Wear analysis of an intervertebral disc replacement analogue: Effect of implant offset
Abstract
Arthrodesis removes the functionality of the motion segment, causing adjacent segment degeneration in 30% of patients. Spinal disc arthroplasty is emerging as an alternative with the first artificial disc replacement FDA approval in 2004. The link between tribological properties and the geometric properties, and therefore kinematic properties, of synovial joint replacements has been extensively studied. However, knowledge on this front is lacking in respect to spinal disc replacements. By designing a fully constrained implant that matches the physiological motion of a spinal motion segment the effects of wear particles will be reduced and the facet joints will be protected from non-physiological loading. A study comparing aligned and misaligned wear interfaces with respect to the center of rotation was conducted to illustrate the importance of mimicking the natural physiological motion as well as surgical placement of the implant. A metal on polyethylene ball and socket articulation was used to replicate current cervical implant designs. The analogues were tested at 2Hz for 5,000,000 cycles in combined lateral bending, axial rotation and flexion/extension. A static axial load of 100 N was applied to simulate the weight load of the head in the cervical discs. Load soak controls were used to account for the effects of fluid absorption in the volumetric wear rate determination. These tests were completed to ASTM standard protocol on a linear actuator controlled four degree of freedom wear simulator at Purdue. A non-significant trend of increased wear in the offset specimens was noted.
Degree
M.S.B.M.E.
Advisors
Nauman, Purdue University.
Subject Area
Biomedical engineering
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