Introduction: The Robert Mathys (RM) Finger is a hinged type of arthroplasty for the metacarpophalangeal and proximal interphalangeal (PIP) joint that compensates ligament instability. The aim of this study is to evaluate the outcomes and complications of RM Finger arthroplasty of the PIP joint.
Materials and methods: A retrospective case series of 19 RM Finger arthroplasties of the PIP joint in 17 patients was performed with a median follow-up of 36 months. The active range of motion (AROM) was measured pre-operatively, at the 6-week follow-up, at the termination of hand therapy, and at the final follow-up. Complications were recorded, as well as pain on a visual analog scale (VAS), stability, deformity, pinch strength, the Michigan Hand Outcomes Questionnaire (MHQ), and the Patient Global Index of Improvement Questionnaire.
Results: One implant fracture occurred. Another patient had an amputation due to stiffness. For the remaining joints, AROM was 61°. One joint mobilization under local anesthesia, one arthrolysis and two extensor tendon reconstructions were also necessary. Pain at the follow-up was 1.2 on the VAS. Relative pinch strength was 69%. Joint stability was restored in all fingers, although one joint had an ulnar deviation of 15°. Eight fingers developed a snapping phenomenon, of which five had a swan neck deformity. One finger had an extension lag with a Boutonnière deformity. MHQ scores were less compared to the unaffected hand. Fifteen patients rated their outcome as improved compared to their pre-operative condition.
Conclusions: RM Finger arthroplasty of the PIP joint restores joint stability with AROM improvement, and with low pain, although it has a high rate of complications.
Level of evidence: IV.
Keywords: Arthroplasty; Mathys; Prosthesis; Proximal inter-phalangeal joint arthroplasty; RM Finger.