Fig. 1: Surgical approach and device design.

a (left to right) Biological thumb with intact native joints and soft tissue. The IP joint is amputated, and native skin covers the residual proximal phalanx. The device is attached to the local bony structures including the residual proximal phalanx and metacarpal. The reverse radial forearm (RRF) and first dorsal metacarpal artery (FDMA) flaps are harvested and rotated about their pedicles to cover the implant. The donor and recipient sites are sutured closed, and the system is allowed to heal. b The implant is made up of four parts: the thumb tip, structural link, driving link, and metacarpal plate. The linkage connects the MCP and IP joints, such that flexion of the biological MCP joint creates flexion of the synthetic IP joint. Static (non-joint) portions of the implant are covered in porous HDPE, and the synthetic IP joint is protected by a flexible cover. A prototype was manufactured in Ti-6Al-4v.