Essen Symposium 

Abstract: To reduce wear in joint bearings of total hip arthroplasty (THA) is the most important issue for improving long term results and implant survival. Due to low wear rates and excellent tribological features in simulator tests Diamond-Like-Carbon coating (DLC) of femoral balls is still discussed as an alternative articulation in THA. This clinical prospective study compares survivorship of DLC-coated femoral heads and of Aluminia-Oxide- (Al 2 O 3 ) heads articulating with Polyethylene (PE). Over a period of two years 101 THA with DLC-coated heads and PE cups (DLC-group) and another 101 THA consisting of Al 2 O 3 heads (Al 2 O 3 -group) and PE cups as well were implanted. Both articulations were based on the same type of cementless hip joint prosthesis. All hips were implanted by one surgeon in consecutive series consisting of 51 Al 2 O 3 and 101 DLC-articulations and further 50 Al 2 O 3 . All perioperative and follow-up data was processed with SPSS®. Survival of THA in both groups was evaluated according to Kaplan-Meier survivorship analysis with an intervall of 90 months (range:78-101). Qualitative surface analysis was performed in nineteen retrieved DLC-heads which were revised for aseptic loosening using field scanning electron microscopy (FE-SEM, XL 30 SFEG Philips, Eindoven NL). 178 patients (88.2 %) were evaluated for follow-up. Fourteen patients died meantimes (nine DLC, five Al 2 O 3 ) with the implant components not revised. Ten patients (five DLC, five Al 2 O 3 ) were lost to follow-up. Both groups were comparable regarding patient age, weight and indications for THA with a normal distribution. Survivorship analysis for aseptic loosening 8.5 years following implantation resulted in a significant difference between both groups with a 54% survival for DLC/PE compared to 88% for Al 2 O 3 /PE bearings (p <0.001). No correlation to variables as age, gender or bodyweight could be detected. Surfaces of nineteen retrieved DLC-heads showed numerous smallest pits of the diamond-carbon layers in different quantity. SEM showed delamination of the carbon layer which caused excessive debris of polyethylene and in some cases even of the metallic substrate of the heads. Despite modern manufacturing technology and excellent experimental results for its tribochemical characteristics and wear, even new DLC-coating of femoral heads is to be considered critically due to very high rates of clinical failure.

Abstract: A new method is proposed for coating implants that produces a metal implant covered in a layer of nano-porous alumina ceramic. These layers are produced by first depositing a layer of aluminium on the implant surface and then anodising it in phosphoric acid to produce the nano-porous structure. This process results in the conversion of the aluminium to alumina containing 6-8wt% phosphate ions. The surface alumina layer is bonded to the substrate via an interfacial layer of fully dense anodised titanium oxide. Mechanical measurements have shown that the shear and tensile strength of this coating are in excess of 20MPa and 10MPa, respectively. The biological performance of nano-porous alumina material has been assessed and shown to be highly favourable, supporting normal osteoblastic activity and maintaining the osteoblastic phenotype. The filling of the nano-porous coating with bioactive material to achieve enhanced biological performance has been investigated using colloidal silica as an analogue for a Bioglass sol. The coating has been loaded with silica by dipping in colloidal silica with a pH of 5.6. Pore filling equivalent to 1.3 wt% SiO 2 in the coating as a whole has been achieved in this way.

Abstract: The structure and phase composition of HAp coatings deposited onto Ti6A14V coupons (50x20x2mm) by atmospheric plasma spraying (APS) were studied by laser-Raman spectroscopy, 31 P-and 1 H-MAS-NMR and 2D- 31 P/ 1 H HETCOR-CP-NMR spectroscopy, and XRD with Rietveld refinement. The samples investigated comprised APS HAp coatings with and without a TiO 2 bond coat as well as coatings incubated for different lengths of time (up to 12 weeks) in simulated body fluid (SBF) under physiological conditions. In APS coatings the presence of a bond coat increased the proportion of well-ordered crystalline HAp at the expense of distorted apatite-like structures such as oxyHAp and oxyapatite, and thermal decomposition products such as tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP), and also decreased the amount of amorphous calcium phosphate (ACP). Incubation in SBF further advanced the proportion of crystalline HAp since the disordered structures, the thermal decomposition products, and ACP exhibit substantially higher solubility.