The Rule of 57: Orthopaedic Trigonometry Made Easy.

Abstract

INTRODUCTION\nThe Rule of 57 is an easy method for planning osteotomies and calculating translations when correcting spine and limb deformities.\n\n\nMETHODS\nThe 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.\n\n\nRESULTS\nThus a 1 mm opening or closing wedge osteotomy with a width of 57 mm would result in 1° of angular correction.\n\n\nDISCUSSION\nThis 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.