Destruction of the metacarpophalangeal joint can result in disabling pain and stiffness. Several therapeutic options are available, including pyrocarbon interposition implants. The primary endpoint of this study was assessment of clinical and radiographic outcomes in 34 patients treated with HAPY® pyrocarbon interposition implants (Tornier, Grenoble, France) with a minimum follow-up of 3 years. The secondary endpoint was to assess complications and the need for revision surgery.

Thirty-four patients (61 implants) who underwent metacarpophalangeal arthroplasty with the HAPY® implant were reviewed with a minimum follow-up of 3 years. The etiology was inflammatory (rheumatoid arthritis) in 18 cases (37 implants), primary osteoarthritis in 16 (21 implants), and post-traumatic in 3 (3 implants).

Preoperative data comprised age, gender, operated finger, etiology (inflammatory, primary or post-traumatic), digital chain mobility, pain assessment on visual analog scale, grip strength on a standardized handheld dynamometer, and functional scores including QuickDASH and the Patient-Rated Wrist/Hand Evaluation. Immediate postoperative radiographs (anteroposterior, lateral and oblique views) centered on the metacarpophalangeal joint were compared with those at last follow-up. Metacarpal and phalangeal implant subsidence were assessed.

At a mean follow-up of 71.5 months, pain score was reduced by a mean 5.4 points: 6.4/10 versus 1/10 (p < 0.001). The mean active range of motion in flexion-extension showed a significant improvement of 27°: 42.9 ° versus 70 ° (p < 0.001). The QuickDASH and Patient-Rated Wrist/Hand Evaluation functional scores significantly improved by a mean 26.7 points (50.6 ± 20.1 versus 23.9 ± 25 (p < 0.001)) and 32.8 points (53.58 ± 21.6 versus 20.77 ± 22.1 (p < 0.001)), respectively. Comparison between pre- and post-operative grip strength did not show a significant difference. 94% of patients reported being satisfied with the procedure, while 6% were dissatisfied or very dissatisfied. One of the dissatisfied patients developed type 1 complex regional pain syndrome, while the other had persistent pain and stiffness.

Mean implant subsidence in the metacarpal was 0.48 mm ± 4.2 mm, and in the first phalanx 3.6 mm ± 9.6 mm. One patient (2.9%) experienced implant dislocation in the immediate postoperative period. No further implant dislocations were observed during follow-up.

The HAPY® interpositional implant provided good clinical and radiographic outcomes for the management of long finger arthritis, offering functional results and improvement in range of motion, comparable to other series. The HAPY® interpositional implant has the advantage of being non-constrained and maximizing bone stock.