[Anatomic reconstruction of hip joint biomechanics: conventional vs. short-stem prosthesis]. / Die anatomische Rekonstruktion des Hüftgelenks: ein Vergleich von Kurz- und Standardschaft.

BACKGROUND: Currently, short cementless femoral stems are alternative implants to treat osteoarthritis in young patients with sufficient bone quality in order to get a more proximal load transfer. The purpose of the present study was to biomechanically compare joint reconstructions resulting from implantations of a short-stemmed and a conventional hip replacement. METHODS: 100 patients (50 short-stemmed and 50 conventional) were retrospectively examined. For evaluation of biomechanical parameters standardised pre- and postoperative X-rays (pelvic AP views) were used and digitally analysed. RESULTS: The horizontal femoral off-set increased within both groups (short: 2.0 mm and conventional: 3.3 mm), with a significant increase in the conventional group. The hip centre of rotation was significantly medialised after both procedures (short: 6.0 mm and conventional: 4.2 mm). Limb length was shorter preoperatively at the arthroplasty side, but increased thereafter (short: 2.1 mm and conventional: 2.6 mm). Compared to the native contralateral side the limb length was almost equal after THA (short: 0.7 mm and conventional: 0.8 mm). CONCLUSIONS: Our study shows that an almost anatomic reconstruction of hip joint biomechanics is possible with a short-stemmed prosthesis compared to a conventional stem, regarding limb length, centre of rotation and offset.

[Anatomic reconstruction of hip joint biomechanics with the bone preserving Silent Micro Hip™ prosthesis]. / Anatomische Rekonstruktion des Hüftgelenks mit der schenkelhalserhaltenden Silent Micro Hip™.

BACKGROUND: The design and the surgical technique of the Silent Micro Hip™ are different compared to other hip stems due to a conical shape for fixation within the metaphyseal femur. The purpose of the present study was to evaluate hip joint biomechanics of the Silent Micro Hip™ in comparison to other implants. Implant-specific differences are highlighted. MATERIAL AND METHOD: 150 consecutive patients (each group 50 Silent Micro Hip™, Nanos™ and SL-Plus™ MIA) were analysed retrospectively. For evaluation of biomechanical parameters pre- and postoperative X-rays (pelvic AP views) were used. RESULTS: The horizontal femoral offset and the limb length showed no significant difference between the Silent Micro Hip™ and the Nanos™ or SL-Plus™ MIA stem at the reconstructed hip. An almost anatomic reconstruction of hip joint biomechanics was reached with all three types of implants. CONCLUSIONS: The Silent Micro Hip™ allows for almost anatomic reconstruction of hip joint biomechanics. Short-term results support the bone-preserving reconstruction with a proximal femoral load transfer. Further studies on the mid- and long-term outcomes are ongoing.

[Revision hip stems: an analysis of the fixation]. / Femorale Revisionsprothesen : Eine Analyse der Verankerung.

BACKGROUND: Revision hip replacements are complicated surgeries because the femoral quality is often reduced by large substance losses. Stem fixation in terms of sufficient primary stability is therefore a great challenge for the orthopaedic surgeon. AIM: The aim of the present study was to examine two currently used prostheses in Germany (MHP and MRP) concerning their ability to securely bridge femoral defects. RESULTS: Up to a segmental metaphyseal defect, both stems showed sufficient fixation in our experimental setup. However, because of its predominantly distal fixation, the MRP stem would unnecessarily bridge proximal bone areas still capable of load bearing. In the presence of a transfemoral approach, the surgeon should favour the distal fixation mode because in this situation the proximal fixation option is absent. Therefore, the isthmus takes a key role for both stem designs.

Medium to long-term results after reconstruction of bone defects at the knee with tumor endoprostheses.

BACKGROUND AND OBJECTIVES: Limb salvage and reconstruction with tumor endoprostheses is considered as therapeutic standard in the treatment of bone defects at the knee. Few studies report long-term results so far. METHODS: Seventy-seven patients who had a cementless or cemented MUTARS endoprosthesis implanted were followed-up for a mean period of 46 months (3-128 months). The defects were due to primary tumor lesions in 69 cases or metastases in 8 cases. The distal femur (n = 49) or the proximal tibia (n = 28) was reconstructed predominantly with cementless implants (femur: 69%, tibia: 92%). The resection of the tumor was intraarticular in 46 and extraarticular in 31 patients. RESULTS: After 10 years probability of limb salvage was 92% with a recurrence rate of 3%. Complications were frequent with a revision rate of 58% and lead to a cumulative probability of survival of the initially implanted prosthesis of 57% after 5 years. Locking mechanism failure (n = 15) and aseptic loosening (n = 13) were the most frequent failure modes. CONCLUSIONS: Regardless of achieving a low recurrence rate and satisfactory functional results, we found a high complication rate after implantation of a megaprosthesis. This was particularly evident for extraarticular resections and cemented fixation, which should be avoided when possible.

[Applications of molecular pathology in the diagnosis of joint infections]. / Molekularpathologische Diagnostik von Gelenkinfektionen.

The diagnosis of infections in patients with arthritis and/or joint prostheses requires interdisciplinary cooperation and the use of up-to-date methods. Massive bacterial infection can be identified by bacterial culture, and minimal infection can be detected by molecular pathological methods. These processes include specific enrichment of bacterial and fungal DNA, amplification, and identification of the DNA by gel electrophoresis, sequencing techniques, and chip technologies.Anamnesis (enteral or urogenital infection), the clinical picture (oligoarthritis), and further parameters (e.g., HLA B27 status) are important for the diagnosis of reactive arthritis. In many cases of reactive arthritis, molecular methods allow detection of bacterial DNA or RNA in synovial fluid or tissue. Molecular pathological methods allow the fast and reliable differential diagnosis of granulomatous synovialitis without prior cultivation of bacteria or fungi. The development of new molecular pathological methods for detecting bacterial and fungal nucleic acids will increase diagnostic accuracy.

[Particle release in metal-on-metal bearings. A risk analysis]. / Partikelfreisetzung bei Metall-Metall-Gleitpaarungen. Eine Risikoanalyse.

Modern metal-on-metal bearings show very low wear rates but release particles and ions from the articulating surfaces into the joint and the whole organism. Especially during the run-in period an increased number of particles is produced. The released metal ions potentially trigger cytotoxic, cancerogenic and allergic reactions, which can impair the patient's health locally or systemically. Many surgeons fear a hypersensitivity reaction to the metal ions of the CoCr alloy in their patients. Today it is assumed that the incidence of these implant-related complications is very low but in some cases it will lead to early failure of the implant. Because the available alternative bearing combinations (ceramic-on-polyethylene and ceramic-on-ceramic) also bear the risk of severe complications, a final statement on the best and safest bearing choice for the patient cannot be made based on the currently existing data.

[Resurfacing for osteonecrosis of the femoral head]. / Oberflächenersatz bei Hüftkopfnekrose.

Osteonecrosis of the femoral head is a disease of the young patient which eventually destroys the hip joint. In the early stage of the disease, treatment options are aimed at preserving the femoral head. Unfortunately, many patients present with late-stage disease (Ficat III and IV).In late-stage disease the treatment of choice is total hip arthroplasty. The high failure rate of total hip arthroplasty in young patients with osteonecrosis of the femoral head, however, made it an unfavourable treatment option. The results of hemiresurfacing (femoral resurfacing) in this patient population have been very disappointing due to high revision rates and insufficient pain relief. More recently, promising short- and mid-term results were reported with the use of total resurfacing with a survivorship of 90-93% after 3.4-10 years. Our own results in 60 patients show an overall survivorship of 92% after a mean follow-up of 4.8 years (1.6-6.5 years). Total hip resurfacing is a valuable treatment option for late-stage osteonecrosis based on recent study results.

[In vitro elution and mechanical properties of antibiotic-loaded SmartSet HV and Palacos R acrylic bone cements]. / In-vitro-Freisetzung von Antibiotika aus SmartSet HV- und Palacos R-Knochenzement und deren Einfluss auf die mechanischen Eigenschaften.

BACKGROUND: The continuing emergence of new bone cements with additional antibiotics makes it important to establish which one will provide the most favourable antibiotic elution. An in vitro antibiotic elution and mechanical study was therefore carried out to compare a newer bone cement, SmartSet, with the established Palacos R cement. METHODS: Samples were prepared with each cement adding 1 g gentamicin, 1 g of vancomycin, or 1 g of gentamicin and vancomycin. The samples were analysed using fluorescence polarisation immunoassay. Mechanical tests were performed to determine whether any significant degradation in the cement strength occurred following addition of the antibiotic. RESULTS: With regards to gentamicin release Palacos R eluted significantly more antibiotic over the study period than SmartSet (p<0.001). Both cements eluted significantly more gentamicin when two antibiotics were added. With respect to vancomycin release there was no significant difference. Palacos R was significantly stronger than SmartSet in the 4-point bending test when the gentamicin + vancomycin antibiotic groups were compared (p=0.01). Palacos R also demonstrated a higher elastic modulus than SmartSet when the gentamicin and gentamicin + vancomycin groups were compared (p=0.03, p=0.005). CONCLUSIONS: Gentamcin shows better release characteristics from Palacos R. Both cements exhibited synergistic release of combined antibiotics.

[Femoral fissure after cement restrictor implantation]. / Femurfissur nach Markraumstopperimplantation.

Cement restrictors are accepted parts of modern cementing technique and reduce the risk of revision. The restrictor should seal the intramedullary cavity to ensure sustained pressurization and optimal cement penetration into cancellous bone. Significant complications after use of a cement restrictor are rarely described. Dislocation and cement leakage are well known problems. We describe the occurrence of a femoral fissure after insertion of a resorbable Gelatine cement restrictor.

[Stability and occlusion of six different femoral cement restrictors]. / Stabilität und Okklusionsverhalten 6 verschiedener femoraler Markraumstopper.

Cement restrictors play an integral part in modern cementing technique in total hip arthroplasty. By sealing the femoral cavity, distal cement leakage is prevented and the intramedullary pressure is increased. Thus both the ability of the cement to interdigitate with bone and secondarily the shear strength of the cement bone interface are enhanced. For this purpose various plug models are available, which differ in design and material. Six different cement restrictors were investigated in a biomechanical model with regard to intramedullary implantation pressure, insertion force and in particular stability and sealing ability. We performed a pressure and stability measurement in artificial saw bones during the insertion and standardised cement application and pressurisation. The REX Cement Stop, which is the only intramedullary expandable cement restrictor, yielded the best results in all of the parameters investigated. The flexible gelatin plugs (Biostop G, IMSET, Plugin Tech) also reached a sufficient canal occlusion and stability, but with slightly higher insertion pressures and forces. However, the more rigid polyethylene restrictors (BUCK, Universal Cement Restrictor) showed a reduced stability and poor sealing ability. The latter devices cannot be recommended for use with modern cementing techniques.

In vitro performance of intramedullary cement restrictors in total hip arthroplasty.

Contemporary cementing techniques in total hip arthroplasty include the use of a cement restrictor to occlude the intramedullary canal. As there are many different designs currently available it was the aim of our study to compare the stability of eight different systems. We investigated the displacement and the ability to occlude the femur of these cement restrictors during standardised cementing of artificial and fresh frozen femora. The maximal intramedullary pressures and the displacement of the plugs were continuously recorded and statistically evaluated. The results revealed significant differences between the tested cement restrictors. The expandable REX Cement Stop and the Exeter Plug achieved the highest stability and the least cement leakage. The more rigid designs (Palacos Plug, BUCK, Universal) in contrast showed inferior performance. Our biomechanical study emphasises the importance of cement restrictor selection, which can have a crucial influence on the fixation of a cemented total hip replacement.

[Fat embolism during total hip arthroplasty. Cementless versus cemented--a quantitative in vivo comparison in an animal model]. / Fettembolie bei der Hüftendoprothesenimplantation. Zementfrei gegen zementiert--ein quantitativer In vivo-Vergleich im Tiermodell.

Thrombembolic complications,which include the fat embolism syndrome, are well-known consequences of cementless and cemented femoral total hip replacement. Thrombembolic phenomena have been demonstrated in clinical and experimental situations with both these fixation techniques, but so far no exact quantification of the intravasated fat emboli has been performed. In a standardized animal model in 15 Merino sheep we investigated the intravasation of fat into the bloodstream during simultaneous bilateral prosthetic implantation (cemented versus cementless). After identical preparation of the intramedullary canal on both sides, a cement restrictor was additionally inserted on the cemented side and the canal was cleaned by 250 ml jet lavage. Catheters in the external iliac veins made it possible to collect the drained blood in two phases, after preparation of the intramedullary canal and during insertion of the prosthesis, and the fat content of these blood samples was measured. The amount of fat that passed into the venous draining system of the femur induced by cemented implantation (2.2749 g; S=+/-1.0079) was twice the amount seen with cementless implantation (1.1586 g; S=+/-0.4555) ( P=0.0002). An obvious effect of the canal preparation was recognizable with the cemented implantation, 8 of the 13 animals evaluated showing a peak in the fat intravasation caused by application of the cement restrictor. Our results emphasize the importance of a thorough preparation of the intramedullary canal, particularly when cemented fixation is performed. The jet lavage,which should be considered mandatory standard in cemented total hip arthroplasty, should be implemented before the insertion of the cement restrictor in order to further reduce the risk of fat embolism.

[Cement delivery depends on cement gun performance and cement viscosity]. / Zementpistoleneffektivität und Viskosität beeinflussen die Qualität der Zementapplikation.

AIM: Retrograde cement application is considered an integral part of the modern femoral cementing technique. Both pressurisation and rapid cement application reduce the risk of interface bleeding and blood laminations. In this context cement gun performance has received little attention. METHOD: In our study we examined the handling characteristics of four different cement delivery systems (Syringe, Vaku-Mix, Optivac and MixOR-System). To allow for cement viscosity as another variable, six different bone cements (Palacos R, Palamed G, CMW 1 Radiopak, CMW 2000, Simplex P, VersaBond) were used with each system. We recorded cement gun performance and measured extrusion times and maximum cement delivery speeds of all possible combinations (gun/mixing system plus cement type). RESULTS: The fastest cement application could be achieved with the Vaku-Mix cement delivery system and the corresponding cement gun (Mark III). With regard to cement type, VersaBond and prechilled Palacos yielded significantly shorter extrusion times than most of the other cements due to their lower viscosities. CONCLUSION: Our results have shown significantly different efficacies of commonly used cement delivery systems/guns in clinical routine. Improved systems should be provided by the suppliers.

[New PMMA bone cements for vacuum mixing systems]. / Neue PMMA-Knochenzemente zur Anwendung in Vakuummischsystemen.

In cemented total hip replacement, fractures and cracks in the cement mantle may facilitate mechanical loosening of the prosthesis. Especially large voids and flaws within the cement can cause fatigue fractures. Reduction of cement porosity is a logical step in the attempt to improve the quality and durability of bone cement. An effective reduction of pores during vacuum mixing requires prechilling of Palacos R at 4 degrees C. For easier handling, new bone cements have been developed with characteristics similar to Palacos R, but with no chilling necessary prior to mixing under vacuum. In our study two newly developed bone cements (Palamed G, VersaBond) and a bone cement used widely in clinics (Palacos R) were mixed in three different vacuum mixing systems (Optivac, MixOR, Palamix). Macro-, micro-, and total porosity and bending strength (ISO 5833) were determined. All three mixing systems proved effective in reducing porosity and showed constant mixing results. All cement specimens that we tested fulfilled the ISO requirements for bending strength. VersaBond yielded the lowest porosities, but showed lower viscosity compared to Palacos R and Palamed G. The new cements are equal in vitro to Palacos R with regard to bending strength, but further clinical studies are necessary before widespread use is advisable.

[Thromboembolic complications related to the use of bone cement in hip arthroplasty--pathogenesis and prophylaxis]. / Thromboembolische Komplikationen bei der Verwendung von Knochenzement in der Hüftendoprothetik--Pathogenese und Prophylaxe.

INTRODUCTION: Cemented total hip arthroplasty (THA) has to be considered a high-risk procedure with respect to cardiovascular complications. The insertion of cement and prosthesis may lead to intravasation of fat and bone marrow into the circulation. METHODS: This article represents a review on the relevant literature about thromboembolic complications associated with the use of bone cement in THA. RESULTS/DISCUSSION: The method of canal preparation and lavage is of paramount importance to reduce the potential embolic load. Additionally, thorough cleaning of the intramedullary cavity (using jet lavage) improves the cement penetration into the bone and increases the shear strength of the bone-cement interface. Modern cementing techniques include the use of high pulsatile lavage, a cement restrictor and cement pressurization. With the application of these techniques a sufficient drainage of the medullary canal should be guaranteed to minimise the risk for thromboembolic complications. During the insertion of cementless implants the intravasation of embolic material seems to be less, but it is likewise possible to have a thromboembolic complication during cementless THA. However, it is not justified as a consequence to use the thromboembolic risk as the main indication for implant choice, in particular as the overall risk of a serious fatal complication is low.

Time course of the serological response to Yersinia enterocolitica O:3 in experimentally infected pigs.

A total of 25 pigs inoculated with Yersinia enterocolitica serovar O:3 and 25 un-inoculated controls were followed weekly by sampling blood and faeces for 70 days post infection (p.i.). All inoculated pigs were faeces culture positive from day 5 to 21 p.i., whereafter shedding of bacteria declined to < 10% of the pigs at day 49 p.i. and to 0% at day 68 p.i. All control pigs remained Y. enterocolitica O:3 culture negative. When examined in an indirect ELISA using purified LPS from Y. enterocolitica 0:3, sera from all inoculated pigs showed significantly higher optical densities (OD) as compared to the control group. All inoculated pigs had seroconverted at day 19 p.i. and remained seropositive until slaughter at day 70 p.i. The maximum mean anti-LPS response was observed at day 33 p.i. with a positive/negative ratio of 780. No cross-reactions were observed with sera from 21 pigs, infected with Salmonella typhimurium. At necropsy at day 70 p.i., Y. enterocolitica O:3 was isolated from the tonsils of 20 inoculated pigs, whereas the rest of the gastrointestinal tract and associated lymph nodes were culture negative. The remaining inoculated pigs and all control pigs were culture negative at necropsy at day 70 p.i. The ELISA seems to be a promising alternative to bacteriological culture for detection of Y. enterocolitica O:3 infection in pig herds.