Outcomes of Unconstrained Proximal Interphalangeal Joint Arthroplasty: A Systematic Review

Background: Unconstrained pyrocarbon and metal-on-polyethylene (MoP) proximal interphalangeal (PIP) joint arthroplasty is an increasingly popular alternative to silicone implants and arthrodesis. This systematic review appraises their outcomes. Methods: 30 studies comprising 1,324 joints (813 pyrocarbon, 511 MoP) were included. Mean patient age was 59 years (38 to 78) and mean follow-up period was 54 months (1.2 to 380). Results: There were mean improvements of 4.5 points (2 to 6.9) in pain Visual Analogue Score, 10.5° (-26 to 58) in range of motion (ROM), 3.1 kg (-4 to 7) in grip strength, 0.6 kg (-1.5 to 2) in pinch strength, and 18 points (-3 to 29) in the Disabilities of the Arm, Shoulder and Hand score, with no significant differences between implant types. ROM gains, in particular, deteriorated over time. Clinical complications were frequent (23%), and significantly more common with pyrocarbon, as were radiographic complications. However, most were mild-moderate and did not necessarily correlate with negative outcomes or dissatisfaction. Overall reoperation rate was 21%, and revision rate 11%, both more frequent with pyrocarbon. Most revisions were within 24 months, beyond which survival was maintained up to ten years. Conclusions: Unconstrained PIP joint arthroplasty is effective at improving pain scores, active ROM, grip/pinch strength, and patient reported outcome measures, particularly in patients with osteoarthritis. Results are generally maintained at least to the medium term, although gains diminish in the longer term. Complication and early revision rates are high, particularly with pyrocarbon implants. The majority of patients express positive attitudes to arthroplasty, with significant improvements in patient-reported outcome measures for both pyrocarbon and MoP implants. Patients with post-traumatic and inflammatory arthropathy are generally less satisfied. There is currently insufficient data to recommend one implant type over another, although the early-to-medium term results of MoP implants are promising. Prospective surveillance via small joint registries is recommended.