9.2.1 Pyrocarbon

Pyrolytic carbon, or pyrocarbon, is a unique material. It has been utilized in replacement of heart valves for many years. ² Its material properties are favorable in many ways. The elastic modulus is very similar to cortical bone. This allows the implant to favorably share the load with bone and minimize stress shielding. It is biologically inert and does not invite an immune-mediated reaction as seen with silicone and polyethylene. The wear characteristics of the articulation are also very favorable. Studies have demonstrated minimal particulate debris from repetitive cyclic loading. Unfortunately, the stems of these implants have no osseous ingrowth and depend primarily on appositional growth of the bone around the implant to help provide stability. Due to its favorable material properties, pyrocarbon has promise when utilized as a hemiarthroplasty. Canine studies have demonstrated that, when compared to cobalt chrome, pyrocarbon yielded no inflammatory response, and generated less surface cracks and promoted more fibrocartilage regeneration against its exposed articulation than cobalt chrome. ³

Pyrocarbon was introduced as a small joint replacement in 1979. ⁴ The implant design has been modified from its original design, particularly the stems. The current design is a ball-and-socket joint that mimics the anatomy of natural MCP joints (Fig. 9.1). Kinematically, the design is similar to that of the native MCP joint, maintaining the arc of curvature and center of rotation.

The surgical technique for insertion is similar to that of silicone implants. A dorsal or transverse incision can be utilized. In patients with inflammatory arthritis, I prefer to expose the joint radial to the extensor tendons through the radial sagittal band, which allows for plication and centralization of the extensor tendons at closure. The capsule is split longitudinally and allows for joint exposure. The MCP joint can then be flexed and the metacarpal head exposed. At the dorsal one-third point of the metacarpal head, a K-wire is inserted longitudinally down the canal of the metacarpal. It helps identify the start point for the alignment and cutting guide of the metacarpal. Fluoroscopy is used to confirm the appropriate insertion point for the guide. Following insertion of the guide, the cutting attachment is placed and the dorsal metacarpal cut is made. The guide is then removed and the rest of the cut is made freehand. The cut is designed to be oblique and protect the collateral ligaments. Resection of the metacarpal head allows visualization of the volar plate and softtissues and release can be performed at this time, if indicated. Following the metacarpal preparation, the proximal phalanx cut can be performed. The alignment/cutting guide is inserted in the canal at the dorsal third junction. Again, a K-wire, followed by fluoroscopic evaluation, helps confirm the appropriate placement of the alignment guide. The cut at the proximal phalanx is perpendicular to the longitudinal axis. The cut is initiated with the guide in place and completed free-hand after removal of the guide.

Broaching is performed up to the largest size that fits the canals. The use of a side-cutting burr can be helpful in preparing the canals to optimize fit. Following broaching, the implant is trialed. At this point, stability can be assessed in both coronal and sagittal planes. Adjustments to the softtissues, such as tightening of collateral ligaments and further volar release, if indicated, can then be performed and prepared for after insertion of the definitive implants. In addition, if the joint is not stable enough following trialing with the surface gliding trials, the system has silicone trials that match the bony cuts as a fallback option. Following placement of the final components, the motion and stability are reassessed. Softtissue balancing is then completed and the extensor tendon centralized.

In patients with osteoarthritis, it is uncommon to perform more than one or two implants in the same setting. Thus, a longitudinal incision is performed. A tendon-splitting approach can generally be utilized. The rest procedure are similar to the above technique, except that softtissue balancing is typically not as necessary.

9.2.2 Surface Replacement Arthroplasty (SRA) MCP joint

The SRA implant pre-dates the pyrocarbon joint. It was designed by Dr. Ronald Linscheid and has been used extensively. Like the pyrocarbon design, it is meant to be anatomic and duplicate the anatomy of the MCP joint. In addition, the bone preparation to fit the implant preserves the ligament and allows for repair/plication/release when indicated. It is a ball-and-socket design that mimics the native force transmission, and aims to maximize joint motion and tendon excursion. In addition, the metacarpal head design is such that it has an offset that helps provide stability with MCP flexion and laxity with extension. Finally, there are radial-ulnar flares that help provide coronal plane stability.

The SRA implant is a metal-polyethylene articulation (Fig. 9.2). The metacarpal component is a cobalt chrome head with a titanium stem. The entire distal component is made of polyethylene. The metacarpal component can be cemented or uncemented; the distal component requires cementation.

The technique is similar to that of the pyrocarbon implants. A dorsal transverse (multiple digits) or longitudinal (single or two digits) incisions can be used. The collateral ligaments are preserved or reflected for later repair. If the collaterals are released for plication, then either the origin or K-wires holes in the dorsal distal metacarpal can be used to tighten the ligament following insertion of the final components. The metacarpal head is resected perpendicular to its axis in a similar manner as cuts would be for silicone systems. However, a second chamfer cut is made to remove the distal volar aspect of the metacarpal. The proximal phalanx cut is perpendicular to its long axis with care taken to protect the volar plate and insertions of the collateral ligaments. The canals are broached to the best fit. The implants are trialed and stability is assessed. The components can then be inserted. The distal component is cemented first and the proximal component is then placed. The ligaments are then advanced, the joint capsule reapproximated, and the tendon centralized.

Rehabilitation protocols vary based on the diagnosis. In patients with rheumatoid arthritis, in the first 3 to 4 weeks following surgery, the MCP joints are immobilized in extension, while allowing for PIP motion. Thereafter, a low profile static splint is made for the patient and an MCP motion protocol is initiated. At 8 to 12 weeks postsurgery, the patient may begin strengthening.

Patients with osteoarthritis tend to have more reliable softtissue stabilizers and therefore are able to progress with therapy sooner. Depending on joint stability and the status of the collateral ligaments, early motion can begin. If collateral ligament tightening is necessary, then a longer period of immobilization (closer to that of patients with inflammatory arthritis) should be utilized.

9.4.1 Pyrocarbon

Since the initial publication by Cook et al, ¹² there have been numerous reviews of outcomes with pyrocarbon MCP arthroplasty. ^{13 , 14 , 15 , 16 , 17 , 18 , 19} Cook et al examined 71 MCP pyrocarbon arthroplasties in 26 patients at an average 12-year follow-up period. ¹² Multiple degenerative etiologies were treated, but the most common was inflammatory arthritis. Kaplan–Meier analysis reviewed an 82% five-year and 81% 10-year survivorship, with a predicted 2% failure per year. Overall motion of the MCP joint was improved by an average of 13 degrees and extension (elevation) of the arc improved 16 degrees, providing the patients a more extended posture and improved hand function. Radiographic outcomes were available in 53 of 71 fingers. Ninety-four percent of the joints maintained their reduction. There was however a notable trend toward recurrent ulnar drift over time, but at the most recent follow-up, the drift was not worse than preoperative measurements. Pain relief overall was excellent. The authors concluded that pyrocarbon was biologically and biomechanically compatible and durable material for arthroplasty of the MCP joint.

Subsequent series have also reported encouraging outcomes, especially for patient with osteoarthritis. Parker et al examined a large series of 130 MCP primary pyrocarbon arthroplasties, of which 116 were available for radiographic analysis, with a mean follow-up of 17 months. ¹⁴ The rheumatoid arthritis group comprised 96 joints while the osteoarthritic patients included 20 joints. Clinical results were generally excellent, with 99% survivorship in this preliminary study. Pain relief was predictable. The ranges of motion and strength were also improved in both groups. Patient satisfaction was greater than 90% at a mean follow-up of 1 year. There were 6% minor and 9% major complications among the cohorts. A 10% major complication rate was seen in the rheumatoid arthritis patients. The main noteworthy complications were two MCP subluxations, two cases of hand dysfunction and drift requiring repeat softtissue balancing, one patient with a dislocation, and one case of stiffness that underwent manipulation under anesthesia. The osteoarthritis group had two “major” complications: one was an extensor tendon disruption; and another was for persistent pain that required explant of the prosthesis. The osteoarthritis group had generally stable overall radiographic appearances with none of the implants demonstrating evidence of loosening. However, the radiographic analysis for the rheumatoid/inflammatory arthritis patients was more worrisome, especially after 1 year. While most were not revised either because the patient was asymptomatic or preferred not to, the dislocation rate increased to 14%. In addition, on the radiographic analysis at over 1 year, nearly all (95%) had an increased radiolucent seam, 55% had axial subsidence, and 45% were noted to have periprosthetic erosions.

Kopylov et al also examined their results of 40 pyrocarbon MCP joint arthroplasties in 14 patients with rheumatoid arthritis. ¹³ At a minimum follow-up of 3 years, all patients had improved pain relief, clinical outcomes, and motion. Two joints in one patient were revised secondary to excessive loosening. However, the study lacked the longer-term radiographic analysis when compared to that of Parker et al.

As previously mentioned, encouraging results have been seen with the use of pyrocarbon MCP arthroplasty for osteoarthritis. Nunez and Citron published a short-term review on the use of pyrocarbon MCP joints in patients with osteoarthritis. ¹⁹ The authors treated seven patients with ten MCP joints with a mean follow-up of 2.2 (range 1–4) years. Pain scores improved significantly from 68 to 3%. In addition, there was no evidence of implant failure or loosening. Overall, there were excellent patient satisfaction scores. They concluded that pyrocarbon MCP arthroplasty is a promising solution for osteoarthritis.

Wall and Stern reviewed 11 cases with a minimum 2-year follow-up (mean 4 years). ¹⁸ Pain relief was excellent and the range of motion improved. However, grip strength did not. All patients were able to return to their prior employment and patient outcome measures were excellent. One finger had subluxation of the extensor tendon and another was revised to arthrodesis secondary to persistent unexplained pain. Radiographically, there was a mean subsidence of 3 mm, but no implant migration, fracture, or dislocation. The authors concluded that pyrolytic carbon MCP arthroplasty was a good surgical option for patients with osteoarthritis.

Simpson-White and Chojnowski also reviewed 18 fingers in ten patients who underwent pyrocarbon MCP arthroplasty for osteoarthritis. ¹⁷ The mean follow-up interval was nearly 5 years (58.6 months). Pain, arc of motion, and patient-related outcome (QuickDASH) measures were all improved. All but one patient was satisfied. One case required revision to silastic implant secondary to altered pinch of their index finger. Similar to Wall and Stern’s report, the authors noted radiographic subsidence of the implants (in some components up to 5mm), but no dislocations or overt loosening. They concluded that they would continue to use pyrocarbon implants in the management of osteoarthritis of the MCP joint.

Finally, Dickson et al reviewed their experience with 51 fingers in 36 patients who underwent pyrocarbon MCP arthroplasty for osteoarthritis. ¹⁶ The mean follow-up period was 103 months. Preoperatively, no consistent pain, motion, or functional scores were measured. However, similar to prior studies, the clinical outcomes were generally excellent. Postoperatively, the mean VAS (1–10) pain score was 0.9 (range 0–7). The MCP joint arc of motion was a mean of 54 degrees (range 20–80) and grip strength was a mean of 25 (range 11–45) kg. The QuickDASH and Patient Evaluation Measures (PEM) scores were a mean of 28.9 (range 0–56.8) and 26.5 (range 10–54), respectively. Overall implant survivorship was 88% at 10 years. The overall complication rate was 20%; four were defined as “early” and five as “late.” Among the early complications, one patient developed complex regional pain syndrome and three had a dislocation. The early dislocations underwent further interventions: one was stable following closed reduction, second was revised to a silicone arthroplasty, and the third was “up-sized” to larger components. Among the late complications there were two cases of stiff MCP joints which underwent manipulation and percutaneous softtissue releases. There was one prosthetic stem fracture and another aseptic loosening occurred; both of these cases were revised to a silicone MCP arthroplasty. Finally, one case of subluxation of the MCP joint was corrected with up-sizing of the components. Interestingly, all implant revisions were performed within the first 18 months following surgery, suggesting of technical issues rather than inherent problems with the implants. The authors conclude that pyrocarbon MCP arthroplasty provides good pain relief, motion, and satisfaction for patients with noninflammatory arthritis.

As previously mentioned, the durability, material properties, and biomechanical characteristics of pyrocarbon lend itself to be used in younger patients and as a hemiarthroplasty. A novel indication for the use of pyrocarbon MCP arthroplasty is to address posttraumatic problems. Houdek et al reviewed the outcome of pyrocarbon MCP arthroplasty and hemiarthroplasty following injuries with non-reconstructable cartilage loss. ⁶ Ten fingers in seven patients were identified that underwent MCP arthroplasty within 24 hours of trauma leaving the joint cartilage either partially or completely damaged. The mechanism of injury in all cases was a saw. Six patients underwent hemiarthroplasty (four distal metacarpal and two proximal phalangeal replacements) and four total MCP joint replacements. The mean follow-up period was 4 years. Clinical outcomes demonstrated a mean arc of MCP motion of 56 degrees (range 30–70). Most patients had no or minimal pain. Since all cases had concomitant softtissue and tendon injuries that also required treatment, approximately half of the patients required a tenolysis 3 to 18 months following the index surgery. No cases of revision, loosening, infection, or dislocation occurred. This study demonstrates that pyrocarbon can be safely utilized to help reconstruct the MCP joints in select cases of trauma resulting in nonrepairable cartilage or joint injury.