Spondylodiscitis of the lumbar spine in a non-immunocompromised host caused by Yersinia enterocolitica O:9

Here presented is an extremely rare case of a spinal osteomyelitis (L5-S1) with epidural empyema in a non-immunocompromised 62-year-old man caused by Yersinia enterocolitica O:9. The infection occurred acutely and required immediate surgical treatment. Y. enterocolitica was cultured from the empyema fluid, wound swabs of the intervertebral disc L5-S1 and stool cultures. Following the surgical decompression and antibiotic treatment, the patient recovered completely, without neurological deficits. A review of the literature revealed only sparse cases of spondylodiscitis due to other Y. enterocolitica serogroups. To our knowledge, we report here the first case of a spondylodiscitis of the lumbar spine caused by Y. enterocolitica serovar O:9 in a non-immunocompromised patient.

Impact of preoperative function on early postoperative outcome after total hip arthroplasty

PURPOSE

To investigate the impact of preoperative functional status on early postoperative outcomes after total hip arthroplasty (THA).

METHODS

39 men and 36 women aged 50 to 76 years who underwent cementless THA for osteoarthritis were followed up for at least 2 years. Patients were evaluated pre- and post-operatively (at 6, 12, and 24 months) using the Harris Hip Score (HHS), 36-item Short Form Health Survey (SF-36), and Western Ontario and McMaster University Osteoarthritis Index (WOMAC). Patients were classified into 3 groups based on their preoperative HHS (poor, <45; intermediate, 45-55; good, >55). Differences between and within groups were compared.

RESULTS

Patients with a poor preoperative HHS had worse early postoperative outcomes in terms of HHS, SF-36, and WOMAC. Postoperative pain and function correlated with preoperative HHS, but postoperative range of motion and deformity did not.

CONCLUSION

Poor preoperative function may affect recovery unfavourably and lead to prolonged pain. Earlier THA in the course of functional decline may associate with better outcomes.

Osteopontin is expressed and functional in human eosinophils

BACKGROUND

Eosinophils are critically involved in allergic inflammation and tissue remodeling. Osteopontin (OPN) is a glycoprotein molecule which exhibits pro-fibrogenic and pro-angiogenic properties and has recently also been implicated in allergic diseases. In this study, we investigated the expression and function of OPN in human eosinophils.

METHODS

Osteopontin mRNA (RT-PCR) and protein (immunofluorescence) expression in peripheral blood eosinophils from atopic human subjects were evaluated. Soluble OPN release was determined in resting and activated eosinophils. The contribution of OPN to eosinophil-induced angiogenesis was determined using the chick embryo chorio- allantoic membrane (CAM) assay and OPN-induced eosinophil chemotaxis was determined (ChemoTx System microplate wells). Finally, OPN expression in bronchoalveolar lavage (BAL) fluids from mild asthmatic and normal control subjects was determined.

RESULTS

Osteopontin is expressed in human eosinophils and is increased following GM-CSF and IL-5 activation. Eosinophil-derived OPN contributes to eosinophil-induced angiogenesis. Recombinant OPN promotes eosinophil chemotaxis in vitro and this effect is mediated by alpha(4)beta(1) integrin binding. Soluble OPN is increased in the bronchoalveolar lavage fluid from mild asthmatic subjects and correlates with eosinophil counts.

CONCLUSIONS

We therefore conclude that OPN is likely to contribute to the process of angiogenesis observed in the airways in asthma.

Cementless total hip replacement: a prospective clinical study of the early functional and radiological outcomes of three different hip stems

INTRODUCTION

Optimal fixation of cementless total hip stems is essential for long-term survival rates.

AIM

The purpose of this prospective study was to evaluate the early clinical and radiological outcomes of two new total hip stems with metaphyseal (Symax®) and predominantly diaphyseal (Hipstar®) anchoring principles in comparison to the well-established straight Zweymueller (SL-Plus®) stem.

METHOD

Clinical and radiological evaluations of 74 patients were undertaken preoperatively as well as at 6 and 12 months postoperatively using the Harris Hip Score (HHS) and Western Ontario and McMaster Universities-Score.

RESULTS

During follow-up no stem had to be revised. The mean preoperative HHS of the three study groups amounted to 54.6 ± 15.7 points. At the 12 months follow-up the mean HHS in the SL-Plus group (n = 22) was 88.3 ± 10.5 points, in the Hipstar group (n = 25) 83.3 ± 15.0 and the in Symax group (n = 27) 83.6 ± 15.1. Due to stress shielding the straight Hipstar stem revealed radiolucent lines in the proximal Gruen zones of about 60%, whereas the SL-Plus stem showed significantly more radiolucent lines (87%). However, subsequent long-term studies must be carried out in order to clarify if the progression of radiolucent lines may influence the clinical result and implant longevity.

A convenient approach for finite-element-analyses of orthopaedic implants in bone contact: modeling and experimental validation

With regard to the growing potential of finite-element-analysis (FEA) in the field of orthopaedic biomechanics, we present an approach helping in the development of appropriate models of the implant-bone compound. The algorithm is based on computed-tomography data of the bone and accordant computer-aided-design (CAD) data of the implant and aims at predicting the bone strains and interface mechanics of the included parts. The developed algorithm was validated exemplary using an acetabular cup in combination with a left and a right fresh-frozen human hemipelvis. The strains under maximum loads during the gait cycle as well as the micromotion in the bone-implant interface were measured and compared to results from equivalent finite-element-analyses. Thereby, we found strong correlation between the calculated and measured principal strains with correlation coefficients of r(2)=0.94 (left side) and r(2)=0.86 (right side). A validation of micromotion was not possible due to limited accuracy of the motion tracking system.

[Alternative materials and solutions in total knee arthroplasty for patients with metal allergy]

The annual number of total knee replacement implantations is rising continuously. A progressive cutaneous hypersensitivity rate against metallic materials in the population has been registered which can lead to an increase of allergy-induced reactions associated with implant loosening in the future although the correlation with an allergic cutaneous sensitisation has not been proven in all cases. On apparent allergy against metallic implant components different alternative solutions to standard endoprostheses should be taken into account for primary implantation or revision of total knee replacement, for example the application of implant components without metallic elements (e.g. ceramics), the use of non-allergic metallic implants, such as titanium or ZrNb alloys, or potential allergy-inducing metallic materials after masking the implant surface using a suitable coating. In the case of primary or revision surgery most patients with metal allergy are treated with a Ti(Nb)N-coated knee implant made of cobalt-chrome or titanium alloys in our hospital. Within an international multi-centre study we are currently implanting a newly developed knee endoprosthesis system with a ceramic femoral component as an alternative.

Response of human osteoblasts exposed to wear particles generated at the interface of total hip stems and bone cement

Aseptic loosening of total hip replacement is mainly caused by wear particles. Abrasive wear occurs at articulating surfaces or as a consequence of micro-motions at the interface between femoral stem and bone cement. Direct impact of wear particles on osteolysis, the remodeling of the bone stock and a directly affected function of osteoblasts was described. The present study examined the response of human osteoblasts exposed to different wear particles, which were generated in a test device providing oscillating micro-motions at the interface between femoral stem and standard bone cement. Characterization of released particles was performed by quantifying the size distribution and the metal content of the wear debris. Human osteoblasts were incubated with particles obtained from hip stems with different material compositions (Ti-6Al-7Nb and Co-28Cr-6Mo) and rough and smooth surface finishings combined with standard bone cement (Palacos(R) R) containing zirconium oxide particles. Commercially pure titanium particles (cp-Ti) and particulate zirconium oxide (ZrO(2)) were used for comparative analyses. The results revealed significant (p < 0.05) reduction of the cell viability after exposure to higher concentration of metallic particles, particularly from Co-based alloys. In contrast, ZrO(2) alone showed significantly less adverse effects on the cells. When increasing metallic particle concentrations massive inhibition was also observed in the release of cytokines including interleukine-6 (IL-6) and interleukine-8 (IL-8), but the expression of Procollagen I and the cell viability showed the highest reduction after exposure to Co-based alloy particles from rough stems.

Limited range of motion of hip resurfacing arthroplasty due to unfavorable ratio of prosthetic head size and femoral neck diameter

BACKGROUND AND PURPOSE

Hip resurfacing arthroplasty is being used more and more frequently. The small ratio in size between the resurfaced femoral head and the relatively thick femoral neck raises the question of whether the range of motion is sufficient, particularly with regard to the high mobility required by younger patients. We analyzed motion in a CAD model.

METHODS

Three-dimensional CAD models of the natural hip were created from CT scans and 8 designs of hip resurfacing prostheses (head diameter between 42 mm and 54 mm combined with a hemispherical cup) were implanted in a virtual sense. We simulated 3 different leg positions and the range of motion was evaluated, considering five different implant positions.

RESULTS

The range of motion of the hip resurfacing designs analyzed was far below the range of motion of stemmed total hip prostheses. None of the resurfacing prostheses provided flexion movements of 90 degrees without impingement. The average range of motion of hip resurfacing arthroplasty was 31-48 degrees below the range of motion of a stemmed total hip replacement with 32-mm head diameter.

INTERPRETATION

The range of motion of the hip resurfacing designs examined was substantially less than that of a conventional total hip prosthesis. Since impingement of the femoral neck on the acetabular component increases the risk of neck fractures, of dislocation and of subsequent implant loosening, the design and position of the implant should be considered before using hip resurfacing arthroplasty as a standard treatment for younger patients.

Experimental evaluation of hyaluronidase activity in combination with specific drugs applied in clinical techniques of interventional pain management and local anaesthesia

BACKGROUND

Hyaluronidase is an enzyme additive used in local anaesthesia and interventional pain reducing procedures such as adhesiolysis of epidural scar tissue after spinal surgery. Only a limited number of studies describe the influence of drugs on hyaluronidase activity. Postulated effects and effectiveness of hyaluronidase are only based on clinical observations.

OBJECTIVE

The aim of this study is to investigate the influence of the combined drugs on the activity of hyaluronidase under standardized conditions and to verify the effectiveness of the enzyme.

DESIGN

An ELISA-based microtiter-technique is used to evaluate the activity of hyaluronidase in combination with local anaesthetics, corticosteroids, NaCl 10%, and iodinated contrast media.

METHODS

Microtiter plates were coated with biotinylated hyaluronate and incubated with hyaluronidase in combination with the above-mentioned drugs. The activity of hyaluronidase was determined by an avidin-peroxidase-based procedure using an ELISA reader. Incubations were carried out at room temperature as well as at 37 degrees C.

RESULTS

The data show that drugs affect the activity of hyaluronidase in different ways. Iodinated contrast media, NaCl (10%), and the absence of corticosteroids reduce hyaluronidase activity. In contrast, higher activities were detected at a lower NaCl concentration (0.9%). We cannot attribute a significant influence to local anaesthetics.

CONCLUSIONS

Hyaluronidase is effective in all combinations with drugs. To get the maximum effect calculated use of accompanying drugs is necessary.

[Bicondylar knee arthroplasty - influence of preoperative functional restriction on early functional postoperative outcome]

AIM

The point of time for total knee arthroplasty has a significant importance due to limited implant survival rate. To what extent the preoperative stage of physical and psychological function limitation, which is increasing with the progression of the osteoarthritis, has an influence on the early functional outcome after total knee arthroplasty should be clarified in a clinical evaluation.

PATIENTS AND METHOD

47 Patients were treated with the same bicondylar knee endoprosthesis system (Type Genia, ESKA Implants, Lübeck). A clinical evaluation was undertaken preoperatively and at 3 and 6 months postoperatively using HSS score, WOMAC index and SF-36 score. In relation to the preoperative HSS score the patients were allocated into three groups depending upon whether their level of function was "good", "average" or "poor". Additionally, all patients were assigned to three body mass index (BMI) groups (< 30, 30 - 35, > 35) which were descriptively analysed.

RESULTS

The preoperative differences in HSS score and SF-36 score in all three groups show a high reduction after 3 and 6 months. Postoperatively there were no significant differences in all three groups at both timepoints. Patients with "poor" preoperative function achieved on average a lower score niveau than patients with preoperative "good" function, but have the benefit of the best function improvement. The early postoperative period (3 months) showed the highest decrease in physical and psychological function derogation. The BMI had no significant influence on the early functional outcome.

CONCLUSION

Therefore, older people should receive early total knee arthroplasty to gain a high postoperative score niveau. In younger patients the indication for implant should be considered essentially because of the limited survival rate. Even in progressive osteoarthritis and extreme functional limitation the bicondylar surface replacement gives the possibility of a good early functional postoperative outcome. Total knee arthroplasty of obese patients is under attention of the perioperative internistic risks, a safe procedure with good functional results and can increase patient's mobility.

Free flap transfer in cranio-maxillofacial surgery: a review of the current data

BACKGROUND

The advances of cranio-maxillofacilal surgery are considerably driven by the evolution of microsurgical techniques. At present, these methods continue to provide new therapeutic options to the field. Especially, free flap transfer has evolved to become an integral part of current treatment protocols for head and neck malignancies. It ensures uneventful wound healing even after previous radiotherapy and can often preserve form and function. For many patients, this may lead to a significant improvement in their quality of life.

OBJECTIVES

This review summarizes aspects of tumor therapy, the impact of radiation, and discusses different techniques of microvascular tissue transfer.

DISCUSSION

Specific advantages in different anatomical sites of the head and neck region are highlighted in contrast to existing alternatives. Selected cases exemplify the use of popular transplants.

SUMMARY

While planning reconstructions, it is important to consider both the functional and aesthetic aspects. The best individual outcome is based on a thoughtful match of available methods to a given defect and the patient's condition.

[Finite element analysis of a cemented ceramic femoral component for the assembly situation in total knee arthroplasty]

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.

Enhanced osteopontin expression in a murine model of allergen-induced airway remodelling

BACKGROUND

Airway remodelling is a central pathophysiological feature of chronic asthma. A wide variety of cytokines and growth factors are likely to be involved in the development of airway remodelling. Osteopontin (OPN) is a cytokine with pro-fibrotic properties; however, its role in airway remodelling in asthma has not been explored.

OBJECTIVE

To determine the expression and cellular sources of OPN in a murine model of chronic allergen-induced airway remodelling.

METHODS

BALB/c mice were sensitized and exposed to ovalbumin (OVA) or saline inhalations for 5 weeks and killed 24 h after the last inhalation. The following parameters of inflammation and remodelling were assessed: differential cell counts in bronchoalveolar lavage (BAL) fluid lung collagen content (colorimetric biochemical assay) and peribronchial smooth muscle content (immunohistochemistry, followed by image analysis). OPN expression in BAL and lung tissue was determined by PCR and ELISA. The cellular source and distribution of OPN were evaluated by immunohistochemistry and immunofluorescence.

RESULTS

OPN expression is up-regulated in lung tissue and in BAL fluid of OVA-treated mice and correlates with collagen content and peribronchial smooth muscle area. In addition, OPN significantly increases collagen deposition in vitro in a murine lung cell line. Cells producing OPN include the airway epithelium and cells of the submucosal inflammatory infiltrate (T cells, eosinophils, and macrophages). Positive staining for OPN was also observed in bronchial tissue from human asthmatic subjects.

CONCLUSION

OPN expression in the lungs is increased in a murine model of allergen-induced chronic airway remodelling, suggesting a role for this cytokine in airway remodelling in asthma.

Depletion of Normal and Malignant B cells with a CD37-specific SMIP molecule

3063

Background: CD37 is a member of the tetraspanin family expressed at high levels by normal mature B cells and by most B cell malignancies. Previously, an antibody to CD37 has been labeled with 131I and tested in clinical trials for therapy of NHL. Treatment with 131I-MB-1, resulted in durable tumor remissions in patients lasting from 4 to 11 months (Press OW, Eary JF, Badger CC, et al. Treatment of refractory non-Hodgkin’s lymphoma with radiolabeled MB-1 (anti-CD37) antibody. J Clin Oncol. 1989;7:1027–1038). Here we assess the functional properties and therapeutic potential of a small modular immunopharmaceutical (SMIP) targeting CD37. Methods: Growth arrest and apoptosis of B lymphoma cell lines was assessed. ADCC activity was evaluated using BJAB targets and human peripheral blood mononuclear cells (PBMC) effectors. Drug-drug interactions were assessed by the Combination Index method. In vivo studies were performed utilizing established human B cell tumor xenografts in nude mice. Results: A CD37-directed SMIP drug candidate mediated growth arrest, apoptosis and ADCC, but not CDC, towards B lymphoma cell lines. The protein showed significant anti-tumor activity in a mouse xenograft model, and selectively depleted normal human B cells in short term cultures of PBMC. When combined with rituximab, the molecule increased apoptosis, C1q binding, and C’ dependent target cell death in vitro, and increased anti-tumor activity in vivo in a xenograft model. Conclusions: In vitro and in vivo characterization of the CD37-targeted SMIP drug suggest a potent capacity to eliminate target cells through combined effects of direct target cell signaling and effector cell recruitment. CD37-mediated growth was synergistic with standard chemotherapies in vitro and showed additive in vivo activity with CD20-targeted therapy. On the basis of these data CD37-directed SMIP therapy is being developed for clinical evaluation against B cell malignancies.

No significant financial relationships to disclose.

Influence of femoral head size on impingement, dislocation and stress distribution in total hip replacement

Dislocation remains a serious complication of total hip replacement. An insufficient range of motion can lead to impingement of the prosthetic neck on the acetabular cup. Together with the initiation of subluxation and dislocation, recurrent impingement can cause material failure in the liner. The objective of this study was to generate a validated finite element (FE) model capable of predicting the dislocation stability of different femoral head sizes with regard to impingement in different implant positions as well as the corresponding stress distribution in the liner. In order to cover posterior and anterior dislocation, two total hip dislocation associated manoeuvres were simulated using a three-dimensional nonlinear finite element model. The dislocation stability of two head sizes was determined numerically and experimentally. After validation, the FE model was used to analyse the dislocation stability of four different head sizes in variable implant positions. Range of motion (ROM) until impingement, the resisting moment that was developed and ROM until dislocation were evaluated. Additionally, stress distribution within the polyethylene liner during impingement and subluxation was determined. For both dislocation modes, a cup position of 45 degrees lateral abduction and 15 degrees up to 30 degrees anteversion resulted in appropriate ROM and dislocation stability. In general, larger head diameters revealed an increase in ROM and higher resisting moments. Stress analysis showed decreased contact pressures at the egress site of the liners with the larger inner diameters during subluxation. The analysis shows that an optimal implant position and a larger head diameter can reduce the risk of dislocation induced by impingement. The finite element model that was developed enables simplification of design variations compared to experimental studies since prototyping and assembling are replaced by prompt numerical simulation.

Finite element analysis of shear stresses at the implant-bone interface of an acetabular press-fit cup during impingement / Finite-Elemente-Berechnung der Schubspannungen im Implantat-Knochen-Interface einer acetabulären Press-Fit-Pfanne bei Impingement

After total hip replacement (THR) impingement of the implant components causes shear stresses at the acetabular implant-bone interface. In the current study the finite element method (FEM) was applied to analyse the shear stresses at a fully bonded implant-bone interface assuming total ingrowth of the cup. The FE model of a press-fit acetabular component and the proximal part of the femoral component incorporates non-linear material and large sliding contact. The model was loaded with a superior-medial joint load of 435 N simulating a two-legged stance. Starting at initial impingement, the femoral component was medially rotated by 20 degrees . The peak tilting shear stress of -2.6 MPa at the impingement site takes effect towards the pole of the cup. The torsional shear stress at the impingement site is zero. On each side of the impingement site, there are extrema of torsional shear stress reaching -1.8 and 1.8 MPa, respectively. The global peak shear stress during impingement may indicate a possible starting point for cup loosening. The pattern of the torsional shear stresses suggests that besides the symmetric lever-out, an additional asymmetrical tilting of the cup occurs that can be explained by the orientation of the applied joint load.

Die Bedeutung der Gleitpaarung beim jüngeren Endoprothesenpatienten

The success and long-term survival rates of modern joint arthroplasty leads to a high patient satisfaction and, together with its technical improvements, has broadened the indications to an increasingly younger population. Limitations to the established systems are the long-term survival rates, which are mainly influenced by wear of the articulating parts and the resulting problems. Beside "classic" long-stemmed cemented shafts articulating with metal against polyethylene, short-stemmed or cup designs with a hard-hard self pairing are increasingly used in total hip arthroplasty. This paper reflects the current state of the art in joint arthroplasty for younger patients with the focus on wear couples and discusses future perspectives. Special interest is focused on the advantages and disadvantages of ceramic bearings, problems with allergies to implant components and the design of endoprostheses with regard to avoidance of impingement.

[Failure analysis of total knee replacement. Basics and methodological aspects of the damage analysis]

Possible causes for failure of total knee endoprostheses represent wear, malpositioning, maldimensioning and inadequate design of the implant components, manufacturing defects, material fatigue, corrosion, overloading, infection, and allergy against implant materials. There is a broad spectrum of methodical approaches for the analysis of failure cases. Substantial information for the damage analysis is provided by clinical and intraoperative findings, photo documentation, radiographic course as well as all-solid, physical and histological investigations. Principal purposes of damage analysis are the avoidance of further damage events and the gain of information for improvement of implant design and material as well as the optimisation of the biocompatibility of implants and wear products. Both a detection system of incidents and implant failures as well as a complete data collection enables early identification of system-specific, accumulated cases of implant failure.

Assessment of cup position from plain radiographs: impact of pelvic tilting

The acetabular cup position after total hip arthroplasty (THA) regarding its inclination and version angles are influential parameters concerning the postoperative range of motion and dislocation stability. Standard anterior-posterior X-rays remain an important diagnostic instrument to observe the postoperative outcome and to secure quality control after THA, where an optimal positioning of the patient is recommended when taking these X-rays. The purpose of this preliminary study was to determine the effect of pelvic tilting regarding the positioning calculation of the acetabular cup from standard radiographs using a modified method according to Pettersson et al. (Acta Radiol Diagn, 23:259-263, 1982). In our model experiment, we were able to show that pelvic tilting to either side causes a considerable difference between the radiographic and calculated version angles following approximately linear functions. However, pelvic tilting to either side, leads, regarding the calculation of the inclination, to an average deviation between radiographic and calculated inclination angles less than 2 degrees .

Severe damage of the femoral head after dislocation and difficult reduction maneuvers after total hip arthroplasty

INTRODUCTION

Aseptic loosening associated with osteolysis and release of wear particles is the main reason for revision of total hip arthroplasty (THA). Damage of femoral heads is well known to increase the wear rate at the articulating surface. Instability and dislocation are serious complications and are the second most frequent reason for revision surgery after THA. In the present work the possible damaging of the femoral head as a result of difficult reduction maneuvers of dislocated THA should be investigated.

PATIENTS AND METHODS

In three cases of total hip dislocation an open reduction was performed after dislocation of primary THA. Thereby one metal and two ceramic femoral heads were retrieved. Each head was analyzed macroscopically and by scanning electron microscopy (SEM) subsequently.

RESULTS

In the first case the SEM analysis revealed severe titanium deposits on the retrieved ceramic head in the case of repeated unsuccessful closed reduction maneuvers. In the second case the retrieved ceramic head showed multiple scratches and a spalling of the surface structure. In the third case the retrieved metal head presented a roughened surface and severe scratches at the articulating area.

DISCUSSION

Difficult reduction maneuvers following total hip dislocation can lead to severe damaging of the femoral head associated with an increase of the surface roughness. While repeated reduction maneuvers can lead to metallic deposits and spalling of the surface of ceramic heads, severe scratches can occur at metal heads. The damaging of the femoral head at the articulating surface can lead to increased wear and subsequent aseptic implant loosening. Therefore, open joint reduction has to be considered in cases of difficult or unsuccessful closed reduction maneuvers to prevent severe femoral head damage which may cause an increased release of wear particles.

A novel test method for evaluation of the abrasive wear behaviour of total hip stems at the interface between implant surface and bone cement

After total hip replacement, some cemented titanium stems show above-average early loosening rates. Increased release of wear particles and resulting reaction of the peri-prosthetic tissue were considered responsible. The objective was to develop a test method for analysing the abrasive wear behaviour of cemented stems and for generating wear particles at the interface with the bone cement.

By means of the novel test device, cemented hip stems with different designs, surface topographies and material compositions using various bone cements could be investigated. Before testing, the cemented stems were disconnected from the cement mantle to simulate the situation of stem loosening (debonding). Subsequently, constant radial contact pressures were applied on to the stem surface by a force-controlled hydraulic cylinder. Oscillating micromotions of the stem (± 250 μm; 3 × 106cycles; 5 Hz) were carried out at the cement interface initiating the wear process.

The usability of the method was demonstrated by testing geometrically identical Ti-6A1-7Nb and Co-28Cr-6Mo hip stems ( n = 12) with definite rough and smooth surfaces, combined with commercially available bone cement containing zirconium oxide particles. Under identical frictional conditions with the rough shot-blasted stems, clearly more wear particles were generated than with the smooth stems, whereas the material composition of the hip stems had less impact on the wear behaviour.

Pitfalls in the use of acetabular reinforcement rings in total hip revision

INTRODUCTION

For the reconstruction of acetabular bone defects different types of acetabular reinforcement rings are being used. In clinical practice, these implants showed to some extent good long-term results. In the present work pitfalls and complications after the implantation of acetabular reinforcement rings as well as possible solutions are being discussed.

MATERIAL AND METHODS

In the first case recurrent dislocation was caused by the malposition of the acetabular component with an impingement of the protruding bone cement and the anterior edge of the acetabular ring as well as muscle insufficiency as a result of the shortening of the leg length. The second case revealed an impingement of the iliopsoas tendon due to a protruding acetabular reinforcement ring. During revision, bone cement was used to smoothen the protruding anterior edge of the acetabular reconstruction ring in order to obtain a relieved sliding of the tendon. Furthermore, we report on the case of a delayed neuropathy of the sciatic nerve after reconstruction of the acetabulum with an acetabular reinforcement ring.

RESULTS

Intraoperatively an impingement of the sciatic nerve at the protruding dorsal edge of the acetabular reinforcement ring and the surrounding scar tissue was found. In a further case an aseptic loosening of an acetabular reinforcement ring caused the formation of an excessive granuloma with a large intrapelvic portion. The granuloma led to persisting senso-motoric deficits of the femoral nerve. In summary, based on these clinical cases possible pitfalls, associated with the use of acetabular reinforcement rings, are shown. The mal-positioning and the intra-operative re-shaping of the implant by the surgeon are pointed out as the substantial factors for the occurrence of an impingement phenomenon and total hip instability. Furthermore, in case of an adequate orientation of the cemented polyethylene insert an improper position of the acetabular ring which results in protruding edges has to be considered as a cause of a prosthetic impingement.

CONCLUSION

The cases presented emphasize the necessity of prevention of such pitfalls intra-operatively as well as accurate analysis of implant failures. Furthermore, they suggest explicit preoperative planning before deciding on the strategy of revision surgery of acetabular reinforcement rings.

Treatment of recurrent dislocation associated with impingement after revision total hip arthroplasty

The authors report a case of total hip replacement in which, following several revision operations ending up in a Girdlestone arthroplasty, a patient presented recurrent episodes of posterior dislocation of his total hip prosthesis after revision using an antiprotrusio cage. The main causes for dislocation were anterior impingement of the neck against the anterior wall of the antiprotrusio cage and slackness of the periarticular musculature, due to shortening and reduced femoral offset. In order to avoid further major reconstruction and minimise the risk of infection recurrence, a limited revision operation was performed to address the factors responsible for the instability: the anterior wall of the antiprotrusio cage was removed and an extension module was added to the femoral component. Good stability of the arthroplasty was achieved with this limited procedure.

Evaluierung des Fügeverhaltens und der Rückhaltekräfte von Schnapp-Pfannen für den künstlichen Hüftgelenkersatz / Evaluation of the assembling and retention forces of constraint liners for total hip replacement

Dislocation is a severe complication after total hip replacement which may cause revision surgery in some cases. The use of constraint inserts that are coupled to the femoral head by a snapping mechanism provides an opportunity for treatment of recurrent dislocations. This study was aimed to investigate the assembling and retention forces of a specific constraint liner. Using a universal testing machine the assembling forces were determined for head sizes of 28 and 32 mm and the clinically mostly used as well as the maximum cup size. Subsequently, under variation of load direction and pull-out velocity the retention forces were investigated. For primary assembly of the head the required compressive forces were in a range from 197 N and 283 N depending on head and cup size (each size n = 3). Repeated assembly led to a decrease of these forces up to 29%. The retention forces always were slightly below the assembling forces, i. e. forces to remove the heads from the inserts were between 183 N and 230 N (each size n = 3). Repeated disconnection caused a decrease of the retention forces up to 16%. An increase of load velocity as well as an oblique load direction resulted in an enhancement of the retention forces. For all investigated implant sizes the retention force for the femoral head was approximately ten-times less than the interface strength between the insert and the metal-back. In case of correct implant handling the risk of disconnection between the tested constraint insert and the corresponding metal-back has not to be considered in clinical practice.

The influence of head and neck geometry on stability of total hip replacement: a mechanical test study

BACKGROUND

Dislocation after replacement may be caused by poor implant design or positioning, or by the surgical approach taken. We evaluated the influence of head and neck design on range of motion and stability (with respect to risk of dislocation) in total hip endoprostheses.

MATERIAL AND METHODS

Using a test device, we determined the stability afforded by different head sizes and neck geometries for various implant positions.

RESULTS

Increasing head diameter led to an enhancement of range of motion as well as resistance against subluxation, and thus to improved stability in any movement combination and implant orientation. Smaller femoral heads were associated with increased risk of dislocation, especially in a poor implant position such as retroversion, and steep positioning of the cup. Skirted metal or mushroom-shaped ceramic heads had a reduced range of motion until impingement of approx. 20 degrees, as compared to spherical standard heads. Furthermore, after identical joint loading, skirted heads dislocated more readily than standard heads with corresponding diameters.

INTERPRETATION

To obtain sufficient joint mobility and stability, neck geometry and implant position should be considered when choosing the femoral head size.

Experimentelle Analyse von neutralen, asymmetrischen und Schnapp-Pfannen für die Hüftendoprothetik

AIM

Recurrent dislocation after total hip replacement is a severe complication, which requires specific treatment and implants. The purpose of the present study was to compare a constraint liner with an elevated rim and standard liner regarding their range of motion and dislocation stability.

METHOD

With a test device, range of motion until impingement (ROM (Imp)) and dislocation (ROM (Lux)) were experimentally analyzed using the above-mentioned insert types of a commercial total hip system. On the basis of movement combinations associated with dislocation, the ROM was determined. Further measuring parameter was the resisting moment against subluxation of the femoral head.

RESULTS

The constraint liners showed clear restriction of the movements "internal rotation combined with 90 degrees flexion and 0 degrees adduction" and "external rotation with 10 degrees extension and 15 degrees adduction" of up to 20 degrees compared to the neutral liner. ROM (Imp) was only decreased by about 8 degrees with the elevated-rim liner. The constraint liners revealed the highest resisting moments in subluxation, however, at adequate orientation in the acetabular cup the elevated-rim liners provided a higher ROM (Lux) of up to 12 degrees. Both designs were superior to the neutral liner at retroversion and steep cup position regarding resisting moment and ROM (Lux).

CONCLUSION

In case of insufficient soft tissue tension the use of constraint liners may increase the dislocation stability, however, in contrast to elevated-rim liners the impingement-free movement interval is clearly reduced. Thus, material damage and high shear stress in the bone interface can result. Therefore, constraint liners should only be used in exceptional cases.