Michael T. Manley

The basis for a second-generation highly cross-linked UHMWPE

Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) decreases wear at the hip by more than 50% compared with conventional UHMWPE. However, melted highly cross-linked polyethylene may be susceptible to fatigue cracking, and annealed highly cross-linked polyethylene may be susceptible to in vivo oxidation. The second-generation highly cross-linked UHMWPE (X3 HXPE) uses a sequential irradiation and annealing process. It preserves mechanical strength properties and has the highest survivorship in functional fatigue testing. The free radical content is low, and its performance under accelerated aging is the same as virgin UHMWPE. Hip simulator studies with 32-mm acetabular components demonstrated 97% wear reduction compared with conventional UHMWPE, and 62% compared with a clinically successful first-generation annealed highly cross-linked polyethylene. The crystallinity, density, and tensile strength of the X3 HXPE material was unchanged by oxidative challenge. X3 HXPE material articulating on cobalt-chromium alloy yields a volumetric wear rate very similar to that of metal-on-metal articulations, but eliminates the concerns of metal ion release. Wear particles generated from the X3 HXPE were the same size as those produced from conventional UHMWPE. Preliminary results suggest X3 HXPE can be used for cups larger than 36 mm.

Ceramic-on-ceramic total hip arthroplasty: update.

This prospective, randomized, multicenter study of alumina ceramic-on-alumina ceramic bearing couples includes 452 patients (475 hips). Their average age was 53 years with approximately two thirds men and 82% with osteoarthritis. At an average 8-year follow-up, clinical results were excellent and cortical erosions significantly less than in the conventional polyethylene-on-metal bearing group. Nine hips have undergone revision of one or both components for any reason. Of the 380 ceramic liners, 2 (0.5%) have fractured requiring reoperation, and 3 (0.8%) ceramic patients reported a transient squeaking sound, one of which had a head and liner change due to groin pain secondary to psoas tendinitis at 5 years. With no revisions for aseptic loosening and minimal cortical erosions, alumina-ceramic bearing couples are performing in a manner superior to the polyethylene-on-metal bearing in this young, active patient population.

Hydroxyapatite-coated femoral components: 15-year minimum followup.

Hydroxyapatite-coated femoral components were introduced to enhance fixation, but concerns were raised about whether the coating would be maintained over time. We therefore determined the long-term clinical and radiographic results of a proximally hydroxyapatite-coated femoral component and compared the mechanical failure rate to other fixation methods at similar lengths of followup. The study group, culled from a large, multicenter prospective study population, consisted of 146 patients (166 hips) with followup of 15 to 18 years. Average age at time of the index procedure was 51 years, and the most common diagnoses were osteoarthritis (71%) and osteonecrosis (11%). Average Harris hip scores were 42.7 preoperatively and 91.5 at most recent followup. Radiographically, one stem showed stable fibrous fixation, and all other unrevised stems were bony stable. Of 13 stem revisions in the study population, only one stem has been revised for aseptic loosening. Forty-nine percent of hips have an osteolytic lesion in proximal areas of Gruen Zones 1, 7, 8, or 14 only. Both the femoral aseptic revision and mechanical failure rates are 0.6% at 15-year minimum followup. The data demonstrate excellent long-term survivorship of this hydroxyapatite-coated femoral component used in a relatively young patient group.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Hospital, Patient, and Clinical Factors Influence 30- and 90-Day Readmission After Primary Total Hip Arthroplasty.

BACKGROUND The purpose of this study was to analyze the hospital, clinical, and patient factors associated with inpatient readmission after total hip arthroplasty (THA) in the Medicare population and to understand the primary reasons for readmission. METHODS The Medicare 100% national hospital claims database was used to identify 442,333 older patients (65+) with a primary THA in 3730 hospitals between 2010 and 2013. A multilevel logistic regression analysis with a clustered data structure was used to investigate the risk of all-cause 30- and 90-day readmission, incorporating hospital, clinical, and patient factors. RESULTS At 30 days, 5.8% (median) of the patients were readmitted, whereas at 90 days, 10.5% (median) were readmitted. Geographic census region, hospital procedure volume, and nonprofit ownership were the only significant hospital factors among those we studied. Overall, clinical factors explained more of the variation in readmission rates than general hospital factors. Use of a perioperative transfusion was associated with 14% greater risk, patients discharged to home had 28% lower risk, and surgeon volume and length of stay were also significant risk factors. The top 5 most frequently reported primary reasons for 30-day readmission in THA were procedure related: dislocation (5.9%), deep infection (5.1%), wound infection (4.8%), periprosthetic fracture (4.4%), or hematoma (3.4%). CONCLUSION These findings support further optimization of the delivery of care-both intraoperative and postoperative-to reduce the broad variation in hospital readmissions.

Which Hospital and Clinical Factors Drive 30- and 90-Day Readmission After TKA?

BACKGROUND The purpose of this study was to analyze the hospital, clinical, and patient factors associated with inpatient readmission after total knee arthroplasty (TKA) in the Medicare population and to understand the primary reasons for readmission. METHODS The Medicare 100% national hospital claims database was used to identify 952,593 older patients (65+) with a primary TKA in 3848 hospitals between 2010 and 2013. A multilevel logistic regression analysis with a clustered data structure was used to investigate the risk of all-cause 30- and 90-day readmission, incorporating hospital, clinical, and patient factors. RESULTS At 30 days, readmission ranged from 0% to 22% (median, 4.9%), whereas at 90 days, readmission ranged from 0% to 32% (median, 8.6%). Geographic census region, hospital procedure volume, rural hospital location, and nonprofit ownership were the only significant hospital factors among those we studied. Evaluation of clinical factors showed use of a perioperative transfusion was associated with 13% greater risk; patients discharged to home had 25% lower risk; and surgeon volume and length of stay were also significant. These effect sizes were at least comparable to patient factors, such as age, gender, comorbidities, and socioeconomic status. The top 5 most frequently reported primary reasons for 30- or 90-day readmission in TKA were surgery and medical related: wound infection, deep infection, atrial fibrillation, cellulitis and abscess of leg, or pulmonary embolism. CONCLUSION The results of this study support further optimization of anti-infection measures, both intraoperative and postoperative, to reduce the broad variation in hospital readmissions.

Torsional resistance and wear of a modular sleeve-stem hip system

The torsional resistance and wear debris generation of the modular sleeve and stem S-ROM total hip system was evaluated. The results indicate that slippage of the sleeve-stem interface may occur under physiological loading conditions. Slippage is more likely to occur if the junction is contaminated by blood or tissue, or if the stem is disengaged and reimplanted into the sleeve. Significant wear debris was generated during cyclic fatigue loading. The wear debris was of the size (less than 10 mum) readily ingested by macrophages. Particles of these dimensions have been associated with osteolysis, implant loosening and pain. Based upon the findings of this study the implantation of this type system must be carefully considered.

Arc-deposited hydroxyapatite-coated cups: results at four to seven years.

A second-generation arc-deposited hydroxyapatite-coated acetabular component was developed after detailed analysis of a failed first-generation grit-blasted hydroxyapatite-coated cup. In our prospective multicenter study we aimed to compare clinical results and survivorship of the newly designed cup to the previous cup and to a similarly designed porous-coated cup during the same time period. The effect of bearing surface-alumina-on-alumina to polyethylene-on-metal-was analyzed. Consecutive patients were assigned randomly to one of three groups: arc-deposited hydroxyapatite-coated cup with alumina-on-alumina bearing surface; porous-coated cup with alumina-on-alumina bearing surface; or porous-coated cup with polyethylene-on-metal bearing surface. A fourth comparison group with a grit-blasted hydroxyapatite-coated cup and polyethylene-on-metal bearing surface was culled from a previous study. Acetabular mechanical failure rate is 0.0%, 0.0%, 1.9%, and 11.2% for the arc-deposited hydroxyapatite-coated, porous-coated with alumina bearing surface, porous-coated with polyethylene-on-metal bearing, and grit-blasted hydroxyapatite-coated cup, respectively, at 4- to 7-years’ followup. There are no cases of acetabular osteolysis or femoral neck scalloping and no radiolucent lines in any zone with the arc-deposited hydroxyapatite-coated cup. The cups with the alumina-on-alumina bearing surface had less scalloping of the femoral neck than those with a polyethylene-on-metal bearing surface. Early results with this second-generation arc-deposited hydroxyapatite-coated cup are promising. Level of Evidence: Therapeutic study, Level I (high-quality randomized trial with statistically significant difference or no statistically significant difference but narrow confidence intervals). See the Guidelines for Authors for a complete description of levels of evidence.

Has Health Care Reform Legislation Reduced the Economic Burden of Hospital Readmissions Following Primary Total Joint Arthroplasty

BACKGROUND The purpose of this study was to determine whether the cost of readmissions after primary total hip and knee arthroplasty (THA and TKA) has decreased since the introduction of health care reform legislation and what patient, clinical, and hospital factors drive such costs. METHODS The 100% Medicare inpatient dataset was used to identify 1,654,602 primary THA and TKA procedures between 2010 and 2014. The per-patient cost of readmissions was evaluated in general linear models in which the year of surgery and patient, clinical, and hospital factors were treated as covariates in separate models for THA and TKA. RESULTS The year-to-year risk of 90-day readmission was reduced by 2% and 4% (P < .001) for THA and TKA, respectively. By contrast, the cost of readmissions did not change significantly over time. The 5 most important variables associated with the cost of 90-day THA readmissions (in rank order) were the nature of the readmission (ie, due to medical or procedure-related reasons), the length of stay, hospitals teaching status, discharge disposition, and hospitals overall total joint arthroplasty volume. The top 5 factors associated with the cost of 90-day TKA readmissions were (in rank order) the length of stay, hospitals teaching status, discharge disposition, patients gender, and age. CONCLUSION Although readmission rates declined slightly, the results of this study do not support the hypothesis that readmission costs have decreased since the introduction of health care reform legislation. Instead, we found that clinical and hospital factors were among the most important cost drivers.