Radiostereometric analysis comparison of wear of highly cross-linked polyethylene against 36- vs 28-mm femoral heads

Short-term outcomes with routine use of size ≥40 femoral heads in THA: A retrospective cohort study

Background

Using larger femoral heads during total hip arthroplasty (THA) may result in a more stable hip. Greater volumetric wear and frictional torque, however, may result in increased postoperative complications. The purpose of this study was to compare outcomes of patients with femoral head size ≥40 mm compared to those with femoral head size <40 mm.

Materials and methods

A retrospective chart review of 504 THAs performed by a single surgeon at a single institution from 2009 to 2016 was conducted. Following exclusions, 131 THAs were identified with femoral heads ≥40 mm and 348 THAs were identified with femoral heads <40 mm. In addition to demographic data, all postoperative complications were recorded. Plain radiographs were used to rule out/in periprosthetic osteolysis and/or acetabular loosening. Chi-square tests and Student's t-tests were used to compare categorical and continuous variables, respectively.

Results

Mean follow-up period for the entire cohort was 5.5 years. Complications with ≥40 mm femoral heads included 1 superficial infection and 1 deep periprosthetic joint infection (PJI). There were no cases of dislocation, osteolysis, acetabular loosening, or trunnionosis. In contrast, complications with <40 mm femoral heads included 9 dislocations and 7 PJIs.

Conclusion

The routine use of large femoral heads (≥40-mm) during THA appears to be a safe option for patients at short-term clinical follow-up. Notably, 0 patients had a clinical course complicated by dislocation, osteolysis, acetabular loosening, or trunnionosis.

Level of evidence

Level III Retrospective Cohort Study.

Ceramic Femoral Heads Exhibit Lower Wear Rates Compared to Cobalt Chrome: A Meta-Analysis

BACKGROUND

Wear between the femoral head and acetabular liners continues to limit the longevity of total hip arthroplasty implants despite advances in implant materials. The purpose of this meta-analysis was to compare linear wear rates of cobalt-chromium (CoCr) and fourth-generation ceramic femoral heads on highly cross-linked polyethylene (XLPE) liners.

METHODS

A systematic review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted to identify all studies between 2003 and 2020 that examined in vivo wear rates of either fourth-generation ceramics or CoCr femoral heads on XLPE liners. Studies were analyzed in a weighted means analysis of wear rates and a random effects meta-analysis.

RESULTS

A total of 36 studies met inclusion criteria (1,657 CoCr and 659 ceramic patients). The pooled, weighted mean wear rate was 0.063 mm/year (standard deviation [SD]: 0.061, confidence interval [CI]: 0.049-0.077) for CoCr and 0.047 mm/year (SD: 0.057, CI: 0.033-0.062; P < .01) for ceramic (P < .01). A meta-analysis of 4 studies directly comparing ceramic and CoCr found that CoCr heads demonstrated 0.029 mm/year more wear than ceramic heads (95% CI: 0.026-0.059, P = .306). Mean wear for 32-mm heads was significantly higher for ceramic (P < .01), while mean wear for 36-mm heads was significantly higher for CoCr (P < .01).

CONCLUSION

Fourth-generation ceramic femoral heads were found to have significantly lower wear rates than CoCr heads. Unlike previous studies, this meta-analysis included only in vivo studies and those with the same generation of highly XLPE liners.

To what extent could the acetabular liner thickness be reduced yet remaining tribologically acceptable in metal-on-vitamin E-diffused crosslinked polyethylene hip arthroplasty?

The aim of the present study was to evaluate how much reduction in acetabular liner thickness could be tribologically acceptable in metal-on-vitamin-E diffused highly crosslinked ultra-high molecular weight polyethylene (Vit-E XLPE) bearings for total hip arthroplasty. We tested thick- (10.3 mm), moderate- (6.3 mm), and thin- (4.3 mm) Vit-E XLPE liners coupled with 28-mm cobalt-chromium femoral heads on a hip simulator to 5 million cycles, and peak contact stress was predicted based on mathematical modeling. Wear damage was also evaluated in terms of surface topology and morphology. Wear simulation demonstrated that the 2-4 mm thickness reduction (6.3 → 4.3 mm and 10.3 → 6.3 mm) did not significantly affect the wear rate for Vit-E XLPE liner, whereas 6-mm reduction (10.3 → 4.3 mm) significantly increased liner wear (by 309%) and head roughness (by 415%). This effect was attributed to a contact stress increase (by 24-41%). However, the wear rates for all thicknesses tested were much lower than those previously reported for thicker non-crosslinked materials. The original crystalline morphology was maintained in all liners after wear. Our results suggest that the 2-4 mm thickness reduction may be tribologically acceptable in Vit-E XLPE liners. However, more severe and longer term simulations are necessary to determine a minimum acceptable thickness.

Wear and migration are not influenced by head size in a vitamin E-infused highly cross-linked polyethylene acetabular cup

BACKGROUND

Aseptic loosening and periprosthetic osteolysis are frequent complications in total hip arthroplasty requiring revision surgery. Highly cross-linked polyethylene (HXLPE) implants have improved wear resistance, permitting larger femoral heads. However, such implants may experience surface cracking, mechanical failure, and oxidative damage. Vitamin E-infused HXLPE (VEPE) implants were therefore developed to reduce oxidation without compromising mechanical strength. We addressed the following questions: (1) Does femoral head size affect the midterm annual polyethylene wear rates of VEPE acetabular cups? (2) Does femoral head size affect the midterm migration rates of VEPE acetabular cups? (3) Are clinical outcomes affected by femoral head size?

HYPOTHESIS

Annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups are independent of femoral head size.

PATIENTS AND METHODS

This was a prospective, multicentre, observational study of patients that underwent total hip arthroplasty. Hips were grouped according to the size of femoral head implanted (28 mm, 32 mm, and 36 mm). We determined annual wear rate and migration rate of VEPE acetabular cups using the Einzel-Bild-Röntgen-Analyse software. Clinically, we assessed the Harris Hip Score and visual analog score for pain and satisfaction.

RESULTS

We followed 253 patients (267 hips) for a mean of 55.0±20.6 months in the 28 mm, 46.2±21.4 months in the 32 mm, and 43.8±22.6 months in the 36 mm group. The annual wear rate was 0.025 mm per year from 1 year to the last follow-up and remained similar between the groups (p>0.05). Also, mean two-dimensional migration rates did not exceed 0.05 mm from 2 years to the last follow-up and remained similar between the groups (p=0.355). Finally, clinical outcomes also did not differ between the groups (p>0.05). Two patients required revision surgery.

DISCUSSION

Femoral head size did not influence midterm annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups. Furthermore, wear and cup migration rates were below the reported values leading to osteolysis and aseptic loosening. Nevertheless, studies with extended follow-up periods will be necessary to confirm these results in the long term.

LEVEL OF EVIDENCE

IV.

Selective screw fixation is associated with early failure of primary acetabular components for aseptic loosening

Selective supplementation of acetabular component fixation with a screw during primary total hip arthroplasty (THA) assumes that the surgeon can detect when an acetabular component needs additional stability. In contrast, nonselective screw users do not alter their practice based on their interpretation of stability and either use screws all or none of the time. We aimed to determine the effect of selective screw use on aseptic acetabular component loosening. We retrospectively reviewed aseptic failures of acetabular components after primaty THA. We compared the survivorship of selective and nonselective supplementation of acetabular fixation with respect to time to revision, obesity, and screw use. Selective screw use (n = 16) was associated with earlier acetabular component aseptic loosening (median: 1.9 years; interquartile range [IQR]: 1.1-5.0) compared to nonselective screw use (n = 22; median: 5.6 years; IQR: 2.0-15.3; P = .010). Selective screw use was independently associated with earlier revision after adjusting for patient obesity. Obesity was associated with selective screw use in 50% of the cases vs 14% of nonselective cases (odds ratio: 6.3; confidence interval: 1.2-25.2; P = .028), possibly reflecting the increased difficulty in achieving acetabular component stability in this and other settings with compromised bone. Surgeons should carefully assess component stability at time of primary THA. If the acetabulum is not stable, the addition of screws alone may not be sufficient for acetabular component stability.

In vivo volumetric and linear wear measurement of reverse shoulder arthroplasty at minimum 5-year follow-up

BACKGROUND

Reverse shoulder arthroplasty is quickly becoming the most frequently performed glenohumeral joint replacement. The purpose of this study was to evaluate the volumetric and linear wear rates of ultrahigh-molecular-weight polyethylene humeral liners in vivo at a minimum 5-year follow-up.

METHODS

Radiostereometric analysis was used to image 15 patients at terminal range of motion in forward flexion, abduction, external rotation, and internal rotation and with the arm at the side. The relative position and orientation of the glenosphere and polyethylene were identified for each arm position. The apparent intersection of the glenosphere into the polyethylene was recorded as wear. Mean volumetric and linear wear rates were recorded, and Pearson correlation coefficients were applied to the 36-mm liners to assess the relationship between the wear rate and term of service.

RESULTS

The mean reverse shoulder arthroplasty term of service at the time of imaging was 8 ± 1 years (range, 6-11 years). The mean volumetric and linear wear rates for the 36-mm liners (n = 13) were 42 ± 22 mm³/yr (r = 0.688, P = .009) and 0.11 ± 0.03 mm/yr (r = 0.767, P = .002), respectively. The mean volumetric and linear wear rates for the 42-mm liners (n = 2) were 114 ± 44 mm³/yr and 0.17 ± 0.01 mm/yr, respectively. No single arm position was able to capture all recorded wear individually.

CONCLUSION

This study showed volumetric and linear wear rates of approximately 40 mm³/yr and 0.1 mm/yr, respectively, for the 36-mm polyethylene liners. The 42-mm liners showed higher wear rates, although a greater number of subjects is required for conclusive results. In vivo wear of reverse total shoulder arthroplasty is multidirectional and perceptible.

The effect of structural parameters of total hip arthroplasty on polyethylene liner wear behavior: A theoretical model analysis

Using large femoral heads in total hip arthroplasty (THA) has been widely advocated to improve the function and longevity of the components. However, increasing the head size has been shown to accelerate polyethylene liner wear. Few studies have investigated the effect of other important structural parameters (such as polyethylene liner thickness, metal cup size, head-liner conformity, loading conditions, etc.) on the biomechanical functions of the THAs. In this study, an analytical model was used to evaluate the polyethylene liner wear characteristics of the THAs (defined using a biomechanical wear factor) with various structural parameters of the THAs and loading conditions. For all the THA systems examined in this study, under the same loading conditions, a larger head leads to increasing contact areas, lower contact stresses, and higher biomechanical wear factors. When the head size is fixed, a decrease in the polyethylene liner thickness or a decrease in the head-liner conformity leads to higher peak contact stresses and smaller contact areas and consequently, lower biomechanical wear factors. This study provides a parametric analysis tool for the optimal design/selection of the THA systems and for prediction of early effects of various structural parameters on the biomechanical function (such as contact stresses) and longevity (such as polyethylene liner wear) of the THA systems.

Radiostereometric Analysis of Stability and Inducible Micromotion After Locked Lateral Plating of Distal Femur Fractures

OBJECTIVES

To evaluate interfragmentary motion over 1 year after distal femoral fracture fixation using radiostereometric analysis (RSA). The secondary aim was to assess whether RSA data are consistent with diagnoses of nonunion.

DESIGN

Prospective cohort study.

SETTING

Level I urban trauma center.

PATIENTS

Sixteen patients between 22 and 89 years of age with distal femoral fracture (OTA/AO type 33).

INTERVENTION

All fractures were treated with a lateral locking plate, and tantalum markers were inserted into the main proximal and distal fracture fragments. RSA was performed at 2, 6, 12, 18, and 52 weeks postoperatively. Both unloaded and loaded RSA measurements were performed.

MAIN OUTCOME MEASUREMENTS

Unloaded fracture migration over time and inducible micromotion at the fracture site in the coronal plane were determined at each follow-up interval.

RESULTS

RSA precision in the coronal plane of interfragmentary motion over time and inducible micromotion were 1.2 and 0.9 mm in the coronal plane, respectively. Two cases required revision surgery for nonunion 1 year postoperatively. For cases of union, unloaded fracture migration stopped being detectable between 12 and 18 weeks, and inducible micromotion was no longer detectable by the 12-week visit. For cases of nonunion, both unloaded migration and inducible micromotion were detected throughout the study period.

CONCLUSIONS

RSA may be used to reliably assess distal femoral fracture healing. RSA revealed differences in cases of union and nonunion by 3 months and more consistently than traditional x-rays.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Large Metal Heads and Highly Cross-Linked Polyethylene Provide Low Wear and Complications at 5-13 Years

BACKGROUND

Highly cross-linked polyethylene (XLPE) is reported to have low rates of linear and volumetric wear at 10-14 years. In a prior study, larger (36 and 40 mm) femoral heads were associated with more volumetric wear, but there were only 12 hips with these heads.

METHODS

We evaluated 107 hips (93 patients, with a mean age of 76 years) with one design of uncemented acetabular component, a 36 (90 hips) or 40 mm (17 hips) metal femoral head, and one electron beam 100 kGy irradiated and remelted XLPE at a mean follow-up of 8 years (range 5-13 years). Selection of these femoral heads was based on several factors, including the perceived risk of dislocation, the outer diameter size of the acetabular component, and liner availability. Measurements of linear and volumetric wear were performed in one experienced laboratory by the Martell method and analyzed using the first-to-last method. Standard radiographs, with additional Judet views, were used to detect periprosthetic osteolysis. Clinical records were used to determine the complications of dislocation, liner fracture, and painful trunnion corrosion.

RESULTS

For the entire cohort, the median linear wear rate was 0.041 mm/y (95% confidence interval, 0.031-0.057) and the median volumetric wear rate was 34.6 mm³/y (95% confidence interval, 31.4-53.5). With the numbers available, there was no difference in linear or volumetric wear between the 36 and 40 mm head sizes. Small, asymptomatic osteolytic lesions were noted in 3 hips (2%). There were 3 patients (3%) with dislocation (2 early and 1 late), but these have not had a revision. There were no revisions for loosening, no liner fracture, and no patient with symptomatic trunnion corrosion.

CONCLUSION

This acetabular component and XLPE with large metal heads had low rates of linear and volumetric wear. Large metal femoral heads did not lead to liner fracture, loosening, or symptomatic trunnion corrosion in this patient population. However, we recommend longer clinical follow-up studies and caution in the routine use of larger metal femoral heads in other, younger patient populations.

Outcome in design-specific comparisons between highly crosslinked and conventional polyethylene in total hip arthroplasty

Background and purpose - Most registry studies regarding highly crosslinked polyethylene (XLPE) have focused on the overall revision risk. We compared the risk of cup and/or liner revision for specific cup and liner designs made of either XLPE or conventional polyethylene (CPE), regarding revision for any reason and revision due to aseptic loosening and/or osteolysis. Patients and methods - Using the Nordic Arthroplasty Register Association (NARA) database, we identified cup and liner designs where either XLPE or CPE had been used in more than 500 THAs performed for primary hip osteoarthritis. We assessed risk of revision for any reason and for aseptic loosening using Cox regression adjusted for age, sex, femoral head material and size, surgical approach, stem fixation, and presence of hydroxyapatite coating (uncemented cups). Results - The CPE version of the ZCA cup had a risk of revision for any reason similar to that of the XLPE version (p = 0.09), but showed a 6-fold higher risk of revision for aseptic loosening (p < 0.001). The CPE version of the Reflection All Poly cup had an 8-fold elevated risk of revision for any reason (p < 0.001) and a 5-fold increased risk of revision for aseptic loosening (p < 0.001). The Charnley Elite Ogee/Marathon cup and the Trilogy cup did not show such differences. Interpretation - Whether XLPE has any advantage over CPE regarding revision risk may depend on the properties of the polyethylene materials being compared, as well as the respective cup designs, fixation type, and follow-up times. Further research is needed to elucidate how cup design factors interact with polyethylene type to affect the risk of revision.

Raman spectroscopy of biomedical polyethylenes

With the development of three-dimensional Raman algorithms for local mapping of oxidation and plastic strain, and the ability to resolve molecular orientation patterns with microscopic spatial resolution, there is an opportunity to re-examine many of the foundations on which our understanding of biomedical grade ultra-high molecular weight polyethylenes (UHMWPEs) are based. By implementing polarized Raman spectroscopy into an automatized tool with an improved precision in non-destructively resolving Euler angles, oxidation levels, and microscopic strain, we become capable to make accurate and traceable measurements of the in vitro and in vivo tribological responses of a variety of commercially available UHMWPE bearings for artificial hip and knee joints. In this paper, we first review the foundations and the main algorithms for Raman analyses of oxidation and strain of biomedical polyethylene. Then, we critically re-examine a large body of Raman data previously collected on different polyethylene joint components after in vitro testing or in vivo service, in order to shed new light on an area of particular importance to joint orthopedics: the microscopic nature of UHMWPE surface degradation in the human body. A complex scenario of physical chemistry appears from the Raman analyses, which highlights the importance of molecular-scale phenomena besides mere microstructural changes. The availability of the Raman microscopic probe for visualizing oxidation patterns unveiled striking findings related to the chemical contribution to wear degradation: chain-breaking and subsequent formation of carboxylic acid sites preferentially occur in correspondence of third-phase regions, and they are triggered by emission of dehydroxylated oxygen from ceramic oxide counterparts. These findings profoundly differ from more popular (and simplistic) notions of mechanistic tribology adopted in analyzing joint simulator data. Statement of Significance This review was dedicated to the theoretical and experimental evaluation of the commercially available biomedical polyethylene samples by Raman spectroscopy with regard to their molecular textures, oxidative patterns, and plastic strain at the microscopic level in the three dimensions of the Euclidean space. The main achievements could be listed, as follow: (i) visualization of molecular patterns at the surface of UHMWPE bearings operating against metallic components; (ii) differentiation between wear and creep deformation in retrievals; (iii) non-destructive mapping of oxidative patterns; and, (iv) the clarification of chemical interactions between oxide/non-oxide ceramic heads and advanced UHMWPE liners.

Accuracy of methods to measure femoral head penetration within metal-backed acetabular components

A number of different software programs are used to investigate the in vivo wear of polyethylene bearings in total hip arthroplasty. With wear rates below 0.1 mm/year now commonly being reported for highly cross-linked polyethylene (XLPE) components, it is important to identify the accuracy of the methods used to measure such small movements. The aims of this study were to compare the accuracy of current software programs used to measure two-dimensional (2D) femoral head penetration (FHP) and to determine whether the accuracy is influenced by larger femoral heads or by different methods of representing the acetabular component within radiostereometric analysis (RSA). A hip phantom was used to compare known movements of the femoral head within a metal-backed acetabular component to FHP measured radiographically using RSA, Hip Analysis Suite (HAS), PolyWare, Ein Bild Roentgen Analyse (EBRA), and Roentgen Monographic Analysis Tool (ROMAN). RSA was significantly more accurate than the HAS, PolyWare, and ROMAN methods when measuring 2D FHP with a 28 mm femoral head. Femoral head size influenced the accuracy of HAS and ROMAN 2D FHP measurements, EBRA proximal measurements, and RSA measurements in the proximal and anterior direction. The use of different acetabular reference segments did not influence accuracy of RSA measurements. The superior accuracy and reduced variability of RSA wear measurements allow much smaller cohorts to be used in RSA clinical wear studies than those utilizing other software programs. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:988-996, 2017.

The rate of wear of second-generation highly crosslinked polyethylene liners five years post-operatively does not increase if large femoral heads are used

AIMS

The increased in vivo resistance to wear of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA) has led to an increased use of larger articulations which have been shown to reduce the incidence of early dislocation. To date, there are few reports of the wear of larger articulations using second generation HXLPE liners. Our prospective cohort study measured the bedding-in and early wear of large (36 mm and 40 mm diameter) articulations involving a second generation X3 HXLPE liner and compared our findings with previous clinical and in vitro studies of the same material.

PATIENTS AND METHODS

The proximal penetration of the femoral head five years post-operatively was measured for 15 patients using radiostereometric analysis (RSA).

RESULTS

The median proximal bedding-in within the first post-operative year was 0.022 mm (interquartile range (IQR) -0.050 to 0.091). The median proximal rate of wear between one and five years was -0.004 mm/year (IQR -0.021 to 0.022). The rates of proximal, medial, 2D or 3D wear between one and five years post-operatively of the X3 HXLPE liner did not increase with larger articulations compared with our previous study of 32 mm articulations.

CONCLUSION

Although reassuring, the use of larger articulations requires continued monitoring to determine whether the low wear observed in the short-term continues to the mid- to long-term. Cite this article: Bone Joint J 2016;98-B:1604-10.

Polyethylene Wear Associated With 26- and 32-mm Heads in Total Hip Arthroplasty: A Multicenter, Prospective Study

BACKGROUND

Although there were many clinical studies of highly cross-linked polyethylene (XLPE) wear among different femoral head diameters, few referred to thickness of XLPE in case larger femoral heads were used because smaller sockets were frequently used for Asian population.

METHODS

This prospective study included 240 hips that underwent primary total hip arthroplasty using XLPE combined with 26-mm (group S) or 32-mm (group L) cobalt-chromium head with maximum follow-up of 10 years. We measured 3-dimensional (3-D) linear penetration rate of XLPE among same implant design groups except head diameter and estimated the validity of thinner XLPE.

RESULTS

Our study demonstrated comparable 3-D linear penetration rates, which were 0.06 ± 0.07 mm/y for group S and 0.03 ± 0.02 mm/y for group L at 10 years after surgery and penetration rates seemed to be almost constant with no significant difference after 3 years. Minimum liner thickness (5.3 mm for 48-mm socket in combination with 32-mm femoral head) and the second thinnest XLPE (6.3 mm in case of socket from 50 mm to 54 mm combined with 32-mm femoral head) was distributed in 25% and 72% with group L, respectively, and there were no significant differences in penetration rates between 5.3-mm- and 6.3-mm-thickness groups.

CONCLUSION

Our study suggested that whether to select 26- or 32-mm diameters of femoral head does not affect XLPE wear in combination with this type of articulation.

Alumina Delta-on-Highly Crosslinked-Remelted Polyethylene Bearing in Cementless Total Hip Arthroplasty in Patients Younger than 50 Years

BACKGROUND

The purpose of this retrospective study was to determine the clinical and radiographic results, prevalence of polyethylene wear and osteolysis, and fracture of alumina delta ceramic femoral head or highly crosslinked, remelted polyethylene (HXLPE) liner associated with the use of alumina delta ceramic femoral head-on-HXLPE bearing in cementless total hip arthroplasty in patients younger than 50 years.

METHODS

We reviewed the cases of 119 patients (130 hips) who underwent a cementless total hip arthroplasty using alumina delta ceramic-on-HXLPE bearing when they were 50 years or younger at the time of surgery. The most common diagnoses were osteonecrosis (51%) and osteoarthritis secondary to developmental dysplastic hip (39%). Osteolysis and polyethylene wear rates were evaluated with use of radiography and computed tomography. In addition, prevalence of fracture of alumina delta ceramic head and polyethylene line was documented. The mean follow-up was 8.3 years (range, 7-9 years).

RESULTS

The mean Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index score, University of California, Los Angeles activity score were 94 points, 14 points, and 8.1 points, respectively, at the final follow-up. No patient had thigh pain. All acetabular components and all but one femoral components were well fixed. The mean annual penetration rate of femoral head was 0.022 ± 0.003 mm/year. No hip had osteolysis or ceramic head or HXLPE liner fracture.

CONCLUSION

Our average 8.3-year results with the use of alumina delta ceramic-on-HXLPE bearing in the patients younger than 50 years suggest that cementless acetabular and femoral components provide a high survival rate without evidence of osteolysis or ceramic head or AXLPE liner fracture.

The Wear Rate of Highly Cross-Linked Polyethylene in Total Hip Replacement Is Not Increased by Large Articulations: A Randomized Controlled Trial

BACKGROUND

Larger articulations reduce the risk of dislocation following primary total hip arthroplasty, leading to increased use of these articulations. The wear rate of highly cross-linked polyethylene (XLPE) is low in standard-diameter articulations but remains unclear in larger articulations. The aim of this randomized controlled trial was to compare the mean wear rates of 36-mm and 28-mm metal-on-XLPE articulations between 1 and 3 years postoperatively.

METHODS

Fifty-six elderly patients undergoing primary total hip arthroplasty were randomized intraoperatively to receive either a 36-mm or 28-mm metal-on-XLPE articulation. Factors that may affect wear were controlled by study design. Wear was measured using radiostereometric analysis.

RESULTS

Mean annual proximal wear rates between 1 and 3 years were 0.00 and 0.01 mm/yr for the 36 and 28-mm articulation cohorts, respectively. No patient had a proximal wear rate of >0.1 mm/yr. Mean wear was very low in all directions, and the wear rate of 36-mm articulations was not significantly greater than that of 28-mm articulations on the basis of proximal, medial 2-dimensional, and 3-dimensional wear.

CONCLUSIONS

The wear rate of a larger 36-mm metal-on-XLPE articulation between 1 and 3 years following primary total hip arthroplasty was low and no greater than that of a 28-mm articulation. However, before a 36-mm metal-on-XLPE articulation is widely recommended, particularly in young active patients, long-term wear rates and association between wear and periprosthetic osteolysis should be determined.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Highly cross-linked polyethylene improves wear and mid-term failure rates for young total hip arthroplasty patients

We compared clinical outcomes and polyethylene wear for 2 young primary THA patient cohorts (<50 years of age) at mid-term follow-up. In total, 72 patients (84 hips) received a coventional polyethylene liner (CPE) and 84 patients (89 hips) received a highly cross-linked polyethylene liner (HXLPE). Mean Harris Hip Score improved to 81 points for both groups. UCLA activity scores were higher for HXLPE patients (6.0 vs 5.3, p = 0.03), with lower mean linear wear (0.02 vs 0.13 mm/year, p<0.001) and lower mean volumetric wear (75.1 vs 229.8 mm3, p<0.001) at an average of 70 months follow-up. No HXLPE patient required revision for wear related concerns, compared to 5 CPE patients with revision for aseptic loosening or impending radiographic failure (0% vs 5.9%, p = 0.02). HXLPE is associated with reduced wear among young, active THA patients without increased risk of early mechanical failure.

Wear and Osteolysis of Highly Crosslinked Polyethylene at 10 to 14 Years: The Effect of Femoral Head Size

BACKGROUND

Highly crosslinked polyethylene (XLPE) was introduced to decrease periprosthetic osteolysis related to polyethylene wear, a major reason for revision of total hip arthroplasty. However, there are few reports of wear and osteolysis at 10 years postoperatively.

QUESTIONS/PURPOSES

(1) What are the linear and volumetric wear rates of XLPE at 10 to 14 years? (2) What is the relationship among linear wear, volumetric wear, and femoral head size? (3) What proportion of hips developed osteolysis and was there a relationship between osteolysis and femoral head size or polyethylene wear?

METHODS

We evaluated a previously reported cohort of 84 hips (72 patients) with one design of an uncemented acetabular component and one electron beam 10-kGy irradiated and remelted XLPE at a mean followup of 11 years (range, 10-14 years). The choice of femoral head size was based on several factors, including the outer diameter size of the acetabular component implanted, the perceived risk of dislocation (including the history of alcohol abuse and patient age), and liner availability from the manufacturer. The femoral head sizes used were 26 mm in 10 hips (12%), 28 mm in 31 hips (37%), 32 mm in 31 hips (37%), 36 mm in eight hips (10%), and 40 mm in four hips (5%). Measurements of linear and volumetric wear were performed in one experienced laboratory by the Martell method and analyzed using the first-to-last method. Standard radiographs, with additional Judet views, were used to detect periprosthetic osteolysis. Statistical analysis of wear and osteolysis compared with head size was performed.

RESULTS

For the entire cohort, the median linear wear rate as 0.024 mm/year (95% confidence interval [CI], 0.016-0.030) and the median volumetric wear rate was 12.19 mm(3)/year (95% CI, 6.6-15.7). With the numbers available, we found no association between femoral head size and linear wear rate. However, larger femoral heads were associated with more volumetric wear; 36/40-mm femoral heads had higher volumetric wear (median 26.1; 95% CI, 11.3-47.1) than did 26-mm heads (median 3.1; 95% CI, 0.7-12.3), 28-mm heads (median 12.3; 95% CI, 3.0-19.3), and 32-mm heads (median 12.9; 95% CI, 6.6-16.8; p = 0.02). Small osteolytic lesions were noted in 12 hips (14%), but with the numbers available, there was no association with head size or volumetric wear rates.

CONCLUSIONS

This uncemented acetabular component and this particular XLPE had low rates of linear and volumetric wear. Small osteolytic lesions were noted at 10 to 14 years but were not related to femoral head size or linear or volumetric wear rates. We recommend additional longer-term clinical followup studies and perhaps alternative imaging studies of patients with XLPE and osteolysis.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Comparison of 10-year clinical wear of annealed and remelted highly cross-linked polyethylene: A propensity-matched cohort study

No previous studies comparing the clinical wear rates of the two different kinds of cross-linked ultra-high-molecular-weight polyethylene (XLPE), annealed and remelted, are available. We compared the creep and steady wear rates of 36 matched pairs (72 hips in total) adjusting for baseline characteristics with propensity score matching techniques. Zirconia femoral heads with 26-mm diameter were used in all cases. The femoral-head cup penetration was measured digitally on radiographs. Significantly greater creep (p=0.006) was detected in the remelted (0.234mm) than annealed (0.159mm) XLPE. However, no significant difference (p=0.19) was found between the steady wear rates (0.003 and 0.008mm/year, respectively) of the annealed and remelted XLPE. Multiple regression analyses showed that remelted XLPE is significant independent variable (p<0.001) that is positively associated with creep. However, the patient age and body weight, cup size, the liner thickness, cup inclination, follow-up periods, and postoperative Merle d'Aubigné hip score had no significant effects (p>0.05) on the steady wear rates. No patients exhibited above the osteolysis threshold of 0.1mm/year, progressive radiolucencies, osteolysis, or polyethylene fracture. This　propensity-matched cohort study document no significant difference in wear resistant performances of annealed and remelted XLPE over an average period of 10 years.

A Novel Method for Assessment of Polyethylene Liner Wear in Radiopaque Tantalum Acetabular Cups: Clinical Validation in Patients Enrolled in a Randomized Controlled Trial

Conventional radiostereometric analysis (RSA) for wear is not possible in patients with tantalum cups. We propose a novel method for wear analysis in tantalum cups. Wear was assessed by gold standard RSA and the novel method in total hip arthroplasty patients enrolled in a randomized controlled trial receiving either titanium or tantalum cups (n=46). The novel method estimated the center of the head using a model based on identification of two proximal markers on the stem and knowledge of the stem/head configuration. The novel method was able to demonstrate a pattern of wear that was similar to the gold standard in titanium cups. The novel method offered accurate assessment and is a viable solution for assessment of wear in studies with tantalum cups.

E-vitamin infused highly cross-linked polyethylene: RSA results from a randomised controlled trial using 32 mm and 36 mm ceramic heads

BACKGROUND

Polyethylene wear has been a major cause of revision of cementless total hip replacements. Highly cross-linked polyethylene has been developed to increase mechanical resistance to wear. However, cross-linking from irradiation of the polyethylene generates free radicals and these can oxidise in vivo and might over time alter the initial mechanical properties. Vitamin-E infused highly cross-linked polyethylene has been developed to reduce the amount of free radicals without compromising the mechanical properties.

PURPOSE

To measure wear of vitamin E infused highly cross-linked polyethylene and compare wear between 2 different head sizes.

METHODS

In a prospective randomised study between 32 mm and 36 mm Biolox® delta heads in 50 hips we analysed the in vivo wear of the E-poly™ with markerless radiostereometry.

RESULTS

Mean (95% CI) wear for the total material was 0.041 mm (0.015-0.066) in the vertical direction and 0.177 mm (0.155-0.200) in the total 3D direction. After the anticipated period of bedding-in we found no statistically significant differences in wear from three months to 2 years in vertical and total 3D directions. Although statistical significant differences between 32 mm and 36 mm heads were found in the total 3D direction we cannot conclude that there are significant clinical important differences in wear comparing these head sizes.

CONCLUSIONS

This study shows promising early results with very low wear, even for 36 mm heads, but long term follow-up is necessary to evaluate if this polyethylene will provide low wear and good mechanical properties in the long-term.

In-vivo degradation of middle-term highly cross-linked and remelted polyethylene cups: Modification induced by creep, wear and oxidation

In this study Raman (RS) and Fourier Transform Infrared (FT-IR) spectroscopic techniques were exploited to study 11 retrieved liners made of remelted highly cross-linked polyethylene (HXLPE), with the intent to elucidate their in-vivo mechanical and chemical degradation. The retrievals had different follow-ups, ranging from a few months to 7 years of implantation time and belong to the first generation of highly cross-linked and remelted polyethylene clinically introduced in 1999, but still currently implanted. Raman assessments enabled to discriminate contributes of wear and creep on the total reduction of thickness in different locations of the cup. According to our results, although the most of the viscoelastic deformation occurred during the first year (bedding-in period), it progressed during the steady wear state up to 7 years with much lower but not negligible rate. Overall, the wear rate of this remelted HXLPE liner was low. Preliminary analysis on microtomed sections of the liners after in-vivo and in-vitro accelerated aging (ASTM F2003-02) enabled to obtain a phenomenological correlation between the oxidation index (OI) and the amount of orthorhombic phase fraction (αc), which can be easily non-destructively measured by RS. Profiles of αc obtained from different locations of the cups were used to judge the oxidative degradation of the 11 retrievals, considering also the ex-vivo time elapsed from the revision surgery to the spectroscopic experiments. Low but measurable level of oxidation was detected in all the short-term retrievals, while in the middle-term samples peaks of OI were observed in the subsurface (up to OI=4.5), presumably induced by the combined effect of mechanical stress, lipid absorption and prolonged ex-vivo shelf-aging in air.

Three Year RSA Evaluation of Vitamin E Diffused Highly Cross-linked Polyethylene Liners and Cup Stability

Vitamin E diffusion into highly cross-linked polyethylene (E-XLPE) is a method for enhancing oxidative stability of acetabular liners. The purpose of this study was to evaluate in vivo penetration of E-XLPE using radiostereometric analysis (RSA). Eighty-four hips were recruited into a prospective 10-year RSA. This is the first evaluation of the multicenter cohort after 3-years. All patients received E-XLPE liners (E1, Biomet) and porous-titanium coated cups (Regenerex, Biomet). There was no difference (P=0.450) in median femoral head penetration into the E-XLPE liners at 3-years comparing cobalt-chrome heads (-0.028mm; inter-quartile range (IQR) - 0.065 to 0.047) with ceramic heads (-0.043mm, IQR - 0.143to0.042). The 3-year follow-up indicates minimal E-XLPE liner penetration regardless of head material and minimal early cup movement.

Durability of highly cross-linked polyethylene in total hip and total knee arthroplasty

This article reviews the history of the development of highly cross-linked polyethylene and provides an in-depth review of the clinical results regarding the durability of highly cross-linked polyethylene (HXLPE) used in total hip arthroplasty (THA) and total knee arthroplasty (TKA). The use of polyethylene as a bearing surface has contributed to the success of THA and TKA; however, polyethylene wear and osteolysis can lead to failure. Ongoing clinical and retrieval studies are required to analyze outcomes at longer-term follow-up.

Precision of radiostereometric analysis (RSA) of acetabular cup stability and polyethylene wear improved by adding tantalum beads to the liner

BACKGROUND AND PURPOSE

In traditional radiostereometric analysis (RSA), 1 segment defines both the acetabular shell and the polyethylene liner. However, inserting beads into the polyethylene liner permits employment of the shell and liner as 2 separate segments, enabling distinct analysis of the precision of 3 measurement methods in determining femoral head penetration and shell migration.

PATIENTS AND METHODS

The UmRSA program was used to analyze the double examinations of 51 hips to determine if there was a difference in using the shell-only segment, the liner-only segment, or the shell + liner segment to measure wear and acetabular cup stability. The standard deviation multiplied by the critical value (from a t distribution) established the precision of each method.

RESULTS

Due to the imprecision of the automated edge detection, the shell-only method was least desirable. The shell + liner and liner-only methods had a precision of 0.115 mm and 0.086 mm, respectively, when measuring head penetration. For shell migration, the shell + liner had a precision of 0.108 mm, which was better than the precision of the shell-only method. In both the penetration and migration analyses, the shell + liner condition number was statistically significantly lower and the bead count was significantly higher than for the other methods.

INTERPRETATION

Insertion of beads in the polyethylene improves the precision of femoral head penetration and shell migration measurements. A greater dispersion and number of beads when combining the liner with the shell generated more reliable results in both analyses, by engaging a larger portion of the radiograph.

Wear of highly crosslinked polyethylene acetabular components

BACKGROUND AND PURPOSE

Wear rates of highly crosslinked polyethylene (XLPE) acetabular components have varied considerably between different published studies. This variation is in part due to the different techniques used to measure wear and to the errors inherent in measuring the relatively low amounts of wear in XLPE bearings. We undertook a scoping review of studies that have examined the in vivo wear of XLPE acetabular components using the most sensitive method available, radiostereometric analysis (RSA).

METHODS

A systematic search of the PubMed, Scopus, and Cochrane databases was performed to identify published studies in which RSA was used to measure wear of XLPE components in primary total hip arthroplasty (THA).

RESULTS

18 publications examined 12 primary THA cohorts, comprising only 260 THAs at 2-10 years of follow-up. The mean or median proximal wear rate reported ranged from 0.00 to 0.06 mm/year. However, differences in the manner in which wear was determined made it difficult to compare some studies. Furthermore, differences in RSA methodology between studies, such as the use of supine or standing radiographs and the use of beaded or unbeaded reference segments, may limit future meta-analyses examining the effect of patient and implant variables on wear rates.

INTERPRETATION

This scoping review confirmed the low wear rates of XLPE in THA, as measured by RSA. We make recommendations to enhance the standardization of reporting of RSA wear results, which will facilitate early identification of poorly performing implants and enable a better understanding of the effects of surgical and patient factors on wear.

Mechanisms of plastic deformation in highly cross-linked UHMWPE for total hip components--the molecular physics viewpoint

Plastic deformation is an unavoidable event in biomedical polymeric implants for load-bearing application during long-term in-vivo service life, which involves a mass transfer process, irreversible chain motion, and molecular reorganization. Deformation-induced microstructural alterations greatly affect mechanical properties and durability of implant devices. The present research focused on evaluating, from a molecular physics viewpoint, the impact of externally applied strain (or stress) in ultra-high molecular weight polyethylene (UHMWPE) prostheses, subjected to radiation cross-linking and subsequent remelting for application in total hip arthroplasty (THA). Two different types of commercial acetabular liners, which belong to the first-generation highly cross-linked UHMWPE (HXLPE), were investigated by means of confocal/polarized Raman microprobe spectroscopy. The amount of crystalline region and the spatial distribution of molecular chain orientation were quantitatively analyzed according to a combined theory including Raman selection rules for the polyethylene orthorhombic structure and the orientation distribution function (ODF) statistical approach. The structurally important finding was that pronounced recrystallization and molecular reorientation increasingly appeared in the near-surface regions of HXLPE liners with increasing the amount of plastic (compressive) deformation stored in the microstructure. Such molecular rearrangements, occurred in response to external strains, locally increase surface cross-shear (CS) stresses, which in turn trigger microscopic wear processes in HXLPE acetabular liners. Thus, on the basis of the results obtained at the molecular scale, we emphasize here the importance of minimizing the development of irrecoverable deformation strain in order to retain the pristine and intrinsically high wear performance of HXLPE components.

Adherence of hip and knee arthroplasty studies to RSA standardization guidelines. A systematic review

BACKGROUND AND PURPOSE

Guidelines for standardization of radiostereometry (RSA) of implants were published in 2005 to facilitate comparison of outcomes between various research groups. In this systematic review, we determined how well studies have adhered to these guidelines.

METHODS

We carried out a literature search to identify all articles published between January 2000 and December 2011 that used RSA in the evaluation of hip or knee prosthesis migration. 2 investigators independently evaluated each of the studies for adherence to the 13 individual guideline items. Since some of the 13 points included more than 1 criterion, studies were assessed on whether each point was fully met, partially met, or not met.

RESULTS

153 studies that met our inclusion criteria were identified. 61 of these were published before the guidelines were introduced (2000-2005) and 92 after the guidelines were introduced (2006-2011). The methodological quality of RSA studies clearly improved from 2000 to 2011. None of the studies fully met all 13 guidelines. Nearly half (43) of the studies published after the guidelines demonstrated a high methodological quality and adhered at least partially to 10 of the 13 guidelines, whereas less than one-fifth (11) of the studies published before the guidelines had the same methodological quality. Commonly unaddressed guideline items were related to imaging methodology, determination of precision from double examinations, and also mean error of rigid-body fitting and condition number cutoff levels.

INTERPRETATION

The guidelines have improved methodological reporting in RSA studies, but adherence to these guidelines is still relatively low. There is a need to update and clarify the guidelines for clinical hip and knee arthroplasty RSA studies.

Wear of a sequentially annealed polyethylene acetabular liner

BACKGROUND AND PURPOSE

We previously reported on a randomized controlled trial (RCT) that examined the effect of adding tobramycin to bone cement after femoral stem migration. The present study examined femoral head penetration into both conventional and highly crosslinked polyethylene acetabular liners in the same group of RCT patients, with a minimum of 5 years of postoperative follow-up.

PATIENTS AND METHODS

Linear penetration of the femoral head into an X3 (Stryker) crosslinked polyethylene (XLPE) liner was measured in 18 patients (19 hips) using radiostereometric analysis (RSA). Femoral head penetration was also measured in 6 patients (6 hips) with a conventional polyethylene liner (CPE), which served as a control group.

RESULTS

The median proximal femoral head penetration in the XLPE group after 5.5 years was 0.025 mm with a steady-state penetration rate of 0.001 mm/year between year 1 and year 5. The CPE liner showed a median proximal head penetration of 0.274 mm after 7.2 years, at a rate of 0.037 mm/year.

INTERPRETATION

The Trident X3 sequentially annealed XLPE liner shows excellent in vivo wear resistance compared to non-crosslinked CPE liners at medium-term implantation. The rate of linear head penetration in the XLPE liners after > 5 years of follow-up was 0.001 mm/year, which is in close agreement with the results of previous studies.

The current state of bearing surfaces in total hip replacement

We reviewed the literature on the currently available choices of bearing surface in total hip replacement (THR). We present a detailed description of the properties of articulating surfaces review the understanding of the advantages and disadvantages of existing bearing couples. Recent technological developments in the field of polyethylene and ceramics have altered the risk of fracture and the rate of wear, although the use of metal-on-metal bearings has largely fallen out of favour, owing to concerns about reactions to metal debris. As expected, all bearing surface combinations have advantages and disadvantages. A patient-based approach is recommended, balancing the risks of different options against an individual’s functional demands.

Cite this article: Bone Joint J 2014;96-B:147–56.

Computerized ellipse method for measuring acetabular version after total hip replacement--a precision study using synthetic and real radiographs

BACKGROUND

Previous work by our group to address the problem of acetabular positioning based on 2D methods resulted in the development of a measurement method with better precision--Liaw's version. This method may help the early diagnosis of acetabular loosening. In the present study, we hypothesized that our computerized ellipse method could improve the precision of measuring acetabular version.

METHODS

We developed our Elliversion software to measure acetabular version. Using total hip replacement (THR) Simulator, 96 radiographs were synthesized with random femoral inclination and 5° to 52° version, half with the femoral head included and half without. These synthetic radiographs and 28 real radiographs were measured with both Elliversion and the trigonometric method twice by one of the authors with a one-week interval between measurements. We then calculated the difference in the repeated measurements. Student's t-test was used for statistical analysis of the measuring error and inter-measurement difference.

RESULTS

In the precision study, for synthetic radiographs including the femoral head, the ellipse method was significantly better than the trigonometric method (p < 0.01). For synthetic radiographs without the femoral head, there was no significant difference between the ellipse method and the trigonometric method (p = 0.19). As for the repeated measurements, for synthetic radiographs including the femoral head, the ellipse method was significantly better than the trigonometric method (p = 0.001), whereas for synthetic radiographs without the femoral head, there was no significant difference between the two methods (p = 0.17). For real radiographs, there was no significant difference between the two measuring methods (p = 0.12). However, if we excluded the four poor-quality radiographs, there was a significant difference between the two measuring methods (p = 0.04).

DISCUSSION

We developed a computerized ellipse method for measuring acetabular version on synthetic radiographs and good-quality real radiographs. This method is characterized by its superior precision as compared to the trigonometric method. With the 2D standardized method (Liaw's version), improving the precision of measurement will help earlier diagnosis of acetabular loosening.

Low early and late dislocation rates with 36- and 40-mm heads in patients at high risk for dislocation

BACKGROUND

Large (36- and 40-mm) femoral heads with highly crosslinked polyethylene liners were introduced to reduce the risk of dislocation after primary total hip arthroplasty (THA), but it is unclear whether the risk is reduced and whether there is osteolysis or liner fracture.

QUESTIONS/PURPOSES

We therefore determined (1) the incidence of early and late (> 5 years) dislocation; (2) the rate of femoral and acetabular component loosening and revision; and (3) the rate of liner fracture and pelvic osteolysis.

METHODS

We retrospectively reviewed 112 patients presumed at high risk for dislocation who had 122 primary THAs: 108 with 36-mm and 14 with 40-mm femoral heads. The risk factors were: age > 75 years (80 hips); proximal femur fracture (18); history of contralateral dislocation (two); history of alcohol abuse (two); large acetabulum > 60 mm (six); and other (14). Patients were evaluated for early (< 1 year) and late (> 5 years) dislocation; rate of reoperation; clinical result with Harris hip score; and standard radiographic analysis for radiolucent lines and osteolysis.

RESULTS

The rate of early dislocation was 4% (five of 122 hips), all with a 36-mm head. There were no late dislocations in 74 hips followed for 5 to 10 years, no revision for acetabular or femoral loosening, and no liner fractured. There were no hips with pelvic osteolysis and seven hips with an acetabular radiolucent line.

CONCLUSIONS

The 36- and 40-mm femoral heads were associated with a low risk of dislocation in high-risk patients undergoing primary THA with no osteolysis or liner fracture.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of level of evidence.

The 2012 John Charnley Award: Clinical multicenter studies of the wear performance of highly crosslinked remelted polyethylene in THA

BACKGROUND

Highly crosslinked polyethylene (HXLPE) in THA was developed to reduce particle-induced periprosthetic osteolysis. A series of clinical studies were initiated to determine the clinical efficacy as judged by patient-reported scores, radiographic osteolysis, and wear analysis of one form of HXLPE.

QUESTIONS/PURPOSES

The purposes of this series of studies were to (1) determine the wear rates of one form of HXLPE; (2) report long-term (7-10 years) patient-reported outcome measures; (3) assess the effect of femoral head size on wear; and (4) determine the incidence of periprosthetic osteolysis.

METHODS

A single-center and two multicenter studies were conducted on 768 primary patients (head size 26-36 mm) undergoing THA at eight medical centers. Patient-reported outcome scores, radiographic grading for osteolysis, and radiographic wear evaluation were performed.

RESULTS

Serial plain radiographs showed no periprosthetic osteolysis in the three studies. The average femoral head penetration rates did not correlate with time in vivo for patients with standard femoral head sizes. Although there was an indication of higher wear in patients with 36-mm diameter femoral heads, it was below the threshold for producing osteolysis.

CONCLUSIONS

The introduction of this HXLPE substantially improved the prognosis of patients after THA up to 13 years as judged by clinical scores, incidence of osteolysis, and polyethylene wear measurements.

LEVEL OF EVIDENCE

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

Modified minimally invasive two-incision total hip arthroplasty using large diameter femoral head

BACKGROUND

Minimally invasive (MI) total hip arthroplasty (THA) is an alternative to standard THA, but has created much controversy among orthopedic surgeons. The authors modified the original minimally invasive two-incision THA technique and used large-diameter (32 mm, 36 mm) ceramic-on-ceramic articulation.

MATERIALS AND METHODS

One hundred and seventy patients that underwent unilateral MI two-incision THA were retrospectively reviewed, and surgical morbidity, functional recovery, radiological properties, and complications were assessed.

RESULTS

Mean Harris hip score (HHS) improved from 41.8 to 96.1 at last followup, and mean Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score from 66.2 to 26.9. The mean lateral opening angle of the acetabular component was 38.2° and the mean stem position was valgus 1.9°. There was an intraoperative femur fracture and one revision surgery due to stem subsidence. No patient had dislocation.

CONCLUSIONS

Our data suggest that this modified technique combined with large ceramic femoral head is safe and reproducible in terms of achieving proper implant positioning and early functional recovery.

Eight-year wear analysis in Longevity highly cross-linked polyethylene liners comparing 26- and 32-mm heads

INTRODUCTION

Although wear reduction of highly cross-linked polyethylene has been demonstrated to be independent of femoral head diameter in some simulation studies, the clinical effects of femoral head diameter on wear of highly cross-linked polyethylene sockets remain unclear. We compared the in vivo wear of Longevity highly cross-linked polyethylene liners at 8-year follow-up using 26- or 32-mm cobalt-chromium heads.

MATERIALS AND METHODS

A retrospective cohort study was performed on 90 cementless total hip arthroplasties (THAs) using Longevity highly cross-linked polyethylene liners combined with 26- (45 THAs) or 32-mm (45 THAs) cobalt-chromium heads. Annual radiographs were analyzed using PolyWare computer-assisted methods and linear and volumetric total head penetration rates and linear and volumetric steady-state wear rates were compared.

RESULTS

The two groups showed similar background data, and no significant differences were identified between groups in total head penetration rate or steady-state wear rate. Steady-state wear rates were negligible. Osteolysis was not observed in any hips in either group.

CONCLUSIONS

At the 8-year follow-up, wear of the Longevity was the same irrespective of the use 26- or 32-mm heads.

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.

History and systematic review of wear and osteolysis outcomes for first-generation highly crosslinked polyethylene

BACKGROUND

Highly crosslinked polyethylene (HXLPE) was introduced to reduce wear and osteolysis in total joint arthroplasty. While many studies report wear and osteolysis associated with HXLPE, analytical techniques, clinical study design and followup, HXLPE formulation and implant design characteristics, and patient populations differ substantially among investigations, complicating a unified perspective.

QUESTIONS/PURPOSES

Literature on first-generation HXLPE was summarized. We systematically reviewed the radiographic wear data and incidence of osteolysis for HXLPE in hip and knee arthroplasty.

METHODS

PubMed identified 391 studies; 28 met inclusion criteria for a weighted-averages analysis of two-dimensional femoral head penetration rates. To determine the incidence of osteolysis, we estimated a pooled odds ratio using a random-effects model.

RESULTS

Weighted-averages analyses of femoral head penetration rates in HXLPE liners and conventional UHMWPE liners resulted, respectively, in a mean two-dimensional linear penetration rate of 0.042 mm/year based on 28 studies (n=1503 hips) and 0.137 mm/year based on 18 studies (n=695 hips). The pooled odds ratio for the risk of osteolysis in HXLPE versus conventional liners was 0.13 (95% confidence interval, 0.06-0.27) among studies with minimum 5-year followup. We identified two clinical studies of HXLPE in TKA, preventing systematic analysis of outcomes.

CONCLUSIONS

HXLPE liner studies consistently report lower femoral head penetration and an 87% lower risk of osteolysis. Reduction in femoral head penetration or osteolysis risk is not established for large-diameter (>32 mm) metallic femoral heads or ceramic femoral heads of any size. Few studies document the clinical performance of HXLPE in knees.

Influence of patient activity on femoral osteolysis at five and ten years following hybrid total hip replacement

We conducted a longitudinal study including patients with the same type of primary hybrid total hip replacement and evaluated patient activity and femoral osteolysis at either five or ten years post-operatively. Activity was measured using the University of California, Los Angeles scale. The primary outcome was the radiological assessment of femoral osteolysis. Secondary outcomes were revision of the femoral component for aseptic loosening and the patients' quality of life. Of 503 hip replacements in 433 patients with a mean age of 67.7 years (30 to 91), 241 (48%) were seen at five and 262 (52%) at ten years post-operatively. Osteolytic lesions were identified in nine of 166 total hip replacements (5.4%) in patients with low activity, 21 of 279 (7.5%) with moderate activity, and 14 of 58 (24.1%) patients with high activity. The risk of osteolysis increased with participation in a greater number of sporting activities. In multivariate logistic regression adjusting for age, gender, body mass index and the inclination angle of the acetabular component, the adjusted odds ratio for osteolysis comparing high vs moderate activity was 3.6 (95% confidence interval 1.6 to 8.3). Stratification for the cementing technique revealed that lower quality cementing increased the effect of high activity on osteolysis. Revision for aseptic loosening was most frequent with high activity. Patients with the highest activity had the best outcome and highest satisfaction. In conclusion, of patients engaged in high activity, 24% had developed femoral osteolysis five to ten years post-operatively.

Do large heads enhance stability and restore native anatomy in primary total hip arthroplasty?

BACKGROUND

Dislocation remains a serious complication in hip arthroplasty. Resurfacing proponents tout anatomic femoral head restoration as an advantage over total hip arthroplasty. However, advances in bearings have expanded prosthetic head options from traditional sizes of 22, 26, 28, and 32 mm to diameters as large as 60 mm. Large heads reportedly enhance stability owing to increased range of motion before impingement and increased jump distance to subluxation. Available larger diameter material combinations include metal- or ceramic-on-highly crosslinked polyethylene and metal-on-metal, each with distinct advantages and disadvantages.

QUESTIONS/PURPOSES

We sought to determine (1) if using larger diameter heads has lowered our dislocation rate; and (2) how closely an anatomic metal-on-metal bearing with diameters to 60 mm replicates native femoral head size.

METHODS

We retrospectively reviewed 2020 primary arthroplasties performed with large heads (≥ 36 mm) in 1748 patients and noted dislocation incidence. In a prospective subset of 89 cases using anatomic heads, native femoral head diameter was measured intraoperatively with calipers by an independent observer and later compared with implanted size.

RESULTS

One dislocation has occurred in 2020 hips for an incidence of 0.05%. The prosthetic head averaged 0.7 mm larger than the native head with 68 of 89 (76%) reconstructed to within ± 2 mm of native size.

CONCLUSIONS

Larger diameter heads have contributed to lower dislocation rates and large-diameter metal-on-metal articulation can provide close anatomic restoration in primary THA.

Wear versus thickness and other features of 5-Mrad crosslinked UHMWPE acetabular liners

BACKGROUND

The low wear rates of crosslinked polyethylenes provide the potential to use larger diameters to resist dislocation. However, this requires the use of thinner liners in the acetabular component, with concern that higher contact stresses will increase wear, offsetting the benefits of the crosslinking.

QUESTIONS/PURPOSES

We asked the following questions: Is the wear of conventional and crosslinked polyethylene liners affected by ball diameter, rigidity of backing, and liner thickness? Are the stresses in the liner affected by thickness?

METHODS

Wear rates were measured in a hip simulator and stresses were calculated using finite element modeling.

RESULTS

Without crosslinking, the wear rate was 4% to 10% greater with a 36-mm diameter than a 28-mm diameter. With crosslinking, wear was 9% lower with a 36-mm diameter without metal backing and 4% greater with metal backing. Reducing the thickness from 6 mm to 3 mm increased the contact stress by 46%, but the wear rate decreased by 19%.

CONCLUSIONS

The reduction in wear with 5 Mrad of crosslinking was not offset by increasing the diameter from 28 mm to 36 mm or by using a liner as thin as 3 mm.

CLINICAL RELEVANCE

The results indicate, for a properly positioned 5-Mrad crosslinked acetabular component and within the range of dimensions evaluated, neither wear nor stresses in the polyethylene are limiting factors in the use of larger-diameter, thinner cups to resist dislocation.

Early reactive synovitis and osteolysis after total hip arthroplasty

BACKGROUND

Little is known about intraarticular pathology following THA prior to the radiographic appearance of osteolysis, primarily due to imaging limitations. MRI has recently been applied to imaging the postarthroplasty hip with the ability to detect periarticular bony and soft tissue pathology; specifically, it is able to detect abnormal synovial patterns and focal bone loss well before the radiographic appearance of osteolysis.

QUESTIONS/PURPOSES

We therefore used MRI to determine the incidence of early reactive synovitis and osteolysis in asymptomatic patients after THA, and whether there is an association between these MRI findings and clinical outcomes or radiographic wear measurements at this early stage.

METHODS

We recruited 31 patients (33 hips) who underwent routine noncemented THA with one of three types of bearing surfaces: metal-on-cross-linked polyethylene (n = 7), ceramic-on-ceramic (n = 12), and ceramic-on-cross-linked polyethylene (n = 14). Patients underwent specialized MRI at a minimum of 12 months (mean, 23 months; range, 12-37 months) after surgery. MR images were analyzed for the presence of synovitis or osteolysis. WOMAC scores, patient assessment questionnaires, and radiographic wear measurements were correlated with MRI findings.

RESULTS

Reactive synovitis was observed in 13 of 33 patients (39%) and focal osteolysis in one of 33 (3%). The presence of synovitis did not correlate with pain, activity level, patient satisfaction or clinical outcome scales, nor did it correlate with radiographic wear measurements at early followup.

CONCLUSIONS

Our observations suggest reactive synovitis is common yet asymptomatic at short-term followup. We do not know either the etiology or the long-term implications of these observations.

Measurement of femoral head penetration in polyethylene using a 3-dimensional CT-scan technique

BACKGROUND

Current techniques for measuring in vivo polyethylene wear suffer from a range of problems, resulting in an unacceptable lack of repeatability and/or insufficient accuracy when they are used to measure the low wear rates associated with new, highly crosslinked polyethylene. We describe an improved CT method for measurement of 3D femoral head penetration in PE acetabular cups that has sufficient accuracy and repeatability to allow assessment of the wear potential of modern implants.

METHOD

The accuracy and repeatability of the CT-scan method was determined by blindly repeating measurements on a precisely calibrated 28-mm prosthetic head and by comparing them with direct metrological measurements on 10 acetabular specimens with in vitro wear from machining, and on 8 explanted acetabular specimens with in vivo wear.

RESULTS

The intra- and interobserver errors in femoral head diameter were 0.036 mm (SD 0.044) and 0.050 mm (SD 0.022), respectively. CT estimated femoral head penetration in both all-poly and metal-backed acetabular components with accuracy ranging from 0.009 to 0.245 mm (mean 0.080; SD 0.067).

INTERPRETATION

We found that the CT method is rapid, is accurate, and has repeatability and ease of availability. Using a slice thickness of 0.0625 mm, this method can detect wear—and also the threshold for the wear rate that causes osteolysis—much earlier than previous methods.

Comparison of steady state femoral head penetration rates between two highly cross-linked polyethylenes in total hip arthroplasty

Given that the manufacture of highly cross-linked polyethylene (HXLPE) is not standardized, the behavior of these materials may vary. Our study compares minimum 5-year steady state femoral head penetration rates using the Martell method, in 2 HXPLEs produced by different manufacturers. Patients received a primary hip arthroplasty using an uncemented acetabular component with an HXLPE liner and a 28-mm femoral head. Forty-seven patients in group A received an HXLPE liner (Reflection XLPE, Smith and Nephew Inc, Memphis, Tenn), and 36 patients in group B received a different HXLPE liner (Longevity, Zimmer Inc, Warsaw, Ind). Average follow-up was 6.42 years in group A and 7.64 years in group B. The steady state head penetration rates were not significantly (P > .05) different between the HXPLE groups over the midterm with 0.026 mm/y and 0.025 mm/y in groups A and B, respectively.

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.

Polyethylene oxidation in total hip arthroplasty: evolution and new advances

Ultra-high molecular weight polyethylene (UHMWPE) remains the gold standard acetabular bearing material for hip arthroplasty. Its successful performance has shown consistent results and survivorship in total hip replacement (THR) above 85% after 15 years, with different patients, surgeons, or designs. As THR results have been challenged by wear, oxidation, and liner fracture, relevant research on the material properties in the past decade has led to the development and clinical introduction of highly crosslinked polyethylenes (HXLPE). More stress on the bearing (more active, overweighted, younger patients), and more variability in the implantation technique in different small and large Hospitals may further compromise the clinical performance for many patients. The long-term in vivo performance of these materials remains to be proven. Clinical and retrieval studies after more than 5 years of in vivo use with HXLPE in THR are reviewed and consistently show a substantial decrease in wear rate. Moreover, a second generation of improved polyethylenes is backed by in vitro data and awaits more clinical experience to confirm the experimental improvements. Also, new antioxidant, free radical scavengers, candidates and the reinforcement of polyethylene through composites are currently under basic research.Oxidation of polyethylene is today significantly reduced by present formulations, and this forgiving, affordable, and wellknown material is still reliable to meet today's higher requirements in total hip replacement.

Early migration characteristics of a hydroxyapatite-coated femoral stem: an RSA study

Measurement of early stem subsidence can be used to predict the likelihood of long-term femoral component loosening and clinical failure. Data that examines the early migration pattern of clinically proven stems will provide clinicians with useful baseline data with which to compare new stem designs. This study was performed to evaluate the early migration pattern of a hydroxyapatite-coated press-fit femoral component that has been in use for over ten years. We enrolled 30 patients who underwent THA for osteoarthritis. The median age was 70 years (range, 55-80 years). Patients were clinically assessed using the Harris hip score. Radiostereometric analysis was used to evaluate stem migration at three to four days, six months, one year and two years. We observed a mean subsidence of 0.73 mm at six months, 0.62 mm at one year and 0.58 mm at two years and a mean retroversion of 1.82° at six months, 1.90° at one year and 1.59° at two years. This data suggests that subsidence is confined to the first six months after which there was no further subsidence. The results from this study can be compared with those from novel cementless stem designs to help predict the long-term outcome one may expect from new cementless stem designs.

Femoral head size and wear of highly cross-linked polyethylene at 5 to 8 years

Wear of highly cross-linked polyethylene is reportedly independent of head size. To confirm that observation we asked in our population whether head size related to wear with one type of electron beam highly cross-linked polyethylene. Of 146 hips implanted, we evaluated complete clinical and radiographic data for 90 patients (102 hips or 70%). The minimum followup was 5 years (mean, 5.7 years; range, 5-8 years). The head size was selected intraoperatively based on the size of the acetabular component and presumed risk of dislocation. Polyethylene wear measurements were performed in one experienced laboratory using the method of Martell et al. There was no hip with pelvic or femoral osteolysis. The median linear wear rate was 0.028 mm/year (mean, 0.04 mm/year), and the median volumetric wear rate was 25.6 mm(3)/year (mean, 80.5 mm(3)/year). Median total volumetric wear was 41.0 mm(3) (mean, 98.5 mm(3)). We found no association between femoral head size and the linear wear rate, but observed an association between larger (36- and 40-mm) head size and volumetric wear rate and total volumetric wear. Although the linear wear rate of polyethylene was not related to femoral head diameter, there was greater volumetric wear (156.6 mm(3)/year) with the 36- and 40-mm heads. Pending long-term studies of large head sizes, we advise caution in using larger femoral heads in young or active patients and in those with a low risk of dislocation.

LEVEL OF EVIDENCE

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