1223 Enhancing Cervical Disk Arthroplasty–Tribological Superiority of Surface Modification using Diffusion Hardened Titanium (DHT) Implants

INTRODUCTION: Commercially available cervical arthroplasty devices vary by composition and mechanical properties. Metal-on-metal (MoM) endplate articulation is associated with significantly higher odds of long-term neurological success, compared to metal-UHMWPE. Current MoM devices use either 90% Ti-6Al-4V and 10% Ti-Carbide (Ti64/TiC) composite/Cobalt-Chromium-Molybdenum alloy (CoCrMo), which are expensive. METHODS: Diffusion hardened titanium (DHT) was obtained by treatment of titanium discs at high temperature by four vendors. Four samples from each DHT were tested in tribometer using bovine calf serum. The pin-on-disc wear was run with dynamic partner of 6mm diameter, at 30N normal load, 1Hz frequency for total linear stroke length of 10mm for 1 hour. Wear rates were evaluated using stylus profilometer (20µm radius diamond-spherical tip). RESULTS: The average CoF between pin and disc of same materials were: 0.2303±0.0023 (TC4), 0.1240±0.0013(E30), 0.1850±0.0008(E80) and 0.2211±0.0204(APT). The CoF for controls were higher: 0.2465±0.0022(CoCrMo) and 0.2445±0.0006(Ti64/TiC). Wear-track depths after pin-on-disc tests were significantly lesser than TDH case depths: 2.223µm(TC4), 0.2385µm(X30), 0.248µm(X80), and 0.41µm(APT). While CoCrMo had comparable 0.619µm wear-track depth, Ti64/TiC was high at 35.75µm. The average volumetric wear rates of disc and pin combinations(in mm3/Nm) respectively were: 4.06x10-7 and 2985x10-7(TC4); 1.95x10-7 and 1.12x10-7(X30); 2.34x10-7 and 6.57x10-7(X80); 1.75x10-7 and 43.3x10-7(APT), 2.91x10-7 and 32.0x10-7(CoCrMo); 1120x10-7 and 69.9x10-7(Ti64/TiC). DHT sample discs have consistent CoF and wear rates against the pins of same materials, comparable to or better than the controls. E30, E80 and APT exhibited consistently excellent friction and wear protection between both discs and pins. CONCLUSIONS: DHT discs can outperform current controls Ti64/TiC and CoCrMo on wear and friction profiles. Therefore, DHT is promising surface modification technique to improve tribological properties of arthroplasty devices.