Introduction Note: To our knowledge the Lenke classifcation has never appeared on the OITE or on the the ABOS Part I. The Lenke classication for adolescent idiopathic scoliosis has gained popularity and consists of three steps Label primary curve at Type 1-6 Assign lumbar modifier (A,B,C) Assign sagittal modifier (-,N,+) Step 1: Identification of primary curve (Type 1-6) Measure regional curves proximal thoracic (PT) main thoracic (MT) thoracolumbar/lumbar (TL/L) Identify major curve (biggest curve) always either MT (Type 1-4) or .MT/L (Type 4*,5,6) Determine if minor curve is structural or not definition of structural > 25° in coronal plane on standing AP and do not bend out to < 25° on bending films OR > 20° in sagital plane Assign Type 1-6 based on chart below Curve Type Curve Name PT** MT TL/L Type 1 MT - Structural (major*) - Type 2 Double thoracic (DT) Structural Structural (major*) - Type 3 Double major (DM) - Structural (major*) Structural Type 4 Triple major (TM) Structural Structural (major*) Structural (major*) Type 5 TL/L - - Structural (major*) Type 6 TL/L-MT - Structural Structural (major*) Structural (major*) - has largest cobb angle and is always structural. In Type 4 can be either MT or FL/L depending on which Cobb is larger **If PT is the largest curve, then by default assign major curve to MT Step 2: Assignment of Lumbar modifiers (A,B,C) Identify apical lumbar vertebrae (ALV) is the inferior lumbar body that falls outside of the curve Draw centeral sacral vertical line (CSVL) and see where it sits in relationship to pedicles of ALV Assign modifer A if CSVL passes between pedicles of apical lumbar vertebrae (ALV) CSVL falls between pedicles of the lumbar spine up to stable vertebra B modifier if CSVL touches pedicle of apical lumbar vertebrae (ALV) C modifier if CSVL does not touch apical lumbar vertebrae (ALV) apex of lumbar curve falls completely off the midline depicting a curve with complete apical translation off the CSVL Step 3: Assignment of Sagittal thoracic modifier (-, N, +) Measure sagital Cobb from T5 to T12 Assign modifier hypokyphotic (-) if < 10° normal if 10-40° hyperkyphotic (+) if >40°