Pyrocarbon implants for the treatment of extensive wrist osteoarthritis have been recently proposed alternatively to more invasive and/or wrist motion-limiting procedures. They may also be used to salvage failed previous wrist surgery. Two type of wrist pyrocarbon implants are available: (1) The Amandys implant is a free radiocarpal interposition creating two new joint surfaces, radiocarpal, and midcarpal; (2) the RCPI implant is a stemmed hemiarthroplasty for the head of the capitate used with a proximal row carpectomy (PRC). As the arthroplasty created with these implants is nonconstrained, their indications require preoperative well-aligned wrist on radiographs.
Surgical technique for their implantation is usually performed dorsally. In any case it requires precise surgery to preserve capsule continuity and ligament attachments during the bone removal. Proper sizing of the implant must avoid overstuffing the joint and any bone impingement must be excluded. The experience of the authors with mid-term follow-up on large series provide encouraging results which seem to not deteriorate with the follow-up. Wrist motion and function are preserved, and pain relief is achieved. Reoperation rates are low for both implants. The most frequent complication is the instability of the implant for the Amandys and the instability of the wrist for the RCPI.
Indications of each implant are not yet well defined and seem to overlap. The Amandys implant appears more suited to treat severe joint destruction while the RCPI implant particularly extends the indications of PRC in the presence of capitate head destruction.
Key wordspyrocarbon – wrist – implant – arthroplasty – interposition – arthritis – rheumatoid – posttraumatic – Amandys – RCPI
28 Pyrocarbon Implants in the Wrist: Amandys and RCPI
The properties of pyrocarbon (an elastic modulus similar to cortical bone, low roughness, a low coefficient of friction, resistance to wear, and biotolerance) make this material suitable for arthroplasty with smooth gliding interface between implant and cartilage or subchondral bone. 1
The pyrocarbon implants contain a central core of graphite (mixed with a little tungsten powder that gives radio-opacity) resurfaced with a radiolucent pyrocarbon layer.
Pyrocarbon arthroplasty for extensive joint destruction of the wrist use two implants:
The Amandys implant which is a free spacer to create a new type of radiocarpal interposition arthroplasty.
The RCPI implant which is a stemmed hemiarthroplasty for the head of the capitate designed to be used with a proximal row carpectomy (PRC).
In this chapter, the surgical technique and midterm results of these two implants are reported.
28.2 Amandys Implant
The aim of the Amandys arthroplasty is to create a radiocarpal or a midcarpal interposition arthroplasty. 2 The implant is a mobile spacer able to glide and rotate over the radius and midcarpal surfaces to dissipate and thus reduce peak loads. This arthroplasty requires minimal osseous resection at the joint margin and thus preserves the bone stock, helping to maintain the carpal height and optimize the function of the principal extrinsic carpal ligaments.
28.2.1 Characteristics of the Implant
The Amandys implant (Wright Medical-Tornier SAS, Bioprofile, Grenoble, France) is an ellipsoid spacer with a quadrielliptic surface creating two asymmetric convex joint surfaces. The two curves of the distal (carpal) surface are less pronounced than those of the proximal (radial) one (Fig. 28.1). The implant has three main axes: an anterior-posterior one corresponding to its width; a transverse one corresponding to its length; and a proximal-distal one corresponding to its thickness. The implant exists in eight sizes varying in length (24–26 mm) and in four thicknesses: small (S—9 mm); medium (M—10.7 mm); large (L—12.4 mm); and extra-large (XL—14.1 mm).
The Amandys implant is used in the treatment of radiocarpal arthritis. It replaces the lunate, two-third of the proximal scaphoid, and the proximal portion of the capitate. The triquetrum is not resected in order to preserve the attachments of the dorsoradial and dorsal intercarpal extrinsic ligaments (Fig. 28.2). The implant has no bone or ligament fixation so it remains free and mobile between the radius and the distal carpal row. Its stability is “ensured” by its congruence with the distal radial articular surface and shaped cavity in the midcarpal bone surfaces and by the posterior and anterior capsuloligamentary structures.
28.2.2 Indications and Contraindications
Correct radiocarpal alignment, efficient capsules and ligaments, and functional wrist flexor and extensor tendons are required for an Amandys interposition implant. Major bone loss or instability as in rheumatoid or post-traumatic wrist is an absolute contraindication. The Amandys arthroplasty can be used as an alternative to a total wrist arthroplasty or total wrist arthrodesis including for radiocarpal or midcarpal osteoarthritis (OA), rheumatoid and post-traumatic arthritis, and Kienböck disease. 3 It can also be used to salvage failed previous wrist surgery, e.g., partial wrist fusion, a silicone implant, proximal row carpectomy, or even a total wrist prosthesis. 4 5
In less severe degenerative arthritis, the Amandys arthroplasty can also be used as an alternative to partial wrist fusion, especially in the elderly.
28.2.3 Surgical Technique
Special attention must be paid to manage the periarticular soft tissue releases during the bone resections, especially the palmar capsule. 6
A dorsal longitudinal approach centered over the middle of the wrist is usually preferred; however, if the wrist is well aligned and stable without the need for major osteoarticular reconstruction, then a radial approach with a radial styloidectomy is possible. The dorsal approach facilitates several aspects: defining the extent of bone resection; performance of bone resection and synovectomy with minimal trauma; distal radial or carpal bone grafting if necessary; preparing the joint surfaces; and assessing the condition of the articular capsule, particularly the palmar capsule.
The dorsal approach is made with an L-shaped capsulotomy incised longitudinally over the radial side of the wrist creating a capsular flap that is reflected ulnarly (Fig. 28.3).
First, the proximal two-third of the scaphoid are removed with an oscillating saw just above the ligament insertions of the dorsal radiocarpal ligament and the radio-scapho-capitate ligament, which must be preserved. The saw cut is made parallel to the frontal and transversal slopes of the radial fossa, i.e., tilted volarly by c. 11 degrees and ulnarly by 22 degrees.
The lunate is then freed from all ligamentous attachments and removed. A corkscrew is used as a joystick to aid this resection. The head of the capitate is removed with a saw. The cut should be at level with that of the ulnar side of the scaphoid saw cut. The ulnar side of the saw cut is made at level with the proximal tip of the hamate. Prominent osteophytes are removed, including possibly a partial radial styloidectomy.
The distal radial articular surface is then smoothed to obtain a concave ovoid surface along both axes matching the Amandys implant. This includes excision of the crest between the scaphoid and lunate fossae of the distal radius. If there is marked laxity or a tear of the palmar capsule, suture plication or reinforcement may be necessary. Any large bone cavities in the radius or the carpus can be curetted and grafted with packed cancellous graft.
Choosing the Size of the Implant
The implant must allow a range as wide as possible of passive mobility of the wrist confirmed intraoperatively with fluoroscopy. Cam effects in extreme positions of flexion, extension, and radial or ulnar deviation cause some implant rotation. They must be eliminated because they will cause implant instability postoperatively. Overstressing the implant, which can induce instability or chronic pain, should be avoided. In doubt, we recommend choosing a smaller implant size. An implant that is too thick will increase the ulnocarpal height which will result in an overconstrained wrist.
Immobilize the wrist in a neutral position with a removable plastic splint for 2 to 3 weeks and then gradually increase mobilization with no restrictions beyond 6 weeks postoperatively.
28.2.4 Associated Procedures
An Amandys arthroplasty can be combined with surgery on other joints around the wrist such as the distal radioulnar joint (DRUJ) (Fig. 28.4). Partial fusion on the triquetro-hamate or scapho-trapezio-trapezoid (STT) joint or combined arthroplasties of the STT or thumb carpometacarpal (CMC) joints can also be performed.
In the Literature
Only a few series have been published, with a maximum follow-up of 42 months. 2 – 8 The surgery appears to give good pain relief and wrist function measured by visual analog scale (VAS), range of motion (ROM), and grip strength. Mobility and grip strength are typically barely changed but patient satisfaction is rated as good.
Early implant instability is the most common complication. In 10% of all published cases, the implant needed repositioning. Two failures in a series of 11 (3%) were reported, both of which were converted to a total wrist arthrodesis. One was due to errors related to an inappropriate indication and inexperience, and the other for chronic pain. 7
Cugola et al 9 compared the results of a case series of 26 total wrist prostheses with a mean follow-up of 6.5 years, to a case series of 10 Amandys implants with a mean follow-up of 3.5 years. The Amandys results gave better pain relief, mobility, and grip strength; none requiring revision. Two total wrist prostheses were revised.
Personal (PB) Experience
In our institution, the 10-year experience with the Amandys implant is based on more than 200 arthroplasties. The main indication (32%) has been degenerative such as severe scapholunate advance collapse (SLAC) or scaphoid nonunion advance collapse (SNAC) wrists, 14% were for rheumatoid arthritis, and 26% had previous wrist surgery. Two cases were converted to total wrist arthrodesis due to implant instability with persistent pain. The revision rate for early implant instability and secondary repositioning was 6%. This rate decreased with our experience, which is indicative of a learning curve.
A series of 51 patients (55 implants) with a mean age of 58 (range 25–84) years was evaluated with a minimum of 5-year (mean 84 mo) follow-up. The results (unpublished) showed improved grip strengths at a mean of 20 kgf (68% of the opposite side) increased from 12 kgf preoperatively. The ROMs were 75 degrees of flexion-extension (66 degrees preoperatively) and 33 degrees radioulnar deviation (30 degrees preoperatively). The patient-related wrist evaluation (PRWE) improved from 63 to 27/100, the Quick-DASH improved from 63 to 34/100, and the mean visual analogue score (VAS) for pain improved from 6.5 to 2.3/10. Patients were satisfied or very satisfied in 86% of cases. A comparison of results at 2 years and at 5 years postoperatively found a significant improvement in grip strength, PRWE, and Quick-DASH scores between these two periods. The radiological results have shown no significant progressive subsidence or misalignment of the implants (Fig. 28.5).
A series of 28 rheumatoid wrist treated with an Amandys implant achieved similar results (unpublished data) at a mean follow-up of 45 months.
These encouraging results have prompted us to extend the indications for using the Amandys to less severe wrist damage as an alternative to a four-corner fusion procedure in grade-3 of SLAC, SCAC (scaphoid chondrocalcinosis advanced collapse), and SNAC wrists especially for patients over 60 years of age. A comparative series (unpublished) of 20 patients with a mean age of 65 years and a mean follow-up of 7 years showed a quicker functional recovery , better improvement of the ROMs, and less complication with the Amandys implant than a four-corner fusion.