Pyrocardan and Pyrodisk implants are made of pyrocarbon and used as interposition arthroplasty for the treatment of the thumb CMC joint osteoarthritis. The aim of interposition implants is to preserve the thumb length to allow normal thumb motion and function.
Pyrodisk is a biconvex disk with a central hole used for a ligamentoplasty to stabilize the implant and the base of the metacarpal. It may be used after partial or total trapeziectomy in any stage of osteoarthritis. Pyrocardan implant is biconcave and rectangular-shaped. It is thinner than Pyrodisk. It is used as an interfacing arthroplasty between the trapezoid and the metacarpal in early stages of osteoarthritis (Eaton’s stage 1, 2 and early stage 3). Its implantation preserves capsuloligamentous soft tissues of the joint and therefore no ligamentoplasty is required.
Mid- to long-term outcomes of these two implants have been reported. They show marked improvement on pain, strength, and function. Recovery seems quicker compared to trapeziectomy. With the follow-up bone tolerance is good and clinical outcomes remain stable or tend to progress. Complication rates are low and survival rates are 94% at 8 years for Pyrodisk and 96.2% at 5.5 years for Pyrocardan. Due to Pyrocarbon material these interposition arthroplasties are well tolerated and have eliminated the problems encountered with silicone implants or metallic and polyethylene total prosthesis used in CMC joint.
Key wordspyrocarbon – CMC joint – implant – arthroplasty – interposition – arthritis – Pyrocardan – Pyrodisk
20 Pyrocardan and Pyrodisk Arthroplasties of the Thumb CMC Joint
Because of the remarkable mechanical properties of the pyrocarbon (elasticity, density, roughness, hardness, and resistance to wear durability) and its biocompatibility, pyrocarbon implants have been proposed as an alternative to silicon and other synthetic implants. They have been used in hand since the 1980s and later in wrist. 1
For the treatment of basal thumb osteoarthritis (OA), two categories of pyrocarbon implants are available:
Hemiarthroplasty implants: They replace the metacarpal surface and are stabilized by an intramedullary metacarpal stem: PyroHemiSpher, CMI, Nugrip (see Chapter 19), and Saddle implants.
Interposition implants: They are placed between two articulating surfaces either after total or partial trapeziectomy for the Pi2 (see Chapter 19) and Pyrodisk implants, or in the trapeziometacarpal (TMC) joint for the Pyrocardan implant. Pyrodisk implant has been used since 2005 2 and Pyrocardan since 2009. 3
The aim of interposition implants is to preserve the thumb length to allow normal thumb motion and function.
20.2.1 Characteristics of the Implant
Pyrodisk implant (Integra Life Sciences, Plainsboro, NJ, USA) (Fig. 20.1) is a nonanatomical interposition shaped as a biconvex disk with a central hole to allow stabilization with an autograft tendon, transferred and passed through the trapezium, the implant, and the thumb metacarpal. Six available sizes exist with various combinations of diameters (14 mm, 16 mm, 18 mm) and heights (5.5 mm, 7 mm, 8 mm, 9 mm).
Pyrodisk implant may be indicated for the treatment of any stages of OA. In the early stages (Eaton’s stage1, 2, and 3), Pyrodisk implant is originally used after partial trapeziectomy. The implant is positioned between the metacarpal and the remaining trapezium (Fig. 20.2). More severe stages of OA may require total trapeziectomy with interposition of Pyrodisk articulated between the metacarpal and the scaphoid (Fig. 20.3).
20.2.3 Surgical Technique
The approach is dorsal over the trapezium. Two to 3 mm of bone is removed with an oscillating saw from the metacarpal base perpendicular from its long axis. The trapezial surface is flattened with the saw with a cut parallel to the metacarpal cut. A reamer is used to dig a small concavity on the trapezium and metacarpal surfaces. In each bone a 3.2-mm drill hole is created obliquely toward the center of the TMC joint in the middle of the cavities starting for the trapezium from the center of the scaphotrapezial joint and for the metacarpal from its dorsal radial aspect. The proper implant diameter is determined by selecting the size that provides the best fit to the diameter of the thumb metacarpal base without overhang. If the best size falls between two available sizes, then the smaller size is chosen. The goal is to achieve a gentle rocking motion of the biconvex disk on the concave surfaces of both the thumb metacarpal base and the trapezium.
Intraoperative fluoroscopy confirms proper sizing.
One of the bundles of the abductor pollicis longus tendon or half of the flexor carpi radialis (FCR) tendon 4 is used as a stabilizer tendon. The distal stump of the distally based tendon is passed through the trapezium, into the resected joint through the selected Pyrodisk implant and into the thumb metacarpal base to exit dorsally through the prepared passage. Gentle traction is applied to the tendon prior to closure to enhance stability. The remaining tendon then is folded back and incorporated into a secure capsular closure.
After surgery, the wrist and thumb are immobilized in a thumb spica plaster orthosis for 3 weeks. A removable orthosis is used during the next 8 to 9 weeks during which the patient performs active range of motion exercises and uses the hand for daily activities. After 11 to 12 weeks, unrestricted activities are allowed.
20.2.4 Results in the Literature
A retrospective series by Barrera-Ochoa et al 2 included 19 patients reviewed at a minimum 5-year follow-up. Eighty-nine percent of patients were satisfied or very satisfied, pain measured 1.7 (visual analog scale [VAS]), Quick-DASH scored 20.2, mobility was not significantly improved, and grip strength (20 kg) increased significantly. The failure rate was 10.5%, associated with painful instabilities, revised by trapeziectomy after 1 year. Long-term outcomes of reported similar results with a survival rate of 94% at 8 years. 5
The series by Mariconda et al 7 included 27 patients reviewed at an average follow-up of 37 months. It showed better results on pain and Quick-DASH score. Ninety-six percent of patients were satisfied or very satisfied. There were no complications or revisions. Radiologically, one implant was dislocated and no bone subsidence was noted.
In indications of perfectly centered rhizarthrosis, Odella et al 7 generally obtained good pain results with Pyrodisk. However their results on strength (a 20% loss) were in contradiction with those of Barrera-Ochoa et al (a 26% gain). 2 They also reported a failure rate of 3% and 3% implant dislocation.
A recent retrospective comparative series 2 of ligament reconstruction and tendon interposition (LRTI) (19 cases) versus Pyrodisk (20 cases) showed a significant better key pinch strength (1.8 kg higher) with the Pyrodisk after a minimum follow-up of 2 years. No differences were found in other functional criteria or in complication rates.
20.2.5 Author’s Experience
The Pyrodisk implant can also be used after total trapeziectomy (Fig. 20.4), as proposed by Vitale et al 8 and Chaise. 9 Like the Pi2 implantation (see Chapter 19), a partial trapezoidectomy is required to medialize the implant and for the treatment of an associated scaphotrapezoid OA (Fig. 20.4). To stabilize the implant a strip of the FCR tendon, 8 or a ligamentoplasty with a thread of Goretex CV/0 9 may be used. This latter implant stabilization technique is simpler and less invasive than that used for the Pi2 implant (see Chapter 19). However, in our experience of more than 80 implants, the failure rate (revised by implant) for chronic pain enduring beyond 1 year was 6% and we found that the overall clinical results, especially regarding pain, seemed inferior to those of the Pi2 implant. Since the Pyrodisk implant is more constrained than the Pi2, pain originating in the bone may be associated with excessive stress peaks. Failure to stabilize the implant and the base of the metacarpal with the follow-up may occur with the follow-up as shown in some cases of our series (Fig. 20.5). It may be due to frictional wear of the ligamentoplasty in the articulating surfaces and can be facilitated by the biconvex shape of the implant.
20.3.1 Characteristics of the Implant
Pyrocardan implant (Wright Medical-Tornier SAS, Bioprofile, Grenoble, France) (Fig. 20.6) is an intra-articular interfacing unconstrained interposition of the TMC joint. 3 It is rectangular-shaped with two perpendicularly opposing tubular concave faces. This geometry is supposed to replicate the carpometacarpal (CMC) joint movements. The implant has a 1-mm central thickness regardless of size. There are 7 variants, between 12 and 18 mm wide. The thickness of the exterior edges is proportional to the implant size. Its placement requires minimal intra-articular bone resection that respects the capsuloligamentary muscle insertions outside the joint space area. 10 Stabilization ligamentoplasty is, therefore, not necessary.