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The popliteal fossa is a shallow depression located posterior to the knee joint. This area is often referred to as the knee "pit" and may develop vascular, nervous, lymphatic, and adipose issues as well as swelling and masses. The fossa houses several important structures that are essential for lower extremity function. Anatomic boundaries of the popliteal fossa include the following: Superomedially, the semimembranosus, and semitendinosus muscles. Superolaterally, the biceps femoris muscle (short and long heads) . Inferomedial and inferolateral, the medial and lateral heads of the gastrocnemius muscle contribute to the lower border, respectively. The plantaris muscle also runs deep to the gastrocnemius to form the inferolateral border. The roof of the fossa, proceeding from most superficial to deep, consists of the skin, superficial fascia, and deep (popliteal) fascia. The floor of the fossa includes the popliteal surface of the femur, the capsule of the knee joint, popliteal ligament, and fascia encasing the popliteus muscle. It is important to understand the involved anatomy of the popliteal fossa because patients could present with posterior knee pain due to multiple etiologies. One of the more common issues involving the posterior knee is a Baker cyst; it has a fluid-filled bursa, which is usually secondary to friction or irritation. Other causes of posterior knee pain could be a popliteal artery aneurysm, lymphadenopathy, thrombophlebitis, and very rarely, sarcomas. Proper diagnosis is essential for effective treatment and management., (Copyright © 2022, StatPearls Publishing LLC.)

A chordoma is a low-grade, slow-growing, but locally invasive and locally aggressive tumor. Chordomas belong to the sarcoma family of tumors. They arise from the remnants of the notochord and occur in the midline along the spinal axis from the clivus to the sacrum, anterior to the spinal cord. The location distribution of chordomas is 50% sacral, 35% skull base, and 15% occur in the vertebral bodies of the mobile spine (most commonly the C2 vertebrae followed by the lumbar then thoracic spine). Overall 5-year survival is approximately 50%, and treatment is en bloc surgical resection followed by high-dose conformal radiation therapy such as proton beam radiation., (Copyright © 2022, StatPearls Publishing LLC.)

The nervous system is a complex network that enables an organism to interact with its surroundings. Sensory components that detect environmental stimuli, and motor components that provide skeletal, cardiac, and smooth muscle control, as well as control of glandular secretions, are coordinated in a system to compel appropriate motor responses to the stimuli or sensory inputs that have been received, stored, and processed. The nervous system is made up of vast neural networks; signaling within these circuits enables thinking, language, feeling, learning, memory, and all function and sensation.  It is well-established that through the plasticity of existing cells our nervous systems can adapt to situations not previously encountered, but it also has been shown that neural stem cells (NSCs) are plastic and involved in creating new connections in adaptation and response to injury. NSCs play a fundamental role in development, and in the ability to respond to stimuli in the environment and injury., (Copyright © 2022, StatPearls Publishing LLC.)

Healthcare in the United States is primarily based on diagnosing disease and subsequently treating the disease. Consider several of the most prominent medical advances of the past century: , (Copyright © 2022, StatPearls Publishing LLC.)

The temporal bone is the thickest bone in the body and requires great force to fracture (1875 pounds or 850 kg of lateral force in one study). The temporal bone houses portions of the internal carotid artery and internal jugular vein, cranial nerves (CN) VII-XI, the middle and inner ear structures, and forms a portion of the middle cranial fossa. Such high-velocity injury to these crucial structures carries the risk of significant morbidity and mortality. The temporal bone is a paired component of the skull base, articulating posteriorly with the occipital bone, superiorly with the parietal bones, and anteriorly with the sphenoid bone creating the occipitomastoid, squamous, and sphenosquamosal sutures, respectively. The temporal bone has complex anatomy including four geographic parts (squamous, mastoid, petrous, tympanic) and numerous named foramen/canals (foramen lacerum, carotid canal, internal acoustic meatus, jugular foramen). : Foramen lacerum: greater petrosal nerve. Carotid canal: internal carotid artery. Internal acoustic meatus: CN VII, CN VIII. Jugular foramen: internal jugular vein, posterior meningeal artery, CN IX, CN X, CN XI. Additionally, there are 3 bony processes (zygomatic, mastoid, styloid). The otic capsule, or bony labyrinth, is the dense portion of the petrous temporal bone that surrounds the membranous labyrinth of the inner ear. This is, in turn, surrounded by the less dense and variably pneumatized petrous apex and the mastoid segment of the temporal bone. From anterior to posterior the otic capsule contains the cochlea, vestibule, and three semicircular canals. , (Copyright © 2022, StatPearls Publishing LLC.)

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with multisystemic involvement. The condition has several phenotypes, with varying clinical presentations from mild mucocutaneous manifestations to multiorgan and severe central nervous system involvement. Several immunopathogenic pathways play a role in the development of SLE. Hargraves described the lupus erythematosus (LE cell) in 1948. Several pathogenic autoantibodies have since been identified. Despite recent advances in technology and understanding of the pathological basis and risk factors for SLE, the exact pathogenesis is still not well known. Diagnosis of SLE can be challenging, and while several classification criteria have been posed, their utility in the clinical setting is still a matter of debate. Management of SLE is dictated by organ system involvement. Despite several agents shown to be efficacious in treating SLE, the disease still poses significant morbidity and mortality risk in patients., (Copyright © 2022, StatPearls Publishing LLC.)

Shoulder dystocia is, by definition, a mechanical problem occurring during a vaginal delivery characterized by one of the following parameters: failure to deliver the fetal shoulders using solely gentle downward traction ; requirement of additional delivery maneuvers are needed to successfully deliver the baby; a documented head-to-body interval of greater than 1 minute. Unpredictable and often unavoidable obstetric emergencies complicate 0.6 to 1.4% of all vaginal deliveries. All obstetric providers are required to be knowledgeable regarding the risk factors and management of shoulder dystocia. Furthermore, shoulder dystocia can lead to obstetric brachial plexopathies such as Erb's or Klumpke's palsies. Injuries to the brachial plexus during birth can be categorized as upper lesions involving C5-6, lower lesions involving C8-T1, or total plexopathies involving C5-T1. , (Copyright © 2022, StatPearls Publishing LLC.)

The interossei muscles are intrinsic muscles of the hand located between the metacarpals. They consist of four (or three) palmar and four dorsal muscles that, respectively. These muscles are responsible for finger adduction and abduction. Synchronously, the palmar and dorsal interossei assist in flexion of the metacarpophalangeal joints and extension of the interphalangeal joints. All interossei muscles receive innervation from the deep ulnar branch of the ulnar nerve. Therefore, any injury to the ulnar nerve may have debilitating implications on specific intrinsic hand muscle functions, including finger abduction and adduction, which is primarily controlled by the interossei muscles.  , (Copyright © 2022, StatPearls Publishing LLC.)

Between each vertebral body of the spine are pads of fibrocartilage-based structures that provide support, flexibility, and minor load-sharing known as the intervertebral discs. These are primarily composed of two layers: (1) a soft, pulpy nucleus pulposus on the inside of the disc and (2) a surrounding firm structure known as the annulus fibrosus. A disruption of the normal architecture of these round discs can lead to a disc herniation or a protrusion of the inner nucleus pulposus, possibly applying pressure to the spinal cord or nerve root and resulting in radiating pain and specific locations of weakness. Slightly more than 90% of herniated discs occur at the L4-L5 or the L5-S1 disc space, which will impinge on the L4, L5, or S1 nerve root. This compression produces radiculopathy into the posterior leg and dorsal foot. If the disc injury progresses to the point of neurologic compromise or limitations with activities of daily living, then surgical intervention may be required to decompress and stabilize the affected segments. In the absence of motor deficits, a nonoperative course of analgesia, activity modification, and injections should be tried for several months. The surgical results for the primarily sciatic pain that has failed conservative treatment are predictable and favorable., (Copyright © 2022, StatPearls Publishing LLC.)

The fascia in the foot is composed of fibrous connective tissue that serves to separate, support, and attach muscles. It can be divided into the superficial fascia and the deep fascia. The superficial fascia is located just beneath the skin and varies in strength depending on where it is in the foot. On the dorsal side of the foot, the superficial fascia is thin and mobile. In contrast, the superficial fascia of the plantar side is thick and has multiple septations that contain fat to provide a cushion for the foot. It also has thick connections with the underlying deep fascia.  The deep fascia is stronger than the superficial fascia. On the dorsal side of the foot, the deep fascia is thin and connected to the inferior extensor retinaculum. It continues laterally and posteriorly to connect with the plantar fascia, which is the name of the deep fascia on the plantar side. Similar to the superficial fascia, the deep fascia is much thicker on the plantar side. The central part of the plantar fascia forms the plantar aponeurosis, which starts proximally at the calcaneus and extends distally into five separate bands that become the digital sheaths. It is supported inferiorly by the superficial transverse metatarsal ligament.  The fascia acts as a border for the five anatomic compartments of the foot, which include the medial compartment, the central compartment, the lateral compartment, the dorsal compartment, and the interosseous compartment.  The medial compartment is bordered inferiorly by the medial plantar fascia, the central compartment is bordered inferiorly by the plantar aponeurosis, and the lateral compartment is bordered inferiorly by the lateral plantar fascia. The plantar aponeurosis also has intermuscular septa that extend superiorly through the foot to divide the medial, central, and lateral compartments. The interosseous compartment is bordered by the plantar and dorsal interosseous fascia. The dorsal compartment is bordered by the dorsal fascia superiorly and by the tarsal bones and dorsal interosseous fascia inferiorly. , (Copyright © 2022, StatPearls Publishing LLC.)

Professional ethics guide the health care staff in their interactions with patients, providers, co-staff and business associates in the workplace. However, there is a need for guidance on the best practices for the professional conduct of physicians and health care personnel in the digital environment. As new social networking platforms gain acceptance, professionalism must be applied in this new setting. In particular, ready access to online platforms leads to instantaneous feedbacks and comments from patients, health care workers, and health providers. In particular, issues of defamation have steadily risen., (Copyright © 2022, StatPearls Publishing LLC.)

The autonomic nervous system consists of the sympathetic and parasympathetic divisions. As the name implies, the lumbar sympathetic block can be utilized to disrupt the nerve supply from the sympathetic chain to the lower extremities. This is useful in treating sympathetic mediators of pain. Specifically, lumbar sympathetic blocks can be used for the treatment of painful conditions such as complex regional pain syndrome, phantom limb pain, hyperhidrosis, painful vascular insufficiencies, and pain from herpes zoster/shingles., (Copyright © 2022, StatPearls Publishing LLC.)

The major and minor psoas muscles and the iliacus muscle make up the iliopsoas musculotendinous unit (IPMU). Commonly called iliopsoas muscle. This complex muscle system can function as a unit or intervene as separate muscles. It is essential for correct standing or sitting lumbar posture, stabilizing the coxofemoral joint, and is crucial during walking and running. The fascia covering the iliopsoas muscle creates multiple fascial connections, relating the muscle to different viscera and muscle areas. Several disorders can affect IPMU at the level of its insertion (tendon) or involving the fleshy part. To solve these dysfunctions, the doctor will indicate which therapy will be most useful, conservative or surgical, as well as physiotherapy or an osteopathic approach. There are multiple anatomical variations of IPMU, and in case of pain and disturbances, it is important to perform instrumental examinations before making a precise diagnosis. With the current scientific knowledge, one can not imagine anatomy as segments but rather as a functional continuum., (Copyright © 2022, StatPearls Publishing LLC.)

The human brain is made up of approximately 86 billion neurons that “talk” to each other using a combination of electrical and chemical (electrochemical) signals. The places where neurons connect and communicate with each other are called synapses. Each neuron has anywhere between a few to hundreds of thousands of synaptic connections, and these connections can be with itself, neighboring neurons, or neurons in other regions of the brain. A synapse is made up of a presynaptic and postsynaptic terminal. The presynaptic terminal is at the end of an axon and is the place where the electrical signal (the action potential) is converted into a chemical signal (neurotransmitter release). The postsynaptic terminal membrane is less than 50 nanometers away and contains specialized receptors. The neurotransmitter rapidly (in microseconds) diffuses across the synaptic cleft and binds to specific receptors. The type of neurotransmitter released from the presynaptic terminal and the specific receptors present on the corresponding postsynaptic terminal is critical in determining the quality and intensity of information transmitted by neurons. The postsynaptic neuron integrates all the signals it receives to determine what it does next, for example, to fire an action potential of its own or not. , (Copyright © 2022, StatPearls Publishing LLC.)

The inferior gluteal nerve branches off the sacral plexus. Its short path is primarily for the innervation of the gluteus maximus muscle. The composition of this nerve is from the dorsal branches of the ventral rami of the fifth lumbar and the first two sacral nerves. It courses inferiorly and medially before exiting the pelvic cavity via the greater sciatic notch.  After exiting the notch, the inferior gluteal nerve passes inferior to the piriformis muscle belly before dividing into several muscular branches supplying the gluteus maximus., (Copyright © 2022, StatPearls Publishing LLC.)

The scapula or shoulder blade is the bone that connects the clavicle to the humerus. The scapula forms the posterior of the shoulder girdle. It is a sturdy, flat, triangular bone. The scapula provides attachment to several groups of muscles. The intrinsic muscles of the scapula include the rotator cuff muscles, teres major, subscapularis, teres minor, and infraspinatus. These muscles attach the scapular surface and assist with abduction and external and internal rotation of the glenohumeral joint. The extrinsic muscles include the triceps, biceps, and deltoid. The third group of muscles includes the levator scapulae, trapezius, rhomboids, and serratus anterior. These muscles are responsible for rotational movements and stabilization of the scapula., (Copyright © 2022, StatPearls Publishing LLC.)

A Baker Cyst, also known as a popliteal or parameniscal cyst, is a fluid-filled sac that forms in the posterior aspect of the knee, typically located between the semimembranosus and medial head of the gastrocnemius.  In adults, Baker's Cysts tend to form in association with degenerative conditions of the knee.  One of the most common associations seen is secondary to degenerative meniscal tears.  Inflammatory conditions and arthritides are also known causes of popliteal cyst formation.  When the cyst forms in association with a meniscal tear, the meniscus serves as a one-way valve and the extruded synovial fluid localizes and consolidates to form a viscous, gel-like material. In children, popliteal cysts more commonly arise as a primary condition.  Unlike adults, popliteal cysts in children arise from a herniated posterior knee joint synovium/capsule., (Copyright © 2022, StatPearls Publishing LLC.)

Osteoporosis is a condition describing a spectrum of overall compromised skeletal microarchitecture with clinical manifestations related to decreasing levels of bone mineral density (BMD)., Spinal cord injuries (SCIs) vary significantly in terms of the range of clinical impact and overall compromise to a patient’s functional outcomes and quality of life. SCIs have long been recognized as a clinical culprit that ultimately leads to osteoporosis. Clinicians are encouraged to recognize and appreciate the similarities and subtle nuances differentiating SCI-induced osteoporosis as a separate and distinct clinical sub-entity of the broader more generalized osteoporosis diagnosis., (Copyright © 2022, StatPearls Publishing LLC.)

The biceps brachii is a large, thick muscle on the ventral portion of the upper arm. The muscle is composed of a short head (caput breve) and a long head (caput longum). The short head originates from the tip of the coracoid process, and the long head originates from the supraglenoid tubercle (tuberculum supraglenoidale) of the glenoid/scapula. Both heads course distally and become a confluent muscle belly before tapering across the anterior aspect of the elbow, eventually inserting onto the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis. The antagonist of the biceps muscle is the triceps brachii muscle., (Copyright © 2022, StatPearls Publishing LLC.)

The wrist joint also referred to as the radiocarpal joint is a condyloid synovial joint of the distal upper limb that connects and serves as a transition point between the forearm and hand. A condyloid joint is a modified ball and socket joint that allows for flexion, extension, abduction, and adduction movements., (Copyright © 2022, StatPearls Publishing LLC.)

Low back pain is one of the most common musculoskeletal complaints encountered in clinical practice. It is the leading cause of disability in the developed world and accounts for billions of dollars in healthcare costs annually. Although epidemiological studies vary, the incidence of low back pain is estimated to be 5% to 10%, with a lifetime prevalence of 60% to 90%. Most occurrences of low back pain are self-limited and will resolve without intervention beyond brief periods of rest, activity modification, and physical therapy. Approximately 50% of cases will resolve within 1 to 2 weeks. Ninety percent of cases will resolve in 6 to 12 weeks. Lumbosacral facet syndrome refers to a clinical condition consisting of various patient-reported symptoms, including unilateral or bilateral back pain radiating to either one or both buttocks, sides of the groin, and thighs, stopping above the knee. It should, however, be noted that in some cases, the symptoms of facetogenic pain may mimic radicular symptoms occurring from herniated discs or compressed roots. The facet joint degenerates secondary to repetitive overuse and everyday activities, eventually leading to microinstability and synovial facet cysts that generate and compress the surrounding nerve roots.  The lumbar facet joint constitutes approximately 15 to 45% of low back pain, with degenerative osteoarthritis as the most common form of facet joint pain. History and physical exam may serve useful in the diagnosis of facet joint syndrome, while imaging with radiographs, CT, and MRI are commonly used yet do not show an effective correlation between clinical symptoms and degenerative spine changes. Diagnostic blocks may indicate facet joints as the source of a patient's back pain, with interventions such as intraarticular steroid injection or neurolysis by radiofrequency or cryoablation to treat facetogenic pain.  , (Copyright © 2022, StatPearls Publishing LLC.)

Researchers do not agree on one comprehensive "fascia" definition. Despite the scientific uncertainty, there is an agreement with medical text that the fascia covers every structure of the body, creating a structural continuity that gives form and function to every tissue and organ.  The fascial tissue has a ubiquitous distribution in the body system; it is able to wrap, interpenetrate, support, and form the bloodstream, bone tissue, meningeal tissue, organs, and skeletal muscles. The fascia creates different interdependent layers with several depths, from the skin to the periosteum, forming a three-dimensional mechano-metabolic structure .  The Fascia and Its Effect on Individual Health  Three large groups of scholars have attempted to define fascia. The Federative Committee on Anatomical Terminology (FCAT), founded in 1989 from the General Assembly of the International Federation of Associations of Anatomists (IFAA), introduced the term "fascia superficialis" and "fascia profunda." The superficial fascia is a “whole loose layer of subcutaneous tissue lying superficial to the denser layer of fascia profunda.” The deep fascia, according to this definition, lies below the superficial fascia, highlighting two fasciae. In 2011, the Federative International Programme on Anatomical Terminologies (FIPAT), in agreement with FCAT, defined the fascia as “a sheath, a sheet, or any other dissectible aggregations of connective tissue that forms beneath the skin to attach, enclose, and separates muscles and other internal organs.” The FIPAT builds on the text of international anatomical terminology. The second definition specifies the term connective tissue, which functions to divide, separate, and support different structures. The connective tissue or fascia begins under the skin, excluding the epidermis from the fascia set. The third group of scholars is the Fascia Nomenclature Committee (2014), born from the Fascia Research Society founded in 2007. The board gave the following description of fascia: “The fascial system consists of the three-dimensional continuum of soft, collagen-containing, loose and dense fibrous connective tissues that permeate the body. It incorporates elements such as adipose tissue, adventitia, and neurovascular sheaths, aponeuroses, deep and superficial fasciae, epineurium, joint capsules, ligaments, membranes, meninges, myofascial expansions, periosteum, retinacula, septa, tendons, visceral fasciae, and all the intramuscular and intermuscular connective tissues including endo-/peri-/epimysium. The fascial system interpenetrates and surrounds all organs, muscles, bones and nerve fibers, endowing the body with a functional structure, and providing an environment that enables all body systems to operate in an integrated manner.” This is the broadest definition of fascia. The concept of a continuum of the collagen and connective structure, the cellular diversity that makes up the fascia, is emphasized. It is this continuum itself that assures the health of the body. These scientific definitions allow healthcare practitioners to make some deductions about fascia. The fascia includes everything that presumes the presence of collagen/connective tissue or from which it is derived. All the tissue considered as "specialized connective tissue" of mesodermal derivation is inserted into the fascial system. These include blood, bone, cartilage, adipose tissue, hematopoietic tissue, and lymphatic tissue. The fascial system has no discontinuity in its path, with layers of different characteristics and properties overlapping. A further research group for the nomenclature of the fascia founded in 2013: FORCE - Foundation of Osteopathic Research and Clinical Endorsement. The FORCE group has recently written several articles, highlighting new concepts to understand the concept of the fascia better: " The fascia is any tissue that contains features capable of responding to mechanical stimuli. The fascial continuum is the result of the evolution of the perfect synergy among different tissues, liquids, and solids, capable of supporting, dividing, penetrating, feeding, and connecting all the districts of the body: epidermis, dermis, fat, blood, lymph, blood and lymphatic vessels, tissue covering the nervous filaments (endoneurium, perineurium, epineurium), voluntary striated muscle fibers and the tissue covering and permeating it (epimysium, perimysium, endomysium), ligaments, tendons, aponeurosis, cartilage, bones, meninges, involuntary striated musculature and involuntary smooth muscle (all viscera derived from the mesoderm), visceral ligaments, epiploon (small and large), peritoneum, and tongue. The continuum constantly transmits and receives mechano-metabolic information that can influence the shape and function of the entire body.", (Copyright © 2022, StatPearls Publishing LLC.)

The genitofemoral nerve arises from the lumbar plexus. It supplies sensation to the skin of the anterior scrotal area in males, mons pubis in females, and the upper segment of the anterior thigh in both males and females. While distinct from the femoral nerve, the genitofemoral nerve originates from the upper lumbar segments L1-L2. It then descends inferiorly, piercing the psoas major muscle before emerging on its anterior surface. The nerve then traverses the retroperitoneum, descending over the anterior surface of the psoas muscle. The nerve continues inferiorly, ultimately separating into two divisions- the femoral and the genital branches. When the genitofemoral nerve reaches the groin area, it enters the deep inguinal ring coursing through the inguinal canal. In males, the nerve continues inferiorly and supplies the skin of the scrotum. In females, the genitofemoral nerve runs alongside the round ligament of the uterus and terminates just superior to the mons pubis and labia majora. Further, after crossing the inguinal ligament, the genitofemoral nerve travels adjacent to the external iliac artery, supplying sensation to the anterior upper thigh., (Copyright © 2022, StatPearls Publishing LLC.)

An ultrasound-guided ulnar nerve block can be used to provide surgical anesthesia or analgesia to the ulnar portion of the hand including the little finger and the ulnar half of the ring finger.  It is primarily used for surgical procedures in the distribution of the ulnar nerve both as a standalone block, combined with ulnar or radial nerve blocks for a complete hand block, or as a rescue method for inadequate brachial plexus blocks. An ulnar nerve block can be used as an alternative to sedation for painful procedures such as fracture reduction, and as a powerful adjunct for acute pain caused by burns. In patients that have sustained multiple lacerations needing repair, regional methods can be used to limit the total amount of local anesthetic used while obtaining surgical anesthesia to the affected area., (Copyright © 2022, StatPearls Publishing LLC.)