COMPLEMENTARY ANGLES - A SIMPLIFICATION OF SAGITTAL PLANE ROTATIONAL ASSESSMENT IN CERVICAL INSTABILITY

The use of complementary angle measurement improves the physician's ab ility to quantify the magnitude of the angle of rotation directly. By constructing a right triangle, with its base determined by the inferio r end plate of the vertebral body, the angle of sagittal plane rotatio n can be determined readily. A perpendicular line drawn from the infer ior end plate of the vertebra to the adjacent superior vertebra's infe rior end plate will create an acute angle. This angle is complementary to the angle of sagittal plane rotation for this motion segment. The sum of two complementary angles, the acute angle described and the ang le of sagittal plane rotation, is equal to 90. Assessment of cervical spinal stability is crucial to the physician caring for traumatized pa tients. A checklist previously was developed by others to evaluate spi nal stability; this relied heavily on the findings of routine lateral radiographs: Differences in the angle of sagittal plane rotational of greater than 11 between adjacent vertebra were equivalent to two point s on this checklist, and five points or more suggested instability.