had not undergone prior resection or treatment. Those undergoing concomitant therapy were excluded. Data extraction was performed independently by two reviewers. Results were pooled using a random-effects model and presented as a forest plot. Primary outcome measures included local recurrence and overall survival. Eleven unique studies were included, consisting of two RCTs and nine non-randomized studies. Overall, there were 12 799 patients. Four studies were included in meta-analysis and the overall pooled effect showed a limited role of radiotherapy in overall survival outcomes when compared to limb-sparing surgery alone HR 1.00 [0.83-1.20] P = 0.41. Descriptive analysis suggests there is limited role of radiotherapy in improving local recurrence outcomes. This study suggests there is limited role for radiotherapy versus limb-sparing surgery alone in low-grade soft-tissue sarcoma. These findings strongly suggest there is lack of high-quality data and that further research must be undertaken prior to forming any strong conclusions regarding the management of low-grade soft-tissue sarcoma. Demonstrating a role for radiotherapy may help improve the quality of excisional margins and thus potentiate limb-sparing surgery.

Patient perspectives of quality of life in chronic limb-threatening ischemia: a qualitative study.

BACKGROUND: Quality of life (QOL) is an outcome that matters to patients with chronic limb-threatening ischemia (CLTI). However, we identified the lack of and need for a CLTI-specific QOL instrument. Our group is developing this instrument which requires a deep understanding of patient perspectives of QOL in CLTI. METHODS: Qualitative inquiry with patient and public involvement was performed in accordance with the Standards for Reporting Qualitative Research. Reflexive thematic analysis of semi-structured interviews was conducted within a constructivist-interpretivist research paradigm. Data were organized and managed in NVivo. Techniques to enhance trustworthiness included maintaining an audit trail, member checking, mentoring, and peer-debriefing. Patient and the public were consulted for feedback on codes, themes, and thematic maps. RESULTS: Thirteen participants (median age: 74 years, range: 43-90 years) with a variety of patient demographics were interviewed. Four themes were developed on QOL in CLTI: (i) 'independence as key to life satisfaction', (ii) 'change in identity when continuity is needed', (iii) 'coping with intractable disease', and (iv) 'not wanting to be alone'. Member checking with patient and public involvement confirmed the relevance and centrality of these themes to the lived experiences of patients with CLTI. CONCLUSIONS: The thematic outputs contribute important insights into what QOL truly means to patients with CLTI and what matters for their QOL. The content validity of the new CLTI-specific QOL instrument is improved by giving patients voice. This study highlights the value of qualitative inquiry and patient and public involvement in vascular surgical research.

A Systematic Review of the Quality of Clinical Practice Guidelines for Chronic Limb-Threatening Ischemia.

BACKGROUND: To assess the quality of clinical practice guidelines (CPGs) for chronic limb-threatening ischemia (CLTI) using the Appraisal of Guidelines for Research and Evaluation II instrument. METHODS: A systematic review of Medline, Embase, and online CPG databases was carried out. Four CPGs on CLTI were identified: Global Vascular Guidelines (GVG), European Society of Cardiology (ESC), American College of Cardiology, and National Institute for Health and Care Excellence guidelines on lower limb peripheral arterial disease. Two independent appraisers analyzed the 4 CPGs using the Appraisal of Guidelines for Research and Evaluation II instrument. CPGs were ranked across 6 domains with 23 items that ranged from 1 (strongly disagree) to 7 (strongly agree). A scaled domain score was calculated as a percentage of the maximum possible score achievable. A domain score of ≥50% and an overall average domain score of ≥80% reflected a CPG of adequate quality recommended for use. RESULTS: GVG had the highest overall score (82.9%), as an average of all domains, and ESC had the lowest score (50.2%). GVG and National Institute for Health and Care Excellence guidelines had all domains scoring >50%, while American College of Cardiology had 5 and ESC had 3. Two domains, rigor of development and applicability, scored the lowest among the CPGs. There was a lack of detail in describing systematic methods used in the literature review, how guidelines were formulated with minimal bias, and the planned procedure for updating the guidelines. Implications of guideline application and monitoring of outcomes after implementations were not explicitly discussed. CONCLUSIONS: The GVG guideline published in 2019 discussing CLTI is assessed to be of high quality and recommended for use. This review helps to improve clinical decision-making and quality of future CPGs for CLTI.

Does a consumer co-designed infographic increase knowledge of physical activity after total knee joint replacement? A randomised controlled trial.

PURPOSE: To determine if a consumer co-designed infographic increased knowledge of physical activity and self-efficacy for exercise after total knee joint replacement surgery. METHODS: Forty-four adults with primary knee joint replacement surgery were recruited from a public and a private hospital in Melbourne, Australia. Participants were randomly allocated to an experimental or control group. The experimental group received a consumer co-designed infographic. All participants received usual care. Primary outcome measures were knowledge of physical activity and self-efficacy for exercise. Outcomes were administered at baseline, week 1 and week 6. Semi-structured interviews with experimental group participants explored the acceptability, implementation and efficacy of the infographic. RESULTS: There were no between-group differences for knowledge of physical activity at week 1 (MD -0.02 units, 95% CI -0.9 to 0.9) or week 6 (MD 0.01 units, 95% CI -0.9 to 0.9). Self-efficacy for exercise increased at week 1 (MD 14.2 units, 95% CI 2.9-25.4) but was not sustained. Qualitative data showed that the infographic was embraced by some participants but not by others. CONCLUSIONS: A consumer co-designed infographic did not improve knowledge of physical activity but may have had a short-term positive effect on self-efficacy for exercise after knee joint replacement. Trial registration ACTRN12621000910808.

Mortality, patient-reported outcome measures, and the health economic burden of prosthetic joint infection.

Prosthetic joint infection (PJI) is one of the most devastating complications for a patient following arthroplasty. This scoping review aims to evaluate the burden of PJI on individual patients and the healthcare system regarding the mortality rate, patient-reported quality of life, and healthcare resource utilisation. Patients with PJI have up to a five-fold higher mortality rate than those who have undergone an uninfected primary arthroplasty. There is an increased use of ambulatory aids and reduced joint function scores in patients with PJI. Global quality of life is poorer, specifically measured by the EQ-5D. Direct hospitalisation costs are two- to five-fold higher, attributed to surgery and prostheses, antibiotics, and a prolonged inpatient stay. There is an immense clinical and health economic burden secondary to PJI worldwide. This is expected to rise exponentially due to the increasing number of primary procedures and an ageing population with comorbidities Improving preventative and treatment strategies is imperative for patients and the healthcare system.

Patients' Views on AI for Risk Prediction in Shared Decision-Making for Knee Replacement Surgery: Qualitative Interview Study.

BACKGROUND: The use of artificial intelligence (AI) in decision-making around knee replacement surgery is increasing, and this technology holds promise to improve the prediction of patient outcomes. Ambiguity surrounds the definition of AI, and there are mixed views on its application in clinical settings. OBJECTIVE: In this study, we aimed to explore the understanding and attitudes of patients who underwent knee replacement surgery regarding AI in the context of risk prediction for shared clinical decision-making. METHODS: This qualitative study involved patients who underwent knee replacement surgery at a tertiary referral center for joint replacement surgery. The participants were selected based on their age and sex. Semistructured interviews explored the participants' understanding of AI and their opinions on its use in shared clinical decision-making. Data collection and reflexive thematic analyses were conducted concurrently. Recruitment continued until thematic saturation was achieved. RESULTS: Thematic saturation was achieved with 19 interviews and confirmed with 1 additional interview, resulting in 20 participants being interviewed (female participants: n=11, 55%; male participants: n=9, 45%; median age: 66 years). A total of 11 (55%) participants had a substantial postoperative complication. Three themes captured the participants' understanding of AI and their perceptions of its use in shared clinical decision-making. The theme Expectations captured the participants' views of themselves as individuals with the right to self-determination as they sought therapeutic solutions tailored to their circumstances, needs, and desires, including whether to use AI at all. The theme Empowerment highlighted the potential of AI to enable patients to develop realistic expectations and equip them with personalized risk information to discuss in shared decision-making conversations with the surgeon. The theme Partnership captured the importance of symbiosis between AI and clinicians because AI has varied levels of interpretability and understanding of human emotions and empathy. CONCLUSIONS: Patients who underwent knee replacement surgery in this study had varied levels of familiarity with AI and diverse conceptualizations of its definitions and capabilities. Educating patients about AI through nontechnical explanations and illustrative scenarios could help inform their decision to use it for risk prediction in the shared decision-making process with their surgeon. These findings could be used in the process of developing a questionnaire to ascertain the views of patients undergoing knee replacement surgery on the acceptability of AI in shared clinical decision-making. Future work could investigate the accuracy of this patient group's understanding of AI, beyond their familiarity with it, and how this influences their acceptance of its use. Surgeons may play a key role in finding a place for AI in the clinical setting as the uptake of this technology in health care continues to grow.

The regulatory challenge of 3D bioprinting.

New developments in additive manufacturing and regenerative medicine have the potential to radically disrupt the traditional pipelines of therapy development and medical device manufacture. These technologies present a challenge for regulators because traditional regulatory frameworks are designed for mass manufactured therapies, rather than bespoke solutions. 3D bioprinting technologies present another dimension of complexity through the inclusion of living cells in the fabrication process. Herein we overview the challenge of regulating 3D bioprinting in comparison to existing cell therapy products as well as custom-made 3D printed medical devices. We consider a range of specific challenges pertaining to 3D bioprinting in regenerative medicine, including classification, risk, standardization and quality control, as well as technical issues related to the manufacturing process and the incorporated materials and cells.

Broken Machines or Active Bodies? Part 3. Five Recommendations to Shift the Way Clinicians Communicate With People Who Are Seeking Care for Osteoarthritis.

SYNOPSIS: In parts 1 and 2 of this series, we highlighted the dominant impairment way of talking about osteoarthritis: talking that frames osteoarthritis as a disease of cartilage worsened by physical activity that can only be "cured" by replacing the joint. An alternative understanding that counters common misconceptions about osteoarthritis, and links physical activity and healthy lifestyles to improvements in symptoms is likely a prerequisite for sustainable behavior change. It is insufficient to tell people with osteoarthritis that regular physical activity is important; people need to understand and experience how physical activity can help. Here, we offer suggestions for how clinicians can shift from focusing on what people cannot do because of osteoarthritis, toward focusing on what people can do to improve their health and maintain "active bodies." J Orthop Sports Phys Ther 2023;53(7):1-6. doi:10.2519/jospt.2023.11881.

What are the core recommendations for gout management in first line and specialist care? Systematic review of clinical practice guidelines.

BACKGROUND: Gout is the most common inflammatory arthritis, increasing in prevalence and burden. Of the rheumatic diseases, gout is the best-understood and potentially most manageable condition. However, it frequently remains untreated or poorly managed. The purpose of this systematic review is to identify Clinical Practice Guidelines (CPG) regarding gout management, evaluate their quality, and to provide a synthesis of consistent recommendations in the high-quality CPGs. METHODS: Gout management CPGs were eligible for inclusion if they were (1) written in English and published between January 2015-February 2022; focused on adults aged ≥ 18 years of age; and met the criteria of a CPG as defined by the Institute of Medicine; and (2) were rated as high quality on the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument. Gout CPGs were excluded if they required additional payment to access; only addressed recommendations for the system/organisation of care and did not include interventional management recommendations; and/or included other arthritic conditions. OvidSP MEDLINE, Cochrane, CINAHL, Embase and Physiotherapy Evidence Database (PEDro) and four online guideline repositories were searched. RESULTS: Six CPGs were appraised as high quality and included in the synthesis. Clinical practice guidelines consistently recommended education, commencement of non-steroidal anti-inflammatories, colchicine or corticosteroids (unless contraindicated), and assessment of cardiovascular risk factors, renal function, and co-morbid conditions for acute gout management. Consistent recommendations for chronic gout management were urate lowering therapy (ULT) and continued prophylaxis recommended based on individual patient characteristics. Clinical practice guideline recommendations were inconsistent on when to initiate ULT and length of ULT, vitamin C intake, and use of pegloticase, fenofibrate and losartan. CONCLUSION: Management of acute gout was consistent across CPGs. Management of chronic gout was mostly consistent although there were inconsistent recommendations regarding ULT and other pharmacological therapies. This synthesis provides clear guidance that can assist health professionals to provide standardised, evidence-based gout care. TRIAL REGISTRATION: The protocol for this review was registered with Open Science Framework (DOI https://doi.org/10.17605/OSF.IO/UB3Y7 ).

Process of change for people with knee osteoarthritis undergoing cognitive functional therapy: a replicated single-case experimental design study.

PURPOSE: To examine the applicability and process of change of Cognitive Functional Therapy (CFT) in the management of pain and disability in people with knee osteoarthritis who were offered knee replacement surgery and had risk factors for poor response to surgery. METHODS: Single-case experimental design with a mixed-methods, repeated measures approach was used to investigate the process of change through CFT in four participants. Qualitative interviews investigated beliefs, behaviours and coping responses, and self-reported measures assessed pain, disability, psychological factors, and function at 25 timepoints. Study registered with the Australian and New Zealand Clinical Trials Registry (ACTRN12619001491156). RESULTS: Qualitative data indicate that CFT promoted helpful changes in all participants, with two responses observed. One reflected a clear shift to a biopsychosocial conceptualisation of osteoarthritis, behavioural re-engagement and the view that a knee replacement was no longer necessary. The other response reflected a mixed conceptualisation with dissonant beliefs about osteoarthritis and its management. Psychological and social factors were identified as potential treatment barriers. Overall, quantitative measures supported the qualitative findings. CONCLUSION: The process of change varies between and within individuals over time. Psychological and social barriers to treatment have implications for future intervention studies for the management of knee osteoarthritis.IMPLICATIONS FOR REHABILITATIONCognitive Functional Therapy is applicable in the management of knee osteoarthritis.Reconceptualisation of osteoarthritis reflected a helpful change.Psychological and social factors emerged as barriers to recovery.

Broken Machines or Active Bodies? Part 2. How People Talk About Osteoarthritis and Why Clinicians Need to Change the Conversation.

SYNOPSIS: How people talk about osteoarthritis may impact outcomes, including uptake of guideline recommendations related to activity-based lifestyles and interventions. In this editorial, we describe 2 key ways of talking, based on findings from our systematic review of 62 qualitative studies exploring the perceptions of people with knee osteoarthritis (n = 1208), their carers (n = 28), and clinicians (n = 2403). Among raw quotes extracted from the studies, we observed a dominant impairment-based way of talking and a participatory based way of talking. These ways of talking form a novel framework to help clinicians understand what people think and do about osteoarthritis. J Orthop Sports Phys Ther 2023;53(6):325-330. doi:10.2519/jospt.2023.11880.

Predicting 30-day readmission following total knee arthroplasty using machine learning and clinical expertise applied to clinical administrative and research registry data in an Australian cohort.

BACKGROUND: Thirty-day readmission is an increasingly important problem for total knee arthroplasty (TKA) patients. The aim of this study was to develop a risk prediction model using machine learning and clinical insight for 30-day readmission in primary TKA patients. METHOD: Data used to train and internally validate a multivariable predictive model were obtained from a single tertiary referral centre for TKA located in Victoria, Australia. Hospital administrative data and clinical registry data were utilised, and predictors were selected through systematic review and subsequent consultation with clinicians caring for TKA patients. Logistic regression and random forest models were compared to one another. Calibration was evaluated by visual inspection of calibration curves and calculation of the integrated calibration index (ICI). Discriminative performance was evaluated using the area under the receiver operating characteristic curve (AUC-ROC). RESULTS: The models developed in this study demonstrated adequate calibration for use in the clinical setting, despite having poor discriminative performance. The best-calibrated readmission prediction model was a logistic regression model trained on administrative data using risk factors identified from systematic review and meta-analysis, which are available at the initial consultation (ICI = 0.012, AUC-ROC = 0.589). Models developed to predict complications associated with readmission also had reasonable calibration (ICI = 0.012, AUC-ROC = 0.658). CONCLUSION: Discriminative performance of the prediction models was poor, although machine learning provided a slight improvement. The models were reasonably well calibrated, meaning they provide accurate patient-specific probabilities of these outcomes. This information can be used in shared clinical decision-making for discharge planning and post-discharge follow up.

Broken Machines or Active Bodies? Part 1. Ways of Talking About Health and Why It Matters.

SYNOPSIS: This editorial series raises awareness among clinicians about how ways of talking about orthopaedic conditions can influence what people who are seeking health care (1) think about their health and (2) what they do to manage their health. In part 1, we introduce you to ways of talking about health, using osteoarthritis as a case study. In part 2, we describe 2 contrasting ways of talking about osteoarthritis and how changing the way you share information and ideas with people seeking care may impact clinical decisions. In part 3, we offer strategies to help you shift the way you communicate with people with osteoarthritis to promote uptake of best practice recommendations and support healthy, active lifestyles. J Orthop Sports Phys Ther 2023;53(5):1-3. doi:10.2519/jospt.2023.11879.

The impact of cost on quality of surgical management in non-metastatic extremity sarcoma: A cross-country narrative literature review with a systematic approach.

BACKGROUND: Extremity sarcoma surgery entails significant costs for patients, governments and insurers. Multiple studies have described individual costs, however, the overall impact of cost on the quality of surgical care remains unclear. OBJECTIVES: A narrative review with a systematic approach was undertaken to compare the impact of cost on the quality of extremity sarcoma care across low-middle-income and high-income countries. DATA SOURCES: MEDLINE, EMBASE, Cochrane, PsycInfo, DARE, NHS-EED, HTA. METHODS: A systematic search was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Inclusion criteria were: discussion of costs and the surgical management of primary extremity sarcoma. There were no restrictions on study design, publication type, date, geographic location or publication status. A data extraction table was used to identify study location, type and findings. RESULTS: 1012 studies were retrieved and 44 met the inclusion criteria. Four additional studies were identified from the reference lists of included articles. 27 studies were published in high-income countries (HIC) including all four full health economic analyses and 20 studies were published in low-middle income countries (LMC). Within LMC, cost impeded access to diagnosis, resection and options for reconstruction. In HIC, cost varied with choice of management, particularly during the long-term postoperative period. CONCLUSIONS: Within LMC, cost impaired the provision of quality, curative care for patients with extremity sarcoma. Within HIC, while costs varied with chosen management, they were not prohibitive to the provision of quality care. Further research is required, specific to both socioeconomic contexts, to further describe the long-term cost-utility of different methods for the surgical management of extremity sarcoma.

High ploidy large cytoplasmic megakaryocytes are hematopoietic stem cells regulators and essential for platelet production.

Megakaryocytes (MK) generate platelets. Recently, we and others, have reported MK also regulate hematopoietic stem cells (HSC). Here we show high ploidy large cytoplasmic megakaryocytes (LCM) are critical negative regulators of HSC and critical for platelet formation. Using a mouse knockout model (Pf4-Srsf3Δ/Δ) with normal MK numbers, but essentially devoid of LCM, we demonstrate a pronounced increase in BM HSC concurrent with endogenous mobilization and extramedullary hematopoiesis. Severe thrombocytopenia is observed in animals with diminished LCM, although there is no change in MK ploidy distribution, uncoupling endoreduplication and platelet production. When HSC isolated from a microenvironment essentially devoid of LCM reconstitute hematopoiesis in lethally irradiated mice, the absence of LCM increases HSC in BM, blood and spleen, and the recapitulation of thrombocytopenia. In contrast, following a competitive transplant using minimal numbers of WT HSC together with HSC from a microenvironment with diminished LCM, sufficient WT HSC-generated LCM regulates a normal HSC pool and prevents thrombocytopenia. Importantly, LCM are conserved in humans.