Tribological investigations of materials used for spine disc implants

Ailments linked to back pain is a serious problem not only medical but also social. Not only elder people but also people in working age suffers from problems related to spine pain. The most common disorders of the spine are pain syndromes of the lumbar part where center of gravity of the human body is located and w here major forces are acting on the vertebrae and intervertebral discs. The market currently offers a variety of spinal implant solutions (FIG 1). In the Metal Forming Institute there is realized research Project entitled Investigations and spine implants functionality evaluation in material and tribological aspects. In the frame of the Project it was designed and manufactured special simulator adapted for intervetebrals pine discs implants investigations. Simulator scheme is presented on FIG. 2. Main goals of the realized Project are: • Investigation of friction-mechanical processes during implant usage. • Evaluation of wear intensity of various types of intervertebral discs and investigations of appearing wear products. • Selection of optimal material and surface machining method providing minimal wear of intervertebral disc elements wear. For experiments there was implant designed by K. Skalski and J. Skoworodko selected [1], which consists of 3 elements: upper liner, lower liner and nucleus pulpous (FIG. 3). Actually there are 3 types of friction couple materials tested: 316L steel - polyethylene UHMWPE – 316L steel, titanium alloy Ti6Al4V – polyethylene UHMWPE and nitrided Ti6Al4V titanium alloy – polyethylene UHMWPE. In fluence of number of cycles on friction coefficient, surface roughness and poliethylene linner thickness change illustrates FIG. 4. As it results from performed investigations, too high hardness level of metal elements (upper and lower clasps) provides to accelerated wear of the polyethylene part. New challenge is application of “metal-metal” friction couple.