What the Surgeon Can Do to Reduce the Risk of Trunnionosis in Hip Arthroplasty: Recommendations from the Literature.

Trunnionosis, defined as wear and corrosion at the head-neck taper connection, is a cause of failure in hip arthroplasty. Trunnionosis is linked to a synergistic combination of factors related to the prosthesis, the patient, and the surgeon. This review presents analytical models that allow for the quantification of the impact of these factors, with the aim of providing practical recommendations to help surgeons minimize the occurrence of this failure mode. A tighter fit reduces micromotion and, consequently, fretting of the taper connection. The paramount parameters controlling the fixation force are the coefficient of friction and the impaction force. The influence of the head diameter, as well as of the diameter and angle of the taper, is comparatively small, but varus alignment of the taper and heads with longer necks are unfavourable under physiologic loads. The trunnion should be rinsed, cleaned, and dried carefully, while avoiding any contamination of the bore-the female counterpart within the head-prior to assembly. Biological debris, and even residual water, might critically reduce the fixation of the taper connection between the head and the neck. The impaction force applied to the components should correspond to at least two strong blows with a 500 g hammer, striking the head with an ad hoc impactor aligned with the axis of the taper. These strong blows should correspond to a minimum impaction force of 4000 N.

Estimating the osteolysis-free life of a total hip prosthesis depending on the linear wear rate and head size.

We present a model to estimate the osteolysis-free life of total hip arthroplasty, depending on linear wear rate and femoral head size. An estimate of the radiologic osteolysis threshold was calculated, which was based on volumetric wear. The osteolysis-free life of the cup was estimated from the quotient of the osteolysis threshold and volumetric wear rate, which was calculated from the linear wear rate. The impact of the direction of linear wear was determined by sensitivity analysis. From our review, we calculated a weighted mean polyethylene volume of approximately 670 mm3 as osteolysis threshold. Osteolysis-free life of less than 20 years was estimated for linear wear rates of 50 µm/year for head sizes of 32 mm or more, or for linear wear rates of 100 µm/year for any head size. For head sizes of 36 and 40 mm with a linear wear rate of 50 µm/year, the osteolysis-free period is estimated to be only 14.10 and 11.42 years, respectively. Sensitivity analysis showed reasonably robust results. With the aim of osteolysis-free life of more than 20 years, our study presents a viable model to determine maximum possible head size for articulations. Osteolysis-free period for 36 and 40 mm head sizes are far too low for conventional polyethylenes. As the threshold wear volume for highly crosslinked polyethylene is, as of yet, unknown, more research is warranted before our model can be generalized to XLPE.

Tribology of total hip arthroplasty prostheses: What an orthopaedic surgeon should know.

Articulating components should minimise the generation of wear particles in order to optimize long-term survival of the prosthesis.A good understanding of tribological properties helps the orthopaedic surgeon to choose the most suitable bearing for each individual patient.Conventional and highly cross-linked polyethylene articulating either with metal or ceramic, ceramic-on-ceramic and metal-on-metal are the most commonly used bearing combinations.All combinations of bearing surface have their advantages and disadvantages. An appraisal of the individual patient's objectives should be part of the assessment of the best bearing surface. Cite this article: Rieker CB. Tribology of total hip arthroplasty prostheses: what an orthopaedic surgeon should know. EFORT Open Rev 2016;1:52-57. DOI: 10.1302/2058-5241.1.000004.

Influence of the clearance on in-vitro tribology of large diameter metal-on-metal articulations pertaining to resurfacing hip implants.

Large-diameter metal-on-metal articulations may provide an opportunity for wear reduction in total hip implants because earlier studies have shown that the formation of a fluid film that completely separates the bearing surfaces is theoretically possible. In such a lubrication mode and under ideal conditions, there is theoretically no amount of wear. Studies have suggested that the two primary parameters controlling the lubrication mode are the diameter and the clearance of the articulation. The goal of the present study was to experimentally investigate the influence of these two parameters on the wear behavior of large-diameter metal-on-metal articulations pertaining to resurfacing hip implants. The results of this in vitro investigation showed that longer running-in periods and higher amounts of running-in wear were associated with larger clearances.

Development and validation of a second-generation metal-on-metal bearing: laboratory studies and analysis of retrievals.

This paper summarizes hip simulator and retrieval studies that were done to optimize 1 design of a second-generation metal-on-metal hip replacement. It was determined that clearance is the first key parameter controlling wear behaviour. The clearance should be as small as possible while as large as necessary to avoid any equatorial contact leading to clamping of the articulation. The minimum clearance should be investigated for each different design. Carbon concentration should be in the range 0.20-0.25% as high carbon concentration alloys have systematically a lower wear rate than low carbon alloys. The wear of clinically retrieved implants confirms the predicted low wear of this implant and confirms the importance of the clearance and the type of cobalt-chrome alloy.

In vivo and in vitro surface changes in a highly cross-linked polyethylene.

Highly cross-linked, ultrahigh-molecular-weight polyethylenes (UHMWPEs) were developed to reduce UHMWPE wear in arthroplasty. These UHMWPEs have manifested an improvement in the wear resistance. Examination of the first retrievals revealed surface features not usually observed on conventional retrievals. A flattening of the machining marks is evident, together with the presence of ripples with microfissures. These ripples were investigated in vitro and on retrievals having a follow-up of up to 15 months. The examinations of all specimens showed that the ripples may be described as folds with microcracks. The depth of the microcracks extended to a maximum of 5 microm and is independent of the mode of loading (up to 27 million cycles). Because of the extreme wear resistance of these UHMWPEs, the folds accumulate on the surface of components.