Aims

Accurate placement of the acetabular component during total hip arthroplasty (THA) is an important factor in the success of the procedure. However, the reported accuracy varies greatly and is dependent upon whether free hand or navigated techniques are used. The aim of this study was to assess the accuracy of an instrument system that incorporates 3D printed, patient-specific guides designed to optimise the placement of the acetabular component.

Introduction

Appropriate acetabular cup orientation is an important factor in reducing instability and maximising the performance of the bearing after Total Hip Arthroplasty (THA). However, postoperative analyses of two large cohorts in the US have shown that more than half of cups are malorientated. In addition, there is no consensus as to what inclination and anteversion angles should be targeted, with contemporary literature suggesting that the orientation should be customised for each individual patient.

The aim of this study was to measure the accuracy of a novel patient specific instrumentation system in a consecutive series of 22 acetabular cups, each with a customised orientation.

Introduction

There is increasing interest in the functional positions the pelvis assumes with activities of daily living and its effect on acetabular cup orientation. A number of systems are commercially available to assess these movements, and attempt to position the acetabular component of a total hip replacement in a patient specific safe zone.

However, these functional positions are assessed pre operatively when the patient still has the arthritis which may affect the range of movement of the hips, and thus affect the functional position of the pelvis. Obviously the planned acetabular position must take into account any changes in the functional movement of the pelvis as a result of the surgery.

Ishida et al showed that a pelvis with more than a 10° anterior tilt when standing can be expected to correct towards neutral by 12 months post-surgery. However many of Ishida's cases were dysplastic. Hip arthritis in the Caucasian population is far less likely due to dysplasia and this may affect these pelvic tilt changes post-operatively.

Introduction

The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures.

Aim

The purpose of the study was to assess the safety of Intra-articular steroid hip injections (IASHI), prior to ipsilateral total hip arthroplasty (THA).

Thermal damage to bone related to the exothermic polymerisation of bone cement (PMMA) remains a concern. A series of studies were conducted to examine PMMA bone interface during cemented arthroplasty.

In vitro and in vivo temperature distributions were performed in the laboratory and human and animal surgery. In vivo (10 patients) measurements of cement temperature during cementing of BHR femoral prosthesis using thermocouples. Intra-operative measurement of cement temperature in BHR in the presence of femoral head cysts was examined in patients. The BHR femoral heads were sectioned to assess cement mantle as well as position of thermocouples. An additional study was performed in sheep with PMMA implanted into cancellous defects. Thermocouples were used to monitor temperature in the cement as well as adjacent bone. Histology and CT was used to assess any thermal damage.

The exothermic reaction of PMMA during polymerization does indeed result in an increase in temperature at the interface with bone. The in vivo study recorded a maximum temperature of 49.12C for approximately three minutes in the cancellous bone underneath the BHR prosthesis. This exposure is probably not sufficient to cause significant injury to the femoral head. The maximum temperature of the cement on the surface of the bone was 54.12C, whereas the maximum recorded in the cement in the mixing bowl was 110.2C.

In the presence of artificial cysts within the bone, however, temperatures generated within the larger cysts, and even at the bone-cement interface of these cysts, reached levels greater than those previously shown to be harmful to bone. This occurred in one case even in the 1 cc cyst.

Routine histology revealed a fibrous layer at the cement bone interface in the sheep study. Fluorescent microscopy demonstrated bone label uptake adjacent to the defect site. Histology did not reveal thermal necrosis in the defects in terms of bony necrosis. CT data was used to measure the amount of PMMA placed into each defect. This analysis revealed a range of volumes that did not seem to influence the histology.

The heat of cement polymerisation in resurfacing as performed in our study is not sufficient to cause necrosis. This may reflect the ability of the body to rapidly conduct heat away by acting as a heat sink. The temperature-conducting properties of the metal prosthesis are also likely to be important.

Introduction: Osteomyelitis remains a rare diagnosis and a difficult one to make. Acute osteomyelitis in the context of sickle cell disease remains the subject of some controversy, particularly with regard to aetiology. It is known that Salmonella species are more commonly the cause of acute bone infection in sickle cell patients than in patients with normal red blood cell morphology, but there has long been an argument as to whether Staphylococcus Aureus is in fact still the most common bacterial cause overall in this patient group, as it is in the population overall. We present a consecutive case series of 12 cases of acute osteomyelitis in paediatric patients in East London over the last twenty years.

Materials and Methods: Retrospective review of 12 consecutive cases. Medical Notes along with microbiology records and radiographic results were cross referenced with a paediatric sickle cell data base held by the haematology department.

Results: 10 of the 12cases had an organism isolated from either blood or bone culture(s). Salmonella spp in cases, S. Aureus in 2 cases and Pseudomonas in the remaining case

Discussion: The question of causative organism is complicated by the fact that most case series’ have bracketed adults and children together, and that conflicting conclusions have resulted from quite small, usually retrospective studies at different times and from different parts of the world – Nigeria, Saudi Arabia and the United States of America. It appears that endemicity is a result of many factors including age; race and socioeconomic factors all play a role.

Conclusion: These results reveal that in our paediatric sickle cell population, Salmonella infection occurs ore commonly than Staphylococcus.

Introduction: Prevalence of femoral neck fracture in resurfacing hip arthroplasty continues to question if failure is technique-related or due to the inherent bone quality. This study aimed to correlate cement penetration profile during resurfacing hip with inherent bone density. The hypothesis is that osteoporotic bone is unable to support the prosthesis leading to fatigue failure.

Methods: Fifteen patients scheduled for total hip replacement (THR) were recruited to undergo resurfacing arthroplasty prior to THR. Each patient was implanted with a resurfacing femoral component (BHR, Smith & Nephew, Memphis, TN). Antibiotic simplex cement was inserted one minute after mixing at 18°C to fill 10% of the femoral component volume. The femoral head-implant section was removed and kept in buffered formalin. The patients then proceeded with standard THR. The femoral head-cement-prosthesis section was separated using electrical discharge (ED) machining technique and CT-scanned. The depth and volume of cement penetration were measured from the CT scans and correlated with femoral neck bone densities.

Results: Cement penetration was compared for three groups of bone density: normal, osteopenic, osteoporotic. Average cement thickness were found to be 0.36 ± 0.16mm (proximal), 0.28 ± 0.11 mm (centre) and 0.12 ± 0.05 mm. During hip resurfacing, cement is forced into the porous structure, e.g. the trabeculae and airspaces when the femoral component is fixed onto the head of the femur. In normal bone, the trabeculae is dense and air spaces occupy a small volume of the bone. Greater cement penetration was expected in osteopenic and osteoporotic bones. However, no significant difference was found between cement thickness and volume against inherent patient bone density (p> 0.05). High viscosity of the cement may have prevented more cement to penetrate the bone. While the exterior cortex of the femoral head is strengthened by a cement layer, the interior structure of the femoral neck is still susceptible to fracture at high loads. In addition, increased bone necrosis due to the exothermic reaction during cement fixation may predispose patients to fracture.

Discussion: Resurfacing hip replacement is a viable technique if the fracture risk can be reduced by gaining the best possible cement penetration. This would provide continuous cement stiffness with the bone.

The aim was to compare the initial pull out strengths of various interference screw devices used for tibial fixation of hamstring grafts and the effect of concentric or eccentric screw position.

Quadrupled tendon grafts were harvested from freshly killed sheep. The grafts were then prepared and fixed in the distal femur using various devices (Intrafix, RCI screw, Wedge screw +/− transfix pin, screw and post) in both concentric and eccentric positions. A single load to failure test was then performed.

The highest pull out strength was with the Intrafix device inserted concentrically (mean 941N). This was significantly higher than the wedge screw inserted concentrically (737N) (p=0.015). This in turn had significantly greater initial pull out strength than the wedge eccentric with post or pin (p=0.03) and the RCI screw (464N) (p=0.00036).

In this sheep model the Intrafix device inserted concentrically had a significantly greater initial pull-out strength than the other interference screws tested. Concentric positioning of an interference screw gave significantly greater initial pullout strength of a quadruple hamstring graft than eccentric positioning. Addition of a cross pin or post made no difference to initial pullout strength.

We compared initial fixation strength of two commonly used tibial side hamstring ACL reconstruction fixation implants – the RCI interference screw and the Intrafix device.

Using a sheep model 36 hamstring grafts were prepared and implanted into the distal femoral metaphyseal bone using either a RCI screw or an Intrafix device. They were then pulled out until failure using an Instron Materials Testing Machine. Maximum strength of graft fixation and mode of failure were recorded.

The average strength of the graft was 48kg using the RCI screw and 90 kg using the Intrafix device. This difference was statistically significant. The maximum pull-out strength was 91kg for the RCI screw and 130 kg for the Intrafix device. The most common mode of failure in the RCI screw fixation was graft shredding on the screw and whole graft pullout whereas in the Intrafix device it was intratendinous failure.

The Intrafix device demonstrated a clear strength advantage over the RCI screw with regard to initial fixation strength. The Intrafix device may reduce tibial side graft creep which is a problem with hamstring ACL reconstruction.

The aim of this surgery was to determine current practice amongst orthopaedic surgeons in New Zealand with regard to Anterior Cruciate Ligament Reconstruction.

All current members of the NZOA were sent a questionnaire on the numbers and proportions of grafts performed, methods of fixation, operative technique and return to sport.

One hundred and ten of 140 questionnaires were returned completed. Ninety two orthopaedic surgeons were performing ACL reconstructions. Eight per cent performed patellar tendon grafts in preference to hamstring grafts, whereas 16% preferred hamstring over patellar tendon grafts. Almost 2000 patellar tendon grafts at an average of just over 20 per surgeon are performed each year compared to just over 500 hamstring grafts at an average of just over 15 per surgeon. Metal interference screws were the most common fixation device in patellar tendon and hamstring grafts.

Patellar tendon grafts are the most common grafts used for ACL reconstruction with 80 % of those surveyed preferring to use patellar tendon over hamstring grafts. Metal interference screws were the most common fixation device. There is reasonable consensus regarding return to activity and sport.