Metatarsophalangeal HAPY® spherical pyrocarbon implant: Technical note.

We present a new arthroplasty concept for the first metatarsophalangeal joint (MTP1) involving the HAPY® pyrocarbon interposition implant. This is a spherical implant that does not integrate into bone. Instead, the goal is to achieve gliding of the implant on the bone/cartilage to maintain the function and mobility of the MTP1 joint. We describe the surgical technique used for its implantation. Since the implant is not anchored into bone, it is stabilized in a spherical cavity hollowed out in the metatarsal head. In a preliminary study of 22 cases with a mean follow-up of 36 (20-79) months, the mean AOFAS score improved from 64 (35-72) preoperatively to 91 (47-100) postoperatively (p<0.05). At the final assessment, no subchondral cyst or osteolysis was visible.