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1.  Does Taper Angle Clearance Influence Fretting and Corrosion Damage at the Head-Stem Interface? A Matched Cohort Retrieval Study 
Seminars in arthroplasty  2013;24(4):246-254.
Previous studies have speculated that modular taper design may have an effect on the corrosion and material loss at the taper surfaces. We present a novel method to measure taper angle for retrieved head taper and stem trunnions using a roundness machine (Talyrond 585, Taylor Hobson, UK). We also investigated the relationship between taper angle clearance and visual fretting-corrosion score at the taper-trunnion junction using a matched cohort study of 50 ceramic and 50 metal head-stem pairs. In this study, no correlation was observed between the taper angle clearance and the visual fretting-corrosion scores in either the ceramic or the metal cohorts.
PMCID: PMC3941749  PMID: 24610994
2.  Can Pin-on-Disk Testing Be Used to Assess the Wear Performance of Retrieved UHMWPE Components for Total Joint Arthroplasty? 
BioMed Research International  2014;2014:581812.
The objective of this study was to assess the suitability of using multidirectional pin-on-disk (POD) testing to characterize wear behavior of retrieved ultrahigh molecular weight polyethylene (UHMWPE). The POD wear behavior of 25 UHMWPE components, retrieved after 10 years in vivo, was compared with 25 that were shelf aged for 10–15 years in their original packaging. Components were gamma sterilized (25–40 kGy) in an air or reduced oxygen (inert) package. 9 mm diameter pins were fabricated from each component and evaluated against CoCr disks using a super-CTPOD with 100 stations under physiologically relevant, multidirectional loading conditions. Bovine serum (20 g/L protein concentration) was used as lubricant. Volumetric wear rates were found to vary based on the aging environment, as well as sterilization environment. Volumetric wear rates were the lowest for the pins in the gamma inert, shelf aged cohort. These results support the utility of using modern, multidirectional POD testing with a physiologic lubricant as a novel method for evaluating wear properties of retrieved UHMWPE components. The data also supported the hypothesis that wear rates of gamma-inert liners were lower than gamma-air liners for both retrieved and shelf aging conditions. However, this difference was not statistically significant for the retrieved condition.
PMCID: PMC4177737  PMID: 25295264
3.  The Latest Lessons Learned from Retrieval Analyses of Ultra-High Molecular Weight Polyethylene, Metal-on-Metal, and Alternative Bearing Total Disc Replacements 
Seminars in spine surgery  2012;24(1):57-70.
Knowledge regarding the in vivo performance and periposthetic tissue response of cervical and lumbar total disc replacements (TDRs) continues to expand. This review addresses the following four main questions: 1) What are the latest lessons learned from polyethylene in large joints and how are they relevant to current TDRs? 2) What are the latest lessons learned regarding adverse local tissue reactions from metal-on-metal, CoCr bearings in large joints and how are they relevant to current TDRs? 3) What advancements have been made in understanding the in vivo performance of alternative biomaterials, such as stainless steel and polycarbonate urethane, for TDRs in the past five years? 4) How has retrieval analysis of all these various artificial disc bearing technologies advanced the state of the art in preclinical testing of TDRs? The study of explanted artificial discs and their associated tissues can help inform bearing selection as well as the design of future generations of disc arthroplasty. Analyzing retrieved artificial discs is also essential for validating preclinical test methods.
PMCID: PMC3418706  PMID: 22904606
total disc arthroplasty; total disc replacement; TDR; ultra-high molecular weight polyethylene; UHMWPE; wear; oxidation; retrieval analysis; explant analysis; stainless steel; polycarbonate urethane; PCU; polyurethane; cobalt chrome; CoCr; metal-on-metal; adverse local tissue reactions
4.  Comparison of in vivo and simulator-retrieved metal-on-metal cervical disc replacements 
Cervical disc arthroplasty is regarded as a promising treatment for myelopathy and radiculopathy as an alternative to cervical spine fusion. On the basis of 2-year clinical data for the PRESTIGE® Cervical Disc (Medtronic, Memphis, Tennessee), the Food and Drug Administration recommended conditional approval in September 2006 and final approval in July 2007; however, relatively little is known about its wear and damage modes in vivo. The main objective was to analyze the tribological findings of the PRESTIGE® Cervical Disc. This study characterized the in vivo wear patterns of retrieved cervical discs and tested the hypothesis that the total disc replacements exhibited similar surface morphology and wear patterns in vitro as in vivo.
Ten explanted total disc replacements (PRESTIGE®, PRESTIGE® I, and PRESTIGE® II) from 10 patients retrieved after a mean of 1.8 years (range, 0.3–4.1 years) were analyzed. Wear testing included coupled lateral bending ( ±4.7°) and axial rotation ( ±3.8°) with a 49 N axial load for 5 million cycles followed by 10 million cycles of flexion-extension ( ±9.7°) with 148 N. Implant surfaces were characterized by the use of white-light interferometry, scanning electron microscopy, and energy dispersive spectroscopy.
The explants generally exhibited a slightly discolored, elliptic wear region of varying dimension centered in the bearing center, with the long axis oriented in the medial-lateral direction. Abrasive wear was the dominant in vivo wear mechanism, with microscopic scratches generally oriented in the medial-lateral direction. Wear testing resulted in severe abrasive wear in a curvilinear fashion oriented primarily in the medial-lateral direction. All retrievals showed evidence of an abrasive wear mechanism.
This study documented important similarity between the wear mechanisms of components tested in vitro and explanted PRESTIGE® Cervical Discs; however, the severity of wear was much greater during the in vitro test compared with the retrievals.
PMCID: PMC4300870  PMID: 25694884
Cervical arthroplasty; Total disc replacement; Biomechanics; Retrieval analysis
5.  Advances in Zirconia Toughened Alumina Biomaterials for Total Joint Replacement 
The objective of this article is to provide an up-to-date overview of zirconia-toughened alumina (ZTA) components used in total hip arthroplasties. The structure, mechanical properties, and available data regarding the clinical performance of ZTA are summarized. The advancements that have been made in understanding the in vivo performance of ZTA are investigated. This article concludes with a discussion of gaps in the literature related to ceramic biomaterials and avenues for future research.
PMCID: PMC4023350  PMID: 23746930
Total hip arthroplasty; alumina; zirconia; oxidized zirconium; zirconia toughened alumina (ZTA); structure; properties; squeaking; phase transformation
6.  Histological characterization of periprosthetic tissue responses for metal-on-metal hip replacement 
The histology of periprosthetic tissue from metal-on-metal (MOM) hip devices has been characterized by a variety of methods. The purpose of this study was to compare and evaluate the suitability of two previously developed aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL) scoring systems for periprosthetic hip tissue responses retrieved from MOM THR systems revised for loosening. Two ALVAL scoring systems (Campbell and Oxford) were used to perform histological analysis of soft tissues from seventeen failed MOM THRs. The predominant reactions for this patient cohort were macrophage infiltration and necrosis, with less than half of the patients (41%) showing a significant lymphocytic response or a high ALVAL reaction (6%). Other morphological changes which varied among patients included hemosiderin accumulation, cartilage formation and heterotopic ossification. Both scoring systems correlated with macrophage and lymphocyte responses and with each other, however given the diversity and variability of the current responses the Oxford-ALVAL system was more suitable for scoring tissues from MOM THR patients revised for loosening. It is important that standardized methods to score MOM tissue responses be used consistently so multiple study results can be compared to one another and a consensus can be generated.
PMCID: PMC4062875  PMID: 24941402
ALVAL; metal-on-metal; necrosis; histology; inflammation; total hip replacement; implant loosening
7.  Retrieval Analysis of Sequentially Annealed Highly Crosslinked Polyethylene Used in Total Hip Arthroplasty 
First-generation annealed and second-generation sequentially annealed, highly crosslinked polyethylenes (HXLPEs) have documented reduced clinical wear rates in their first decade of clinical use compared with conventional gamma inert-sterilized polyethylene. However, for both types of annealed HXLPE formulations, little is known about their reasons for revision, their in vivo oxidative stability, and their resistance to mechanical degradation.
We asked whether retrieved sequentially annealed HLXPE acetabular liners exhibited: (1) similar reasons for revision; (2) lower oxidation; (3) improved resistance to wear and degradation of mechanical properties; and (4) improved resistance to macroscopic evidence of rim damage when compared with acetabular liners fabricated from single-dose annealed HXLPE.
One hundred eighty-five revised acetabular liners in two cohorts (annealed and sequentially annealed) were collected in a multicenter retrieval program between 2000 and 2013. We controlled for implantation time between the two cohorts by excluding annealed liners with a greater implantation time than the longest term sequentially annealed retrieval (5 years); the mean implantation time (± SD) for the annealed components was 2.2 ± 1.4 years, and for the sequentially annealed liners, it was 1.2 ± 1.2 years. Reasons for revision were assessed based on medical records, radiographs, and examinations of the retrieved components. Oxidation was measured at the bearing surface, the backside surface, the locking mechanism, and the rim using Fourier transform infrared spectroscopy (ASTM F2102). Penetration was measured directly using a micrometer (accuracy: 0.001 mm). Mechanical behavior (ultimate load) was measured at the superior and inferior bearing surfaces using the small punch test (ASTM F2183). We used nonparametric statistical testing to analyze for differences in oxidation, penetration rates, and ultimate load when adjusting for HXLPE formulation as a function of implantation time.
The acetabular liners in both cohorts were revised most frequently for instability, loosening, and infection. Oxidation indices (OIs) of the sequentially annealed liners were lower than annealed liners at the bearing surface (mean OI difference = 0.3; p < 0.001), the backside surface (mean OI difference = 0.2; p < 0.001), and the rim (mean OI difference = 2.6; p < 0.001). No differences were detected in linear penetration rates between the cohorts (p = 0.10). Ultimate strength at the bearing surface of the HLXPE was not different between sequentially annealed and annealed cohorts (p = 0.72).
We observed evidence of in vivo oxidation in retrieved annealed and, to a lesser extent, retrieved sequentially annealed acetabular liners. However, we observed no association between the levels of oxidation and clinical performance of the liners.
Clinical Relevance
The findings of this study document the oxidative and mechanical behavior of sequentially annealed HXLPE. The reduced oxidation levels in sequentially annealed liners support the hypothesis that annealing in sequential steps eliminates more free radicals. However, as a result of the short-term followup, analysis of longer-term retrievals is warranted.
PMCID: PMC4317461  PMID: 25537808
8.  Retrieval analysis of PEEK rods for posterior fusion and motion preservation 
European Spine Journal  2013;22(12):2752-2759.
The purpose of this study was to analyze explanted PEEK rod spinal systems in the context of their clinical indications. We evaluated damage to the implant and histological changes in explanted periprosthetic tissues.
12 patients implanted with 23 PEEK rods were revised between 2008 and 2012. PEEK rods were of the same design (CD Horizon Legacy, Medtronic, Memphis TN, USA). Retrieved components were assessed for surface damage mechanisms, including plastic deformation, scratching, burnishing, and fracture. Patient history and indications for PEEK rod implantation were obtained from analysis of the medical records.
11/12 PEEK rod systems were employed for fusion at one level, and motion preservation at the adjacent level. Surgical complications in the PEEK cohort included a small dural tear in one case that was immediately repaired. There were no cases of PEEK rod fracture or pedicle screw fracture. Retrieved PEEK rods exhibited scratching, as well as impressions from the set screws and pedicle screw saddles. PEEK debris was observed in two patient tissues, which were located adjacent to PEEK rods with evidence of scratching and burnishing.
This study documents the surface changes and tissue reactions for retrieved PEEK rod stabilization systems. Permanent indentations by the set screws and pedicle screws were the most prevalent observations on the surface of explanted PEEK rods.
PMCID: PMC3843804  PMID: 23887771
PEEK rods; Posterior fusion; Retrieval analysis; Tissue response; Revision
9.  Reasons of Revision for First-Generation Highly Crosslinked Polyethylenes 
The Journal of arthroplasty  2010;25(6 Suppl):67-74.
Over a ten-year period, we prospectively evaluated the reasons for revision for contemporary and highly crosslinked polyethylene formulations in a multicenter retrieval program. 212 consecutive retrievals were classified as conventional gamma-inert sterilized liners (n=37), annealed (Crossfire™, n=72), or remelted (Longevity™, XLPE, Durasul; n=93). The most frequent reasons for revision were loosening (35%), instability (28%) and infection (21%) and were not related to polyethylene formulation (p = 0.17). Annealed and remelted liners had comparable linear penetration rates (0.03 and 0.04 mm/y, respectively, on average) and were significantly lower than conventional retrievals (0.11 mm/y; p ≤ 0.0005). This retrieval study including first-generation highly crosslinked liners demonstrated lower wear than conventional polyethylene. While loosening remained the most prevalent reason for revision, we could not demonstrate a relationship between wear and loosening. The long-term clinical performance of first-generation highly crosslinked remains promising, based on the mid-term outcomes of the components documented in this study.
PMCID: PMC2946323  PMID: 20541895
Ultra-high molecular weight polyethylene; UHMWPE; revision; total hip replacement; total hip arthroplasty; crosslinking; wear
10.  Mechanical Properties, Oxidation, and Clinical Performance of Retrieved Highly Crosslinked Crossfire Liners after Intermediate-Term Implantation 
The Journal of arthroplasty  2009;25(4):614-623.e2.
Sixty Crossfire (Stryker Orthopaedics, Mahwah, NJ) liners were consecutively revised after an average of 2.9 years (range: 0.01 – 8.0 years) for reasons unrelated to wear or mechanical performance of the polyethylene. Femoral head penetration was measured directly from 42 retrievals implanted for over 1 year. Penetration rate results (0.04 mm/y, on average; range: 0.00-0.13 mm/y) confirmed decreasing wear rates with longer in vivo times. Overall, we observed oxidation levels at the bearing surface of the 60 liners (0.5, on average; range: 0.1-1.7) comparable to those of non-implanted liners (0.5, on average; range: 0.3-1.1) and preservation of mechanical properties. We also measured elevated oxidation of the rim (3.4, on average; range: 0.2-8.8) that was correlated with implantation time. Rim surface damage, however, was observed in only 3/60 (5%) cases. Retrieval analysis of the three rim-damaged liners did not reveal an association between surface damage and the reasons for revision.
PMCID: PMC2876196  PMID: 19520545
Mechanical properties; oxidation; wear; hip arthroplasty; highly crosslinked ultra-high molecular weight polyethylene
11.  Retrieval analysis of motion preserving spinal devices and periprosthetic tissues 
SAS Journal  2009;3(4):161-177.
This article reviews certain practical aspects of retrieval analysis for motion preserving spinal implants and periprosthetic tissues as an essential component of the overall revision strategy for these implants. At our institution, we established an international repository for motion-preserving spine implants in 2004. Our repository is currently open to all spine surgeons, and is intended to be inclusive of all cervical and lumbar implant designs such as artificial discs and posterior dynamic stabilization devices. Although a wide range of alternative materials is being investigated for nonfusion spine implants, many of the examples in this review are drawn from our existing repository of metal-on-polyethylene, metal-on-metal lumbar total disc replacements (TDRs), and polyurethane-based dynamic motion preservation devices. These devices are already approved or nearing approval for use in the United States, and hence are the most clinically relevant at the present time. This article summarizes the current literature on the retrieval analysis of these implants and concludes with recommendations for the development of new test methods that are based on the current state of knowledge of in vivo wear and damage mechanisms. Furthermore, the relevance and need to evaluate the surrounding tissue to obtain a complete understanding of the biological reaction to implant component corrosion and wear is reviewed.
PMCID: PMC4365601  PMID: 25802641
Dynamic motion preservation; Artificial discs; Retrieval analysis; Explant analysis; Polyurethane; Ultra-high molecular weight polyethylene; PU; UHMWPE; Mechanical testing; Chemical analysis; Histology; Wear particles wear debris
12.  What is the correlation of in vivo wear and damage patterns with in vitro TDR motion response? 
Spine  2008;33(5):481-489.
Background Context
Total disc replacements (TDRs) have been used to reduce pain and preserve motion. However, the comparison of polyethylene wear following long-term implantation to those tested using an in vitro model had not yet been investigated.
The purpose of this study was to correlate wear and damage patterns in retrieved TDRs with motion patterns observed in a clinically validated in vitro lumbar spine model. We also sought to determine whether one-sided wear and motion patterns were associated with greater in vivo wear.
Study Design
This two-part study combined the evaluation of retrieved total disc replacements with a biomechanical study using human lumbar spines.
Patient Sample
38 CHARITÉ lumbar artificial discs were retrieved from 32 patients (24 female, 75%) after 7.3 years average implantation (range: 1.8 to 16.1y). The components were implanted at L2/L3 (n=1), L3/L4 (n=2), L4/L5 (n=20), and L5/S1 (n=15). All the implants were removed due to intractable back pain and/or facet degeneration. In addition, they were removed due to subsidence (n=10), anterior migration (n=3), core dislocation (n=2), lateral subluxation (n=1), endplate loosening (n = 2), and osteolysis (n=1). In parallel, 7 new implants were evaluated at L4-L5 and 13 implants at L5-S1 in an in vitro lumbar spine model.
Outcome Measures
Retrieval analysis included evaluation of clinical data, dimensional measurements and assessment of the extent and severity of PE surface damage mechanisms. In vitro testing involved the observation of motion patterns during physiological loading.
For the retrievals, each side of the PE core was independently analyzed at the rim and dome for the presence of machining marks, wear, and fracture. 35 cores were further analyzed using MicroCT to determine whether the wear was one-sided, or symmetrically distributed. For the in vitro study the new implants were tested under physiologic loads (flexion-extension with a compressive follower preload) using a validated cadaveric lumbar spine model. The center of the prosthesis was 2 mm posterior to the mid-point of the vertebral body endplate in mid-sagittal plane. Motion patterns of the in vitro-tested implants were tracked using sequential video-flouroscopy.
Substantial variability was observed in the wear patterns of the retrievals. 15/35 retrieved cores (43%) displayed one-sided wear patterns. The median dome penetration was 0.2 mm (range: 0.06 to 0.9 mm) and the median penetration rate was 0.04 mm/y (range: 0.01 to 0.2 mm/y). No significant difference in penetration or penetration rate was observed between retrievals with one-sided and symmetric wear patterns (p >0.05). Significant correlations were observed between implantation time and penetration (rho = 0.46, p = 0.004) and penetration rate (rho = −0.48, p = 0.003). In the in vitro study, there was clear visual evidence of motion at both articulations in 8/20 implantations. In additional 8/20 cases, there was some evidence of motion at both articulations; however, the predominant motion occurred at the top articulation. In 4/20 implantations motion could be visually detected only at the top articulation. Core entrapment and pinching was observed in 7/20 cases as the segment was extended, and was associated with visual evidence of core bending or deformation in 5/20 cases.
PMCID: PMC2430937  PMID: 18317190
total disc arthroplasty; total disc replacement; lumbar spine; CHARITÉ; degenerative disc disease; artificial disc; in vitro motion response; wear; surface damage; fracture; impingement; ultra; high molecular weight polyethylene; UHMWPE
13.  Oxidative properties and surface damage mechanisms of remelted highly crosslinked polyethylenes in total knee arthroplasty 
International Orthopaedics  2013;37(4):611-615.
Remelted highly crosslinked polyethylenes (HXLPEs) were introduced in total knee replacement (TKR) starting in 2001 to reduce wear and particle-induced lysis. The purpose of this study was to investigate the damage mechanisms and oxidative stability of remelted HXLPEs used in TKR.
A total of 186 posteriorly stabilised tibial components were retrieved at consecutive revision operations. Sixty nine components were identified as remelted HXLPE. The conventional inserts were implanted for 3.4 ± 2.7 years, while the remelted components were implanted 1.4 ± 1.2 years. Oxidation was assessed using Fourier transform infrared spectroscopy.
Remelted HXLPE inserts exhibited lower oxidation indices compared to conventional inserts. We were able to detect slight regional differences within the HXLPE cohort, specifically at the bearing surface.
Remelted HXLPE was effective at reducing oxidation in comparison to gamma inert sterilised controls. Additional long-term HXLPE retrievals are necessary to ascertain the long term in vivo stability of these materials in TKR.
PMCID: PMC3609978  PMID: 23397564
14.  Is Increased Modularity Associated With Increased Fretting and Corrosion Damage in Metal-On-Metal Total Hip Arthroplasty Devices? 
The Journal of arthroplasty  2013;28(8 0):2-6.
This retrieval study documents taper damage at modular interfaces in retrieved MOM THA systems and investigates if increased modularity is associated with increased fretting and corrosion. One hundred thirty-four (134) heads and 60 stems (41 modular necks) of 8 different bearing designs (5 manufacturers) were analyzed. Damage at the shell–liner interface of 18 modular CoCr acetabular liners and the corresponding 11 acetabular shells was also evaluated. The results of this study support the hypothesis that fretting and corrosion damage occurs at a variety of modular component interfaces in contemporary MOM THAs. We also found that modularity of the femoral stem was associated with increased damage at the head. An analysis of component and patient variables revealed that dissimilar alloy pairing, larger head sizes, increased medio-lateral offsets and longer neck moment arms were all associated with increased taper damage at the modular interfaces.
PMCID: PMC3971476  PMID: 23910820
total hip arthroplasty; modularity; fretting; corrosion; metal on metal
15.  Mechanical Properties of Retrieved Highly Crosslinked (Crossfire) Liners after Short-Term Implantation 
The Journal of arthroplasty  2005;20(7):840-849.
This study reports on detailed analyses of retrieved, annealed crosslinked liners. Twelve crosslinked liners (Crossfire, Stryker Orthopaedics, Mahwah, NJ) of the same Omnifit design were retrieved at revision surgery by one institution after an average 1.9 years (0.02 to 4.8 years) in vivo. In each case, the revision surgery was performed for reasons unrelated to wear. The mechanical properties and extent of oxidation of all inserts were characterized using a standard small punch test and measurement of the oxidation index. Results indicated that there was no association between implantation time and either mechanical properties or extent of oxidation for the inserts near the worn bearing surface. Slight variation in properties was observed as a function of sampling location, with the properties near the unworn surface displaying the greatest relative variability. We conclude that the variability in polyethylene properties observed in this small study was not clinically significant for these short term-implanted, annealed crosslinked liners.
PMCID: PMC1350161  PMID: 16230233
Mechanical properties; oxidation; wear; hip arthroplasty; highly crosslinked ultra-high molecular weight polyethylene
16.  Characteristics of highly cross-linked polyethylene wear debris in vivo 
Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm3/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm3/gm tissue) or by component wear volume rate (mm3/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance.
PMCID: PMC3928672  PMID: 23436587
total hip replacementhighly cross-linked polyethyleneosteolysiswear debrisbiological activity
17.  Estimating Risk in Medicare Patients With THA: An Electronic Risk Calculator for Periprosthetic Joint Infection and Mortality 
Although risk factors for periprosthetic joint infection (PJI) and mortality after total hip arthroplasty (THA) have been identified, interactions between specific patient risk factors are poorly understood. Therefore, it is difficult for surgeons to counsel patients on their individual risk of PJI or mortality after THA.
We evaluated the interaction between patient clinical and demographic factors on the risk of PJI and mortality after THA and developed an electronic risk calculator for estimating the patient-specific risk of PJI and mortality in Medicare patients with THA.
We used the Medicare 5% sample claims database to calculate the risk of PJI within 2 years and mortality within 90 days after THA in 53,252 Medicare patients with primary THAs between 1998 and 2009. Logistic regression using 29 comorbid conditions, age, sex, race, and socioeconomic status were used as inputs to develop an electronic risk calculator to estimate patient-specific risk of PJI and mortality after THA.
The overall 2-year risk of PJI and 90-day risk of mortality after primary THA were 2.07% and 1.30%, respectively. White women aged 70 to 74 years with alcohol abuse, depression, electrolyte disorder, peptic ulcer disease, urinary tract infection, rheumatologic disease, preoperative anemia, cardiopulmonary (cardiac arrhythmia, congestive heart failure, ischemic heart disease, chronic pulmonary disease) comorbidities, and peripheral vascular disease were at highest risk for PJI. White women aged 65 to 69 years with electrolyte disorder, hemiplegia/paraplegia, hypertension, hypothyroidism, metastatic tumor, preoperative anemia, coagulopathy, cardiopulmonary (congestive heart failure, chronic pulmonary disease) and psychiatric (psychoses, depression) comorbidities, malignancies, and peripheral vascular disease were at highest risk for mortality. An electronic risk calculator was developed to estimate the risk of PJI and mortality in Medicare patients with THA.
This electronic risk calculator can be used to counsel Medicare patients regarding their patient-specific risks of PJI and mortality after THA.
Level of Evidence
Level II, prognostic study. See the Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC3549162  PMID: 23179112
18.  Do Dynamic Cement-on-Cement Knee Spacers Provide Better Function and Activity During Two-stage Exchange? 
Implantation of an antibiotic bone cement spacer is used to treat infection of a TKA. Dynamic spacers fashioned with cement-on-cement articulating surfaces potentially facilitate patient mobility and reduce bone loss as compared with their static counterparts, while consisting of a biomaterial not traditionally used for load-bearing articulations. However, their direct impact on patient mobility and wear damage while implanted remains poorly understood.
We characterized patient activity, surface damage, and porous structure of dynamic cement-on-cement spacers.
We collected 22 dynamic and 14 static knee antibiotic cement spacers at revision surgeries at times ranging from 0.5 to 13 months from implantation. For these patients, we obtained demographic data and UCLA activity levels. We characterized surface damage using the Hood damage scoring method and used micro-CT analysis to observe the internal structure, cracking, and porosity of the cement.
The average UCLA score was higher for patients with dynamic spacers than for patients with static spacers, with no differences in BMI or age. Burnishing was the only prevalent damage mode on all the bearing surfaces. Micro-CT analysis revealed the internal structure of the spacers was porous and highly inhomogeneous, including heterogeneous dispersion of radiopaque material and cavity defects. The average porosity was 8% (range, 1%–29%) and more than ½ of the spacers had pores greater than 1 mm in diameter.
Our observations suggest dynamic, cement-on-cement spacers allow for increased patient activity without catastrophic failure. Despite the antibiotic loading and internal structural inhomogeneity, burnishing was the only prevalent damage mode that could be consistently classified with no evidence of fracture or delamination. The porous structure of the spacers varied highly across the surfaces without influencing the material failure.
PMCID: PMC3830086  PMID: 22476896
19.  In Vivo Oxidation and Surface Damage in Retrieved Ethylene Oxide-sterilized Total Knee Arthroplasties 
Gas sterilization (eg, ethylene oxide [EtO] and gas plasma) was introduced for polyethylene to reduce oxidation due to free radicals occurring during radiation sterilization. Recently, oxidation has been observed in polyethylenes with undetectable levels of free radicals, which were expected to be oxidatively stable. It is unclear whether in vivo oxidation will occur in unirradiated inserts sterilized with EtO.
We analyzed the oxidation, mechanical behavior, and surface damage mechanisms of tibial inserts of a single design sterilized using EtO.
We collected 20 EtO-sterilized tibial inserts at revision surgeries. We assessed oxidative using Fourier transform infrared spectroscopy and mechanical properties using the small punch test. Surface damage was assessed using damage scoring techniques and micro-CT.
Oxidation indexes were low and uniform between the regions. The subtle changes did not affect the mechanical properties of the polymer. The dominant surface damage modes included burnishing, abrasion, and third-body wear. There was no evidence of delamination in the retrievals.
The retrieved EtO-sterilized UHMWPE retrievals remained stable with respect to both oxidative and mechanical properties for up to 10 years in vivo. We did observe slight measurable amounts of oxidation in the inserts; however, it was far below levels that would be expected to compromise the strength of the polymer.
Clinical Relevance
Due to the stable oxidative and mechanical properties, EtO-sterilized tibial components appear to be an effective alternative to gamma-sterilized inserts, at least in short-term implantations.
PMCID: PMC3369100  PMID: 22125241
20.  Do Ceramic Femoral Heads Reduce Taper Fretting Corrosion in Hip Arthroplasty? A Retrieval Study 
Previous studies regarding modular head-neck taper corrosion were largely based on cobalt chrome (CoCr) alloy femoral heads. Less is known about head-neck taper corrosion with ceramic femoral heads.
We asked (1) whether ceramic heads resulted in less taper corrosion than CoCr heads; (2) what device and patient factors influence taper fretting corrosion; and (3) whether the mechanism of taper fretting corrosion in ceramic heads differs from that in CoCr heads.
One hundred femoral head-stem pairs were analyzed for evidence of fretting and corrosion using a visual scoring technique based on the severity and extent of fretting and corrosion damage observed at the taper. A matched cohort design was used in which 50 ceramic head-stem pairs were matched with 50 CoCr head-stem pairs based on implantation time, lateral offset, stem design, and flexural rigidity.
Fretting and corrosion scores were lower for the stems in the ceramic head cohort (p = 0.03). Stem alloy (p = 0.004) and lower stem flexural rigidity (Spearman’s rho = −0.32, p = 0.02) predicted stem fretting and corrosion damage in the ceramic head cohort but not in the metal head cohort. The mechanism of mechanically assisted crevice corrosion was similar in both cohorts although in the case of ceramic femoral heads, only one of the two surfaces (the male metal taper) engaged in the oxide abrasion and repassivation process.
The results suggest that by using a ceramic femoral head, CoCr fretting and corrosion from the modular head-neck taper may be mitigated but not eliminated.
Clinical Relevance
The findings of this study support further study of the role of ceramic heads in potentially reducing femoral taper corrosion.
PMCID: PMC3773155  PMID: 23761174
21.  When Do Patient-reported Assessments Peak after Revision Knee Arthroplasty? 
The best timing for patient visits after revision TKA is unclear. Predictors of pain and function reported in the literature typically look at the influence at a given time that might not be ideal if the score is not at a peak or the earliest possible time. Moreover, most reports of predictors include revisions for infection, which typically have a poorer outcome, or for other indications with variable outcome.
We therefore determined (1) the trend of recovery after revision TKA to determine the best time to measure the peak patient-reported pain and function scores and (2) the influence of comorbidities and age on the patterns of recovery.
We prospectively followed 120 patients who had revision TKAs from 2003 to 2008. The patients were assessed within 6 weeks before surgery and at 12 weeks, 1 year, and annually thereafter. We obtained WOMAC and SF-36 scores at each visit. We used a linear mixed model analysis to assess predictors. The minimum followup was 2 years (mean, 3 years; range, 2–7 years).
The majority of improvements in the WOMAC and SF-36 scores occurred during the first year after surgery after which the scores stabilized. One of the seven independent preoperative variables studied (comorbidities) predicted a trend toward improvement of WOMAC pain, WOMAC function, and SF-36 bodily pain scores. The greater the numbers of comorbidities, the worse were the scores. Age, gender, BMI, indication for surgery, and surgeon did not independently influence the WOMAC or SF-36.
Our data suggest that one of the times for patient visits after revision TKA should be 1 year after surgery. This time allows for key discrimination of implant performance. The data also confirm that patients with a greater number of comorbidities had less functional benefit from revision surgery.
Level of Evidence
Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3348290  PMID: 22057821
22.  Clinical, radiological, histological and retrieval findings of Activ-L and Mobidisc total disc replacements: a study of two patients 
European Spine Journal  2012;21(Suppl 4):513-520.
This study evaluates the short-term clinical outcome, radiological, histological and device retrieval findings of two patients with second generation lumbar total disc replacement (TDR).
Materials and methods
The first patient had a single level L4-L5 Activ-L TDR, the second patient a L4-L5 Mobidisc and L5-S1 Activ-L TDR. The TDRs were implanted elsewhere and had implantation times between 1.3 and 2.8 years.
Plain radiographs and CT-scanning showed slight subsidence of the Activ-L TDR in both patients and facet joint degeneration. The patients underwent revision surgery because of recurrent back and leg pain. After removal of the TDR and posterolateral fusion, the pain improved. Histological examination revealed large ultrahigh molecular weight polyethylene (UHMWPE) particles and giant cells in the retrieved tissue surrounding the Mobidisc. The particles in the tissue samples of the Activ-L TDR were smaller and contained in macrophages. Retrieval analysis of the UHMWPE cores revealed evidence of minor adhesive and abrasive wear with signs of impingement in both TDR designs.
Although wear was unrelated to the reason for revision, this study demonstrates the presence of UHMWPE particles and inflammatory cells in second generation TDR. Long-term follow-up after TDR is indicated for monitoring wear and implant status.
PMCID: PMC3369030  PMID: 22245852
Total disc replacement; Disc degeneration; (Un)constrained; Revision surgery; Polyethylene wear
23.  Polyethylene Wear in Retrieved Reverse Total Shoulder Components 
Reverse total shoulder arthroplasty has been used to treat rotator cuff tear arthropathy, proximal humeral fractures and for failed conventional total shoulder prostheses. It has been suggested that polyethylene wear is potentially higher in reverse shoulder replacements than in conventional shoulder replacements. The modes and degree of polyethylene wear have not been completely elucidated. The purpose of this study was to evaluate polyethylene wear patterns in seven specimens retrieved at revision arthroplasty and identify factors that may be associated with increased wear.
Reverse total shoulder components were retrieved from 7 patients during revision arthroplasty for loosening and/or pain. Pre-operative glenoid tilt and placement, and scapular notching were evaluated using pre-operative radiographs. Polyethylene wear was evaluated using microCT and optical microscopy.
Wear on the rim of the polyethylene humeral cup, was identified on all retrieved components. The extent of rim wear varied from a penetration depth of 0.1 to 4.7 mm. We could not demonstrate a correlation between scapular notching and rim wear. However, rim wear was more extensive when the inferior screw had made contact with the liner. Metal on metal wear between the humeral component and the inferior screw of one component was also observed. Wear of the intended bearing surface was minimal.
Rim damage was the predominant cause of polyethylene wear in our retrieved specimens. Direct contact between the humeral component and inferior metaglene screws is concerning because this could lead to accelerated UHMWPE wear and also induce mechanical loosening of the glenoid component.
PMCID: PMC3189419  PMID: 21724419
Reverse Total Shoulder Arthroplasty; UHMWPE; Impingement; Scapular Notching; Wear; Retrieval
24.  Are periprosthetic tissue reactions observed after revision of total disc replacement comparable to the reactions observed after total hip or knee revision surgery? 
Spine  2012;37(2):150-159.
Study design
Comparative study.
To compare periprosthetic tissue reactions observed after total disc replacement (TDR), total hip arthroplasty (THA) and total knee arthroplasty (TKA) revision surgery.
Summary of background data
Prosthetic wear debris leading to particle disease, followed by osteolysis, is often observed after THA and TKA. Although the presence of polyethylene (PE) particles and periprosthetic inflammation after TDR has been proven recently, osteolysis is rarely observed. The clinical relevance of PE wear debris in the spine remains poorly understood.
Number, size and shape of PE particles, as well as quantity and type of inflammatory cells in periprosthetic tissue retrieved during Charité TDR (n=22), THA (n=10) and TKA (n=4) revision surgery were compared. Tissue samples were stained with hematoxylin/eosin and examined by using light microscopy with bright field and polarized light.
After THA, large numbers of PE particles <6 µm were observed, which were mainly phagocytosed by macrophages. The TKA group had a broad size range with many larger PE particles and more giant cells. In TDR, the size range was similar to that observed in TKA. However, the smallest particles were the most prevalent with 75% of the particles being <6 µm, as seen in revision THA. In TDR, both macrophages and giant cells were present with a higher number of macrophages.
Both small and large PE particles are present after TDR revision surgery compatible with both THA and TKA wear patterns. The similarities between periprosthetic tissue reactions in the different groups may give more insight in the clinical relevance of PE particles and inflammatory cells in the lumbar spine. The current findings may help to improve TDR design as applied from technologies previously developed in THA and TKA with the goal of a longer survival of TDR.
PMCID: PMC3145819  PMID: 21336235
25.  International survey of primary and revision total knee replacement 
International Orthopaedics  2011;35(12):1783-1789.
Total knee arthroplasty (TKA) is currently the international standard of care for treating degenerative and rheumatologic knee joint disease, as well as certain knee joint fractures. We sought to answer the following three research questions: (1) What is the international variance in primary and revision TKA rates around the world? (2) How do patient demographics (e.g., age, gender) vary internationally? (3) How have the rates of TKA utilization changed over time?
The survey included 18 countries with a total population of 755 million, and an estimated 1,324,000 annual primary and revision total knee procedures. Ten national inpatient databases were queried for this study from Canada, the United States, Finland, France, Germany, Italy, the Netherlands, Portugal, Spain, and Switzerland. Inpatient data were also compared with published registry data for eight countries with operating arthroplasty registers (Denmark, England & Wales, Norway, Romania, Scotland, Sweden, Australia, and New Zealand).
The average and median rate of primary and revision (combined) total knee replacement was 175 and 149 procedures/100,000 population, respectively, and ranged between 8.8 and 234 procedures/100,000 population. We observed that the procedure rate significantly increased over time for the countries in which historical data were available. The compound annual growth in the incidence of TKA ranged by country from 5.3% (France) to 17% (Portugal). We observed a nearly 27-fold range of TKA utilization rates between the 18 different countries included in the survey.
It is apparent from the results of this study that the demand for TKA has risen substantially over the past decade in countries around the world.
PMCID: PMC3224613  PMID: 21404023

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