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Anthony Anderson
Anthony Anderson

Buy Pyrolytic Carbon

X.L. acknowledges financial support from the National Natural Science Foundation of China (grants 11522218 and 11720101002) and the National Basic Research of China (grant 2015CB932500). H.G. acknowledges funding from the National Science Foundation (grant DMR-1709318). J.R.G. acknowledges financial support by the US Department of Energy, Office of Basic Energy Sciences (DOE-BES) under grant DE-SC0006599. A.V. acknowledges the financial support of the Resnick Sustainability Institute at Caltech. The authors thank G. R. Rossman for assistance with Raman spectroscopy measurements, J. Yao for help with SIMS measurements and K. Narita for assistance with density measurements of pyrolytic carbon.

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63-year-old female with a long history of osteoarthritis. Note the silicone implant and deformity of the left index PIP joint (left x-ray). The osteoarthritic PIP joints in the right index (right x-ray) and left middle fingers will be replaced by pyrocarbon implants.

Abstract:The articulating surfaces of four different sizes of unused pyrolytic carbon proximal interphalangeal prostheses (PIP) were evaluated though measuring several topographical parameters using a white light interferometer: average roughness (Sa); root mean-square roughness (Sq); skewness (Ssk); and kurtosis (Sku). The radii of the articulating surfaces were measured using a coordinate measuring machine, and were found to be: 2.5, 3.3, 4.2 and 4.7 mm for proximal, and 4.0, 5.1, 5.6 and 6.3 mm for medial components. ANOVA was used to assess the relationship between the component radii and each roughness parameter. Sa, Sq and Ssk correlated negatively with radius (p = 0.001, 0.001, 0.023), whilst Sku correlated positively with radius (p = 0.03). Ergo, the surfaces with the largest radii possessed the better topographical characteristics: low roughness, negative skewness, high kurtosis. Conversely, the surfaces with the smallest radii had poorer topographical characteristics.Keywords: roughness parameters; surface topography; skewness; kurtosis; pyrolytic carbon; proximal interphalangeal joint

Osteochondral defects continue to be a clinical treatment challenge, and when left untreated, may cause pain and functional impairment. Pyrolytic carbon is a unique isotropic biomaterial used in heart valve and small joint replacements due to its excellent wear properties and biocompatibility with bone and articular cartilage. Therefore, a proposed solution is to utilize a focal pyrolytic carbon hemiarthroplasty implant as an alternative resurfacing treatment strategy for isolated cartilage lesions.

A proposed solution is a focal hemiarthroplasty implant, intended for use as an alternative resurfacing treatment strategy for isolated lesions in patients who are too young for TKAs [1] or not good candidates for regenerative procedures. Focal hemiarthroplasty devices using pyrolytic carbon [15], metal alloys [15, 16], polymer composites [17], and ceramic composites [18] have been investigated for a number of anatomical locations with varying results. Several previous studies have shown that even when the shape and design of the implant closely match the surface, the implant material properties may be detrimental to the opposing articular cartilage in the long-term due to differences in elastic modulus [15, 19, 20]. A mismatch in elastic properties contributes to higher stresses around the implant-bone interface, which leads to bone loss due to stress shielding, followed by bone resorption and implant loosening [21, 22].

The objective of this study was to use a canine model to evaluate the in vivo histologic response and function of a pyrolytic carbon implant in the medial femoral condyle of the knee and to compare the results to those obtained using an identical Co-Cr alloy implant.

All animals tolerated the procedures well, had uneventful recoveries, and remained in good health until time of sacrifice. Within 4 weeks postoperative, all animals were ambulatory without evidence of lameness or impairment, and had normal stance bilaterally without evidence of non-weight bearing or pain during walking. Lameness scores did not exceed a grade of 2 (generally noted bilaterally), and evidence of slight lameness did not persist beyond week 3. One animal had three occurrences of right hindlimb lameness (Co-Cr alloy implant) at 14, 17, and 25 days postoperative, in which the contralateral hindlimb (pyrolytic carbon implant) was normal.

Review of postoperative radiographs showed adequate placement of all implants (Fig. 3). There was no radiographic evidence of loosening of the implants during the course of this study. Radiolucency around the pyrolytic carbon implant was the result of the radiolucent pyrolytic carbon coating thickness, and this was accounted for in the observations.

At 12 weeks, gross observations (Fig. 4) of the pyrolytic carbon implanted knees showed no evidence of articular cartilage damage or color change; no joint capsule hypertrophy, osteophyte formation, or meniscal changes related to the implant; and normal appearance of the synovial fluid. Gross observations of the Co-Cr alloy implanted knees showed no evidence of articular cartilage damage, one instance of opaque articular cartilage, two instances of joint capsule hypertrophy, one instance of osteophyte formation, and one instance of mild degeneration/streaking and thin, translucent appearance of the medial meniscus.

At 24 weeks, observation of the pyrolytic carbon implanted knees revealed one knee with moderate degeneration of the cartilage and minimal changes to the medial tibial plateau. For the Co-Cr alloy implanted knees, two had minimal fibrillation/degeneration of the cartilage on both the medial femoral condyle and medial tibial plateau surfaces, one with slight opacity changes in the articular cartilage, one with a thickened joint capsule, one osteophyte presence, one medial meniscus with mild degeneration/streaking, and no finding related to the gross appearance of the ligaments.

At 52 weeks, two of the pyrolytic carbon implanted knees had moderate degenerative changes of the cartilage on the medial femoral condyle with no changes on the medial tibial plateau surfaces and both had slight opacity changes to the articular cartilage. An osteophyte was present on one knee with mild streaking on the rim of one medial meniscus. All ligaments appeared normal. For the Co-Cr alloy implanted knees, one knee had moderate fibrillation/degeneration of the cartilage on both the medial femoral condyle and the medial tibial plateau surfaces and the articular cartilage was discolored. One knee had a thickened joint capsule with hypertrophy of the lateral collateral ligaments, two knees had condylar osteophytes, and one knee had a medial meniscus with evidence of moderate degeneration and a thinned, translucent appearance.

52-week histologic sections: microradiographs of pyrolytic carbon (top) and Co-Cr alloy (bottom) implants. Note radiolucent pyrolytic carbon coating surrounding radio-dense substrate (2)

This study demonstrated that a pyrolytic carbon hemiarthroplasty implant material was superior to identical Co-Cr alloy implants. Less cartilage degeneration was observed in the cartilage adjacent to and in the vicinity of the pyrolytic carbon implants compared to the Co-Cr alloy implants in the medial femoral condyle at all evaluation periods. Surface cartilage wear, degradation, and cellular change were reduced when articulating against the pyrolytic carbon implants. In particular, changes in the tibial cartilage observed for the pyrolytic carbon group at 52 weeks were seen as early as 12 weeks for the Co-Cr alloy group. Both implant groups achieved a similar degree of direct bone-implant apposition at 12, 24, and 52 weeks.

The HemiCAP consists of a bone fixation element and an articular component connected by a Morse taper. The bearing surface is Co-Cr-Mo alloy with titanium plasma spray on the underside for bone ongrowth. The biological and functional response of the HemiCAP was investigated in goats [16]. Radiologically, there was no evidence of implant failure or loosening nor any gross degenerative changes. Histological analysis showed new trabecular bone abutting the implant in all specimens at 1 year postoperatively. The medial femoral condyle cartilage lateral to the implant was fibrocartilage-like, whereas it was hyaline cartilage-like medial to the implant [16]. Histologic examination of the proximal tibia cartilage surface opposing the HemiCAP implant was characterized by the presence of fibrillations, similar to those observed in this study for the Co-Cr alloy group. Given its high fatigue and high wear resistance, biocompatibility, reduced elastic modulus, and propensity for SAPL adhesion to form a boundary lubricant, pyrolytic carbon offers the potential for improved clinical performance of implants for this partial joint resurfacing application compared to Co-Cr alloy.

Another limitation to this study is the small number of animals, which may skew statistical elements. However, bilateral surgery allows for intra-animal pair-wise comparison and therefore a reduced number of animals needed for the study. It also allows a direct comparison of the two implant materials. Studies performed in a larger sheep model comparing pyrolytic carbon implants to a chondroplasty control group are underway.

In summary, the use of pyrolytic carbon as a hemiarthroplasty implant material was shown to be superior to Co-Cr alloy, which is the material that is currently being used in a marketed clinically available hemiarthroplasty knee device. Less degeneration was observed in the cartilage adjacent to and in the vicinity of the pyrolytic carbon implants compared to the Co-Cr alloy implants in the medial femoral condyle at all evaluation periods out to 1 year. There was also less wear, degradation, and cellular changes of the tibial cartilage surface when articulating against the pyrolytic carbon implants. Changes in the tibial cartilage observed for the pyrolytic carbon group at 52 weeks were seen as early as 12 weeks for the Co-Cr alloy group. Again, larger sheep models comparing a clinical pyrolytic carbon device to control chondroplasty-treated defects are underway. 041b061a72


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