Patient education programmes prior to hip and knee arthroplasty reduce anxiety and create realistic expectations. While traditionally delivered in-person, the Covid-19 pandemic has necessitated change to remote delivery. We describe a ‘Virtual Joint School’ (VJS) model introduced at Ysbyty Gwynedd, and present patient feedback to it.

Eligible patients first viewed online educational videos created by our Multi-Disciplinary Team (MDT); and then attended an interactive virtual session where knowledge was reinforced. Each session was attended by 8–10 patients along with a relative/friend; and was hosted by the MDT consisting of nurses, physiotherapists, occupational therapists, and a former patient who provided personal insight. Feedback on the VJS was obtained prospectively using an electronic questionnaire.

From July 2022 to February 2023, 267 patients attended the VJS; of which 117 (44%) responded to the questionnaire. Among them, 87% found the pre-learning videos helpful and comprehensible, 92% felt their concerns were adequately addressed, 96% felt they had sufficient opportunity to ask questions and 96% were happy with the level of confidentiality involved. While 83% felt they received sufficient support from the health board to access the virtual session, 63% also took support from family/friends to attend it. Only 15% felt that they would have preferred a face-to-face format. Finally, by having ‘virtual’ sessions, each patient saved, on average, 38 miles and 62 minutes travel (10,070 miles and 274 hours saved for 267 patients).

Based on the overwhelmingly positive feedback, we recommend implementation of such ‘Virtual Joint Schools’ at other arthroplasty centres as well.

Abstract

The final alignment of Patient Specific Instrumentation (PSI) TKA relies on the accuracy and the correct placement of the 3-D moulds, precision of saw cuts, soft tissue balancing and cementing technique. We aimed to compare the predicted alignment between PSI and Articulated Surface Mounted (ASM) computer navigation. Eight consecutive patients underwent knee replacement using MRI based PSI (Zimmer) with planning of 0º femoral and tibial mechanical alignment. After placing the conventional cutting blocks over the pins (placed according to PSI), the predicted alignment of cuts was verified with ASM navigation. PSI technique was used regardless of navigation values and alignment was compared.

Good correlation was found for tibial cuts (maximum variation: coronal plane – 1º, sagittal plane – 2º) and femoral cuts in the sagittal plane (maximum variation 2º). However, in two patients the coronal plane variation in femur was > 2º (3º and 4º respectively). Navigation predicted combined final alignment of 5º valgus and 4º valgus in these patients. However, long leg standing x-rays revealed neutral and 1º valgus alignment in those two patients respectively, matching closely with PSI prediction. Final alignment in long-leg standing x-rays were independently reported by a musculoskeletal radiologist. Six knees were in neutral mechanical alignment (including the 2 navigation predicted outliers). The remaining 2 knees had a maximum deviation of 2 degrees from neutral. We conclude that there was overall good correlation between PSI and navigation. Even in cases where navigation predicted more than 3º combined varus/valgus alignment, PSI prediction was more accurate on long leg views.

Patient specific instrumentation (PSI) is the latest advancement in total knee arthroplasty (TKA), which claims to improve alignment, simplify the surgical process, forecasts the component size and reduces the operating time. We discuss our experience of preoperative planning using default settings and making changes where necessary.

We analysed prospectively collected data in 100 consecutive PSI knee replacements (Zimmer®) performed in our institute during the period February to August 2012. All patients underwent MRI scans of the ipsilateral hip, knee and ankle joints. From the images, Materialise® (Leuven, Belgium) provided 3D model of the knee on which preoperative planning was done using PSI software. All default plans were checked and appropriate changes were made before the senior author approved final plan for preparation of patient specific moulds.

We made 636 changes (6.36 changes per knee) preoperatively from the default settings. In only 4% of the patients, the primary cuts needed revision. Thus in 96% of the cases, the primary cuts allowed optimal alignment and gap balancing with appropriate soft tissue release. Our preoperative planning predicted 99% of femoral and 98% of tibial component sizes definitively implanted.

Our results show the importance of the surgeon's input in approving preoperative planning with this technique.

Aim

To determine the outcome, the need for revision surgery, quality of life (QOL) of patients and the financial implications of instability following successful closed reduction of dislocation after primary total hip arthroplasty (THA).

Purpose: The goal of this study is to compare patients’ perception of their hip or knee joint following joint replacement surgery.

Method: A total of 357 patients who underwent hip or knee joint surgery were included in the study. Of the patients who had knee replacement surgery, 46 had unicompartmental knee replacement (UKR) and 119 had total knee replacement (TKR). In the group of patients who had hip replacement surgery, 98 underwent hip resurfacing (SRA) and 97 had total hip replacements (THR). The perception patients had of their replaced articulation as well as functional outcome scores such as the WOMAC and SF-36 were measured at one year post-surgery and compared between the four groups.

Results: Although global satisfaction and clinical outcome scores were excellent in all four groups, WOMAC scores at 1–2 year follow-up were significantly different between hip or knee replacement surgery (p< 0.0001). Also, the perception that patients had of their reconstructed joint was significantly different between the hip and knee groups (p< 0.001). Half of patients from the hip group considered their replaced hip “as a natural joint” and 76% considered their joint as having no functional limitations compared to only 19% and 39% respectively for the knee group. Of patients with knee joint surgery, 14% (20/165) considered their joint as “artificial with important limitations” as opposed to only 1% (2/195) of those who had hip joint surgery. There were no significant differences in Womac scores or perception when comparing TKR and UKR or THR and SRA patients. Perception was strongly correlated to Womac scores for all four groups (R²=0.951).

Conclusion: Hip and knee joint replacement surgery are recognized as highly effective medical interventions in terms of cost/benefit ratio in current medical practice. It is remarkable to see that replacement of each of these articulations can yield vastly different results in terms of patient function, perception and satisfaction. From this study, it is clear that research in prosthetic development and surgical techniques should be focused on the interventions such as knee joint replacement, which are not yet capable of offering both a high level of function and satisfaction to patients.

Introduction: More than 140,000 joint replacements are carried out in England and Wales per annum costing from £4000 to £7000 each (1, 2). Implant costs are relatively fixed but there are considerable variations in length of stay [LOS] following surgery. The National Audit office estimated that a reduction of two days per patient could save the NHS £15.5 million per year (2).

A specialist orthopaedic ward for elective arthroplasty was opened in Bangor in 2008 in an attempt to address these issues. The staff per bed ratio remained the same as in the general orthopaedic wards but beds were “ring fenced” and strict infection control measures protocols were implemented. This audit aimed to assess the effect of the specialist ward on LOS following arthroplasty.

Method: Retrospective data on length of stay, demographics and surgical site infections [SSI] were collected for the six months before and six months after the specialist ward was opened. Only primary lower limb arthroplasty data was evaluated and LOS was calculated from day of operation to the day of discharge. Statistical analysis was performed on the length of stay with SPSS software using the two-sample t-test and Mann-Whitley U test.

Results: Patients were managed by the same surgical teams in the same theatres but nursed in different ward settings. Group 1 included 222 patients managed in general orthopaedic wards and group 2 included 191 patients, managed in the ring fenced ward. The mean age for total hip replacements was 70.8 in group 1 and 71.2 years in group 2. The mean age for total knee replacements was 70.9 years in group 1 and 69.2 years in group 2. The overall mean LOS for both procedures was 7.61 days (95% CI: 7.14 – 8.07) in group 1 compared with 5.67 days (95% CI: 5.28 – 6.06) group 2. This was statistically significant (p< 0.001). The mode was 7 days in group 1 compared with 4 days in group 2. Three SSIs were noted in group 1 and zero in group 2.

Conclusions: This audit demonstrates a two day reduction in LOS for patients managed in a ring fenced ward. The reasons for the reduction are multi factorial but include a trend for reduced SSI. Overall reduced stay frees up resources for other use and may reduce costs. Other units may benefit from similar dedicated wards in response to growing demand for arthroplasty within a system of fixed resources.

Introduction: Better clinical outcome is generally reported after hip resurfacing when compared to conventional 28mmTHA. This may simply be the consequences of biased patient selection, patient perception or the advantageous use of larger diameter femoral heads in HR. The true clinical benefits of HR can only be assessed by comparison with LDH-THA in a blinded randomized study to eliminate/reduce those biases. This was the aim of the study.

Materials and Methods: Charnley class A patients were randomized between HR or LDH-THA and kept blinded for one year. Clinical data, gait analysis, postural balance evaluations and functional tests were performed preoperatively, at 3, 6, 12 and 24 months postoperatively. 14 normal patients served as controls.

Results: 24 patients were assigned to each group. There was no significant difference in WOMAC, SF-36, activity scores, and patient satisfaction. A slight advantage was observed for HR during the functional reach test (postural balance) and for LDH-THA during the step test (speed, strength and balance), all other tests showing no differences. Both groups quickly reached controls value for all tests by 3 months.

Discussion: We have failed to demonstrate a clear difference in outcome between HR and LDH-THA. Both groups fully recovered quickly. The postulated clinical advantages of HR over 28mmTHA most likely result from using a larger head in highly motivated patients. The only clear advantage of HR over LDH-THA remains proximal femoral bone conservation, although with the excellent durability of currently used femoral stems, HR has to demonstrate comparable survivorship before bone conservation is considered a true benefit.

Background: Moore et al. recently described five radiological signs (absence of radiolucent line, zone 2 osteo-penia, superolateral buttress, inferomedial buttress and radial trabeculae) for predicting osseointegration of porous coated uncemented acetabular components in the long term. The positive predictive value for a stable fixation was 96.9% when three or more signs were present. 83% of the cups with one or no signs were unstable.

Aim: To evaluate the prevalence of these signs in clinically well functioning uncemented acetabular components in the short term and to evaluate whether there is a difference acetabular components with different modulus of elasticity.

Materials and methods: The preoperative, immediate postoperative and the latest (minimum 2 years) radiographs of 196 hip replacements with 2 different acetabular components: a 2.9 mm, thin, flexible, macro textured titanium component (Allofit, Zimmer) and a 4 mm thick, stiff, titanium plasma sprayed chrome-cobalt component (Durom, Zimmer) were reviewed by two independent observers searching for the five osseointegration signs. The observers also looked for conventional signs of loosening including: continuous radiolucency of more than 2 mm, component migration of more than 3 mm, component rotation, or the presence of broken screws.

Results: 95 Allofit components and 101 Durom components were available for evaluation. None of the hips were considered loose according to conventional criteria and were well functioning. Out of the new osseointegration signs, at least one sign was present in 100 % of the cases, two signs or more in 30%, three signs or more in 5% and four signs in 1%. There was no difference between the two types of cups. In addition, superolateral buttress and zone 2 osteopenia were also present in preoperative/immediate postoperative radiographs in 8% and 4% of respectively.

Conclusion: Apart from absence of radiolucency, very few of the five osseointegration signs were present at short term follow-up of two very different well functioning uncemented acetabular components designs. We conclude they are not useful in evaluation of unce-mented acetabular components at a follow up of 2–5 years. Further study at mid-term follow-up might reveal whether the bony adaptive changes occur with time.

Purpose: The aim of our study was to compare the precision and effectiveness of a CT-free computer navigation system against conventional technique (using a standard mechanical jig) in a cohort of unselected consecutive series of hip resurfacings.

Method: 139 consecutive Durom hip resurfacing procedures (51 navigated and 88 non-navigated) performed in 125 patients were analysed. All the procedures were done through a posterior approach by two surgeons and the study cohort include the hip resurfacings done during the transition phase of the surgeons’ adoption of navigation.

Results: There were no significant differences in the patients caracteristics, native neck-shaft angles, component sizes and blood loss between the two groups. There was a significant difference in the operative time between the two groups (111 minutes for the navigated group versus 105 minutes for the non-navigated group; p=0.048). There were 4 cases of notching in the non-navigated group. There was no other intra-operative technical problem in either of the groups nor were there any femoral neck fractures. No significant difference was found between the mean post-operative stem-shaft angles (138.5° for the navigated group versus 139.0° for the non navigated group, p=0.740). However there was a significant difference in the difference between the planned stem-shaft angle versus the post-operative stem-shaft angle (0.4° for the navigated group versus 2.1° for the non-navigated group; p=0.005). While, none of the cases in the navigated group had a post-operative stem-shaft angle with more than 5° deviation from the planned neck-shaft angle when compared to 33 cases (38%) in the non-navigated group (p≤0.001). For a given patient with a target angle set, it is estimated that positioning precision using the navigation is 1.3° +/− 0.9°, compared to 4.4° +/− 3.6° without navigation (p< 0.0001).

Conclusion: Hip resurfacing is a technically demanding procedure with a steep learning curve. Varus placement of the femoral component and notching have been recognised as important factors associated with early failures following hip resurfacing. While conventional instruments allowed reasonable alignment of the femoral component, our study has shown that use of computer navigation allows more accurate placement of the femoral component even when the surgeons had a significant experience with conventional technique.

The adequacy of cement mantles around some impaction-grafting systems has been criticised yet good clinical results have been reported. This study investigates this contradiction by asking

Does cement mantle thickness affect cement penetration depth?

Twelve artificial femora were prepared to simulate cavitary defects. Porcine cancellous bone was morselized. The defect was reconstructed by impaction grafting, using a size 0, 1 or 2 tamp. Bone cement was injected, and a size 0, 1 or 2 Exeter stem inserted. By using all nine tamp/prosthesis combinations, 0–4 mm thick cement mantles were produced. Femora were positioned in a testing machine and loaded with 2500 cycles of 2500 N. Prosthesis subsidence and retroversion were measured. Each femur was sliced transversely and the sections digitised. Solid cement mantle thickness and cement penetration depth were measured using image analysis. Correlation analysis was used to find if tamp/stem mismatch (nominal mantle thickness) influenced actual solid mantle thickness and cement penetration. We then analysed if tamp size, stem size, solid mantle thickness or cement penetration determined stem subsidence and retroversion.

Cement mantles were produced with an average thickness of 1.7–2.2 mm, with largest variations proximally (1.5–2.8 mm). Average cement penetration was 0.3–2.0 mm, with largest variations proximally (0.4–3.5 mm). Thicker solid mantles gave less penetration (r=−0.62). Stem subsidence ranged from 0.4–2.5 mm and correlated significantly with tamp size (r=0.59, p< .05). Better correlations were found with solid mantle thickness (r=0.90, p< 0.05) and cement penetration depth (r=−0.81). Stem retroversion ranged from 0.1–2.0 degrees and correlated with stem size (r=−0.53) but not with tamp size.

Tamp/stem mismatch determined the thickness of the solid cement mantle around impaction-grafted stems, and thinner mantles were associated with deeper cement penetration. Thinner mantles and deeper penetration were associated with reduced stem subsidence. Stem retroversion was associated with stem size only, and larger for thinner stems. Thinner cement mantles will therefore be associated with deeper penetration and reduced stem subsidence upon loading. This association may explain the good long-term results of impaction-grafted Exeter stems, despite deficient solid cement mantles.

Background: Leg length equality and femoral offset restoration are important parameters related to success of total hip arthroplasty (THA). However, it is not uncommon for errors to occur during surgery which can lead to less optimal functional result and potential source for litigation. Several techniques that are commonly used to assess leg length and femoral offset during THA include pre-operative templating, intra-operative measurements with a ruler using bony landmarks, assessing soft tissue tension and using measurement device with a reference pin in the iliac crest. We have previously reported on our precision to reconstruct the diseased hip with THA done without navigation. Post-operative radiographic analysis demonstrated that leg length was restored to within +/− 4mm of the contralateral side in only 60% of the patients with 4 patients needing a shoe lift. With regards to femoral offset reconstruction, it was increased by a mean of 5.1 mm and restored to within +/− 4mm of the normal contralateral side in only 25% of patients.

Computer navigation has proven to be a more precise tool to achieve optimal positioning of THA implants and precise biomechanical reconstruction of the hip joint. However, performing complete THA using navigation is complex including the requirement to change the position of the patient during registration. A recent stand-alone CT-free hip navigation software from Orthosoft Inc allows navigation to be used for limb length and offset measurements during THA. We report our results from a preliminary study using this technique in 14 hips undergoing THA.

In this technique, a tracker is placed over the iliac crest. There is no need to fix a tracker on the femur. Registration of the following are done: greater trochanter (using a screw), patella (using an ECG lead) and the plane of the operating table (using three points on the surface of the operating table in a triangular configuration). The centre of rotation of the hip is determined by either mapping the acetabulum or by using the appropriate sized calibrated reamer. With the definitive acetabular component in place, the new center of rotation is registered and the hip is reduced with trial femoral component. Re-registration of the new position of the greater trochanter and patella allows the computer to calculate the relative change in the limb length and offset compared to the pre-operative status. The differences in the pre-operative and post-operative limb length and offset were calculated using Imagika software and compared with the navigated values recorded by the computer.

The mean absolute error for the relative change in the limb length as measured by the computer when compared to the radiographic measurement was 1.25 mm with a standard deviation of 1.77 mm. The mean absolute error for the relative change in the offset as measured by the computer when compared with the radiographic measurement was 2.96 mm with a standard deviation of 2.56 mm. The process of navigation was quick and on average adds 10 minutes to the operative time.

Our preliminary study shows that the accuracy of the navigation software is very good in estimating the change in the limb length intra-operatively with a maximum error of 3 mm. The accuracy was also good in estimating the offset (3 mm or less except in one case where the error was 5 mm and this may be due to technical error in registration). This compares favorably with our own data on THA done without navigation. This easy to use navigation technique has the potential to decrease the magnitude of error in restoration of limb length and offset during THA.

We thank Francois Paradois and Michael Lanigan from Orthosoft Inc. for their technical advice.

The aim of our study was to compare the precision and effectiveness of a CT-free computer navigation system against conventional technique (using a standard mechanical jig) in a cohort of unselected consecutive series of hip resurfacings.

One hundred and thirty nine consecutive Durom hip resurfacing procedures (51 navigated and 88 non-navigated) performed in 125 patients were analysed. All the procedures were done through a posterior approach by two surgeons and the study cohort include the hip resurfacings done during the transition phase of the surgeons’ adoption of navigation.

There were no significant differences in the gender, age, height, weight, BMI, native neck-shaft angles, component sizes and blood loss between the two groups. There was a significant difference in the operative time between the two groups (111 minutes for the navigated group versus 105 minutes for the non-navigated group; p=0.048). There were 4 cases of notching in the non-navigated group and none in the navigated group. There were no other intra-operative technical problems in either of the groups nor were there any femoral neck fractures.

No significant difference was found between the mean post-operative stem-shaft angles (138.5° for the navigated group versus 139.0° for the non navigated group, p=0.740). However there was a significant difference in the difference between the planned stem-shaft angle versus the post-operative stem-shaft angle (0.4° for the navigated group versus 2.1° for the non-navigated group; p=0.005). There was significantly more scatter in the difference between the post-operative stem-shaft angle and the planned stem-shaft angle in the non-navigated group (standard deviation = 3.6°) when compared with the navigated group (standard deviation = 0.9°; Levene’s test for equality of variances = p≤0.01). No case in the navigated group showed a post-operative stem-shaft angle of more than 5° deviation from the planned neck-shaft angle when compared to 33 cases (38%) in the non-navigated group (p≤0.001). While only 4 cases (8%) in the navigated group had a postoperative stem-shaft angle deviating more than 3° from the planned stem-shaft angle, this occurred in 50 cases (57%) in the non-navigated group (p≤0.001).

Hip resurfacing is a technically demanding procedure with a steep learning curve. Varus placement of the femoral component and notching have been recognised as important factors associated with early failures following hip resurfacing. While conventional instruments allowed reasonable alignment of the femoral component, our study has shown that use of computer navigation allows more accurate placement of the femoral component even when the surgeons had a significant experience with conventional technique.

Aim: To investigate whether cement mantle thickness influence early migration of the stem after impaction grafting.

Methods: Twelve artificial femora were prepared to mimic cavitary defects. After compacting morselized bone into the cavities, Exeter stems were cemented in place. By using all combinations of three sizes tamps and stems (0, 1 and 2), we created cement mantles of 0, 1, 2, 3 and 4 mm thickness. Bones with stems were placed in a testing machine and loaded cyclically to 2,500 N while measuring stem migration. Statistical analysis was by regression analysis. Outcomes were stem subsidence and retroversion, predictors were mantle thickness, tamp size and stem size.

Results: Average stem subsidence after 2500 cycles when using size 1 tamp and stem (2 mm mantle) was 0.94 mm. For a 0 mm mantle, subsidence was 0.59 mm and for a 4 mm mantle it was 2.54 mm. Cement mantle thickness significantly influenced stem subsidence (r=0.68, p=0.015). Cement mantle thickness also significantly influenced stem retroversion (r=0.62, p=0.031). Cement mantle thickness was a better predictor of stem stability than tamp or stem size.

Discussion: Concern exists that inadequate cement mantles may affect stability of impaction-grafted stems. In our study, larger difference between tamps and stems gave substantially more subsidence and rotation, whereas a smaller difference reduced them. Concerns over thin mantles may have been premature.

Aims: The aims of our study were:

to measure the total metal content in cell saver blood recovered during revision hip arthroplasty,

Materials and methods: We analysed the levels of metallic debris and metal ions in cell saver blood in nine patients undergoing revision hip replacement. Using inductively coupled plasma mass spectrometry (ICP-MS), the levels were measured for titanium, aluminium, vanadium, chromium, cobalt, nickel and molybdenum. The metal ion levels were analysed using a dilution technique and the total metal content levels (particulate debris and ions) were analysed with a digestion technique.

Results: Significantly higher levels of metal ions and metal debris were found in the pre-processed blood compared with the processed blood (after centrifuging and washing). The ion levels in the processed blood were not high enough to cause a significant increase in the patients’ immediate post-operative blood ion levels when compared with pre-operative levels.

Discussion: There are markedly elevated levels of metal ions and particulate metal debris in the blood salvaged during revision total hip arthroplasty. The processing of the recovered blood in a commercial “cell saver” significantly reduces the total metal load that is re-infused. Re-infusion of salvaged blood does not result in elevated metal ion levels in the immediate post-operative period.

Aim: To determine the outcome and need for subsequent surgery in patients following successful closed reduction of dislocation after primary total hip arthroplasty (THA) and the financial implications of re-operation.

Methods: Data was retrospectively obtained from radiographs and patient case notes for all dislocated primary hip replacements presenting to the University Hospital of Wales from January 2000 till November 2005. Records were analysed with a minimum of 1 year follow-up to determine the outcome and need for subsequent surgery following successful closed reduction of dislocation after primary THA. Factors studied include age at primary surgery, indications, components, approach, head size, duration since surgery and direction of dislocation

Results: Over the 6 year study period, 98 patients presented with 100 first time dislocated primary total hip replacements. All the dislocations underwent successful closed reduction. 62 (62%) hips re-dislocated more that once. At minimum follow up of 1 year, 7 patients had died and were excluded from the final study group. Of the remaining 93 hips, 46 patients have had no further surgery. 44 THA’s have undergone revision procedures and 3 are waiting to have revision surgery (51% in total). Of those who have undergone revision surgery, 7 hips re-dislocated since and 3 of those needed further re-revision.

Discussion: Dislocation following primary THA remains a problem with varying dislocation rates quoted in the literature. In our series, 51% of patients presenting with dislocation required revision surgery. All patients in this series had 28 mm or smaller femoral heads. The financial impact of the burden of revision surgery continues to increase. In this series in isolation the cost of revision surgery totalled greater that £500,000.

Aim: To investigate the outcome following revision total hip arthroplasty (THA) using 36 mm and 40 mm modular femoral heads.

Methods: Details were retrieved from our arthroplasty database regarding all revision THAs done in our unit using 36 mm and 40 mm femoral heads. Follow-up information was obtained from patient records and telephone conversation.

Results: The cohort considered totalled 107 revision THAs, 93 using a 36 mm head and 14 using a 40 mm head. All received either highly cross-linked UHMWPE liners or metal on metal liners. The indications for revisions were recurrent instability in eight, periprosthetic fracture in 11, second stage revision in 24, fracture of the femoral stem in one and aseptic loosening in the remaining 63. At a minimum follow up of one year, information was not available for five but they did not have any record of dislocation. Out of the remaining 102 patients, dislocation occurred in 4 hips (3.9%). None of the revisions done with 40 mm head dislocated. In two of the dislocations, the initial indication for revision THA was recurrent instability and if they are excluded, the dislocation rate was 1.96%.

Discussion: Dislocation and the sequalae of recurrent instability remains a significant problem following revision THA and the existing literature varies greatly in the quoted dislocation rates. We believe that the use of 36 mm and 40 mm femoral heads in our unit has been a major factor in low (3.6%) dislocation rate following revision THA. To date there have been no problems encountered resulting from the use of highly cross-linked UHMWPE.

Purpose: The aims of our study were: (i) to measure the total metal content in cell saver blood recovered during revision hip arthroplasty, (ii) to evaluate the efficacy of centrifuging and washing the recovered blood in reducing the metal content, (iii) to investigate whether transfusion of the salvaged blood resulted in a significant increase in the metal ion levels in the patients’ blood in the immediate post-operative period.

Materials and methods: We analysed the levels of metallic debris and metal ions in cell saver blood in nine patients undergoing revision hip replacement. Using inductively coupled plasma mass spectrometry (ICP-MS), the levels were measured for titanium, aluminium, vanadium, chromium, cobalt, nickel and molybdenum. The metal ion levels were analysed using a dilution technique and the total metal content levels (particulate debris and ions) were analysed with a digestion technique.

Results: Significantly higher levels of metal ions and metal debris were found in the pre-processed blood compared with the processed blood (after centrifuging and washing). The ion levels in the processed blood were not high enough to cause a significant increase in the patients’ immediate post-operative blood ion levels when compared with pre-operative levels.

Conclusion: There are markedly elevated levels of metal ions and particulate metal debris in the blood salvaged during revision total hip arthroplasty. The processing of the recovered blood in a commercial ‘cell saver’ sig-nificantly reduces the total metal load that is re-infused. Re-infusion of salvaged blood does not result in elevated metal ion levels in the immediate post-operative period.

Purpose: To investigate whether cement mantle thickness influence early migration of the stem after impaction grafting

Methods: Twelve artificial femora were prepared to mimic cavitary defects. After compacting morselized bone into the cavities, Exeter stems were cemented in place. By using all combinations of three sizes tamps and stems (0, 1 and 2), we created cement mantles of 0, 1, 2, 3 and 4 mm thickness. Bones with stems were placed in a testing machine and loaded cyclically to 2,500 N while measuring stem migration. Statistical analysis was by regression analysis. Outcomes were stem subsidence and retroversion, predictors were mantle thickness, tamp size and stem size.

Results: Average stem subsidence after 2500 cycles when using size 1 tamp and stem (2 mm mantle) was 0.94 mm. Cement mantle thickness significantly influ-enced stem subsidence (r=0.68, p=0.015). For a 0 mm mantle, subsidence was 0.59 mm and for a 4 mm mantle it was 2.54 mm. Cement mantle thickness also signifi-cantly influenced stem retroversion (r=0.62, p=0.031). Cement mantle thickness was a better predictor than tamp or stem size.

Discussion: Concern exists that inadequate cement mantles may affect stability of impaction-grafted stems. In our study, larger difference between tamps and stems gave substantially more subsidence and rotation, whereas a smaller difference reduced them. Concerns over thin mantles may have been premature.

Introduction: Surface replacement of the hip has been proposed as an alternative to total hip replacement, particularly in young active patients. The suggested benefits include preservation of bone stock for future revision surgery and avoidance of proximal femoral stress protection, which can cause bone resorption. However, following femoral head resurfacing, femoral neck fracture can occur.

The aim of this study was to compare the strain pattern in intact and resurfaced femurs using validated third generation composite femurs and rosette strain gauges.

Methods: Rosette strain gauges were applied to an intact and a resurfaced third generation composite femur at three sites; narrowest part of the lateral surface of the neck, narrowest part of the medial surface of the neck and medial surface at the level of lesser trochanter. The femurs were loaded with axial loads of 600N, 800N and 1000N sequentially. The tests were repeated thrice for each femur. Maximum and minimum principal strains were calculated.

Further tests were carried out in which an abductor load was included in the model. Testing was done at 600N and repeated thrice for each femur. The principal strains were calculated and compared with the the principal strains without the abductor load.

Results: The maximum principal strains in the resurfaced femur were approximately 50% higher in the lateral surface of the neck and about 30% higher in the lesser trochanteric region when loaded without including an abductor force. Inclusion of the abductor force decreased the strain particularly at the lateral surface of the neck by approximately 45% in the intact femur and approximately 25% in the implanted femur. Even with the inclusion of the abductor load the strain in the resurfaced femur remained more than 50% higher at the lateral surface of the neck and 20% higher in the lesser trochanteric region.

Conclusion: Our study suggests that proximal femoral stress protection will not occur following surface replacement of the hip. The increased strain at the lateral surface of the neck could result in fracture, particularly if there is notching of the neck or if abductor function has been compromised, which can happen particularly with the direct lateral approach.