All articles starting with O
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Osteoradionecrosis of the mandible
Osteoradionecrosis of the mandible (mandibular ORN), exposed nonhealing irradiated jaw bone lasting over 3 months after head and neck radiotherapy; incidence 4-8%, treated with PENTO drugs or free-flap reconstruction.
Osteosarcoma
Osteosarcoma, also called osteogenic sarcoma, is the most common primary malignant bone tumor, arising from osteoblasts that produce osteoid. It affects adolescents in long bones near the knee; chemotherapy plus surgery raised five-year survival from about 20% to 50-60%, plateaued for decades.
Osteosclerosis
Osteosclerosis (ostéosclérose, osteoesclerosis): increased bone density causing hardening or fragility, coded ICD-11 FB80.4. Coined by Lobstein in 1833 opposite osteoporosis; hereditary (osteopetrosis, sclerosing dysplasias) or acquired (fluorosis, myelofibrosis, osteoblastic metastases).
Osteosclerotic bone dysplasia
Osteosclerotic bone dysplasia, also called Raine syndrome (OMIM 259775), is a rare autosomal recessive neonatal bone dysplasia caused by FAM20C mutations, marked by generalized osteosclerosis, facial dysmorphism, intracerebral calcifications, and lethal or non-lethal hypophosphatemic rickets forms.
Osteosclerotic metaphyseal dysplasia
Osteosclerotic metaphyseal dysplasia (OMD, OSMD, OMIM 615198) is an ultrarare autosomal recessive osteopetrosis caused by LRRK1 mutations, marked by metaphyseal osteosclerosis, osteopenic diaphyses, developmental delay, and fewer than 10 reported cases.
Osteospermum
Osteospermum, the daisybushes or African daisies, is a genus of 74 accepted species in Asteraceae tribe Calenduleae, native from St. Helena and Egypt to South Africa and Arabia, with hard, winged, pappus-less achenes and popular ornamental hybrids.
Osteosynthesis
Osteosynthesis is the surgical joining of broken bone fragments with implants such as plates, screws, intramedullary nails, or wires, holding them firmly in position while the fracture heals.
Osteotomy
An osteotomy is a surgical operation in which a bone is cut and realigned, such as the high tibial osteotomy for knee arthritis, to relieve pain and delay joint replacement.
Osterberg cell test
The Osterberg cell test, commonly called the O-cell test, is a deep foundation load test in which a sacrificial internal jack loads a pile from within.
Osterburken
Osterburken, Germany: Roman fort on the Upper German-Raetian Limes, built about 160 CE, cohort fort of 2.14 ha plus 185–192 CE annex, garrisoned by Aquitanian cohort and Brittonum numerus, with Mithraeum and beneficiarii shrine.
Östergötland
Östergötland is a province in southeastern Sweden, bordering Lake Vättern and the Baltic Sea, one of medieval Sweden's two main agricultural core areas with Västergötland.
Östergötland County
Östergötlands län (county code 05), a county in southeastern Sweden formed in 1634, with 13 municipalities, 472,529 inhabitants (2025), and its two dominant cities Linköping and Norrköping.
Osterøy
Osterøy: municipality and island in Vestland county, Norway, northeast of Bergen. Island area 330 km², Norway's largest inland island surrounded by saltwater; municipality formed 1964 from Haus, Hamre, Hosanger, Bruvik; center Lonevåg, population about 8,200.
Osterreichisches olympisches comite
The Österreichisches Olympisches Comité, also known as the Austrian Olympic Committee or ÖOC, is the non-profit association founded in 1908 that organizes and finances Austria's teams at the Olympic Games.
Osterrieth Range
The Osterrieth Range is a mountain range extending northeast to southwest along the southeast coast of Anvers Island, in the Palmer Archipelago off the Antarctic Peninsula.
Östers IF
Östers IF, founded 20 April 1930 in Växjö as Östers FF, is a Swedish football club with four Allsvenskan titles (1968, 1978, 1980, 1981), the 1977 cup, and home at Visma Arena; relegated from Allsvenskan in 2025.
Östersunds FK
Östersunds FK (ÖFK), Swedish football club founded 1996 in Östersund; rose from the fourth tier to the 2017/18 Europa League round of 32 under Graham Potter, won the 2017 Swedish Cup, then declined financially and now plays in Superettan.
Osterwalder–Schrader axioms
The Osterwalder–Schrader axioms are mathematical conditions on Euclidean Green's functions that determine a unique relativistic quantum field theory, established by Konrad Osterwalder and Robert Schrader in 1973.
Ostfalen
Ostfalen (Eastphalia), historical German region between Weser and Elbe, Harz and Lüneburg Heath; eastern Saxon group first attested 775; survives in Eastphalian dialects, a UNESCO Geopark, and Ostfalia University.
Osthe (ஒஸ்தே)
Osthe (ஒஸ்தி), also spelled Osthi, is a 2011 Tamil masala action-comedy directed by Dharani, the official Tamil remake of Dabangg, starring Silambarasan as inspector Osthe Velan with Sonu Sood reprising his villain role; released 8 December 2011 with music by S. Thaman.
Ostia (Rome)
Ostia, also known as Lido di Ostia, is Rome's seaside district on the Tyrrhenian Sea at the Tiber's mouth, near the ancient ruins of Ostia Antica.
Ostia Antica
Ostia Antica, the archaeological park of ancient Rome's harbor city at the Tiber mouth (Latin ostium), founded as a castrum in the 4th century BC, at its 2nd-century-AD peak home to some 50,000 people, excavated since 1802.
Ostinato
Ostinato (plural ostinati), Italian for "obstinate," is a short melodic, rhythmic, or harmonic pattern repeated persistently in the same voice at fixed pitch. Distinguished from sequence, pedal point, and drone; basis of ground bass, passacaglia, chaconne, riffs, loops, and vamps.
Ostjuden
Ostjuden (German for Eastern Jews), Ostjude singular: term for East European, mainly Yiddish-speaking Jews in German-speaking Central Europe; a construct of German-Jewish self-definition and a central anti-Semitic stereotype from the nineteenth century onward.
Ostoja of Bosnia
Stjepan Ostoja, died September 1418, was King of Bosnia in two reigns, 1398–1404 and 1409–1418: deposed by magnates, restored after Hungarian victory, succeeded by his son Stjepan Ostojić.
Ostpolitik
Ostpolitik, or Neue Ostpolitik, was West Germany's Eastern policy under Willy Brandt and Egon Bahr from 1969: treaties with the USSR, Poland, and the GDR accepting post-war borders, in exchange for rapprochement and human contacts.
Ostracism (ὀστρακισμός)
Ostracism (ὀστρακισμός) was the Athenian democratic procedure of exiling one citizen for ten years by potsherd vote with a 6,000-vote quorum; instituted under Cleisthenes, first used 487 BCE, last recorded with Hyperbolos c. 417 BCE.
Ostracod
Ostracods (Ostracoda, seed shrimps) are tiny bivalved crustaceans, mostly 0.2–2 mm, living in nearly all aquatic habitats; the most abundant arthropods in the fossil record from the Ordovician onward, used to date rocks and reconstruct past environments.
Ostracon of Prince Sethherkhepshef
The Ostracon of Prince Sethherkhepshef is a painted limestone ostracon naming a son of Ramesses III, found in the Valley of the Queens and kept in Turin.
Ostracon of Senemut
The Ostracon of Senemut is a limestone flake bearing a hieratic list of workmen conscripted for labor, dated to year 16 and found near Senenmut's tomb TT353 at Deir el-Bahri.