Length-modulating total joint prosthesis and method

A length-adjustable total hip joint prosthesis, comprising:

• a femoral prosthetic stem comprising a distal stem portion and a proximal stem portion,
• a rectangular housing disposed within the proximal stem portion, wherein the femoral prosthetic stem is configured for insertion into an intramedullary space of a femur, wherein the housing comprises:
• a permanent magnetic rod configured for circumferential rotation, wherein the rod is rotationally coupled to an input gear,
• a first gear set comprising a first plurality of parallel spur gears, wherein the first gear set is operatively coupled to the input gear,
• a second gear set comprising a second plurality of parallel spur gears, wherein the first and the second gear sets intermesh in parallel, and
• a lengthening screw having a first portion disposed within the housing and rotationally coupled to an output gear and a second portion extending out of the housing;
• and
• an implant neck comprising a threaded internal cavity along a length thereof configured for receiving the second portion of the lengthening screw, wherein a proximal part of the implant neck is configured for coupling to an implant head, and the implant head is configured for insertion into an acetabulum,
• wherein the permanent magnetic rod and the lengthening screw are distinct and separate from one another,
• wherein rotation of the permanent magnetic rod in a first axial direction through a plurality of rotations causes the implant neck to move toward the housing to effect a decrease in a length of the prosthesis, and wherein rotation of the permanent magnetic rod in a second axial direction through a plurality of rotations causes the implant neck to move away from the housing to effect an increase in a length of the prosthesis.