Peter Ellison

Survival rates and causes of revision in cemented primary total knee replacement: A report from the Norwegian Arthroplasty Register 1994–2009

We evaluated the rates of survival and cause of revision of seven different brands of cemented primary total knee replacement (TKR) in the Norwegian Arthroplasty Register during the years 1994 to 2009. Revision for any cause, including resurfacing of the patella, was the primary endpoint. Specific causes of revision were secondary outcomes. Three posterior cruciate-retaining (PCR) fixed modular-bearing TKRs, two fixed non-modular bearing PCR TKRs and two mobile-bearing posterior cruciate-sacrificing TKRs were investigated in a total of 17 782 primary TKRs. The median follow-up for the implants ranged from 1.8 to 6.9 years. Kaplan-Meier 10-year survival ranged from 89.5% to 95.3%. Coxs relative risk (RR) was calculated relative to the fixed modular-bearing Profix knee (the most frequently used TKR in Norway), and ranged from 1.1 to 2.6. The risk of revision for aseptic tibial loosening was higher in the mobile-bearing LCS Classic (RR 6.8 (95% confidence interval (CI) 3.8 to 12.1)), the LCS Complete (RR 7.7 (95% CI 4.1 to 14.4)), the fixed modular-bearing Duracon (RR 4.5 (95% CI 1.8 to 11.1)) and the fixed non-modular bearing AGC Universal TKR (RR 2.5 (95% CI 1.3 to 5.1)), compared with the Profix. These implants (except AGC Universal) also had an increased risk of revision for femoral loosening (RR 2.3 (95% CI 1.1 to 4.8), RR 3.7 (95% CI 1.6 to 8.9), and RR 3.4 (95% CI 1.1 to 11.0), respectively). These results suggest that aseptic loosening is related to design in TKR.

Wear particles and ions from cemented and uncemented titanium-based hip prostheses—A histological and chemical analysis of retrieval material

Wear debris-induced inflammation is considered to be the main cause for periprosthetic osteolysis in total hip replacements (THR). The objective of this retrieval study was to examine the tissue reactions and exposure to metal ions and wear particles in periprosthetic tissues and blood samples from patients with titanium (Ti)-based hip prostheses that were revised due to wear, osteolysis, and/or aseptic loosening. Semiquantitative, histological tissue evaluations in 30 THR-patients revealed numerous wear debris-loaded macrophages, inflammatory cells, and necrosis in both groups. Particle load was highest in tissues adjacent to loosened cemented Ti stems that contained mainly submicron zirconium (Zr) dioxide particles. Particles containing pure Ti and Ti alloy elements were most abundant in tissues near retrieved uncemented cups. Polyethylene particles were also detected, but accounted only for a small portion of the total particle number. The blood concentrations of Ti and Zr were highly elevated in cases with high abrasive wear and osteolysis. Our findings indicate that wear particles of different chemical composition induced similar inflammatory responses, which suggests that particle size and load might be more important than the wear particle composition in periprosthetic inflammation and osteolysis.

Is there still a place for the cemented titanium femoral stem? 10,108 cases from the Norwegian Arthroplasty Register.

Background and purpose Despite the fact that there have been some reports on poor performance, titanium femoral stems intended for cemented fixation are still used at some centers in Europe. In this population-based registry study, we examined the results of the most frequently used cemented titanium stem in Norway. Patients and methods 11,876 cases implanted with the cemented Titan stem were identified for the period 1987–2008. Hybrid arthroplasties were excluded, leaving 10,108 cases for this study. Stem survival and the influence of age, sex, stem offset and size, and femoral head size were evaluated using Cox regression analyses. Questionnaires were sent to the hospitals to determine the surgical technique used. Results Male sex, high stem offset, and small stem size were found to be risk factors for stem revision, (adjusted RR = 2.5 (1.9–3.4), 3.3 (2.3–4.8), and 2.2 (1.4–3.5), respectively). Patients operated in the period 2001–2008 had an adjusted relative risk (RR) of 4.7 (95% CI: 3.0–7.4) for stem revision due to aseptic stem loosening compared to the period 1996–2000. Changes in broaching technique and cementing technique coincided with deterioration of the results in some hospitals. Interpretation The increased use of small stem sizes and high-offset stems could only explain the deterioration of results to a certain degree since the year 2000. The influence of discrete changes in surgical technique over time could not be fully evaluated in this registry study. We suggest that this cemented titanium stem should be abandoned. The results of similar implants should be carefully evaluated.

In vitro simulation and quantification of wear within the patellofemoral joint replacement

Quantification of the wear rate in vitro is now considered an essential step in the development of a new joint replacement prior to clinical trials. However, little research exists around in vitro simulation of wear in the patellofemoral joint (PFJ) despite over 200,000 being implanted annually within the European Union. A method to simulate wear in the laboratory using four input degrees of freedom within the PFJ of total knee replacement (TKR) has been developed. Wear simulation was validated through comparison of functional kinematics and patellar surface damage modes produced in vitro to clinical outcomes. The technique has been shown to replicate the prescribed in vivo kinematics in a reproducible and repeatable manner. The wear scar areas were similar to those found in vivo. However, geometrical measurements of wear were not reliable due to creep and geometry changes. As has been found previously with tibial inserts, geometrical determination of wear volume was not found to be an effective method of comparing wear from simulators and retrievals. Change in volume calculated gravimetrically was seen to be the most repeatable measure of patellar wear in vitro.

Experimental investigation of the effect of surface roughness on bone-cement-implant shear bond strength.

Debonding of cemented bone implants is regarded as a major contributor to complications. The relationship between shear bond strength and surface roughness has been investigated, however there are inconsistencies in the trends reported in different studies. The shear strength between poly(methyl methacrylate) bone-cement and sand blasted cobalt-chromium and titanium alloy surfaces was measured to investigate the relationship between interfacial shear strength and surface topology. Surface roughness was quantified by a power law relationship fitted to Fourier spectra as well as three traditional parameters (arithmetical average roughness (Ra), volume of interdigitation (Rr), and RMS slope (Rdq)). We found that the interfacial shear strength is directly proportional to the exponent of the surfaces power spectra (P2) and Rdq, but not to Ra and Rr. However, Rdq is shown to be critically dependent on sampling frequency, making it sensitive to measurement settings. P2 was found to be a robust measure of the surface roughness being independent of sampling frequency.

Coordinating Retrieval and Register Studies Improves Postmarket Surveillance

BackgroundThe relative risk of revision of the Titan® femoral stem due to aseptic loosening increased after 2000; however, the reasons for this have not been established. A retrieval analysis was initiated with the aim of delineating the failure mechanism.Questions/PurposesWe asked whether aseptic loosening in stems after 2000 was associated with (1) appearance of osteolytic lesions, (2) wear particle exposure, (3) stem damage, or (4) changes to the implant or surgical instrumentation.MethodsFemoral stems, cement, tissue, and radiographs were collected from 28 patients. We assessed the development of osteolytic lesions in 17 patients. Exposure to wear particles was quantified in 18 patients. Stem damage was assessed in 15 patients. We observed differences in the implants by examination of 24 retrieved stems. Information concerning changes to instrumentation was requested from the manufacturer.ResultsWe found osteolysis in all patients receiving implants after 2000, which was associated with a median dose of cement and stem particles of 14,726/mm2. Abrasion covered 59% of the surface of stems implanted from 1999. We identified geometric changes to the stem, the percent weight of aluminum in the stem’s oxide layer decreased from 25% to 14% after 1997 and the rasp used to prepare the femoral cavity changed to a broach in 1999.ConclusionsStems implanted from 2000 failed through osteolysis induced by particles released from the cement and implant. Changes to implant geometry, surface oxide layer, and surgical tools occurred in the same time frame as the reduction in survivorship.

Biological activity of polyethylene wear debris produced in the patellofemoral joint

Polyethylene wear is considered a threat to the long term survival of total knee replacements. The aim of this study was to investigate the contribution that resurfacing the patella makes to wear debris-induced osteolysis following total knee replacement. Ultra-high molecular-weight polyethylene wear particles were isolated from simulator lubricant. Particle shape, size, and volume distributions were recorded allowing the osteolytic potential of the wear debris produced in the patellofemoral joint to be estimated using the concept of specific biological activity and functional biological activity. Values were compared with those reported for the tibiofemoral joint. Specific biological activity for the patellofemoral joint was not significantly different from the values for the tibiofemoral joint of total knee replacement devices, and therefore, has a similar potential to stimulate osteolytic cytokine release from macrophages. Functional biological activity was significantly lower for the patellofemoral joint compared with the tibiofemoral joint. Functional biological activity was significantly lower for the patellofemoral joint compared with the fixed bearing and rotating platform total knee replacement devices. However, as patellar resurfacing is commonly fitted as part of a total knee replacement system, this results in a 20% increase in overall functional biological activity for the system. Therefore, implanting a patellar resurfacing will increase the potential for osteolysis in the knee.

Coupling of dynamics and contact mechanics of artificial hip joints in a pendulum model

Abstract To date, fully coupled dynamics and contact mechanics analysis is still limited by expensive computational cost and long computing time and has not been addressed comprehensively, particularly in the hip joint. To understand the influence of different parameters on the biomechanics of the total hip replacement (THR) and improve its design, two numerical approaches were developed and implemented in finite element models to investigate the coupling between the dynamics response and the contact mechanics for three different THR configurations, metal-on-polyethylene (MOP), metal-on-metal (MOM), and ceramic-on-ceramic (COC). The dynamic force and the contact pressure distribution at the bearing surfaces from the two methods were predicted and compared. The influences of various parameters (motion angle, load applied in the pendulum, friction coefficient, geometry, and material properties) were subsequently investigated. From the comparisons, the decoupled method, based on the rigid-body dynamics and the quasi-static elastic contact mechanics, was adequate to predict the performance of the THRs efficiently. The load had the greatest influence on the dynamics/contact mechanics among other factors.

The influence of sea water in oil emulsion on bearing performance

Abstract The lubricant in the bearings of ships can be easily polluted by sea water. Too much sea water may deteriorate the bearing performance and result in catastrophic failure; therefore, the lubricant should be changed regularly to prevent this. It is important to investigate the effect of adding sea water to mineral oil on the tribological performance of these bearings. In the present study, different amounts of sea water of 1, 2, and 3 per cent (by mass) were mixed with a typical mineral oil with a viscosity of 46 mm2/s at 40 °C and tested in 12 identical journal bearings under different operation conditions of rotational speed and load. For each case, the temperature within the oil film, the loci of the shaft centre, the power consumption, and the viscosity of the emulsion were measured. In parallel to these measurements, a CFD simulation was performed for the test bearings to estimate the friction force and load capacity. The experimental measurements and the computational predictions were compared. A maximum amount of sea water that can be tole-rated in the mineral oil was established for the normal working conditions of the journal bearing.

Wear of a Mobile Bearing Uni-Compartmental Knee Replacement Prosthesis: A Comparison of In Vitro and In Vivo Wear Rates

Wear induced osteolysis is cited as the primary cause of aseptic loosening in knee replacements. It has been postulated that mobile bearing (MB) knee prostheses reduce wear as they allow lower contact stress through high congruency between components while maintaining a wide range of joint motion. In vitro wear simulations are preclinical tests for predicting the performance of new designs of partial and total knee replacements. This study investigates the wear of a leading design of MB uni-compartmental knee replacement (UKR) by quantifying the in vitro wear rate and linear penetration of the polyethylene meniscal bearing. Three medial and three lateral MB UKRs (Uniglide, Corin, Ltd., U.K.) were tested in a three station wear simulator using force control as defined in ISO 14243-1. Volumetric wear was determined gravimetrically every half million cycles (MC) up to 10 MC. Maximum linear penetration wear was measured after 10 MC. Volumetric wear rates of 1.65±0.28 mm3/MC (mean±SD) and 1.66±0.31 mm3/MC were recorded for the medial and lateral bearings, respectively, and the wear of all bearings was linear. Previous simulator studies have reported mean wear rates of 3.8 to 10.4 mm3/MC for MB UKRs. Maximum linear penetration wear rates of 0.013±0.001 mm/MC and 0.012±0.001 mm/MC were recorded for the medial and lateral bearings, respectively, after 10 MC. This was in agreement with that reported for well functioning MB UKRs through in vivo measurement (0.01 mm/year) and compared favourably to that reported for fixed bearing designs (0.15 mm/year). The results of this study show that in vitro measurements correlate well to in vivo measurements of wear. This indicates that the current in vitro methodology for the simulation of wear in MB UKRs is a valid tool for preclinical assessment of MB UKR prostheses.