Objectives

The accuracy and precision of two new methods of model-based radiostereometric analysis (RSA) were hypothesised to be superior to a plain radiograph method in the assessment of polyethylene (PE) wear.

Introduction and Objectives: Our aim is to determine the influence that the orientation and position of the components has on polyethylene wear in a non-cemented total hip replacement (THR) model. Materials and Methods: We studied a series of 50 THRs in which both components were coated with hydroxyapatite and polyethylene that had been sterilized by gamma radiation in an atmosphere of oxygen. Polyethylene wear was checked regularly throughout the study (mean 128 months, minimum 120 and maximum 139) using a computer program. We studied the relationship of wear with version and abduction of the acetabular component and the location of the center of rotation in the pre and postoperative periods as determined by X-rays of the teardrop and the tip of the greater trochanter. Results: The mean annual rate of wear was 0.17 mm (SD: 9.75). A statistically significant correlation was seen between the vertical angle of inclination of the acetabular component and a greater annual rate of polyethylene wear (Pearson correlation = 0.451, p = 0.001). No relationship was found between wear and the other variables studied. Discussion and Conclusions: Studies carried out over more than 10 years make it possible to assess the effect of the position of the components on polyethylene wear in THR. Although these results cannot be extrapolated to other types of friction or other surface pairs that undergo friction, the vertical position of the acetabular component favors wear of polyethylene sterilized in an atmosphere of air and should be avoided

Background. Polyethylene wear in both cemented and uncemented total hip arthroplasty (THA) lead to generation of particles with their access to the interface which has been responsible for periprosthetic osteolysis and subsequent loosening of cup and stem. Many studies have been published studying the pattern of polyethylene wear and its relation to the type of implant (cemented/ uncemented cup or ceramic/metal head) used. No study in our knowledge has strictly focused on the effect of cemented versus uncemented stem on the polyethylene wear rates. We tried to compare the polyethylene wear rates reckoned with software (Poly Ware REV 7) of ultra high molecular weight polyethylene (UHMWPE) in hybrid and uncemented THA and its effect on complications of total hip replacements. Method. We retrospectively reviewed pre-matched 56 patients in uncemented group with 112 patients in hybrid group on the basis of polyethylene wear rate, revision rates and clinical issues, with mean follow up of 9.42 and 7.25 years (yrs.) respectively. Results. Mean polyethylene wear rate in uncemented group was 0.048 milli metres per year (mm/yr.) and it was 0.082 mm/yr. in hybrid. Wear rate in hybrid group ceramic head (0.072mm/yr.) was significant when compared to wear rate ceramic head in uncemented group (0.053mm/yr.), also we found significant difference of poly wear in the metallic group as well. There was no difference in stem loosening and cup osteolysis in low wear (<.05 mm/yr.) and high wear group (>.05mm/yr.) in both uncemented and hybrid THA. Conclusion. The revision was significantly higher in uncemented group but when adjusted with the age, it is equivocal. We found significant difference in polyethylene wear rates, but no significant difference in clinical performance and revisions among the two groups of uncemented THA and hybrid THA when compared on a mid-term 8 to 10 yrs. Follow up. Keywords. Total Hip Arthroplasty; Polywear; Uncemented THA; Hybrid THA

Purpose: This study was conducted on explanted uni-compartmental prostheses with a flat polyethylene plateau without metal backing. We search for clinical factors influencing polyethylene wear. Material and methods: This series included 30 polyethylene inserts divided into two groups. Group A included revision procedures performed for a reason other than implant loosening (wear of the other compartment, femoropatellar problems). Group B implants were explanted after loosening. The duration of implantation of the 13 implants in group A was 126 months (mean, range 11–218 months); it was 167 months (range 137–224) in group B. Remaining insert thickness was measured with a micormetric device, mitutoyo, allowing palpation of the worn surface with a precision of 3 microns. The volume of the femoral penetration into the polyethylene was calculed in two ways to separate penetration related to polyethylene deformation from penetration related to polyethylene wear. The micrometric device palpated the surface of the polyethylene enabling calculation of the sum of the volumes corresponding to wear and deformation. To measure the volume corresponding to wear, the explanted pieces were weighed and the result was compared with implants of the same size which had never been implanted. Polyethylene wear was calculated from the weight loss and and polyethylene density. The difference between the two calculation methods was attributed to polyethylene deformation. Results: Mean residual thickness of the polyethylene in group A without loosening was 7.16 mm, compared with 4.5 mm in group B. The volumetric femoral penetration into the polyethylene was a mean 19 mm3 per year in group A and 65 mm3 per year in group B. This imprint obtained with the micormetric measuring device was greater than the wear determined by weighing. This difference was about 25%. The decreased thickness of the implant was thus undoubtedly due, for three quarters, to wear alone. One quarter being attributed to polyethylene deformation. In group A (without loosening), each supplementary year of implantation corresponded to a decrease in the rate of wear of about 12% per yar, which would suggest that the wear mechanism is an abrasion and that with time the femoral and tibial implants become more congruent decreasing the rate of wear. Inversely in group B, each supplementary year of implantation after onset of loosening was associated with a 9% increase in the annual rate of wear. Microscopic examination of the group A implants demonstrate that abraison was the main mechanism of wear. In group B, delamination was observed, particularly when the loosening was associated with anterior cruciate ligament tear or major persistent deformation. Discussion: The rates and mechanisms of polyethylene wear in unicompartmental prostheses are different for non-loosened implants and for loosened implants. Taking into account the fact that polyethylene deformation participates for about one quarter of the decreased thickness over time, adjunction of a metal back would appear indispensable for thin inserts

Purpose: Polyethylene wear in total hip arthroplasty remains the most limiting factor for implant survival. Several predictive factors are well identified, but the position of the articulating pieces remains to be studied in detail. We searched for a correlation between polyethylene wear and the position of the femoral and acetabular pieces, particularly the femoral offset. Material and methods: Sixty-six patients underwent total hip arthroplasty for osteoarthritis or osteonecrosis. The patients were reviewed at 10.8 years (four bilateral prostheses). The preoperative, immediate postoperative (1 month) and last follow-up (10 years) AP pelvis views were digitalized. A dedicated software traced the different axes for measurement. Wear at ten years, femoral offset, cup eccentration or medialisation, ascent or descent, and cup inclination were measured. Results: Mean polyethylene wear was 1.23 mm at ten years with linear curve of 0.11 mm/yr. Preoperative femoral offset was restored in 71.4% of the cases. Univariate regression analysis revealed that only femoral offset was correlated with less wear at ten years. Polyethylene wear at ten years fell from 1.26 mm for preoperative offset restitution less than 98% to 1.13 mm for restitution greater than 102%. Discussion: Image processing allowed greater accuracy in the measurement of polyethylene wear. The rate of wear reported in the literature ranges from 0.1 to .015 mm/yr. Restitution of femoral offset guarantees less wear due to the reduction in the resultant force applied on the articulation as well as stress on the implants. Furthermore hip stability is improved. Several factors are involved in production of wear debris and correct restitution of the centre of rotation is only one of the elements which reduce wear. Conclusion: Wear was not excessive in this series. Among the position parameters, only femoral offset had an influence, having a beneficial effect on polyethylene wear. This emphasises the importance of having a wide variety of implants available in order to respond to the different anatomic presentations of the femur

Introduction. It has been shown in vitro that human monocytes can phagocytose submicron polyethylene wear particles generated from total hip arthroplasties (THA) with highly cross-linked polyethylene inlays. The aim of our study was to detect the presence and possible phagocytosis of such particles in peripheral blood monocytes of patients with respective THA. Patients and methods. All patients were operated using the same implant, the cementless SL Plus stem; Bicon cup and a cross-linked polyethylene insert Rexpol (Smith and Nephew). Besides clinical and radiographic check-up, blood samples were collected at follow-up and analyzed by flow cytometry. Polyethylene can be identified by its auto fluorescence when stimulated by a laser with the wavelength of fluorescein isothiocyanate (FITC). Presence of wear particles in monocytes was identified by determination of their size and granularity. Some samples were scrutinized by confocal laser scanning microscopy to correlate the intracellular position of the particles. Blood samples of patients without total joint replacement served as controls. Results. 18 samples of patients with THA were compared to 18 controls. Flow cytometry didn't show any difference of size, granularity and auto fluorescence of the investigated cells between the two groups. Furthermore confocal laser scanning microscopy was unable to establish the intracellular position of the auto fluorescence. There were 11 female and 7 male patients with a mean age of 70,4 years at the time of surgery and an average body mass index of 32 (23 – 41). Average follow-up time was 6,5 years (6 – 8 years). 2 patients had been revised, one for a periprosthetic fracture postoperatively, the other for cup loosening at 5 years. Radiographically there were no signs of loosening. Conclusion. Flow cytometry and confocal laser scanning microscopy were unable to detect submicron polyethylene wear particles in human monocytes in vivo following THA. This could be due to a lack of sensitivity or/and specificity although the in vitro study showing phagocytosis of submicron particles in vitro applied the same methods. The analysis could be too early if the number of wear particles hasn't possibly reached a critical mass at 6.5 years. Potentially the conclusion of the in vitro study is inapplicable and human monocytes are unable to phagocytose polyethylene wear particles. In any case further research in this field seems necessary

Polyethylene wear in total knee arthroplasty (TKA) is a complex and mutifactorial process. It is generally recognized that wear is directly related to a material wear factor, contact stress, and sliding distance. Conventional methods of predicting polyethylene wear in TKA mainly focus on peak contact stress or subsurface shear stress using finite element method analysis. By incorporating kinematics and contact stress, a new predictor for polyethylene wear in TKA (“Wear Index”) has been developed. The Wear Index was defined by multiplying deformation by femoro-tibial sliding velocity. The purpose of this study was to determine the predictive value of the Wear Index for polyethylene wear in TKA using both a numeric and an in vitro model. Four commercially available total knee prostheses were modeled for this study. Deformation and sliding velocity were calculated based on the three-dimensional geometry of the components and the gait kinematic inputs using Hertz’s formula. One specimen of each of the four types of total knee prostheses was mounted on a custom-designed knee simulator. Vertical loads and flexion-extension uni-axial motion were simulated using computer controlled servohydraulic actuators. The same gait kinematic inputs used in the theoretical study were used in the simulation test. After the simulations, the surface of the tibial insert was examined microscopically and macroscopically and compared with the theoretically generated Wear Index. This study showed a high correlation between the numeric model and the simulation. The depth of wear on the tibial insert correlated significantly with the Wear Index. Microscopic findings also demonstrated a good correlation between the Wear Index and observed wear patterns. Sliding velocity is an important factor for understanding wear in TKA. In conclusion, this study suggests that the Wear Index is a reliable predictor of polyethylene wear in TKA, as it incorporates both contact stress and kinematics in its calculation

In total knee arthroplasty, polyethylene wear has been a major cause of revision surgery. However, it is sometimes difficult to determine the time of revision surgery in elderly people due to their concomitant diseases. Therefore, the brace for measuring polyethylene wear under computed tomography was developed. Methods. The brace works by strapping a femoral component tightly to a polyethylene insert by applying compression force between the sole of the foot and the thigh. Holes of 1, 2, 5, 10 mm in diameter and 0.1, 0.2, 0.5 and 1 mm in depth were created in the posteromedial part of polyethylene inserts. The inserts were provided from Teijin-nakashima Co. ltd. (Jodo, Okayama, Japan). The Hi-tech knee artificial joint (Teijin-nakashima Co. ltd.) was applied to a cadaveric knee and CT images of the knee were taken with a combination of insets with varying diameters and depths holes, using Aquilion ONE (Toshiba Medical Systems Corporation, Ohtawara, Japan). The finding conditions were as follows, Voltage; 120V, Current; 5A, slice thickness; 0.5 mm helical. The patient, who received total knee arthroplasty over 15 years ago, wore the brace and was examined using computed tomography. Afterward, the patient received revision surgery to replace the worn insert into new one. The removed insert was measured with a three-dimensional measuring machine (Cyclon, Mitsutoyo Co. ltd., Kawasaki, Japan). Results. At a 1.0 mm depth, all holes could be detected. At a 0.5 mm depth, holes of 2, 5, 10 mm in diameter could be detected. At a 0.1∼0.2 mm depth, there was no hole detected. After revision surgery, a three-dimensional measuring machine revealed a 1.8 mm thickness of the insert on the medial side. The CT reconstruction image showed a1.84 mm thickness similar to the virtually measured figure. Conclusion. The brace and CT imaging was useful for the detection of polyethylene wear

Introduction: Polyethylene wear debris is the main contributing factor that leads to aseptic loosening and osteolysis. The main objective of this study was to evaluate the role of hydroxyapatite (HA) in third-body polyethylene wear in total hip arthroplasty. Materials: 199 primary cementless THA’s (174 patients) performed by a single surgeon were enrolled in a prospective randomized study comprising hydroxyapatite and non-hydroxyapatite coated femoral implants. The femoral component had metaphyseal-diaphyseal fit design with proximal plasma sprayed titanium circumferential porous coating. The hydroxyapatite coating was 50 – 75 micrometers over the porous surface with the components of identical design. The acetabular component was plasma sprayed titanium porous coated shell without hydroxyapatite. T he polyethylene liners were machined molded from ram extruded Hi-fax 1900H polyethylene resin gamma-sterilized in argon (inert) gas. Clinical and Radiographic evaluation was performed employing HSS scores and Engh criteria. Results: At a mean follow-up of 5 years, the radiographs of 83 HA and 73 Non-HA hips were evaluated by two independent observers utilizing computer-assisted wear analysis on digitized standardized radiographs described by Martell et al (1997). The radiographs were also evaluated for osteolysis or aseptic loosening. The mean linear wear rate in HA group was 0.19mm/yr and in the non-HA group was 0.21mm/yr, which was not significant (p> 0.05). There was no case of osteolysis or aseptic loosening of any component. Both groups had comparable outcomes in terms of HSS scores, walking ability and sports participation. Discussion: This study has attempted to demonstrate through an appropriately controlled in vivo study that hydroxyapatite does not play a significant role in third-body polyethylene wear in THA at a mean follow-up of five years. The concern of three-body wear with hydroxyapatite coating is no greater than porous coated cementless implants

Introduction: The Step Activity Monitor (SAM) is a microprocessor worn on the ankle that measures ambulatory activity in real time. Methods: Activity magnitudes, speed parameters and activity patterns were analyzed in 31 patients with 37 primary total hips. Wear was measured from digitized radiographs using a validated two-dimensional, edge detection-based computer algorithm. Results: On average, patients walked 5.6 hours per day (range: 1.9–9.8); averaging 5,266 gait cycles (range: 1,737–11,805), at 20 cycles/minute (range: 12.7–32.8) with a maximum speed of 63 cycles/minute (range: 45.0–88.0). Fast and very fast walking (30–49 and > 50 cycles/minute) accounted for 9.4% and 4.4% of total walking time. Patients started and stopped walking about 66 times per day (range: 34–113), with about 81 cycles between stops (range: 28.1-200.1) in average active intervals of 5.3 minutes (range: 3.3–10.3). There was no difference in the average number of gait cycles between females and males. However, polyethylene wear per million cycles was significantly higher in males (p=0.006). Even after adjustment for greater height and weight in males, their wear rate was still significantly higher (p< 0.01). Males walked at a higher average speed (p=0.07), spent 33.9% more time walking fast or very fast, had 4% more starts/stops per day, with 13% less strides between stops. The percentage of time spent walking slow (5–9 cycles/minute) was negatively correlated to wear (p< 0.05). Discussion and Conclusion: The SAM allows assessment of patterns and intensity of joint use. Similar to a set of automobile tires, polyethylene wear is a function of the amount and type of use; faster walking with more frequents starting and stopping is associated with a higher polyethylene wear rate. As the clinical performance of crosslinked polyethylenes is being monitored, it is critical to consider the influence of the amount and type of patient activity on wear

Materials and Methods: This study included careful analysis of 24 knees with polyethylene wear in which revision surgery was performed. Preoperative evaluations included (1) single-leg standing AP, lateral and stress view, (2) dynamic weight-bearing lateral radiographs, and (3) manual test under anesthesia. Intraoperatively, (1) morphologic change of the worn inserts, (2) rotational alignment of tibia-femoral articulation (3) motion behavior of the joint following trial insertion was observed. Based on the above evaluation, 20 knees were revised with 3-component revision by constrained PS knees. The remaining 3 knees received isolated insert exchange. Results: During the follow-up of 2–6 years, good and excellent results were obtained in all 21 patients who received three-component revision with Osteonics series IV constrained PS prosthesis. The mean HSS score was 92 and the mean ROM was 112 degrees. In the three patients receiving exchange of a thicker polyethylene only, two failed with the same mechanism 15 months and 23 months later and received re-revision. The X-ray of the remaining patient at 5-year F/U revealed impending failure. Discussion: Based on our preoperative plain/dynamic radiographs and intraoperative findings, we postulate that tibial polyethylene wear is attributed to retained PCL in the absence of ACL, excessive posterior slope of tibial cut, rotational mismatch of tibia-femoral rotation and abnormal condylar lift-off in weight-bearing phase. With passage of time and progression of wear, secondary ligamentous decompensation and multidirectional instability may develop as a result of abnormal kinematics. Therefore, by isolated exchange of insert, the failure mechanism remains unchanged and secondary ligamentous instability persists. Eventually the new insert will fail again. Conclusion: In revision surgery of tibial polyethelene wear, both the primary cause of failure and the secondary ligamentous instability must be addressed. The author strongly advocate that, in addition to reversal of the primary failure mechanism by 3-component revision, the use of a constrained PS prosthesis is mandatory to overcome the secondary soft tissue decompensation

Purpose: This study was designed to establish the poly-ethylene wear rates in the Oxford medial unicompert-mental knee replacement. Introduction: The Oxford meniscal bearing knee was introduced as a design to reduce polyethylene wear. There has been one previous retrieval study of the Oxford UKA, which reported very low wear rates in some specimens, but abnormal patterns of wear in others, including impingement. There has been no further investigation of these abnormal wear patterns. Methods: Forty-seven bearings were retrieved from patients who had received a medial Oxford UKA for anteromedial osteoarthritis of the knee, none of which had previously been studied. Mean time to revision was 8.4 years (SD 4.1) and 20 had been implanted for over 10 years. The macroscopic pattern of polyethylene wear and the linear penetration (dial gauge measurement) was recorded for each bearing. Results: The mean linear penetration rate (LPR) was 0.07mm/year. The patterns of wear fell into 4 categories, each with a different LPR; 1) No abnormal macroscopic appearance, n=16 (LPR = 0.01mm/year), 2) Abnormal macroscopic wear with extra-articular impingement, n=16 (LPR = 0.05mm/year), 3) Abnormal macroscopic wear with intra-articular impingement, n=6 (LPR = 0.10mm/year), 4) Abnormal macroscopic wear with impingement and signs of incongruous articulation, n=9 (LPR = 0.14mm/year). The differences in LPR were statistically significant (p< 0.05). Conclusion: The results show that very low polyethylene wear rates are possible if the device functions normally. However if the bearing displays abnormal function (extra-articular, intra-articular impingement or incongruous articulation) wear rates increase significantly

Introduction: Polyethylene wear debris is the main contributing factor that leads to aseptic loosening and osteolysis. The main objective of this study was to evaluate the role of hydroxyapatite (HA) in third-body polyethylene wear in total hip arthroplasty. Materials: 199 primary cementless THA’s (174 patients) performed by a single surgeon were enrolled in a prospective randomized study comprising Hydroxyapatite and non-hydroxyapatite coated femoral implants. The femoral component had metaphyseal-diaphyseal fit design with proximal plasma sprayed titanium circumferential porous coating. The hydroxyapatite coating was 50 – 75 micrometers over the porous surface with the components of identical design. The acetabular component was plasma sprayed titanium porous coated shell without hydroxyapatite

Introduction: Computer-based wear analysis is currently the most accurate method for determining the in vivo wear rates of polyethylene liners during total hip arthroplasty. MRI of a total hip is emerging as the best method for determining the intra-articular volume of particulate debris. The purpose of this study is to determine if there is a correlation between polyethylene wear and the development of particle load in patients with highly crosslinked (HXLP) liners. Materials and Methods: 20 well-functioning total hips (7 metal heads against HXLP liners and 13 ceramic heads against HXLP liners) in 18 young active individuals were analyzed using the following criteria: femoral head penetration of the liner was measured by Roman (ROntgen Monographic ANalysis) software and particulate load was calculated by MRI criteria as described by Potter et al. Clinical and radiographic analyses were performed using HSS, WOMAC, and criteria defined by DeLee, Charnley, and Engh. The average age of the patients was 57 (Range 45–67) and average follow-up was 1.6 y (range 1.0 – 3.0 y). Results: All implants appeared well osteointegrated with no radiographic evidence of osteolysis. All patients had well-functioning total hips with a greater than one mile daily walking tolerance. A trend towards correlation was observed between increased polyethylene wear and increased particulate volumes. Average HXLP wear was 0.03 mm (range −0.19 to 0.27 mm) and average particle volume was 841 (range 6951 to 0). One patient in particular recorded 0.27 mm of polyethylene wear, mild particle disease and a particle disease volume of 3321 at 1.6 years follow-up. However, statistical significance could not be achieved with these data points. Conclusions: There appears to be a relationship between polyethylene wear as measured by computer-based systems and particulate volume as measured by MRI. Limitations of the current methodology include the inability of computer-based systems to detect precise levels of minimal wear with HXLP liners, and the highly sensitive MRI images which may be detecting more than just wear debris

Lewinnek's safe zone recommendation to minimise dislocations was a target of 5–25° for anteversion angle and 30–50° for inclination angle. Subsequently, it was demonstrated that mal-positioning of the acetabular cup can also lead to edge loading, liner fracture, and greater conventional polyethylene wear. The purpose of this study was to measure the effect of acetabular cup position on highly crosslinked polyethylene wear in total hip arthroplasty (THA) at long-term follow-up. We identified all patients that underwent primary THA with a minimum of 10 years follow-up using an institutional database in London, Ontario, Canada. Patients with a single implant design consisting of a 28 mm cobalt chromium head and highly crosslinked polyethylene liner (ram extruded, GUR 1050, 100 kGy gamma irradiated, remelted, ethylene oxide sterilised) were selected for inclusion. In total, 85 hips from 79 recruited patients were analysed. Patients underwent a supine radiostereometric analysis (RSA) exam in which the x-ray sources and detectors were positioned to obtain an anterior-posterior and cross-table lateral radiograph. Acetabular cup anteversion angle, inclination angle, and 3D penetration rate (including wear and creep) were measured from the stereo radiograph pairs. At a mean follow-up of 13 years (range, 10–17 years) the mean penetration rate was 0.059 mm/year (95% CI: 0.045 to 0.073 mm/year). Mean anteversion angle was 18.2° (range, −14 to 40°) and mean inclination angle was 43.6° (range, 27 to 61°). With respect to the Lewinnek safe zone, 67% hips met the target for anteversion angle, 77% met the target for inclination angle, and 51% met the target for both. There was no correlation between anteversion angle and penetration rate (r = −0.14, p = 0.72) or between inclination angle and penetration rate (r = 0.11, p = 0.35). There was also no difference (p = 0.07) in penetration rate between hips located within the Lewinnek safe zone for both anteversion angle and inclination angle (mean 0.057 mm/year, 95% CI: 0.036 to 0.079 mm/year) and those outside the safe zone (mean 0.062 mm/year, 95% CI: 0.042 to 0.083 mm/year). Acetabular cup position had no effect on the wear rate of highly crosslinked polyethylene at long-term follow-up. Although care should still be taken to correctly position the acetabular cup for stability, highly crosslinked polyethylene is a forgiving bearing material that can withstand a wide range of cup positions without negatively impacting longevity due to wear

The Low Contact Stress (LCS) mobile-bearing total knee replacement (TKR) was designed to minimize polyethylene wear, aseptic loosening and osteolysis. However, registry data suggests there is a significantly greater revision rate associated with the LCS TKR. The primary aim of this study was to assess long-term survivorship of the LCS implant. Secondary aims were to assess survival according to mechanism of failure and identify predictors of revision. We retrospectively identified 1091 LCS TKRs that were performed between 1993 and 2006. There was incomplete data available 33 who were excluded. The mean age of the cohort was 69 (SD 9.2) years and there were 577 TKRs performed in females and 481 in males. Mean follow up was 14 years (SD 4.3). There were 59 revisions during the study period: 14 for infection, 18 for instability, and 27 for polyethylene wear. 392 patients died during follow up. All cause survival at 10-year was 95% (95%CI 91.7–98.3) and at 15-year was 93% (95%CI 88.6–97.8). Survival at 10-years according to mechanism of failure was: infection 99% (95%CI 94–100%), instability 98% (95%CI 94–100%), and polyethylene wear 98% (95%CI92–100). Of the 27 with polyethylene wear only 19 had associated osteolysis requiring component revision, the other 8 had simple polyethylene exchanges. Cox regression analysis, adjusting for confounding variables, identified younger age was the only predictor of revision (hazard ratio 0.96, 95%CI 0.94–0.99, p=0.003). The LCS TKR demonstrates excellent long-term survivorship with a low rate of revision for osteolysis, however the risk is increased in younger patients

The purpose of this study was to precisely measure the 10-year polyethylene wear rate of primary total hips using Radiostereometric analysis (RSA) comparing Oxidized Zirconium (OxZi) to cobalt chrome (CoCr) femoral heads articulating with highly cross-linked polyethylene (XLPE). RSA was performed on 46 patients who underwent total hip arthroplasty − 23 who received OxZi femoral heads and 23 who received CoCr heads in combination with XLPE at a minimum of 10 years follow-up. All patients had identical THR systems implanted except for the femoral head utilized. The Centre Index method was utilised to assess total wear rates (from index surgery until final evaluation) using a dedicated RSA Software program (UmRSA Digital Measure v.2.2.1). In addition, the Martell technique was used to subtract head penetration occurring in the first 1–2 years (i.e. bedding-in phase) to allow calculation of the ‘steady state’ wear rates. There were no significant differences in demographics (i.e age, BMI, gender) between the groups. The average time from surgery of the RSA examinations was 11.7 and 12.6 years for the CoCr and OxZi groups respectively. Using the Centre Index Method to calculate total head penetration, wear rates were slightly higher in the OxZi group (0.048 +/− 0.021mm/year) compared to the CoCr group (0.035 +/− 0.017mm/year) with no statistical difference between the groups (p= 0.02). After correction for the bedding-in period, there was no statistically significant difference in mean ‘steady-state’ wear rate between OxZi (0.031 +/− 0.021mm/year) and CoCr (0.024 +/− 0.019mm/year) at 10 year follow up (p= 0.24). A comparison of preoperative and postoperative SF12, HHS, and WOMAC scores showed no statistical difference between the groups. RSA demonstrated the 10 year in-vivo wear rates of both bearing combinations to be well below the threshold for osteolysis. There was no significant difference between either the total or ‘steady-state’ wear rates of the OxZi and CoCr groups at 10 years

Introduction. Periprosthetic osteolysis following total hip arthroplasty is caused mainly by polyethylene wear particles and necessitates revision surgery at some stage even in the presence of well-fixed implants. Therefore, methods to estimate the polyethylene wear become important, with manual wear measurement methods as the main outcome measurement even in the presence of computer-assisted measurement methods on account of easy availability and simplicity in their use with reasonable accuracy. The purposes of this study were to quantify the accuracy and reproducibility of the slide presentation software method on clinical radiographs and to compare it with that of the previously described Livermore's method, and to determine the usefulness of the slide presentation software methods for highly cross linked polyethylene wear measurement. Materials and Methods. 81 hips out of 61 patients who underwent primary total hip arthroplasty between October 2000 and January 2006 were retrospectively evaluated for polyethylene wear by two independent observers using the Livermore's and the slide presentation software methods. All the hips were implanted with highly cross linked polyethylene acetabular liners with cementless acetabular components. The 28 mm sized cobalt chrome alloy femoral heads were used in all cases. The mean age of the patients was 50.8 years(range, 27–73 years), and the mean follow-up period was 6.6 years (range, 2–11 years). Paired radiographs were analyzed using the Livermore's and the slide presentation software method. For the Livermore's methods, radiographs were magnified to 200%, printed, and readings taken with digital calipers with an accuracy of 0.01 mm(Figure 1). For the slide presentation software method, we used Microsoft Office PowerPoint software(Microsoft Corp., Redmond, WA, USA) as described in a previous our study(Figure 2). Results. The mean polyethylene wear rate in 81 hips measured by the Livermore's method was found to be 0.071±0.12 and 0.081±0.09 mm/year by observer 1 and 2 respectively. The mean polyethyelene wear rate measured by slide presentation software method was found to be equally 0.069±0.07 mm/year by observer 1 and 2. Interobserver and intraobserver variance were evaluated using Pearson correlation coefficient. Correlation coefficients for interobserver variance were 0.802 for the Livermore's method and 0.979 for the slide presentation software method. Correlation coefficient for intraobserver variance were 0.777 for the Livermore's method and 0.965 for the slide presentation software method in observer 1, 0.303 for the Livermore's method and 0.941 for the slide presentation software method. The mean time consumed in each radiographic measurement with the Livermore's method was 15.52 minutes (range, 10.67–22 minutes) as compared to 9.55 minutes (range, 5.42–13.5 minutes) measured with the slide presentation software method (p < 0.001). Conclusion. The slide presentation software method was more accurate in serial intra-observer measurements and more reproducible in inter-observer readings for polyethylene wear than the traditional Livermore method, and was simple to use and less time consuming. Not all orthopaedic surgeons have access to CT for measuring polyethylene wear, hence the use of this type of manual method becomes a necessity on account of its easy availability and repeatability in serial measurements

Early migration of the acetabular and femoral component after total hip replacement has shown to be a good predictor of implant failure. The only current technique available for this measurement is RSA. An entirely new technique for the measurement of component migration and polyethylene wear has been developed. Required are a single CT of the patients’ pelvis and femur, and routine serial postoperative antero-posterior (AP) and lateral radiographs. A CT scan of the patients pelvis and proximal femur is performed either pre or post-operatively. This CT is used to build a solid model of the patients’ bony anatomy. CAD models of the femoral and acetabular component are obtained from the manufacturer and all four solid models are imported into custom software. Ray tracer (RT) technology is the computer generation of images of a solid model placed between a camera and a screen. It has been adapted to reproduce the radiological setup used to take clinical AP and lateral radiographs. The four solid models (pelvis, acetabular component, femoral component, femoral shaft) are each placed in the RT. Manipulation of each solid model is performed (6 degrees of freedom, x, y, z translation, and rotation about the x, y, z axis) using Artificial Intelligence, until an outline of the solid model generated by the ray tracer is identical to the outline of the AP and lateral radiograph of that patient. Change in relative positions of each solid model over time (pelvis acetabular component represents acetabular migration, acetabular component femoral stem represents polyethylene wear, and femoral stem femur represents femoral migration) are recorded. Validation to measure accuracy of the technique has been performed using computer models, and femoral and acetabular prostheses implanted into a cadaver. Despite significant variations in the position of the pelvis and leg during the obtaining of post-operative radiographs, this new technique was able to measure polyethylene wear and component migration with accuracy similar to that of RSA (0.25 mm in the AP plane). Further testing and validation is required, but this technique offers promise for the future in being able to retrospectively measure component migration and poly-ethylene wear, using a single CT scan and routine clinical postoperative radiographs

Objectives. Bone void fillers are increasingly being used for dead space management in arthroplasty revision surgery. The aim of this study was to investigate the influence of calcium sulphate bone void filler (CS-BVF) on the damage and wear of total knee arthroplasty using experimental wear simulation. Methods. A total of 18 fixed-bearing U2 total knee arthroplasty system implants (United Orthopedic Corp., Hsinchu, Taiwan) were used. Implants challenged with CS-BVF were compared with new implants (negative controls) and those intentionally scratched with a diamond stylus (positive controls) representative of severe surface damage (n = 6 for each experimental group). Three million cycles (MC) of experimental simulation were carried out to simulate a walking gait cycle. Wear of the ultra-high-molecular-weight polyethylene (UHMWPE) tibial inserts was measured gravimetrically, and damage to articulating surfaces was assessed using profilometry. Results. There was no significant difference (p  >  0.05) between the wear rate of implants challenged with CS-BVF (3.3 mm. 3. /MC (95% confidence interval (CI) 1.8 to 4.8)) and the wear rate of those not challenged (2.8 mm. 3. /MC (95% CI 1.3 to 4.3)). However, scratching the cobalt-chrome (CoCr) significantly (p < 0.001) increased the wear rate (20.6 mm. 3. /MC (95% CI 15.5 to 25.7)). The mean surface roughness of implants challenged with CS-BVF was equivalent to negative controls both after damage simulation (p = 0.98) and at the conclusion of the study (p = 0.28). Conclusion. When used close to articulating surfaces, a low-hardness, high-purity CS-BVF had no influence on wear. When trapped between the articulating surfaces of a total knee arthroplasty, CS-BVF did not scratch the surface of CoCr femoral components, nor did it increase the wear of UHMWPE tibial inserts compared with undamaged negative controls. Cite this article: R. M. Cowie, S. S. Aiken, J. J. Cooper, L. M. Jennings. The influence of a calcium sulphate bone void filler on the third-body damage and polyethylene wear of total knee arthroplasty. Bone Joint Res 2019;8:65–72. DOI: 10.1302/2046-3758.82.BJR-2018-0146.R1