Comparison of in vivo wear between polyethylene liners articulating with ceramic and cobalt-chrome femoral heads

Polyethylene wear of dual mobility cups: a comparative analysis based on patient-specific finite element modeling

Purpose

Concerns remain about potential increased wear with dual mobility cups related to the multiple articulations involved in this specific design of implant. This finite element analysis study aimed to compare polyethylene (PE) wear between dual mobility cup and conventional acetabular component, and between the use of conventional ultra-high molecular weight PE (UHMWPE) and highly cross-linked PE (XPLE).

Methods

Patient-specific finite element modeling was developed for 15 patients undergoing primary total hip arthroplasty (THA). Five acetabular components were 3D modeled and compared in THA constructs replicating existing implants: a dual mobility cup with a 22.2-mm-diameter femoral head against UHMWPE or XLPE (DM22PE or DM22XL), a conventional cup with a 22.2-mm-diameter femoral head against UHMWPE (SD22PE) and a conventional cup with a 32-mm-diameter femoral head against UHMWPE or XLPE (SD32PE or SD32XL).

Results

DM22PE produced 4.6 times and 5.1 times more volumetric wear than SD32XL and DM22XL (p < 0.0001, Cohen’s d = 6.97 and 7.11; respectively). However, even if significant, the differences in volumetric wear between DM22XL and SD32XL as well as between DM22PE and SD22PE or SD32PE were small according to their effect size (p < 0.0001, Cohen’s |d|= 0.48 to 0.65) and could be therefore considered as clinically negligible.

Conclusion

When using XLPE instead of UHMWPE, dual mobility cup with a 22.2-mm-diameter femoral head produced a similar amount of volumetric wear than conventional acetabular component with a 32-mm-diameter femoral head against XLPE. Therefore, XLPE is advocated in dual mobility cup to improve its wear performance.

Microtextured CoCrMo alloy for use in metal-on-polyethylene prosthetic joint bearings: multi-directional wear and corrosion measurements

The longevity of metal-on-polyethylene (MoP) prosthetic hip joint bearings, in which a polished CoCrMo femoral head articulates with a polyethylene liner, may be limited by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. This study uses laser surface texturing to manufacture a pattern of shallow spherical microtexture features on a polished CoCrMo surface. Gravimetric wear measurements of a highly-crosslinked polyethylene pin articulating with a CoCrMo disc under multi-directional shear demonstrate that polyethylene wear is reduced by more 50% when articulating with a microtextured as opposed to a polished CoCrMo disc. Electrochemical measurements also show that laser texturing does not negatively affect the corrosion potential of CoCrMo.

Using a patterned microtexture to reduce polyethylene wear in metal-on-polyethylene prosthetic bearing couples

The longevity of metal-on-polyethylene prosthetic hip joint bearings, in which a CoCrMo femoral head articulates with a polyethylene liner, is often limited by polyethylene wear and osteolysis caused by polyethylene wear particles. Current approaches to reduce polyethylene wear include improving the mechanical properties of the polyethylene liner, and/or manufacturing ultra-smooth articulating surfaces. In contrast, this experimental work shows that adding a patterned microtexture of concave "dimples" to a polished CoCrMo surface significantly reduces polyethylene wear by promoting the formation of an elastohydrodynamic lubricant film, which reduces contact between the CoCrMo and polyethylene bearing surfaces. Using a gravimetric method to measure polyethylene pin wear during pin-on-disc experiments, it was demonstrated that microtextured CoCrMo caused reduced polyethylene wear compared to polished CoCrMo surfaces. Wear was quantified for different polyethylene materials currently used in commercial prosthetic hip joint bearings, and for several microtexture geometries. It was also documented by correlating polyethylene wear with surface topography measurements that the patterned microtexture reduced contact between the articulating bearing surfaces.

Long-term wear of dual mobility total hip replacement cups: explant study

PURPOSE

Dual mobility THA implantations are increasing. THA survival of more than 15 years is considered long-term survival based on the Charnley prosthesis, which has a median wear rate of 39 to 98 mm³/year. What is the median wear rate of dual mobility THA cups and its repartition on the liner volume? What are the factors influencing dual mobility wear?

METHODS

Thirty-five explants were analysed. The liners were entirely mapped with a fully automatic stripe light scanner that uses green LED light.

RESULTS

The liners had a median wear rate of 38 mm³/year. The distribution of the wear between the two bearings varied greatly. No factor was found influencing wear volumes.

CONCLUSIONS

The median annual wear of dual mobility liners is at least as low as the wear of cemented polyethylene liners and lower than equivalent cementless liners. The two articulations of the dual mobility THA do not cause more wear.

LEVEL OF EVIDENCE

Level IV - case series.

The case for ceramic-on-polyethylene as the preferred bearing for a young adult hip replacement

The optimum choice of bearing surfaces in total hip arthroplasty, particularly in the younger and more active patient, remains controversial. Despite several studies demonstrating good long-term results for the metal-on-polyethylene articulation, there has been a recent vogue towards the utilisation of hard-on-hard bearings for younger patients due, in part, to concerns regarding polyethylene induced osteolysis. However, well-documented complications concerning metal-on-metal bearings and the risk of fracture in ceramic-on-ceramic bearings have raised concerns regarding the principle of the hard-on-hard bearing in the active patient. With recent technological advancements in the manufacture of both polyethylene and alumina ceramics, the in vitro properties of each material with regards to strength and toughness have been significantly improved. In addition, ceramic femoral heads have consistently been shown to produce less in vivo polyethylene wear than similar sized metal heads. This paper aims to critically review the biomechanical, in vivo and clinical studies related to the use of the ceramic on polyethylene bearing, and highlights its potential use as the preferred bearing for a young adult hip replacement.

A randomized controlled trial comparing Oxinium and cobalt-chrome on standard and cross-linked polyethylene

The purpose of the investigation was to assess the clinical and radiographic outcomes in four bearing surfaces. Eighty patients (91 hips) undergoing total hip arthroplasty between 2004 and 2007 were randomized to one of four bearing surfaces: (1) cobalt-chrome (CoCr) and ultra-high molecular weight polyethylene (UHMWPE); (2) CoCr and XLPE; (3) Oxinium and UHMWPE; and (4) Oxinium and XLPE. The mean follow-up for this study was 6.8 years. There were no significant differences in clinical outcomes. The linear wear rates for the four groups were 0.241 mm/year, 0.076 mm/year, 0.238 mm/year and 0.061 mm/year respectively. HXLPE results in significantly less wear than UHMWPE. However, we found no significant reduction in wear rate by using Oxinium in place of CoCr femoral heads at early follow-up.

A patterned microtexture to reduce friction and increase longevity of prosthetic hip joints

More than 285,000 total hip replacement surgeries are performed in the US each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component, lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to improve the mechanical properties of the polyethylene component, and to manufacture ultra-smooth articulating surfaces. In contrast, we show that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. We have used a lubrication model to design the geometry of the patterned microtexture, and experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints.

10-year follow-up wear analysis of first-generation highly crosslinked polyethylene in primary total hip arthroplasty

Our goal was to report a 10-year follow up of linear penetration rates for HCLPE, and to determine whether a difference exists between penetrations measured on pelvis or hip anterior-posterior radiographs. We reviewed 48 total hip arthroplasties where a first-generation HCLPE liner was used. Femoral head penetration was measured on both AP pelvis and hip radiographs. Total wear and wear rate at 10 years were 1.26 mm and 0.122 mm/y, respectively. The rate decreased significantly after the first 2-3 years, plateauing at a wear rate of 0.05 mm/y for the last 5 years. The AP hip total wear and wear rate were 1.38 mm and 0.133 mm/y respectively, while rates were 1.13 mm and 0.109 mm/y respectively for the pelvis radiographs (P<.05). We found a significant difference in measurements of linear penetration when comparing AP pelvis vs. hip radiographs with lower rates recorded using an AP pelvis.

More than 50% reduction of wear in polyethylene liners with alumina heads compared to cobalt-chrome heads in hip replacements: a 10-year follow-up with radiostereometry in 43 hips

BACKGROUND AND PURPOSE

Excessive wear of acetabular liners in hip replacements may lead to osteolysis and cup loosening. Different head materials are currently used. We measured differences in wear between alumina and cobalt-chrome heads with the same polyethylene liner.

PATIENTS AND METHODS

39 patients (43 hips) with osteoarthritis were included in a study with 10-year follow-up. Wear was measured as proximal and 3D penetration of the head in the liner with radiostereometry (RSA). All the patients were followed clinically with Harris hip score (HHS) for up to 10 years. Radiolucent lines and osteolytic lesions were assessed on plain radiographs.

RESULTS

With alumina heads, proximal wear (95% CI) after 10 years was 0.62 (0.44-0.80) mm as compared to 1.40 (1.00-1.80) mm in the cobalt-chrome group. For 3D wear, the results were 0.87 (0.69-1.04) mm for alumina heads and 1.78 (1.35-2.21) mm for cobalt-chrome heads. Median (range) HHS was 98 (77-100) in the alumina group and it was 93 (50-100) in the cobalt-chrome group (p = 0.01). We found no difference in osteolysis between the groups.

INTERPRETATION

We found better wear properties with alumina heads than with cobalt-chrome heads. We recommend the use of alumina heads in patients in whom a high wear rate might be anticipated.

A comparison of polyethylene wear between cobalt-chrome ball heads and alumina ball heads after total hip arthroplasty: a 10-year follow-up

Study design

This is a retrospective study comparing polyethylene wear between ceramic ball heads and metal ball heads in total hip arthroplasty.

Background

The ceramic-on-polyethylene bearing option has been introduced as an alternative to metal-on-polyethylene to minimize polyethylene wear debris and reduce subsequent osteolysis and aseptic loosening. However, the reported data were debatable. We designed this retrospective study to compare polyethylene wear between alumina ceramic ball heads and cobalt-chrome ball heads.

Methods

Bilateral simultaneous primary total hip arthroplasty was performed in 22 patients between January 2002 and December 2002, with one side using metal-on-polyethylene bearing surface and the other side using alumina ceramic-on-polyethylene bearing surface. After 10 years of follow-up, the wear rate of polyethylene liner on both sides was measured using the Dorr method and compared.

Results

The annual wear rate of the polyethylene liner was 0.133 mm with a standard deviation of 0.045 in the metal-on-polyethylene group and 0.056 mm with a standard deviation of 0.032 in the ceramic-on-polyethylene group. The wear rate per year was significantly lower in the ceramic-on-polyethylene group (p < 0.001).

Conclusions

Although the implication is still controversial, our study showed that the use of ceramic head lowered the liner wear rate.

Clinical relevance

Ceramic is harder and more resistant to scratching than cobalt-chrome. By increasing polyethylene liner survivorship and decreasing potential osteolytic response and aseptic loosening, ceramic head is a better alternative than cobalt-chrome head.

Wear analysis of chamfered elongated acetabular cup liners

This study investigated the wear phenomena of chamfered acetabular cup liners. The liners have three parameters at the lengthened rim: the length of the elongation, the depth of the cup and the chamfer angle. Using published wear volume equations for cylindrically elongated liners, this study analysed the volume of the chamfer to obtain the exact theoretical wear volume of the chamfered liner. The criteria described in our previous paper were used to verify the accuracy of the proposed methodology. The results showed that a shallow cup depth (<2 mm) and a chamfer angle of about 30° could significantly reduce the wear volume arising from the elongation. When the chamfer angle was increased further, this effect became progressively less significant. The results suggest that a chamfer angle up to about 30° is appropriate, but the angle should not be larger than required to obtain the minimum femoral range of motion (ROM). The results of this study can also be integrated with the analysis of the kinetics and kinematics of liners. A compromise design incorporating a lower wear volume, sufficient ROM and a lower contact stress should be possible.

Less wear with aluminium-oxide heads than cobalt-chrome heads with ultra high molecular weight cemented polyethylene cups: a ten-year follow-up with radiostereometry

PURPOSE

Wear is a major contributor to osteolysis and aseptic loosening of total hip replacements (THR). Both alumina (Al(2)O(3)) and cobalt-chrome (CoCr) femoral heads are commonly used. We investigated wear comparing alumina heads to cobalt-chrome heads against conventional cemented polyethylene (PE) cups for up to ten years.

METHODS

Linear wear was measured with radiostereometry (RSA). Our material was derived from two prospective randomised trials that investigated fixation of femoral stems, not wear, and was evaluated retrospectively (Level III).

RESULTS

The mean (95% CI) proximal head penetration was 0.96 mm (0.68-1.23) in the cobalt-chrome group and 0.42 mm (0.30-0.53) in the alumina group at ten years (P = 0.001). The mean (95% CI) 3D penetration was 1.07 mm (0.79-1.35) and 0.53 mm (0.38-0.63), respectively, at ten years (P = 0.001).

CONCLUSION

Alumina heads performed better than cobalt-chrome heads in this study after ten-year follow-up.

Wear patterns of, and wear volume formulae for, cylindrically elongated acetabular cup liners

This study analyzed the wear patterns of, and wear volume formulae for, cylindrically elongated acetabular cup liners. The geometric patterns of the wear surface were first classified, then wear volume formulae were derived by integral calculus. SolidWorks((R)) software or published formulae were used to verify the accuracy of the proposed formulae. The analytical results showed that the wear shape of the liner can be categorized into seven wear patterns, including the special case of wear at 90 degrees , and the seven corresponding wear formulae were derived. In addition, wear of the cylindrical elongation might add considerably to the volume loss of the liner, depending on the height and shape of the elongation and the depth and direction of the linear penetration, being maximally 21% in the investigated model. The proposed wear formulae and patterns will be useful for more accurate performance evaluation of existing hip components implanted in patients and for the designing of new hip components.

Alumina-on-Polyethylene Bearing Surfaces in Total Hip Arthroplasty

The long-term durability of polyethylene lining total hip arthroplasty (THA) mainly depends on periprosthetic osteolysis due to wear particles, especially in young active patients. In hip simulator study, reports revealed significant wear reduction of the alumina ceramic-on-polyethylene articulation of THA compared with metal-on-polyethylene bearing surfaces. However, medium to long-term clinical studies of THA using the alumina ceramic-on-polyethylene are few and the reported wear rate of this articulation is variable. We reviewed the advantages and disadvantages of ceramicon- polyethylene articulation in THA, hip simulator study and retrieval study for polyethylene wear, in vivo clinical results of THA using alumina ceramic-on-polyethylene bearing surfaces in the literature, and new trial alumina ceramic-onhighly cross linked polyethylene bearing surfaces.

Early catastrophic acetabular failure in Furlong total hip replacements

The use of uncemented hip arthroplasty prostheses with ceramic articulations are popular, especially in the young, because of a perceived reduction in wear. We highlight a complication of ceramic on polyethylene articulating couples not previously described in the Furlong replacement. Despite widespread metalosis and particulate debris, osteolysis was not initially seen. The contamination compromised subsequent revision.

The effect of total hip arthroplasty cup design on polyethylene wear rate

Using 743 total hip arthroplasties that included 6 hemispheric porous-coated cup designs, this study used a multiple linear regression to identify those factors that influenced polyethylene wear rates. Wear rates for each hip were based on serial head penetration measurement made with computer-assisted techniques. Implant factors associated with an increased wear rate included terminal sterilization with a non-cross-linking chemical surface treatment, a 4-mm lateralized liner, a cobalt-chrome femoral head, and a longer shelf life for liners gamma-irradiated in air. After accounting for these implant characteristics and patient factors, wear rates among the 6 cup designs were not significantly different (P = .89). Although polyethylene wear is frequently characterized for specific implant designs, this study demonstrated that there are several common factors that influence polyethylene wear rates.

Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear

BACKGROUND

A dark metallic-appearing smear, resembling a lead pencil mark, may be seen on a ceramic femoral head component at revision total hip arthroplasty. The purpose of this study was to investigate the hypothesis that such a mark on a retrieved ceramic femoral head is associated with increased surface roughness of the head and increased polyethylene liner wear in total hip replacement.

METHODS

Fifteen ceramic prosthetic femoral heads retrieved from fifteen patients at revision arthroplasty were examined in this study. Thirteen heads had been in vivo for an average of 10.8 years (range, 7.8 to 14.2 years). The remaining two heads had been in vivo for less than one month. The surface roughness characteristics of the explanted ceramic heads, the linear wear of the polyethylene liner, and the patient activity levels after the primary replacement and before the revision were determined.

RESULTS

Four of the thirteen ceramic heads that had been in vivo for >/=7.8 years had severe smears (>6% of the surface area), and the remaining nine heads had slight smears (<6% of the surface area). The two heads that had been in vivo less than one month had severe smears. The mean Ra and Rpm, the values for surface roughness, were 44.95 nm and 571.15 nm, respectively, in the hips with slightly smeared regions and 180.77 nm and 1245.88 nm, respectively, in the hips with severely smeared regions (p = 0.002). The mean linear liner wear rate was 0.10 mm/yr in the hips with slightly smeared heads and 0.19 mm/yr in the hips with severely smeared heads (p = 0.002). The activity score for all patients was 5 or 6 points on a 6-point scale.

CONCLUSIONS

The results of this study confirm the hypothesis that a visual dark metallic-appearing smear on a ceramic femoral head correlates with increased surface roughness of the head and increased polyethylene wear. These findings imply that contact of a ceramic femoral head with a metallic material, such as may occur with femoral head reduction or dislocation of a total hip replacement, is best avoided to prevent this metallic smear phenomenon.

The measurement of creep in ultrahigh molecular weight polyethylene: a comparison of conventional versus highly cross-linked polyethylene

Quantification of creep of highly cross-linked polyethylene would enable separation of creep from wear when evaluating femoral head penetration into polyethylene. We compared creep magnitude of a highly cross-linked versus conventional polyethylene in the laboratory. Twelve acetabular liners of each material were tested, 6 of which had a 32-mm inner diameter (ID) and 6 had 28-mm ID. Creep was measured using coordinate measuring machines during loading at 2 Hz without motion to 4 million cycles. Penetration into 32-mm ID conventional liners reached 97 microm versus 107 microm for highly cross-linked material, not significant. Penetration into 28-mm conventional liners was 132 microm versus 155 microm for highly cross-linked material (P = .017). Ninety percent of the creep had occurred by 2.5 million cycles.

Cementless acetabular revision with the Harris-Galante porous prosthesis. Results after a minimum of ten years of follow-up

BACKGROUND

Revisions of the acetabular component of a total hip arthroplasty have a higher rate of complications, particularly loosening and dislocation, than do primary procedures. The purpose of this study, in which the results of a consecutive series of revisions performed with the Harris-Galante Porous acetabular component by a single surgeon were evaluated at an average of twelve years, was to quantify the complications and outcomes of acetabular revision.

METHODS

Clinical and radiographic results were evaluated to assess loosening, lysis, radiolucencies, and trochanteric union in 188 hips (170 patients) treated between 1984 and 1990. One hundred and twenty-two hips in 110 patients were followed for at least ten years, which was required for inclusion in the study. Thirty-one patients (thirty-six hips) died less than ten years postoperatively, and twenty-nine patients (thirty hips) were lost to or refused to return for follow-up.

RESULTS

The average Harris hip score was 78 points at an average of 12.5 years after revision, which was a 29-point improvement compared with the preoperative score. The rate of repeat revision because of aseptic loosening of the acetabular shell was 4% (five of 122). The rate of repeat revision of the shell for any reason was 15% (eighteen of 122). Eight unrevised sockets were loose radiographically, for a total rate of aseptic loosening of 11% (thirteen of 122).

CONCLUSIONS

This study demonstrated that most acetabular revisions with this cementless hemispherical socket were successful. Few structural grafts and no cages were used.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.

Long-term in vivo wear performance of porous-coated acetabular components sterilized with gamma irradiation in air or ethylene oxide

This study evaluated the long-term in vivo wear performance of 2 groups of well-functioning cementless acetabular cups sterilized by different methods. The first group included 31 hips that were implanted with AML TriSpike cups (DePuy, Warsaw, IN) sterilized by gamma-irradiation in air. The second group included 28 hips implanted with Arthropor cups (Joint Medical Products, Stamford, CT) that were sterilized with ethylene oxide. Time-dependent variations in the radiographic wear rates were compared within each group. Changes in the wear rates between 4- and 16-year follow-up times for the TriSpike cups were not significant (P=.09), and there was no evidence to suggest a trend toward substantially increasing wear rates with longer follow-up times. Among the Arthropor cups, the wear rates remained relatively constant between 2 and 14 years of follow-up evaluation. Although clinically apparent late increases in radiographic head penetration rates were not evident, we will continue to monitor all patients for evidence of accelerated wear at late follow-up.

Effect of terminal sterilization with gas plasma or gamma radiation on wear of polyethylene liners

BACKGROUND

Although terminal sterilization with gamma radiation in air promotes cross-linking, which improves wear resistance, it also results in free radicals, which can oxidize and degrade the mechanical properties of polyethylene liners used for total hip arthroplasty. For this reason, non-cross-linked polyethylene components have also been sterilized with chemical surface treatments, such as gas plasma. In this study, we tested the hypothesis that conventional polyethylene liners cross-linked by sterilization with gamma radiation in air had better in vivo wear performance than non-cross-linked liners sterilized with gas plasma.

METHODS

We retrospectively reviewed the wear rates in a series of hips treated with a Duraloc 100 cup, a 28-mm femoral head, and an Enduron liner that had been sterilized with either gamma radiation (sixty-one hips followed for a mean of 5.2 years) or gas plasma (sixty-three hips followed for a mean of 3.9 years). The irradiated liners had been stored with access to ambient oxygen for an average of 1.0 year (range, 0.05 to 5.72 years) prior to implantation. Multiple linear regression was used to assess the effect of the sterilization method on the wear rate while accounting for the possible influence of other factors, including liner geometry, femoral head material, patient gender, cup abduction angle, and age at surgery.

RESULTS

The polyethylene liners that had been sterilized with gamma radiation in air had a significantly lower wear rate than did the gas-plasma-sterilized liners (0.097 compared with 0.19 mm/yr, p < 0.001). The sterilization method (p < 0.001) and age at surgery (p = 0.001) were the only factors that we analyzed that correlated with the wear rate.

CONCLUSIONS

The in vivo wear of conventional polyethylene liners that had been sterilized with gamma radiation in air was, on the average, 50% less than that of non-cross-linked liners sterilized with gas plasma.

LEVEL OF EVIDENCE

Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Total hip arthroplasty with use of the cementless Zweymüller Alloclassic system. A ten to thirteen-year follow-up study

BACKGROUND

The Zweymüller Alloclassic total hip arthroplasty system is widely used, although few intermediate-term studies have been published. The purpose of the present study was to evaluate the clinical and radiographic results of this system after ten years.

METHODS

One hundred and twenty-four consecutive primary total hip arthroplasties were performed with the Zweymüller Alloclassic cementless system at our institution between February 1988 and March 1991, and 104 hips (ninety-four patients) were retrospectively reviewed after a minimum duration of follow-up of ten years. The mean age of the patients at the time of the arthroplasty was 62.3 years (range, twenty-five to seventy-seven years). The mean duration of follow-up was 11.3 years. Standard radiographs were made for all patients immediately after the operation, at six and twelve months, and annually thereafter for at least ten years. Cox multivariate regression analysis was performed to assess the influence of various factors on survival of the implant.

RESULTS

The cumulative probability of not having a revision of any prosthetic component for any reason was 94.1% (95% confidence interval, 91.9% to 96.3%) at twelve years in the best-case scenario and 85.3% (95% confidence interval, 82.1% to 88.5%) at twelve years in the worst-case scenario for the entire series of 124 hips. Among the 104 hips in the follow-up study, three acetabular components and no stems were revised. Two hips had level-4 pain according to the system of Merle D'Aubigné and Postel. Seven acetabular components (7%) were loose at twelve years, and all stems had radiographic evidence of stable fixation. Acetabular cup loosening was related to a vertical cup angle (p = 0.0008, Student t test), acetabular wear of > or =1 mm (p = 0.001, Fisher exact test), and a 32-mm femoral head (p = 0.001, Fisher exact test). Although femoral osteolysis was seen in eighteen hips (17%) at twelve years, all osteolytic cavities were proximal and focal.

CONCLUSIONS

The Zweymüller Alloclassic prosthesis, particularly its femoral stem, demonstrated good results and durable fixation at a minimum of ten years of follow-up.

Cementless total hip arthroplasty with a close proximal fit and short tapered distal stem (third-generation) prosthesis

This study presents the results of a prospective, consecutive series of 50 patients (60 hips) who were observed for a minimum of 6 years after they had a primary total hip arthroplasty with a cementless Duraloc 100 series cup (DePuy, Warsaw, IN) with a close proximal fit and short tapered distal stem prosthesis (IPS hip; DePuy, Leeds, UK). There were 37 men and 13 women; the mean age was 46.6 years (range, 26 to 70 years). The mean follow-up was 6.3 years (range, 6 to 7 years). The mean preoperative Harris hip score was 42 points, which improved to 96 points at the final follow-up examination. The prevalence of transitory thigh pain was 2%. All hips had a satisfactory fit of the femoral stem in coronal (average, 88%) and sagittal (average, 94%) planes. There was no aseptic loosening or revision of the components. The wear rate per year was 0.23 mm. Four hips (7%) had osteolysis in the calcar femorale <1 cm in diameter. Although there was no aseptic loosening of the components, a low incidence of osteolysis, and a low incidence of thigh pain, a high rate of polyethylene liner wear in these young patients is a problem.

A literature review of the association between wear rate and osteolysis in total hip arthroplasty

The establishment of a polyethylene wear rate threshold for the development of osteolysis at the hip would allow surgeons to identify patients at risk for osteolysis and to implement selective, more frequent follow-up. We reviewed publications that met certain criteria for wear and osteolysis measurement. Based on this review, the incidence of osteolysis increases as the rate of wear increases. The literature indicates that osteolysis rarely is observed at a wear rate of <0.1 mm/y. We suggest that a practical wear rate threshold of 0.05 mm/y would eliminate osteolysis. This wear threshold suggests that the new cross-linked polyethylenes would reduce osteolysis, provided that in vivo wear rates mirror those observed in vitro. To facilitate future comparison of published data, we suggest that longitudinal wear studies adopt consistent edge detection-based wear measurement techniques and uniform osteolytic lesion classification and measurement schema.

Total hip replacement with a cementless acetabular component and a cemented femoral component in patients younger than fifty years of age

BACKGROUND

We have been using hybrid total hip arthroplasty (a cementless acetabular component and a cemented stem) in young patients. The purpose of this study was to determine the prevalence of aseptic loosening, polyethylene wear, and osteolysis after the use of this technique.

METHODS

We studied a prospective consecutive series of sixty-four primary hybrid total hip replacements in fifty-five patients younger than fifty years old. There were forty-three men and twelve women; the average age at the time of the index operation was 43.4 years. The average duration of follow-up was 9.4 years. We used a cementless acetabular component without screw-holes and a cemented femoral component with a 22-mm head in all hips. Clinical follow-up with use of Harris hip ratings and radiographic follow-up were performed at six weeks; at three, six, and twelve months; and yearly thereafter. The sequential annual linear and volumetric wear rates were measured, and bone-remodeling and osteolysis were assessed.

RESULTS

The mean preoperative Harris hip score was 44 points, which increased to 95 points at the time of final follow-up. No hip had aseptic loosening. One hip (2%) was revised because of late infection. The average linear wear (and standard deviation) was 0.96 +/- 0.066 mm, with an average annual rate of 0.096 +/- 0.013 mm. The average volumetric wear was 364.7 +/- 25.2 mm (3), with an average annual rate of 43.4 +/- 3.5 mm (3). Six hips (9%) had an osteolytic lesion of <1 cm in diameter in the calcar femorale (zone 7).

CONCLUSIONS

Our results show that a hybrid arthroplasty with a cementless acetabular component and a smooth cemented femoral component (Ra, 0.6 mm) is effective for primary total hip replacement in young patients. Although there was no aseptic loosening and a low prevalence of osteolysis at the latest follow-up evaluation, the high rates of linear and volumetric wear of the polyethylene liner in these young patients remain a concern.

Polyethylene wear of the porous-coated anatomic total hip arthroplasty with an average 11-year follow-up

The purpose of this study was to identify the factors that affect polyethylene wear of 55 porous-coated anatomic total hip arthroplasties after 9 to 14 years selected from a study population of 311 implants. The average three-dimensional linear, two-dimensional linear, and volumetric wear rates were 0.096 mm/y, 0.052 mm/y, and 34 mm3/y. Negative wear was noted in 7 patients using two-dimensional techniques. Significantly higher volumetric wear rate was observed for men (48 mm3/y) compared with women (24 mm3/y; P<.01), for patients <60 years old (45 mm3/y) compared with patients >60 years old (25 mm3/y; P<.01), and for 32-mm femoral heads (54 mm3/y) compared with 26-mm femoral heads (29 mm3/y; P<.01). Volumetric wear rate for patients having small (39 mm3/y) and large (65 mm3/y) areas of osteolysis were 2 and 3 times greater than for patients having no osteolysis (21 mm3/y) (P<.01).