Cobb angle

The Cobb angle is a measurement of bending disorders of the vertebral column such as scoliosis and traumatic deformities.

89° Cobb angle measurement of a levoscoliosis

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.^[1] However, the endplates are generally parallel for each vertebra, so not all sources include usage of a superior versus inferior endplate in the definition.^[2]

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.^[3]

Cobb angles are preferably measured while standing, since laying down decreases Cobb angles by around 7–10°.^[4]

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.^[5]

Severity

Severity	Cobb angle
Not scoliosis	<10°[6]
Mild scoliosis	10–30°
Moderate scoliosis	30–45°[7]
Severe scoliosis	>45°[7]

Those with Cobb angle of more than 60° usually have respiratory complications.^[7]

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.^[8]

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.^[9] It has subsequently been adapted to classify sagittal plane deformity, especially in the setting of traumatic thoracolumbar spine fractures.

References

1. Brian D. Coley (2013). Caffey's Pediatric Diagnostic Imaging (12 ed.). Elsevier Health Sciences. p. 1429. ISBN 978-1455753604.
2. Fred F. Ferri (2017). Ferri's Clinical Advisor 2018 E-Book. Elsevier Health Sciences. p. 1150. ISBN 978-0323529570.
3. Schmitz, A.; Jaeger, U.; Koenig, R.; Kandyba, J.; Gieske, J.; Schmitt, O. (2001). "Sagittale Cobb-Winkel-Messungen bei Skoliose mittels MR-Ganzwirbelsäulenaufnahme". Zeitschrift für Orthopädie und ihre Grenzgebiete. 139 (4): 304–07. doi:10.1055/s-2001-16915. ISSN 0044-3220. PMID 11558047. S2CID 260354772.
4. Keenan, Bethany E; Izatt, Maree T; Askin, Geoffrey N; Labrom, Robert D; Pearcy, Mark J; Adam, Clayton J (2014). "Supine to standing Cobb angle change in idiopathic scoliosis: the effect of endplate pre-selection". Scoliosis. 9 (1): 16. doi:10.1186/1748-7161-9-16. ISSN 1748-7161. PMC 4193912. PMID 25342959.
5. Keynan, Ory; Fisher, CG; Vaccaro, A; Fehlings, MG; Oner, FC; Dietz, J; Kwon, B; Rampersaud, R; Bono, C; France, J; Dvorak, M (Mar 1, 2006). "Radiographic measurement parameters in thoracolumbar fractures: a systematic review and consensus statement of the spine trauma study group" (PDF). Spine. 31 (5): E156–65. doi:10.1097/01.brs.0000201261.94907.0d. PMID 16508540. S2CID 39799085. Archived from the original (PDF) on 9 October 2013. Retrieved 15 December 2012.
6. Page 89 in: Dr. Kevin Lau. The Complete Scoliosis Surgery Handbook for Patients: An In-Depth and Unbiased Look Into What to Expect Before and During Scoliosis Surgery. Health In Your Hands. ISBN 978-9810785925.
7. Page 460 in: Konrad E. Bloch, Thomas Brack, Anita K. Simonds (2015). ERS Handbook: Self-Assessment in Respiratory Medicine. European Respiratory Society. ISBN 978-1849840781.{{cite book}}: CS1 maint: multiple names: authors list (link)
8. Greiner KA (2002). "Adolescent idiopathic scoliosis: radiologic decision-making". Am Fam Physician. 65 (9): 1817–22. PMID 12018804.
9. Cobb JR. Outline for the study of scoliosis. The American Academy of Orthopedic Surgeons Instructional Course Lectures. Vol. 5. Ann Arbor, MI: Edwards; 1948.