1 Design rational. 1.1 Implant

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1 1 Design rational 1.1 Implant The Pyrocardan is a rectangular shaped implant made out of two tubular concavities opposed perpendicularly to one another. In its center the implant is 1 mm thick. The thickness of the edge of the implant depends on its size. Seven sizes are available for the use in the TM joint. They are defined by the length of the implant measured in millimeters and ranking from 12 (XXS) to 18 (XXL). The implant is positioned in the TM joint so that its length is in the medio-lateral axis of the joint line and its antero-posterior concavity is opposed to the trapezial joint surface. 1.2 Pyrocarbon Pyrocarbon is deposited onto a graphite substrate of carbon atoms by the thermal decomposition of a gaseous hydrocarbon at high temperature, using a process called Chemical Vapor Deposition (CVD). Pure Pyrocarbon implants offer advantages over polyethylene and metal implants. Pyrocarbon has an elastic modulus that is similar to cortical bone, which reduces stress shielding. In addition, Pyrocarbon is gaining widespread acceptance for use in orthopedics due to its excellent biocompatibility, extremely low friction coefficient, and high resistance to wear. Bone vs. ceramic Hard Bone vs. polyethylene Soft Bone vs. pyrocarbon Ideal The use of ceramic (harder than bone) and polyethylene (softer than bone) implant leads to unbalanced constraints dispersion in the articulation. Red color shows abnormal constraints peak. It could lead to bone subsidence (ceramic implant) of implant remodeling and wear (polyethylene implant). Finite element analysis - bone vs. implant (ceramic, polyethylene, pyrocarbon) 1

2 T O R N I E R P y r o c a r b o n T r a p e z o m e t a c a r p a l i n t e r p o s i t i o n i m p l a n t 2 Indications Meets the surgical indications for stage 1, 2 and early stage 3 rhizarthrosis according to Dell classification by offering an alternative to sliding prostheses and partial or total trapezectomies, with or without interposition or hemiprostheses. 3 Contra-indications The use of the Pyrocardan implant is contraindicated in the following cases (non exhaustive list): Acute or chronic infectious pathologies of any etiology and localization; Major carpal instability; Major tendon damage in the external dorsal compartment and cutaneous or neurovascular sequelae on the extension side of the wrist; High trapeziometacarpal osteoarthritis (too great deformation of the joint); Neuromuscular or psychiatric pathologies which might jeopardize the postoperative care; Insufficient bone support; Pregnancy; Known or suspected allergy to the material. 4 Surgical technique 4.1 Incision Two approaches can be performed: Dorsal approach The dorsal approach is recommended in case of trapezometacarpal arthritis with subluxation. The skin incision is dorsal and either straight or V shaped and slightly distal to trapezometacarpal joint. The tendon of the extensor pollicis longus is set to the medial side of the incision and the tendon of the extensor pollicis brevis to the lateral side to expose the base of the first metacarpal. 2

3 A rectangular capsulo-periosteal flap is cut out from the base of the metacarpal at an average of 10 mm distal to the joint and between the insertion of the abductor pollicis longus laterally and a line prolonging the ulnar edge of the metacarpal. The capsulo-periosteal flap is detached from the base of the metacarpal using the periosteal elevator. The capsulo-periosteal flap remains attached proximally and is folded over to expose the joint line Antero-lateral approach The antero-lateral approach is recommended only in case of trapezometacarpal arthritis with no subluxation. The skin incision is straight on the lateral border of the TM joint. Cutaneous branches of the radial nerve are gently dorsaly retracted. The lateral border of the thenar muscles is detached from the base of the metacarpal and the lateral side of the TM joint. The capsule is opened with a longitudinal incision palmarly to the APL tendon. 3

4 T O R N I E R P y r o c a r b o n T r a p e z o m e t a c a r p a l i n t e r p o s i t i o n i m p l a n t 4.2 Bone preparation Whatever approach is chosen (dorsal or anterolateral), joint preparations and placement of the trial and sterile implant are similar procedures. The purpose being to resect both pics of trapezium and metacarpal saddle shape. Intra-articular bony resections are done with a thin oscillating saw Metacarpal preparation The dorsal and palmar edges of the metacarpal are sawed off while preserving the center of the articulation (the deepest area of the anterio-posterior concavity). Those resections result in reshaping the initial metacarpal saddle shape by smoothing its anteroposterior concavity and keeping its medio-lateral anatomical convexity Trapezium preparation The medial horn of trapezium, which is often prolonged by an osteophyte, is removed. Its lateral horn is less protruding and can be removed with a saw, a rongeur or a burr. Those resections result in reshaping the initial trapezium saddle shape by smoothing its mediolateral concavity and by keeping its antero-posterior anatomical convexity. 4

5 Surgical technique - radial approach Correction of trapezium displasia When the joint line is very oblique, the medial horn is resected even more to obtain a horizontal joint line perpendicular to the metacarpal axis of the first column Joint synovectomy Perform a total synovectomy of the joint and of the dorsal capsulo-periosteal flap. Special care is taken to free the palmar recess of the trapezium and to resect the osteophyte that often forms there Joint surfaces milling An ovoid burr is used to smooth the bone cuts. The metacarpal side is roughly shaped into a sphere. The new shaped cylindrical antero-posterior convexity of the trapezium is refined with the ovoid burr. Make sure to preserve the subchondral bone in the center of the trapezium and the metacarpal. 5

6 T O R N I E R P y r o c a r b o n T r a p e z o m e t a c a r p a l i n t e r p o s i t i o n i m p l a n t 4.3 Trial Implant setting The implant size is chosen, among a set of color coded trial implants, so that the trapezium is totally covered. Metacarpal side, trapezium side and antero-posterior axis of trial implants are clearly identified with laser marks to facilitate orientation. Fluoroscopy control is used to check the proper size and positioning of the implant and to make sure no cam effect is observed in the full range of motion of the metacarpal. 6

7 4.4 Sterile implant setting The Pyrocarbon implant sides cannot be identified with laser marks. In case of doubt, check orientation while comparing sterile implant with its corresponding trial implant and using the trial stowage slot of the Correct Orientation Template. The Pyrocardan is a rectangular shaped implant made out of two tubular concavities opposed perpendicularly to one another. The medio-lateral bend faces the prepared metacarpal base. The antero-posterior bend faces the trapezium surface. 4.5 Closure Dorsal approach The dorsal capsulo-periosteal flap is firmly reinserted without overmuch tension to the dorsal base of the metacarpal with three trans-osseous, absorbable sutures 3/0 or with absorbable bone anchors Antero-lateral approach For closure, the two edges of the capsule are stitched together, the thenar muscles are replaced over it and their fascia reattached Subluxation joint reduction In the presence of a persistent metacarpal subluxation despite the implant positioning, the capsulo-periosteal flap is reinserted more laterally on the dorsal side of the metacarpal, in order to oppose subluxation forces. The metacarpal thus remains centered on the trapezium Skin closure is performed with an absorbable 4/0 subcuticular suture. 5 Postoperative care and rehabilitation A thick dressing ensures immediate postoperative immobilization and is replaced the following day by a removable thermoplastic splint. The patient is advised to wear the splint at all times during 15 days. Self-reeducation exercises of the first column are done by the patient starting from the fifteenth day after dressing removing. After the fifteenth day the splint should be worn if needed only at night or during manual activities during the day until the fourth week. 7

8 T O R N I E R P y r o c a r b o n T r a p e z o m e t a c a r p a l i n t e r p o s i t i o n i m p l a n t 6 Clinical case examples Clinical example N 1 Woman 56 years old, secretary, right dominant hand Follow-up at 18 months Clinical example N 2 Man, 47 years old, working man, left non-dominant hand Follow-up at 13 months 8