2009 Nicolas Andry Award: Clinical Biomechanics of Third Body Acceleration of Total Hip Wear

Abstract

Aseptic loosening attributable to wear-related osteolysis historically has been the predominant cause of failure in THA. Advances in low-wear bearing couples show great promise to substantially reduce this long-standing problem. However, there always has been striking variability in wear rate in any given cohort of patients who are similarly implanted, with some individuals typically experiencing near order-of-magnitude elevations above group mean. Third-body wear is likely a major contributor to many of these most osteolysis-prone outliers. For the patients affected, third-body effects may obviate many of the gains otherwise achieved by contemporary bearing surface improvements. Toward heightening visibility in terms of consequences for patients, this review paper summarizes an interrelated series of investigations quantifying construct level manifestations of third-body wear. Long-term followup of a unique group of patients with elevated third-body challenge shows statistically significant and clinically important wear-rate increases. A series of finite element models, validated physically, shows the linkage of location of third-body damage with variability of volumetric wear-rate acceleration and shows the effects of various implant factors, surgeon factors, and patient factors in the presence of third-body challenge. Finally, a mechanism for third-body debris access to wear-critical locations on the bearing surface is identified analytically and corroborated in laboratory experiments and implant retrievals.

Polyethylene Wear is Related to Patient-specific Contact Stress in THA

“…Conventional UHMWPE cups were implanted in all THAs included in this study. Modern crosslinked polyethylenes exhibit considerably lower wear related to contact stress [36] and other factors like thirdbody wear [5] might be more important for its wear in vivo. Sixth, current contact stress modeling is based on the assumption of elastic deformation of polyethylene.…”

“…Model simulations focus on estimating the effects of various prosthesis designs on polyethylene wear. The models suggest the geometry of the prosthesis, ie, the radius of the femoral head [25], polyethylene cup thickness [22], or cup inclination [33,34] and the contact surface properties, ie, femoral head roughness [5], influence wear. The wear rate assessed using these mathematical models [25,33,34,38] agrees well with the wear measured in a clinical study [20], suggesting an important role of contact stress in mechanical damage of the polyethylene surface.…”

THA Retrievals: The Need to Mark the Anatomic Orientation of the Femoral Head

“…Computational wear simulation avoids these problems, and the FE wear formulations used in this study have been well-validated against physical wear simulations [8, 10, 11]. For femoral heads that were undamaged, had scratches, or had a roughened area (similar to a scrape), wear calculation errors between the physical and computational models were less than 5% [11], 10% [8], and 10% [10], respectively. These validations were based on conventional PE; similar wear acceleration results, relative to undamaged cases, would be expected for highly crosslinked PE.…”

“…Femoral head scratches and scrapes, along with their corresponding lip heights and R a values, were modeled at their respective damage locations. A finite element model for PE liner wear, experimentally validated for conventional polyethylene [8, 10, 11], was then implemented in ABAQUS v6.9.1, using the adaptive meshing capabilities of the UMESHMOTION subroutine. PE liner wear was computed using the Archard wear formula [12], which calculates the spatial distribution of wear depth as a function of local contact pressure, sliding distance, and a wear coefficient based on the tribological properties of the surfaces in contact.…”

Prediction of contact mechanics in metal-on-metal Total Hip Replacement for parametrically comprehensive designs and loads

“…Analytical and numerical methods of calculating THR bearing contact mechanics enable evaluation of design concepts (Antoine et al, 2006;Brown et al, 2009;Goodman and Keer, 1965;Hertz, 1896;Yew et al, 2003). However, in-vivo mechanics can be affected by a combination of design and loading parameters which can limit the applicability of these approaches.…”