Force-controlled autodistraction

A force-controlled autodistraction system for lengthening a bone in a limb, comprising:

• a distractor coupled to a first fixator and to a second fixator, the distractor having a distractor stiffness;
• the first fixator configured to be coupled to a first portion of the bone;
• the second fixator configured to be coupled to a second portion of the bone, the first and second portions being on opposite sides of an osteotomy of the bone;
• a motor controllable to produce a continuous distractor displacement of the first fixator away from the second fixator such that the first portion of the bone is distracted in an axial direction of the bone from the second portion of the bone at a distraction rate;
• a distractor displacement sensor configured to measure the distractor displacement in the axial direction;
• a force sensor configured to measure a resistant force in the limb caused by the distractor displacement;
• and
• a controller operably coupled to the force sensor, the distractor displacement sensor, and the motor, the controller being configured to determine a variable axial limb stiffness based on the resistant force, the distractor displacement, and the distractor stiffness, the variable axial limb stiffness being the resistant force divided by the axial distractor displacement, the controller being further configured to use closed-loop feedback to control the motor to adjust the distraction rate such that the variable axial limb stiffness matches a desired axial limb stiffness by increasing the distraction rate if the variable axial limb stiffness is less than the desired axial limb stiffness and by decreasing the distraction rate if the variable axial limb stiffness is greater than the desired axial limb stiffness.