Improvements to the calibration of the MST Thomson scattering diagnostic.

Calibration of the Madison Symmetric Torus Thomson scattering system has been refined to improve temperature fluctuation measurements. Multiple avalanche photodiodes have been directly calibrated for use as reference detectors during calibration, improving accuracy and ease of use. From the absolute calibration we calculate corrections to the gain for variation in detector operating temperature. We also measure the spatial uniformity of detector responsivity for several photodiodes, and present a method of accounting for non-uniformity in the calibration process. Finally, the gain and noise enhancement are measured at multiple wavelengths to improve temperature and uncertainty measurements.

In vivo comparative wear study of traditional and highly cross-linked polyethylene in total hip arthroplasty.

In this study, we compare the in vivo wear performance of electron beam-irradiated, postirradiation-melted, highly cross-linked polyethylene (HXLPE) and traditional UHMWPE via the Martell method. Seventy hips with HXLPE performed at the Massachusetts General Hospital had 138 radiograph pairs for wear analysis and a 31.2-month average follow-up (range, 24-44 months). An age-matched, sex-matched, and body mass index-matched subgroup of 111 hips with 214 acceptable radiograph pairs and a 4-year follow-up from our previously published study on traditional polyethylene performed at Rush-Presbyterian-St. Luke's Medical Center served as a control group. Martell wear analysis was performed for each group. Overall and steady-state wear rates were compared via a specialized t test. The steady-state wear in the HXLPE arm was observed after 2.0 years, was 0.007 mm/y, and was significantly less than the steady-state wear in the traditional arm (0.174 mm/y) (P = .003). Highly cross-linked polyethylene penetration rate was not affected by sex, age, activity, or body mass index by Mann-Whitney analysis.

Alpha-tocopherol-doped irradiated UHMWPE for high fatigue resistance and low wear.

Longevity of total joints has been compromised by wear and fatigue of ultrahigh molecular weight polyethylene (UHMWPE) components. Crosslinking reduces UHMWPE wear, but combined with postirradiation melting, also reduces its fatigue strength, therefore limiting its use in high-stress applications. We hypothesized that a lipophilic antioxidant (alpha-tocopherol, alpha-T) can protect UHMWPE against oxidation eliminating the need for postirradiation melting of crosslinked UHMWPE and improve its fatigue strength. To test these hypotheses, 65- and 100-kGy irradiated, alpha-T-doped and subsequently gamma-sterilized UHMWPE were used. (I) alpha-T-doped irradiated UHMWPEs showed significantly lower oxidation levels (0.48+/-0.25 and 0.44+/-0.06) compared to 100-kGy irradiated UHMWPE (3.74+/-0.16) after 5 weeks of accelerated aging at 80 degrees C in air. (II) Wear rate of alpha-T-doped irradiated UHMWPE (1.9+/-0.5, and 0.9+/-0.1mg/million cycles (MC) for 65- and 100-kGy irradiated UHMWPE, respectively) were comparable to that of 100-kGy irradiated/melted UHMWPE (1.1+/-0.7mg/million cycles). (III) The stress intensity factor at crack inception ( DeltaKi) of 100-kGy irradiated UHMWPE increased significantly upon doping with alpha-T from 0.74 to 0.87MPam(1/2) ( p<0.01 ). The DeltaKi for the 100-kGy irradiated and melted UHMWPE, currently in clinical use, was 0.55MPam(1/2). Doping with alpha-T eliminated the need for postirradiation melting to protect irradiated UHMWPE against long-term oxidation. The fatigue strength was improved by 58% for alpha-T-doped 100-kGy irradiated UHMWPE compared to irradiated and melted UHMWPE. The increase in oxidative stability of alpha-T-doped UHMWPE is attributed to the ability of alpha-T to react with peroxy free radicals on lipid chains and arrest the oxidation reactions. The improved fatigue strength is attributed to the increase in plasticity of UHMWPE due to the lipophilic nature of alpha-T.

The three revolutions in acetabular revision surgery for total hip replacement: 1. Definite and 2. Probable.

Acetabular revision surgery has been and remains a difficult challenge in total hip replacement surgery. Cemented acetabular revisions have not worked out as well as would be desirable. With the introduction of the hemispherical cementless acetabular component, either pressfit or fixed with screws, a major change has been accomplished in the problem of fixation. This is the first revolution in acetabular revision surgery. The second and third revolutions are potential and important. The second revolution that may take place is the reduction in periprosthetic osteolysis, secondary to the use of highly crosslinked, melted, polyethylene. The third potential revolution is the reduction in the incidence of dislocation that could result from the use of heads of larger diameter. The in vitro studies suggest that certain highly crosslinked polyethylenes can be used with a larger head diameter without the risk of a major increase in particulate debris. Potentially this could address many of the issues of the high incidence of dislocation following acetabular revisions. In addition, the combination of a large head and a highly crosslinked polyethylene has allowed a new form of constrained acetabular component to be designed. This many be another advance in terms of the problems of recurrent dislocation.

Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: a new concept.

The design of femoral and acetabular components of metal-on-polyethylene total hip arthroplasty implants has been dominated by the limitations of the wear properties of ultra-high molecular weight polyethylene (UHMWPE). As a result, the commonest femoral head diameters used range from 22 to 32 mm, the latter producing maximal volumetric wear. Cross-linking has been shown to improve significantly the wear resistance of acetabular components when tested in vitro against conventional femoral head sizes (22-32 mm). We expanded the study of the wear behavior of 1 type of electron-beam cross-linked UHMWPE with femoral head diameters ranging from 22 to 46 mm. The simulated gait studies showed that wear was independent of head size for the range of femoral head sizes studied. Even for the 46-mm femoral head, wear was reduced significantly using criteria of gravimetric and geometric measurements and morphologic appearance of the machining marks out to 11 million cycles of simulated gait.

A novel constrained acetabular liner design with increased range of motion.

One treatment strategy for recurrent dislocation after total hip arthroplasty is the use of a constrained acetabular component. A major drawback of currently available constrained components is the limited range of motion (ROM). We present a novel constrained component that employs a monopolar, highly cross-linked polyethylene liner with cutouts oriented to allow increased ROM, while maintaining constraint against dislocation. ROM and lever-out tests comparing this novel design with a conventional constrained component showed that the cutaway monopolar component allowed ROM substantially greater than a currently available design. The lever-out torque for the cutaway monopolar constrained component was 243% higher than the conventional constrained component. This novel constrained acetabular component offers promise for providing excellent constraint against dislocation, while maintaining a wide ROM.

A critical assessment of proximal macrotexturing on cemented femoral components.

We analyzed the cement-metal interface of 3 different types of femoral components that had proximal macrotexturing after in vitro insertion and after fatigue testing designed to produce debonding and micromotion. These components were compared with clinical retrieval specimens. The cement did not flow into the macrotexturing; rather, hollow, brittle volcanoes or calderas were formed. These fragile protrusions of cement become worn down or abraded by debonded components. This abrasion of cement may contribute to the early and aggressive osteolysis seen in some of these early failures with proximal macrotextured components. The formation of these volcanos and calderas can be aborted by placing bone-cement onto the macrotexturing before stem insertion. This simple technique allows the macrotexturing to be filled with cement.

An electronic database for outcome studies that includes digital radiographs.

We report on acquisition of key data from the clinical medical record, surgical data, radiologic studies, and patient surveys for a novel digital total hip arthroplasty (THA) registry that includes electronic capture of digital radiographic images into a database on an internet platform for query. We now have the ability to collect demographic and operative data, including the operative note, discharge summary, surgery data, and Digital Imaging Communications in Medicine (DICOM) radiology images. Steps are being completed to assemble office encounters, hospital procedural codes, and implant bar codes. Two examples include a THA surgery record and a THA outcome study with plain radiograph set. Analysis of such data could suggest ways to improve clinical practice.

Association between hospital and surgeon procedure volume and outcomes of total hip replacement in the United States medicare population.

BACKGROUND: The mortality and complication rates of many surgical procedures are inversely related to hospital procedure volume. The objective of this study was to determine whether the volumes of primary and revision total hip replacements performed at hospitals and by surgeons are associated with rates of mortality and complications. METHODS: We analyzed claims data of Medicare recipients who underwent elective primary total hip replacement (58,521 procedures) or revision total hip replacement (12,956 procedures) between July 1995 and June 1996. We assessed the relationship between surgeon and hospital procedure volume and mortality, dislocation, deep infection, and pulmonary embolus in the first ninety days postoperatively. Analyses were adjusted for age, gender, arthritis diagnosis, comorbid conditions, and income. Analyses of hospital volume were adjusted for surgeon volume, and analyses of surgeon volume were adjusted for hospital volume. RESULTS: Twelve percent of all primary total hip replacements and 49% of all revisions were performed in centers in which ten or fewer of these procedures were carried out in the Medicare population annually. In addition, 52% of the primary total hip replacements and 77% of the revisions were performed by surgeons who carried out ten or fewer of these procedures annually. Patients treated with primary total hip replacement in hospitals in which more than 100 of the procedures were performed per year had a lower risk of death than those treated with primary replacement in hospitals in which ten or fewer procedures were performed per year (mortality rate, 0.7% compared with 1.3%; adjusted odds ratio, 0.58; 95% confidence interval, 0.38, 0.89). Patients treated with primary total hip replacement by surgeons who performed more than fifty of those procedures in Medicare beneficiaries per year had a lower risk of dislocation than those who were treated by surgeons who performed five or fewer of the procedures per year (dislocation rate, 1.5% compared with 4.2%; adjusted odds ratio, 0.49; 95% confidence interval, 0.34, 0.69). Patients who had revision total hip replacement done by surgeons who performed more than ten such procedures per year had a lower rate of mortality than patients who were treated by surgeons who performed three or fewer of the procedures per year (mortality rate, 1.5% compared with 3.1%; adjusted odds ratio, 0.65; 95% confidence interval, 0.44, 0.96). CONCLUSIONS: Patients treated at hospitals and by surgeons with higher annual caseloads of primary and revision total hip replacement had lower rates of mortality and of selected complications. These analyses of Medicare claims are limited by a lack of key clinical information such as operative details and preoperative functional status.

Hybrid revision total hip arthroplasty: a 7-year follow-up study.

The hybrid method for fixation of total hip arthroplasty (THA) has shown excellent results during the first decade in primary operations. To investigate its role in revision surgery, data on 48 revision THAs in 45 patients that met the inclusion criteria were gathered prospectively, using HGP cementless acetabular components and precoated cemented femoral components inserted with so-called second generation femoral cementing technique in each case. For the 48 hips during an average follow-up period of 7.4 years, no acetabular components was loose or had pelvic lysis. One acetabular component was revised for recurrent dislocation; 1 of 48 femoral components was revised for aseptic loosening and 1 for periprosthetic fracture. Three additional femoral stems (6%) were loose. In this small series, the hybrid concept for revision of failed nonseptic THAs has shown excellent results.

Matched-pair analysis of cemented and cementless acetabular reconstruction in primary total hip arthroplasty.

In a matched-pair study of primary total hip arthroplasty, 45 all-polyethylene cemented acetabular components were compared with 45 cementless, hemispheric, titanium acetabular components. At 9 to 12 years, 1 of the cemented acetabular components was revised for aseptic loosening, and 14 (31%) were radiographically loose. Nine (20%) cemented acetabular components had pelvic osteolysis. In the cementless acetabular component group, 2 well-fixed components were revised. No components were radiographically loose, and 3 (7%) had pelvic osteolysis. Thirty-eight (97%) of the patients in each group were satisfied with the surgery. The clinical results of the cemented and cementless components were excellent. The cementless components had less loosening (P <.001) than the cemented components.

The Harris hip score: comparison of patient self-report with surgeon assessment.

Outcome evaluations are of primary concern in contemporary medical practice. Questionnaires are being used increasingly to provide input data for such outcomes evaluation. This study comprised 50 primary total hip arthroplasties in 36 patients who had undergone the procedure at least 12 months before enrollment. Each patient completed a self-report Harris Hip Score (HHS) 30 days before a formal evaluation by an independent orthopaedic surgeon that included a HHS. Comparison was made between the completed responses to the individual items on the self-report HHS and surgeon-assessed HHS. Concordance of item response and kappa statistic were calculated. Overall the self-report and surgeon-assessed HHS showed excellent concordance. The results of this study support the use of the HHS as a self-report instrument.

A new pin-on-disk wear testing method for simulating wear of polyethylene on cobalt-chrome alloy in total hip arthroplasty.

Hip simulator studies show that the wear of ultra-high molecular weight polyethylene against a cobalt alloy head depends on the wear path, especially the combination of a predominantly linear wear direction on which is superimposed motions in different directions. We postulated that multidirectional motion was necessary to generate realistic wear rates in pin-on-disk testing. To assess this hypothesis, a new pin-on-disk tester was developed, capable of unidirectional and bidirectional motion. Unidirectional motion produced no detectable wear. The rectangular motion produced wear rates, surface morphologies, and wear particles consistent with human acetabular specimens. The results for 1 Hz and 2 Hz were similar.

Identification and quantification of irradiation in UHMWPE through trans-vinylene yield.

trans-Vinylene unsaturations generated in ultrahigh-molecular-weight polyethylene (UHMWPE) after radiation treatment scales linearly with the absorbed dose level, and can serve as an internal dosimeter for determining the radiation dose level for sterilizing or crosslinking UHMWPE. We measured the trans-vinylene concentration using infrared spectroscopy and generated calibration curves for ultrahigh-molecular-weight polyethylene (ram-extruded GUR 1050) after cold e-beam, cold gamma, and warm e-beam irradiations. The trans-vinylene content increased linearly with the absorbed dose level in all cases except with cold gamma irradiation at dose levels higher than approximately 70 kGy. At that dose level the trans-vinylene content of the warm irradiated samples was higher than those of the cold irradiated samples. Following postirradiation melting, the trans-vinylene content of the gamma irradiated samples increased. Such trans-vinylene quantification can be an internal dosimeter for crosslinked UHMWPE when radiation is used for improving its wear resistance or sterilizing the device made thereof. It can also be utilized to assess the spatial uniformity of the absorbed radiation dose level.

Cross-linked polyethylene: why the enthusiasm?

If these materials behave in vivo as they do in vitro and if no unexpected complications occur, periprosthetic osteolysis should be reduced, the duration of THR success should be greater, and the percentage of complications should be lower. Femoral loosening, socket loosening, and pelvic and femoral lysis should be reduced. There should be fewer revisions and dislocations and a greater range of motion. [Table: see text] If these improvements come to pass, use of the new materials may be an important advance in THR surgery.

A novel method of cross-linking ultra-high-molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties. Recipient of the 1999 HAP Paul Award.

Increasing cross-linking has been shown in vitro and in vivo to improve markedly the wear resistance of ultra-high-molecular-weight polyethylene (UHMWPE). The reduction in the mechanical properties of polyethylene under certain methods used to produce cross-linking has been a concern, however. These reductions are known to result from the processes used to increase the cross-link density and could affect the device performance in vivo. We present a novel method of increasing the cross-link density of UHMWPE in which UHMWPE is irradiated in air at an elevated temperature with a high-dose-rate electron beam and subsequently is melt-annealed. This treatment improves markedly the wear resistance of the polymer as tested in a hip simulator, while maintaining the mechanical properties of the material within national and international standards. This method leads to the absence of detectable free radicals in the polymer and, as a result, excellent resistance to oxidation of the polymer.

Loss of heterozygosity mapping at chromosome arm 16q in 712 breast tumors reveals factors that influence delineation of candidate regions.

Loss of heterozygosity (LOH) at the long arm of chromosome 16 occurs in at least half of all breast tumors and is considered to target one or more tumor suppressor genes. Despite extensive studies by us and by others, a clear consensus of the boundaries of the smallest region of overlap (SRO) could not be identified. To find more solid evidence for SROs, we tested a large series of 712 breast tumors for LOH at 16q using a dense map of polymorphic markers. Strict criteria for LOH and retention were applied, and results that did not meet these criteria were excluded from the analysis. We compared LOH results obtained from samples with different DNA isolation methods, ie., from microdissected tissue versus total tissue blocks. In the latter group, 16% of the cases were excluded because of noninterpretable LOH results. The selection of polymorphic markers is clearly influencing the LOH pattern because a chromosomal region seems more frequently involved in LOH when many markers from this region are used. The LOH detection method, i.e., radioactive versus fluorescence detection, has no marked effect on the results. Increasing the threshold window for retention of heterozygosity resulted in significantly more cases with complex LOH, i.e., several alternating regions of loss and retention, than seen in tumors with a small window for retention. Tumors with complex LOH do not provide evidence for clear-cut SROs that are repeatedly found in other samples. On disregarding these complex cases, we could identify three different SROs, two at band 16q24.3 and one at 16q22.1. In all three tumor series, we found cases with single LOH regions that designated the distal region at 16q24.3 and the region at 16q22.1. Comparing histological data on these tumors did not result in the identification of a particular subtype with LOH at 16q or a specific region involved in LOH. Only the rare mucinous tumors had no 16q LOH at all. Furthermore, a positive estrogen content is prevalent in tumors with 16q LOH, but not in tumors with LOH at 16q24.3 only.

Wear and periprosthetic osteolysis: the problem.

The dominant long-term problem in total hip replacement surgery, and an important problem in total knee replacement surgery, is wear of the polyethylene and its resulting periprosthetic osteolysis. Several of the key features of this unique disease are presented focusing on the importance of periprosthetic osteolysis, comprehension of the general progressive nature of periprosthetic osteolysis, understanding of the diverse radiographic evidence of this disease, and the consequences that can occur from the disease.