Polyethylene wear, osteolysis and acetabular loosening with an HA-coated hip prosthesis. A follow-up of 94 consecutive arthroplasties

Favourable clinical outcomes following cemented arthroplasty after metal-on-metal total hip replacement: a retrospective study with a mean follow-up of 10 years

BACKGROUND

Given the unexpected high rate of failure following metal-on-metal total hip replacement (MoM-THR), it is expected that more MoM-THR patients will experience revision. The long-term outcomes regarding the primary MoM-THR revised to cemented THR (CTHR) remain controversial. The purpose of this retrospective review was to evaluate the long-term outcomes of patients who underwent conversion from MoM-THR to CTHR.

METHODS

A total of 220 patients (220 hips) who underwent a conversion of primary MoM-THR to CTHR from March 2006 to October 2016 were retrospectively reviewed. The primary outcomes were the functional outcomes assessed using the Harris hip scores (HHS) and major radiographic outcomes. Follow-ups occurred at 3 months, 6 months, 1 year, 2 years, and then every two years after revision.

RESULTS

Mean follow-up was 10.1 years (5-13 years). Distinct improvements were detected in the mean HHS between the preoperative and last follow-up analysis (62.35[±8.49] vs. 84.70[±14.68], respectively, p < 0.001). The key orthopaedic complication rate was 18.2% (27/148). Seven (4.7%) cases experienced a CTHR failure at a mean of 3.4 (±1.2) years after revision MoM-THR, mostly attributed to recurrent dislocation.

CONCLUSION

CTHR might yield an acceptable functional score and a low rate of the key orthopaedic complications.

Structural and Chemical Hierarchy in Hydroxyapatite Coatings

Hydroxyapatite coatings need similarly shaped splats as building blocks and then a homogeneous microstructure to unravel the structural and chemical hierarchy for more refined improvements to implant surfaces. Coatings were thermally sprayed with differently sized powders (20–40, 40–63 and 63–80 µm) to produce flattened homogeneous splats. The surface was characterized for splat shape by profilometry and Atomic force microscopy (AFM), crystal size by AFM, crystal orientation by X-ray diffraction (XRD) and structural variations by XRD. Chemical composition was assessed by phase analysis, but variations in chemistry were detected by XRD and Raman spectroscopy. The resulting surface electrical potential was measured by Kelvin probe AFM. Five levels of structural hierarchy were suggested: the coating, the splat, oriented crystals, alternate layers of oxyapatite and hydroxyapatite (HAp) and the suggested anion orientation. Chemical hierarchy was present over a lower range of order for smaller splats. Coatings made from smaller splats exhibited a greater electrical potential, inferred to arise from oxyapatite, and supplemented by ordered OH⁻ ions in a rehydroxylated surface layer. A model has been proposed to show the influence of structural hierarchy on the electrical surface potential. Structural hierarchy is proposed as a means to further refine the properties of implant surfaces.

Fracture of the Neck of a Modern Cementless, Titanium Femoral Stem

Intraprosthetic fracture of a femoral component is a rare but devastating complication after total hip arthroplasty (THA). We present the case of a 68-year-old man who presented with acute hip pain approximately 8 years after a left THA with a modern cementless, titanium femoral component. Radiographs revealed a fracture of the midportion of the neck of the stem, below the level of the trunnion. The patient underwent an isolated 1-component revision THA with a modular exchange. To our knowledge, this is the only reported case of a catastrophic failure fracture of this particular prosthesis.

Evidence for Gender-Specific Bone Loss Mechanisms in Periprosthetic Osteolysis

Osteolysis adjacent to total hip replacement (THR) prostheses is a major cause of their eventual failure. Periprosthetic osteolysis is associated with the production of bioactive particles, produced by the wear of articulating prosthesis surfaces. Wear particles invade the periprosthetic tissue, inducing inflammation and bone resorption. Previous studies have shown that osteocytes, the most numerous cell type in mineralised bone, can respond to wear particles of multiple orthopaedic material types. Osteocytes play important roles in bone resorption, regulating bone resorption by osteoclasts and directly through osteocytic osteolysis, also known as perilacunar remodelling. In this study, we perform a histological analysis of bone biopsies obtained from cohorts of male and female patients undergoing either primary THR surgery or revision THR surgery for aseptic loosening. The osteocyte lacunae area (Ot.Lac.Ar) and percentage lacunar area/bone area (%Ot.Lac.Ar/B.Ar) were significantly larger overall in revision THR bone than bone from similar sites in primary THR. Analysis by patient gender showed that increased Ot.Lac.Ar, indicative of increased perilacunar remodelling, was restricted to female revision samples. No significant differences in osteoclast parameters were detectable between the cohorts. These findings suggest previously unrecognised gender-specific mechanisms of bone loss in orthopaedic wear particle-induced osteolysis in humans.

Enhancement effect on antibacterial property of gray titania coating by plasma-sprayed hydroxyapatite-amino acid complexes during irradiation with visible light

The aim of this study was to reveal the mechanism of enhancement of antibacterial properties of gray titania by plasma-sprayed hydroxyapatite (HAp)-amino acid fluorescent complexes under irradiation with visible light. Although visible-light-sensitive photocatalysts are applied safely to oral cavities, their efficacy is not high because of the low energy of irradiating light. This study proposed a composite coating containing HAp and gray titania. HAp itself functioned as bacteria catchers and gray titania released antibacterial radicals by visible-light irradiation. HAp-amino acid fluorescent complexes were formed on the surface of the composite coating in order to increase light intensity to gray titania by fluorescence, based on an idea bioinspired by deep-sea fluorescent coral reefs. A cytotoxicity assay on murine osteoblastlike cells revealed that biocompatibility of the HAp-amino acid fluorescent complexes was identical with the that of HAp. Antibacterial assays involving Escherichia coli showed that the three types of HAp-amino acid fluorescent complexes and irradiation with three types of light-emitting diodes (blue, green, and red) significantly decreased colony-forming units. Furthermore, kelvin probe force microscopy revealed that the HAp-amino acid fluorescent complexes preserved the surface potentials even after irradiation with visible light, whereas those of HAp were significantly decreased by the irradiation. Such a preservative effect of the HAp-amino acid fluorescent complexes maintained the bacterial-adhesion performance of HAp and consequently enhanced the antibacterial action of gray titania.

Similar polyethylene wear between cemented and cementless Oxford medial UKA: a 5-year follow-up randomized controlled trial on 79 patients using radiostereometry

Background and purpose - Hydroxyapatite (HA)-coated implants have been associated with high polyethylene wear in hip arthroplasties. HA coating as a promoter of wear in knee arthroplasties has not been investigated. We compared the wear-rate of the polyethylene bearing for cemented and cementless HA-coated Oxford medial unicondylar knee arthroplasties (UKA). Secondarily, we investigated whether wear-rates were influenced by overhang or impingement of the bearing. Patients and methods - 80 patients (mean age 64 years), treatment-blinded, were randomized to 1 of 3 Oxford medial UKA versions: cemented with double-pegged or single-pegged femoral component or cementless HA-coated with double-pegged femoral component (ratios 1:1:1). We compared wear between the cemented (n = 55) and cementless group (n = 25) (ratio 2:1). Wear, impingement, and overhang were quantified between surgery and 5-year follow-up using radiostereometry. Clinical outcome was evaluated with the Oxford Knee Score. Results - The mean wear-rate for patients without bearing overhang was 0.04 mm/year (95% CI 0.02-0.07) for the cemented group and 0.05 mm/year (CI 0.02-0.08) for the cementless group. The mean difference in wear was 0.008 mm/year (CI -0.04 to 0.03). No impingement was identified. Half of the patients had medial bearing overhang, mean 2.5 mm (1-5). Wear increased by 0.014 mm/year for each mm increment in overhang. The mean Oxford Knee Score was 39 for the cementless group and 38 for the cemented group at the 5-year follow-up. Interpretation - The wear-rates were similar for the 2 fixation methods, which supports further use of the cementless Oxford medial UKA. However, a caveat is a relatively large 95% CI of the mean difference in wear-rate. Component size and position is important as half of the patients presented with an additional increase in wear-rate due to medial bearing overhang.

Measurement outcomes from hip simulators

Simulation of wear in total hip replacements has been recognised as an important factor in determining the likelihood of clinical success. However, accurate measurement of wear can be problematic with factors such as number and morphology of wear particles produced as well as ion release proving more important in the biological response to hip replacements than wear volume or wear rate alone. In this study, hard-on-hard (CoCr alloy, AgCrN coating) and hard-on-soft (CoCr alloy and CrN coating on vitamin E blended highly cross-linked polyethylene) bearing combinations were tested in an orbital hip simulator under standard and some adverse conditions. Gravimetric wear rates were determined for all bearings, with cobalt and where applicable, silver release determined throughout testing. Isolation of wear particles from the lubricating fluid was used to determine the influence of different bearing combinations and wear conditions on particle morphology. It was found that cobalt and silver could be measured in the lubricating fluid even when volumetric wear was not detectable. In hard-on-hard bearings, Pearson’s correlation of 0.98 was established between metal release into the lubricating fluid and wear volume. In hard-on-soft bearings, coating the head did not influence the polyethylene wear rates measured under standard conditions but did influence the cobalt release; the diameter influenced both polyethylene wear and cobalt release, and the introduction of adverse testing generated smaller polyethylene particles. While hip simulators can be useful to assess the wear performance of a new material or design, measurement of other outcomes may yield greater insight into the clinical behaviour of the bearings in vivo.

Severe Periprosthetic Metallosis and Polyethylene Liner Failure Complicating Total Hip Replacement: The Cloud Sign

We present a case of an 85-year-old woman with extensive metallosis of the left hip joint secondary to prosthetic polyethelene liner dislocation and wear. Radiographs demonstrated amorphous cloudy radiodensities surrounding the prosthesis, a feature we have called the “cloud sign.” The presence of amorphous cloudy radiodensities as a radiographic sign of metallosis has not been previously described to our knowledge.

Does a titanium-coated polyethylene press-fit cup give reliable midterm results?

BACKGROUND

Uncemented acetabular components have demonstrated low revision rates and high patient satisfaction but with concerns regarding increased costs compared with monoblock cups. Some newer lower-cost uncemented monoblock options have become available in the last decade, but limited data are available on their performance.

QUESTIONS/PURPOSES

(1) Does an uncemented, titanium-backed all-polyethylene acetabular cup provide reliable fixation? (2) What is the frequency and what are the causes for revision with this cup?

METHODS

Between 2004 and 2008, we elected to use an uncemented, titanium-backed all-polyethylene acetabular cup in older patients with limited physical demands. We performed 615 hip replacements in 550 patients with greater than 5 years of clinical and radiographic followup. When patients who were dead (80 hips in 75 patients), lost to followup (98 hips in 93 patients), or revised (three hips in three patients) were excluded, there were 434 hips in 379 patients for comparison of the postoperative and 5-year radiographs. Two observers not involved in the index surgical procedures (NH, HS) assessed radiographs for signs of migration or loosening. Some degree of early movement sometimes is seen before cup stabilization; however, to be conservative, we defined cups with greater than 3° of change of position (even if they subsequently stabilized) as potentially at risk and report them separately. Revision surgery, time from the index procedure, and the reason for revision were recorded from the New Zealand Joint Registry.

RESULTS

By 5 years there was a median change in inclination of 2° (range, 0°-13°; 95% confidence interval [CI], 2.0-2.4; p < 0.001) and 2° of anteversion (range, 0°-11°; 95% CI, 2.0-2.4; p < 0.001). Although at last followup all cups appeared to have stabilized with no radiolucent lines or medial migration, 22% of the cups (94 of 434) had moved more than 3° and so were deemed to be potentially at risk. There were 11 revision procedures (of 429 hips; 2.5%) of which six were for recurrent dislocation, four for femoral fracture, and one for femoral loosening to give an overall all-cause revision rate for all components of 0.25 per 100 component years (95% CI, 0.13-0.43). No revisions were performed for acetabular loosening.

CONCLUSIONS

The short- to medium-term results of this all-polyethylene monoblock cup demonstrated a low frequency of revision. However, 94 cups were identified as potentially at risk based on movement of > 3° before apparent stabilization. Although those patients seem to be doing well enough now, the current duration of followup may not be sufficient to know that these cups will be durable, because other ongrowth designs have demonstrated a high frequency of late failure after apparent early success.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Surveillance of Arc2f polyethylene after 15 years of implantation

BACKGROUND

To investigate the behavior of Arc2f polyethylene (PE) component after a minimum of 15 years post implantation and its possible reasons for failure.

METHODS

Between January 1988 and March 1995, 557 cementless total hip arthroplasties were performed in 578 patients. A total of 435 patients (450 hips) were followed up for 18.6 years (range 15-22).

RESULTS

At 10 years follow-up no cup needed revision surgery. After 15 years of implantation, we observed massive PE wear in 140 cups (31%) with large osteolytic lesions. A revision procedure was performed in all cases. Exchange only of the PE liner was sufficient in 78 cases, whilst in 59 the cup was also revised. PE insert thickness and the type of prosthetic head were found to be related to PE wear.

CONCLUSIONS

We postulate that the massive failure seen is attributed to the manufacturing of the PE insert. We advocate following all patients that have an implant lasting a decade after implantation for routine monitoring to identify those at risk for accelerated PE wear.

Outcomes at least 10 years after cemented PF® (Zimmer) total hip arthroplasty: 83 cases

INTRODUCTION

Cementless total hip arthroplasty (TKA) is gaining ground over cemented TKA. The objective of this study was to assess survival rates of a cemented THA implant (PF(®), Zimmer), after at least 10 years and to assess changes in acetabular bone structure.

MATERIAL AND METHODS

Eighty-three ceramic-on-polyethylene THA prostheses were implanted between 1998 and 2001. Clinical outcomes were assessed using the Harris hip score and Postel Merle d'Aubigné score. For each hip, radiographs were examined for acetabular radiolucent lines, geodes, and granulomas; in addition, changes in bone structure and trabeculae were assessed comparatively to the other hip and classified from no change to severe osteolysis. Changes in trabeculae served to assess the loads applied to the bone. Polyethylene wear was assessed using the Livermore method.

RESULTS

A single patient was lost to follow-up. At last follow-up, 16 patients had died and six were contacted and had not required revision surgery; the remaining 52 patients (59 THAs) were re-evaluated and none had evidence of loosening. The Harris hip score at last evaluation was 91.6 compared to 60.5 preoperatively. No hips had evidence of acetabular osteolysis. For two hips, the radiographs showed complete acetabular radiolucent lines less than 2mm in width, with no mobilisation. Trabecular distribution was homogeneous with no stress shielding. Mean annual rate of wear was 0.08mm. No instances of femoral component loosening were recorded; granulomas involving no more than five Gruën zones were seen in three cases.

DISCUSSION

This study confirms the reliability of cemented THA, with a 12-year survival rate of 98.3%, in keeping with earlier data. Thus, our results establish that cemented ceramic-on-polyethylene prostheses remain valid options for THA.

LEVEL OF EVIDENCE

IV.

Development of a femoral stem providing strong anchorage and facilitated removal. An experimental study in goats

OBJECTIVE

Prosthetic elements must be securely anchored to bone. Should revision surgery be necessary, preservation of bone stock is crucial. The goal of this study was to develop and assess a femoral stem combining secure anchorage and facilitated removal in a goat model.

METHODS

The development of the uncemented femoral stem was part of an innovation process to fulfill the combined requirements. The stem was designed with two longitudinal semicircular grooves to accommodate a drill bit to unanchor the stem. These grooves were interconnected by canals, each 1 mm in diameter. The surface was partly coated with hydroxyapatite (HA). The stems were inserted in the left hip of 35 goats. Perioperatively, the grooves were filled with autologous bone grafts, and standard cemented canine acetabular component and head were used. The pull-out force was measured six months postoperatively. Following randomization, 11 animals had the grooves of the stem drilled to remove anchoring tissue. Twelve animals were left undrilled (controls).

RESULTS

There was a significant difference in mean pull-out force between the group that had been drilled (1526 N) compared with the controls (2033 N, p = 0.028). Most of the HA had been resorbed.

CLINICAL SIGNIFICANCE

The stems had a high retention force. The procedure for un-anchoring by drilling significantly reduced the pull-out force.

A histological study of retrieved Cambridge acetabular components

A new uncemented acetabular component, the Cambridge cup, has been designed to mimic the anatomy and physiology of subchondral bone in order to minimise stress shielding and enhance long-term component stability. Cambridge cups were implanted in a cohort of 50 women who presented with displaced sub-capital fracture of the femoral neck. The cups were manufactured with an hydroxyapatite (HA) coating. Twenty six cups were implanted after removal of the HA. Twelve Cambridge cups were retrieved post-mortem between two and 84 months after implantation. Histological and histomorphometric testing was undertaken to analyse the residual HA coating thickness, bone apposition to the implant surface and particulate wear debris in the surrounding tissues. The HA-coated implants showed significantly greater bone apposition to the implant surface with significantly less fibrous tissue formation than the uncoated implants. Where HA resorption occurred, bone and bone marrow was seen adjacent to the implant. Excessive wear of the ultra high molecular weight polyethylene liner was not seen. The HA-coated components demonstrated good initial bone implant bonding and the flexible carbon polymer appeared to maintain stability following HA resorption. The uncoated implants showed little or no bony apposition but had a fibrous membrane apposed to the implant surface. This may be explained by a combination of micro-motion at the bone implant interface and having a component surface finish that was poorly suited to osseous attachment. Hydroxyapatite coated acetabular components can provide reliable osseous attachment. Subsequent HA resorption need not compromise medium-term osseous fixation to an appropriate implant surface.

An in vivo evaluation of bone response to three implant surfaces using a rabbit intramedullary rod model

Our study was designed to evaluate osseointegration among implants with three surface treatments: plasma-sprayed titanium (P), plasma-sprayed titanium with hydroxyapatite (PHA), and chemical-textured titanium with hydroxyapatite (CHA). Average surface roughness (Ra) was 27 microns for the P group, 17 microns for the PHA group, and 26 microns for the CHA group. Bilateral distal intramedullary implants were placed in the femora of thirty rabbits. Histomorphometry of scanning electron microscopy images was used to analyze the amount of bone around the implants at 6 and 12 weeks after implantation. Greater amounts of osseointegration were observed in the hydroxyapatite-coated groups than in the noncoated group. For all implant surfaces, osseointegration was greater at the diaphyseal level compared to the metaphyseal level. No significant differences were seen in osseointegration between the 6 and 12 week time points. Although the average surface roughness of the P and the CHA groups was similar, osseointegration of the CHA implants was significantly greater. The results of this in vivo lapine study suggest that the presence of an hydroxyapatite coating enhances osseointegration despite similarities in average surface roughness.

The effects of acetabular shell deformation and liner thickness on frictional torque in ultrahigh-molecular-weight polyethylene acetabular bearings

The purposes of this study were to determine if there were differences in the frictional torque generated between spherical acetabular shells and acetabular shells deformed as a result of implantation and to evaluate how changes in polyethylene insert thickness and head diameter affected these frictional torque data. An established bench top model was used for mechanical testing. A total of 70 samples were tested. Acetabular shells were impacted into polyurethane foam that was designed to create spherical or deformed shell models. We found that deformed acetabular shells produced higher frictional torque than spherical shells. Also, larger femoral head sizes produced greater frictional torque than smaller femoral head sizes. For the deformed models, the thicker polyethylene inserts produced greater frictional torque than the thinner polyethylene inserts.

Inferior survival of hydroxyapatite versus titanium-coated cups at 15 years

Hydroxyapatite (HA) particles have long been suspected to disintegrate from implant surfaces, become entrapped in joint spaces of orthopaedic bearing couples, and start a cascade leading to progressive polyethylene (PE) wear, increased osteolysis, and aseptic loosening. We compared cup revision at 15 years' followup in a randomized group of patients with 26 cementless THA components with titanium (Ti) versus first-generation HA coating. We also assessed radiographic PE wear and osteolysis to the 12-year followup or end point revision at a minimum of 5 years (mean, 10.9 years; range, 5-12.6 years). Two Ti-coated cups (17%) and eight HA-coated cups (57%) were revised at 15 years' followup. Femoral head penetration rate was 0.46 mm/year (standard deviation, 0.26) with the HA-coated cups (n = 12) and 0.38 mm/year (standard deviation, 0.14) with the Ti-coated cups (n = 10); we observed a wide variance of linear wear with the HA-coated cups. We also observed a positive association between high wear rate and revision, and between a high volume of osteolysis and revision. Our findings suggest inferior survival of medium-thickness spray-dried HA-coated cups with individual cases of excessive PE wear and premature cup failure. These findings apply to first-generation modular cups and may not apply to other cup designs and new HA-coating technologies.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

High revision rate of hydroxyapatite-coated ABG-I prosthesis

BACKGROUND

The aim of this study was to investigate the causes of the high revision rate of the hydroxyapatite-coated Anatomique Benoist Girard (ABG-I) prosthesis.

METHODS

We performed 204 total hip arthroplasties (THAs) at our hospital between March 1992 and December 1996. Of the 204 THA patients, 129 were followed up; the mean duration of follow-up was 12.2 years (range 10.0-14.5 years). There were 113 male patients and 16 female patients, with an average age of 53 years (30-83 years) at the time of surgery. The reasons for THA were avascular necrosis in 119 hips, acetabular dysplasia in 8 hips, and traumatic arthritis in 2 hips.

RESULTS

The Harris hip score was 47.3 preoperatively and 86.4 at the last follow-up. The linear polyethylene wear was an average of 0.29 mm/year. Acetabular osteolysis was seen in 113 cases (88%). Altogether, 61 (47.2%) acetabular cups were revised for aseptic loosening in 38 hips, polyethylene wear and osteolysis in 20 hips, recurrent dislocation in 2 hips, and deep infection in 1 hip. Femoral osteolysis was observed in 100 cases (77.5%). The femoral stem was revised in 4 hips (3.1%).

CONCLUSION

We observed that the fatal detriment to ABG-I acetabular cup survival in long-term follow-up was periacetabular osteolysis followed by aseptic loosening.

Uncemented stems in hip replacement--hydroxyapatite or plain porous: does it matter? Based on a prospective study of HA Omnifit stems at 15-years minimum follow-up

For many years, acrylic cement has been regarded as the unique available means for a long term and secure fixation of components in hip arthroplasty. A new generation of uncemented implants coated in hydroxyapatite (HA) has arisen since the mid-1980s, aiming to provide a 'biological interface' between metal and surrounding bone, and thus the hydroxyapatite interface was defined some years ago as a distinct entity from both cemented and 'plain porous' fixation. Based upon our 20-year experience with the HA Omnifit stem, this paper aims to discuss the efficiency of hydroxyapatite as a means of fixation for femoral components in hip arthroplasty, then examine whether the addition of a calcium phosphate layer induces any adverse effects, and finally make comparisons between HA-coated versus porous hip stems reported in the literature. With respect to fixation of femoral components in hip arthroplasty we report excellent results from the partially coated HA Omnifit stem in our series, with 99.20% of survival rate at 17-year follow-up, these results being consistent and similar to other HA series in the literature. HA 'uncemented' fixation can therefore be considered reliable and efficient. Furthermore, two decades of hydroxyapatite coatings have resulted in the identification of no major adverse effects. In fact calcium phosphate ions participate in the physiological turn-over of bone remodelling, and the HA coating is replaced by new bone formation without any fibrous tissue layer. Since HA particles are biodegradable and do not produce any inflammatory reaction in the surrounding bone, fears of osteolysis or third body wear due to HA debris have not been confirmed. Finally, comparison between HA versus plain porous femoral components through the literature has demonstrated better results with HA than porous alone both in terms of the quantity and quality of bone remodelling, and the potential migration and subsidence of the stem.

Failure of dual radius hydroxyapatite-coated acetabular cups

Introduction

Many kind of hydroxyapatite-coated cups were used, with favorable results in short term studies; it was supposed that its use could improve osteointegration of the cup, enhancing thus stability and survivorship. The purpose of this study is to analyze the long term behavior of the hemispheric HA coated, Dual Radius Osteonics cup and to discuss the way of failure through the exam of the revised components and of both periacetabular and osteolysis tissue.

Materials and Methods

Between 1994 and 1997, at the Department of Orthopedic Sciences of the Insubria University, using the posterolateral approach, were implanted 276 Dual Radius Osteonics^® in 256 patients, with mean age of 63 years.

Results

At a mean follow-up of 10 years (range 8–12 years), 183 cups in 165 patients, were available for clinical and radiographical evaluation. 22 Cups among the 183 were revised (11%). The cause of revision was aseptic loosening in 17 cases, septic loosening in one case, periprosthetic fracture in another case, osteolysis and polyethylene wear in two cases and, finally, recurrent dislocations in the last one. In the remaining patients, mean HHS increased from a preoperative value of 50,15 to a postoperative value of 92,69. The mean polyethylene wear was 1,25 mm (min. 0,08, max. 3,9 mm), with a mean annual wear of 0,17 mm. The mean acetabular migration on the two axis was 1,6 mm and 1,8 mm. Peri-acetabular osteolysis were recorded in 89% of the implants (163 cases). The cumulative survivorship (revision as endpoint) at the time was 88,9%.

Conclusion

Our study confirms the bad behavior of this type of cup probably related to the design, to the method of HA fixation. The observations carried out on the revised cup confirm these hypotheses but did not clarify if the third body wear could be a further problem. Another interesting aspect is the high incidence of osteolysis, which are often asymptomatic becoming a problem for the surgeon as the patient refuses the possibility of a revision.

Catastrophic failure of ceramic-polyethylene bearing total hip arthroplasty

Complications of ceramic-polyethylene bearing total hip arthroplasty (THA) include osteolysis, loosening, dislocation, and component failure. Catastrophic acetabular component failure involves severe damage to both the polyethylene liner and metal shell. This case study presents the first reported complete wear-through of the acetabular portion of a ceramic-polyethylene arthroplasty presenting as a dislocation and a review of the literature. In this study, a patient's alumina ceramic femoral head penetrated the polyethylene liner and titanium shell and presented as a dislocated THA. The contributing factors for this catastrophic failure include young patient age, high activity level, thin polyethylene liner, backside wear, component positioning, polyethylene sterilization with gamma irradiation in air, and lack of appropriate follow-up. Revision THA was performed without complications.

Measurement of extent of bone ongrowth and hydroxyapatite absorption in retrieved acetabular cups

BACKGROUND

To understand why hydroxyapatite (HA)-coated acetabular cups did not produce satisfactory results, we measured the extent of bone ongrowth and HA absorption of the retrieved cups.

METHODS

Between March 1992 and June 1998, a total of 289 patients underwent total hip arthroplasty with an HA-coated ABG (Anatomical Benoist Giraud) prosthesis in our hospital. We revised 71 cups in our hospital, 43 of which were included in this study. The cups were in situ for an average of 80.4 months. We revised 21 cups for polyethylene wear and osteolysis, 20 for loosening, and 2 for recurrent dislocation. The outer surfaces of the cups were subdivided by two circular grooves into three areas: central, middle, peripheral. Bone ongrowth and HA absorption was measured in terms of area and thickness. The areas were graphically calculated using a computer imaging analysis system. The thickness of the HA coating remaining on the retrieved cup was measured by an x-ray coating thickness measurement instrument.

RESULTS

Of the 43 cups, 37 had bone ongrowth. Bone ongrowth was observed on the central surface in 23 cups, on the middle surface in 27 cups, and on the peripheral surface in 15 cups; 6 of the 37 cups had bone ongrowth only in the groove. Altogether, 37 cups showed bone ongrowth on 6.43% of the outer acetabular surface. HA absorption appeared in all 43 cups, and an average 63.21% of the HA coating area was absorbed. there was a proportional relation between the rate of HA absorption and implantation duration, but there was no consistent trend between the thickness of the HA coating and implantation duration.

CONCLUSIONS

We suggest that progressive HA absorption and minimal bone ongrowth are related to the failure of HA-coated acetabular cups at long-term follow-up after total hip arthroplasty.

Ten- to twelve-year follow-up of the furlong hydroxyapatite-coated femoral stem and threaded acetabular cup in patients younger than 65 years

We reviewed 82 patients who had 92 primary Furlong uncemented hydroxyapatite (HA)-coated total hip replacements inserted between 1988 and 1992. All patients had the Furlong HA-coated stem and screw in acetabular cup with a 28-mm alumina oxide ceramic modular head. The mean age at the time of primary total hip arthroplasty was 54 years (range, 31-67 years). At 10 years, we reviewed 64 patients (72 total hip arthroplasties). Eight had died (10 total hip arthroplasties), 3 could not attend for follow-up, 2 were lost to follow-up, and 5 were revised (2 for infection and 3 for acetabular loosening and recurrent dislocation). We conclude that the Furlong HA-coated total hip replacement is a good prosthesis for patients younger than 65 years, with a cumulative survival rate of 94.29% at 10 to 12 years using revision as the end point.

Excellent long-term survival of an uncemented press-fit stem and screw cup in young patients: follow-up of 75 hips for 15-18 years

BACKGROUND

The long-term results of uncemented total hip arthroplasties vary widely due to differences in design, metal alloy, coating, surface structure, and porosity.

PATIENTS AND METHODS

We retrospectively studied 75 cementless Zweymuller SL stems in combination with Endler titanium-backed threaded cups (Z-E) in 70 patients. 35 patients were women, and the mean age at surgery was 52 (24-68) years. 16 patients died and 1 emigrated, 7 patients (of which 1 later died) subsequently underwent revision, and the remaining 47 patients with 50 original arthroplasties were followed up after a median of 16 (15-18) years.

RESULTS

Revision of 8 hips resulted in an 18-year Kaplan-Meier estimated overall survival rate of 88% (CI: 79-96). 6 of 7 cup revisions were due to liner wear and osteolysis, and 1 was due to aseptic loosening. 2 of 3 stem revisions were due to femoral loosening and 1 was due to fracture of the neck of the stem. The clinical results were good, with a mean Harris hip score of 89 (54-100). Half of 70 hips in 65 patients had ectopic bone formation. All unrevised implants were radiographically stable, with a mean liner wear of 0.07 mm/year.

INTERPRETATION

These long-term results demonstrate that the combination of a Zweymuller SL stem and an Endler titanium-backed screw cup is a good hip arthroplasty in young and active patients. A prefixed polyethylene liner is a drawback, necessitating exchange of the whole cup in cases with polyethylene wear.

Hydroxyapatite porous coating and the osteointegration of the total hip replacement

INTRODUCTION

The main purpose of this study is to evaluate the efficacy of the plasma sprayed, combined porous titanium alloy/HA coating in promoting bony ingrowth and mechanical stabilization of total hip implants. The performance of the titanium alloy/HA type coated hip prostheses and the one of the same shape but without any coating, is compared in this paper.

MATERIAL AND METHODS

The implants were manufactured from titanium alloy VT-6 (ASTM F-136). The hip stems utilized in the control group were identical to those subsequently coated. The coating consists of a plasma deposited first layer of porous titanium alloy (TiAl(6)V(4)), similar in composition to the forged substrate and a plasma deposited second layer of over-sprayed hydroxyapatite, Ca(10)(PO(4))6(OH)2. Coating is located in the critical area of the hip stems, where high fixation interface strength is desired, i.e. in the proximal area of the stem where the highest stresses occur. The porous titanium alloy/hydroxyapatite (HA) coated femoral stems were implanted in 50 patients. The results were compared with a control group of 50 patients with the same type of endoprosthesis, but without the porous titanium alloy/HA coating. Both groups of patients were operated on and evaluated by the same orthopedic surgeons with a mean follow up of 11.4 years in the HA group and 10.6 years in the control group.

RESULTS

HHS in the control group was preoperatively 35.5 points (range 26-49) and 85.1 points (range 54-100) in the time of the last control. HHS in the HA group was preoperatively 34.1 points (range 27-56) and 94.4 points (range 89-100) in the time of the last control. In 28 cases (56%) of the control group a range of translucencies were obvious. These translucent lines, however, did not appear with any of the patients in the coated implant group except one infection stem migration.

CONCLUSION

Experience with the HA-type coated hip implants demonstrates substantially higher degree and quality of osteointegration in the porous titanium alloy/HA type implants.

In vitro andin vivo biological responses of plasma-sprayed hydroxyapatite coatings with posthydrothermal treatment

This study was undertaken to evaluate the effect of post-hydrothermal treatment on the biological responses of the plasma-sprayed hydroxyapatite (HA)-coated Ti-6Al-4V implant system both in vitro and in vivo. After hydrothermal treatment, the HA coating (HAC) shows the high mechanical strength and indices-of-crystallinity, denser microstructure, lower concentrations of amorphous and impurity phases, when compared with the as-sprayed HAC. The in vitro cell-culture studies, using UMR106 osteoblast-like cell, demonstrated no signifiacnt cell growth on both surface of as-sprayed and hydrothermal-treated HACs during 10-day culture. The in vivo studies, using the transcortical implant model in the femora of goats, evaluated the histological responses of two coatings. After 6 week of implantation, using backscattered electron images, no substantial histological variations in the extents of new bone apposition and new bone healing between the two HACs were observed. However, the as-sprayed HAC, owing to the dissolution induced the granular particles dissociated from the HAC, showed the statically lower extent of new bone apposition than hydrothermal-treated HAC at 12 weeks. The results suggest that hydrothermal treatment could be used to improve the mechanical strength, crystallinity, and phase composition of HAC, which are important factors of long-term fixation and stability of implant. Besides, the treated HAC could also achieve the initial fixation of implant in clinical use.

Improved bone ingrowth and fixation with a thin calcium phosphate coating intended for complete resorption

Bonit is claimed to be a resorbable electrochemically deposited calcium phosphate coating consisting mainly of brushite, which is a hydroxyapatite precursor. This study involved a comparison of Ti6Al4V screw-shaped implants with and without a 15 +/- 5 microm Bonit coating in rabbit tibia and femur, after 6 and 12 weeks of insertion. The biomechanical removal torque test showed significantly increased values for the coated implants after 12 weeks (p < 0.05) but not after 6 weeks of integration. Higher bone-implant contact was found for the coated implants in the tibia after 6 weeks and for both tibial and femoral screws after 12 weeks (p < 0.05). There was no difference in the inflammatory reaction around the implants, and possible grains of the coating could be detected after 6 weeks, but not after 12 weeks of follow-up. This unloaded short-term study has shown promising results for the easily applicable and resorbable coat (Bonit) compared to uncoated titanium-alloy implants.

Long-term results of HA coated threaded versus HA coated hemispheric press fit cups: 287 hips followed for 11 to 16 years

INTRODUCTION

There are many studies on the short and medium term results of hydroxyapatite (HA) coated acetabular components, but information on survival in the longer run is sparse. In this paper, we report 11 to 16 years follow up results of HA coated threaded versus HA coated hemispherical press fit cups.

PATIENTS AND METHODS

During the years 1988-1993, we performed 323 primary total hip replacements in 276 patients with an HA coated acetabular component. In 128 cases we used a HA coated threaded cup, and in 195 cases a HA coated hemispherical press fit cup was inserted. There were 189 women and 87 men aged 15-79 (mean 48) years. During follow-up, 14 patients died and 21 patients would not come for the follow-up examination as they were doing quite well with their prostheses. These patients were censored at their last control examination. This left 241 patients (287 hips) followed for 11 to 16 (mean 13) years after the operation.

RESULTS

During the follow-up period 48 press fit cups and 9 threaded cups were revised, none because of infection. Survival analyses indicated a cumulative survival of the threaded HA coated cup of 0.91 (95% CI: 0.86-0.97) at 16 years with one patient at risk. The cumulative survival of the HA coated press fit cup was 0.74 (0.69-0.80) at 15 years with no patient at risk. The difference is significant (P = 0.0002). Wear and age was significantly associated with revision (P < 0.0001 and 0.0002, respectively), and wear was significantly (P < 0.0001) associated with osteolysis.

CONCLUSION

These results indicate that HA coated threaded cups provide satisfactory bony interlock to resist force loads in the long run whereas the HA coated hemispherical press fit cups do not.

Long-term follow-up (11 years plus) results of JRI (Furlong) total hip arthroplasty in young patients: cause for concern regarding acetabular cup?

We describe the clinical and radiological long-term outcomes of 77 primary total hip replacements in 69 patients using the fully hydroxyapatite-coated JRI (Furlong) total hip replacement. The total cases followed up were 77 hips, performed at a mean duration of 11 years and 2 months. Twelve hips could not be followed up for various reasons, which are discussed in the results section. The mean Harris hip score was 89. Seventeen acetabular cups were revised for aseptic loosening. Only one femoral stem was revised, for fracture. By Engh's criteria there were a further two unstable cups with no symptoms, and all femoral stems were stable. Kaplan-Meier survivorship analysis revealed a survival of 98.8% for the femoral stem, 78.7% for the acetabular cup, and a combined survival of 77.8% for both components. Our findings suggest that the JRI (Furlong) hip gives a durable femoral stem implant fixation, whereas the prosthesis-bone interface achieved with the acetabular component is questionable.

Early failure of hemispheric hydroxyapatite-coated acetabular cups

Total hip arthroplasties with hydroxyapatite coatings have shown encouraging results after early-term followup. We presumed hydroxyapatite-coating on a smooth hemispheric press-fit acetabular cup would enhance bone osseointegration and maintain stability of cup after midterm (minimum 5-year) followup. Sixty-three patients had 70 consecutive total hip arthroplasties. Five patients (eight hips) died from problems unrelated to surgery. The remaining patients (62 hips) were followed up for an average of 7 years (range, 6-9 years). The mean age of the patients was 49 years (range, 23-61 years). The average Harris hip score improved from 59 points (range, 32-82 points to 82 points (range, 37-100 points) at final followup. There were seven acetabular component revisions. Of the 55 unrevised cups, 47 hips (85%) were stable by bony ingrowth, five hips (9%) were fibrous stable, and three hips (5%) were unstable with cup migration. Osteolysis around the cup was observed in 18 hips (33%). The average polyethylene wear rate was 0.15 mm/year. Survival rates of the cups at 6 and 8 years were 94.3% and 60.5%, respectively. Total hip arthroplasties using an hydroxyapatite-coated smooth hemispheric acetabular cup showed an unexpected high failure rate in terms of fixation, occurrence of osteolysis, and revision after midterm followup.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

[Long term bone behavior in total primary hip arthroplasty with a fully hydroxyapatite-coated femoral stem: a continuous series of 120 cases with twelve years follow-up]

PURPOSE OF THE STUDY

Cementless hydroxyapatite-coated total prostheses have proven their reliability for more than twenty years. The intimate contact between the receiver bone and the implant allows "union" between the inert and living material. Osteointegration is maintained over time. The purpose of this work was to study the long-term reaction of femoral bone to wear debris after insertion of cementless hydroxyapatite implants.

MATERIAL AND METHODS

One hundred twenty implants constituted a continuous series of total hip arthroplasties performed since 1989 for primary joint degeneration in patients followed for at least twelve years. The same femoral implant totally coated with hydroxyapatite was used for all patients in combination with a metal cup and a polyethylene insert. Twelve years later, twenty-seven patients had died, five were contacted by telephone, and three were lost to follow-up, giving a study population of 85 total hip arthroplasties with complete review and radiographic data. Clinical and radiological findings are reported with a measure of polyethylene wear and femoral bone behavior in contact with femoral implants.

RESULTS

At twelve year follow-up, there were no cases of implant loosening. Clinical outcome was satisfactory, 90% of the hips were pain free. Radiologically, mean polyethylene wear was 0.1 mm per year with calcar changes (zone VII) in 27% and trochanter changes (zone I) in 14%. There was no evidence of osteolysis extension or granuloma formation in the shaft zone. Implant survival at twelve years was 99.1% (97.2-100%).

DISCUSSION

Hydroxyapatite-coated cementless implants resist well to polyethylene wear debris. At twelve years, osteolysis caused by macrophage activation remained limited to zones I and VII. There appeared to be an intimate plug between the implant and the living bone preventing wear debris migration along the implant as was visualized along the entire length of the implant. Polyethylene wear was however real and the risk of osteolysis remains a threat to implant stability. Improved survival of hydroxyapatite-coated total hip implants will thus depend on improvements in the weight-bearing couple.

Grit-blasted and hydroxyapatite-coated total hip arthroplasty: an 11- to 14-year follow-up study

We report long-term results of the first clinical trial of hydroxyapatite-coated total hip arthroplasty conducted in Japan. The hemispherical cup and the straight-tapered stem were made of titanium alloy with a grit-blasted, hydroxyapatite-coated surface. The surface roughness before and after hydroxyapatite coating was 1.4 microm and 3.4 microm, respectively. Thirty-three patients (35 hips) were followed prospectively; of these, 1 patient was lost to follow-up, 5 were deceased at the latest follow-up, and 27 were followed for 11 to 14 years. Two cups and one stem (two patients) were revised. Survivorship, with radiological acetabular loosening as the endpoint, was 62.3% at 14 years. At the latest radiological follow-up, stable fixation with bone ongrowth was achieved in 46% of the acetabular cups and 89% of the femoral stems. Acetabular cups with host bone coverage of less than 60% had a high rate of failure. The suboptimal result of the hydroxyapatite-coated smooth cup indicates that porous coatings under the hydroxyapatite coating would be beneficial for hydroxyapatite-coated total hip implants, especially for the acetabular components.

No effect of hydroxyapatite particles in phagocytosable sizes on implant fixation: An experimental study in dogs

The influence of wear debris on bone healing around orthopedic implants is debated. Hydroxyapatite (HA) particles and polyethylene (PE) particles have been shown to have a negative effect on osteoblast cultures in vitro. The present study investigated the in vivo effects of HA and PE particles on the mechanical fixation and gap healing around experimental HA implants. Nonloaded implants (n = 30) were inserted bilaterally into the proximal tibia of 15 dogs with a 2-mm gap to the bone. The peri-implant gap was either (1) empty (n = 6) or filled with (2) hyaluronic acid (n = 8), (3) hyaluronic acid and HA particles (n = 8), or (4) hyaluronic acid and PE particles (n = 8). After 4 weeks, the animals were killed. The implant interface was evaluated by pushout testing until failure and by histomorphometry. Both HA and PE particles were found to be phagocytosed by macrophage-like cells in the interfacial tissue. HA particles were also integrated in newly formed bone. We found no negative effect of the particulate material on mechanical fixation of the implants or on bone formation around the implants.

Clinical and radiological results of hydroxyapatite-coated acetabular cups

We prospectively studied a consecutive series of 60 primary total hip arthroplasties in 52 patients. All patients had a hydroxyapatite-coated hemispherical acetabular cup (OCTOFIT). Mean patient age was 52.5 (34-73) years. In 38 hips, a 28-mm and in 22 hips a 32-mm diameter cobalt-chrome femoral head was used. We could follow 53 hips for a mean of 81 (28-125) months. Four cups were revised because of osteolysis, and in another six cups, slight osteolysis without migration was seen. The average annual linear wear rate was 0.05 mm (+/-0.05) for 28-mm heads and 0.16 mm (+/-0.09) for 32-mm heads (p<0.0001). Survivorship analysis predicted a survival rate of 86+/-6.7% at 10 years.

Direct two-incision total hip replacement without fluoroscopy

A new direct anatomic two-incision approach for total hip replacement without the use of fluoroscopy is described. The anterior incision is the distal one third of a Smith-Peterson approach and the posterior incision is the proximal one third of the Moore approach. It has been used on 142 unselected consecutive.

The contribution of coating microstructure to degradation and particle release in hydroxyapatite coated prostheses

Plasma-sprayed coatings of hydroxyapatite powder are widely used on hip replacements. Commercially, they are supplied by a large number of companies and thus offer different coating design philosophies. This study focuses on a retrieved prosthetic stem that exhibited coating loss on the femoral stem occurring concurrently with third-body wear. The purpose of the research was to establish possible links between the coating microstructure and the clinical findings. A coated stem and cup were sectioned and the cross section was prepared to reveal the coating microstructure. Characterization included X-ray diffraction, FTIR spectroscopy, and crystalline particle quantification within the coating. It was found that the coating has a high amorphous content that provides fast resorption. The amount of crystalline particles increased on the distal location of the stem, the threads of the acetabular shell, and was generally higher on the cup. Accelerated degradation illustrated how the coating may be a particle-generating source by preferential dissolution of the amorphous phase, possibly allowing liberation of crystalline areas and other particulates at the substrate-coating interface. Such particles mainly include the less soluble hydroxyapatide formed from unmelted particles in the plasma or recrystallisation in the coating, but may also include entrapped grit lodged in the substrate during the roughening process. This study accents the importance of coating microstructure in understanding coating resorption.

Comparison of hydroxyapatite and hydroxyapatite tricalcium-phosphate coatings

This study compared the effects of hydroxyapatite (HA) coating and biphasic HA/tricalcium-phosphate (HA/TCP) coating on the osseointegration of grit-blasted titanium-alloy implants. Each coated implant was compared with uncoated grit-blasted implants as well. The implants were press-fit into the medullary canal of rabbit femora, and their osseointegration was evaluated 3 to 24 weeks after surgery. The coated implants had significantly (P<.05) greater new bone ongrowth than the uncoated implants (HA, 56.1 +/- 3.1%; HA/TCP, 53.8 +/- 2.6%; uncoated, 32.2 +/- 1.4% of the implant perimeter, 12 weeks). Unmineralized tissue (cartilage and osteoid) was seen on the uncoated implants but never on the coated implants. The coated implants had significantly (P<.05) greater interfacial shear strength than the uncoated implants (HA, 4.1 +/- 0.4 MPa; HA/TCP, 4.8 +/- 0.5 MPa; uncoated, 2.6 +/- 0.2 MPa, 12 weeks). There was no difference between HA and HA/TCP coating in regard to new bone growth or interfacial shear strength. These data show a comparable enhancement effect of HA and HA/TCP coatings on the osseointegration of titanium-alloy implants.

A retrospective clinical and radiographic review of 173 hydroxyapatite-coated screw cups with 5- to 10-year follow-up, showing low revision rates for fixation failure

We reviewed the midterm results of 173 hydroxyapatite-coated screw cups. The average follow-up was 6.5 years (range, 5-9 years). The follow-up rate was 93%. Patients were assessed using the Merle D'Aubigne-Postel clinical scoring scale and by radiographic review. Two patients had revision surgery for recurrent dislocation (1.2%), 3 patients were revised for aseptic loosening (1.7%), 1 patient underwent revision surgery because of deep prosthetic infection (0.6%), and 2 patients were revised for polyethylene wear without loosening (1.2%), which gave a total revision rate of 4.7%. The average postoperative Merle D'Aubigne-Postel scores were 5.7 for pain, 5.5 for range of motion, and 5.4 for function.

Cementation of a polyethylene liner into a metal shell. Factors related to mechanical stability

BACKGROUND

Various clinical situations may make polyethylene liner exchange desirable in the setting of a well-fixed metal shell. Options have included a simple polyethylene liner exchange or revision of the entire acetabular shell. A recently introduced technique involves cementation of a new liner into a well-fixed metal shell. The purposes of this study were to quantify the mechanical integrity of this method of liner fixation, to evaluate the factors that may influence immediate liner fixation, and to compare this construct with a standard locking mechanism.

METHODS

One modular acetabular cup design was evaluated. Variables that may contribute to the mechanical integrity of the construct were evaluated via lever-out and multiaxis dislocation testing methods. The variables included the size of the liner (undersized versus oversized), type of liner (all-polyethylene versus modular design), modification of the modular liner (unmodified versus grooved), and groove configuration (cruciform versus circumferential). Metal shells with and without screw-holes were also tested. The modular locking mechanism was used as the control.

RESULTS

None of the constructs failed at the cement-metal interface. All undersized liners required significantly higher loads to failure than either the controls (p < 0.001) or the oversized liners (p < 0.001). Oversized unmodified liners failed at significantly lower loads than the controls did (p < 0.01). The creation of circumferential grooves in the oversized liners significantly improved the strength of the constructs (p < 0.01), making them comparable with the controls. No significant differences were found among the four undersized groups (p > 0.3). The standard locking construct (control) and the oversized unmodified construct failed at a force of 2000 N in the multiaxis dislocation test. No other construct failed with use of this test mode.

CONCLUSIONS

Cementation of a polyethylene liner into a metal shell can be stronger than a conventional locking mechanism if the liner is undersized. Cementation of an oversized liner into a shell should be performed with caution. The long-term durability of this fixation remains unknown.

Medium-term results of the ABG total hip arthroplasty in young patients

A total of 66 patients (71 hips) <65 years old (average age, 55.4 years; range, 26-65 years) received a proximally hydroxyapatite-coated femoral prosthesis with a hemispheric metal-backed, hydroxyapatite-coated acetabular cup (ABG hip, Howmedica International, Staines, UK), with an average follow-up of 4.8 years (range, 2-7 years). All operations were performed by 1 surgeon in a district general hospital. The average preoperative Harris hip score and Merle d'Aubigné score were 59.8 and 9.6, which rose to 92.7 and 16.3 at the longest follow-up. Most patients were satisfied with the outcome, with only 2 patients complaining of intermittent thigh pain. Survivorship analysis predicted a survival rate of 96.87% at 7 years. There were 2 revisions, one to reposition an acetabular cup and one for an undersized femoral component. Radiographic changes were consistent with bone remodeling. There were no radiolucencies around the acetabular cup, but we noted eccentric polyethylene wear in 37 (60%) inserts ranging from 0.4 to 4 mm (annual wear average, 0.25 mm/y; range, 0.063-0.76 mm/y). There were no loose femoral stems. Osseointegration was achieved in all cases, with only 1 case developing endosteal cavitation in Gruen zone 2. Cancellous densification was found to be mainly in zones 2 and 6 (67.2% and 55.7%), extending distally in zones 3 and 5 (52.4% and 50.8%). Hypertrophy of the femoral shaft was less prominent and was noted mostly distally, in zones 3, 4, and 5 (11.4%, 18.3%, and 18.3%), extending proximally in zones 2 and 6 (8.1% and 13.1%). The ABG hip can achieve excellent results in the medium term, but polyethylene wear of the acetabular insert should be noted with concern.

Elemental and morphological identification of third-body particulate and calcium stearate inclusions in polyethylene components

Third-body particulate such as human bone chips, hydroxyapatite, and bone cement are considered contributing factors in accelerated wear in total joint replacement. Particulate wear debris is now considered the major contributing factor in aseptic loosening of total joint replacements. The ability to distinguish between different third-body particulate is necessary to better understand wear mechanisms when conducting implant retrieval analysis. The objective of this investigation is to demonstrate that backscattered electron imaging with correlated energy dispersive X-ray analysis can accurately identify third-body particulate in retrieved polyethylene components. It is important that this technique can also distinguish between third-body particulate and normal inclusions in the polyethylene such as calcium stearate, based on the distinct morphology and elemental composition of each material. Therefore, the ability to distinguish third-body particulate from calcium stearate inclusions is essential in gaining a better understanding of the contributing factors associated with coating separation and accelerated wear observed in clinically retrieved polyethylene components.

Total hip replacement with an entirely hydroxyapatite-coated prosthesis: 5 years' follow-up of 94 consecutive hips

The first 100 consecutive entirely hydroxyapatite (HA)-coated hip arthroplasties in 86 patients (mean age, 56.2 years [range, 32-73 years]; female-to-male ratio, 75:25) were followed with standardized radiographs annually up to 5 years. All components developed 100% intimate bone-implant contact, being gradually reduced to 99.5%+/-3.8% by 2 partial periacetabular lines and on the femoral side to 94.0%+/-6.1% and 96.5%+/-5.2% in the frontal and lateral planes by lines along 75 stems, mostly in zones 1 and 8. Bone formation took place adjacent to the prostheses regularly, with gap filling and comprehensive periprosthetic bone remodeling, stabilizing at 3 years. No adverse stress shielding was found. The clinical results were excellent without thigh pain. We believe that all components were bonded directly to bone, promoted by the reliable primary fixation and the osteoconductive effect of HA.