Sacroiliac Joint: The immovable joint formed by the lateral surfaces of the SACRUM and ILIUM.Sacroiliitis: Inflammation of the SACROILIAC JOINT. It is characterized by lower back pain, especially upon walking, fever, UVEITIS; PSORIASIS; and decreased range of motion. Many factors are associated with and cause sacroiliitis including infection; injury to spine, lower back, and pelvis; DEGENERATIVE ARTHRITIS; and pregnancy.Spondylarthritis: Inflammation of the joints of the SPINE, the intervertebral articulations.Joint DiseasesSpondylitis, Ankylosing: A chronic inflammatory condition affecting the axial joints, such as the SACROILIAC JOINT and other intervertebral or costovertebral joints. It occurs predominantly in young males and is characterized by pain and stiffness of joints (ANKYLOSIS) with inflammation at tendon insertions.Low Back Pain: Acute or chronic pain in the lumbar or sacral regions, which may be associated with musculo-ligamentous SPRAINS AND STRAINS; INTERVERTEBRAL DISK DISPLACEMENT; and other conditions.Injections, Intra-Articular: Methods of delivering drugs into a joint space.Pelvic Bones: Bones that constitute each half of the pelvic girdle in VERTEBRATES, formed by fusion of the ILIUM; ISCHIUM; and PUBIC BONE.Tuberculosis, Osteoarticular: Tuberculosis of the bones or joints.Joints: Also known as articulations, these are points of connection between the ends of certain separate bones, or where the borders of other bones are juxtaposed.Sacrum: Five fused VERTEBRAE forming a triangle-shaped structure at the back of the PELVIS. It articulates superiorly with the LUMBAR VERTEBRAE, inferiorly with the COCCYX, and anteriorly with the ILIUM of the PELVIS. The sacrum strengthens and stabilizes the PELVIS.Nerve Block: Interruption of NEURAL CONDUCTION in peripheral nerves or nerve trunks by the injection of a local anesthetic agent (e.g., LIDOCAINE; PHENOL; BOTULINUM TOXINS) to manage or treat pain.Back Pain: Acute or chronic pain located in the posterior regions of the THORAX; LUMBOSACRAL REGION; or the adjacent regions.Ilium: The largest of three bones that make up each half of the pelvic girdle.Pelvic Girdle Pain: Discomfort associated with the bones that make up the pelvic girdle. It occurs frequently during pregnancy.Manipulation, Orthopedic: The planned and carefully managed manual movement of the musculoskeletal system, extremities, and spine to produce increased motion. The term is sometimes used to denote a precise sequence of movements of a joint to determine the presence of disease or to reduce a dislocation. In the case of fractures, orthopedic manipulation can produce better position and alignment of the fracture. (From Blauvelt & Nelson, A Manual of Orthopaedic Terminology, 5th ed, p264)Pubic Bone: A bone that forms the lower and anterior part of each side of the hip bone.Pain, Referred: A type of pain that is perceived in an area away from the site where the pain arises, such as facial pain caused by lesion of the VAGUS NERVE, or throat problem generating referred pain in the ear.Spondylitis: Inflammation of the SPINE. This includes both arthritic and non-arthritic conditions.Zygapophyseal Joint: The joint that occurs between facets of the interior and superior articular processes of adjacent VERTEBRAE.Arthritis, Infectious: Arthritis caused by BACTERIA; RICKETTSIA; MYCOPLASMA; VIRUSES; FUNGI; or PARASITES.Sciatica: A condition characterized by pain radiating from the back into the buttock and posterior/lateral aspects of the leg. Sciatica may be a manifestation of SCIATIC NEUROPATHY; RADICULOPATHY (involving the SPINAL NERVE ROOTS; L4, L5, S1, or S2, often associated with INTERVERTEBRAL DISK DISPLACEMENT); or lesions of the CAUDA EQUINA.ArthritisLumbosacral Plexus: The lumbar and sacral plexuses taken together. The fibers of the lumbosacral plexus originate in the lumbar and upper sacral spinal cord (L1 to S3) and innervate the lower extremities.Spine: The spinal or vertebral column.Anesthetics, Local: Drugs that block nerve conduction when applied locally to nerve tissue in appropriate concentrations. They act on any part of the nervous system and on every type of nerve fiber. In contact with a nerve trunk, these anesthetics can cause both sensory and motor paralysis in the innervated area. Their action is completely reversible. (From Gilman AG, et. al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th ed) Nearly all local anesthetics act by reducing the tendency of voltage-dependent sodium channels to activate.HLA-B27 Antigen: A specific HLA-B surface antigen subtype. Members of this subtype contain alpha chains that are encoded by the HLA-B*27 allele family.Osteitis: Inflammation of the bone.Knee Joint: A synovial hinge connection formed between the bones of the FEMUR; TIBIA; and PATELLA.Pain Measurement: Scales, questionnaires, tests, and other methods used to assess pain severity and duration in patients or experimental animals to aid in diagnosis, therapy, and physiological studies.Lumbar Vertebrae: VERTEBRAE in the region of the lower BACK below the THORACIC VERTEBRAE and above the SACRAL VERTEBRAE.Anesthesia, Local: A blocking of nerve conduction to a specific area by an injection of an anesthetic agent.Pain Management: A form of therapy that employs a coordinated and interdisciplinary approach for easing the suffering and improving the quality of life of those experiencing pain.Biomechanical Phenomena: The properties, processes, and behavior of biological systems under the action of mechanical forces.