Design and Test of Surgical Procedure and Fixation Strategies of a Novel Finger Joint Implant
Pardis Farjam is a PhD student in the department Biomedical Device Design and Production Technology. Promotors are prof.dr.ir. G.J. Verkerke and dr.ir. J. Rouwkema from the faculty of Engineering Technology.
Osteoarthritis (OA) is a prevalent type of degenerative arthritis resulting from cartilage wear and tear, predominantly affecting joints like the knee, hand, and hip. Specifically, hand OA often impacts multiple hand joints, leading to significant patient loss of function and discomfort and substantial costs related to diagnostics, treatment, and productivity losses.
When conservative treatments fail to alleviate pain and functional issues in hand OA, surgical intervention becomes necessary. Numerous arthroplasty implants exist for various finger joints, but often complications occur, like implant loosening and dislocation. Despite advancements in joint prosthetic design, the overall outcome has shown minimal improvement over time.
The APRICOT® (Anatomically Precise Revolutionary Implant for bone Conserving Osteoarthritis Treatment) patented by Aurora Medical Ltd (Chichester, UK) represents a ground-breaking solution to address the challenges posed by existing finger joint implants for osteoarthritis. This innovative implant is specifically tailored for small joints affected by osteoarthritis, offering a self-lubricated polymeric sac that mimics the natural joint’s low-friction characteristics. Unlike conventional implants, APRICOT® facilitates full joint range of motion through its unique caterpillar-like internal motion, supported by an internal lubricant coating that minimizes friction. Currently in its proof-of-concept phase, the APRICOT® project aims to overcome significant challenges associated with osteoarthritis treatment in small joints.
Key objectives of this thesis include identifying a required anchoring system for secure implant fixation, establishing an effective implantation strategy, and designing and testing specialized surgical instruments to facilitate the implantation process.
First, the initial section investigates the APRICOT® implantation process is described, identifying the essential surgical tools required for its successful placement. We demonstrate an innovative articulating joint distractor specifically designed for APRICOT® implantation, developed through a systematic design approach. After designing and manufacturing a prototype using this method, its functionality was confirmed through a cadaver trial. This articulating joint distractor can create a 2 mm gap between the joint’s articulating surfaces and allows for adjustable angulation, enhancing exposure of the joint area while ensuring a stable hand position for surgeons to operate on. Conventional surgical instruments are inadequate in ensuring correct APRICOT® placement, leading to the design of specialized tweezers tailored for this task. The effectiveness and advantage of this developed instrument were validated in cadaver experiments. Utilizing these specific tweezers facilitates a straightforward and fast APRICOT® implantation procedure without the need for bone sawing or the removal of healthy tissues.
Next, strategies were designed and investigated investigates strategies to ensure the stability of the APRICOT® implant within the joint capsule. A comprehensive review study was conducted to highlight advancements in fixation techniques for managing joint disorders. This review identifies three primary fixation methods: mechanical techniques, tissue-ingrowth approaches, and (bio-)adhesives. Following that, specifically, these methods’ applicability for the APRICOT® implant were evaluated, which resulted in selected mechanical options, (bio-)adhesives, and coating strategies to maintain the stability of the APRICOT® both in the short-term and long-term. In testing implant stability within a custom-made MCP joint simulator, findings indicated that fixing the implant to the head of the metacarpal bone ensures stability for up to 1 million continuous cycles of extension and flexion. While a patient’s natural movement might be constrained by the joint capsule, limiting potential migration, our focus was on ensuring that the APRICOT® doesn’t deform or displace within the joint due to is flexibility and forces acting on it. Encouragingly, a low-adhesion double-sided tape effectively stabilized the implant over 1 million cycles. This suggests that enhancing friction between the APRICOT® and joint surfaces would fully secure it within the joint capsule. Furthermore, suture retention tests demonstrated that APRICOT® films withstood expected post-implantation forces. Specifically, after subjecting a suture-anchored sample to 1 million flexion cycles, no suture failures occurred, affirming the viability of using suture anchors for dorsal fixation of the APRICOT®. Additionally, the research explores the potential of calcium phosphate coatings on flexible Polycarbonate urethane (PCU) foils to promote osteointegration. Techniques to deposit both amorphous and semi-crystalline Calcium phosphate (CaP) coatings on PCU foils have been developed and tested. Preliminary in vitro assessments indicate that these coatings maintain cell viability and even have the potential to enhance calcium deposition. Further, in-vivo studies assessed the biocompatibility of PCU foils, both with and without coatings, confirming their suitability to be implanted in-site.
To conclude, this thesis investigated the comprehensive steps necessary for the implantation and anchoring of the innovative APRICOT® concept. Using a custom-made thumb MCP joint simulator, the stability of the APRICOT® implant was assessed. When the joint underwent continuous flexion and extension, the APRICOT® prototypes remained stationary relative to the proximal phalanx base. To prevent sliding between the implant and the metacarpal head, the central portion of the dome-shaped component should be affixed directly to the metacarpal head using adhesive. Yet, once the implant is placed inside the joint capsule, the adjacent tissues and joint capsule further increase its stability, minimizing potential shifts between the implant and the metacarpal head. Furthermore, any adhesive considered for this specific application must exhibit biocompatibility. With the surgical tools developed in this study and following the developed surgical protocol, we assume that the APRICOT® can be efficiently implanted in roughly 10 minutes under local anaesthesia. This method presents an opportunity to deploy the APRICOT® at earlier osteoarthritis stages without compromising surrounding tissues.
