This chapter describes the development of the anatomically designed, unconstrained Tactys total joint proximal interphalangeal (PIP) replacement, as well as its particularities and clinical results, both in the literature and in the experience of the author and the developers. The operative procedure is described in detail, together with caveats and surgical tips and tricks.
Key wordsPIP joint – surface arthroplasty – proximal interphalangeal joint – prosthesis – implant
13 Third-Generation PIP Joint Arthroplasty: Tactys
There are three main types of surgery for functionally disabling degenerative arthritis of the proximal interphalangeal (PIP) joint: denervation, arthrodesis, and arthroplasty. Whatever the choice, they all aim to alleviate pain while preserving a useful level of function, not only for the finger itself, but for the hand as a whole. The final decision is based upon the general needs of the patient, any specific requirements, and the state of all the fingers both symptomatic and asymptomatic. Bone stock and quality in the symptomatic finger may be further considerations.
Among the implant arthroplasties, silicone spacers have long been the only solution and are still in use and often considered the gold standard. 1 In addition to their simplicity and ease of implantation, they give relatively consistent results, but their usage is most commonly recommended for low-demand patients. Meanwhile, implants made of various more rigid materials have been developed in order to improve the outcomes. 2 Anatomically designed metallic, ceramic, or pyrocarbon implants have been developed to improve ranges of motion, stability, and longevity. 3 , 4 , 5 However, due to the delicate balance of forces, PIP prosthetic replacement is fraught with complications. 6 , 7 The Tactys implant was designed to address these issues.
The Tactys modular prosthesis (Stryker–Memometal, Bruz, France) is a total gliding, unconstrained, modular surface replacement prosthesis with an anatomic design. Started in 2008 by a group of hand surgeons from Belgium, France, and Switzerland together with engineers of the Memometal company, it was set out to imitate the condylar surfaces of the proximal phalanx and the concavities at the base of the middle phalanx, as well as the subtle incongruency and tribological peculiarities as found in nature (Fig. 13.1). The development focused on anatomical premises and studies regarding the size of the phalanges, the form of the condyles, 8 the natural surface incongruency between them and the base of the middle phalanx, as well as the tribology and lubrication.
Our fundamental hypothesis was that a prosthesis anatomically and physiologically as close as possible to the natural model would achieve the best results. Special attention was paid to the morphology and dimensions of the joint surfaces. 9 , 10
The second major concern is fixation of the implant to bone to achieve early implant stability and long-term fixation including in cases of deficient bone stock. Press-fit fixation was chosen.
Some modularity was considered essential to be able to treat different fingers in different sized hands in men and women.
13.3 Characteristics of the Implant
The Tactys prosthesis is made of four components (Fig. 13.2). The proximal and distal medullary components are made of titanium partially coated with hydroxyapatite in the metaphyseal region in order to ensure secondary bony fixation without making subsequent revision too difficult if required. The stems are designed to be relatively short, especially the distal stem, in order to allow for distal interphalangeal (DIP) joint arthrodesis. The proximal convex joint surface is made of ultrahigh-density polyethylene while the distal concave surface is made of chrome-cobalt alloy. The four components (two stems and two articulations) are available in four different sizes for considerable surgical flexibility (Fig. 13.3).
13.3.1 Surgical Technique
The surgery is performed under axillary block with a tourniquet. Via a dorsal curvilinear incision over the PIP joint, the joint is accessed through a longitudinal transtendinous approach with the central slip detached from the base of the middle phalanx. A synovectomy is performed and peripheral osteophytes removed. While preserving the collateral ligaments, the condyles are removed from the head of the proximal phalanx with a thin oscillating saw resecting perpendicular to the long axis of the proximal phalanx. The cartilage remnants and the underlying sclerotic bone at the base of the middle phalanx are removed sparingly either with a saw or a drill aiming to create a flat surface strictly perpendicular to the long axis of the middle phalanx (Fig. 13.4). The gap approximator (Fig. 13.5) is inserted between the two phalanges to estimate the gap width, thus defining the size and the thickness of the distal surface component. Resection can be adjusted if necessary. Proximal and middle phalanges are then reamed to the appropriate stem size as measured with the stem gauge. Proximally the entry point is placed slightly dorsally, whereas it is strictly central in the middle phalanx. For the less experienced surgeon, preinserted pins and fluoroscopic control are mandatory to achieve the correct alignment. Both stems should be inserted so that their articular ends lie flush with the bone surfaces. Using the dedicated palmar cutting guide, the volar edge of the condyles is removed with a saw, taking care to protect the volar plate. Two millimeters of the dorsal cortical ridge over the stem must be removed for the polyethylene component to fit well against the end of the proximal phalanx (Fig. 13.6). The proximal and distal resurfacing components can then be selected to fit the size of the bone surfaces aiming to be slightly smaller/larger than the bone ends. The thickness of the implants is adjusted so that the joint is stable laterally without excessive tension axially. The tenodesis effect should ideally be restored (passive PIP extension in full wrist flexion and PIP flexion in full wrist extension). When the four trials are in place the finger is assessed fluoroscopically. The trials are removed and replaced by the final implants in the following order: proximal stem, distal stem, proximal polyethylene surface, distal chrome-cobalt surface (Fig. 13.7). The joint is carefully washed out and all bone debris removed. The central slip is sutured with interrupted slow-absorbable stitches (4–0 suture) with or without bone reattachment at the base of the middle phalanx. A clinical case (middle finger) is shown intraoperatively (Fig. 13.8) and the postoperative 1-year course is shown in Fig. 13.9.
A palmar plaster slab is applied holding the metacarpophalangeal (MCP) joint in flexion and the PIP joint in extension for 2 to 3 days. Self-mobilization is started after the first dressing is changed. The finger is protected by a removable thermoformed splint for 3 to 4 weeks postoperatively.