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Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 474 - 474
1 Dec 2013
Panagiotidou A Meswania J Hua J Muirhead-Allwood SK Skinner JA Hart A Blunn G
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Introduction:

There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers.

Methods:

An inverted hip replacement setup was used (ASTM F1875-98). 28 mm Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth surface finish. Wear and corrosion of taper surfaces were compared after samples were sinusoidally loaded between 0.1 kN and 3.1 kN for 10 million cycles at 4 Hz. In test 1 rough mini stem tapers were compared with rough standard stem tapers whilst in test 2 rough mini stem tapers were compared with smooth mini stem tapers. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed between rough mini stem tapers and smooth mini stem tapers under loaded and non-loaded conditions.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXIX | Pages 22 - 22
1 Sep 2012
Sandiford N Muirhead-Allwood S Skinner J Hua J Peter W
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Introduction

Optimal results from uncemented total hip arthroplasty (THA) requires the prosthesis to obtain initial stability, restoration of biomechanics, bone contact along the ingrowth surface and uniform stress transfer to the proximal femur. Anatomic variation within the population makes this difficult to reproduce in every patient. To achieve optimal fit and fill of the proximal femur, options are reshaping the canal or creating an implant which precisely fits the patient's anatomy. The former increases bone loss and risks weakening the supporting bone, creating areas of stress concentration or shielding. Computer assisted design-computer assisted manufacture (CAD-CAM) femoral components were designed to overcome these issues. We present the long term results of CAD-CAM femoral components used in primary THA.

Methods

This was a prospective study looking at a consecutive, single surgeon series of THA's. Patients were reviewed pre operatively then at 6 weeks, 3 and 12 months post operatively and then yearly. Clinical as well as radiological review was performed at each visit and Harris Hip Score (HHS), Oxford Hip Score (OHS) and Western Ontario McMaster's (WOMAC) scores were calculated. Kaplan-Meier survival analysis was performed.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXIX | Pages 26 - 26
1 Sep 2012
Sandiford N Muirhead-Allwood S Skinner J Hua J Peter W
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Introduction

The variability of the endosteal geometry after removal of the femoral component can make proximal fit difficult to achieve with an ‘off the shelf’ prosthesis. Whatever the anatomy of the proximal femur, it is important to achieve immediate stability, preserve bone stock and protect the femur from cortical defects which can lead to subsequent fracture. In revision Total Hip Arthroplasty (THA) this requires a large inventory of modular components. The use of custom computer-assisted design-computer-assisted manufacture (CAD-CAM) components negates this need. Little has been published on the use of custom-made components in revision THA. We report the results of a cohort of patients who underwent revision THA using CAD-CAM femoral components.

Methods

A prospective study was performed between 1991 and 1998. A consecutive series of patients who had revision THA using custom components were assessed clinically and radiologically. The design of the femoral components was governed by the existing femoral bone stock. Patients were reviewed pre operatively then at 6 weeks, 3months and 12 months postoperatively and then annually. Radiographs were assessed at each visit and Oxford, Harris and WOMAC hip scores were calculated


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XL | Pages 79 - 79
1 Sep 2012
Vanhegan I Jassim S Sturridge S Ahir S Hua J Witt J Nielsen P Blunn G
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Introduction

A new conservative hip stem has been designed to address the complex problem of total hip arthroplasty in the younger population.

Objectives

To assess the stability and strain distribution of a new conservative hip stem.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXIX | Pages 23 - 23
1 Sep 2012
Lee P Smitesh P Hua J Gupta A Hashemi-Nejad A
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Introduction

Many patients who had previous proximal femoral osteotomies develop deformities that may not be amenable to total hip replacement (THR) with standard off-the-shelf femoral stems. Previous studies have shown high revision rates (18% at 5–10 years follow-up). Computer-assisted-design computer-assisted-manufacture (CAD-CAM) femoral stems are indicated but the results are not known. We assessed the clinical results of THR using CAD-CAM femoral stems specifically for this group of patients.

Methods

We included patients with previous proximal femoral osteotomy and significant deformity who underwent THR with CAD-CAM femoral stem operated by the senior author (AHN) from 1997 with a minimum of 5 years follow-up. We noted revision rates, associated complications and functional outcome. Radiological outcomes include assessment for loosening defined as development of progressive radiolucent lines around implant or implant migration.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXIV | Pages 16 - 16
1 Jul 2012
White J Ahir S Hua J
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Hip resurfacing arthroplasty is emerging as an increasingly popular, conservative option for the treatment of end-stage osteoarthritis in the young and active patient. Despite the encouraging clinical results of hip resurfacing, aseptic loosening and femoral neck fracture remains concerns for the success of this procedure.

This study used finite element analysis (FEA) to analyse the stresses within proximal femoral bone resulting from implantation with a conservative hip prosthesis. FEA is a computational method used to analyse the performance of real-world structures through the development of simplified computational models using essential features.

The aim of this study was to examine the correlation between the orientation of the femoral component of a hip resurfacing prosthesis (using the Birmingham Hip Resurfacing as a model) and outcomes during both walking and stair climbing. The outcomes of interest were stresses in the femoral neck predisposing to fracture, and bone remodelling within the proximal femur.

Multiple three-dimensional finite element models of a resurfaced femur were generated, with stem-shaft angles representing anatomic (135°), valgus (145°), and varus (125°) angulations. Applied loading conditions included normal walking and stair climbing. Bone remodelling was assessed in both the medial and lateral cortices.

Analyses revealed that amongst all orientations, valgus positioning produced the most physiological stress patterns within these regions, thereby encouraging bone growth. Stress concentration was observed in cortical and cancellous bone regions adjacent to the rim of the prosthesis. As one would expect, stair climbing produced consistently higher stress than walking. The highest stress values occurred in the varus-orientated femur during both walking and stair climbing, whilst anatomic angulation resulted in the lowest stress values of all implanted femurs in comparison to the intact femur.

This study has shown through the use of FEA that optimising the stem-shaft angle towards a valgus orientation is recommended when implanting a hip resurfacing arthroplasty. This positioning produces physiological stress patterns within the proximal femur that are conducive to bone growth, thus reducing the risk of femoral neck fracture associated with conservative hip arthroplasty.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXV | Pages 95 - 95
1 Jun 2012
Hua J Muirhead-Allwood S Sandiford A Skinner J Walker P
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Total hip replacements have shown great benefits to patients through relief of pain and restoration of function. However, because of the extensive variation in the size and shape of the femoral canal, especially for the situation encountered in the revision hip arthroplasty, standard uncemented hip systems with a limited number of sizes are unable to provide an accurate fit in every case. This study showed clinical results of 112 primary total hip replacements and 158 revision total hip replacements, using custom made CAD-CAM (Computer Aided Design-Computer Aided Manufactured) hip prostheses inserted between 1992 and 1998.

For primary hip replacements, the implants were designed to produce proximal line-to-line fit with the femoral bone and to provide optimal biomechanical environment of the hip. The stem was HA coated, 53 males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). The average duration of the follow up was 24 years (10 – 17 years). The mean Harris Hip Score (HHS) was improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) was improved from 43.1 to 18.2 and the mean WOMAC hip score was improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. In the whole follow-up period, the survival of the femoral stem alone was 100%.

For revision hip replacements, the implants were designed using our design strategies of graduate approach to different revision situation based on Paprosky's classification of femoral bone defect. The implants were HA coated; some of them had distal cutting flutes. A total of 158 patients (97 males and 61 females) who had operation between 1991 and 1998 were followed up, among them 138 cases were due to aseptic loosening, 6 cases were periprosthetic fractures and 14 cases were infection. The average age was 63.1 years (range 34.6 – 85.9 years). The minimum follow up was 10 years (range 10 – 12 years). The mean Harris Hip Score was improved from 44.2 to 89.3, mean Oxford Hip Score was improved from 41.1 to 18.2 and the mean WOMAC hip score was improved from 52.4 to 12.3 respectively. 6 cases required further revision surgery, among them 3 were due to aseptic implant loosening, the overall survivorship at ten years was 97%.

The CAD-CAM hip stems are able to provide optimal implant fixation and restore hip function for every patient regardless their original femoral shape, bone condition and biomechanics of the hip. The excellent medium to long term clinical results justifies the use of CAD-CAM custom hip stems.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XVI | Pages 11 - 11
1 Apr 2012
Muirhead-Allwood S Sandiford NA Skinner JA Hua J Walker PS
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We present the medium to long term clinical results of 112 Uncemented custom Computer Assisted Design Computer Assisted Manufactured (CAD-CAM) total hip arthroplasties performed between 1992 and 1998 in 111 patients. Fifty three males and 58 females were included. Mean age was 46.2 years (range 24.6yrs - 62.2 yrs). Average duration of follow up was 156 months (120 – 204 months). The mean Harris Hip Score (HHS) improved from 42.4 to 90.3, mean Oxford Hip Score (OHS) improved from 43.1 to 18.2 and the mean WOMAC hip score improved from 57.0 to 11.9. There was 1 revision due to failure of the acetabular components but there were no failures of the femoral components. There were no revisions for aseptic loosening. The worst case survival in this cohort of custom femoral components at an average 13 year follow up (range 10-17 years) was 98.2% (95% Confidence interval 95% to 99%). Survival of the femoral component alone was 100%.

These results are comparable with the best medium to long term results for femoral components used in primary total hip arthroplasty (THA) with any means of fixation.