The effect of anterior–posterior shear load on the wear of ProDisc-L TDR

Abstract

The current wear-testing standard (ISO18192-1) for total disc replacement (TDR) requires only four degrees of freedom (DOF) inputs: axial load, flexionextension, lateral bending and axial rotation. The study aim was to assess the effect of an additional DOF, anterior-posterior (AP) shear on the wear of the ProDisc-L TDR. A 5DOF simulator was used to test ProDisc-L implants under 4DOF and 5DOF conditions. The 4DOF conditions were defined by ISO18192-1 whilst the 5DOF used ISO18192-1 conditions with the addition of an AP load of ?175 and -140 N (anterior and posterior, respectively), extrapolated from in vivo data. The implants were mounted such that the polyethylene insert could be removed for gravimetric measurements. Tests were run using bovine serum (15 g/l protein concentration) as a lubricant for five million cycles (MC), with measurements repeated every 1 MC. The mean wear rate in the 4DOF test was 12.7 ± 2.1 mg/MC compared to 11.6 ± 1.2 mg/MC in the 5DOF test. There were marked differences in the wear scars between 4DOF and 5DOF simulations. With 4DOF, wear scars were centralised on the dome of the insert, whilst 5DOF scars were larger, breaching the anterior rim of the dome causing deformation at the edge. The 4DOF wear test showed similar gravimetric wear rates to previously published ISO-tested TDRs. The addition of AP load was found to have no significant effect on the overall wear rate. However, there were pronounced differences in the respective wear scars, which highlights the need for more research in order to understand the factors that influence wear of TDR.

Wear and biological effects of a semi-constrained total disc replacement subject to modified ISO standard test conditions

“…Its verification and the general methodology used in TDR testing is described in detail in Ref. [12]. The TDR assemblies (n=6) were tested while totally submerged in a lubricant of bovine serum and were reused for each study.…”

“…The replacement disc in vivo operates under unknown lubricant conditions, which could be argued will be of lower protein concentration since the natural intervertebral disc is not a synovial joint. The protein concentration used was lower than the ISO 18192-1 standard, however, previous tests have also been done at this level [9,10,12]. The 10 million cycles stipulated in the ISO standard was not adhered to due to the excessive amount of time this would have taken.…”

“…Every 1/3 million cycles the each test cell was cleaned using a standard protocol described in Ref. [12]. Serum from each station was collected every million cycles and stored at -20°C until required for wear particle isolation.…”

“…Existing knowledge of semi-constrained TDR in vitro wear has been derived using ISO [12][13][14][15][16] and ASTM [14,16] (purely curvilinear, zero cross shear motion) methodologies. The tribological behaviour under moderate crossing path motion (as opposed to purely curvilinear motion), changes in loading, total articulation angle and their effect on wear are not fully understood or quantified.…”

PEEK (Polyether-ether-ketone) Based Cervical Total Disc Arthroplasty: Contact Stress and Lubrication Analysis

“…Implantation of of a porous coated cervical disc arthroplasty into goats showed no inflammatory response from wear debris after six months implanted in the animals [37]. Lumbar disc arthroplasty have been studied in more detail [38][39][40], but a direct comparison with cervical discs is unwise due to the different motions and loads.…”