Edge loading in metal-on-metal hips: low clearance is a new risk           factor

Underwood, Richard; Zografos, Angelos; Sayles, R.S.; Hart, Alister; Cann, P. M.

doi:10.1177/0954411911431397

Cited by 95 publications

(112 citation statements)

References 29 publications

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“…During this period there is an increased risk of wear. Poorly aligned components will promote edge loading and increased contact pressures (Underwood et al, 2012); our results indicate these films are very sensitive to increased pressures (Myant et al, 2012). Edge loaded contacts may mimic scratch-like behaviour, completely stripping the surface film and accelerating wear.…”

Section: Implications For Hip Implant Lubricationmentioning

confidence: 71%

The effect of transient conditions on synovial fluid protein aggregation lubrication

Myant

Cann

2014

Journal of the Mechanical Behavior of Biomedical Materials

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Little is known about the prevailing lubrication mechanisms in artificial articular joints and the way in which these mechanisms determine implant performance. The authors propose that interfacial film formation is determined by rheological changes local to the contact and is driven by aggregation of synovial fluid proteins within the contact inlet region. A direct relationship between contact film thickness and size of the protein aggregation within the inlet region has been observed.In this paper the latest experimental observations of the protein aggregation mechanism are presented for conditions which more closely mimic joint kinematics and loading. Lubricant films were measured for a series of bovine calf serum solutions for CoCrMo femoral component sliding against a glass disc. An optical interferometric apparatus was employed to study the effects of transient motion on lubricant film formation. Central film thickness was measured as a function of time for a series of transient entrainment conditions; start-up motion, steady-state and non-steadystate uni-directional sliding, and bi-directional sliding. The size of the inlet aggregations was found to be dependent upon the type of transient condition. Thick protective protein films were observed to build up within the main contact region for all uni-directional tests. In contrast the inlet aggregation was not observed for bi-directional tests. Contact film thickness and wear was found to be directly proportional to the presence of the inlet protein phase. The inlet phase and contact films were found to be fragile when disrupted by surface scratches or subjected to reversal of the sliding direction.

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Section: Implications For Hip Implant Lubricationmentioning

confidence: 71%

The effect of transient conditions on synovial fluid protein aggregation lubrication

Myant

Cann

2014

Journal of the Mechanical Behavior of Biomedical Materials

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“…Fisher11 has explained that adverse conditions that can cause rim contact in hip joint replacement relate to translational and rotational malpositioning of the bearing. With rotational malposition of the cup, such as the cup being positioned in steep inclination or with excessive anteversion, the contact patch developed at the bearing surface may intersect the cup rim, and this situation can be compounded by varied bearing designs such as sub‐hemispheric cups and lower bearing clearance or by deflection of the cup bearing during fixation 14. Additionally, translational malpositioning can produce a more severe contact condition and edge loading 15.…”

Section: Introductionmentioning

confidence: 99%

Effect of microseparation on contact mechanics in metal‐on‐metal hip replacements—A finite element analysis

2014

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Some early failures of metal‐on‐metal (MoM) hip replacements associated with elevated wear have caused concerns for the use of this bearing combination. Simulator studies have shown that microseparation and its associated rim contact and edge loading may produce the most severe wear in MoM bearings. It is generally recognized that this high wear can be attributed to the high contact stress of the head on the rim of the cup. In this study, an improved finite element contact model that incorporates an elastic‐perfectly plastic material property for cobalt‐chrome alloy of the metal bearing was developed in an attempt to provide an accurate prediction of the stress and strain for the rim contact. The effects of the microseparation displacement (0.1−2 mm), cup inclination angle (25−65°) and cup rim radius (0.5−4 mm) on the contact stress/strain were investigated. The results show that a translational displacement >0.1 mm under a load >0.5 kN can produce a highly concentrated contact stress at the surface of the cup rim which can lead to plastic deformation. This study also suggests that the magnitude of translational displacement was the major factor that determined the severity of the contact conditions and level of stress and strain under microseparation conditions. Future studies will address the effect of surgical translational and rotational malposition and component design on the magnitude of microseparation, contact stress and strain and severity of wear. © 2014 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 103B: 1312–1319, 2015.

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“…Second, we also learned that serum ion levels [16] vary between HRA designs. We used the Conserve 1 Plus prostheses in our study, and although one could infer that the same pathologic process may be occurring with other implants, our study remains limited to this specific device because coverage and radial clearance between femoral and acetabular components affect component wear [28] and the magnitude of the blend radius is likely to influence bone remodeling in hips with radiographic signs of impingement. Future aggregate research may provide a wider spectrum of the effects of impingement on CoS and CrS levels across multiple implants and identify which factors affect the susceptibility of a device to impingement and/or increased serum ion levels.…”

Section: Discussionmentioning

confidence: 99%

Does Femoral Neck to Cup Impingement Affect Metal Ion Levels in Hip Resurfacing?

Duff

Johnson

Wassef

et al. 2013

Clin Orthop Relat Res

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Background Impingement of the femoral neck with the acetabular component after metal-on-metal hip resurfacing arthroplasty (HRA) is a possible cause of edge loading and accelerated bearing wear. No attempt has been made to correlate radiographic impingement signs and blood metal ion levels. Questions/purposes We (1) compared serum cobalt (CoS) and chromium (CrS) concentrations between patients with and without radiographic impingement signs treated with unilateral HRA, (2) determined whether divot depth on the femoral neck correlated with CoS and CrS, and (3) assessed the predictive value of radiographic impingement signs for high levels of CoS and CrS. Methods A retrospective radiographic review of 141 patients with CoS and CrS analyses yielded 21 patients with and 120 without radiographic impingement signs (controls). Radiographic measurements included divot depth and orientation of the acetabular component to compute the contact patch to rim distance, a measure of functional head coverage. We defined a patient as having radiographic impingement signs if a remodeling of the femoral neck cortex showed a depression matching the predicted path of an impinging acetabular component. CoS and CrS were analyzed by inductively coupled plasma mass spectrometry and the radiographs were taken within 12 months of the last blood draw. Results Median CoS and CrS were greater in the impingement group than in controls in patients with less than 10-mm contact patch to rim distances. Divot depth did not correlate with CoS or CrS. In predicting elevated ion levels (C 7 lg/L), the presence of a radiographic impingement sign showed a sensitivity of 50% for CoS and 33% for CrS and a specificity of 87% for both CoS and CrS. Conclusions Radiographic impingement signs influenced CoS and CrS only when the functional head coverage was insufficient due to poor socket positioning. Radiographic impingement signs alone were not a good predictor of elevated metal ion levels. Level of Evidence Level III, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.

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Edge loading in metal-on-metal hips: low clearance is a new risk factor

Cited by 95 publications

References 29 publications

The effect of transient conditions on synovial fluid protein aggregation lubrication

The effect of transient conditions on synovial fluid protein aggregation lubrication

Effect of microseparation on contact mechanics in metal‐on‐metal hip replacements—A finite element analysis

Does Femoral Neck to Cup Impingement Affect Metal Ion Levels in Hip Resurfacing?

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