Aims

Manual impaction, with a mallet and introducer, remains the standard method of installing cementless acetabular cups during total hip arthroplasty (THA). This study aims to quantify the accuracy and precision of manual impaction strikes during the seating of an acetabular component. This understanding aims to help improve impaction surgical techniques and inform the development of future technologies.

Aims

Cementless acetabular components rely on press-fit fixation for initial stability. In certain cases, initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity, and number of strikes) may affect component fixation. This study seeks to answer the following research questions: 1) how does impaction technique affect a) bone strain generation and deterioration (and hence implant stability) and b) seating in different density bones?; and 2) can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular component?

The hip's capsular ligaments (CL) passively restrain extreme range of motion (ROM) by wrapping around the native femoral head/neck, and protect against impingement and instability. We compared how CL function was affected by device (hip resurfacing arthroplasty, HRA; dual mobility total hip arthroplasty, DM-THA; and conventional THA, C-THA), and surgical approach (anterior and posterior), with and without CL surgical-repair. We hypothesized that CL function would only be preserved when native head-size (HRA/DM-THA) was restored.

CL function was quantified on sixteen cadaveric hips, by measuring ROM by internally (IR) and externally rotating (ER) the hip in six functional positions, ranging from full extension with abduction to full flexion with adduction (squatting). Native ROM was compared to ROM after posterior capsulotomy (right hips) or anterior capsulotomy (left hips), and HRA, and C-THA and DM-THA, before and after CL repair.

Independent of approach, ROM increased most following C-THA (max 62°), then DM-THA (max 40°), then HRA (max 19°), indicating later CL engagement and reduced biomechanical function with smaller head-size. Dislocations also occurred in squatting after C-THA and DM-THA. CL-repair following HRA restored ROM to the native hip (max 8°). CL-repair following DM-THA reduced ROM hypermobility in flexed positions only and prevented dislocation (max 36°). CL-repair following C-THA did not reduce ROM or prevent dislocation.

For HRA and repair, native anatomy was preserved and ligament function was restored. For DM-THA with repair, ligament function depended on the movement of the mobile-bearing, with increased ROM in positions when ligaments could not wrap around head/neck. For C-THA, the reduced head-size resulted in inferior capsular mechanics in all positions as the ligaments remained slack, irrespective of repair.

Choosing devices with anatomic head-sizes (HRA/DM-THA) with capsular repair may have greater effect than surgical approach to protect against instability in the early postoperative period.

The hip joint capsular ligaments (CL) passively restrain extreme range of motion (ROM) by wrapping around the native femoral head, and protect against impingement, edge loading wear and dislocation. This study compared how ligament function was affected by device (hip resurfacing arthroplasty, HRA; dual mobility total hip arthroplasty, DM-THA; and conventional THA, C-THA), with and without CL repair. It was hypothesized that ligament function would only be preserved when native anatomy was preserved: with restoration of head-size (HRA or DM-THA) and repair.

Eight normal male cadaveric hips were skeletonised, retaining the hip capsule. CL function was quantified by measuring ROM by internally (IR) and externally rotating (ER) the hip in six functional positions, ranging from full extension with abduction to full flexion with adduction (squatting). Native ROM was compared to ROM after posterior capsulotomy and HRA, and C-THA and DM-THA, before and after surgical CL repair.

ROM increased most following C-THA (max 62°), then DM-THA (max 40°), then HRA (max 19°), indicating later engagement of the capsule and reduced biomechanical function with smaller head-size. Dislocations also occurred in squatting after C-THA and DM-THA. CL-repair following HRA restored ROM to the native hip (max 8°). CL-repair following DM-THA reduced ROM hypermobility in flexed positions only and prevented dislocation (max 36°). CL-repair following C-THA did not reduce ROM or prevent dislocation.

When HRA was combined with repair, native anatomy was preserved and ligament function was restored. For DM-THA with repair, ligament function depended on the movement of the mobile bearing resulting in near-native function in some positions, but increased ROM when ligaments were unable to wrap around the head/neck. Following C-THA, the reduced head-size resulted in inferior capsular mechanics in all positions as the ligaments remained slack, irrespective of repair.

Choosing devices with anatomic head-sizes (resurfacing or dual-mobility) and repairing the capsular ligaments may protect against instability in the early postoperative period.

Background

The hip joint capsular ligaments passively restrain extreme range of motion (ROM), protecting the native hip against impingement, subluxation, edge loading and dislocation. This passive protection against instability would be beneficial following total hip arthroplasty (THA), however the reduced femoral head diameter postoperatively may prevent a wrapping mechanism that is essential to capsular ligament function in the native hip. Therefore we hypothesized that, post-THA, the reduced femoral head size would prevent the capsular ligaments protective biomechanical function.

The hip joint capsule passively restrains extreme range of motion protecting against impingement, dislocation and possibly edge loading. These functions would be advantageous following total hip arthroplasty (THA) however the degree of capsular excision, preservation and/or repair greatly varies between surgeons/approaches. Therefore, we asked: how does THA affect capsular ligamentous biomechanics? Which factors have the biggest influence?

For this laboratory based, cadaveric model, THA was performed through the acetabular medial wall, thus preserving the entire hip capsule. A previously published testing rig was used to measure capsular function by internally and externally rotating the hip in each of five hip positions (standing, sitting, gait heel strike, and two impingement risk positions, full flexion with adduction & extension with abduction). N=8 hips were tested both before and after THA allowing for repeated measurements between the native and replaced hip.

The ROM before the capsule engaged increased following THA (p<0.05), indicating reduced biomechanical function. Internal rotation was affected more than external rotation. Increasing neck length restored the ROM more towards the native condition. Increasing head size also had a small positive effect, but less than neck length.

Following THA, the capsular ligaments were no longer able to wrap around the smaller femoral head thereby limiting their ability to restrain excessive hip movement. The anterior capsule is affected less than the posterior, and may benefit from being preserved length. A repair to the posterior capsule should compensate for the reduced THA head size in order to restore function.

The current, most popular recommendation for cup orientation, namely the Lewinnek box, dates back to the 70's, that is to say at the stone age of hip arthroplasty. Although Lewinnek's recommendations have been associated with a reduction of dislocation, some complications, either impingement or edge loading related, have not been eliminated. Early dislocations are becoming very rare and most of them probably occur in “outlier” patients with atypical pelvic/hip kinematics. Because singular problems usually need singular treatments, those patients need a more specific personalised planning of the treatment rather than a basic systematic application of Lewinnek recommendations. We aim in this review to define the potential impacts that the spine-hip relations (SHRs) have on hip arthroplasty. We highlight how recent improvements in hip implants technology and knowledge about SHRs can substantially modify the planning of a THR, and make the «Lewinnek recommendations» not relevant anymore. We propose a new classification of the SHRs with specific treatment recommendations for hip arthroplasty whose goal is to help at establishing a personalized planning of a THR. This new classification (figures 1 and 2) gives a rationale to optimize the short and long-term patient's outcomes by improving stability and reducing edge loading. We believe this new concept could be beneficial for clinical and research purposes.

In approximately 20 years, surgical treatment of femoro-acetabular impingement (FAI) has been widely accepted, and its indications refined. However, the current approach of the disease prevents a good understanding of its pathophysiology, and numerous uncertainties remain. Comprehending inter-individual spine-hip relations (SHRs) can further clarify the pathophysiology of impingement, and explain occasional surprising mismatch between clinical assessment and imaging or intraoperative findings. The rational is simple, the more the spino-pelvic complex is mobile (sagittal ROM) and the more the hip is protected against hip impingement but would probably become at risk of spine-hip syndrome if the spino-pelvic complex comes to degenerate. Grouping patients based on their spine-hip relation can help predict and diagnose hip impingement, and assess the relevance of physiotherapy. With the proposed new classification of FAIs, every patient can be classified in homogeneous groups of complexity of treatment. The primary aim of this paper is to raise awareness of the potential impact that the spine-hip relations have on the hip impingement disease. Two new classifications are proposed, for FAIs and SHRs that can help surgeons in their comprehension, and could be beneficial in clinical and research areas.

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.

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.

Introduction

Metal on metal hip resurfacing arthroplasty (MoM HR) has the highest revision rates according to the UK National Joint Registry. Revisions for lesions associated with soft tissue necrosis (pseudotumors) have been associated with poor outcomes. There is a relative paucity of information on early revision of painful HR prostheses. We present the results of a series of patients who underwent early revision of painful MoM HR procedures.

Introduction

There is no consensus on the ideal management of young, active patients with disabling coxarthrosis. Within this group, patients with femoral head defects secondary to cysts or avascular necrosis pose particular challenges. Resurfacing arthroplasty is contraindicated and the results of traditional total hip arthroplasty are suboptimal in this group. The BMHR was designed to offer a bone conserving option for these patients. We report the outcome of this device in the short term.

Introduction

The National Joint Registry has recently identified failure of large head metal on metal hip replacements. This failure is associated with the high torque at the interface of standard modular taper junction leading to fretting and corrosion. A number of manufacturers produce mini spigots, which in theory, provide a greater range of motion as the neck head junction is reduced. However, the relative torque to interface ratio at this junction is also increased. In this study we investigated hypothesis that the use of small spigots (minispigots) will increase wear and corrosion on modular tapers.

Patients with osteochondrodysplasia frequently require Total Hip Arthroplasty at a younger age, as a result of early degenerative disease of the hip joint. The outcome of Modular Total Hip Arthroplasty in this group of patients has been reported previously. In this retrospective study we evaluated the outcome of custom made (CADCAM) Total Hip Arthroplasty in patients with osteochondrodysplasia.

Between 1974 and 2009, twenty one CADCAM Total Hip Arthroplasty procedures were performed in fourteen patients in our institution. There were eight female and six male patients, with the mean age at time of surgery of 40.95 years (20 to 78). The patients were followed up clinically and with the Harris hip score for a mean of 7.12 years (0.5 to 17 years).

Four of the twenty-one hips (23.8%) required revision surgery at a mean of 11.54 years (6.5 to 17 years); one required it for aseptic loosening of the femoral component; one required complete revision of the acetabular component; one required exchange of acetabular liner; and one was for symptomatic non-union of a lesser trochanter avulsion.

This study shows encouraging clinical outcomes of custom made (CADCAM) Total Hip Arthroplasty in patients with osteochondrodysplasia,

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.

SUMMARY

We report a prospective study of clinical data collected pre, intra and post operation to remove both cup and head components of 118 failed, current generation metal on metal (MOM) hips. Whilst component position was important, the majority were unexplained failures and of these the majority (63%) had cup inclination angles of less than 55 degrees. Poor biocompatibility of the wear debris may explain many of the failures.

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.

Introduction: Excellent early and medium term results have been reported for hip resurfacing. This is a minimum 5 year clinical outcome review of the resurfacings performed by a single surgeon in an independent series.

Methods: There were 329 resurfacings (302 patients). The mean follow-up is 6.6 years (5 to 9.2). 2 patients were lost to follow-up and 6 have died due to unrelated causes. The mean age at the time of surgery was 56.0 years (28.2 to 75.5). Mann-Whitney U-test was used to analyse change in hip scores, and survival analysis was performed using the Kaplan-Meier analysis using SPSS statistical software package.

Results: The mean Harris Hip Score was 51.3 (7 to 91) pre-operatively and 94.3 (24 to 100) postoperatively (p< 0.001). The mean Oxford hip scores was 38.3 (16 to 60) pre-operatively and 15.9 (12 to 46) postoperatively (p< 0.001). The mean Western Ontario and McMaster Universities Osteoarthritis Index score was 47.9 (5 to 96) pre-operatively and 6.9 (0 to 58) postoperatively (p< 0.001). The University of California Los Angeles activity scale was 4.7 (1 to 9) pre-operatively and 7.5 (3 to 10) post-operatively (p< 0.001). Mean satisfaction at the latest follow up was 9.3 (3–10) out of 10.

There were ten revisions. Kaplan-Meier analysis showed survival of 96.5% (95% confidence interval 94.7 to 98.4) at 7 years taking revision for any cause as the end-point. There was a 3.9 times higher failure rate in women compared to men.

Discussion: Medium term results of hip resurfacing in this independent series are excellent and are comparable to those from the pioneering centre. Failure rates are significantly higher in women compared to men. Long term follow up results are still awaited, however careful consideration should be made when selecting patients for hip resurfacing particularly in women.

Introduction: The London Implant Retrieval Centre (LIRC) was founded to investigate the high incidence of unexplained failures of Metal-on-Metal (MoM) hips. A multidisciplinary team analyse the failed hips, investigations include CT and MRI scans, blood and synovial fluid tests, wear measurements, X-rays and clinical data from the explanting surgeons.

Wear measurements of 100 explanted hips have been carried out on a Taylor Hobson 365 Roundness Machine using the LIRC Wear Protocol. It was found that 50% of explanted cups were wearing less than 5 μm/year and 60% of components were wearing less than 10 μm/year. Wear tests on hip joint simulators predict wear rates between 2 and 8 μm/year. However, 6% of cups are wearing faster than 100 μm/year, with 16% of cups have wear patches deeper than 100 μm and that 4% have a wear patch deeper than 300 μm.

Discussion: This paper considers the common characteristics of components in this very high wearing category. Engineering parameters such as head/cup clearance, surface finish, form errors and head cup contact conditions are investigated. This is correlated with clinical data and other results from the LIRC.

Cup position is an important factor, all of the high wearing components are outside the Lewinick’s Box, however it is shown that mal position is does not always lead to extreme wear. Further analysis is taking place to calculate the size of the contact patch between head and cup (based on patient data and biomechanics) and the proximity of the contact patch to the edge of the cup.

Conclusion: The study of explanted components shows that 6% exhibit extreme wear, and although several “risk” factors can be identified, it is not clear why only a proportion of these components show extremely high wear rates. This is the subject of current investigation.

Introduction: Excellent early and medium term results have been reported for hip resurfacing. This is a minimum 5 year clinical outcome review of the resurfacings performed by a single surgeon in an independent series.

Methods: There were 329 resurfacings (302 patients). The mean follow-up is 6.6 years (5 to 9.2). 2 patients were lost to follow-up and 6 have died due to unrelated causes. The mean age at the time of surgery was 56.0 years (28.2 to 75.5). Mann-Whitney U-test was used to analyse change in hip scores, and survival analysis was performed using the Kaplan-Meier analysis using SPSS statistical software package.

Results: The mean Harris Hip Score was 51.3 (7 to 91) pre-operatively and 94.3 (24 to 100) postoperatively (p< 0.001). The mean Oxford hip scores was 38.3 (16 to 60) pre-operatively and 15.9 (12 to 46) postoperatively (p< 0.001). The mean Western Ontario and McMaster Universities Osteoarthritis Index score was 47.9 (5 to 96) pre-operatively and 6.9 (0 to 58) postoperatively (p< 0.001). The University of California Los Angeles activity scale was 4.7 (1 to 9) pre-operatively and 7.5 (3 to 10) post-operatively (p< 0.001). Mean satisfaction at the latest follow up was 9.3 (3–10) out of 10.

There were ten revisions. Kaplan-Meier analysis showed survival of 96.5% (95% confidence interval 94.7 to 98.4) at 7 years taking revision for any cause as the end-point. There was a 3.9 times higher failure rate in women compared to men.

Discussion: Medium term results of hip resurfacing in this independent series are excellent and are comparable to those from the pioneering centre. Failure rates are significantly higher in women compared to men. Long term follow up results are still awaited, however careful consideration should be made when selecting patients for hip resurfacing particularly in women.

We prospectively evaluated the long-term outcome of 158 consecutive patients who underwent revision total hip replacement using uncemented computer-assisted design-computer-assisted manufacture femoral components. There were 97 men and 61 women. Their mean age was 63.1 years (34.6 to 85.9). The mean follow-up was 10.8 years (10 to 12).

The mean Oxford, Harris and Western Ontario and McMaster hip scores improved from 41.1, 44.2 and 52.4 pre-operatively to 18.2, 89.3 and 12.3, respectively (p < 0.0001, for each). Six patients required further surgery. The overall survival of the femoral component was 97% (95% confidence interval 94.5 to 99.7). These results are comparable to those of previously published reports for revision total hip replacement using either cemented or uncemented components.

We present the 10- to 17-year results of 112 computer-assisted design computer-assisted manufacture femoral components. The total hip replacements were performed between 1992 and 1998 in 111 patients, comprising 53 men and 58 women. Their mean age was 46.2 years (24.6 to 62.2) with a mean follow-up of 13 years (10 to 17). The mean Harris Hip Score improved from 42.4 (7 to 99) to 90.3 (38 to 100), the mean Oxford Hip Score from 43.1 (12 to 59) to 18.2 (12 to 51) and the mean Western Ontario MacMasters University Osteoarthritis Index score from 57.0 (7 to 96) to 11.9 (0 to 85). There was one revision due to failure of the acetabular component but no failures of the femoral component. There were no revisions for aseptic loosening. The worst-case survival in this cohort of custom femoral components at 13.2 years follow-up was 98.2% (95% confidence interval 95 to 99). Overall survival of this series of total hip replacements was 97.3% (95% confidence interval 95 to 99).

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

Background: There is no consensus on the most appropriate prosthesis for treating osteoarthritis (OA) of the hip in young, highly active patients. Modern hip resurfacing is bone conserving, more stable and theoretically easier to revise than total hip arthroplasty. Early results of metal on metal resurfacing have been promising. We have compared two well matched cohorts of patients with regard to function, pain relief and patient satisfaction.

Methods: This prospective study included 2 cohorts of well matched patients treated with hip resurfacing (137 patients, 141 hips) and custom uncemented (CADCAM) stems (134 patients, 141 hips). All procedures were performed by a single surgeon. Outcome measures included Oxford, WOMAC and Harris hip scores. Statistical analysis was performed using the unpaired student’s t- test.

Results: One hundred and thirty four and 137 patients were included in the hip replacement and resurfacing groups respectively. The mean age of these patients was 54.6 years. The mean duration of follow up for the resurfacing group was 19.2 months compared to 13.4 months for the replacement group.

Pre operative oxford, Harris and WOMAC scores in the THA group were 41.1, 46.4 and 50.9 respectively while the post operative scores were 14.8, 95.8 and 5.0. In the HR group, pre- operative scores were 37.0, 54.1 and 45.9 respectively compared to 15.0, 96.8 and 6.1 post operatively. The degree of improvement was similar in both groups.

Conclusion: There was no significant difference in short term outcome between the groups of patients treated with hip resurfacing and total hip arthroplasty in the short term.

Introduction: While the explant device has made revision of uncemented acetabular components technically easier, the unique design of the Birmingham Hip Resurfacing(BHR) acetabular component precludes the use of the standard explant extractor. The dual radius geometry of this socket causes impingement and damage to the curved blade of this device.

A novel adaptor was designed to correct for the differential radii and enable removal of the well fixed BHR socket with the explant. We present the results of our initial experience with this device.

Method: A prospective study was performed to evaluate the effectiveness of this device for revising the well fixed BHR socket. All cases were performed by a single surgeon via a posterior approach.

The explant cup extractor was used with its standard centering head and curved blades. The size of the explanted cup, last reamer size and size of the implanted component were recorded

Results: Three males and 7 females were included. Their average age was 58.1 years (48–65). Average time to revision of the BHR sockets was 24.2 months (7–40). Average explanted cup size was 51mm (46–58) and final reamer size 53.8mm (51–59). Average final socket size was54.8 (50–62). Overall there was a mean 2.8.mm size difference between the explanted cup and the final reamer.

Discussion: The thickness of the blade of the explant was 2mm therefore only 0.8 mm of bone was lost on average. The device enables a simple reproducible removal of the well fixed BHR sockets with preservation of acetabular bone stock.

Introduction: Approximately 0.5 % of patients with metal on metal hip replacements develop post operative pain which is thought to be due to an immune reaction to metal wear particles, known as Aseptic Lymphocyte Dominated Vasculitis Associated Lesion (ALVAL). Treatment usually requires revision to a non metal on metal hip.. Is the development of ALVAL more likely in those patients with high wear rates?

Methods: Retrieved Metal on Metal (MOM) hip implants; periprosthetic tissue and blood samples were obtained from patients (n = 18) undergoing revision for unexplained pain at a mean of 2 years post operatively. The following variables were measured:

linear wear rate (depth of the femoral head and acetabular socket wear patch/time from operation);

All implants and tissue samples were analysed against control samples from patients undergoing revision of MOM hips for fractured femoral neck or impingement.

Results: Linear wear rates of retrieved implants, and blood levels of cobalt and chromium from patients with unexplained plain were greater than from control patients. Histolopathological analysis of tissue showed dense inflammatory infiltrates with healthy looking endothelial cells in all vessels from both patient groups.

Discussion and Conclusion: A painful MOM hip was associated with high wear rates and blood metal levels. The local inflammatory response was similar to “ALVAL”, ie lymphocyte dominated, but not exclusive to those patients with unexplained pain. We question whether ALVAL represents a vasculitis, or merely a classical lymphocyte driven inflammatory tissue response to metal debris particles.

We carried out a cross-sectional study with analysis of the demographic, clinical and laboratory characteristics of patients with metal-on-metal hip resurfacing, ceramic-on-ceramic and metal-on-polyethylene hip replacements. Our aim was to evaluate the relationship between metal-on-metal replacements, the levels of cobalt and chromium ions in whole blood and the absolute numbers of circulating lymphocytes. We recruited 164 patients (101 men and 63 women) with hip replacements, 106 with metal-on-metal hips and 58 with non-metal-on-metal hips, aged < 65 years, with a pre-operative diagnosis of osteoarthritis and no pre-existing immunological disorders.

Laboratory-defined T-cell lymphopenia was present in13 patients (15%) (CD8⁺ lymphopenia) and 11 patients (13%) (CD3⁺ lymphopenia) with unilateral metal-on-metal hips. There were significant differences in the absolute CD8⁺ lymphocyte subset counts for the metal-on-metal groups compared with each control group (p-values ranging between 0.024 and 0.046). Statistical modelling with analysis of covariance using age, gender, type of hip replacement, smoking and circulating metal ion levels, showed that circulating levels of metal ions, especially cobalt, explained the variation in absolute lymphocyte counts for almost all lymphocyte subsets.

Introduction and aim: We have previously shown an association between whole blood metal ions and reduced CD8+ T cells in patients with unilateral metal on metal (MOM) hip resurfacings. Our aim was to substantiate this controversial finding with a follow up cohort of larger numbers of patients before further immunological investigation.

Method: We measured lymphocyte subset counts and whole blood Cobalt and Chromium in 2 groups of patients: a Birmingham hip resurfacing group (n=100); and a metal on polyethylene MOP hip arthroplasty group (n=34). Metal ions were measured using inductively-coupled mass spectrometry (ICP-MS) with a Dynamic Reaction Cell (DRC). The detection limit was 10 parts per trillion. All hip components were well fixed, clinically and radiologically.

Results: Cobalt and chromium levels were significantly elevated in the MOM resurfacing group compared to the MOP group (p< 0.0001). There was a statistically significant decrease in the MOM resurfacing groups’ level of CD8+cells (T cytotoxic) (p=0.005) when analysed by a Mann-Whitney U test. There was no significant difference between levels of CD4+ (T helper cells), CD19+ (B cells) and CD16/56+ (Natural Killer cells). A threshold level of blood cobalt and chromium ions for depression of total numbers CD8+ T cells was observed.

Conclusions: This follow up cohort of 100 MOM hip resurfacing patients has replicated the association of reduced CD8+ T cells and raised metal ion levels observed in our founder cohort. This was specific to CD8+ T cells. We are now more certain that this association needs further detailed immunological investigation.

Introduction: We have previously shown an association between whole blood metal particles from unilateral metal on metal (MOM) hip resurfacing and reduced CD8+ T cells (JBJS Br April 2006). There are no reported clinical effects of these findings. Certain patients maybe at high risk of developing clinical effects; one such group is patients with bilateral hip resurfacings. There are no published studies of bilateral hip resurfacings. Our aim was to investigate the association between whole blood metal ions and reduced CD8+ T cells in a follow up cohort of bilateral MOM hip resurfacings.

Method : Peripheral blood samples were analysed from patients with bilateral MOM hip resurfacings (n=25), unilateral hip resurfacings (n=34) and metal on polyethylene (MOP) hip arthroplasty (n=34). Samples were analysed for: lymphocyte subsets (FACS analysis); whole blood cobalt and chromium ion levels (using inductively-coupled mass spectrometry). Xrays revealed all hip components were well fixed.

Results : When compared to patients with standard MOP hip replacements there was a 30% reduction in both the bilateral and unilateral resurfacing groups’ level of CD8+ cells (T cytotoxic) (p=0.010). All other lymphocyte subgroups were not significantly different. There was evidence of a threshold effect of raised metal ions and reduced CD8+ T cells but no evidence of a dose-response relationship.

Conclusions : Bilateral MOM hip resurfacing is associated with a reduced CD8+ T cell count when compared to MOP hip arthroplasty. This association is not significantly different from the levels seen after unilateral MOM hip resurfacing.

Introduction: Impaction allografting is a technique that is used at revision where the bone stock in the femur is poor. Femoral heads are ground to create morsellised bone, which is impacted down the femur prior to the cementing a new stem into the canal. The results of this technique are variable and there is a high incidence of stem migration. This variation in results may be due to the degree of bone loss or the techniques used to impact the graft. The aim of this study was to quantify the forces currently used in revision hip surgery with impaction allografting.

Methods: To enable these measurements the Exeter slap hammer (Stryker Howmedica) was altered to include a load washer. The load washer had a special cable welded to it so that sterilisation could still be conducted in an autoclave. During surgery the end of the load washer cable is passed to the operator, who is able to connect it to a laptop computer. A specially written Labview program is then used to store the data and determine the impaction forces. The load washer is mounted within the hammer at the point of impact between the sliding mass and the hammer, consequently it is reading the force transmitted to the hammer, not that transmitted to the graft chips. Calibration was performed in an in vitro experiment with a second load washer, which found that the force in the hammer is three times that in the impactor. The force is so much less because it is taken up in the hammer’s inertia.

Conclusions: The impaction forces have been measured during eight operations performed by three different surgeons. The study shows variability between surgeons, and variability between patients operated on by the same surgeon. These readings show that the forces travelling through the impactor range between three to eleven time body weight.

Introduction: The Resurfacing Hip has been increasingly popular for younger patients. Femoral neck fractures are still the main complication. The problems associated with cement such as thermal necrosis, cement debris and lack of long-term biological fixation, combined with the general use of cementless fixation in young patients invite the question whether a cementless component can be used for resurfacing hip replacement. Given that the cement may reinforce the femoral head preventing collapse, an additional question regarding the effect of bone density in cemented and cementless fixation can be asked. The hypotheses of the study are that:

High bone density will increase the yield point and stiffness of the femoral head and therefore improve the implant fixation.

Materials and Methods: Thirty-six femoral head specimens were obtained from consented patients receiving routine hip arthroplasty. The heads were stored frozen at −20oC until use. pQCT was used to analyse trabecular bone density within each head. Specimens were ranked according to bone density and were assigned to high and low bone density groups. Cemented and cementless fixations were then alternatively assigned to individual heads in each group. Thus the 4 groups included in the study were: High density cemented, high density cementless, low density cemented, and low density cementless. Implantation of Birmingham resurfacing hips was carried out according to recommended surgical procedures. For cementing groups, surgical simplex P bone cement was used. Each sample was potted in a cylindrical polyethylene block for testing. A compressive load up to 5 or 10 KN using a Hounsfield Universal Testing Machine were applied on each sample at a rate of 1 mm min-1. Load versus displacement graphs were plotted for all tests. Yield point and stiffness were measured for each sample.

Results:

For yield point, there is no significant difference between cemented or cementless resurfacing (4169 ± 1420 N vs. 3789 ± 1461 N; P = 0.434). However, the high density heads provide a significantly higher yield point than low density heads (4749 ± 1145 N vs. 3208 ± 1287 N; P = 0.01).

Discussion: Bone density plays an important role in resurfacing hip arthroplasty. Higher bone density will reduce the incidence of fractures comparing with lower density. Therefore, resurfacing THR for the older patients and those with sub-optimal bone density should be used with caution. Consequently, it is suggested that a bone density scan should be routinely applied for those patients who are considered for resurfacing hip replacement. There is no difference between the cemented and cementless fixation in reducing femoral head failure, though cement will increase the stiffness of the bone. The study suggests that cementless resurfacing hip could be an alternative design with its clinical advantages of long-term osseointegration if implant is coated with bio-active materials.

Introduction: To investigate the head/neck interface of total hip replacements and to see whether the use of small spigots (minispigots) results in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this.

Methods: In the total hip replacement combinations the heads were made of cobalt-chrome (CoCr) and the stems of titanium alloy (Ti). Firstly wear and corrosion of minisigots were compared with standard spigots (Test 1) and secondly, these minispigots were compared with another minispigot with a smoother taper surface finish (Test 2). The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. The specimens surface parameters and profiles were measured before & after the test. Electrochemical static corrosion tests were carried out on the rough & smooth minispigots from Test 2 where the current was measured with constant potential under loaded and non-loaded conditions. A cyclical sinusoidal load of 1500-200 Newtons for 1000 cycles at ~1 Hz was used. Pitting tests measured the current while increasing and then decreasing the potential of non-loaded and loaded specimens. Two newly manufactured rough and smooth minispigots were subjected to the same electrochemical corrosion tests.

Results: In Test 1 the results demonstrated that pre-test the surfaces of the female tapers were similar for all heads. Post-testing the Ra values on the female tapers had become greater for the minispigots compared with standard spigots. An abrupt change was noted on the surface profile of the female taper where it was in contact with the male Ti taper, indicating the the CoCr head had corroded. The Ti male tapers were unchanged. Scanning electron microscopy showed that the coarser profile in the corroded region of the CoCr was similar to the profile on the Ti male taper. Pitting corrosion was evident in the grooves on the CoCr. In Test 2 the smooth spigots were not affected, but in the rough minispigots, Ra values had increased in the female tapers. Static corrosion tests showed evidence of fretting in the rough but not the smooth minispigots. When comparing new rough & smooth minispigots, static corrosion testing with clyclical loading showed that for minispigots with a rough finish the current fluctuated with each cycle. Pitting scans showed a greater hysteresis with the rough minispigot compared with the smooth minispigot indicating potentially greater corrosion in the former.

Conclusion: The cobalt-chrome/titanium alloy combinations where the surface finish on the male taper was coarse, corrosion was increased in minispigots compared with standard spigots. This was due to the smaller area of contact of the minispigot at the interface. This corrosion appears to be mediated through the mechanism of fretting corrosion. Surface finish was crucial and corrosion of the minispigot was reduced if the surface finish was smooth. Manufacturers should investigate the effect of surface finish on the corrosion of their tapers particularly where cobalt-chrome/titanium alloy combinations are used.

Here we present the results of functional outcome of 531 patients (aged from 27.6 to 88.7, mean 62.6) who have had the Trilogy (Zimmer; Warsaw IN, USA) acetabular shell implanted for 5 years or longer. All patients operated at our unit between 20/1/1992 and 31/3/2004 were included, looking at both Primary (431) and Revision (100) hip arthroplasties. All surgery was performed by the senior surgeon using the Trilogy shell and liners. The Trilogy acetabular shell was used with either an ultra-high molecular weight polyethylene liner or ceramic liner, along with a wide variety of femoral stems, mainly: Harris Pre-coat stem (183 patients, Zimmer), Versys cemented stem (102 pts, Zimmer), CADCAM (140 pts, Stanmore), and HAC Furlong (96 pts, JRI). There were a variety of other stems, including Exeter and Pro-femur. 48 patients had revision of socket only.

Functional outcome was assessed by three questionnaires: the Oxford Hip Questionnaire (12 best function-60 worst), the Harris Hip Score (100 best to 0 worst), and the WOMAC Hip Score (0 best-96 worst).

Patients filled in these questionnaires at every postoperative follow-up clinic. These were compared with the pre-operative scores obtained from questionnaires which the patients completed retrospectively. Mean follow up questionnaire times were 76.5 months postoperatively for primary arthroplasties, and 70.6 months for the revision arthroplasties.

For primary arthroplasty mean scores improved from 40.8 pre-operatively to 16.4 post-operatively (Oxford), 43.9 to 92.9 (Harris), and 51.8 to 9.4 (WOMAC) (all p< 0.05). For revision arthroplasty mean scores improved from 39.1, 41.7, and 49.3 pre-operatively to 19.6, 88.0, and 12.5 (all p< 0.05).

No patients required re-operation for loosening, one patient dislocated at day 5.

We can conclude that the Trilogy acetabular component is a versatile acetabular implant which can be used with a wide range of femoral components, both in primary and revision Total Hip Arthroplasty, with successful functional outcome scores greater than 5 years after implantation.

Aims: To investigate whether the use of mini-spigots result in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this. Methods: The heads were cobalt chrome and the stems titanium alloy. Firstly wear and corrosion of standard spigots were compared with mini-spigots and secondly, these mini-spigots with another mini-spigot with a smoother surface finish. The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. Then samples were sectioned and the surface parameters measured and interfaces investigated using scanning electron microscopy. Static corrosion tests were used under loaded and non-loaded conditions and pitting tests for non-loaded samples. Results: Pre-experimentation the surfaces of the female tapers were similar for all heads. At the end of the first test the surface parameters on the female tapers had become significantly greater (p=0.034) for the mini-spigots compared with standard spigots and an abrupt change noted on the surface profile of the female taper where it contacted the male taper, indicating that the cobalt chrome head had corroded. Scanning electron microscopy showed that the coarser profile in the corroded region of the cobalt chrome head was similar to the profile on the titanium stem taper. Pitting corrosion was evident in the grooves on the cobalt chrome. The smooth mini-spigots were less affected. Conclusions: In cobalt chrome- titanium alloy combinations where the surface finish on the taper is coarse, corrosion is increased on a mini spigot compared with standard spigot. Surface finish is crucial and corrosion of the mini spigot is reduced if the surface finish is smooth.

We present a case report of postoperative pain following THR, which was initially diagnosed as infection. The salutary message is that the correct diagnosis was a secondary tumour.

A fifty three year old man had a primary right total hip replacement for osteoarthritis, using an uncemented CAD CAM (computer aided design, computer aided manufacture) prosthesis with a Trilogy cup. Postoperatively he recovered uneventfully, with a normal range of movement and good function; there were no radiographic abnormalities noted at the time. Two years after operation, he developed pain in the right thigh. His doctor referred him for investigation of his back, which was normal. He was then seen by an orthopaedic surgeon who diagnosed infection, based on an X-ray that revealed a destructive lesion of the upper femur. He was referred back to the senior author, who felt that the X-ray was more suggestive of tumour than infection; further investigation, with MRI and ultrasound confirmed the presence of a tumour; isotope bone scanning revealed it to be solitary. A needle biopsy showed follicular thyroid tumour to be present; this was confirmed by immunohistochemistry. His past medical history included a history of hemithyroidectomy eight years prior to the hip replacement – this was for what was believed to be a benign thyroid nodule. CT of his chest revealed multiple lung metastases.

Review of the X-ray taken six months post-operatively suggests, in retrospect, that the destructive process had already begun. He has been treated with a total thyroidectomy and radiotherapy to the right hip with encouraging early results. He is also having chemotherapy for the pulmonary metastases. Thyroid tumours metastasise by blood and commonly occur in bone; the proximal femur is a frequent site for metastasis. It is likely that the occurrence is coincidental.

Intra-operative infiltration of local anaesthetic into peri-operative tissue has become part of the protocol of many units worldwide. It is claimed that this reduces post operative pain and improves the speed of mobilisation thereby improving the comfort of the patient and decreasing the hospital stay.

In order to test the validity of this concept we conducted a prospective randomised controlled clinical trial of 100 patients undergoing primary total hip arthroplasty or hip resurfacing. All procedures were performed by one surgeon (Miss Muirhead-Allwood) using a posterior-lateral approach. Patients were randomised to receive 30ml of 0.5% Marcaine injected under direct vision at the time of closure or no injection (placebo).

Post-operatively patients in both groups received a standardised regime of intravenous infusion of diclofenac for 48 hours and ‘rescue’ intramuscular injections of morphine on demand.

Patients’ pain levels post-operatively were independently recorded using both a verbal rating score (VRS) and a visual analogue scale (VAS) at regular intervals for the first five post-operative days. Periodicity of requests for opiate analgesia was documented. Time taken to reach mobility ‘goals’ were also documented as was time taken to discharge and patient satisfaction with the whole process.

Our results show no significant difference in the two groups previously defined and we suggest that routine use of intracapsular local anaesthetic is not indicated in primary hip replacements and surface replacements provided an adequate post-operative pain regime is already in use.

We report a surgical technique for arthroplasty of the deformed hip after poliomyelitis.

A fifty three year old man presented to our unit with a long-standing history of hip problems since contracting poliomyelitis at the age of two. Unusually, both of his hips were affected. He had been operated on twice for his right hip. This had left him with a deformed upper femur with significant shortening. The right hip was sub-luxed on presentation; this was due to a markedly dysplastic acetabulum.

The polio and subluxation meant his muscles were weak and stretched. Like other authors, we were keen to achieve a stable hip. The senior author felt that a fully constrained socket would carry the following disadvantages:

Reduced range of movement.

An alternative approach, using a large diameter unconstrained metal on metal articulation, was employed; stability was achieved with the large head and the relatively small socket still preserved bone stock. The components chosen were a 52mm MMT, Birmingham acetabular resurfacing prosthetic, articulating with a 46mm chromium cobalt head. A fluted stem CAD CAM (computer aided design, computer aided manufacture) femoral prosthesis was used, as he needed to fully weight-bear from the outset, because of the weakness in his left leg.

He has a good, pain-free range of movement. This represents a novel solution for arthroplasty in hips surrounded by weakened musculature. It avoids dramatic limitation of movement whilst minimising the bone stock loss and risk of dislocation. The patient is delighted with the medium term results.