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Biomedical subjects

A W McCaskie

Publications and source records attributed to A W McCaskie.

At least 19 recordsLinked to original sources
PubMed2006

Removal of acetabular bone in resurfacing arthroplasty of the hip: a comparison with hybrid total hip arthroplasty.

Resurfacing arthroplasty of the hip is being performed more frequently in the United Kingdom. The majority of these patients are younger than 55 years of age, and in this group the key benefits include conservation of femoral bone stock and the potential reduction in the rate of dislocation afforded by the larger resurfacing head. Early aseptic loosening is well recognised in patients younger than 55 years of age, and proponents of resurfacing believe that the improved wear characteristics of the metal-on-metal bearing may improve the long-term survival of this implant. There has been some concern, however, that resurfacing may not be conservative of acetabular bone. We compared a series of 33 consecutive patients who had a hybrid total hip arthroplasty with an uncemented acetabular component and a cemented femoral implant, with 35 patients undergoing a Birmingham hip resurfacing arthroplasty. We compared the diameter of the implanted acetabulum in both groups and, because they were not directly comparable, we corrected for patient size by measuring the diameter of the contralateral femoral head. The data were analysed using unpaired t-tests and analysis of covariance. There was a significantly larger acetabulum in the Birmingham arthroplasty group (mean diameter 56.6 mm vs 52.0 mm; p < 0.001). However, this group had a significantly larger femoral head diameter on the contralateral side (p = 0.03). Analysis of covariance revealed a significant difference between the mean size of the acetabular component implanted in the two operations. The greatest difference in the size of acetabulum was in those patients with a larger diameter of the femoral head. This study shows that more bone is removed from the acetabulum in hip resurfacing than during hybrid total hip arthroplasty, a difference which is most marked in larger patients.

Acetabulum↗
PubMed2006

Should we reconsider all-polyethylene tibial implants in total knee replacement?

The role of modular tibial implants in total knee replacement is not fully defined. We performed a prospective randomised controlled clinical trial using radiostereophotogrammetric analysis to compare the performance of an all-polyethylene tibia with a metal-backed cruciate-retaining condylar design, PFC-Sigma total knee replacement for up to 24 months. There were 51 patients who were randomised into two treatment groups. There were 10 subsequent withdrawals, leaving 21 all-polyethylene and 20 metal-backed tibial implants. No patient was lost to follow-up. There were no significant demographic differences between the groups. At two years one metal-backed implant showed migration > 1 mm, but no polyethylene implant reached this level. There was a significant increase in the SF-12 and Oxford knee scores after operation in both groups. In an uncomplicated primary total knee replacement the all-polyethylene PFC-Sigma tibial prosthesis showed no statistical difference in migration from that of the metal-backed counterpart. There was no difference in the clinical results as assessed by the SF-12, the Oxford knee score, alignment or range of movement at 24 months, although these assessment measures were not statistically powered in this study.

Aged↗
PubMed2006

Are national guidelines for total hip replacement in the UK reflected in practice?

INTRODUCTION: A cross-sectional study was performed to compare the practice of total hip replacement (THR) in the UK against national guidelines. MATERIALS AND METHODS: A postal questionnaire was sent to all fellows of the British Orthopaedic Association. RESULTS: Of the 1587 questionnaires sent out, 966 (60.9%) were returned. Of these, 706 (73.1%) were available for data collection and analysis. CONCLUSIONS: Consensus was observed in several areas including the use of pre-admission clinics and modern cementing techniques. Facilities deemed necessary for THR surgery such as HDU/ITU back-up, ultra-clean air and dedicated orthopaedic wards are almost universally available. However, a lack of consensus is evident in many areas including the process of obtaining written consent, thrombo-embolic prophylaxis, duration of antibiotic prophylaxis, supervision of trainee surgeons and follow-up arrangements. The proliferation in the range of implants, particularly aimed at 'younger' patients, available to surgeons has once again been highlighted.

Arthroplasty, Replacement, Hip↗
PubMed2005

Dynamic creep and mechanical characteristics of SmartSet GHV bone cement.

The restrained dynamic creep behaviour and mechanical properties of SmartSet GHV bone cement have been investigated at both room temperature and body temperature. It was found that the bone cement behaves significant differently at room temperature from that at body temperature. The test temperature had a strong effect on the creep performance of the bone cements with a higher creep rate observed at body temperature at each loading cycle. For both temperatures, two stages of creep were identified with a higher creep rate during early cycling followed by a steady state creep rate. The relationship between creep deformation and loading cycle can be expressed by a Hyperb 1 model. As a visco-elastic material, the sensitivity of bone cement to the temperature change was evident during mechanical testing. Compared to the mechanical strength at room temperature, a decreased value was demonstrated at body temperature. The bending modulus was very sensitive to the change in testing temperature, where a reduction of 52% was recorded. A significant reduction in compressive and bending strength, 31 and 23% were recorded respectively. The effect of temperature on bending strength was less apparent, where only 13% reduction was exhibited at body temperature compared to room temperature.

Bone Cements↗
PubMed2005

Comparison of offset in Birmingham hip resurfacing and hybrid total hip arthroplasty.

Hip resurfacing is being performed more frequently in the United Kingdom. The possible benefits include more accurate restoration of leg length, femoral offset and femoral anteversion than occurs after total hip arthroplasty (THA). We compared anteroposterior radiographs from 26 patients who had undergone hybrid THA (uncemented cup/cemented stem), with 28 who had undergone Birmingham Hip Resurfacing arthroplasty (BHR). We measured the femoral offset, femoral length, acetabular offset and acetabular height with reference to the normal contralateral hip. The data were analysed by paired t-tests. There was a significant reduction in femoral offset (p = 0.0004) and increase in length (p = 0.001) in the BHR group. In the THA group, there was a significant reduction in acetabular offset (p = 0.0003), but femoral offset and overall hip length were restored accurately. We conclude that hip resurfacing does not restore hip mechanics as accurately as THA.

Acetabulum↗
PubMed2004

Opsonization of polyethylene wear particles regulates macrophage and osteoblast responses in vitro.

The cellular reaction to wear debris may result in the failure of an artificial joint's fixation to the skeleton. The influence of debris opsinization on cell activity has received little attention. This study seeks to establish whether different proteinaceous culture environments may invoke variant cellular responses to debris challenge. Consideration of the zeta potential of a low density polyethylene particle group and an ex vitro ultrahigh molecular weight polyethylene particle group revealed that the nature of the protein adsorbants is related to the concentration of the proteins in solution. Furthermore, the composition of the adsorbed layer was shown to vary with the spectra of proteins in solution. In standard cell culture conditions zeta potential approached zero, indicating the high probability of particle agglomeration. Cell challenge studies with U937 macrophages showed that BSA and FCS protein adsorption mediated increased cell adhesion, while bovine IgG showed little change over control values. No changes in behavior of osteoblastic cells were observed in similar experiments.

Adsorption↗
PubMed2004

The use of digital X-ray radiogrammetry and peripheral dual energy X-ray absorptiometry in patients attending fracture clinic after distal forearm fracture.

Despite the fact that 50% of postmenopausal women with Colles' fracture have evidence of osteoporosis, the vast majority of women with forearm fractures are neither investigated nor treated for osteoporosis. Digital X-ray radiogrammetry (DXR) provides an attractive option in patients with distal forearm fracture, as it requires no additional X-rays over and above those performed as part of clinical management. We have compared DXR analysis of nonstandardised plain films taken routinely in accident and emergency with peripheral dual energy X-ray absorptiometry (pDXA) in a group presenting with distal forearm fracture. Women presenting with a fracture of the distal forearm underwent pDXA measurements of the calcaneus. Plain X-rays performed at the time of presentation were taken to allow adequate fracture treatment. No additional radiographer training or standardisation of films was performed. The DXR technique relies upon visualisation of the metacarpal shafts and this was not visualised on 123 of 201 (61%) films. The AP plain film was thus assessed using DXR for BMD in the remaining 78 patients with a mean age of 70.6 years (SE = 1.3). Mean BMD for DXR was 0.46 g/cm2 (SE = 0.01) and for pDXA was 0.40 g/cm2 (SE = 0.01). The correlation between BMD measured using the two techniques was 0.55 (P < 0.001). Although DXR measurements could not be performed in all patients, this proportion could easily be increased by routinely including the metacarpal shaft region in X-rays obtained after suspected distal forearm fracture. The correlation between the pDXA and DXR results is comparable with those reported between DXA measurements at the forearm, spine and hip. Our study suggests that DXR may provide a feasible method for the assessment of future fracture risk. The potential advantage of DXR over calcaneal pDXA measurements is that standard forearm X-ray obtained as part of fracture management could be used.

Absorptiometry, Photon↗
PubMed2004

Pre-heating of components in cemented total hip arthroplasty.

Fatigue fractures which originate at stress-concentrating voids located at the implant-cement interface are a potential cause of septic loosening of cemented femoral components. Heating of the component to 44 degrees C is known to reduce the porosity of the cement-prosthesis interface. The temperature of the cement-bone interface was recorded intra-operatively as 32.3 degrees C. A simulated femoral model was devised to study the effect of heating of the component on the implant-cement interface. Heating of the implant and vacuum mixing have a synergistic effect on the porosity of the implant-cement interface, and heating also reverses the gradients of microhardness in the mantle. Heating of the implant also reduces porosity at the interface depending on the temperature. A minimum difference in temperature between the implant and the bone of 3 degrees C was required to produce this effect. The optimal difference was 7 degrees C, representing a balance between maximal reduction of porosity and an increased risk of thermal injury. Using contemporary cementing techniques, heating the implant to 40 degrees C is recommended to produce an optimum effect.

Arthroplasty, Replacement, Hip↗
PubMed2003

A preliminary hip joint simulator study of the migration of a cemented femoral stem.

A hip joint simulator that can be used to evaluate the outcome of the cemented total hip replacement has been designed, manufactured and evaluated. The simulator produces motion of a cemented hip construct in the extension/flexion plane, with a socket to rotate internal/externally. At the same time a dynamic loading cycle is applied to the construct. A validation test was performed on a cemented femoral stem within a novel composite femur. The study demonstrates the value of using a hip joint simulator to evaluate the outcome of the cemented hip construct. A complex migration pattern of the cemented hip prosthesis with respect to load cycling was observed, demonstrated in vitro comparable prosthesis migration behaviour, both the stem migration and migration patterns, to that found clinically.

Cementation↗
PubMed2002

Creep behavior comparison of CMW1 and palacos R-40 clinical bone cements.

The restrained dynamic creep behaviors of two clinical bone cements, Palacos R-40 and CMW1 have been investigated at room temperature and body temperature. It was found that the two cements demonstrated significantly different creep deformations, with Palacos R-40 bone cement demonstrating higher creep strain than CMW1 bone cement at each loading cycle. For both cements, two stages of creep were identified with a higher creep rate during early cycling followed by a steady-state creep rate. The test temperature had a strong effect on the creep performance of the bone cements with higher creep rate observed at body temperature. The relationship between creep deformation and loading cycles can be expressed by single logarithmic model. The SEM examinations revealed that CMW1 bone cement is more sensitive to defects within the specimen especially to the defects at the edges of the specimen than Palacos R-40 bone cement. However, in the absence of micro-cracks or defects within the inner surface layer, the dynamic loading (at less than 10.6 MPa) is unlikely to produce micro-cracks in the CMW1 bone cement. The different behaviors between the two bone cements may be attributed to differences in chemical compositions and molecular weight distributions.

Journal Article↗
PubMed2001

Current cementing techniques in hip hemi-arthroplasty.

To assess the use of modern cementing techniques in hip hemi-arthroplasty a postal questionnaire was sent during 1998 to all British Orthopaedic Training Association (B.O.T.A.) members regarding use of cement, type of cement, bone preparation and cementing technique. The results of this survey were compared to a similar survey in 1994 to assess any change in practice. Two hundred and eighty-six trainees responded to the 1998 survey, 352 to the 1994 survey. The use of uncemented prostheses had decreased from 31.3 in 1994 to 21.7% in 1998. Normal viscosity Palacos cement remains the most common cement in use, 64.3% in 1998. The use of antibiotic loaded cement has increased from 53.7 in 1994 to 67.9% in 1998. For bone preparation 47.3% of trainees in 1998 used a modern technique (syringe irrigation/pulsed lavage, brushing, gauze packing) compared to 35.1% in 1994. Modern cement insertion (retrograde gun, cement restriction and sustained pressure) was carried out by 39.3% in 1998 compared to 28.5% in 1994. Overall 27.2% of trainees used modern cementing techniques in hip hemi-arthroplasty, compared to 19.4% in 1994. Modern cementing techniques are used by a minority of British orthopaedic trainees, but in comparison to 1994 their use has increased.

Arthroplasty, Replacement, Hip↗
PubMed2001

Some failure modes of four clinical bone cements.

The fracture or failure behaviours of four commercial acrylic-based bone cements have been examined in tensile, bending and compression modes, and their mechanical properties are reviewed. It was found that Palacos R-40 bone cement had high radiopaque agent concentration, with high surface hardness. It exhibited a much lower bending strength and bending modulus compared with the other three bone cements (CMW1, CMW2000 and Simplex P). The textures of tensile fracture surfaces produced were similar for the four bone cements studied. The fracture surface was fragmented by crevices, which developed through the matrix and around large undissolved polymethylmethacrylate (PMMA) beads. Three bands with different features existed on the bending fracture surfaces, with an abrupt transition between them. It appears that the agglomerates of zirconium dioxide particles are implicated in Palacos R-40 bone cement fracture surface. The examination of compressive failed specimens revealed that a 'yielded crack band' existed across the transverse section. Plastic deformation resulted in the PMMA beads being squashed in the longitudinal direction and dilated in the transverse direction.

Biomechanical Phenomena↗
PubMed2001

Radiological features predictive of aseptic loosening in cemented Charnley femoral stems.

The radiological features of the cement mantle around total hip replacements (THRs) have been used to assess aseptic loosening. In this case-control study we investigated the risk of failure of THR as predictable by a range of such features using data from patients recruited to the Trent Regional Arthroplasty Study (TRAS). An independent radiological assessment was undertaken on Charnley THRs with aseptic loosening within five years of surgery and on a control group from the TRAS database. Chi-squared tests were used to test the probability of obtaining the observed data by chance, and odds ratios were calculated to estimate the strength of association for different features. Several features were associated with a clinically important increase (>twofold) in the risk of loosening, which was statistically significant for four features (p < 0.01). Inadequate cementation (Barrack C and D grades) was the most significant feature, with an estimated odds ratio of 9.5 (95% confidence interval 3.2 to 28.4, p < 0.0001) for failure.

Case-Control Studies↗
PubMed2000

A comparison of 2 modern femoral cementing techniques: analysis by cement-bone interface pressure measurements, computerized image analysis, and static mechanical testing.

Modern cementing techniques aim to improve microinterlock and to reduce aseptic loosening. The Norwegian and Swedish Arthroplasty Registers have shown an increased risk of revision using reduced-viscosity cement. We have compared 2 modern cementing techniques using retrograde insertion of normal-viscosity and reduced-viscosity cements. Laboratory-simulated arthroplasty was performed in paired human femora. Performance was evaluated by measuring pressures generated during cementation, cement penetration, and shear strength of the prosthesis-cement and bone-cement interfaces. Large differences exist between these 2 modern techniques. Despite no statistical differences between the pressure measurements with the 2 techniques, greater penetration of reduced-viscosity cement was found proximally, with a trend toward increased penetration of the more viscous cement distally. Areas of greater cement penetration with reduced-viscosity cement proximally produced higher values of ultimate shear strength. Both techniques showed a progressive increase in the shear strength as the level of the section progressed toward the tip of the prosthesis. There is a trend with both techniques for the distal fixation to be stronger.

Arthroplasty, Replacement, Hip↗
PubMed1999

The inadequacy of standard radiographs in detecting flaws in the cement mantle.

Radiological assessment of the cement mantle is used routinely to determine the outcome of total hip replacement. We performed a simulated replacement arthroplasty on cadaver femora and took standard postoperative radiographs. The femora were then sectioned into 7 mm slices starting at the calcar, and high-resolution faxitron radiographs were taken of these sections. Analysis of the faxitron images showed that defects in the cement mantle were observed up to 100 times more frequently than on the standard films. We therefore encourage the search for a better technique in assessing the cement mantle.

Arthroplasty, Replacement, Hip↗