Polyetheretherketone as an alternative bearing surface in total knee arthroplasty
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1
University College London, Institute of Orthopaedics and Musculoskeletal Science, United Kingdom
Introduction: For reasons attributed to stress shielding and the possibility of metal ion generation in TKA, research interest has been directed towards all polymeric, isoelastic arthroplasty. Based on its favorable mechanical properties and clinical success especially in spinal surgery, we investigate polyetheretherketone (PEEK) as alternative biomaterial to cobalt chromium (CoCr) femoral components in metal free TKA. Theoretical advantages of an all polymer TKA include, physiological stress in the distal femur, better radiographic visualisation of the bone implant interface especially with CT and MRI, cheaper production cost of prostheses and elimination of biological reaction to metal – which may be one of the reasons for unexplained knee pain following TKA. This study investigated the wear performance of PEEK and carbon reinforced PEEK (CFR-PEEK) as bearing materials in an all polymer TKA using a unidirectional pin on plate test. We hypothesized that reduced wear is generated from PEEK or CFR-PEEK bearings when compared with metal on polyethylene (MoP) bearings and that this combination may provide a suitable alternative in TKA.
Materials and Methods: A validated modification of ASTM F732 was used as the test protocol. Twenty millimeter diameter spherically ended pins with a radius of 25mm were articulated against 40mm diameter plates. A load of 1000N was applied to generate a contact stress of ≈70MPa, similar to high contact stresses previously reported in non congruent knee designs. Ten material combinations were tested as shown in Table 1.
Articulations were lubricated with 25% newborn calf serum containing 0.3% sodium azide to retard bacteria growth and 20mM EDTA to prevent calcium deposition. Three repeats of the pin on plate combinations (including 2 passive soak controls to correct for fluid uptake) were tested for 2 million cycles (MC) at a sliding cycle frequency of 1Hz and with a track length of 20 mm. Lubricant fluid was subjected to an acid digestion protocol (ISO 17853:2011). Wear particle morphology was characterized using SEM and image analysis software.
Results and Discussion: All CFR-PEEK articulations were stopped either due to high friction, black discoloration of lubricant fluid or excessive wear of the counter-surfaces with CFR PEEK-on-UHMWPE generating 400 fold wear loss (458.52 X 10-3 mm3/MC) compared with CoCr-on-UHMWPE (1.67 X 10-3 mm3/MC). Linear wear rates were noted from all polyethylene plates. PEEK-on-XLPE showed a similar wear rate to metal on polyethylene (MoP) bearings (Fig 1). Wear particle morphology and sizes measured as equivalent circle diameter from PEEK-on-XLPE articulations (0.17 ± 0.12µm) were similar to that observed from CoCr-on-XLPE articulations (0.19 ± 0.16µm); p= 0.067.
Conclusion: Under high contact stresses, PEEK-on-XLPE articulations generated volumetric wear similar to that observed in MoP bearings. From these results, it may be possible to replace CoCr in TKA with PEEK which may be beneficial because of the low elastic modulus and elimination of biological activity to metal alloy, however CFR PEEK was found unsuitable as a bearing surface for an all polymer TKA.
Invibio Biomaterial Solutions for supplying PEEK and CFR PEEK; Orthoplastics for supplying Highly Cross-linked Polyethylene
Keywords:
joint replacement,
biomaterial,
wear,
Polymeric material
Conference:
10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016.
Presentation Type:
General Session Oral
Topic:
Biomaterials in musculoskeletal orthopeadics and tissues
Citation:
Adesina
T,
Blunn
GW and
Coathup
MJ
(2016). Polyetheretherketone as an alternative bearing surface in total knee arthroplasty.
Front. Bioeng. Biotechnol.
Conference Abstract:
10th World Biomaterials Congress.
doi: 10.3389/conf.FBIOE.2016.01.02122
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Received:
27 Mar 2016;
Published Online:
30 Mar 2016.
*
Correspondence:
Dr. Melanie J Coathup, University College London, Institute of Orthopaedics and Musculoskeletal Science, London, United Kingdom, m.coathup@ucl.ac.uk