Hannah J. Lundberg

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

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.

Kinetically critical sites of femoral head roughening for wear rate acceleration in total hip arthroplasty.

Polyethylene wear acceleration from (scratching) damage to the femoral head is a recognized hazard from constructs prone to generate third-body debris, but the phenomenon is nebulous and therefore often is subordinated to more direct and immediate considerations. To help delineate tangible quantitative relationships between counterface roughening and accelerated polyethylene wear, an experimentally validated sliding-distance-coupled finite element model of total hip replacement wear was adapted to incorporate regions of localized femoral head roughening. This computational formulation was used systematically to identify the sites on the femoral head for which a given severity of local roughening (parameterized in terms of roughening patch size and tribologic wear coefficient) was most consequential in terms of elevated polyethylene wear. Two such sites, of nominally comparable kinetic importance, were consistently evident throughout a wide range of roughening severities. These critical sites were located quasi-superiorly near the sagittal midline of the head, one slightly anterior and one slightly posterior of the coronal midline.

Effects of episodic subluxation events on third body ingress and embedment in the THA bearing surface.

In total joint arthroplasty, third body particle access to the articulating surfaces results in accelerated wear. Hip joint subluxation is an under-recognized means by which third body particles could potentially enter the otherwise closely conforming articular bearing space. The present study was designed to test the hypothesis that, other factors being equal, even occasional events of femoral head subluxation greatly increase the number of third body particles that enter the bearing space and become embedded in the acetabular liner, as compared to level-walking cycles alone. Ten metal-on-polyethylene hip joint head-liner pairs were tested in a multi-axis joint motion simulator, with CoCrMo third body particles added to the synovial fluid analog. All component pairs were tested for 2h of level walking; half were also subjected to 20 intermittent subluxation events. The number and location of embedded particles on the acetabular liners were then determined. Subluxation dramatically increased the number of third body particles embedded in the acetabular liners, and it considerably increased the amount of scratch damage on the femoral heads. Since both third body particles and subluxation frequently occur in contemporary total hip arthroplasty, their potent synergy needs to be factored prominently into strategies to minimize wear.

Association of third body embedment with rim damage in retrieved acetabular liners.

Third-body effects are a major cause of the substantial variability of wear in total hip replacements. One potential mechanism by which third-body debris can access wear-critical central regions of closely conforming metal-on-polyethylene bearing couples is by fluid convection during incidents of subluxation accompanying neck-on-liner impingement. To provide evidence for this premise, we determined the association of severity of liner rim indentation damage (indicative of impingement frequency/vigor) and the presence of embedded third-body debris in 194 implants retrieved at revision. Rim damage was graded using the five-point Hospital for Special Surgery scale. Particle embedment was assessed both manually and by means of an image analysis computer program that detected the composition, size, and location of each particle. Sixty-eight percent of the cups showed rim indentation damage. We found an association between severity of rim damage and presence of embedded debris. There was substantial nonuniformity of the spatial distribution of the embedded debris, with the predominance of embedded debris at intermediate latitudes. These findings support the premise of convection of debris-laden joint fluid during lever-out subluxation as a mechanism for wear-consequential third-body particles to gain access to highly loaded regions of the bearing surface, thus potentiating increased wear.

Tribocorrosion and oral and maxillofacial surgical devices.

The release of metal ions or material particles, or both, into tissues that surround implanted medical or dental devices can create postimplantation complications. These rare but disturbing events are mainly caused by the mechanical movements of the components of the implant against each other, coupled with the influences of local biochemical and electrochemical factors. Mechanical movement of the components of implants against each other results in friction and wear, the study of which is called tribology. The tribology of an implanted device depends on the patients activity and is affected by variables such as load, frequency, and the surface properties of the components of the implant that are in contact. Local biochemical and electrochemical factors include the ambient pH, and concentrations of protein and oxygen. The effect on local tissues and extracellular fluid can produce biochemical or electrochemical responses to the implant material in the surrounding solution, which is termed corrosion. The combined effect of these mechanical, biochemical, and electrochemical factors is known as tribocorrosion. In this paper we will provide a brief overview of the basic principles of tribocorrosion, and its current status and future perspectives, to create awareness and interest, and to inspire research into its effects on implantable devices in oral and maxillofacial surgery. The information garnered from such investigations, appropriately applied, will not only improve present devices but also will lead to the development of superior ones, ultimately improving care and outcomes for patients.

A parametric approach to numerical modeling of TKR contact forces

In vivo knee contact forces are difficult to determine using numerical methods because there are more unknown forces than equilibrium equations available. We developed parametric methods for computing contact forces across the knee joint during the stance phase of level walking. Three-dimensional contact forces were calculated at two points of contact between the tibia and the femur, one on the lateral aspect of the tibial plateau, and one on the medial side. Muscle activations were parametrically varied over their physiologic range resulting in a solution space of contact forces. The obtained solution space was reasonably small and the resulting force pattern compared well to a previous model from the literature for kinematics and external kinetics from the same patient. Peak forces of the parametric model and the previous model were similar for the first half of the stance phase, but differed for the second half. The previous model did not take into account the transverse external moment about the knee and could not calculate muscle activation levels. Ultimately, the parametric model will result in more accurate contact force inputs for total knee simulators, as current inputs are not generally based on kinematics and kinetics inputs from TKR patients.

Mechanical, chemical and biological damage modes within head‐neck tapers of CoCrMo and Ti6Al4V contemporary hip replacements

Total hip replacement (THR) failure due to mechanically assisted crevice corrosion within modular head-neck taper junctions remains a major concern. Several processes leading to the generation of detrimental corrosion products have been reported in first generation modular devices. Contemporary junctions differ in their geometries, surface finishes, and head alloy. This study specifically provides an overview for CoCrMo/CoCrMo and CoCrMo/Ti6Al4V head-neck contemporary junctions. A retrieval study of 364 retrieved THRs was conducted which included visual examination and determination of damage scores, as well as the examination of damage features using scanning electron microscopy. Different separately occurring or overlapping damage modes were identified that appeared to be either mechanically or chemically dominated. Mechanically dominated damage features included plastic deformation, fretting, and material transfer, whereas chemically dominate damage included pitting corrosion, etching, intergranular corrosion, phase boundary corrosion, and column damage. Etching associated cellular activity was also observed. Furthermore, fretting corrosion, formation of thick oxide films, and imprinting were observed which appeared to be the result of both mechanical and chemical processes. The occurrence and extent of damage caused by different modes was shown to depend on the material, the material couple, and alloy microstructure. In order to minimize THR failure due to material degradation within modular junctions, it is important to distinguish different damage modes, determine their cause, and identify appropriate counter measures, which may differ depending on the material, specific microstructural alloy features, and design factors such as surface topography.

Examination of failed retrieved temporomandibular joint (TMJ) implants.

UNLABELLED In the management of end-stage temporomandibular joint disorders (TMD), surgeons must often resort to alloplastic temporomandibular joint (TMJ) total joint replacement (TJR) to increase mandibular function and form, as well as reduce pain. Understanding wear and failure mechanisms of TMJ TJR implants is important to their in vivo longevity. However, compared to orthopedic TJR devices, functional wear of failed TMJ TJR implants has not been examined. Not only do wear and corrosion influence TJR implant in vivo longevity, but so does reactivity of peri-implant tissue to these two events. The aim of this study was to examine and report on the wear of retrieved, failed metal-on-metal (MoM), metal-on-polymer (MoP), and titanium-nitride coated (TiN Coated) TMJ TJR implant components. A total cohort of 31 TMJ TJR devices were studied of which 28 were failed, retrieved TMJ TJRs, 3 were never implanted devices that served as controls. The mean time from implantation to removal was 7.24 years (range 3-15), SD 3.01. Optical microscopy, White Light Interferometry (WLI), Scanning Electron Microscopy (SEM), and Raman spectroscopy were utilized to characterize the surfaces of the devices. Data was acquired and evaluated by analyzing alloy microstructure. Substantial surface damage was observed between the articulating areas of the condylar head and the glenoid fossa components. Damage included pitting corrosion, evidence of deposited corrosion products, specific wear patterns, hard phases, surface depressions, and bi-directional scratches. Electrochemical analysis was performed on the MoM Control, retrieved, failed MoM, and TiN Coated devices. Electrochemical tests consisted of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) tests conducted using the condylar head of the retrieved failed devices. EIS confirmed material properties as well as corrosion kinetics in vivo help to mitigate corrosion as reflected by the Raman spectroscopy results. In summary, this study demonstrated the role of wear and corrosion interactions on the early failure of TMJ TJR devices. Since the materials employed in most orthopedic TJR devices are similar to those used in TMJ TJR implants, studies such as this can provide data that will improve future embodiment paradigms for both. Further studies will include in vitro investigation of corrosion kinetics and the underlying tribocorrosion mechanism of TMJ TJR devices. STATEMENT OF SIGNIFICANCE An attempt is made in this study, to examine the retrieved TMJ implants and conduct surface and electrochemical analysis; further a translation research approach is employed to compare the observations from the total hip replacement (THR) retrievals. A total cohort of 31 TMJ TJR devices were studied of which 28 were failed, retrieved TMJ TJRs, 3 were never implanted devices that served as controls. Data was acquired and evaluated by analyzing alloy microstructure. Substantial surface damage was observed between the articulating areas of the condylar head and the glenoid fossa components. Electrochemical analysis was performed on the MoM Control, retrieved, failed MoM, and TiN Coated devices. This study demonstrated the role of wear and corrosion interactions on the early failure of TMJ TJR devices. Since the materials employed in most orthopedic TJR devices are similar to those used in TMJ TJR implants, a comparison study was conducted.

Comparison of ISO Standard and TKR Patient Axial Force Profiles during the Stance Phase of Gait

Preclinical endurance testing of total knee replacements (TKRs) is performed using International Organization for Standardization (ISO) load and motion protocols. The standards are based on data from normal subjects and may not sufficiently mimic in vivo implant conditions. In this study, a mathematical model was used to calculate the axial force profile of 30 TKR patients with two current implant types, 22 with NexGen and eight with Miller-Galante II Cruciate-Retaining TKRs, and statistically compare the axial force specified by the ISO standard to the TKR patients. Significant differences were found between the axial forces of both groups of TKR patients and the ISO standard at local maxima and minima points in the first half of stance. The force impulse (area under the axial force curve, representing cumulative loading) was smaller for the ISO standard than the TKR patients, but only for those with NexGen implants. Waveform analysis using the coefficient of multiple correlation showed that the ISO and TKR patient axial force profiles were similar. The combined effect of ISO standard compressive load and motion differences from TKR patients could explain some of the differences between the wear scars on retrieved tibial components and those tested in total joint simulators.

Grand Challenge Competition: A Parametric Numerical Model to Predict In Vivo Medial and Lateral Knee Forces in Walking Gaits

Numerical models are necessary to estimate forces through the knee joint during activities of daily living. However, the numerous muscles and soft tissues crossing the knee joint result in a computationally indeterminate problem. The recent availability of measured contact force data from telemeterized total knee replacements (TKRs) has given researchers the chance to validate models, but telemeterized TKRs represent only a few patients with a specific implant type. Computational models remain necessary to bridge the gap between the small instrumented patient population with a particular implant and larger patient populations executing various activities. Abstracted gait data from another lab tests the versatility of any model to accurately predict forces of TKR patients performing a variety of gaits with disparate implant types. In this study, we calculate and examine the differences between medial and lateral contact forces in level walking and medial thrust gait trials from a freely provided dataset1.© 2012 ASME