One potential approach to addressing the current hip and knee arthroplasty backlog is via adoption of surgical prioritisation methods, such as use of pre-operative health related quality of life (HRQOL) assessment. We set out to determine whether dichotomization using a previously identified bimodal EuroQol Five-Dimension (EQ-5D) distribution could be used to triage waiting lists.

516 patients had data collected regarding demographics, perioperative variables and patient reported outcome measures (pre-operative & 1-year post-operative EQ-5D-3L and Oxford Hip and Knee Scores (OHS/OKS). Patients were split into two equal groups based on pre-operative EQ-5D Time Trade-Off (TTO) scores and compared (Group1 [worse HRQOL] = −0.239 to 0.487; Group2 [better HRQOL] = 0.516 to 1 (best)). The EQ5D TTO is a widely used and validated HRQOL measure that generates single values for different combinations of health-states based upon how individuals compare x years of healthy living to x years of illness.

We identified that those in Group1 had significantly greater improvement in post-operative EQ-5D TTO scores compared to Group2 (Median 0.67vs.0.19; p<0.0001 respectively), as well as greater improvement in OHS/OKS (Mean 22.4vs16.4; p<0.0001 respectively). Those in Group2 were significantly less likely to achieve EQ-5D MCID attainment (OR 0.13, 95%CI 0.07–0.23; p<0.0001) with a trend towards lower OHS/OKS MCID attainment (OR 0.66, 95%CI 0.37–1.19; p=0.168). There was no statistically significant difference in adverse events.

These finding suggest that a pre-operative EQ-5D cut-off of ≤0.487 for hip and knee arthroplasty prioritisation may help to maximise clinical utility and cost-effectiveness in a limited resource setting post COVID-19.

The rising prevalence of osteoarthritis, associated with an ageing population, is expected to deliver increasing demand across Scotland for arthroplasty services in the future. Understanding the scale of potential change to operative workflow is essential to ensure adequate provision of services and prevent prolonged waiting times that can cause patient harm. This future service demand for primary and revision hip arthroplasty across Scotland, and the rest of the U.K., is hitherto unknown.

We set out to provide projections of future primary & revision hip arthroplasty out to 2038 utilising historical trend data (2008–2018) from the Scottish Arthroplasty Project. All analyses were performed using the Holt's exponential smoothing projection method with the forecast package in R statistics. Results were adjusted for projected future population estimates provided by National Records of Scotland. Independent age & sex group predictions were also performed. All results are presented per 100,000 population at-risk per year (/100k/year).

The predicted rise of primary hip arthroplasty for all ages is from 120/100k/year in 2018 to 152/100k/year in 2038, a 27% increase. Based on a static 3 day length of stay average this would see 4280 additional patient bed days required for primary hip arthroplasty patients per annum. The number of revision hip arthroplasty procedures for all ages is projected to fall from 14/100k/year to 4/100k/year based on historical trend data. This does not however take into account the suspect increase in primary arthroplasty numbers that is likely to influence future revision rates.

Anticipated future demand for primary hip arthroplasty will require significant additional resource and funding to prevent deterioration in quality of care and an increase in patient wait times. Demand for revision arthroplasty is set to decrease, likely on account of improved implant materials, technique, and understanding of best practice to minimise complication risk. This doesn't however take into account the impact of the complex interaction between an increasing primary arthroplasty rate and revision risk. Understanding presented projections of changes to arthroplasty demand is key to future service delivery.

Dupuytrens disease is a fibrosing condition of the palmar aponeurosis and its extensions within the digits. Normal fascial fibres running longitudinally in the subcutaneous tissues of the palm become thickened and form the characteristic nodules and cords pathognomonic of Dupuytrens disease. A wide variety of surgical interventions exist, of these the partial fasciectomy remains the most conventional and widely used technique. Minimally invasive surgical treatments such as needle fasciotomy are, however, becoming increasingly popular. Dupuytrens disease remains a challenging condition to treat as recurrence is universally found with all surgical interventions. Although recurrence may be related to the severity of the disease, there are currently no research tools other than clinical examination to examine changes in the diseased tissue postoperatively and predict likelihood of long-term success.

Magnetic Resonance Imaging (MRI) may be of value for the study of Dupuytren disease, at present its use has been greatly underexplored. We wished to carry out a pilot study in order to examine the possibility of using 3.0 Tesla MRI to study Dupuytren tissue and then furthermore to examine the potential changes post-operatively following percutaneous fasciotomy.

Five patients set to undergo percutaneous needle fasciotomy were recruited and consented for the study. All patients underwent MRI scanning of the affected hand pre-operatively and at two weeks post-operatively. Scanning was carried out in the 3.0 Tesla research MRI scanner at Aberdeen Royal Infirmary. Patients were placed prone in the MRI scanner with the hand outstretched above the head in the so-called “Superman” position. A specially designed wrist and hand coil was used. Under the expertise of radiographers and physicists, image capture encompassed four novel scanning sequences in order to make a volumetric three-dimensional image sample of the affected hand. MIPAV software (Bethesda, Maryland) was used for image analysis.

Scanning revealed well defined anatomy. The Dupuytren cord arose from the palmar aponeurosis tissue which is deep to the palmar skin and subcutaneous tissue. It was distinctly different to deep structures such as the flexor tendons and intrinsic hand muscles which appeared with a uniform low and high signal respectively. The Dupuytren tissue had a heterogeneous signal on both T1 and T2 images. On T1 the tissue signal appeared high to intermediate, similar to that of bone and muscle, but low areas of signal were observed diffusely in an irregular fashion throughout. On T2 the tissue had a low signal throughout with some focal areas of high signal. Dupuytren tissue was mapped using MIPAV software for pre- and post-operative comparisons. Signal intensity, surface area and volume of the cords and fasciotomy sites were explored.

Our initial results suggest MRI can be used to study Dupuytren tissue. Such a research tool may be of use to study the natural history of Dupuytren disease and furthermore, the response to medical and surgical interventions.

The Adora RSA (NRT, Denmark) is a new stereo X-ray system custom built for Radeostereometry. Images are acquired using CXDI50C digital detectors (Canon, Netherlands). Analysis software was written locally to detect both Tantalum markers and the spherical head of the hip implant, and for RSA reconstruction and kinematic analysis.

To assess geometric reproducibility, a planar grid phantom was constructed with 1400 2mm markers in a grid pattern over a 350 by 430 mm glass plate. Additionally 25 tantalum markers of each diameter 1.0, 0.8 and 0.5 mm were added within a 120mm square of the grid. The phantom was imaged repeatedly with translation and rotation over the detector. For small phantom movements of up to 10mm over the detector, very small measurement errors were observed of median 2 microns, maximum 6 microns. For larger movements, the errors increased to median 5 microns and maximum 50 microns. Errors also increased with decreasing exposure.

For RSA validation, an acetabular PE cup was cemented to a Sawbone pelvis. Tantalum markers were inserted into the pelvis (10), cement (4), and cup (10). A 28mm metal head was fixed to the cup. The phantom was imaged repeatedly without movement, then moved in translation (up to 100 mm) and rotation (all axes, up to 45 degrees), and with full X-ray repositioning. Precision errors were calculated on the assumption of no relative movement between components.

Results are given for repositioning movement categorised as none, small (less than 25mm or 15 degrees), medium (less than 50mm or 30 degrees), and large. For the head, the mean total point motion error was 4, 10, 14 and 24 micrometers. Mean error of segment fitting was less than 60 microns with no markers rejected from the composite segment of 24 markers. Cup migration total translation error was 10, 16, 24, and 35 micrometers with rotation errors less than 0.05 degrees.

Observed RSA errors were small, increasing with phantom movement. This is consistent with the geometric uniformity tests. X-ray exposure and tissue thickness were also identified as factors in precision. We conclude this system has excellent precision for Radiostereometry.

The reinfusion of perioperative cell salvage is one method employed to reduce exposure to donor blood. Data on the safety of this process, however, are scant. Notably, the effect of intraoperative, washed cell salvage reinfusion on prothrombotic markers has not been demonstrated. The risk of postoperative venous thromboembolism following major orthopaedic operations is not insignificant. The study objective was to assess the effect of cell salvage reinfusion on coagulation and platelet activation.

Twenty-one patients undergoing elective primary hip operations were recruited. Nine patients received washed cell salvage intraoperatively, and were compared with 12 patients undergoing similar surgery that did not. Two patients in the cell salvage group also received postoperative, unwashed cell salvage. Blood samples were collected pre-operatively, immediately post-operatively, and one day post-operatively for assays of platelet activation markers, P-selectin expression and fibrinogen binding by flow cytometry in diluted whole blood; coagulation activation marker, thrombin-antithrombin complex (TAT); D-dimer by ELISA, thrombin generation by chromogenic assay, and full blood count. Samples of cell salvage material were also analysed for prothrombotic markers.

There were no significant differences between the groups preoperatively. Postoperatively haemoglobin levels did not differ significantly between the cell salvage group and controls. Postoperative TAT and D-dimer were significantly higher in the cell salvage group compared with controls (p<0.05). One day postoperatively, there were significantly higher platelet P-selectin expression (p=0.006) and platelet fibrinogen binding (p=0.004) in the cell salvage group compared with controls. The white cell count (WCC) was also significantly higher (p=0.04). In the intraoperative washed cell salvage material, and in postoperative cell salvage, the platelet count was low, but significant proportions of platelets were activated, and levels of D-dimer were elevated compared with venous blood. The postoperative salvage material also contained high levels of TAT.

The results from this pilot study show the induction of a prothrombotic state following reinfusion of intraoperative, washed cell salvage in recipients undergoing primary elective hip operations. An inflammatory response to reinfusion is also indicated by the raised WCC. Further investigation into the safety of cell salvage is indicated.

Prosthesis migration and acetabular cup wear are useful short term measurement which may predict later implant outcome. However, the significance of the magnitude and pattern of the migration is very much dependent on the specific design studied. This study aimed to characterise patterns of migration by following four cemented femoral stem designs using Radiostereometry (RSA) within a prospective randomised longitudinal trial.

164 patients undergoing cemented femoral hip replacement for osteoarthritis were randomised to receive either an Exeter (Howmedica Stryker), Ultima Tapered Polished Stem (TPS) (Depuy), Ultima Straight Stem (USS) (Johnson and Johnson) or Elite Plus (Depuy) stem. Each subject received the OGEE PE cemented acetabular component (Depuy). RSA examinations were performed at 1 week and 6, 12, 18, 24 and 60 months post surgery. They were analysed using the UMRSA system (RSA Biomedical AB, Umea, Sweden), and our local geometric stem measurement software. 149 patients had RSA measurements available to 2 years, and 96 patients to 5 years. Differences were analysed using mixed linear modelling (SPSS).

Median linear proximal cup wear rate reduced to a minimum of 0.02-0.06mm/year in year two. Between 2 and 5 years the wear rate increased, being significantly higher for the Elite.

Cup migration was small but continuous. At 2 years it was median 0.3mm proximally, increasing to 0.5 mm at 5 years. Median rotations were less than 0.3 degrees.

Proximal migration was positive and increasing at all time points for all stems. For the tapered polished designs, while the overall magnitude was significantly higher, the rate of migration significantly decreased, whereas for the other stem designs it did not.

The TPS stem showed a tendency for posterior tilt which was significant compared to the other stems at 5 years.

All stems tended to retroversion, with the USS significantly less than the others and the Elite showing and relative increase at 5 years.

In summary migration patterns are characterised by the stem design, including where there were only small changes between designs. We are now testing measured migrations as predictors of outcome, and will continue to follow this group of patients to 10 years.

Due to its popularity of intramedullary nails (IMN) high success rate, newer design (titanium) IMN system have been introduced to replace stainless steel system. However the stability provided by the titanium IMN

may not be adequate, there by influencing the union rate.

We aimed to compare the results of both IMN systems via prospective clinical study and biomechanical testing using RSA.

Introduction: Impaction allografting is an established method for restoring deficient bone during revision arthroplasty of the hip. Graft augmentation with synthetic materials has been proposed and evaluated experimentally. Our aim was to assess clinically whether migration and wear of implants with a synthetic graft mix would be equivalent to pure allograft.

Materials and Methods: Patient inclusion criteria were: acetabular and or femoral defects from aseptically loosened primary THR undergoing cemented revision with impaction grafting; age 55–80 years; initial diagnosis of osteo arthritis; good health with reasonable daily activity level. Patients were randomized to receive either pure allograft or a 50% mixture with a porous hydroxyapatite material (Apapore60, Apatech, UK). Revision was with the Exeter stem, antibiotic Simplex cement (Stryker Howmedica Ltd), and Ogee cup (Depuy Int. Ltd., Leeds, UK). Tantalum markers were inserted into the pelvis, cup, femur, cement and graft in order to measure migration with radiostereometry (RSA). Patients received a sequence of RSA examinations up to 2 years. A total of 26 patients (18 for the femur) have been analysed.

Results: At 2 years no significant differences were seen in cup wear, or migration of the cup, femoral and pelvic graft markers. Stem migration occurred mainly at the stem cement interface. The rate of distal migration for the femoral head was greater for pure allograft in the first year (p < 0.05), however this rate reduced significantly in year two. Higher medial migration in year one was observed for the proximal medial cement mantle for allograft (p < 0.05).

Conclusions: Improved stability and normal cup wear were observed in a randomized clinical study for a synthetically augmented allograft. This agrees with experimental findings¹. Longer follow up with increased patient numbers is recommended to confirm these findings.

Introduction: Bone loss following hip replacement is common. Its role in prosthesis stability and survival is a concern. DXA allows the assessment of adaptive bone remodelling and resorption. We prospectively examined longitudinal bone density changes affecting the Elite Plus [DePuy International Ltd], Leeds, UK), the Ultima Straight Stem (USS) [DePuy], the Exeter [Stryker Howmedica International Ltd, London, UK] and the Ultima Tapered Polished Stem (TPS) [DePuy] to determine whether bone loss was design dependent.

Methods: 164 patients were randomised to one of 4 stem designs. Patients received DXA peri-prosthetic examinations using the LUNAR EXPERT-XL at 7 days, then at

6, 12, 18 and 24 months. Custom analysis software was used to improve precision. Zones were excluded if identified as affected by heterotopic ossification post surgery. For each group the mean and standard error was determined for each follow up. 137 had follow up data to 24 months.

Results: Considering the whole peri-prosthetic region, all stems lost 5–9% BMD in the first 6 Months. The USS lost the most bone and the tapered stems, the Exeter and the TPS the least. Over the next 18 months changes were no more than 2%. The greatest losses were in the proximal zones, ranging between 8 and 20%. The USS lost significantly more (p < 0.05) than the others at 24 months. In zone 5 the TPS exhibited significantly higher recovery than the other designs at 24 months.

Discussion: Whilst the bone remodelling of the two tapered designs was largely equivalent, they exhibited a significant difference in the distal medial region. This study shows evidence that non-subsiding stems lose more bone than tapered subsiding designs.

Introduction: Heterotopic ossification (HO) is common post total hip replacement. Dual energy x-ray absorptiometery (DXA) is an established technique used to assess peri-prosthetic, bone mineral density (BMD) changes in the femur following surgery. The effect of HO on these measurements has not previously been reported. In this study we investigated the incidence and distribution of HO and the extent to which it affected peri-prosthetic DXA results.

Methods: As part of a two-year, prospective, primary cemented THR trial, 137 patients were assessed at six month intervals with DXA as well as anterior-posterior and lateral radiographs. HO was identified from radiographs and then further localised to the seven femoral Gruen zones using DXA subtraction imaging.

Results: HO affected at least one Gruen zone in 46% of study patients. The mean BMD in zone 1 dropped to 89% of the postoperative value in unaffected patients by six months whereas it actually increased to 102% in the HO patients (p< 0.001). This 12% difference persisted throughout the duration of the trial. Zone two was affected in 17 patients and a significant gain of 5% was noted in these patients at 12 months (p< 0.05). From observation of AP x-rays alone, 12% of the HO cases would have been missed.

HO was found to be significantly associated with male gender and increasing age at time of operation. Surgical approach to the hip also had an effect, osteotomies producing a greater incidence of HO formation.

Discussion: HO has a dramatic effect on BMD values determined by DXA. This has not previously been reported and may have affected other peri-prosthetic studies. We recommend careful screening for HO when reporting femoral peri-prosthetic BMD changes.

Introduction: Dual Energy x-ray absorptiometery (DXA) is a useful tool for the assessment of peri-prosthetic bone mineral changes following total joint replacement. In order to assess these changes the precision of the DXA technique must be optimised. While patient positioning is an important factor, the role of the analysis software should also be considered. We developed and applied a new image analysis method to data from the EXPERT-XL fan beam densitometer (LUNAR GE, USA) aiming to improve reproducibility of bone region and tissue type determination by the analysis software.

Methods: 60 patients with cemented THR received repeat same day DXA examinations. These were initially analysed strictly according to the manufacturer’s femoral peri-prosthetic protocol. A modification of this protocol was attempted allowing further small corrections to the tissue typing by the operator. The scans were then reanalysed using locally developed image analysis to accurately determine the bone, prosthesis and Gruen zone boundaries. The coefficient of variation (CV) was calculated from the differences of the repeat examinations for each of the seven Gruen zones and for the whole peri-prosthetic region.

Results: The average zone CV was 5%. The poorest was zone 1 (10%) and best zone 4 (2%). With the operator corrections there was an overall 4% improvement. With our method there was an overall 40% reduction in variation (average CV 3%, maximum 4%, minimum 2%). The whole region CV was 3.1% for the standard method 2.7% modified and 1.3% for our method.

Discussion: Our method significantly improved the reproducibility of EXPERT analysis. This study demonstrates the high dependency of DXA precision on robust regional analysis.

Synthetic graft expanders have recently been developed for use in impaction grafting revision hip arthroplasty, but their true role has yet to be determined.

We performed a series of experiments to investigate the properties of one such porous hydroxyapatite material (IG-Pore, ApaTech Ltd). IG-Pore was mixed with fresh-frozen human allograft chips and impacted into composite femoral models with a similar biomechanical profile to human bone (Sawbones Europe). Exeter hip prostheses (Stryker Howmedica Ltd) were implanted with cement and each model was axially loaded for 18000 cycles at physiological levels using an Instron servohydraulic materials testing machine. Four test groups with 0%, 50%, 70% and 90% IG-Pore were used, and there were eight femora in each group.

Pre- and post-loading radiostereometric analysis was performed to characterise migration of the prosthesis. Total subsidence was measured and was separated into that occurring at the prosthesis-cement and cement-femur interfaces. Cyclical compression and expansion of the graft-containing models was measured using the Instron.

Median values (interquartile range) for total subsidence were 0.43 mm (0.28 to 0.55) for the pure allograft group, 0.31 mm (0.20 to 0.55) for the 50% IG-Pore group, 0.23 mm (0.07 to 0.34) for the 70% allograft group and 0.13 mm (0.06 to 0.18) for the 90% IG-Pore group. These differences were statistically significant (p=0.034, Kruskal-Wallis). Subsidence at the prosthesis-cement interface was also lower for IG-Pore containing models (p=0.019, Kruskal-Wallis), although there was no significant difference at the cement-femur interface. Specimens with a higher proportion of IG-Pore showed smaller cyclical movements on loading (p=0.005, ANOVA).

Higher proportions of IG-Pore do appear to reduce subsidence in a mechanical model of impaction grafting. A randomised clinical trial using RSA to compare a 50% IG-Pore/allograft mix with pure allograft is in progress to investigate the use of this material as a bone graft expander in the clinical setting.

Impaction grafting procedures have found a widespread role in revision hip arthroplasty. Synthetic graft expanders have recently been introduced, but the optimal ratio of expander to allograft is unknown.

We performed a series of in vitro experiments to investigate the optimal ratio for one commercially available porous hydroxyapatite material (IG-Pore, ApaT-ech Ltd). IG-Pore was mixed with fresh frozen human allograft chips from osteoarthritic femoral heads and with blood. Graft was impacted into fibre-glass femoral models (Sawbones Europe) with a similar biomechanical profile to human bone, and Exeter hip prostheses (Stryker Howmedica Ltd) were cemented in place. Each model was loaded using an Instron servohydraulic materials testing machine for 18000 cycles. The magnitude and frequency of the loading cycle was based on physiologically measured values. Four test groups with 0%, 50%, 70% and 90% IG-Pore were used, with eight femora in each group.

Tantalum marker beads were attached to the prosthesis, the femoral model and the cement mantle, and radio-stereometric analysis (RSA) was performed pre- and post- loading to determine migration and rotation of the prosthesis in each axis. Pre-loading films were repeated in sixteen cases for precision measurements, and twelve specimens had delayed post-loading films performed to measure any re-expansion of the unloaded graft.

The primary end-point was RSA-measured subsidence of the prosthesis, defined as vertical movement of the tip. Median subsidence was 0.43mm, 0.31mm, 0.24mm and 0.13mm in the 0%, 50%, 70% and 90% IG-Pore groups respectively (P=0.034, Kruskal-Wallis test). The precision, given as the median absolute difference, was 0.0065mm.

All specimens showed a cyclical compression and expansion throughout the loading cycle. Specimens with a higher proportion of IG-Pore tended to be more resistant to this and the mean values for cyclical movement were 1.76 0.27mm, 1.65 0.21mm, 1.57 0.18 mm and 1.45 0.14mm for the 0%, 50%, 70% and 90% IG-Pore groups.

Higher proportions of IG-Pore appear to reduce subsidence in impaction grafting. Other issues such as the handling qualities of the graft and the biological effect of synthetic materials also need to be considered, however. A randomised clinical trial using RSA to evaluate a 50% IG-Pore/allograft mix in comparison to pure allograft is ongoing in our institution, and we hope that this will answer some of these questions definitively.

The use of roentgen stereophotogrammetric analysis (RSA) in the assessment of total hip arthroplasty is well recognised as an accurate technique in the measurement of small movements of implants. The technique requires the insertion of tantalum beads into a stable location in the bone at the time of surgery. Failure of bead insertion leads to unstable extra-osseous beads that require to be excluded from the analysis. Previous studies have reported an incidence of extra-osseous beads in the proximal femur of between 2% and 13%. In order to further improve the accuracy of the RSA technique, we have developed a test criterion for exclusion of unstable osseous beads in RSA of total joint replacements.

Using specifically developed software each bead’s movement was determined relative to the rest of the beads in the bone segment. The bead movement was determined for radiologically identified extra-osseous beads, which were assumed loose, and for the remaining intra-osseous beads which were suitable for analysis. Analyses with a condition number greater than 100 were rejected. The rate of motion was calculated from consecutive examinations. Unstable beads were identified as those having a median rate greater than a given threshold. The sensitivity and specificity for detecting extra-osseous beads was calculated for different thresholds of median bead motion.

In 149 RSA hip study patients, 43 extra-osseous beads that could be analysed were identified and a group of 36 osseous beads were selected as a control group. This resulted in an optimum threshold of 0.36mm that gave a sensitivity of 89% and a specificity of 86% for detecting unstable (extra-osseous) beads. The remaining 1428 beads, which were assumed to be osseous, were then tested with this threshold, which gave a sensitivity of 84% and a specificity of 79%.

The median extra-osseous bead rate of movement at 6, 12, 18 and 24 months were 2.24, 0.78, 1.03 and 1.31mm respectively and for osseous beads were 0.27, 0.19, 0.18 and 0.19mm. As both groups of beads appear to show a “bedding in” period, with a higher median bead movement in the first 6 months, the test was repeated with the first 6 month period excluded from the criteria. An optimal threshold of 0.37mm was found to have a sensitivity of 73% and a specificity of 87% for identifying an extra-osseous bead.

While most radiographically classified osseous beads identified as unstable may be false-positives, it is probable that some are extra-osseous but not visibly so on radiographs. The specificity of this technique is likely to be further improved with the increased precision from digital scanning techniques. Tantalum beads in general appear to be relatively unstable in the first 6 months, consistent with the expected osteo-intergration of the bead. This new criterion for bead instability allows automatic exclusion of unstable beads increasing the reliability of the RSA technique both in future studies and retrospectively to existing data.

Introduction and Aims: Stem migration determined by Radiostereometry (RSA) typically requires markers attached to the stem. Previous studies with marker-less stems either detem1ined movement of the prosthesis head only, or approximate the stem to a simple geometric model. We compare the precision of this method to one utilising a surface model of the implan.

Method: The first method assumes axially symmetric distal stem (SDS) and hence calculates the stem tip and axis. The method was implemented as an addition to UMRSA (RSA Biomedical AB, Umea, Sweden). Applied originally to manual measurement of radiographs, it is now also implemented as automated digital image analysis for use with Digital UMRSA. The second method (ASRSA) matches a three-dimensional surface model of the stem to the digitised images. Exeter stem models were supplied by the manufacturer (Stryker Howmedica Osteonics, France). Clinical precision of each method was determined from repeat same day RSA examinations obtained from an ongoing study.

Results: Clinical precision, given as the 99% confidence interval, was calculated as 3.5 times the median absolute difference of the repeat measurement. Patient and radiographic equipment were repositioned for the repeat examination. All repeat pairs were from different patients. For analysis, 43 pairs were available for the manual SDS method and 23 for digital SDS. For ASRSA, only nine pairs of Exeter stems had 3D models available for analysis. ASRSA translational precision was 0.1mm transverse, 0.1mm axial, and 0.2mm sagittal. Rotational precision was 0.3 degrees transversely, 0.9 degrees axially and 0.2 degrees sagittally. Digital analysis improved the precision of the SDS method considerably compared to manual analysis, in particular axial rotation from 3.1 to 1.3 degrees and sagittal translation from 0.8 to 0.4mm, however it was still between 1.4 and five times worse than the ASRSA method.

The poor result of the SDS method in axial rotation is probably due to the breakdown of axial symmetry, whereas the excellent result of the ASRSA method is comparable to that published for marked stems. Current results are limited in number and type of implant; further work is now being carried out in larger numbers and with more stems.

Conclusion: Surface model-based digital RSA can give a precision comparable to that for implants with attached markers. This has important implications, since it can dramatically increase the power of migration results where beads have not been used and can be applied to RSA studies retrospectively.

Aims: To develop a threshold criteria for exclusion of unstable osseous beads in radiostereometric analysis (RSA) of total joint replacements. Methods: Bead movement was determined for radiologically identified extra-osseous beads which were assumed loose, and for intra-osseous beads as a stable control group. Analyses with a condition number greater than 100 were considered unreliable and rejected. The median rate of total motion over 2 years was used to identify a threshold that identifies unstable beads. Results: In 149 RSA hip study patients 44 extra-osseous beads that could be analysed were identified and 36 osseous control beads were randomly selected. The sensitivity and specificity for detecting extra-osseous beads was calculated for different thresholds of median bead motion (see ROC curve). An optimal threshold of 0.36mm was found to have a sensitivity of 89% and a specificity of 86% for identifying an extra-osseous bead.

Conclusions: Extra-osseous beads are more unstable than osseous beads and are should be removed from RSA analysis series. This new criteria allows automatic exclusion of unstable beads increasing the reliability of the RSA study.

Aims Intro: Radiostereometry (RSA) is a powerful tool for assessment of prosthesis migration in total hip replacement. Typically marker beads are inserted into the bone and into turrets inserted into the prosthesis. Where the prosthesis can not be beaded valuable information may be lost. We present two methods that determine the three-dimensional prosthesis position using geometric models. Method: The þrst method approximates the stem of the prosthesis to an axially symmetric cylinder and spherical head. The method is fast but may lead to errors due to the cylinder approximation. The second uses accurate three-dimensional surface models of each implant model. Clinical precision was determined from repeat same day RSA examinations. Results: Given as 99% precision limit rotation ranged from 0.4 degrees (sagittal) to 2.5 degrees (axial) for the cylinder method (n = 38), compared to 0.2 degrees (sagittal) to 0.6 degrees (axial) for the 3d model (n = 6). Translations were similar ranging from 0.2mm axial to 0.7mm sagittal. Conclusion: Model based RSA can give useful results where beads can not be implanted into the prosthesis. Although the primary method gives good results these are less precise than that for beaded RSA. Simulations infer a potential accuracy for the method of a few microns, however this is currently limited by the closeness of correspondence of an individual stem to its model. The method here is applicable to any implant type. Accurate 3D models are required, however for new designs these should be available.

Aims: To examine vibration levels produced by orthopaedic air tools and the prevalence of upper limb symptoms in orthopaedic surgeons. Methods: A preliminary measurement of vibration levels produced by six air powered orthopaedic saws was followed by a national survey of orthopaedic surgeons and controls. A health surveillance questionnaire of symptoms associated with Hand Arm Vibration Syndrome (HAVS) was sent to 1200 orthopaedic surgeons (test group) and 1200 gynaecological surgeons (controls). Results: Measured accelerations of the saws were 3.42 to 10.7 m/sec² using BSI standards and 90.5 to 182 m/sec⁻² using NIOSH standards. These vibration levels are compatible with those reported to cause significant upper limb symptoms

Survey responses were received from 741(61.7%) of the test group and 748 (62.3%) of the control group. A statistically significant increase in the prevalence of the neurological symptoms was seen among orthopaedic surgeons (p< 0.001). A significant increase in musculoskeletal problems (p< 0.008) and muscle pain (p< 0.004) was also found. No significant difference was seen in the prevalence of vascular symptoms. The neurological symptoms were not related to other potential medical causes. Conclusions: Orthopaedic surgeons report an excess of upper limb symptoms and these may be linked to vibration exposure at work.

The quantification of local bone blood flow in man has not previously been possible, despite its importance in the study of normal and pathological bone. We report the use of positron emission tomography, using 15O-labelled water, to measure bone blood flow in patients with closed unilateral fractures of the tibia. We compared fractured and unfractured limbs; alterations in blood flow paralleled those found in animal models. There was increased tibial blood flow at the fracture site as early as 24 hours after fracture, reaching up to 14 times that in the normal limb at two weeks. Blood flow increase was less in displaced than in undisplaced fractures. The muscle to bone ratios of blood flow were similar to those in previous animal work using other techniques. Positron emission tomography will allow study of human bone blood flow in vivo in a wide variety of pathological conditions.

We have assessed the current range of synthetic splinting bandages, using physical and mechanical tests and the subjective opinions of patients, volunteers and orthopaedic staff. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive, and potentially more hazardous.