Dieter Christian Wirtz

Critical evaluation of known bone material properties to realize anisotropic FE-simulation of the proximal femur.

PURPOSE In a meta-analysis of the literature we evaluated the present knowledge of the material properties of cortical and cancellous bone to answer the question whether the available data are sufficient to realize anisotropic finite element (FE)-models of the proximal femur. MATERIAL AND METHOD All studies that met the following criteria were analyzed: Youngs modulus, tensile, compressive and torsional strengths, Poissons ratio, the shear modulus and the viscoelastic properties had to be determined experimentally. The experiments had to be carried out in a moist environment and at room temperature with freshly removed and untreated human cadaverous femurs. All material properties had to be determined in defined load directions (axial, transverse) and should have been correlated to apparent density (g/cm(3)), reflecting the individually variable and age-dependent changes of bone material properties. RESULTS Differences in Youngs modulus of cortical [cancellous] bone at a rate of between 33% (58%) (at low apparent density) and 62% (80%) (at high apparent density), are higher in the axial than in the transverse load direction. Similar results have been seen for the compressive strength of femoral bone. For the tensile and torsional strengths, Poissons ratio and the shear modulus, only ultimate values have been found without a correlation to apparent density. For the viscoelastic behaviour of bone only data of cortical bone and in axial load direction have been described up to now. CONCLUSIONS Anisotropic FE-models of the femur could be realized for most part with the summarized material properties of bone if characterized by apparent density and load directions. Because several mechanical properties have not been correlated to these main criteria, further experimental investigations will be necessary in future.

A modular femoral implant for uncemented stem revision in THR

Abstract We present the early results of 142 uncemented femoral stem revisions using the modular MRP-Titan system. There were 70 cases with marked preoperative femoral bone defects (Paprosky type 2C and type 3); and bone grafts were used in 31 cases. At a mean follow-up of 2.3 years five cases were re-revised due to dislocation and two due to aseptic loosening. The mean Harris hip score improved from 37.4 preoperatively to 92.4. In 122 cases progressive bone regeneration on X-ray was seen; and no further osteolysis was observed.Résumé  Nous avons évalué les premiers résultats de 142 opérations de changement de la prothèse fémorale sans ciment avec le système MRP-Titan modulaire. Dans 70 cas on a observé avant l’intervention des altérations importantes du fémur (typ 2C et typ 3 après Paprosky). Une greffe osseuse dans la zone de défaut n`a été nécessaire que dans 31 cas. Pendant un temps postopératoire de 2.3 années en moyenne, deux implant a dûêtre changéà cause d`un descellement aseptique de la prothèse. Une deuxième opération a été nécessaire dans cinq cas à cause de luxations répétées. Au niveau fonctionnel, on mesure une amélioration du score de Harris de 37.4 points à 92.4 points. Dans 122 cas on a trouvé un rétablissement de la structure osseuse avec une régénération dans la zone de défaut. Des ostéolyses locales n`ont pas été visibles.

Interleukin-6: a potential inflammatory marker after total joint replacement.

Abstract In a prospective study C-reactive protein (CRP) and interleukin-6 (IL-6) measurements were taken serially in 30 patients before and after 20 total hip arthroplasties (THR) and 10 total knee arthroplasties (TKR). There were no peri- and postoperative complications. Postoperatively the IL-6 serum concentration increased rapidly and peaked 6 h postoperatively at maximum levels (399±140 pg/ml). There was a mean half-life of 15 h and thereafter a rapid return to normal concentrations. In comparison, the postoperative CRP concentration rose more slowly and reached maximum levels (138±54 mg/l) on the second postoperative day. There was thereafter a slow descent with a mean half-life of 62 h. There was no significant difference between the patients with THR and those with TKR (P>0.05). IL-6 is therefore a superior marker for the inflammatory phase after THR and TKR.Résumé Nous avons contrôlé la ”C-Reactive Protein” (CRP) et l’”Interieukin-6” (IL-6) chez 30 patients avant et après l’implantation de 20 prothèses totales de la hanche et 10 prothèses totales du genou. L’évolution péri- et postopératoire chez tous les patients était sans complications. Les valeurs de la CRP étaient déterminées par turbidimétrie immunologique et les valeurs de l’IL-6 étaient déterminées par dosage immunologique des enzymes. La concentration de IL-6 dans le sérum augmentait très vite après l’opération et atteignait, 6 h après, ses valeurs maximales. Par contre les concentrations du CRP augmentaient moins vite et atteignaient leurs valeurs maximales seulement le 2’jour après l’opération. La détermination de IL-6 s’avère très adaptée pour le contrôle de l’évolution chimique après implantation d’une prothèse totale.

Diagnostic and therapeutic management of lumbar and thoracic spondylodiscitis – an evaluation of 59 cases

Abstract Fifty-nine patients with spondylodiscitis (SD) of the thoracic and/or lumbar spine were followed-up clinically and radiologically [X-ray, computed tomography (CT), magnetic resonance imaging (MRI)] over a mean time of 2.2 years (1–6.5 years). All patients without abscess formation (n = 35) were treated conservatively. Out of the group with abscess formation (n = 24) 6 patients were also treated conservatively, 11 were drained under CT control and 7 were operated. At time of diagnosis, “signs of florid inflammation” were seen in 60% of the roentgenograms, in 93% of the CTs and in all of the MRIs. The sensitivity to differentiate between SD with and without abscess formation was 85% by MRI and 69% by CT. “Signs of regressive inflammation” and “signs of increasing osseous consolidation”, essential facts for starting remobilization, could first be seen using CT 6 weeks after onset of therapy. Using MRI these signs were seen with a considerable delay at 12 weeks. Clinically, only 3 of the 59 analyzed patients developed recurrent SD. In conclusion, MRI is the radiological method of choice for establishing the diagnosis of SD, in particular with regard to differentiating between cases with and without abscess formations. In contrast, CT is superior for performing success control after treatment. Therapeutically, conservative, minimal-invasive and operative procedures are not rival but rather complementary.

Surface pretreatments for medical application of adhesion

Medical implants and prostheses (artificial hips, tendono- and ligament plasties) usually are multi-component systems that may be machined from one of three material classes: metals, plastics and ceramics. Typically, the body-sided bonding element is bone.The purpose of this contribution is to describe developments carried out to optimize the techniques , connecting prosthesis to bone, to be joined by an adhesive bone cement at their interface. Although bonding of organic polymers to inorganic or organic surfaces and to bone has a long history, there remains a serious obstacle in realizing long-term high-bonding strengths in the in vivo body environment of ever present high humidity.Therefore, different pretreatments, individually adapted to the actual combination of materials, are needed to assure long term adhesive strength and stability against hydrolysis. This pretreatment for metal alloys may be silica layering; for PE-plastics, a specific plasma activation; and for bone, amphiphilic layering systems such that the hydrophilic properties of bone become better adapted to the hydrophobic properties of the bone cement. Amphiphilic layering systems are related to those developed in dentistry for dentine bonding.Specific pretreatment can significantly increase bond strengths, particularly after long term immersion in water under conditions similar to those in the human body. The bond strength between bone and plastic for example can be increased by a factor approaching 50 (pealing work increasing from 30 N/m to 1500 N/m).This review article summarizes the multi-disciplined subject of adhesion and adhesives, considering the technology involved in the formation and mechanical performance of adhesives joints inside the human body.

Interleukin-6 in serum and in synovial fluid enhances the differentiation between periprosthetic joint infection and aseptic loosening.

The preoperative differentiation between septic and aseptic loosening after total hip or knee arthroplasty is essential for successful therapy and relies in part on biomarkers. The objective of this study was to assess synovial and serum levels of inflammatory proteins as diagnostic tool for periprosthetic joint infection and compare their accuracy with standard tests. 120 patients presenting with a painful knee or hip endoprosthesis for surgical revision were included in this prospective trial. Blood samples and samples of intraoperatively acquired joint fluid aspirate were collected. White blood cell count, C-reactive protein, procalcitonin and interleukin-6 were determined. The joint aspirate was analyzed for total leukocyte count and IL-6. The definite diagnosis of PJI was determined on the basis of purulent synovial fluid, histopathology and microbiology. IL-6 in serum showed significantly higher values in the PJI group as compared to aseptic loosening and control, with specificity at 58.3% and a sensitivity of 79.5% at a cut-off value of 2.6 pg/ml. With a cut-off >6.6 pg/ml, the specificity increased to 88.3%. IL-6 in joint aspirate had, at a cut-off of >2100 pg/ml, a specificity of 85.7% and sensitivity of 59.4%. At levels >9000 pg/ml, specificity was almost at 100% with sensitivity just below 50%, so PJI could be considered proven with IL-6 levels above this threshold. Our data supports the published results on IL-6 as a biomarker in PJI. In our large prospective cohort of revision arthroplasty patients, the use of IL-6 in synovial fluid appears to be a more accurate marker than either the white blood cell count or the C-reactive protein level in serum for the detection of periprosthetic joint infection. On the basis of the results we recommend the use of the synovial fluid biomarker IL-6 for the diagnosis of periprosthetic joint infection following total hip and knee arthroplasty.

Spinal stabilization in Duchenne muscular dystrophy: principles of treatment and record of 31 operative treated cases.

The aim of this study was to report results of prophylactic spinal stabilization in patients with Duchenne muscular dystrophy. There is still debate regarding the ideal instrumentation. A prospective study of a consecutive series of 31 patients stabilized with the ISOLA system from D2 to S1 will be presented. The mean follow-up was 22 months (range, 1-60 months). The evaluation of the Cobb angle and pelvic obliquity revealed the following: 1) Cobb angle: preoperation, 48.6 degrees (range, 22-82 degrees); postoperation, 12.5 degrees (range, 0-30 degrees); follow-up, 12.5 degrees (range, 0-42 degrees); and 2) pelvic obliquity: preoperation, 18.2 degrees (range, 3-40 degrees); postoperation, 3.8 degrees (range, 0-13 degrees); follow-up, 5.1 degrees (range, 0-14 degrees). Spinal stabilization with the ISOLA system was found to be a suitable treatment for scoliosis owing to Duchenne muscular dystrophy. It should be carried out after loss of ambulation as soon as a progressive curve of more than 20 degrees is documented. The complication rate was found to be high.

The morse taper junction in modular revision hip replacement : a biomechanical and retrieval analysis

All biomaterials used for total joint surgery are subjected to wear mechanisms. Morse taper junctions of modular hip revision implants are predilection sites for both fretting and crevice corrosion, dissociation and breakage of the components. The aim of this study is to quantify wear and study metallurgical changes of Morse taper junctions of in-vitro and in-vivo loaded modular revision stems. Three modular revision stems (MRP-Titan, Peter Brehm GmbH, Germany) were loaded by a servohydraulic testing machine. The loads and conditions used exceeded by far the values required by ISO-standard 7206. The tests were performed with maximum axial loads of 3,500 N to 4,000 N over 10-12 x 10(6) cycles at 2 Hz. Additionally, the female part of the taper junctions were coated with blood and bone debris. The free length of the implant was set to 200 mm. One other MRP stem was investigated after retrieval following 5.5 years of in-vivo use. All contact surfaces of the modular elements were assessed by visual inspection, optical microscopy and scanning electron microscopy (SEM). The degree of plastic deformation of the male part of the morse taper junction was determined by contouroscopy. None of the morse taper junctions broke or failed mechanically. Corrosion and wear affected all tapers, especially at the medial side. The retrieved implant showed no cracks and the amount of debris measured only one third of that for the stems tested in-vitro. The present retrieval and laboratory investigations have proven, that the morse taper junctions of the MRP-titanium stem are stable and resistant to relevant wear mechanisms. The longevity of the junctions for clinical use is given. If an optimal taper design is selected, the advantages of modular femoral components in total hip revision arthroplasty will outweigh the possible risks.

Outcomes of a Modular Intercalary Endoprosthesis as Treatment for Segmental Defects of the Femur, Tibia, and Humerus

BackgroundResection of diaphyseal bone tumors for local tumor control and stabilization often results in an intercalary skeletal defect and presents a reconstructive challenge for orthopaedic surgeons. Although many options for reconstruction have been described, relatively few studies report on the functional outcomes and complications of patients treated with modular intercalary endoprostheses.Questions/purposesThe objectives of this study were to examine clinical outcomes after reconstruction with a modular intercalary endoprosthesis with a specific focus on (1) the rate of complication or failure; (2) differences in complication rates by anatomic site; (3) functional results as assessed by the Musculoskeletal Tumor Society System (MSTS); and (4) differences in complication rate between patients treated with cemented versus noncemented fixation.MethodsWe conducted a retrospective chart review of patients treated with a modular intercalary endoprosthesis from three musculoskeletal oncology centers from 2008 to 2013. The indication for use of this intercalary endoprosthesis was segmental bone loss from aggressive or malignant tumor with sparing of the joint above and below and deemed unsuitable for biologic reconstruction. No other implant was used for this indication during this period. During this period, 41 patients received a total of 44 intercalary implants, which included 18 (40%) humeri, 5 (11%) tibiae, and 21 (48%) femora. There were 27 (66%) men and 14 (34%) women with a mean age of 63 years (range, 18–91 years). Eight patients (20%) had primary bone tumors and 33 (80%) had metastatic lesions. Thirty-five (85%) patients were being operated on as an initial treatment and six (15%) for revision of a previous reconstruction. Twenty-nine (66%) procedures had cemented stem fixation and 15 (34%) were treated with noncemented fixation. The overall mean followup was 14 months (range, 1–51 months). Patients with primary tumors had a mean followup of 19 months (range, 4–48 months) and patients with metastatic disease had a mean followup of 11 months (range, 1–51 months). Causes of implant failure were categorized according to Henderson et al. [19] into five types as follows: Type I (soft tissue failure), Type II (aseptic loosening), Type III (structural failure), Type IV (infection), and Type V (tumor progression). At 2 years of followup, 38 (93%) of these patients were accounted for with three (7%) lost to followup. MSTS functional assessment was available for 39 of 41 patients (95%).ResultsAt latest followup of these 41 patients, 14 (34%) patients were dead of disease, two patients (5%) dead of other causes, seven (17%) are continuously disease-free, one (2%) shows no evidence of disease, and 17 (41%) are alive with disease. There were 12 (27%) nononcologic complications. Five (11%) of these were Type II failures occurring in noncemented implants between the stem and bone, and six (14%) were Type III failures occurring in cemented implants at the clamp-rod implant interface. One patient developed a deep infection (2%, Type IV failure) and underwent removal of the implant. Additionally, one patient (2%, Type V failure) was treated by amputation after local progression of his metastatic disease. Complications were more common in femoral reconstructions than in tibial or humeral reconstructions. Twelve of 21 patients (57%) with femoral reconstructions had complications versus 0% of tibial or humeral reconstructions (0 of 23; odds ratio [OR], 62; 95% confidence interval [CI], 3–1154; p < 0.0001). The mean overall MSTS score was 77%. Implants with cemented fixation (29) had higher mean MSTS scores when compared with implants with noncemented (15) fixation (84% versus 66%, p = 0.0017). The complication rate was 33% in noncemented cases and 21% in cemented cases (p = 0.39); however, Type II failure at the bone-stem interface was associated with noncemented fixation and Type III failure at the clamp-rod interface was associated with cemented fixation (OR, 143; 95% CI, 2.413–8476; p = 0.0022).ConclusionsThe results of this study indicate that this modular intercalary endoprosthesis yields equivalent results to other studies of intercalary endoprostheses in terms of MSTS scores. We found that patients treated with intercalary endoprostheses in the femur experienced more frequent complications than those treated for lesions in either the humerus or tibia and that the femoral complication rate of this endoprosthesis is higher when compared with other studies of intercalary endoprostheses for femoral reconstruction. Further studies are still needed to determine the long-term outcomes of this endoprosthesis in patients with primary tumors where longevity of the implant is of more importance than in the metastatic setting. We recommend cemented fixation for this intercalary modular endoprostheses because this provides improved MSTS scores and allows immediate return to weightbearing, which is of advantage to metastatic patients with limited lifespans.Level of EvidenceLevel III, therapeutic study.

A new adhesive technique for internal fixation in midfacial surgery

BackgroundThe current surgical therapy of midfacial fractures involves internal fixation in which bone fragments are fixed in their anatomical positions with osteosynthesis plates and corresponding screws until bone healing is complete. This often causes new fractures to fragile bones while drilling pilot holes or trying to insert screws. The adhesive fixation of osteosynthesis plates using PMMA bone cement could offer a viable alternative for fixing the plates without screws. In order to achieve the adhesive bonding of bone cement to cortical bone in the viscerocranium, an amphiphilic bone bonding agent was created, analogous to the dentin bonding agents currently on the market.MethodsThe adhesive bonding strengths were measured using tension tests. For this, metal plates with 2.0 mm diameter screw holes were cemented with PMMA bone cement to cortical bovine bone samples from the femur diaphysis. The bone was conditioned with an amphiphilic bone bonding agent prior to cementing. The samples were stored for 1 to 42 days at 37 degrees C, either moist or completely submerged in an isotonic NaCl-solution, and then subjected to the tension tests.ResultsWithout the bone bonding agent, the bonding strength was close to zero (0.2 MPa). Primary stability with bone bonding agent is considered to be at ca. 8 MPa. Moist storage over 42 days resulted in decreased adhesion forces of ca. 6 MPa. Wet storage resulted in relatively constant bonding strengths of ca. 8 MPa.ConclusionA new amphiphilic bone bonding agent was developed, which builds an optimizied interlayer between the hydrophilic bone surface and the hydrophobic PMMA bone cement and thus leads to adhesive bonding between them. Our in vitro investigations demonstrated the adhesive bonding of PMMA bone cement to cortical bone, which was also stable against hydrolysis. The newly developed adhesive fixing technique could be applied clinically when the fixation of osteosynthesis plates with screws is impossible. With the detected adhesion forces of ca. 6 to 8 MPa, it is assumed that the adhesive fixation system is able to secure bone fragments from the non-load bearing midfacial regions in their orthotopic positions until fracture consolidation is complete.