All articles starting with O

Osteocraniostenosis

Osteocraniostenosis (gracile bone dysplasia, osteocraniosplenic syndrome, OMIM 602361) is a lethal autosomal dominant skeletal dysplasia from FAM111A mutations, with cloverleaf skull, gracile bones, splenic hypo/aplasia, and perinatal death.

Osteocyte

Osteocyte: the most abundant bone cell, an embedded former osteoblast forming the lacunocanalicular network; mechanosensor directing remodeling via sclerostin and RANKL, endocrine via FGF23.

Osteofibrous dysplasia

Osteofibrous dysplasia (OFD) is a rare, benign fibro-osseous bone lesion that typically affects the tibia in children before age 10, causing swelling, pain, or bowing.

Osteogenesis imperfecta

Osteogenesis imperfecta (brittle bone disease, OI) is a group of inherited connective tissue disorders causing fragile bones, frequent fractures, dentinogenesis imperfecta, and hearing loss; COL1A1/COL1A2 mutations cause about 90 percent of cases, with no FDA-approved drug therapy.

Osteoglosphonic dysplasia

Osteoglosphonic dysplasia (osteoglophonic dysplasia, OGD, Fairbank-Keats syndrome) is a rare autosomal dominant FGFR1 skeletal dysplasia with craniosynostosis, unerupted teeth, rhizomelic short stature, and non-ossifying fibromas; about 24 cases reported.

Osteoglossidae

Osteoglossidae, the bony-tongue fish family (arowanas, arapaimas, Heterotis) of Osteoglossiformes; freshwater fishes of South America, Africa, Asia, and Australia with a toothed tongue-and-parasphenoid bite.

Osteology

Osteology is the branch of anatomy concerned with the structure and function of bones, informing the study of evolution and the treatment of osteoporosis and fractures.

Osteolysis

Osteolysis (osteolytic lesion, disappearing bone) is bone destruction from resorption exceeding formation; types include periprosthetic osteolysis from wear debris, distal clavicle, and acro-osteolysis, ICD-11 FB86.2.

Osteomalacia

Osteomalacia, or adult rickets, is softening of adult bones from impaired mineralization, usually due to vitamin D deficiency; causes bone pain, muscle weakness, pseudofractures, and is treated with vitamin D, calcium, and phosphate.

Osteomesopyknosis

Osteomesopyknosis, also called axial osteosclerosis, is a very rare benign autosomal dominant bone dysplasia causing patchy sclerosis of the spine and pelvis, mild back pain, normal labs, first described in France in 1979.

Osteomyelitis

Osteomyelitis, bone infection, is inflammation of bone caused mainly by bacteria, chiefly Staphylococcus aureus, reaching bone by blood, contiguous spread, or trauma; treated with antibiotics and debridement.

Osteomyelitis of the jaws

Osteomyelitis of the jaws, also called jaw or mandibular osteomyelitis, is a polymicrobial inflammatory bone infection of the mandible or maxilla, usually odontogenic, treated by debridement plus antibiotics, with suppurative and sclerosing forms.

Osteomyelitis or osteitis

Osteomyelitis (bone infection) and osteitis, covering routes of infection, bone-biopsy diagnosis, imaging, 4-6 week antibiotic courses, debridement, diabetic foot osteomyelitis, and guideline evidence gaps.

Osteon

Osteon (Haversian system): the microscopic structural unit of compact bone, a cylinder of 4–20 concentric lamellae around a central Haversian canal carrying blood vessels and nerves, bounded by cement lines in secondary osteons and renewed by BMU remodeling.

Osteonecrosis of the jaw

Osteonecrosis of the jaw (ONJ), also called MRONJ or formerly BRONJ, is nonhealing exposed jawbone linked to bisphosphonates, denosumab, and antiangiogenic drugs, triggered mainly by tooth extraction.

Osteopathia striata-cranial sclerosis syndrome

Osteopathia striata-cranial sclerosis syndrome, or Horan-Beighton syndrome, is a rare X-linked dominant bone disorder with skull thickening, macrocephaly, cleft palate, and hearing loss, caused by AMER1 gene variants.

Sep 29, 2026

Osteopathic manipulative treatment

Osteopathic manipulative treatment (OMT), also known as osteopathic manipulative medicine, is hands-on treatment by osteopathic physicians using techniques like muscle energy and myofascial release to correct somatic dysfunction.

Osteopathic medicine in the United States

Osteopathic medicine in the United States, also called American osteopathy, is a medical branch whose DOs have full physician licenses and extra training in hands-on manipulative treatment.

Osteopathic Physicians

Osteopathic physicians (DOs) are fully licensed U.S. physicians trained in osteopathic medicine, founded by A.T. Still in 1874; they prescribe, perform surgery, practice all specialties, and comprise about 11% of U.S. physicians.

Osteopathy

Osteopathy, founded by Andrew Taylor Still in 1874, is a healthcare system using osteopathic manipulative treatment; in the US DOs are fully licensed physicians, elsewhere osteopaths are manual therapists, with best evidence for musculoskeletal pain.

Osteopenia

Osteopenia, or low bone mass, is reduced bone mineral density with a T-score between −1 and −2.5, below normal but above the osteoporosis threshold; diagnosed by DXA, managed with exercise, calcium, vitamin D, and selective drug treatment.

Osteopetrosis

Osteopetrosis, or marble bone disease and Albers-Schönberg disease, is a rare inherited disorder causing overly dense, brittle bones from defective osteoclasts, with severe infantile autosomal recessive and milder autosomal dominant forms.

Osteopetrosis with renal tubular acidosis

Osteopetrosis with renal tubular acidosis, also called carbonic anhydrase II deficiency, Guibaud-Vainsel syndrome, or marble brain disease, is a rare autosomal recessive CA2-gene disorder combining osteopetrosis, mixed proximal and distal RTA, and cerebral calcification.

Sep 29, 2026

Osteoplasty

Osteoplasty is a surgical procedure that reshapes, repairs, or grafts bone to restore skeletal structure and function, covering open bone grafting and percutaneous cement injection for painful lesions.

Osteopontin

Osteopontin (OPN, SPP1) is a secreted phosphorylated glycoprotein of the SIBLING family, found in bone and all body fluids, acting as cell-attachment protein and cytokine; elevated in cancer, atherosclerosis, and rheumatic disease, and studied as a biomarker.

Osteoporosis

Osteoporosis, also called postmenopausal or senile osteoporosis, is a silent bone disease of low bone mass (T-score ≤ −2.5) and deteriorated microarchitecture causing fragility fractures; 8.9 million fractures occur yearly, and bisphosphonates, denosumab, and anabolics reduce risk.

Osteoporosis of disuse

Osteoporosis of disuse (disuse osteoporosis, ICD-11 FB83.12): bone loss from lack of mechanical loading in spinal cord injury, immobilization, bed rest, and spaceflight, with high resorption, low formation, and incomplete recovery.

Osteoporosis-oculocutaneous hypopigmentation syndrome

Osteoporosis-oculocutaneous hypopigmentation syndrome (OOCHS, Hernández-Fragoso syndrome, OMIM 601220) is an autosomal recessive rare disease combining congenital hypopigmentation, visual impairment, osteoporosis, and skeletal anomalies, with only a few reported cases.

Osteoporosis-pseudoglioma syndrome

Osteoporosis-pseudoglioma syndrome (OPPG, OMIM 259770) is a rare autosomal recessive LRP5 disorder causing congenital blindness and severe juvenile osteoporosis with fractures; treated with bisphosphonates.