Introduction and Objective

Medial Knee Osteoarthritis (MKO) is associated with abnormal knee varism, this resulting in altered locomotion and abnormal loading at tibio-femoral condylar contacts. To prevent end-stage MKO, medial compartment decompression is selectively considered and, when required, executed via High Tibial Osteotomy (HTO). This is expected to restore normal knee alignment, load distribution and locomotion. In biomechanics, HTO efficacy may be investigated by a thorough analysis of the ground reaction forces (GRF), whose orientation with respect to patient-specific knee morphology should reflect knee misalignment. Although multi-instrumental assessments are feasible, a customized combination of medical imaging and gait analysis (GA), including GRF data, rarely is considered. The aim of this study was to report an original methodology merging Computed-Tomography (CT) with GA and GFR data in order to depict a realistic patient-specific representation of the knee loading status during motion before and after HTO.

Hypoxic Inducible Factor and Hypoxic mimicking agents (HMA) trigger the initiation and promotion of angiogenic-osteogenic cascade events. However, there has been paucity of studies investigating how HIF could be over expressed under chronic hypoxic conditions akin to that seen in sickle cell disease patients to help form a template for tackling the matter of macrocellular avascular necrosis. Angiogenesis and osteogenesis are tightly coupled during bone development and regeneration, and the hypoxia-inducible factor-1 alpha (HIF-1) pathway has been identified as a key component in this process studies have shown. There are still no established experimental models showing how this knowledge can be used for the evaluation of bone implant integration and suggest ways of improving osseointegration in sickle cell disease patients with hip arthroplasty and thereby prevent increased implant loosening. The aim of this study is to help develop an in vitro experimental model which would mimic the in vivo pathologic state in the bone marrow of sickle cell disease patients. It also seeks to establish if the hypoxic inducible factor (HIF) could be over expressed in vitro and thus enhancing osseointegration. MG63 osteoblastic cells were cultured under normoxia and hypoxic conditions (20%; and 1% oxygen saturation) for 48 and 72 hours. Cobalt chloride was introduced to the samples in order to mimic true hypoxia. Cells cultured under normoxic conditions and without cobalt chloride was used as the control in this study. The expression of the hypoxic inducible factor was assessed using the reverse transcriptase qualitative polymerase chain reaction (RT-qPCR). There was increased expression of HIF1-alpha at 72hours as compared to 48hours under the various conditions. The level of expression of HIF increased from 48hrs (mean rank= 4.60) to 72hrs (mean rank =5.60) but this difference was not statistically significant, X2(1) = 0.24, p =0.625. The mean rank fold change of HIF in hypoxic samples decreased compared to the normoxic samples but this difference was not statistically significant, X2(1) = 0.54, p= 0.462. Therefore, the expression of HIF is only increased with prolonged hypoxia as seen in the 72hours samples. The expression of HIF increased in samples with CoCl2 (mean rank=5.17), compared with samples without CoCl2 (mean rank 4.67), however this was not statistically significant, X2(1) = 0.067, p=0.796, p value > 0.05. The over expression of HIF was achieved within a few days (72hours) with the introduction of Cobalt Chloride, which is a mimetic for hypoxia similar to the in vivo environment in sickle cell disease patients. This is an in vitro model which could help investigate osseointergation in such pathologic bone conditions.

It is well documented that implant loosening rate in sickle cell disease patients is higher than that seen in patients with hip arthroplasty from other indications. The Hypoxic inducible factor(HIF) - is activated in the microcellular hypoxic environment and this through a cascade of other enzymatic reactions promotes the activity of other factors and further help enhance angiogenesis and osteogenesis. The aim of this study was to investigate and propose a potential model for investigating osseointegration in a hypoxic microcellular environment using osteoblasts(MG63).

Human MG63 osteoblastic cells were cultured under normoxia and hypoxic conditions (20%; and 1% oxygen saturation) for 72 hours under two different condition- with and without cobalt chloride. The samples cultured under normoxic condtions without cobalt chloride acted as control. Using qualitative polymerase chain reaction-(qPCR) - HIF expression was assessed under the above conditions in relation to the control.

The results showed there was significant expression of the HIF 1 alpha protein under hypoxic condition with cobalt chloride in comparison with the control samples- all at 72hours incubation. Mann-Whitney U test was used to deduce level of significance of fold change.(p=0.002; <0.05). This was deemed as being a significant difference in the level of expression of HIF compared to the control.

The results show that the hypoxic inducible factor can be expressed using the above tested

experimental invitro-model with significant results which can be a foundation for further research into improving hip implant prosthesis design to help enhance osseo-integration in sickle cell disease patient with AVN.

Introduction

The THR is the second most successful and cost-effective surgical procedure of all time. Data shows that hip cup failure is a significant problem. The aim of this study is to improve methods of cemented cup fixation through validation experiments and FEA.

Introduction

The majority of primary total hip arthroplasty (THA) procedures performed throughout the world use modular junctions, such as the trunnion-head interface; however, the failure of these press-fit junctions is currently a key issue that may be exacerbated by the use of large diameter heads. Several factors are known to influence the strength of the initial connection, however, the influence of different head sizes has not previously been investigated. The aim of the study was to establish whether the choice of head size influences the initial strength of the trunnion-head connection.

Metal on metal hip resurfacing (MMHR) is a popular procedure for the treatment of osteoarthritis in young patients. Several centres have observed masses, arising from around these devices, we call these inflammatory pseudotumours. They are locally invasive and may cause massive soft tissue destruction. The aim of this study was to determine the incidence and risk factors for pseudotumours that are serious enough to require revision surgery.

In out unit, 1,419 MMHRs were performed between June 1999 and November 2008. All revisions were identified, including all cases revised for pseudotumour. Pseudotumour diagnosis was made by histological examination of samples from revision. A Kaplan-Meier survival analysis was performed, Cox regression analysis was used to estimate the independent effects of different factors.

The revision rate for pseudotumour increased with time and was 4% (95% CI: 2.2% to 5.8%) at eight years. Female gender was a strong risk factor: at eight years the revision rate for pseudotumours in men was 0.5% (95% CI 0% to 1.1%), in women over 40 it was 6% (95% CI 2.3% to 10.1%) and in women under 40 it was 25% (95% CI 7.3% to 42.9%) (p< 0.001). Other factors associated with an increase in revision rate were, small components (p=0.003) and dysplasia (p=0.019), whereas implant type was not (p=0.156).

We recommend that resurfacings are undertaken with caution in women, especially those younger than 40 years of age, but they remain a good option in men. Further work is required to understand the patho-aetiology of pseudotumours so that this severe complication can be avoided.

Introduction Polyethylene wear debris is an important cause of failure in cemented total hip arthroplasty. As a result of the biological response to debris at the bone-cement interface, osteolysis and subsequent failure occurs in both femoral and acetabular components. Most acetabular components and liners are made of ultra high molecular weight polyethylene (UHMWPE). Cross-linking UHMWPE has been shown to significantly reduce abrasive wear in hip simulator studies. The wear rates measured in vitro do not always correlate with the wear rates measured in clinical studies[1]. Some new polyethylenes have shown catastrophic wear in clinical studies despite encouraging hip simulator study results[2]. The aim of this study was to compare the wear of standard UHMWPE to that of cross-linked UHMWPE (Longevity, Zimmer, Warsaw, USA)

Patients and Methods This was a prospective, double blind, randomised control trial. 50 subjects were recruited, all of whom received the cemented CPT stem and uncemented Trilogy liner (Zimmer, UK). Subjects were randomised to receive either a standard Trilogy liner or a Longevity liner at the time of operation. Both liners are identical in appearance. All liners were of a neutral configuration. RSA was used to measure linear wear. This was calculated by measuring the distance between the centre of the femoral head and the centre of the acetabular liner. The preliminary results of the study are presented.

Results Both groups underwent significant wear over two years. The two year linear wear of the cross-linked UHMWPE was 0.3mm (+/− 0.06mm, p< 0.001). The two year linear wear of the standard UHMWPE was 0.39mm (+/− 0.04mm, p< 0.001). No significant difference existed between the two groups (p=0.24). Both cohorts had around 0.15 to 0.2 mm of measured wear per year. Cross-linked UHMWPE therefore underwent less wear than standard UHMWPE at two years, however this difference was not statistically significant.

Discussion This study suggests that Longevity UHMWPE has similar wear properties to standard UHMWPE in the first two years following implantation. This does not correlate with in vitro hip simulator studies of Longevity polyethylene, which show a significantly lower wear rate than standard UHMWPE. It suggests that hip simulator studies may be of little value in predicting in vivo wear rates and that all new types of polyethylene should be evaluated clinically and radiologically prior to general release. Whether both cohorts continue to wear at similar rates will only be revealed through continued observation.

Aim: To compare the kinematic profile of two types of TKRs – a single-axis design Vs a polyradial design, with that of the normal knee.

Methodology: An in-vivo fluoroscopic analysis was carried out as part of a four-armed prospective randomised trial comparing the clinical outcome of two commonly used types of TKRs each with posterior cruciate retaining -CR and sacrificing –CS models. The kinematic profile was obtained by measuring patella tendon angle at specific angles of knee flexion using an established fluoroscopic method whilst the patients performed close and open chain exercises. The data was compared with the kinematic profile of the normal knee.

Results: Fifty-five patients who had undergone TKR at least one year prior, were invited to take part in this ethically approved study. They were matched for age and gender and had a similar clinical outcome.

The kinematic profile of single axis design TKR was closer to normal especially near extension. During mid-flexion, abnormal anterior femoral translation was noticed with the polyradial design. No significant difference was noted between CR and CS designs.

Conclusions: Kinematics after a TKR differed from that of a normal knee. Reproducible differences were found between the two designs, which may predict mode of failure and longevity.