Geometric variations of the hip joint can give rise to abnormal joint loading causing increased stress on the articular cartilage, which may ultimately lead to degenerative joint disease. In-vitro simulations of total hip replacements (THRs) have been widely reported in the literature, however, investigations exploring the tribology of two contacting cartilage surfaces, and cartilage against metal surfaces using complete hip joint models are less well reported. The aim of this study was to develop an in-vitro simulation system for investigating and comparing the tribology of complete natural hip joints and hemiarthroplasties with THR tribology. The simulation system was used to assess natural porcine hip joints and porcine hemiarthroplasty hip joints. Mean friction factor was used as the primary outcome measure to make between-group comparisons, and comparisons with previously published tribological studies. In-vitro simulations were conducted on harvested porcine tissue. A method was developed enabling natural acetabula to be orientated with varying angles of version and inclination, and natural femoral heads to be potted centrally with different orientations in all three planes. Acetabula were potted with 45° of inclination and in the complete joint studies, natural femoral heads were anatomically matched and aligned (n=5). Hemiarthroplasty studies (n=5) were conducted using cobalt chrome (CoCr) heads mounted on a spigot (Figure 1), size-matched to the natural head. Natural tissue was fixed using PMMA (polymethyl methacrylate) bone cement. A pendulum friction simulator (Simulator Solutions, UK), with a dynamic loading regime of 25–800N, ± 15° flexion-extension (FE) at 1 Hertz was used. The lubricant was a 25% (v/v) bovine serum. Axial loading and motion was applied through the femoral head and frictional torque was measured using a piezoelectric transducer, from which the friction factor was calculated.Introduction
Method
Contact between the femoral head and rim of the acetabular liner in total hip replacements has been linked to adverse tribological performance that may potentially shorten the lifespan of the prosthesis. Predicting the size and location of the contact area can be done computationally, however, experimental validation of these models is challenging due to the conforming nature of the bearing surfaces. This study aimed to develop a method of accurately determining the Metal-on-polyethylene and ceramic-on-polyethylene samples, with a nominal diameter of 36mm (DePuy Synthes, Leeds, UK), were tested with the cups orientated using a combination of inclination (equivalent to 45°, 55° and 65° in-vivo) and version (−20°, 0°, 20° and 40°) angles. The liners, which were first gold hard-coated (EMSCOPE SC 500, Quarum Technologies, UK), were inserted into a Pinnacle® titanium shell, and femoral heads were mounted on a vertical spigot (Figure 1). A single-station multi-axis electromechanical hip joint simulator (Prosim, Simulator Solutions, UK) was used to position the samples with 18.7° flexion, 6.2° adduction and 8.3° external rotation, congruous with just after heel strike (ISO 14242-1), and apply a 3kN static axial load through the centre of the femoral head. The contact area was generated by manually turning the head about the vertical axis of the centre of rotation of the applied load, removing the gold hard-coating from the contacting areas. The contact area was determined from photographs of the acetabular cup using SolidWorks (Dassault Systèmes, US) and ImageJ (National Institutes of Health, US) software packages. Three repeats under each combination of cup angles were completed, and the mean contact area and 95% confidence limits were determined for each bearing under all cup angle combinations.Introduction
Method
