Oakley CK, Janssen SAK, Pankratz JP, McCumber TL, Treffer KD, Olinger AB. Validity of the Rule of Threes and Anatomical Relationships in the Thoracic Spine. J Am Osteopath Assoc 2018;118(10):645–653. doi: https://doi.org/10.7556/jaoa.2018.143.
Download citation file:
The location of the more superficial thoracic spinous processes is used to help osteopathic physicians locate the deeper and more difficult-to-palpate thoracic transverse processes. In 1979, Mitchell et al proposed the thoracic rule of threes to describe the relationship of the spinous processes to the transverse processes in the thoracic spine. This rule is currently taught at osteopathic medical schools. The rule of threes separates the thoracic vertebrae into 3 distinct groups, each with a different relationship between transverse processes and spinous processes. In 2006, Geelhoed et al proposed a new relationship between the spinous processes and transverse processes for all thoracic vertebrae (ie, Geelhoed's rule).
To determine which anatomical relationship—the rule of threes or Geelhoed's rule—is most accurate in locating the transverse processes and to define anatomical relationships between thoracic spinous and transverse processes.
The thoracic spinous and transverse processes of 44 formalin-embalmed human cadavers were dissected, marked, and photographed. Six different measurements per vertebra were made between spinous processes and transverse processes in the thoracic spine. Geelhoed's protocol was used to determine the validity of each rule. The measurements were analyzed for additional relationships between thoracic spinous processes and transverse processes. Group 1 consisted of vertebrae T1 to T3 and T12; group 2 consisted of T4 to T6 and T11; and group 3 consisted of T7 to T10.
Of the 528 vertebrae measured, 0% of the first group vertebrae, 10.8% of the second group vertebrae, and 69.3% of the third group vertebrae followed the rule of threes. In total, 26.7% of vertebrae followed the rule of threes, whereas 62.3% of vertebrae followed Geelhoed's rule. Additional relationships worth noting include the distance between the transverse process and the adjacent caudal transverse process on the same side is approximately 25.4 mm (1 inch), and the distance between the transverse processes of the same vertebra is approximately 50.8 mm (2 inches) for male T3-T10 vertebrae and female T1-T12 vertebrae.
According to our findings, the rule of threes is not as accurate anatomically as Geelhoed's rule in locating the transverse processes of the thoracic spine. This study suggests osteopathic medical schools should teach Geelhoed's rule rather than the rule of threes.
a Measurements in the red box were used to test group 1 for the rule of threes. Measurements in the green boxes were used to test group 2 for the rule of threes. Measurements in the blue box were used to test group 3 for the rule of threes. Measurements in the purple box were used to test Geelhoed's rule. Black boxes highlight other noteworthy measurements not related to either rule.
b Negative values for measurement 2 indicate the spinous process of a vertebra was above the transverse processes of the caudal vertebra.
c Measurement 1 minus half of the average of measurement 3 on the right and left.
d The P value (calculated using the t test) indicates comparisons of male and female means for all measurements (#1 through #6). A significant difference was found between all male and female means except for measurement 5L.
Abbreviations: L, left; NA, not applicable; R, right.
This PDF is available to Subscribers Only
View Article Abstract & Purchase Options