Wartime Military Orthopaedics

Military orthopaedic surgeons are faced with hardship and decreased morale. Surgeons have frequent deployments and practice inefficiencies resulting in poor retention rates. The purpose of this analysis is to report demographics and factors effecting military retention. A survey was sent to all members of the Society of Military Orthopedic Surgeons. The survey obtained demographic information, as well as factors affecting retention and termination of service. Data was compared between subset groups within the total respondent population. Of active-duty personnel, 38.5% plan on staying in the military until retirement. Most surgeons entered into the military due to a desire to serve their country, while most people leave service due to higher pay as a civilian. A minority of military orthopaedic surgeons achieve military retirement; however, increased pay, increased control over practice, and decreased frequency of deployments are factors that could improve retention rates. (Journal of Surgical Orthopaedic Advances 30(2):116-119, 2021).

A microRNA Signature for Impaired Wound-Healing and Ectopic Bone Formation in Humans

BACKGROUND

Heterotopic ossification (HO) is characterized by the abnormal growth of ectopic bone in soft tissues, frequently occurring within the military population because of extensive orthopaedic combat trauma. MicroRNAs (miRNAs) are small noncoding RNAs that act as post-transcriptional regulators of gene expression. We hypothesized that a clinically relevant miRNA signature could be detected in patients following injury that progressed to form HO (HO+) or did not form HO (HO-).

METHODS

Tissue samples were obtained from injured servicemembers during their initial surgical debridements, and miRNA profiling was performed using a real-time miRNA polymerase chain reaction (PCR) array. Primary mesenchymal progenitor cells (MPCs) were harvested from debrided traumatized human muscle tissue, and cells were isolated and cultured in vitro. Mimic miRNAs were transfected into MPCs, followed by downstream in vitro analyses.

RESULTS

The investigation of the miRNA expression profile in the tissue of HO+ compared with HO- patients demonstrated a molecular signature that included the upregulation of miR-1, miR-133a, miR-133b, miR-206, miR-26a, and miR-125b. Transfection of each of these mature miRNAs into MPCs followed by osteogenic induction demonstrated that miR-1, miR-133a, miR-133b, and miR-206 enhanced osteogenic differentiation compared with control treatments. In silico and in vitro analyses identified the transcription factor SOX9 as a candidate downstream target of miR-1 and miR-206 miRNAs.

CONCLUSIONS

Our data demonstrated a molecular signature of miRNAs in the soft tissue of wounded servicemembers that was associated with the development of HO, providing novel insights into the underlying molecular mechanisms associated with posttraumatic HO.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Morphology and chemical identity of periarticular and vascular calcification in a patient with the rare genetic disease of arterial calcification due to deficiency of CD73 (ACDC)

A 54-year old female patient with the genetic disease of arterial calcification due to deficiency of CD73 was studied under the Undiagnosed Disease Program of the National Institutes of Health. She presented with symptoms of claudication in her 40s and later developed arthritic symptoms, ectopic calcification in her left hand and severe arterial calcifications of the lower extremities. Since little was known about the composition of the calcifications in arterial calcification due to deficiency of CD73, we investigated their chemical identity and microscopic morphology in this patient with imaging and x-ray diffraction analysis. We found that, microscopically, the bulk calcifications consisted of fragments of either solid or porous internal structure. Both periarticular and arterial calcifications were primarily hydroxyapatite crystals of the same crystalline anisotropy, but different crystalline grain sizes. This was consistent with the presence of hydroxyapatite crystals along with birefringent calcium pyrophosphate dihydrate crystals in the synovial fluid of the patients by polarized light microscopy. The result suggests that tissue calcification in both locations follow a similar biochemical mechanism caused by an increase in extracellular tissue-nonspecific alkaline phosphatase activity.

Factors Considered When Ranking Military Orthopedic Surgery Residency Candidates

INTRODUCTION

The intangible personal characteristic grit has become a popular topic of concentration within contemporary psychology studies. Grit is defined as persistent work on a focused topic for an extended period of time until a desired goal is achieved. Its application to physician selection and development is not well known. We sought to determine which factors were considered most important among leadership within the U.S. Army's orthopedic surgical training programs when selecting applications and ascertain if grit was one of the primary factors.

MATERIALS AND METHODS

A standardized, 18-question survey was sent to all program chairs, program directors, and assistant program directors at the six U.S. Army orthopedic surgery residency programs. Questions included demographic factors pertaining to both the individual and their respective training program. Participants were asked to rank, in order, the 10 most important variables when considering applicants. Each variable was ranked using a point system (1-10 with 10 as the best score), referred to as the factor score (FS). Further statistical analyses using descriptive statistics, paired t-test, and ANOVA were performed and reported.

RESULTS

The response rate was 83% (15/18). The most important variable considered was the applicant's performance on their audition rotation (FS = 9.8), which was significantly more important than any other variable (P = 0.001). The second most important variable was the applicant's USMLE scores (FS = 7.13), followed by involvement in research (FS = 5.60) and conscientiousness (FS = 4.73), respectively. Grit was considered the fifth most important variable (FS = 4.27). There was no significant difference in the ranking of grit among the different programs (P = 0.282). In applicants with low United States Medical Licensing Examination scores according to leadership idiosyncrasy, their audition rotation was considered a redeeming portion of their application (P = 0.02) followed by their level of grit.

CONCLUSIONS

The most important factor when considering an orthopedic surgery applicant was how well the applicant performed on an audition rotation, followed by their United States Medical Licensing Examination scores. Grit has become an important consideration in resident selection.

Surgical Repair of Acute TFCC Injury

Triangular fibrocartilage complex tears are a common source of ulnar-sided wrist pain and distal radioulnar joint instability. Symptoms recalcitrant to conservative management or injuries in high-demand athletes may indicate surgical management. Both open and arthroscopic techniques offer improvements in objective measures, patient-centered outcome scores, and return to work, but may be complicated by nerve irritation, persistent wrist instability, and pain. Recently developed knotless arthroscopic techniques are not well studied but may limit morbidity.

Acute Complications in Total Wrist Arthroplasty: A National Surgical Quality Improvement Program Review

Background  The study sought to assess the patient-based variables, surgical risk factors, and postoperative conditions associated with readmission after total wrist arthroplasty (TWA). Materials and Methods  All patients undergoing TWA were identified from the National Surgical Quality Improvement Program dataset from 2005 to 2016. Patient demographics, medical comorbidities, surgical characteristics, and outcomes were examined to isolate predictors for readmission within 30 days postoperatively. Results  A total of 57 patients were identified to have undergone TWA. The average patients were 62.3 (13.8) years old, female (57.7%), and most were treated in the outpatient setting (67.3%). Comorbid conditions included smoking (17.3%), diabetes (15.4%), and chronic steroid therapy (15.4%). No complications were identified in the 30-day postoperative period. There was a trend for increasing utilization of TWA over the years included. Conclusion  TWA is a safe procedure with low complication rates in the acute postoperative period. Increasing utilization is likely a result of improved outcomes and cost-effectiveness of TWA. Level of Evidence  This is a Level II, prognostic study.

Capitolunate Arthrodesis: A Systematic Review

PURPOSE

To compile and review the indications, outcomes, and complications of capitolunate arthrodesis (CLA).

METHODS

We performed a literature search identifying 33 articles, 6 of which met inclusion criteria, including 80 patients. Included publications contained the results of CLA with minimum 12-month follow-up between 2000 and 2018. Data were pooled and analyzed focusing on the primary outcomes of union and complications.

RESULTS

Average age of patients was 48 years (range, 22-86 years), median follow-up was 34 months (range, 12-198 months), and most common indication was scaphoid nonunion advanced collapse (59%). Nearly half underwent a concomitant triquetrum excision (49%). Most patients were pain-free (78%) and returned to work (92%). Grip strength and visual analog pain scale both improved after CLA. Whereas 96% fused within a reported 42 to 210 days (median, 70 days), 11% of patients had complications including nonunion (3.8%) and loose hardware (6.3%). The reoperation rate was 14%, including wrist arthrodeses and wrist arthroplasty.

CONCLUSIONS

Capitolunate arthrodesis is a feasible option for scapholunate advanced collapse and scaphoid nonunion advanced collapse wrists with complications similar to those encountered in 4-corner arthrodesis.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Global Excision of Severe Heterotopic Ossification of the Shoulder: A Case Report

CASE

A 21-year-old man sustained a closed glenohumeral fracture/dislocation as a pedestrian struck by a motor vehicle. He was treated nonoperatively and developed severe post-traumatic heterotopic ossification (HO) with near-complete shoulder ankylosis. We present our technique for safe surgical excision.

CONCLUSIONS

Excision led to improvements in motion and quality of life at 1 year postoperatively. Recommendations for successful HO excision around the shoulder include excision after at least 180 days, appropriate preoperative imaging to include cross-sectional imaging and a 3D model, intraoperative fluoroscopy, well-serviced instruments, preparation for iatrogenic fracture and/or neurovascular injury, meticulous hemostasis, postoperative HO prophylaxis, immediate postoperative therapy, and involvement of a multidisciplinary team.

Outcomes and Return to Work Following Complex Nerve Lacerations in the Volar Forearm in an Underserved Spanish-Speaking Population

Purpose

Lacerations to the ulnar and median nerve in the volar forearm have demonstrated considerable long-term clinical and socioeconomic impacts on patients. The purpose of this study was to evaluate the outcomes of complex volar forearm lacerations involving one or more major peripheral nerves in an economically disadvantaged patient population.

Methods

In this study, a retrospective analysis of 61 patients who sustained lacerations to the median nerve, ulnar nerve, or both with volar wrist lacerations was performed. Each patient’s preinjury and postinjury occupation, dominant extremity, and demographic variables were evaluated. Sensation recovery, motor recovery, Disabilities of the Arm, Shoulder, and Hand scores, visual analog scale scores, cold intolerance, and return to work were evaluated at 3, 6, and 12 months after the injury.

Results

Patients with isolated median nerve injuries demonstrated improved motor recovery compared with patients with isolated ulnar nerve injuries. Patients with combined nerve injuries had worse sensation recovery and motor recovery, and lower rates of return to work than either group of patients with isolated nerve injuries. Manual laborers had worse motor recovery and lower rates of return to work than did patients who were office workers.

Conclusions

Patients with combined median and ulnar nerve injuries have worse functional recovery and lower rates of return to work than do patients with isolated median or isolated ulnar nerve injuries at 1 year. Manual laborers demonstrated worse functional recovery and lower rates of return to work compared with office workers at 1 year.

Type of study/level of evidence

Therapeutic III.

Peripheral nerve repair throughout the body with processed nerve allografts: Results from a large multicenter study

BACKGROUND

Peripheral nerve damage resulting in pain, loss of sensation, or motor function may necessitate a reconstruction with a bridging material. The RANGER® Registry was designed to evaluate outcomes following nerve repair with processed nerve allograft (Avance® Nerve Graft; Axogen; Alachua, FL). Here we report on the results from the largest peripheral nerve registry to-date.

METHODS

This multicenter IRB-approved registry study collected data from patients repaired with processed nerve allograft (PNA). Sites followed their own standard of care for patient treatment and follow-up. Data were assessed for meaningful recovery, defined as ≥S3/M3 to remain consistent with previously published results, and comparisons were made to reference literature.

RESULTS

The study included 385 subjects and 624 nerve repairs. Overall, 82% meaningful recovery (MR) was achieved across sensory, mixed, and motor nerve repairs up to gaps of 70 mm. No related adverse events were reported. There were no significant differences in MR across the nerve type, age, time-to-repair, and smoking status subgroups in the upper extremity (p > .05). Significant differences were noted by the mechanism of injury subgroups between complex injures (74%) as compared to lacerations (85%) or neuroma resections (94%) (p = .03) and by gap length between the <15 mm and 50-70 mm gap subgroups, 91 and 69% MR, respectively (p = .01). Results were comparable to historical literature for nerve autograft and exceed that of conduit.

CONCLUSIONS

These findings provide clinical evidence to support the continued use of PNA up to 70 mm in sensory, mixed and motor nerve repair throughout the body and across a broad patient population.

In vivo model of human post-traumatic heterotopic ossification demonstrates early fibroproliferative signature

Background

The relationship between the tissue injury healing response and development of heterotopic ossification (HO) is poorly understood. Here we compare a rat blast model and human traumatized muscle from a blast injury to study the early signatures of osteogenesis and fibrosis during the formation of HO.

Methods

Rat and human tissues were characterized using histology, scanning electron microscopy, immunohistochemistry, as well as gene and protein expression analysis. Additionally, animals and humans were assessed radiographically for HO formation following injury.

Results

Markers of bone formation were dramatically increased in tissue samples from both humans and rats, and both displayed increased fibroproliferative regions within the injured tissues and elevated expression of markers of tissue fibrosis such as TGF-β1, Fibronectin, SMAD3 and PAI-1. Markers of inflammation and fibrosis (ACTA, TNFα, BMP1 and BMP3) were elevated at the RNA level in both rat and human samples. By day 42, bone formation in the rat blast model appeared similar in radiographs compared to human patients who progressed to develop post-traumatic HO.

Conclusions

Our data demonstrates that a similar early fibrotic response is evident in both the rat blast model and the human tissues following a traumatic injury and demonstrates the relevance of this animal model for future translational studies.

Dispelling the Myth of Work-Related de Quervain's Tenosynovitis

De Quervain's Tenosynovitis (DQT) is a common condition characterized by pain about the dorsal-radial aspect of the wrist, just proximal to the radial styloid. The condition is precipitated by a thickened first dorsal compartment and its tendons. The impression that DQT is caused from work-related injury is misdirected, as no study has established an association between hand usage at work or trauma with DQT. Physicians should exercise caution when discussing the causes and natural history of DQT with symptomatic patients.

Gender Disparities Within US Army Orthopedic Surgery: A Preliminary Report

INTRODUCTION

Women account for approximately 15% of the active duty US Army, and studies show that women may be at an increased risk of musculoskeletal injury during sport and military training. Nationally, the field of orthopedic surgery comprises 14% women, lagging behind other surgical fields. Demographics for US Military orthopedic surgeons are not readily available. Similarly, demographic data of graduating medical students entering Military Medicine are not reported. We hypothesize that a gender disparity within military orthopedics will be apparent. We will compare the demographic profile of providers to our patients and hypothesize that the two groups are dissimilar. Secondarily, we examine the demographics of military medical students potentially entering orthopedics from the Uniformed Services University of the Health Sciences (USUHS) or the Health Professions Scholarship Program.

METHODS

A census was formed of all US Army active duty orthopedic surgeons to include staff surgeons and residents, as well as US Army medical student graduates and orthopedic patients.

RESULTS

There are 252 Army orthopedic surgeons and trainees; 26 (10.3%) are women and 226 (89.7%) are men. There were no significant demographic differences between residents and staff. Between 2014 and 2017, the 672 members of the USUHS graduating classes included 246 Army graduates. Of those, 62 (25%) were female. Army Health Professions Scholarship Program graduated 1,072 medical students, with women comprising 300 (28%) of the group. No statistical trends were seen over the 4 yr at USUHS or in Health Professions Scholarship Program. In total, 2,993 orthopedic clinic visits during the study period were by Army service members, 23.6% were women.

CONCLUSION

There exists a gender disparity among US Army orthopedic surgeons, similar to that seen in civilian orthopedics. Gender equity is also lacking among medical students who feed into Army graduate medical education programs. The gender profile of our patient population is not reflected by that of providers. Because patients prefer providers of the same gender, this is a limitation to patient satisfaction and access to care for musculoskeletal injuries. Further study is underway to identify perceptions and potential causes of these disparities, including the critical perspective of our patients. In addition to the inherent benefits offered by diversity (e.g., expanding the talent pool and more perspectives for decision-making), ultimately it affords a greater ability to maintain a fit and ready force.

Outcome measures after medial ulnar collateral ligament reconstructions in a military population

BACKGROUND

Medial ulnar collateral ligament (MUCL) reconstruction outcomes are well described in competitive throwers but not in nonthrowers. This investigation elucidated epidemiologic variables, functional outcomes, and prognostic factors after MUCL reconstruction in young active patients.

METHODS

United States military service members undergoing MUCL reconstruction were isolated using the Management Analysis and Reporting Tool (M2) database from 2009 to 2016. Demographics, injury characteristics, and surgical variables were extracted. Multivariate analysis was performed, discerning variables predictive of postoperative functional outcomes, complications, and reoperation.

RESULTS

Sixty-six patients met inclusion criteria, and 47% participated in throwing sports. Of these, 36.4% reported a throwing mechanism of injury (MOI), 60.6% reported an acute trauma MOI, 59% reported preoperative ulnar nerve symptoms, and 39.4% experienced symptoms postoperatively. At final follow-up, average Disabilities of the Arm, Shoulder and Hand (DASH) and Mayo Elbow Performance Score (MEPS) scores were 10.8 ± 16.2 and 87.6 ± 17.1, respectively. A total of 86.4% reported no disability (DASH < 30), and 83.3% experienced good or excellent outcomes (MEPS >74). Age < 30 years, dominant arm injury, competitive throwing history, and throwing MOI correlated with improved DASH and MEPS scores, push-up count, postoperative pain and instability, and rates of ulnar nerve symptoms (P < .05). Psychiatric diagnosis and preoperative stiffness and instability were associated with lower outcome scores (P < .05). Ulnar nerve interventions did not correlate with presence or absence of postoperative ulnar nerve symptoms.

CONCLUSIONS

MUCL reconstruction demonstrates a high good-to-excellent outcome rate and low complication and revision rates in young active individuals with intense upper extremity demands. Nonthrowing MOIs and psychiatric pathology are associated with postoperative complications and poorer outcomes.

The Differentiation Stage of Transplanted Stem Cells Modulates Nerve Regeneration

In regenerative medicine applications, the differentiation stage of implanted stem cells must be optimized to control cell fate and enhance therapeutic efficacy. We investigated the therapeutic potential of human induced pluripotent stem cell (iPSC)-derived cells at two differentiation stages on peripheral nerve regeneration. Neural crest stem cells (NCSCs) and Schwann cells (NCSC-SCs) derived from iPSCs were used to construct a tissue-engineered nerve conduit that was applied to bridge injured nerves in a rat sciatic nerve transection model. Upon nerve conduit implantation, the NCSC group showed significantly higher electrophysiological recovery at 1 month as well as better gastrocnemius muscle recovery at 5 months than the acellular group, but the NCSC-SC group didn’t. Both transplanted NCSCs and NCSC-SCs interacted with newly-growing host axons, while NCSCs showed better survival rate and distribution. The transplanted NCSCs mainly differentiated into Schwann cells with no teratoma formation, and they secreted higher concentrations of brain-derived neurotrophic factor and nerve growth factor than NCSC-SCs. In conclusion, transplantation of iPSC-NCSCs accelerated functional nerve recovery with the involvement of stem cell differentiation and paracrine signaling. This study unravels the in vivo performance of stem cells during tissue regeneration, and provides a rationale of using appropriate stem cells for regenerative medicine.

Virtual stress testing of fracture stability in soldiers with severely comminuted tibial fractures

Virtual stress testing (VST) provides a non-invasive estimate of the strength of a healing bone through a biomechanical analysis of a patient's computed tomography (CT) scan. We asked whether VST could improve management of patients who had a tibia fracture treated with external fixation. In a retrospective case-control study of 65 soldier-patients who had tibia fractures treated with an external fixator, we performed VST utilizing CT scans acquired prior to fixator removal. The strength of the healing bone and the amount of tissue damage after application of an overload were computed for various virtual loading cases. Logistic regression identified computed outcomes with the strongest association to clinical events related to nonunion within 2 months after fixator removal. Clinical events (n = 9) were associated with a low tibial strength for compression loading (p < 0.05, AUC = 0.74) or a low proportion of failed cortical bone tissue for torsional loading (p < 0.005, AUC = 0.84). Using post-hoc thresholds of a compressive strength of four times body-weight and a proportional of failed cortical bone tissue of 5%, the test identified all nine patients who failed clinically (100% sensitivity; 40.9% positive predictive value) and over three fourths of those (43 of 56) who progressed to successful healing (76.8% specificity; 100% negative predictive value). In this study, VST identified all patients who progressed to full, uneventful union after fixator removal; thus, we conclude that this new test has the potential to provide a quantitative, objective means of identifying tibia-fracture patients who can safely resume weight bearing. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:805-811, 2017.

Quality of healing: defining, quantifying, and enhancing skeletal muscle healing

Skeletal muscle injury is common in everyday physical activity and athletics, as well as in orthopedic trauma and disease. The overall functional disability resulting from muscle injury is directly related to the intrinsic healing properties of muscle and extrinsic treatment options designed to maximize repair and/or regeneration of muscle tissue all while minimizing pathologic healing pathways. It is important to understand the injury and repair pathways in order to improve the speed and quality of recovery. Recent military conflicts in Iraq and Afghanistan have highlighted the importance of successfully addressing muscular injury and showed the need for novel treatment options that will maximize functional regeneration of the damaged tissue. These severe, wartime injuries, when juxtaposed to peacetime, sports-related injuries, provide us with interesting case examples of the two extreme forms of muscular damage. Comparing and contrasting the differences in these healing pathways will likely provide helpful cues that will help physicians recapitulate the near complete repair and regeneration in less traumatic injuries in addition to more severe cases.

Characterization of discrete subpopulations of progenitor cells in traumatic human extremity wounds

Here we show that distinct subpopulations of cells exist within traumatic human extremity wounds, each having the ability to differentiate into multiple cells types in vitro. A crude cell suspension derived from traumatized muscle was positively sorted for CD29, CD31, CD34, CD56 or CD91. The cell suspension was also simultaneously negatively sorted for either CD45 or CD117 to exclude hematopoietic stem cells. These subpopulations varied in terms their total numbers and their abilities to grow, migrate, differentiate and secrete cytokines. While all five subpopulations demonstrated equal abilities to undergo osteogenesis, they were distinct in their ability to undergo adipogenesis and vascular endotheliogenesis. The most abundant subpopulations were CD29+ and CD34+, which overlapped significantly. The CD29+ and CD34+ cells had the greatest proliferative and migratory capacity while the CD56+ subpopulation produced the highest amounts of TGFß1 and TGFß2. When cultured under endothelial differentiation conditions the CD29+ and CD34+ cells expressed VE-cadherin, Tie2 and CD31, all markers of endothelial cells. These data indicate that while there are multiple cell types within traumatized muscle that have osteogenic differentiation capacity and may contribute to bone formation in post-traumatic heterotopic ossification (HO), the major contributory cell types are CD29+ and CD34+, which demonstrate endothelial progenitor cell characteristics.

Human mesenchymal stem cells generate a distinct pericellular zone of MMP activities via binding of MMPs and secretion of high levels of TIMPs

Mesenchymal stem cells (MSCs) are attractive candidates for inclusion in cell-based therapies by virtue of their abilities to home to wound sites. However, in-depth characterization of the specific effects of MSCs on their microenvironments is needed to realize their full therapeutic potentials. Furthermore, since MSCs of varying properties can be isolated from a diverse spectrum of tissues, a strategic and rational approach in MSC sourcing for a particular application has yet to be achieved. For example, MSCs that activate their proteolytic environments may promote tissue remodeling, while those from different tissue sources may inhibit proteases and promote tissue stabilization. This study attempts to address these issues by analyzing MSCs isolated from three adult tissue sources in terms of their effects on their proteolytic microenvironments. Human bone marrow, adipose, and traumatized muscle derived MSCs were compared in their soluble and cellular-associated MMP components and activity. For all types of MSCs, MMP activity associated with the cell surface, but activity levels and MMP profiles differed with tissue source. All MSC types bound exogenous active MMPs at their surfaces. MSCs were also able to activate exogenous proMMP-2 and proMMP-13. This is in marked contrast to the MSC soluble compartment, which strongly inhibited MMPs via endogenous TIMPs. The exact TIMP used to inhibit the exogenous MMP differed with MSC type. Thus, MSCs saturate their environment with both MMPs and TIMPs. Since they bind and activate MMPs at their surfaces, the net result is a very controlled pericellular localization of MMP activities by MSCs.

Inducible expression of neurotrophic factors by mesenchymal progenitor cells derived from traumatically injured human muscle

Peripheral nerve damage frequently accompanies musculoskeletal trauma and repair of these nerves could be enhanced by the targeted application of neurotrophic factors (NTFs), which are typically expressed by endogenous cells that support nerve regeneration. Injured muscle tissues express NTFs to promote reinnervation as the tissue regenerates, but the source of these factors from within the muscles is not fully understood. We have previously identified a population of mesenchymal progenitor cells (MPCs) in traumatized muscle tissue with properties that support tissue regeneration, and our hypothesis was that MPCs also secrete the NTFs that are associated with muscle tissue reinnervation. We determined that MPCs express genes associated with neurogenic function and measured the protein-level expression of specific NTFs with known functions to support nerve regeneration. We also demonstrated the effectiveness of a neurotrophic induction protocol to enhance the expression of the NTFs, which suggests that the expression of these factors may be modulated by the cellular environment. Finally, neurotrophic induction affected the expression of cell surface markers and proliferation rate of the MPCs. Our findings indicate that traumatized muscle-derived MPCs may be useful as a therapeutic cell type to enhance peripheral nerve regeneration following musculoskeletal injury.

Mesenchymal stem cell therapy for attenuation of scar formation during wound healing

Scars are a consequence of cutaneous wound healing that can be both unsightly and detrimental to the function of the tissue. Scar tissue is generated by excessive deposition of extracellular matrix tissue by wound healing fibroblasts and myofibroblasts, and although it is inferior to the uninjured skin, it is able to restore integrity to the boundary between the body and its environment. Scarring is not a necessary process to repair the dermal tissues. Rather, scar tissue forms due to specific mechanisms that occur during the adult wound healing process and are modulated primarily by the inflammatory response at the site of injury. Adult tissue-derived mesenchymal stem cells, which participate in normal wound healing, are trophic mediators of tissue repair. These cells participate in attenuating inflammation in the wound and reprogramming the resident immune and wound healing cells to favor tissue regeneration and inhibit fibrotic tissue formation. As a result, these cells have been considered and tested as a likely candidate for a cellular therapy to promote scar-less wound healing. This review identifies specific mechanisms by which mesenchymal stem cells can limit tissue fibrosis and summarizes recent in vivo studies where these cells have been used successfully to limit scar formation.