Force-controlled autodistraction for lengthening a bone is disclosed. A distractor is coupled to first and second fixators that are coupled to first and second portions of the bone, respectively, on opposite sides of an osteotomy of the bone. A motor produces a motion of the first fixator relative to the second fixator such that the first portion of the bone is distracted from the second portion of the bone. A force sensor measures a resistant force to the motion, and a distractor displacement sensor measures a distractor displacement. A controller is operably coupled to the force sensor, the distractor displacement sensor, and the motor. The controller is configured to determine a variable limb stiffness using the resistant force, the distractor displacement, and a known distractor stiffness of the distractor, and to adjust a gain of the motor such that the variable limb stiffness matches a desired limb stiffness.