Cobb's angle

Original Editor ­ Bo Hellinckx

Top Contributors - Ginika Jemeni, Ellen De Boitselier, Jayati Mehta, Bo Hellinckx and Oyemi Sillo

Definition

The Cobb Angle is used as a standard measurement to determine and track the progression of scoliosis. Dr John Cobb invented this method in 1948.[1] 
Scoliosis cobb.gif

How to calculate Cobb angle.

Cobb suggested that the angle of curvature be measured by drawing lines parallel to the upper border of the upper vertebral body and the lower border of the lowest vertebra of the structural curve, then erecting perpendiculars from these lines to cross each other, the angle between these perpendiculars being the ‘angle of curvature’.[2] 

Clinically relevant anatomy

See Scoliosis

Significance

The Cobb Angle helps a doctor to determine what type of treatment is necessary.

A Cobb Angle of 10 degrees is regarded as a minimum angulation to define Scoliosis.

Between 15 and 20 degrees: Some studies say that the patient does not require any specific treatment, but just needs regular check-ups to see if the curve is progressing until bone-maturity. A study from Weiss et al. says the patient requires physical therapy with treatment free intervals (6-12 weeks without physical therapy ). The physical therapy contains exercise sessions initiated at the physical therapist’s office, plus a home exercise program (2-7 sessions a week, after 3 months one session every 2 weeks may be enough).

Between 20 and 40 degrees: An orthopaedic doctor will generally prescribe a back brace to keep the spine from developing more of a curve. There are several braces for sale in the market, some worn for 18 to 20 hours a day and others only at night. Which type of brace the doctor will prescribe depends on the patient’s lifestyle, discipline and the severity of the curve. A study from Weiss et al. says a scoliosis intensive rehabilitation program is necessary. This includes a 3- to 5 week intensive program (4 to 6 hour training sessions a day).

40 – 50 degrees or more: Surgery may be required to correct the curve. There are several surgical procedures. A frequent recurring procedure is the “spinal fusion”, to link the vertebrae together so that the spine cannot longer continue to curve.[1][3][4]

Epidemiology[4]

The prevalence of adolescent idiopathic scoliosis when defined as a curvature > 10 degrees is 2-3%.

The prevalence of curvatures > 20 degrees is between 0.3 and 0.5%.

The prevalence of curvatures > 40 degrees are found in less than 0.1% of the population.


Limitations

A number of recognised limitations of the Cobb angle are recognised and caution should be used in assuming that sequential measurements are correct when little change is evident. Some recognised limitations include :[5]

  • intraobserver and interobserver variation (at least 5-10° variation)
  • rotation: minor rotation of patients between examinations can significantly change measurements (may be as high as 20° variation); consistent positioning must, therefore, be obtained
  • diurnal variation: in the same patient on the same day, curvature increases during the day (~5° variation)

References

  1. 1.0 1.1 Musculoskeletal Consumer Review (2009) Cobb angle and scoliosis, geraadpleegd op 24/11/2012, http://www.coreconcepts.com.sg/mcr/cobb-angle-and-scoliosis/ 3
  2. James, J. (1976) Scoliosis, Churchill Livingstone, London, pg 7-11 1A
  3. Tan, J. (2012) Measuring the Cobb angle and scoliosis, geraadpleegd op 26/11/2012, http://www.health-articles.co.uk/measuring-the-cobb-angle-and-scoliosis/ 5
  4. 4.0 4.1 Weiss H. et al. (2006) Indications for conservative management of scoliosis, Scoliosis Journal, geraadpleegd op 29/11/12, http://www.scoliosisjournal.com/content/pdf/1748-7161-1-5.pdf 1A
  5. https://radiopaedia.org/articles/cobb-angle