MTP Prosthesis (ReFlexion™) for Hallux Rigidus

Abstract

ABSTRACT Severe osteoarthritis of the first metatarsophalangeal joint is classically treated with an arthrodeses or a resection arthroplasty. Although endoprostheses for the first metatarsophalangeal joint had been introduced 50 years ago, they have not reached wide acceptance yet. The use of silicone spacers with their encouraging early results have been markedly decreased after the side effects (bony cyst, synovitis, implant failure) occurred. Since then, several attempts have been made to design total metatarsophalangeal joint replacements. The ReFlexion™ prosthesis, for example, consists of 3 components: a metatarsal stem, a phalangeal stem, and a metatarsal head. All components are interchangeable and available in 3 sizes. Due to the quality of the cancellous bone, the components can be inserted with or without cement. Because the surgical technique is guided by an appropriate instrumentation device to facilitate positioning of the implants, the release of the plantar capsule, including a debridement of the sesamoids, seems to be more demanding. Data from our prospective mid-term study (follow-up 39 months) revealed encouraging results for pain relief and range of motion. According to the score of the American Orthopaedic Foot & Ankle Society, the results improved from 51 points preoperatively to 74 points postoperatively. Assessing the radiographs, we observed radiolucent lines in 25% of the phalangeal components and in 10% of the metatarsal components. These findings were mainly attributed to a cemented fixation technique and did not impair the clinical results. Although we had mainly operated on hallux rigidus deformities, we observed multiplanar malalignment (60.5%) after the operation, including slight hallux valgus or hallux varus and plantar subluxation of the proximal phalanx. With regard to the relief of pain and the functional impairment, further attempts should been made to improve implant properties, that is, fixation to the bone, resurfacing of the plantar metatarsal aspect, and a semiconstrained design to stabilize the joint in the transverse plane.