Andrew Naylor

In vitro wear testing of the PyroCarbon proximal interphalangeal joint replacement: Five million cycles of flexion and extension

Clinical results of the PyroCarbon proximal interphalangeal joint replacement are inconsistent with various complications reported. To address this, in vitro testing was conducted using finger joint simulators. Two PyroCarbon proximal interphalangeal prostheses were tested in a lubricant of dilute bovine serum to 5 × 106 cycles of flexion–extension (90°–30°) with dynamic forces of 10 N applied. At intervals of 3000 cycles testing ceased and a static load of 100 N was applied to simulate gripping. In addition, two ‘control’ prostheses were immersed alongside the test prostheses to account for lubricant absorption. Wear and roughness averages (Ra) were measured every 1 × 106 cycles. Minimal wear for all of the components was measured with a negligible increase in Ra for most of the components. One condyle of one component increased in Ra over the 5 × 106 cycles with a value above the recommended 50 nm. Unidirectional marks were visible on the condyle from micrographs, consistent with an abrasive wear mode.

Evaluating the Surface Topography of Pyrolytic Carbon Finger Prostheses through Measurement of Various Roughness Parameters

The articulating surfaces of four different sizes of unused pyrolytic carbon proximal interphalangeal prostheses (PIP) were evaluated though measuring several topographical parameters using a white light interferometer: average roughness (Sa); root mean-square roughness (Sq); skewness (Ssk); and kurtosis (Sku). The radii of the articulating surfaces were measured using a coordinate measuring machine, and were found to be: 2.5, 3.3, 4.2 and 4.7 mm for proximal, and 4.0, 5.1, 5.6 and 6.3 mm for medial components. ANOVA was used to assess the relationship between the component radii and each roughness parameter. Sa, Sq and Ssk correlated negatively with radius (p = 0.001, 0.001, 0.023), whilst Sku correlated positively with radius (p = 0.03). Ergo, the surfaces with the largest radii possessed the better topographical characteristics: low roughness, negative skewness, high kurtosis. Conversely, the surfaces with the smallest radii had poorer topographical characteristics.

Failure of an ACCIS metal-on-metal hip resurfacing prosthesis: A case report

The introduction of coatings on joint replacements was intended to reduce wear volumes, prevent corrosion and reduce metal ion release. However, retrieval analysis to confirm their in vivo performance has been limited. The aim of study was to examine the coating on a retrieved hip prosthesis to determine whether substantial damage or wear had occurred. A single advanced ceramic-coated implant systems titanium niobium nitride-coated hip resurfacing prosthesis was retrieved for examination. Wear volumes and surface roughness were measured to quantify the damage to the articulating surfaces. The coating had been completely removed from substantial parts of both the femoral head and the acetabular cup, corresponding to areas of wear as measured by a coordinate measuring machine. The total wear rate (61 mm3/year) was high and corresponded with the high metal ion levels recorded pre-operatively (83 ppb chromium and 110 ppb cobalt). Roughness data indicated that the coating has a lower roughness than the substrate and substantially lower than the boundary between the coating and the substrate. The wear rate is very high and it is likely that damage to the coating resulted in accelerated wear of the prosthesis. No sudden change between the boundary of the substrate and the coating was observed that would indicate delamination or failure of the coating substrate interface layer. While coatings may offer some theoretical benefits, they may also result in catastrophic failure of the prosthesis.

In Response to Michael Wininger’s Commentary: Common Roadblocks for Biomaterials Metrologists

I welcome Winingers commentary [1], and I would like to take the opportunity to address some of the issues raised.[...].