Head Taper Research Articles

Focus variation measurement and advanced analysis of volumetric loss at the femoral head taper interface of retrieved modular replacement hips in replica

This paper offers a technique for non-contact assessment of material volume loss at the femoral head taper interface of modular replacement hips with novel use of the focus variation principle. A novel 3D to areal data conversion technique also allows powerful areal data analysis techniques to be applied to point cloud (3D) measurements for volume loss optimisation. Accurate characterisation of retrieved femoral head tapers is important to assess their in vivo performance particularly with respect to the bio toxicity of wear and corrosion products.A cohort of 8 retrieved femoral heads showing a wide range of degradation (0.5mm3 < volume loss < 12mm3) [1] was selected for the development of this technique. Using this common cohort of retrieved hips, the current technique was benchmarked against the well proven roundness measurement machine (RMM) method. This existing technique generates areal (2.5D) data and exploits a range of existing areal analysis techniques to optimise volume loss assessment. For benchmarking continuity and to exploit the same areal techniques, volume loss analysis for the current technique was carried out using the software written for the existing RMM method.The focus variation instrument’s integrated language was used to write script to convert (un-wrap) the taper surface 3D data into areal format.The current method shows a mean absolute difference in volume loss of 14% (-12% signed) from that of the benchmark with a range of 1% to 27%. The spread of measured values is significantly higher for the current method than for the benchmark. However, it is noted that replication can offer the advantage of capturing the whole taper surface on some taper types where physical access is limited for a stylus based roundness method.The current technique is also compared to the existing Redlux™ technique in which replicated female tapers are measured using a confocal instrument. The current technique is shown to have comparable performance to the Redlux™ technique but offers a more sophisticated methodology for volume loss analysis. In addition the current technique offers new instrumentation and analysis tools to the field.Small uncontrolled casting variations are noted in the current technique, resulting in poorer performance with small volume loss samples where the influence of this effect is most pronounced. However, given the simplified assumptions of the volume loss calculation where results may be skewed by deposits, some uncertainty will be evident with any approach.

Can We Avoid Implant-selection Errors in Total Joint Arthroplasty?

Implant selection in the operating room is a manual process. This manual process combined with complex compatibility rules and inconsistent implant labeling may lead to implant-selection errors. These might be reduced using an automated process; however, little is known about the efficacy of available automated error-reduction systems in the operating room. (1) How often do implant-selection errors occur at a high-volume institution? (2) What types of implant-selection errors are most common? We retrospectively evaluated our implant log database of 22,847 primary THAs and TKAs to identify selection errors. There were 10,689 THAs and 12,167 TKAs included during the study period from 2012 to 2017; there were no exclusions and we had no missing data in this study. The system provided an output of errors identified, and these errors were then manually confirmed by reviewing implant logs for each case found in the medical records. Only those errors that were identified by the system were manually confirmed. During this time period all errors for all procedures were captured and presented as a proportion. Errors identified by the software were manually confirmed. We then categorized each mismatch to further delineate the nature of these events. One hundred sixty-nine errors were identified by the software system just before implantation, representing 0.74 of the 22,847 procedures performed. In 15 procedures, the wrong side was selected. Twenty-five procedures had a femoral head selected that did not match the acetabular liner. In one procedure, the femoral head taper differed from the femoral stem taper. There were 46 procedures in which there was a size mismatch between the acetabular shell and the liner. The most common error in TKA that occurred in 46 procedures was a mismatch between the tibia polyethylene insert and the tibial tray. There were 13 procedures in which the tibial insert was not matched to the femoral component according to the manufacturer's guidelines. Selection errors were identified before implantation in all procedures. Despite an automated verification process, 0.74% of the arthroplasties performed had an implant-selection error that was identified by the software verification. The prevalence of incorrect/mismatched hip and knee prostheses is unknown but almost certainly underreported. Future studies should investigate the prevalence of these errors in a multicenter evaluation with varying volumes across the involved sites. Based on our results, institutions and management should consider an automated verification process rather than a manual process to help decrease implant-selection errors in the operating room. Level IV, therapeutic study.

Material loss at the femoral head taper

There are limited published data detailing the volumetric material loss from tapers of conventional metal-on-polyethylene (MoP) total hip arthroplasties (THAs). Our aim was to address this by comparing the taper wear rates measured in an explanted cohort of the widely used Exeter THA with those measured in a group of metal-on-metal (MoM) THAs. We examined an existing retrieval database to identify all Exeter V40 and Universal MoP THAs. Volumetric wear analysis of the taper surfaces was conducted using previously validated methodology. These values were compared with those obtained from a series of MoM THAs using non-parametric statistical methodology. A number of patient and device variables were accounted for using multiple regression modelling. A total of 95 Exeter MoP and 249 MoM THAs were examined. The median volumetric loss from the MoM cohort was over four times larger than that from the MoP cohort (1.01 mm3 vs 0.23 mm3, p < 0.001), despite a significantly shorter median period in vivo for the MoM group (48 months vs 90 months, p < 0.001). Multiple regression modelling indicated that the dominant variables leading to greater female taper material loss were bearing diameter (p < 0.001), larger female taper angles (p < 0.001), and male titanium stem tapers (p < 0.001). Consistent with the long-term clinical success of the device, the volumetric material loss from Exeter femoral head tapers was, in general, small compared with that from larger-diameter MoM head tapers. Cite this article: Bone Joint J 2018;100-B:1310-9.

Head Taper Corrosion Causing Head Bottoming Out and Consecutive Gross Stem Taper Failure in Total Hip Arthroplasty

BackgroundTaper corrosion in total hip arthroplasty for bearings with metal heads against polyethylene has developed from an anecdotal observation to a clinical problem. Increased taper wear and even gross taper failure have been reported for one particular design. It is hypothesized that corrosion of the female head taper results in taper widening, allowing the cobalt-chromium head to turn on the stem and wear down the softer titanium alloy by abrasive wear, ultimately causing failure. The purpose of this study is to investigate the time course of this process and the general role of taper dimensions and material in this problem. MethodsRetrieved cobalt-chromium alloy heads (n = 30, LFIT; Stryker, Mahwah, NJ) and Ti-12Mo-6Zr-2Fe (TMZF) stems (n = 10, Accolade I; Stryker) were available for analysis. Taper material loss was determined using three-dimensional coordinate measurements and scanning. The pristine tip clearance between head and stem was analytically determined. The influence of taper material and taper size on taper deformation and micromotion was investigated using a finite element model. ResultsMaterial loss at the head taper increased with time in situ up to a volume of 20.8 mm3 (P < .001). A mean linear material loss above 76 μm at the head taper was analytically confirmed to result in bottoming out, which was observed in 12 heads. The finite element calculations showed significantly larger deformations and micromotions for a small 11/13 TMZF taper combined with a distinctly different micromotion pattern compared to other materials and taper designs. ConclusionA 11/13 TMZF taper design with 36-mm head diameters bears a higher risk for corrosion than larger tapers made from stiffer materials. Failures of this combination are not restricted to the head sizes included in the recall. Patients with this implant combination should be closely monitored.

Prediction of taper performance using quasi static FE models: The influence of loading, taper clearance and trunnion length.

The head-neck taper junction has been widely reported to corrode leading to adverse tissue reactions. Taper corrosion is a poorly understood phenomenon but has been associated with oxide layer damage and ingress of corrosive physiological fluids. Micromotion may damage the oxide layer; although little is understood about the prevailing stresses which cause this. The ingress of fluid around the joint space into the taper will depend on the taper contact position and the separation of the interfaces during loading. The current work reports on the effect of taper clearances and trunnion length on the taper surface stresses and the taper gap opening. These were determined for CoCr/Ti taper interfaces using FE under loading conditions including walking and stair climb as well as hip simulator load profiles. Shorter trunnions and stair climb loading were shown to generate the greatest taper gaps (82 µm) and also the largest surface stresses (1200 MPa) on the head taper. The largest taper gaps were associated with smaller taper contact areas. Clearances within ±0.1° had no effect on the taper gaps generated, as the tapers engaged over comparable lengths; the taper gap opening was dependent upon the taper engagement length rather than location (proximal or distal) of contact. The walking profile or variants applied by hip simulators, was insufficient to differentiate between taper designs and evaluate differences in the magnitudes of taper gaps. The use of more demanding activity such as stair climb during in vitro evaluations could provide better predictions of taper performance in vivo. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 138-148, 2019.

Influence of Assembly Force and Distraction on the Femoral Head-Taper Junction

BackgroundThis study investigates if the placement of femoral heads (trials and actual implants) using varying impaction forces causes physical compromise to the trunnion. MethodsTrunnion and head taper wear patterns were evaluated after impaction and removal of new femoral stem trunnions and ceramic heads at various impaction loads (2 kN, 4 kN, or 6 kN, n = 6/group). In addition, trunnion wear patterns were measured after plastic trials were hand-placed on new trunnions and underwent range of motion testing in a Hip Simulator (n = 5). ResultsThere was no significant difference in trunnion or head surface deviation, taper angle, or surface roughness in any groups preimpaction and postimpaction and removal. There was no significant surface trunnion damage from assembly and range of motion testing of the plastic femoral head trial. ConclusionsThe use of femoral head trials and the concurrent impaction and removal of a new femoral head were not associated with significant trunnion surface damage for the impaction loads observed in this study.

Five Hundred Fifty-five Retrieved Metal-on-metal Hip Replacements of a Single Design Show a Wide Range of Wear, Surface Features, and Histopathologic Reactions.

In 2010, a widely used metal-on-metal hip implant design was voluntarily recalled by the manufacturer because of higher than anticipated failure rates at 5 years. Although there was a large published range of revision rates, numerous studies had reported a higher risk of revision for excessive wear and associated adverse tissue reactions when compared with other metal-on-metal total hips. The reasons for this were suggested by some to be related to cup design features. From retrievals of ASR metal-on-metal implants and tissue samples obtained at revision surgery, we asked the following questions: (1) What were the common and uncommon surface features? (2) What were the common and uncommon linear and volumetric wear characteristics? (3) Were there common taper corrosion characteristics? (4) What aseptic lymphocytic vasculitis-associated lesion (ALVAL) features were present in the tissues? Five hundred fifty-five ASRs, including 23 resurfacings, were studied at one academic research center. Features of wear (eg, light and moderate scratching), damage (eg, deposits, gouges), and bone attachment on the porous coating were semiquantitatively ranked from 0 (none) to 3 (> 75%) based on the amount of a feature in each region of interest by the same experienced observer throughout the study. Visible features of head taper corrosion were ranked (Goldberg score) from 1 (none) to 4 (severe) by the same observer using a previously published scoring method. An experienced tribologist measured component wear depth using a coordinate measuring machine and quantified wear volume using previously validated methods. All available tissues were sampled and examined for features of ALVAL and scored from 0 to 10 by a single observer using a method they previously developed and published. A score from 0 to 4 is considered low, 5 to 8 is considered moderate, and 9 or 10 is considered high with regard to the risk of metal hypersensitivity features in the tissues. The most common bearing surface features were light and moderate scratches and removal or postremoval damage. Discoloration and deposits were commonly observed on femoral heads (55% [305 of 553]) and less commonly on cups (30% [165 of 546]). There was no evidence of impingement or dislocation damage. There was typically a small amount of bone attachment in at least one of eight designated regions of interest (84% [460 of 546]); extensive or no bone attachment was uncommon. Edge wear was highly prevalent. The maximum wear of 469 cups (88%) occurred near the edge, whereas the maximum wear of 508 femoral heads (94%) occurred between the pole and 45° from the pole. The median combined head-cup wear volume was 14 mm (range, 1-636 mm). One hundred sixty-nine pairs (32%) had a combined wear volume of < 10 mm, 42 pairs (8%) had volumetric wear of > 100 mm, and 319 pairs (60%) had wear volume between 10 and 100 mm³. Seventy-four percent of tapers (390 of 530) received a Goldberg score of 4, 22% (116 of 530) a score of 3, < 5% (24 of 530) a score of 2, and none received a score of 1. The most frequent ALVAL score was 5 out of 10 (35 of 144 hips [24%]) and ranged from 2 (one hip) to 10 (nine hips); 92 of 144 (64%) had a moderate score, 17 of 144 (12%) had a high score, and 35 (24%) had a low score. Although edge wear was prevalent, in most cases, this was not associated with high wear. The increased diameter and decreased coverage angle of the ASR design may have resulted in the observed high incidence of edge wear while perhaps decreasing the risk for impingement and dislocation. The role of bearing wear in the revisions of metal-on-metal implants is controversial, because it is known that there is a large range of in vivo wear rates even within the same implant type and that patient variability affects local tissue responses to wear debris. The observations from our study of 555 retrieved ASR implant sets indicate that there was a wide range of wear including a subset with very high wear. The results suggested that the failure of the ASR and ASR XL was multifactorial, and the failure of different subgroups such as those with low wear may be the result of mechanisms other than reaction to wear debris.

Retrieval Analysis of Large-Head Modular Metal-on-Metal Hip Replacements of a Single Design

BackgroundThere are limited publications examining modular metal-on-metal (MoM) total hip implants in which a comprehensive analysis of retrieved components is performed. This study examines 24 retrieved modular MoM implants from a single manufacturer and compares retrieval analytics; bearing surface damage, wear, and modular taper corrosion against patient, surgical and implant characteristics to elucidate significant associations. MethodsClinical, patient, and surgical data were collected including age, body mass index, blood metal ion levels, and cup inclination. Damage assessment was performed visually in addition to surface profilometry. Acetabular liners and femoral heads were measured for volumetric wear. Femoral head taper bores were similarly measured for material removal due to corrosion and fretting. ResultsPatients with MoM-related reasons for revision showed significantly higher levels of blood metal ion levels. Bearing wear was strongly associated with blood metal ion levels and was significantly increased in cups placed more vertically. Younger patients tended to have higher body mass indices as well as poorer cup placement. ConclusionThis work details a broad range of analyses on a series of modular MoM total hip implants from a single manufacturer of which there are few published studies. Acetabular cup inclination angle was deemed a primary cause of revision surgery through increased MoM wear, high metal ion levels in the blood, and subsequent adverse local tissue reactions. Heavy patients can increase the surgical difficulty which was shown to be related to poor cup placement in this cohort.

Effect of Bearing Type on Taper Material Loss in Hips From 1 Manufacturer

BackgroundNumerous studies have reported on clinical significant volumes of material loss and corrosion at the head-stem junction of metal-on-metal (MOM) hips; less is understood about metal-on-polyethylene (MOP) hips. We compared the effect of bearing type (MOM vs MOP) on taper material loss for a hip system of a single design. MethodsIn this cohort study, we recruited retrieved MOM (n = 30) and MOP (n = 22) bearing hips that were consecutively received at our center. We prospectively collected associated clinical and imaging data. We measured the severity of corrosion and volumes of material loss at each head taper surface and used multivariate statistical analysis to investigate differences between the 2 bearing types. ResultsThe median rate of material loss for the MOM and MOP groups was 0.81 mm3/y (0.01-3.45) and 0.03 mm3/y (0-1.07), respectively (P < .001). Twenty-nine of 30 MOM hips were revised for adverse metal reactions, compared with 1 of 22 MOP hips. ConclusionMOP hips lost significantly less material from their taper junctions than MOM hips. Our results can reassure patients with MOP Pinnacle hips that they are unlikely to experience clinically significant problems related to material loss from the taper junction.

The Influence of Contamination and Cleaning on the Strength of Modular Head Taper Fixation in Total Hip Arthroplasty

BackgroundIntraoperative interface contamination of modular head-stem taper junctions of hip implants can lead to poor fixation strength, causing fretting and crevice corrosion or even stem taper fracture. Careful cleaning before assembly should help to reduce these problems. The purpose of this study was to determine the effect of cleaning (with and without drying) contaminated taper interfaces on the taper fixation strength. MethodsMetal or ceramic heads were impacted onto titanium alloy stem tapers with cleaned or contaminated (fat or saline solution) interfaces. The same procedure was performed after cleaning and drying the contaminated interfaces. Pull-off force was used to determine the influence of contamination and cleaning on the taper strength. ResultsPull-off forces after contamination with fat were significantly lower than those for uncontaminated interfaces for both head materials. Pull-off forces after application of saline solution were not significantly different from those for uncontaminated tapers. However, a large variation in taper strength was observed, pull-off forces for cleaned and dried tapers were similar to those for uncontaminated tapers for both head materials. ConclusionIntraoperative contamination of taper interfaces may be difficult to detect but has a major influence on taper fixation strength. Cleaning of the stem taper with saline solution and drying with gauze directly before assembly allows the taper strength of the pristine components to be achieved. Not drying the taper results in a large variation in pull-off forces, emphasizing that drying is essential for sufficient and reproducible fixation strength.

Influence of the compliance of a patient's body on the head taper fixation strength of modular hip implants

BackgroundThe strength of the modular fixation between head and stem taper of total hip replacement implants should be sufficient to minimise relative motion and prevent corrosion at the interface. Intraoperatively the components are assembled by impaction with a hammer. It is unclear whether the effective compliance of the patient's body modifies the strength of the taper interface under impaction assembly. The purpose of this study was to assess the influence of the compliance of the patient's body on the taper fixation strength. MethodsCobalt-chrome and ceramic femoral heads were assembled with titanium alloy stem tapers in the laboratory under impaction. Impaction forces were applied with a constant energy, defined by the drop height of the impactor, according to standard experimental procedure. The compliance of the patient was simulated in the laboratory by varying the stiffness of springs mounted below the stem taper. Pull-off forces between head and neck were measured to determine fixation strength. FindingsDecreasing spring stiffness had no effect on the applied peak impaction forces during assembly or on the pull-off forces. Pull-off forces showed no difference between metal and ceramic head materials. InterpretationPull-off forces and impaction forces were independent of the spring stiffness below the stem taper, indicating that the compliance of the patient has no effect on the taper fixation strength. Impaction testing in the laboratory can therefore be performed under rigid fixation, without accounting for the compliance of the patient.

Variation in taper surface roughness for a single design effects the wear rate in total hip arthroplasty.

Material loss from the head-stem taper junction of total hip arthroplasty (THA) is implicated in adverse reactions to metal debris (ARMD); the mechanisms for this are multi-factorial. We investigated the relationship between the roughness of the "as manufactured" taper surface and the wear rate from this junction. Fifty retrieved Pinnacle metal-on-metal (MOM) bearings paired with a Corail stem were included in the study. Multivariable statistical analysis was performed to determine the influence of taper roughness on material loss rate after controlling for other confounding surgical, implant, and patient factors. The surface roughness of the "as manufactured" head taper surface was associated with the rate of material loss from this surface. Four of eighteen roughness variables taken from ISO 4,287 and ISO 13,565-2 were significant: The Reduced Peak Height (Rpk, the protruding peaks above the core) (p = 0.004), Material Ratio 1 (Mr1, the ratio of the protruding peaks above the core) (p = 0.002), Area of the Peak Region (A1, the area of the Abbott-Curve that contains the peaks from the profile) (p = 0.003) and the Skewness (Rsk, the asymmetry of the height distribution corresponding to the height or depth of surface features) (p = 0.03). We found a large variability in the measured values with a median (range) of 0.50 (0.05-2.98), 11.98 (0.46-39.98), 30.89 (0.15-581.00), and 0.04 (-0.73-0.84), respectively. A 1-unit increase in Rpk was associated with a 73% increase in the taper wear rate. The variability of "as manufactured" surface roughness has a significant effect on taper material loss. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1784-1792, 2017.

Corrosion of the Head-Stem Taper Junction-Are We on the Verge of an Epidemic?: Review Article.

The modular head taper junction has contributed to the success of total hip arthroplasty (THA) greatly. Taper corrosion and wear problems reported for large and extra-large metal-on-metal bearings as well as for bi-modular THA stems have cast doubt on the benefit of the taper interface. Presently, corrosion problems are being reported for nearly all kinds of artificial hip joints incorporating metal heads, questioning taper connections in general. This study aimed to review the mechanical and electrochemical relationships that may lead to taper corrosion, which have been reported more commonly in recent literature, and to also review the contribution of patient characteristics and surgical techniques involved in taper assembly that may contribute to the problem. The search criteria "(corrosion) AND (hip arthroplasty) AND (taper OR trunnion)" and "(hip arthroplasty) AND ((pseudotumor) OR (pseudo-tumor))" in PubMed and the JAAOS were used for the literature search. In addition, the arthroplasty registers were considered. Most studies acknowledge the multifactorial nature of the problem but concentrate their analysis on taper and implant design aspects, since this is the only factor that can be easily quantified. The sometimes conflicting results in the literature could be due to the fact that the other two decisive factors are not sufficiently considered: the loading situation in the patient and the assembly situation by the surgeon. All three factors together determine the fate of a taper junction in THA. There is no single reason as a main cause for taper corrosion. The combined "outcome" of these three factors has to be in a "safe range" to achieve a successful long-term taper fixation. No, this is not the beginning of an epidemic. It is rather the consequence of disregarding known mechanical and electrochemical relationships, which in combination have recently caused a more frequent occurrence-and mainly reporting-of corrosion issues.

Does Taper Size Have an Effect on Taper Damage in Retrieved Metal-on-Polyethylene Total Hip Devices?

BackgroundTaper design has been identified as a possible contributor to fretting corrosion damage at modular connections in total hip arthroplasty systems, but variations in as-manufactured taper interfaces may confound this analysis. This study characterized taper damage in retrievals with 2 different taper sizes but comparable taper surface finishes and investigated if fretting and corrosion damage is related to taper size in the context of a multivariable analysis for metal-on-polyethylene bearings. MethodsA total of 252 cobalt chromium femoral heads were identified in a collection of retrievals: 77 with taper A and 175 with taper B. Implantation time averaged 5.4 ± 6.0 years (range, 0-26 years). Explants were cleaned and analyzed using a 4-point semiquantitative method. Clinical and device factors related to head taper fretting corrosion damage were assessed using ordinal logistic regression with forward stepwise control. Components were then selected to create 2 balanced cohorts, matched on significant variables from the multivariable analysis. ResultsIncreased head offset (P < .001), longer implantation time (P = .002), heavier patients (P < .001), and more flexible tapers (P < .001) were associated with increased taper fretting and corrosion damage. When damage scores were compared between the balanced groups, no significant differences were found. ConclusionThese results suggest that fretting and corrosion damage is insensitive to differences in taper size. The final model derived explains almost half of the fretting corrosion damage observed and identifies contributing factors that are consistent with other in vitro and retrieval studies.

Does Surface Topography Play a Role in Taper Damage in Head-neck Modular Junctions?

There are increasing reports of total hip arthroplasty failure subsequent to modular taper junction corrosion. The surfaces of tapers are machined to have circumferential machining marks, resulting in a surface topography of alternating peaks and valleys on the scale of micrometers. It is unclear if the geometry of this machined surface topography influences the degree of fretting and corrosion damage present on modular taper junctions or if there are differences between modular taper junction material couples. (1) What are the differences in damage score and surface topography between CoCr/CoCr and CoCr/Ti modular junctions? (2) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/CoCr couples? (3) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/Ti couples? Damage on stem and head tapers was evaluated with a modified Goldberg score. Differences in damage scores were determined between a group of 140 CoCr/CoCr couples and 129 CoCr/Ti couples using a chi-square test. For a subgroup of 70 retrievals, selected at random, we measured five variables, including initial stem taper machining mark height and spacing, initial head taper roughness, flexural rigidity, and taper angle mismatch. All retrievals were obtained at revision surgeries. None were retrieved as a result of metal-on-metal failures or were recalled implants. Components were chosen so there was a comparable number of each material couple and damage score. Machining marks around the circumference of the tapers were measured using white light interferometry to characterize the initial stem taper surface topography in terms of the height of and spacing between machining mark peaks as well as initial head taper roughness. The taper angle mismatch was assessed with a coordinate measuring machine. Flexural rigidity was determined based on measurements of gross taper dimensions and material properties. Differences of median or mean values of all variables between material couples were determined (Wilcoxon rank-sum tests and t-tests). The effect of all five variables along with time in situ on stem and head taper damage scores was tested with a multiple regression model. With 70 retrievals, a statistical power of 0.8 could be achieved for the model. Damage scores were different between CoCr/CoCr and CoCr/Ti modular taper junction material couples. CoCr/CoCr stem tapers were less likely to be mildly damaged (11%, p=0.006) but more likely to be severely damaged (4%, p=0.02) than CoCr/Ti stem tapers (28% and 1%, respectively). CoCr/CoCr couples were less likely to have moderately worn head tapers (7% versus 17%, p=0.003). Stem taper machining mark height and spacing and head taper roughness were 11 (SD 3), 185 (SD 46), and 0.57 (SD 0.5) for CoCr/CoCr couples and 10 (SD 3), 170 (SD 56), and 0.64 (SD 0.4) for CoCr/Ti couples, respectively. There was no difference (p=0.09, p=0.1, p=0.16, respectively) for either factor between material couples. Larger stem taper machining mark heights (p=0.001) were associated with lower stem taper damage scores, and time in situ (p=0.006) was associated with higher stem taper damage scores for CoCr/CoCr material couples. Stem taper machining marks that had higher peaks resulted in slower damage progression over time. For CoCr/Ti material couples, head taper roughness was associated with higher stem (p=0.001) and head taper (p=0.003) damage scores, and stem taper machining mark height, but not time in situ, was associated with lower stem taper damage scores (p=0.007). Stem taper surface topography was related to damage scores on retrieved head-neck modular junctions; however, it affected CoCr/CoCr and CoCr/Ti couples differently. A taper topography of circumferential machining marks with higher peaks appears to enable slower damage progression and, subsequently, a reduction of the reported release of corrosion products. This may be of interest to implant designers and manufacturers in an effort to reduce the effects of metal release from modular femoral components.

Clinical significance of corrosion of cemented femoral stems in metal-on-metal hips: a retrieval study.

The clinical significance of corrosion of cemented femoral stems is unclear. The purpose of this retrieval study was to: (1) report on corrosion at the stem-cement interface and (2) correlate these findings with clinical data. We analysed cemented stems (n = 36) composed of cobalt-chromium (CoCr) and stainless steel (SS) in a series of revised metal-on-metal hips. We performed detailed inspection of each stem to assess the severity of corrosion at the stem-cement interface using a scale of 1 (low) to 5 (severe). We assessed the severity of corrosion at each stem trunnion and measured wear rates at the head taper and bearing surfaces. We used non-parametric tests to determine the significance of differences between the CoCr and SS stems in relation to: (1) pre-revision whole blood Co and Cr metal ion levels, (2) trunnion corrosion, (3) bearing surface wear and (4) taper material loss. The corrosion scores of CoCr stems were significantly greater than SS stems (p < 0.01). Virtually all stem trunnions in both alloy groups had minimal evidence of corrosion. The median pre-revision Co levels of implants with CoCr stems were significantly greater than the SS stems (p < 0.01). There was no significant difference in relation to pre-revision Cr levels (p = 0.521). There was no significant difference between the two stem types in relation to bearing wear (p = 0.926) or taper wear (p = 0.148). Severe corrosion of cemented femoral stems is a common finding at our retrieval centre; surgeons should consider corrosion of CoCr stems as a potential source of metal ions when revising a hip.

Ceramic-on-Poly Femoral Head Fractures: What's Going On?

As outlined in our January 16, 2013, editorial , “The Case Report Redefined with JBJS Case Connector ,” one important role of JBJS Case Connector is to alert the orthopaedic community about a potentially problematic device or therapy. When two or more such cases with similar mechanisms appear, we will identify the procedure or implant as a “watchable” intervention. While this system is not statistically conclusive and may or may not be supported by other published case reports or registry data, the intention is to sharpen the focus of clinicians on the potential for similar problems and thereby enhance clinical outcomes and patient safety. The “Watch” designation may also encourage others to report related difficulties and enlist the orthopaedic community to either demonstrate that these are isolated, unrelated cases or sharpen the focus further on rigorously evaluating the intervention. Where appropriate, we may identify brand, model, or implant-lot specifics. In total hip arthroplasty (THA), a fractured ceramic head is a catastrophic but thankfully very rare event. Most case reports of ceramic head fractures involve ceramic-on-ceramic articulations, but this “Watch” describes three cases of femoral head fractures involving ceramic-on-polyethylene bearings. Moreover, the fractures occurred in association with little or no postsurgical trauma. Ceramic hip components are often chosen for younger patients in an effort to minimize long-term wear. On the downside, unlike metal, ceramic components can fracture. Ceramic femoral head fractures arise from four main factors: trauma; material or manufacturing defects; non-compatible, damaged, or contaminated femoral stem/head taper connections; or other suboptimal surgical techniques. The ceramics industry has a more-than-forty-year track record of continuous improvement in hip-component manufacturing. CeramTec, the main U.S. player in this arena, first introduced ceramic hip components in 1974; those first-generation femoral heads had a fracture rate of 0.026%. By 2003, when CeramTec introduced its fourth-generation BIOLOX …

Trunnion Troubles in Modular Hip Implants.

As outlined in our January 16, 2013 editorial, “The Case Report Redefined with JBJS Case Connector , ” one important role of JBJS Case Connector is to alert the orthopaedic community about a potentially problematic device or therapy. When two or more such cases with similar mechanisms appear, we will identify the procedure or implant as a “watchable” intervention. While this system is not statistically conclusive and may or may not be supported by other published case reports or registry data, the intention is to sharpen the focus of clinicians on the potential for similar problems and thereby enhance clinical outcomes and patient safety. The “Watch” designation may also encourage others to report related difficulties and enlist the orthopaedic community to either demonstrate that these are isolated, unrelated cases or sharpen the focus further on rigorously evaluating the intervention. Where appropriate, we may identify brand, model, or implant-lot specifics. Of the five Watch articles that have been published in JBJS Case Connector, three—including this one—have focused on total hip arthroplasty (THA). Our very first Watch in September 2013 discouraged surgeons who implant dual-mobility hips from using a “mix-and-match” strategy with components from different manufacturers. Our January 2014 Watch about THA cautioned hip surgeons to be wary about using long-necked and skirted-head modular hip designs. In both of those Watch articles, we emphasized how head-neck modularity has helped orthopaedists achieve important biomechanical objectives—such as adjusting version, limb length, and offset—to maximize implant function and longevity. Modularity also facilitates easier revisions and lowers inventory costs. But we also made the point that modularity increases the number of interfaces at which corrosion can occur, making prosthetic materials more vulnerable to compression, shear forces, and bending stresses. The arthroplasty community currently feels that the advantages gained from modularity outweigh the risks, but we …

Quantification of the Contact Area at the Head-Stem Taper Interface of Modular Hip Prostheses.

Corrosion of modular taper junctions of hip implants may be associated with clinical failure. Taper design parameters, as well as the intraoperatively applied assembly forces, have been proposed to affect corrosion. Fretting corrosion is related to relative interface shear motion and fluid ingress, which may vary with contact force and area. It was hypothesised in this study that assembly forces modify the extent and distribution of the surface contact area at the taper interface between a cobalt chrome head and titanium stem taper with a standard threaded surface profile. Local abrasion of a thin gold coating applied to the stem taper prior to assembly was used to determine the contact area after disassembly. Profilometry was then used to assess permanent deformation of the stem taper surface profile. With increasing assembly force (500 N, 2000 N, 4000 N and 8000 N) the number of stem taper surface profile ridges in contact with the head taper was found to increase (9.2±9.3%, 65.4±10.8%, 92.8±6.0% and 100%) and the overall taper area in contact was also found to increase (0.6±0.7%, 5.5±1.0%, 9.9±1.1% and 16.1±0.9%). Contact was inconsistently distributed over the length of the taper. An increase in plastic radial deformation of the surface ridges (-0.05±0.14 μm, 0.1±0.14 μm, 0.21±0.22 μm and 0.96±0.25 μm) was also observed with increasing assembly force. The limited contact of the taper surface ridges at lower assembly forces may influence corrosion rates, suggesting that the magnitude of the assembly force may affect clinical outcome. The method presented provides a simple and practical assessment of the contact area at the taper interface.

Otto Aufranc Award: Large Heads Do Not Increase Damage at the Head-neck Taper of Metal-on-polyethylene Total Hip Arthroplasties.

Fretting and corrosion at head-neck junctions of total hip arthroplasties (THAs) have been associated with adverse local tissue reactions in patients with both metal-on-polyethylene (MoP) and metal-on-metal (MoM) prostheses. Femoral head size contributes to the severity of fretting and corrosion in large-diameter MoM THAs, but its impact on such damage in MoP THAs remains unknown. (1) Is femoral head size associated with increased fretting or corrosion at the head-neck junction in MoP total hips? (2) Is duration of implantation associated with increased fretting or corrosion? The severity of fretting/corrosion on surfaces of head tapers and stem trunnions was visually examined in 154 MoP THAs retrieved as part of 3282 revision surgeries performed at our institution between January 1, 2007, and December 31, 2013. Fretting and corrosion damage were subjectively graded by two independent observers on a 1 to 4 scale, and their relations to head size, alloy combinations, taper/trunnion design, length of implantation (LOI), and location were investigated. Differences in scores never exceeded one grade, and this occurred in only 17% of examined implants. With the available implants, the study provided 88% power to detect differences of 0.5 in fretting or corrosion scores in these analyses. Fretting and corrosion of the tapers and the trunnions were not affected by head size (p = 0.247, p = 0.471, p = 0.837, and p = 0.868, respectively), although taper/trunnion design affected taper fretting (p = 0.005) and corrosion (p = 0.0031) and trunnion fretting (p = 0.0028). Head taper fretting (observed in 73% of heads) increased with LOI, but head taper corrosion (noted in 93% of heads) was not affected. Trunnion fretting (observed in 86% of stems) was more severe in mixed-alloy combinations and with increased LOI and was more severe proximally. Trunnion corrosion (noted in 72% of stems) was also location-dependent with greater corrosion distally. Fretting and corrosion are regular occurrences in MoP THAs, but neither damage type was related to femoral head size. Conversely, taper design, LOI, and alloy combination affected the severity of both fretting and corrosion. Although it has been suggested that trunnion corrosion seen in MoP bearings is a function of larger diameter heads, our data suggest that larger femoral heads may be used for increased damage at the modular junction of MoP THAs.