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Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 158 - 158
1 May 2012
G. ERT D. S A. T P. M H. SG S. G D. WM
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The direction of penetration of the femoral head following total hip replacement has been shown at revision to be superomedial, superior or superolateral. However, it is important to study well functioning components to describe normal patterns of wear. The aim of this study was to characterise the 3D direction of penetration in standard and HXLPE.

A prospective double blind randomised control trial was conducted using Radiostereometric Analysis (RSA). Fifty-four subjects were randomised to receive hip replacements with either UHMWPE liners or HXLPE liners. All subjects received a cemented CPT stem and uncemented Trilogy acetabular component (Zimmer, Warsaw, IN, USA). The 3D penetration of the head into the socket was determined to a minimum of 7 years.

The direction of penetration between one and seven years was in a superior and lateral direction for both groups. In the HXLPE group there was no significant penetration in the coronal or sagittal planes (superiorly 0.009 mm/yr, 95% confidence interval, ±0.045, p1 = 0.68, laterally 0.003mm/yr, CI 0.031, p1 = 0.85). In the UHMWPE group there was significant penetration 0.059 mm/yr superiorly (CI 0.042, p1 = 0.01) and 0.049 mm/yr laterally (CI 0.044, p1 = 0.03). The anterior-posterior steady state penetration was not significant in either group (HXLPE p1 = 0.39, UHMWPE p1 = 0.37).

We have previously demonstrated that the penetration in the first year is creep-dominated and is in the proximal direction. From one year onwards the superolateral direction of penetration is probably due to wear. The steady-state wear direction is the same in both bearings types. It is likely that creep occurs in the direction of the Joint Reaction Force i.e. superomedial, whereas wear is perpendicular to the axis of rotation and therefore superolateral. This work may enable us to develop more accurate models for predicting wear in total hip arthroplasty.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 153 - 153
1 May 2012
K. B B. L T. G S. G J. W
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Background

Despite aggressive debridement, thorough irrigation, administration of systemic antibiotics and staged treatment, many open fractures still become infected. A graft that can promote bone regeneration and prevent infection could decrease complications. Polyurethane (PUR) scaffolds have been previously shown in separate studies to be non-toxic, osteoconductive, can promote bone growth through BMP delivery and prevent infection by having sustained release of an antibiotic. This scaffold can deliver both BMP and vancomycin simultaneously; the purpose of this study is to determine if the co-delivery of the antibiotic inhibits bone formation.

Methods

Using an established critical size defect rat femur model, the amount of bone formation created by PUR scaffolds containing low and high doses of rhBMP-2 (2.4 μg and 22.4 μg respectively) and 0.8 mg vancomycin (8% of graft by weight) were compared to scaffolds that contained rhBMP-2 without antibiotics. After 4 weeks, the femurs were harvested and bone growth was assessed using microCT.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 10 - 10
1 May 2012
R. DS L. M P. R S. G
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Introduction

Bearing surfaces used for total hip arthroplasty must have characteristics including bio-compatibility, low friction and low wear rate. Bearing combinations are generally characterised as Soft on Hard/Hard. In general, all newer bearing combinations have reduced wear but may present with other issues that impact on patient outcomes.

Materials

The Australian Orthopaedic Association – National Joint Replacement Registry classifies bearing surfaces into six categories. These are metal on polyethylene, ceramic on polyethylene, metal on metal, ceramic on ceramic, ceramic on metal and a sixth category relating to a small number of procedures where the bearing surface is yet to be classified. 147,422 conventional total hip arthroplasty procedures have been recorded by the Registry between 1 September 1999 and 31 December 2008 and analysis has been performed of the cumulative percentage revision in relation to bearing surface.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 25 - 25
1 May 2012
Y-M. K S. G D. S A. K P. M H.S. G D M
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Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify the wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure.

A total of 30 contemporary MoMHRA implants in two groups were investigated: (1) 8 MoMHRA implants revised due to pseudotumour; (2) 22 MoMHRA implants revised due to other reasons of failure. The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo.

In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with: (1) significantly higher median linear wear rate of the femoral component: 8.1 um/year (range 2.75-25.4 um/year) vs. 1.97 um/year (range 0.82-13.00 um/year), p=0.002; and (2) significantly higher median linear wear rate of the acetabular component: 7.36 um/year (range 1.61-24.9 um/year) vs. 1.28 um/year (range 0.18-3.33 um/year), p=0.001. Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing.

Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study is the first to confirm that pseudotumour occurs when there is increased wear at the MoM articulation. Furthermore, edge-loading may be the dominant wear generation mechanism in patients with pseudotumour.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 175 - 175
1 May 2012
S. J A. L S. G L. S A. W M. R
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Background

Every trainee in Trauma and Orthopaedics (T&O) in the UK and Ireland records their operative experience via the Faculty of Health Informatics eLogbook. Since August 2009, all doctors were subject to the full European Working Time Directive (EWTD) restrictions of 48 hours of work per week. We have previously shown that the implementation of shift working patterns in some units in preparation for these restrictions reduced training opportunities by 50% (elective surgical exposure). We have now analysed the national data to establish whether operative experience has fallen since August 2009.

Methods

All operative data recorded nationally by trainees (all years, all supervision levels) between the 3 months of August to October 2007, 2008 and 2009 were compared. Data were available for 1091 ‘validated’ training grade surgeons (ST3-8 or equivalent) in 2007, 1103 in 2008 and 767 in 2009. Mean operative figures were calculated per trainee for each of the 3-month time periods.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 121 - 121
1 May 2012
A. P S. G J. O V. S S. D
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Background

Unicompartmental knee replacement (UKR) is an established treatment for single compartment end-stage knee arthrosis with good recorded survivorship. Although often used in more active younger patients, patient selection remains controversial. To identify risk factors for early failure we compared patients with UKR failure requiring revision to total knee replacement (TKR) with a control group.

Methods & Results

Between September 2002 and 2008, 812 Oxford Mobile Bearing Medial UKRs were implanted. 21 implants (20 patients) required revision to TKR within 5 years. The leading cause for revision was lateral compartment disease progression (11 patients). In the revision group, 17 patients were female (81%), average age at index surgery was 64.1 (range 48-81) and average BMI 31.8 (range 24.4-41.5). In the control group of all patients who underwent UKR during this period, 348 patients were female (44%), average age was 65.0 (range 36-89) and average BMI 31.2 (range 21.0-61.0).

Radiological assessment of the tibiofemoral valgus (TFV) angle for revision patients was compared with an age and sex matched control group. In the revision group, average TFV angle was +1.5 pre-operatively and +6.1 post-operatively with an average change of +4.6. In the control group average TFV angle was -0.4 pre-operatively and +4.3 post-operatively with an average change of +4.7.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXI | Pages 6 - 6
1 May 2012
S G
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Introduction

The resurgence of TB worldwide has several underlying causes, but HIV infection has undoubtedly been a key factor in the current TB epidemic. Since TB is endemic in the developing world the influence of HIV is of concern, particularly with the emergence of multi-drug-resistant strains. The remarkable susceptibility of patients with AIDS to develop TB has shown the critical role of CD4 lymphocytes in protective immunity. In the absence of immunological surveillance by CD4 cells, 5-10% of persons with latent foci of TB reactivate each year.

Aim

This paper highlights the presentation and outcome following treatment in HIV patients with spinal TB.