Abstract: An apparatus for lengthening bones is disclosed including a plurality of frame elements (12) spaced apart from one another. The frame elements are U-shaped for at least partially enclosing the bone, and two elements may be connected to fully enclose the bone. Fixation elements (14) that transfix the bone approximately perpendicular to its long direction are secured to the frame elements. Telescopically extendable tensioning elements (16) connect the frame elements together and fix them in position relative to one another. The frame elements (12) include a plurality of rows (18, 18') of longitudinal slots (20, 20', 20"). The tensioning elements (16) are clamped to the frame elements at aligned slots and the fixation elements (14) are similarly clamped to the appropriate slots in the corresponding frame elements. The tensioning elements include three threaded sections with a first section including a spindle and sleeve with a second and third threaded section threaded into the first section.