The Rule of 57: Orthopaedic Trigonometry Made Easy.

Introduction: The Rule of 57 is an easy method for planning osteotomies and calculating translations when correcting spine and limb deformities.

Methods: The rule is based on the mathematical principle that a circle with a radius of 57 mm has a circumference of 360 mm where each 1° of the circle subtends an arc of 1 mm in length.

Results: Thus a 1 mm opening or closing wedge osteotomy with a width of 57 mm would result in 1° of angular correction.

Discussion: This basic geometric shape can be extrapolated in many ways to determine proper alignment for preoperative planning, performing osteotomies, understanding guided growth, and executing a variety of deformity corrections.