Introduction

The Primoris® femoral stem was designed to preserve bone and maintain normal stress to the proximal femur, thereby minimizing stress-shielding. The implant is anchored in the femoral neck and metaphysis without diaphysial involvement and differs from other neck prothesis by: a) Elliptical shape to fit the inner neck dimensions. b) On top of Ti– porous-coating electrochemically deposited hydroxy apatite (Bonemaster®) c) The surgical technique aims to enhance initial implant stability by compaction of neck and metaphyseal cancellous bone.

Prosthetic joint infection is one of the most challenging complications of joint alloplasty and the diagnosis remains difficult. The aim of the study was to investigate the bacterial flora in surgical samples from 22 prosthetic patients using a panel of culture-independent molecular methods including broad range 16S rRNA gene PCR, cloning, sequencing, phylogeny, quantitative PCR (qPCR), and fluorescence in situ hybridization (FISH). Concomitant samples were cultured by standard methods.

Molecular methods detected presence of bacteria in samples from 12 of 22 patients. Using clone libraries a total of 40 different bacterial species were identified including known pathogens and species not previously described in association with prosthetic joint infections. The predominant species were Propionibacterium acnes and Staphylococcus epidermidis; polymicrobial infections were found in 9 patients. Culture-based methods showed bacterial growth in 8 cases with the predominant species being S. epidermidis. Neither anaerobic bacteria (including P. acnes) nor any of the species not previously described in implant infections were isolated. Additionally, 7 of the 8 culture positive cases were monomicrobial. Overall, the results of culture-based and molecular methods showed concordance in 11 cases (hereof 9 negative by both methods) and discrepancy in 6 cases. In the remaining 5 cases, culture-based methods identified only one species or a group of bacteria (e.g., coagulase negative staphylococci or coryneform rods), while culture-independent molecular methods were able to detect several distinct bacterial species including a species within the group identified by culture. A qPCR assay was developed to assess the abundance of Propionibacterium while S. aureus was quantified by a published S. aureus qPCR assay. These quantifications confirmed the findings from the clone library approach and showed the potential of qPCR for fast detection of bacteria in orthopedic samples. Additionally, both single cells and microcolonies were visualized using FISH and confocal scanning laser microscopy.

In conclusion, the molecular methods detected a more diverse bacterial flora in prosthetic joint infections than revealed by standard culture-based methods, and polymicrobial infections were more frequently observed. The pathogenesis of these microorganisms and their role in implant-associated infections needs to be determined.

Introduction

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

Chordoma is the second most common primary malignant tumor of the spine. These tumors rarely metastasize but are considered malignant and, when present in younger individuals, can be aggressive. In the setting of unresectable primary, recurrent, or metastatic tumors the current armamentarium of adjuvant therapy for this condition is very limited. Recent research, however, has identified potential targets for immunotherapy, including the tumor associate antigens High Molecular Weight Melanoma Associated Antigen (HMW-MAA) and B7H3.

The goal of this investigation was to correlate expression of B7H3 and HMW-MAA in chordoma tumors with disease severity and clinical outcome.

Tissue MicroArrays (TMA) were constructed using an automated arrayer to include 70 conventional chordoma tumors obtained from archives at our institution. Triplicate cores (0.6 mm in diameter) from each sample were created and two sets of cores were created for each chordoma specimen. One triplicate sample was incubated in a closed humid chamber with a pool of HMW-MAA-specific mAb, while the other was incubated with mAb specific for B7H3. Samples were washed in PBS and incubated with a secondary antibody for one hour. Staining was evaluated independently by two researchers and scored using validated systems. A retrospective chart review was performed for each chordoma specimen to determine demographic data, disease course, disease status at final follow-up and mortality. Clinical outcomes were then correlated to the expression of HMW-MAA and B7H3 within the chordoma lesions. Kaplan-Meier curves and Cox proportional hazard regression analysis were utilized to facilitate comparisons.

Chordoma tumors from 70 patients were included in this study. Average age at the time of presentation was 57.4 years (31–88 years). Average follow-up was 5.5 years (3.6 months-21 years). Forty-three patients developed recurrences and 10 had metastatic disease. Twenty-three patients (33%) had died of disease at the time of final follow-up. Ninety-seven percent of chordoma tumors stained positive for B7H3 while 44% stained positive for HMW-MAA. No correlation could be drawn between clinical course, recurrence rate, or mortality and tumor expression of B7H3 and HMW-MAA. Kaplan-Meier analysis did demonstrate a shorter survival time for patients whose tumors stained positive for HMW-MAA compared to those whose tumors were negative for the antigen.

The goal of this investigation was to correlate expression of B7H3 and HMW-MAA in chordoma tumorswith disease severity and clinical outcome. Results indicate that expression of HMW-MAA may be predictive of more aggressive disease and shorter survival. HMW-MAA and especially B7H3, in light of its near universal expression in the chordoma tumors studied here, may serve as potential targets for adjuvant immunotherapy.

INTRODUCTION: Medial open-wedge HTO is an alternative in the treatment of medial knee OA for the young and active patient. However this technique leaves an open gap that requires stable fixation to achieve bony healing. As a bone substitute injectable calcium-phosphate-cements could be an alternative to autograft.

MATERIAL AND METHODS: Biomechanical testings were performed on open wedge HTO to investigate load to failure and displacement after cyclic loading (viscous and/or damaged material response). A medial 10 mm open-wedge osteotomy was performed on 7 pairs of composite (Sawbone) left tibiaes, and 8 pairs of preserved cadaver tibiaes. Osteosynthesis where performed with the Dynafix system. In half of the bones the gap was filled with 15 g of Calcibon®. The composite tibiaes were loaded at a ramp speed of 20 mm/min and failures of the constructs were recorded visually. On the cadaver tibiaes, cyclical loading were performed with a maximum load of 2250 N.

RESULTS: Filling of the gap with Calcibon® resulted in significant different load-to-failure patterns with failure at 10.2 kN compared to 2.7 kN in the group without Calcibon®. Displacement at the end of cyclical loading was 1.2 mm in the group with Calcibon® and 2.7 mm in the group without Calcibon®. This difference also was significant.

CONCLUSION: The injectable calcium-phosphate-cement Calcibon® enhances primary stability during load to failure and during cyclical loading in open wedge osteotomies on proximal tibia. Clinical studies are performed to investigate whether Calcibon® has any clinical advantage on wedge healing and stability.

Introduction & Aims: A new femoral component for hip arthroplasty has been designed for a younger patient population. The design makes use of a higher femoral cut, which conserves bone stock, increasing options for future revision surgery. It uses the existing load bearing properties of the proximal femur, and therefore distributes load more evenly. The stem is longer than that of a resurfacing, so will be easier to insert at the correct orientation, minimising failure rates in inexperienced hands. The cross-sectional dimensions have been designed to produce torsional stability. The collar maximises the loading of the calcar, reducing stress resorption. The surface is hydroxyapatite coated and porous, which will produce a long-term biological fixation.

This project assessed the long-term stability of this design at different orientations, by measuring the change in surface strain distribution following its insertion.

Methods: Ten composite bones were coated in a Photoelastic material, positioned at a simplified single leg stance, and loaded at 2.3 KN. The surface strain was measured at one-centimetre intervals down the medial cortex. Then the prostheses were inserted into the bone at 135°, 145° and 125° to the femoral shaft, and the surface strains reread.

Results: The results were compared with an FEA model, and analysed statistically using the Wilcox signed rank test. The prosthesis inserted at 135° produced no significant difference in surface strain distribution compared with the intact bone.

Conclusions: This study suggests this stem design will be stable in the long term following insertion, and there were no areas of excessively high or low strain.

Objectives: Antimicrobial agents exert their effect inside the interstitial space, which is the site of many infections. Recently, microdialysis was applied to cortical and cancellous bone for the evaluation of gentamicin. The principle of microdialysis is to introduce a semipermeable membrane into bone and perfuse it with liquid, thus enabling dynamic measurements to be made.

The aim of this investigation was to measure pharmacokinetics of a Gentacoll sponge in bone tissue by microdialysis.

Materials and Methods: Nine pigs were randomized to either wet or dry application of a Gentacoll sponge (10cm* 10cm) into the bone marrow of tibia. Two catheters were inserted into cancellous bone tissue, one 1 cm (MD_1cm) and one 2 cm (MD_2cm) apart from the aimed location of the sponge. Then, the Gentacoll sponge was implanted. Wet application was defined as; the sponge was wetted in 2 mL. blood. Dry application was defined as usual surgical procedure. Concentrations of gentamicin were measured in serum and microdialysates on an Abbott Drug Analyser. Data presented are median (range). A rank sum test was performed for statistical analysis. A p-value below 0,05 was considered significant..AUC describes the total amount of gentamicin that passed though the tissue.

Results: The AUC_{6h, serum wet} was 92 (72–129) and AUC_{6h, serum dry} was 196 (142–626) mg*minute/L (P=0.02). The C_{peak, wet-group} was 120 mg/L (33–585) and C_{peak, dry-group} 178 mg/L(59–1294), (P=0.31). The overall (n=9) AUC_MD1cm was 24431 mg*minute/L (5.155–152.855) and similar the AUC_MD2cm 13759 mg*minute/L (6.351–74.573) (P=0,25). The C_{peak, MD 1cm} was 106 (41–354) (P=0.21). was 209 (33–1294) and C_{peak, MD 2cm}

Conclusions: This first study applied microdialysis for pharmacokinetic measurements of a local implant. The distribution of local applied antibiotics into bone tissue is difficult to measure. The small sample size precludes a detailed analysis, but previous found variation on the distribution of gentamicin from a Gentacoll sponge is reproduced in this work. It seems that neither application nor distance had impact on the initial pharmacokinetic of Gentacoll in bone tissue.