# Functional Outcomes of Spherical Pyrocarbon HAPY Metacarpophalangeal Interposition Arthroplasty for Long Fingers: A Retrospective Study of 16 Cases

## TL;DR

This study shows that a new pyrocarbon implant for MCP joint arthritis improves pain and mobility with few complications over 2-8 years.

## Contribution

Reports short- to mid-term clinical and radiological outcomes of a novel spherical pyrocarbon MCP implant.

## Key findings

- Significant pain reduction and improved joint mobility observed after 2-8 years of follow-up.
- No major complications like dislocation or infection were reported.
- Radiological results showed good implant positioning and bone integration in most cases.

## Abstract

Metacarpophalangeal (MCP) joint osteoarthritis is a major cause of pain and functional limitation. When conservative treatment fails, arthroplasty is a surgical option, with silicone implants historically being the most widely used. The HAPY spherical metacarpal pyrocarbon implant is a new prosthetic solution. This study aims to evaluate the clinical and radiological outcomes of this spherical pyrocarbon MCP implant.

This single-center retrospective study included 16 patients who underwent MCP arthroplasty with the HAPY implant for osteoarthritis with a follow-up of more than 2 years. Clinical evaluation included pain (visual analog scale), range of motion, and disabilities of the arm, shoulder, and hand score, and grip strength. Complications were also recorded. Radiological assessment focused on implant positioning, bone erosion, peri-implant bone remodeling, proximal migration, and material integrity.

After a mean follow-up of 48 months (range: 24–95 months), functional outcomes demonstrated considerable improvement in MCP flexion (41° ± 10° to 64° ± 20°), pain reduction (visual analog scale: 7.4 ± 1 to 0.8 ± 0.9), and improvement in the disabilities of the arm, shoulder, and hand score (42.5 ± 11.3 to 20.2 ± 22.5). Grip strength remained stable. No complications such as dislocation, instability, or infection were reported. Radiological outcomes showed proper implant positioning in 62.5% of cases, with moderate peri-implant bone remodeling and a low incidence of proximal migration or considerable erosion.

The HAPY spherical pyrocarbon interposition arthroplasty for the metacarpophalangeal joint demonstrates satisfactory short- to mid-term outcomes, with consderable improvements in pain relief and joint mobility. Radiological findings support good bone tolerance with signs of progressive integration, despite moderate erosion and bone remodeling in some cases. These results are consistent with outcomes reported for other pyrocarbon implants. A multicenter study with a longer follow-up is needed to confirm the durability and safety of this technique.

Therapeutic IV.