First discovered by Friedenstein in 1976, mesenchymal stem cells (MSCs) are adult stem cells found throughout the body that share a fixed set of characteristics. Discovered initially in the bone marrow, this cell source is considered the gold standard for clinical research, although various other sources—including adipose tissue, dental pulp, mobilised peripheral blood and birth-derived tissues—have since been identified. Although similar, MSCs derived from different sources possess distinct characteristics, advantages and disadvantages, including their differentiation potential and proliferation capacity, which influence their applicability. Hence, they may be used for specific clinical applications in the fields of regenerative medicine and tissue engineering. This review article summarises current knowledge regarding the various sources, characteristics and therapeutic applications of MSCs.Keywords: Mesenchymal Stem Cells; Adult Stem Cells; Regenerative Medicine; Cell Differentiation; Tissue Engineering.

Only select tissues and organs are able to spontaneously regenerate after disease or trauma, and this regenerative capacity diminishes over time. Human stem cell research explores therapeutic regenerative approaches to treat various conditions. Mesenchymal stem cells (MSCs) are derived from adult stem cells; they are multipotent and exert anti-inflammatory and immunomodulatory effects. They can differentiate into multiple cell types of the mesenchyme, for example, endothelial cells, osteoblasts, chondrocytes, fibroblasts, tenocytes, vascular smooth muscle cells, and sarcomere muscular cells. MSCs are easily obtained and can be cultivated and expanded in vitro; thus, they represent a promising and encouraging treatment approach in orthopedic surgery. Here, we review the application of MSCs to various orthopedic conditions, namely, orthopedic trauma; muscle injury; articular cartilage defects and osteoarthritis; meniscal injuries; bone disease; nerve, tendon, and ligament injuries; spinal cord injuries; intervertebral disc problems; pediatrics; and rotator cuff repair. The use of MSCs in orthopedics may transition the practice in the field from predominately surgical replacement and reconstruction to bioregeneration and prevention. However, additional research is necessary to explore the safety and effectiveness of MSC treatment in orthopedics, as well as applications in other medical specialties.

The Stewart-Treves syndrome is a rare and deadly entity, which is defined as angiosarcoma arising in the setting of chronic lymphedema. It typically presents in women who develop lymphedema in the upper extremity secondary to axillary lymph node dissection for breast cancer surgery. It is extremely uncommon in the lower extremities as a result of idiopathic chronic lymphedema. Here, we present the case of a 63-year-old female patient with idiopathic chronic lymphedema of the lower extremities having morbid obesity (BMI 82.6) and multiple comorbidities. She developed multiple confluent, hemorrhagic and necrotic elevated purple-black papules in the lower extremities, for which the initial diagnosis was cellulitis. Because there was no improvement with antibiotics, a lower extremity ultrasound and biopsy was performed which showed multiple masses in the left inner upper calf with solid and cystic components. The pathology results of the punch biopsies were consistent with angiosarcoma. Immunohistochemical studies revealed positivity for CD31, FLI-1, and a high Ki-67 proliferation rate. Because of the patient's weight and medical comorbidities, no further extensive diagnostic tests were performed to detect metastatic disease, and because of contraindications, no further medical treatment was provided. The patient subsequently died 1 month after diagnosis.

Among various infections, chronic osteomyelitis is one of the most challenging in terms of treatment. This infection is more common among patients with open fractures and those who have undergone elective orthopedic procedures. The treatment of osteomyelitis requires high antibiotic doses and an aggressive and multifaceted surgical approach. The use of parenteral antibiotics alone, without debridement, is not sufficiently effective, due to the formation of sequestra and the low vascularity of the affected area. The surgical options available for patients with chronic osteomyelitis include sequestrectomy, curettage, and intramedullary reaming, although these procedures usually result in bone defects that require further surgical intervention. Polymethyl methacrylate or calcium phosphate beads, impregnated with antibiotics, are commonly placed in such cases; however, this option has several disadvantages, including the need for future removal of cement, uncontrollable local release of antibiotics, and the need for broad-spectrum agents. The resulting bone defects also require additional treatments involving vascularized fibula grafting, intramedullary nails, use of techniques like Masquelet and Ilizarov, and even soft tissue transfers. All of these methods have certain limitations, such as the eventual requirement of more than one surgical event. Certain growth factors aid in the development and vascularization of new bone, such as bone morphogenetic proteins (BMPs) and insulin-like growth factor I (IGF-1). We propose that nanoparticles of BMPs, IGL-1, and microorganism-specific antibiotics can be placed on the surface of intramedullary nails. These nanoparticles can be attached to various different polymeric materials such as poly(d,l-lactide), which is a biocompatible and biodegradable polymer, and can be positioned in several layers, to ensure controlled and systematic release. The placement of nanoparticles at the infection site alone will also ensure local delivery of the drugs only to the required areas. Moreover, these intramedullary nails will be useful for both infected non-unions and mal-unions. Over time, the nanoparticles will eradicate the infection and stimulate new healthy bone formation, whereas the intramedullary nail itself will provide constant stability and immobilization. This model provides new and revolutionary ideas for the development of individualized technologies in medicine.

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Key Clinical MessageInvolvement of the central nervous system in sarcoidosis is rare; neurosarcoidosis, although unusual, can present as leptomeningitis. The diagnosis is usually difficult because of the vague and broad symptomatology; therefore, a prompt diagnosis should be made, and adequate treatment should be administered to reduce morbidity and mortality.

Quadricuspid aortic valve (QAV) is an anatomic valvular variant, with a prevalence of 0.008% to 0.033% in the general population, and 1.46% in patients that undergo aortic valve replacement. The QAV can be an isolated valvular abnormality or associated with other congenital heart defects. In this article, we present three of the few reported cases of QAV in the Hispanic population, all of which were asymptomatic and without evidence of hemodynamic alterations or other associated heart defects. Additionally a literature review is provided.

Key Clinical MessageIn older adults with first‐time psychiatric manifestations, physical disorders such as systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) must be considered, even in patients with cognitive dysfunction and/or dementia. Here, we describe the case of a 77‐year‐old woman with psychosis who was later diagnosed with SLE and APS.