Once Annealed Highly Cross-Linked Polyethylene Exhibits Low Wear at 9 to 15 Years.

A once annealed highly cross-linked polyethylene (HXLPE) was introduced in 1998. Concerns regarding its long-term performance and oxidative resistance exist because of the presence of retained free radicals. The authors studied 48 patients with 50 hip implants having an average age of 62 years. They were followed for 9 to 15 years. The purpose of this study was to determine linear wear rate and the incidence of osteolysis and/or mechanical failure. At an average follow-up of 12.2 years, the annual linear wear rate was 0.018 mm (SD, 0.024 mm). No mechanical failures or osteolysis have been found to date. The clinical performance of this HXLPE continues to meet expectations despite the presence of free radicals. [Orthopedics. 2016; 39(3):e565-e571.].

Second-Generation Annealed Highly Crosslinked Polyethylene has Low Wear at Mean Seven Year Follow-up.

First-generation once annealed highly crosslinked polyethylene (HXLPE) has perfomed well for over 10 years but the presence of free radicals remain a concern. A second-generation sequentially annealed HXLPE was developed to further reduce wear, maintain mechanical strength, and enhance oxidative resistance.

High survivorship with a titanium-encased alumina ceramic bearing for total hip arthroplasty.

BACKGROUND: Although ceramic-on-ceramic bearings for total hip arthroplasty (THA) show promising results in terms of bearing-surface wear, fracture of the bearing, insertional chips, and squeaking remain a concern. QUESTIONS/PURPOSES: Our primary objective of this report was to determine overall survivorship of a titanium-encased ceramic-on-ceramic bearing couple. Our secondary objectives were to evaluate for ceramic fracture, insertional chips, osteolysis, and device squeaking. METHODS: Six surgeons at six institutions implanted 194 patients (209 hips) with an average age of 52 years with cementless hips and alumina ceramic bearings. One hundred thirty-seven patients (146 hips) have 10-year followup (70%). We determined Kaplan-Meier survivorship of the bearing surface and implant system and collected radiographic and clinical data to evaluate for osteolysis and squeaking. RESULTS: Survivorship using revision for any reason as the end point was 97% at 10 years and survivorship end point bearing surface failure or aseptic loosening of 99%. There was one ceramic insert fracture (0.5%), there were no insertional chips, there was no visible osteolysis on AP and lateral radiographs, and there was a 1% patient-self-reported incidence of squeaking at the last clinical followup. Six hips underwent revision (3.7%). CONCLUSIONS: Ceramic bearings for THA with a titanium-encased insert have high survivorship at 10 years followup and a fracture risk of 0.5%. We found at last followup on routine radiographs no evidence of osteolysis, and no patient has been revised for squeaking or has reported dissatisfaction with the clinical result because of noise. IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Periprosthetic fractures around a cementless hydroxyapatite-coated implant: a new fracture pattern is described.

BACKGROUND: Periprosthetic fractures can occur both intraoperatively and postoperatively with implantation of cementless tapered stems. QUESTIONS/PURPOSES: In a large cohort of patients receiving cementless, proximally hydroxyapatite-coated femoral implants, we answered the following questions: What was the incidence of intraoperative and postoperative fractures associated with the implant? What were the fracture patterns as classified by the Vancouver classification system? Did the Vancouver classification represent the fracture patterns found? How were the fractures treated and what were the treatment outcomes; that is, how many fractures healed and did the stems osseointegrate? METHODS: We evaluated 1039 hips (932 patients) from three prospective studies. The hips were divided into three groups: no fractures, intraoperative fractures, and postoperative fractures. Demographic differences among the groups were noted. Postoperative fractures were classified using the Vancouver classification system. We judged stem stability using Engh's criteria and fracture union was determined by the treating surgeon and confirmed by the authors. RESULTS: We identified 58 periprosthetic fractures in the 1039 hips (5.6%): 38 intraoperative (3.7%) and 20 postoperative (1.9%). Eleven of the postoperative fractures were classifiable by the original Vancouver classification system and nine were of the newly described "clamshell" variety, not classifiable by this system. No intraoperative fractures extended below the lesser trochanter. Twenty-five of these fractures were treated with a single cable or cerclage wire. The remaining received no specific treatment. Of the 20 postoperative fractures, five were treated nonoperatively. All stems osseointegrated. CONCLUSIONS: Both intraoperative and postoperative fractures can be managed with success when the stem is stabilized or found to be osseointegrated. An adjustment to the Vancouver classification is suggested to include the clamshell fracture, which has not been previously described.

Ceramic bearings for total hip arthroplasty have high survivorship at 10 years.

BACKGROUND: Ceramic bearings were introduced to reduce wear and increase long-term survivorship of total hip arthroplasty. In a previous study comparing ceramic with metal-on-polyethylene at 5 to 8 years, we found higher survivorship and no osteolysis for the ceramic bearings. QUESTIONS/PURPOSES: We asked whether ceramic bearings have equal or superior survivorship compared with that for metal-on-polyethylene at longer followup; we also determined survivorship of the implant systems, the presence or absence of radiographic osteolysis, and incidence of device squeaking. METHODS: Five surgeons at five sites have followed 189 patients (216 hips) for a minimum of 10 years and average of 10.3 years (range, 10-12.4 years) comparing alumina ceramic bearings (144 hips) with cobalt chrome-on-polyethylene bearings (72 hips). We determined Kaplan-Meier survivorship of the bearing surface and implant systems and collected radiographic and clinical data. RESULTS: We observed no difference between the control metal-on-polyethylene and the alumina-bearing couple cohorts with regard to bearing-related failures (98.9% versus 99.1%). Revisions for any reason occurred in 10.5% of the control patients and 3.1% of the patients with alumina bearings. All femoral implants remain well fixed (100%), whereas one acetabular component (1%) is unstable in the control group. Osteolysis occurred in 26% of the control patients and in none of the patients with alumina bearings. Squeaking occurred in two of 144 hips (1.4%) of the patients with ceramic bearings. CONCLUSIONS: Patients receiving the ceramic-on-ceramic bearings had fewer revisions for any reason and less osteolysis than the control metal-on-polyethylene at 10 years. Our data suggest ceramic bearings continue to provide an option for the young and more active patient and provide for a measure to compare other new alternative bearings that are currently available. LEVEL OF EVIDENCE: Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Second-generation annealed highly cross-linked polyethylene exhibits low wear.

BACKGROUND: Compared with conventional polyethylene, first-generation highly cross-linked polyethylenes have low wear, but controversy exists regarding their reduced mechanical strength and/or retained free radicals. Second-generation highly cross-linked polyethylenes have been developed to reduce wear, maintain mechanical strength, and have oxidative resistance, but it is unclear whether they do so. QUESTIONS/PURPOSES: The primary objective of this study therefore was to determine if a second-generation annealed material has low linear wear at 5 years followup. Secondary objectives were to evaluate for overall survivorship, implant fixation, osteolysis, and effect of socket inclination on wear. METHODS: In a multicenter prospective study, we radiographically evaluated 155 patients (167 hips) at 3 years, 124 patients (132 hips) at 4 years, and 46 patients (51 hips) at 5 years. The linear head penetration rate was measured at 6 weeks, 1 year, and yearly through 5 years. RESULTS: The head penetration per year after the first year of bedding-in was 0.024 mm per year at 3 years, 0.020 mm per year at 4 years, and 0.008 mm per year at 5 years. The average wear rate over 5 years was 0.015 mm per year and represents a 58% improvement over a first-generation annealed highly cross-linked polyethylene. The Kaplan-Meier survivorship (revision for any reason) was 97.8%. We revised no hip for bearing surface failure and observed no osteolysis. Socket inclination did not affect linear wear. CONCLUSIONS: These data suggest the linear wear rate for a second-generation annealed highly cross-linked polyethylene is no greater than that for historic controls of first-generation highly cross-linked polyethylenes, and no untoward complications were encountered with this new material. LEVEL OF EVIDENCE: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Ceramic-on-ceramic hip outcome at a 5- to 10-year interval: has it lived up to its expectations?

This study reports revision and complication rates of a single cementless double-wedged tapered stem with an alumina-alumina bearing over 10 years since the beginning of premarket clinical trials. Of 930 hips (848 patients) implanted by 9 surgeons, there were 19 revisions at mean follow-up of 5.9 years compared to 10 revisions in the 123 hips implanted with the polyethylene control group at mean 7.8 years. The ongoing safety of alumina-alumina bearings is demonstrated through excellent (96.8%) survivorship at 10 years. Twenty-one patients reported 23 incidences of noise described as clicking, squeaking, popping, or creaking. Eight patients with 9 hips described the noise as squeaking, most occurring rarely and only 1 occurring frequently in a patient subsequently revised for a reason aside from the squeaking.

Continued improved wear with an annealed highly cross-linked polyethylene.

BACKGROUND: Highly cross-linked polyethylene (HXLPE), created by disrupting the molecular structure of polyethylene, then through the application of heat, encourages creation of new cross-links in the process, resulting in a material with improved wear resistance. The impetuses for this new technology were the unsatisfactory wear properties and subsequent osteolysis of noncross-linked polyethylene. A 72% reduction in wear using highly cross-linked polyethylenes (HXLPE) compared with conventional polyethylene at 5 years was described previously. The longest term followup studies on HXLPE range from 2 to 6 years. QUESTIONS/PURPOSES: We therefore addressed the following questions: (1) Does the improvement in wear observed at the earlier followup continue to 7 to 10 years? (2) What is the incidence of osteolysis in this group of patients and in the control group? METHODS: We retrospectively reviewed 38 prospectively followed patients who had 42 hips with an annealed HXLPE who were followed a minimum of 7 years (average, 8.6 years; SD=1; range, 7-10.3 years). Wear and osteolysis were compared with those of a control group of 39 patients (40 hips) from a US Investigational Device Exemption (IDE) prospective, randomized study begun in 1996 with conventional polyethylene and followed for a minimum of 6 years (average, 7.5 years; SD=1.1; range, 6-10.2 years). Linear head penetration was measured from AP radiographs at early, 1-year, 5-year, and most recent followups. RESULTS: At the average followup, annual linear wear was 0.031 mm (SD=0.014) for the HXLPE and 0.141 mm (SD=0.080) for the control group, a 78% reduction. No mechanical failure of the polyethylene was noted in either group. Incidence of osteolysis was 50% in the control group (all lesions confined to proximal Gruen Zones 1 and 7) compared with no cases in the investigational group. CONCLUSIONS: We observed an improvement in wear and no mechanical failures with this annealed material. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Ceramic materials as bearing surfaces for total hip arthroplasty.

During the past decade, advances in total hip arthroplasty component design have produced implants with reliable clinical results in regard to fixation. The foremost unresolved challenge has been the development of bearing surfaces that can withstand the higher demands of younger and more active patients. New alternative bearings with superior wear characteristics that minimize debris include ceramic-on-ceramic, metal-on-metal, and highly cross-linked polyethylenes in combination with ceramic or metal. Alumina-on-alumina ceramic bearings are extremely hard and scratch resistant and provide superior lubrication and wear resistance compared with other bearing surfaces in clinical use. Survivorship revision for any reason for the alumina ceramic bearings at 10 years was significantly higher compared with metal-on-polyethylene. Bearings currently being studied because of their encouraging wear performance in the laboratory are an alumina matrix (82% alumina, 17% zirconia, 0.3% chromium oxide), zirconium oxide, and ceramic-on-cobalt-chromium.

Late remodeling around a proximally HA-coated tapered titanium femoral component.

UNLABELLED: Most bone remodeling is thought to occur within the first few years after THA. Loss of bone density later may be associated with stress shielding or normal bone loss of aging. We evaluated remodeling changes over time with a proximally hydroxyapatite-coated tapered titanium stem. We evaluated plain radiographs of 143 hips for cancellous condensation, cortical hypertrophy, cortical porosis, cortical index, and canal fill at early postoperative, 5, 10, and 15 years. Average age was 51 years at THA; 69 patients (77 hips) (53%) were women; and 102 hips (71%) had primary osteoarthrosis. Based on radiographic findings at 15 years, hips were divided into three subgroups: 43 (30%) demonstrated minimal remodeling changes; 53 (37%) demonstrated cortical hypertrophy evident before 5 years; and 47 (33%) demonstrated additional late remodeling and cortical porosis, most often after 10 years. Hips with poorer bone (Dorr Types B or C) and, when including only hips with osteoarthrosis, more female hips had cortical porosis at 15 years. Late radiographic changes in patients with porosis appear more similar to that associated with an extensively rather than proximally coated stem. Whether continued bone adaptation and bone loss of aging will eventually threaten implant stability is unknown, but at 15 years, all 143 implants remained well fixed and clinically asymptomatic. LEVEL OF EVIDENCE: Level III, retrospective study. See the Guidelines for Authors for a complete description of levels of evidence.

The classification of implants: class I, II, III.

Medical implants fall under the larger category of medical devices, which are defined as products used for medical purposes in patients, in diagnosis and/or treatment. There are three classes of devices that are controlled by the Food and Drug Administration (FDA). Class I devices present the lowest safety risk and are only subject to general controls; Class II devices require general and special controls involving labeling requirements, mandatory performance standards and adequate surveillance; Class III devices must have the same general and special controls as Class I and II devices, and undergo scientific review. Class III is the most scientifically rigorous classification of medical devices and encompasses most of the orthopedic implants on the market today. In this paper, different categories of orthopedic implants will be discussed, including the development of artificial anterior cruciate ligament (ACL) grafts and FDA approval of alumina ceramic-on-ceramic (COC) total hip prostheses.

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.

Ceramic-on-ceramic total hip arthroplasty early dislocation rate.

Wear debris from metal-on-polyethylene articulation in conventional total hip arthroplasty can limit the implant's longevity. Modern ceramic material with high wear resistance and low fracture risk has the potential to extend the lifetime of total hip arthroplasty, which makes the procedure potentially more suitable for young, active patients. Concerns with brittle ceramic material include fracture risk, the "squeak" phenomenon, and potentially a higher dislocation rate secondary to limited neck lengths and liner options. We therefore determined the early dislocation rate in modern ceramic-on-ceramic total hip arthroplasty. In 1635 total hip arthroplasties performed over the 9-year period (1996-2005), we observed three anterior and 15 posterior dislocations (1.1%). All were treated successfully, one with a revision and 17 with closed reduction under general anesthesia. Ceramic-on-ceramic total hip arthroplasty can be a good alternative bearing surface with a low dislocation rate.

Return to athletic activity after total hip arthroplasty. Consensus guidelines based on a survey of the Hip Society and American Association of Hip and Knee Surgeons.

A web-based survey was developed to evaluate joint arthroplasty surgeon's preferences for the return to sporting activities after total hip arthroplasty. This survey listed 30 groups of activities (37 specific sports) and was sent to all members of the Hip Society and American Association of Hip and Knee Surgeons. All surgeons were asked to grade each activity as follows: allow, allow with experience, not allowed, or undecided. Results were computed using a power analysis, Z test, and chi(2) test to determine statistical significance. There were a total of 549 responses giving an overall response rate of 72%, with 93% (92/99) of the Hip Society members and 72% (522/727) of American Association of Hip and Knee Surgeons members responding to the survey. Consensus guidelines and postoperative timing for the return to specific activities are presented.

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.

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.

Translating the results of randomized trials into clinical practice: the challenge of warfarin candidacy among hospitalized elderly patients with atrial fibrillation.

BACKGROUND AND PURPOSE: Numerous studies have documented under use of warfarin particularly among elderly patients. A better understanding of the discrepancy between trials and clinical practice will help inform stroke prevention strategies in this vulnerable age group. The study objective was to prospectively assess the use of antithrombotic therapy among a contemporary cohort of patients with atrial fibrillation at the time of hospital discharge. In addition to baseline characteristics, we sought to define the physician-cited reason for not prescribing warfarin for each patient. METHODS: Patients with atrial fibrillation were prospectively identified and followed to hospital discharge. Enrolled patients were > or =65 years of age, not taking warfarin on admission, and had their longitudinal care provided at our institution. Predictors of warfarin use were determined and physician-cited contraindications were compared across age groups. RESULTS: Fifty-one percent (n=206) of patients were discharged on warfarin: 75% of those 65 to 69 years of age, 59% 70 to 79, 45% 80 to 89, and 24% age > or =90 years. Of the remaining 199 patients, 83% had > or =2 major risk factors for stroke, and 98% were felt to have contraindications including nearly 25% who were unable to tolerate warfarin in the past. Among patients age > or =80, falling was the most often physician-cited reason for not prescribing warfarin (41%) followed by hemorrhage (28%). CONCLUSIONS: Our findings suggest that many elderly patients at high risk for stroke may not be optimal candidates for anticoagulant therapy. There is a pressing need for alternative stroke prevention strategies for this expanding patient population.