Metallic contacts in hip replacements are susceptible to wear and corrosion processes which lead to the release of particles and metal ions. Adverse local tissue reactions (ALTRs) and systemic manifestations to solid and soluble debris can be debilitating for the patients. It is believed that particles originating from CoCrMo taper junctions trigger more severe body reactions compared to debris from MoM hip bearings. The body's reaction is highly dependent on particle characteristics, such as size, morphology, composition and aggregation state, which can reflect the specific wear and corrosion conditions at the site of release.

Here we proposed to investigate wear and corrosion flakes collected from around CoCrMo tapers at the time of revision. The particles were initially characterised with scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). This revealed the microstructure of the corrosion products, which appeared to be made of smaller metallic aggregates, entrapped in a biological matrix. The in depth characterisation of the particles released from the organo-metallic composite, was performed with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), both fitted with EDX. The investigation revealed clusters and individual nanoparticles, as small as 3 nm, which represent the building blocks of the large corrosion flakes, reported and characterised in the past mainly with low resolution microscopy techniques. The majority of the particles consisted of Cr and O, potentially in the form of chromium oxides, with little evidence of Co and Mo. Particles size distribution (PSD) provided by STEM and TEM characterisation showed statistically different results. The STEM technique was able to resolve tiny particles found in close proximity and provided a PSD shift towards the smaller end of the size range.

The study is the first to show microscopy evidence of Cr rich nanoparticles (3–60 nm) released in vivo from the modular taper interface, which can have important health implications caused by their increased potential to disseminate and corrode within the body.

Using a femoral head from one manufacturer on the stem of another manufacturer poses the risk that the taper interface between the components do not contact correctly and the performance of the joint will be impaired. The cohorts in this study are a combination of modular Birmingham Hip Resurfacing (BHR) and Adept femoral heads on CPT stems. The study reviews the geometry of the taper interfaces to establish if the taper clearance angles was outside of the normal range for other taper interfaces. In addition the rates of material loss from the bearings and taper and a ranking of the stem damage were reviewed to determine if the levels of loss were above that seen for other similar joints.

The material loss analysis demonstrated that the rates or levels of loss from the bearings, taper and stem are no different to levels published for manufacturer matched joints and in many cases are lower. The results demonstrate that the taper clearance angles for the mixed manufacturer joints (BHR-CPT: 0.067 to −0.116, Adept-CPT: 0.101 to −0.056) were within the range of other studies and manufacturer matched clearances (0.134 to −0.149).

Using components from different manufacturers has not in this instance increased the level of material loss from the joints, when compared to other similar manufacturer matched joints.

Background

Large diameter chrome cobalt modular heads in hip replacement surgery have caused one of the biggest challenges to face orthopaedic surgeons, manufacturers and regulators in a generation. Increasing numbers of retrieved implants offer the opportunity to look in detail at the modes of failure of these devices.

Introduction

Metal on metal hip arthroplasty continues to be controversial. Emerging evidence suggests that there are multiple modes of failure, and that the results of revision surgery are influenced by host and implant factors.

Introduction:

Cemented femoral components have been used in hip replacement surgery since its inception. For many patients this works well, but recent retrieval studies^1–4 and more fundamental studies^{5, 6} have highlighted the issues of damage and material loss from the both matt and polished cemented stems.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal articulating surface wear has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as quantitative assessment of wear volume. This study aimed to assess and compare qualitatively tapers from small and large diameter MOMTHR's. Tapers from 3 retrieval groups were analysed. Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Gp 3 (control): 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. RedLux profiling of tapers produced a taper angle and 3D surface maps. The taper angles were compared to those obtained using CMM measurements. There was no difference between groups in mean 12/14 taper angles or bearing surface volumetric and linear wear. Only LHMOMs showed transfer of pattern from stem trunnion to head taper, with clear demarcation of contact and damaged areas.3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in the form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from well functioning small diameter, with poorly functioning LHMOMTHR's using the above technique.

Pseudotumour formation is being reported with increasing frequency in failing metal-on-metal hip resurfacings and replacements. This mode of failure complication has also been reported with metal-on-polyethylene bearing bearings when it is usually associated with evidence of surface corrosion and no apparent wear at the head–neck taper.

We present a case with evidence of taper wear and damage secondary to corrosion in an uncemented total hip replacement with a metal on polyethylene articulation (TMZF (Titanium, Molybdenum, Zirconium and Ferrous) Accolade® stem, Trident® HA coated acetabular shell, Low Friction Ion Treatment (LFIT™) Cobalt-Chrome anatomic head (40 mm), X3® polyethylene liner)

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion/taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from small diameter with LHMOMTHR's. 3 groups of retrieval tapers were analysed (Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Group 3: 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. Both bearing surfaces and head tapers were measured for wear using the Redlux profiling non contact measurement system. Measurements included taper angle and 3D surface maps. Taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion. 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group alone. Discussion: Differences in appearance of the taper surface between LHMOMTHRs and MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities.

Osteoporosis (OP) results in a reduction in the mechanical competence of the bone tissue of the sufferers. In skeletal sites such as the proximal femur and the vertebrae, OP manifests itself in low trauma fragility fractures which are debilitating for the patient. The relationships between the compressive strength of cancellous tissue and its apparent density are well established in studies of the past. Recently the authors have presented a method able to assess the fracture toughness properties of cancellous bone (1), a challenging cellular material which can exhibit large elasto-plastic deformations. The in-vitro measurement of fracture toughness alongside the customary compressive strength can provide a comprehensive assessment of the mechanical capacity of cancellous bone, which will reflect closer its ability to resist crack initiation. The aims of the present study were: (1) to examine whether the observed fracture toughness deterioration can also be detected by non-invasive quantitative ultrasound (QUS); and (2) to provide rational evidence for the well proven ability of QUS to predict directly ‘risk of fracture’. 20 femoral heads were obtained from donors undergoing emergency surgery for a fractured neck of femur. QUS investigations of the calcaneus, proximal phalanx and distal radius were undertaken within 72 hours of surgery. 128 fracture toughness samples and 20 compression cores were manufactured and tested. Two clinical QUS systems were used to obtain in-vivo scan data and then directly compared those to the density, porosity and the fracture mechanics of tissue extracted from the same individuals. The results demonstrated not only that there was a significant link between in-vivo determined QUS values for the calcaneus and finger to the density of the density of the femoral head; but that there was also a significant link between the QUS results from the calcaneus and the fracture toughness of the cancellous bone from the femoral head. These results point towards a systemic effect of osteoporosis which affects similarly different parts of the skeleton and supports the use of clinical QUS systems as a diagnostic tool for the prediction of fracture risk.

The Oxford medial unicompartmental knee replacement has been shown to provide good long-tern results in numerous studies with survivorship at 10 years ranging from 82% to 100%. This prospective study describes the survival of 265 Oxford unicompartmental knee replacements implanted in one centre from 1995-2009. 8 were lost to follow up. 40 of the 265 knees were revised. For operation performed from1995-1999 the risk of revision at 5 years was 10%, operations from 2000-2004 the risk of revision was 15% and from 2005-2009 the risk of revision at 5 years was 36%.

This study demonstrates that since 2005 there has been a significant increase in early failure of the Oxford unicompartmental knee at this institution and discusses the possible reasons for this.

Aim

To compare the results of total knee replacement in a consecutive series of morbidly obese patients (body mass index (BMI) > 40 kg/m²) with a matched group of non-obese (BMI< 30 kg/m²) patients.

Introduction To assess five-year survivorship and clinical outcome following unicompartmental knee replacement (UKR) and total knee replacement (TKR) in pre-operatively matched patient groups.

Methods From a prospective database of over 600 patients undergoing knee replacement for osteoarthritis, 70 primary Oxford UKRs (62 patients) were matched pre-operatively with 70 primary PFC TKRs (68 patients) for age, sex, body mass index, knee range of movement and Knee Society Score (KSS). The two groups were assessed at six, eighteen, thirty-six and sixty months following knee replacement and compared for survivorship of the prosthesis (with failure defined as revision for any reason or ‘worst-case’ assuming all patients lost to follow up are revised), post-operative ROM achieved and clinical outcome based on the KSS (reported as separate knee and function score).

Results Three (5 percent) patients in the UKR group and two (3 percent) in the TKR group were unavailable for follow-up at five years. Five-year survivorship based on revision for any reason was 90 percent (95 percent Confidence Interval (CI): 82 to 98) for UKR and 100 percent (95 percent CI: 100 to 100) for TKR (log rank test: p=0.009). The ‘worst-case’ five-year survivorship (assuming all patients lost to follow up are revised) was 85 percent (95 percent CI: 76 to 94) for UKR and 97 percent (95 percent CI: 93 to 100) for TKR (log rank test: p=0.02). The mean post-operative ROM achieved was 105.3 degrees following UKR and 98.3 degrees following TKR (difference 7.0 (95 percent CI 3.3 to 10.6), p< 0.001). There was no difference in the KSS between the two groups for the knee score (difference 0.1 (95 percent CI: −4.3 to 4.5), p=0.9) and function score (difference 2.6 (95 percent CI: −1.7 to 6.9), p=0.2).

Conclusion In comparable patients with osteoarthritis of the knee, survivorship remains superior for TKR at five years. The ROM achieved is greater for UKR but there is no difference in the overall clinical outcome following UKR or TKR. We believe that UKR should only be performed in carefully selected cases because mid-term clinical outcome is similar following UKR or TKR and the complication rate may be higher for UKR.

Aim To compare clinical outcome and complication rates in obese and non-obese patients five years following primary Total Knee Replacement (TKR) for osteoarthritis.

Methods 328 primary TKRs (283 patients) performed between 1995–1999 at a single institution, were followed up prospectively at intervals of 6, 18, 36 and 60 months following surgery and the clinical outcome based on the Knee Society Clinical rating system (subdivided into a Knee Score (KS) and Function score (FS)) recorded at each follow-up interval. The following complications were also recorded: peri-operative mortality, superficial wound infection, deep wound infection, deep vein thrombosis, and revision rate. Three separate comparisons were undertaken by subdividing the study sample into two sub-groups: (1) Group A comprised two subgroups based on body mass index (BMI) – Non-obese (BMI 15–30, 181 TKRs) or Obese (BMI> 30, 147 TKRs). (2) Group B comprised only female patients divided into two sub-groups based on BMI – ‘Non-obese females’ (BMI 15–30, 84 TKRs) or Obese females (BMI> 30, 87 TKRs). (3) Group C comprised two sub-groups based on body weight alone – weight < 100kg (300 TKRs) or weight > 100kg (28 TKRs). A repeated measures split-plot analysis of variance (SPANOVA) was used to evaluate the difference in the clinical outcome at five years between the sub-groups in Group A, B and C. The complication rates were also compared.

Results There was no significant difference in the KS at five years between sub-groups in Group A (p=0.2), B (p=0.2) or C (p=0.3). There was a statistically significant difference in the FS between the subgroups in Group A (p=0.01) and B (p=0.02) but the effect size (relative magnitude of the difference between means) was small (partial eta squared = 0.02 and 0.03, for Group A and B respectively). There was no significant difference in the FS between sub-groups in Group C (p=0.5). There was no significant difference in the complication rate between the sub-groups in Group A, B or C (p> 0.2 for all complications).

Conclusion Obesity does not influence clinical outcome, peri-operative mortality and complication rates five years following TKR. Further studies are required to determine the long-term success of TKR in obese patients.

Introduction and Aims: Venous Thromboembolism is a common complication following a hip replacement. Recently the pulmonary embolism prevention study was published. It reported that aspirin decreased the fatal pulmonary embolism rate in patients admitted with a fracture neck of femur. In addition, new products (synthetic factor X inhibitor-Fondaparinux, and a direct thrombin inhibiter-Desirudin) have been reported to be more effective than low molecular weight heparin in preventing asymptomatic deep vein thrombosis. We felt it was important to repeat a survey, done in 1997, on the use of thromboembolism prophylaxis among British Orthopaedic Surgeons.

Method: A single page questionnaire was sent out to all 1308 consultants – orthopaedic surgeons who were members of the British Orthopaedic Association. Those who did not respond were sent a reminder letter.

Results: We achieved a 72% response rate. All surgeons use some form of prophylaxis. Eighty-five percent of surgeons use pharmacological prophylaxis. Low molecular weight heparin is used by 55% of surgeons. Twenty percent of surgeons use aspirin as their only form of pharmacological prophylaxis. Less than 1% (five consultants) use early mobilisation alone and nearly 2% (13 consultants) use graded stockings and early mobilisation as their only form of prophylaxis. Seventy-four percent of surgeons have a unit policy. Thirty percent have changed their regime in the last three years.

Conclusion: The majority of British orthopaedic surgeons still use pharmacological thromboprophylaxis. There has been a significant increase in the use of Aspirin, from 5% to 30%. Aspirin is often combined with a mechanical prophylaxis. This has led to an increase in the use of intermittent calf compression (3% to 22%), and foot pumps (12% to 19%). Low molecular weight heparin use has fallen by 10%.

Venous thrombo-embolism is a common complication following hip replacement. The recently-published pulmonary embolism prevention study reported that aspirin decreased the fatal pulmonary embolism rate in patients with femoral neck fractures. In addition, new products (synthetic factor X-inhibitor Fondaparinux and direct thrombin-inhibiter Desirudin) have been reported to be more effective than low-molecular-weight heparin in preventing asymptomatic DVT. We thought it important to update the 1997 survey on thrombo-embolism prophylaxis by British Orthopaedic Surgeons.

A single page questionnaire was sent to 1308 members of the British Orthopaedic Association who are consultant orthopaedic surgeons. Those who did not respond received a reminder. We had a 72% response rate.

All surgeons use some form of prophylaxis, with 85% using pharmacological agents. Low-molecular-weight heparin is used by 55% of surgeons, while 20% use only aspirin. Fewer than 1% (five consultants) use early mobilisation and nearly 2% (13 consultants) use graded stockings and early mobilisation as their only prophylactic measures. Unit policies govern 74% of surgeons. In the last 3 years, 30% have changed their regime.

Most British orthopaedic surgeons still use pharmacological thromboprophylaxis. The use of aspirin has increased from 5% to 30%. Aspirin is often combined with a mechanical prophylactic. The use of intermittent calf compression has increased from 3% to 22% and of foot pumps from 12% to 19%. The use of low-molecular-weight heparin has fallen by 10%.

Introduction and Aims: Several non-comparative studies for uni-compartmental knee replacement (UKR) and total knee replacement (TKR) have been published, but few provide a direct comparison in well-matched patients. The aim of this study was to assess five-year survivorship and the quality of outcome following UKR and TKR in pre-operatively matched patient groups.

Method: From a prospective database of over 600 patients undergoing knee replacement for osteoarthritis, 70 primary medial Oxford UKRs (62 patients) were matched pre-operatively with 70 primary Kinematic TKRs (68 patients) for age, sex, body mass index, active range of movement (ROM) and Knee Society Score (KSS). The two groups were assessed at six, 18, 36 and 60 months following knee replacement and compared for survivorship of the prosthesis (with failure defined as revision for any reason or ‘worst-case’ assuming all patients lost to follow-up are revised), quality of outcome based on the KSS (reported as separate knee and function score) and the ROM achieved.

Results: Three (4%) patients in the UKR group and two (3%) in the TKR group were unavailable for follow-up at five years. Five-year survivorship (Kaplan-Meier methodology) was significantly different for the two groups using revision for any reason as an endpoint – 90% for UKR, 100% for TKR (log-rank test, p=0.01). Assuming all patients lost to follow-up were revised, the ‘worst-case’ five-year survivorship was also significantly different for the two groups – 85% for UKR, 97% for TKR (log-rank test, p=0.02). Analysis of the KSS at six, 18, 36 and 60 months showed no significant difference between the two groups for the knee score (p=0.48) and the function score (p=0.1). The ROM achieved at five years was greater for the UKR group and the difference was statistically significant (UKR: Least square mean 105 degrees, standard error 1.2; TKR: Least square mean 98 degrees, standard error 1.2, p< 0.001).

Conclusion: In comparable patients with osteoarthritis of the knee, survivorship remains superior for TKR at five years. The ROM achieved is greater for UKR, but there is no difference in the overall quality of outcome following UKR or TKR. We believe that UKR should only be performed in carefully selected cases because mid-term functional outcome is similar following UKR or TKR and the complication rate may be higher for UKR.

Venous Thromboembolism is a common complication following a hip replacement. Recently the pulmonary embolism prevention study was published. It reported that aspirin decreased the fatal pulmonary embolism rate in patients admitted with a fracture neck of femur. In addition new products (synthetic factor X inhibitor -Fondaparinux, and a direct thrombin inhibiter-Desirudin) have been reported to be more effective than low molecular weight heparin in preventing asymptomatic deep vein thrombosis. We felt it was important to repeat a survey, done in 1997, on the use thromboembolism prophylaxis among British Orthopaedic Surgeons.

A single page questionnaire was sent out to all 1308 consultants Orthopaedic surgeons who were members of the British Orthopaedic Association. Those who did not respond were sent a reminder letter.

We achieved a 72% response rate. All surgeons use some form of prophylaxis. Eighty five percent of surgeons use pharmacological prophylaxis. Low molecular weight heparin is used by 55% of surgeons. Twenty percent of surgeons use aspirin as their only form of pharmacological prophylaxis. Less than 1% (5 consultants) use early mobilisation alone and nearly 2% (13 consultants) use graded stockings and early mobilisation as their only form of prophylaxis. Seventy four percent of surgeons have a unit policy. Thirty percent have changed their regime in the last 3 years.

The majority of British Orthopaedic surgeons still use pharmacological thromboprophylaxis. There has been a significant increase in the use of Aspirin from 5% to 30%. Aspirin is often combined with a mechanical prophylaxis. This has led to an increase in the use of intermittent calf compression (3% to 22%), and foot pumps (12% to 19%). Low molecular weight heparin use has fallen by 10%.

The majority of British Orthopaedic surgeons still use pharmacological thromboprophylaxis. There has been a significant increase in the use of Aspirin from 5% to 30%. Aspirin is often combined with a mechanical prophylaxis. This has led to an increase in the use of intermittent calf compression (3% to 22%), and foot pumps (12% to 19%). Low molecular weight heparin use has fallen by 10%.