Cobb angle
{{Short description|Measurement of scoliosis}}
The Cobb angle is a measurement of bending disorders of the vertebral column such as scoliosis and traumatic deformities.
Definition and method
It is defined as the greatest angle at a particular region of the vertebral column, when measured from the superior endplate of a superior vertebra to the inferior endplate of an inferior vertebra.{{cite book|url=https://books.google.com/books?id=AmZgmGG4Dz0C&pg=PR929|title=Caffey's Pediatric Diagnostic Imaging|author=Brian D. Coley|edition=12|publisher=Elsevier Health Sciences|year=2013|page=1429|isbn=978-1455753604}} However, the endplates are generally parallel for each vertebra, so not all sources include usage of a superior versus inferior endplate in the definition.{{cite book|url=https://books.google.com/books?id=wGclDwAAQBAJ&pg=PA1150 |title=Ferri's Clinical Advisor 2018 E-Book|page=1150|author=Fred F. Ferri|publisher=Elsevier Health Sciences|year=2017|isbn=978-0323529570}}
Unless otherwise specified it is generally presumed to refer to angles in the coronal plane, such as projectional radiography in posteroanterior view. In contrast, a sagittal Cobb angle is one measured in the sagittal plane such as on lateral radiographs.{{cite journal|last1=Schmitz|first1=A. |last2=Jaeger|first2=U.
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|title=Sagittale Cobb-Winkel-Messungen bei Skoliose mittels MR-Ganzwirbelsäulenaufnahme|journal=Zeitschrift für Orthopädie und ihre Grenzgebiete|volume=139|issue=4|year=2001|pages=304–07|issn=0044-3220|doi=10.1055/s-2001-16915|pmid=11558047 |s2cid=260354772 }}
Cobb angles are preferably measured while standing, since laying down decreases Cobb angles by around 7–10°.{{cite journal|last1=Keenan|first1=Bethany E|last2=Izatt|first2=Maree T|last3=Askin|first3=Geoffrey N|last4=Labrom|first4=Robert D|last5=Pearcy|first5=Mark J|last6=Adam|first6=Clayton J|title=Supine to standing Cobb angle change in idiopathic scoliosis: the effect of endplate pre-selection|journal=Scoliosis|volume=9|issue=1|pages=16|year=2014|issn=1748-7161|doi=10.1186/1748-7161-9-16|pmid=25342959|pmc=4193912 |doi-access=free }}
Uses
It is a common measurement of scoliosis.
The Cobb angle is also the preferred method of measuring post-traumatic kyphosis in a recent meta-analysis of traumatic spine fracture classifications.{{cite journal|last=Keynan|first=Ory|author2=Fisher, CG|author3=Vaccaro, A|author4=Fehlings, MG|author5=Oner, FC|author6=Dietz, J|author7=Kwon, B|author8=Rampersaud, R|author9=Bono, C|author10=France, J|author11=Dvorak, M|title=Radiographic measurement parameters in thoracolumbar fractures: a systematic review and consensus statement of the spine trauma study group.|journal=Spine|date=Mar 1, 2006|volume=31|issue=5|pages=E156–65|pmid=16508540|url=http://library.tasmc.org.il/Staff_Publications/publications%202006/keynan.pdf|access-date=15 December 2012|doi=10.1097/01.brs.0000201261.94907.0d|s2cid=39799085|archive-url=https://web.archive.org/web/20131009011025/http://library.tasmc.org.il/Staff_Publications/publications%202006/keynan.pdf|archive-date=9 October 2013|url-status=dead}}
Severity
Those with Cobb angle of more than 60° usually have respiratory complications.
Scoliosis cases with Cobb angles between 40 and 50 degrees at skeletal maturity progress at an average of 10 to 15 degrees during a normal lifetime. Cobb angles of more than 50 degrees at skeletal maturity progress at about 1 to 2 degrees per year.{{cite journal |vauthors=Greiner KA |title=Adolescent idiopathic scoliosis: radiologic decision-making |journal=Am Fam Physician |volume=65 |issue=9 |pages=1817–22 |year=2002 |pmid=12018804 }}
History
The Cobb angle is named after the American orthopedic surgeon John Robert Cobb (1903–1967). It was originally used to measure coronal plane deformity on radiographs with antero-posterior projection for the classification of scoliosis.Cobb JR. Outline for the study of scoliosis. The American Academy of Orthopedic Surgeons Instructional Course Lectures. Vol. 5. Ann Arbor, MI: Edwards; 1948. It has subsequently been adapted to classify sagittal plane deformity, especially in the setting of traumatic thoracolumbar spine fractures.
References
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