Development and Finite Element (FE) analysis of a novel short hip stem concept.

Introduction: In order to improve the anchorage behavior of short hip stems, this development project aims at designing a short hip stem concept that preserves the femoral neck and minimizes interference with the physiological stress distribution of the femur. The new design will be evaluated according to ISO 7206-4 which is the standard for testing Implants for surgery. Methods: Basic CAD models based on an established short stem prosthesis were created and evaluated using finite element analysis. The best design was further developed to achieve a more deformable stem while maintaining stability. The model was validated through in vitro testing. Results: The "H-Beam" short stem showed a higher degree of deformation of approximately 142-144% compared to the established short stem. The FE model had a relative error of 0.98% and 1.07% compared to the in vitro tests. An operating procedure was outlined for this new short stem design. Discussion: The FE model is deemed valid due to small differences in comparison to in vitro testing. The short-stem prosthesis is more flexible and can be easily adapted to individual anatomy during surgery. The prosthesis length is similar to conventional prostheses, but the new stem design could allow better and faster osteointegration while preserving the cancellous bone structure.

Acoustical determination of primary stability of femoral short stem during uncemented hip implantation.

BACKGROUND: Preparing the medullary space of the femur aims to create an ideal form-fitting of cementless implants to provide sufficient initial stability, which is crucial for osseous integration, ensuring good long-term results. Hammering the implant into the proximal femur creates a press-fit anchoring of the endoprosthesis in the medullary space. Implanting the optimal size of the shaft for best fitting should avoid damage to the bone. Modified acoustic signals in connection with implantation are being detected by surgeons and might be related to the primary stability of the implant. METHODS: This study aims to explore the relationship between frequency sound patterns and the change in stem stability. For this purpose, n = 32 Metha® short stems were implanted in a clinical setting by the same surgeon. During implantation, the sounds were recorded. To define a change in the acoustic system response during the operation, the individual blows of the implantation sequence were correlated with one another. FINDINGS: An algorithm was able to subdivide through sound analysis two groups of hammer blows (area 1 and area 2) since the characteristics of these groups showed significant differences within the frequency range of 100 Hz to 24 kHz. The edge between both groups, detected by the algorithm, was validated with expert surgeons' classifications of the same data. INTERPRETATION: In conclusion, monitoring, the hammer blows sound might allow quantification of the primary stability of the implant. Sound analysis including patient parameters and a classification algorithm could provide a precise characterization of implant stability.

Retrospective clinical and X-ray-based outcome analysis of a short-stem hip arthroplasty taking into account the operative learning curve over 7 years in the 3-year control course.

INTRODUCTION: Self-monitoring is crucial to work progressively with a high-quality standard. A retrospective analysis is a valuable tool for studying the postoperative outcome of a prosthesis and for evaluating the learning process for the surgeon. MATERIALS AND METHODS: The learning process of one surgeon was analysed in 133 cases of hip arthroplasty. These were divided into seven groups representing the surgical years 2008-2014. Over the course of 3 postoperative years, a total of 655 radiographs were analysed at regarding three radiological quality parameters (centrum-collum-diaphyseal angle (CCD angle), intramedullary fit&fill ratio (FFR), and migration) and ancillary outcome parameters (Harris Hip Score (HHS), blood loss, operating time, and complications). This period was divided into five times: 1st-day post-op, 6 M, 12 M, 24 M, and 36 M. Bivariate Spearman's correlation analysis and pairwise comparisons were performed. RESULTS: The total collective achieved a proximal FFR of over 0.8. The distal prosthesis tip migrated and was located on the lateral cortex within the first months. The CCD angle initially showed a variation with a subsequent constant course. The HHS showed a significant increase (p < 0.001) to over 90 points postoperatively. Over time, the operating time and blood loss decreased. Intraoperative complications existed only at the beginning of the learning phase. A learning curve effect can be determined for almost all parameters by comparing the subject groups. CONCLUSIONS: Operative expertise was shown to gain through a learning curve, whereby postoperative results corresponded to the system philosophy of the short hip stem prosthesis. The distal FFR and the distal lateral distance could represent the principle of the prosthesis, which overall could be an interesting approach for verification of a new parameter.

Development and validation of an algorithm to determine the minimal factors needed for non-invasive measurement of the in vivo primary stability of cementless hip implants.

Aseptic loosening is a frequent cause for revision of endoprosthesis. X-ray examinations like Radio-Stereometry-Analysis (RSA) are among the most widely used in vivo methods for its detection. Nevertheless, this method is not used routinely because of bone marker and related radiation exposure. This work aims at creating a new in vivo concept to detect implant stability measuring micromotions without x-ray and to develop a corresponding algorithm. Based on the assumption of contactless measurement, the input parameters for the algorithm are the distances of each ultrasound sensor to the object (prosthesis and bone) and its position. First, the number of parameters necessary for a precise reconstruction and measurement of micromotions between objects had to be defined. Therefore, the algorithm has been tested with simulations of these parameters. Two experimental measurements, either using contact sensors or ultrasound, were used to prove the accuracy of the algorithm. Simulations indicate a high accuracy with three distances as initial parameters for each object. Contact measurements show precise representation of micromotion, and the contactless measurements show the possibility of detecting various materials with a high resolution. This work lays the foundations for non-invasive detection of micromotions between the implant-bone interface.

Short Stem for Total Hip Arthroplasty (THA) - Overview, Patient Selection and Perspectives by Using the Metha® Hip Stem System.

Short stem hip replacement has not only gained attention but also significance over the past decades. However, there still remains uncertainty regarding the correct indications for these stems. Even companies, producing implants, have varying recommendations that are more likely based on a well-meant advice than on statistically evaluated data. Thus, it is important to evaluate the advantages and disadvantages of a short stem prosthesis. The goal of this paper is to reveal some of the existing uncertainty in this field, by analyzing the Metha® short hip stem system. This paper does not only focus on general aspects but also discusses some more specific problems, such as avascular necrosis and post-rheumatic diseases, as well as hip dysplasia and coxarthrosis. The aim is also to convey the opportunity to indicate this type of implant for elderly and obese patients as well as for femoral misalignments following post-Perthes disease, post-traumatic deformities or other malpositions of the hip.

Interleukin-1 Induces the Release of Lubricating Phospholipids from Human Osteoarthritic Fibroblast-like Synoviocytes.

(1) Background: Synovial fluid (SF) from knee joints with osteoarthritis (OA) has increased levels of phospholipids (PL). We have reported earlier that TGF-ß and IGF-1 stimulate fibroblast-like synoviocytes (FLS) to synthesize increased amounts of PLs. The current study examined whether IL-1ß induces the release of PLs in FLS and the underlying mechanism. (2) Methods: Cultured human OA FLS were treated with IL-1ß alone and with pathway inhibitors or with synthetic liver X receptor (LXR) agonists. Cholesterol hydroxylases, ABC transporters, apolipoproteins (APO), LXR, sterol regulatory binding proteins (SREBPs), and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) were analyzed by RT-PCR, Western blot, and ELISA. The release of radiolabeled PLs from FLS was determined, and statistical analysis was performed using R (N = 5-9). (3) Results: Like synthetic LXR agonists, IL-1ß induced a 1.4-fold greater release of PLs from FLS. Simultaneously, IL-1ß upregulated the level of the PL transporter ABCA1 and of cholesterol hydroxylases CH25H and CYP7B1. IL-1ß and T0901317 stimulated the expression of SREBP1c, whereas only T0901317 enhanced SREBP2, HMGCR, APOE, LXRα, and ABCG1 additionally. (4) Conclusions: IL-1ß partially controls PL levels in OA-SF by affecting the release of PLs from FLS. Our data show that IL-1ß upregulates cholesterol hydroxylases and thus the formation of oxysterols, which, as natural agonists of LXR, increase the level of active ABCA1, in turn enhancing the release of PLs.

How do the geometries of the broach handles relate to the distribution of force and moments in a femoral model?

The continuous improvement of minimally invasive hip endoprostheses surgery comes with a change in geometries of surgery instruments like the broach handles. Consequently, depending on the handles' curvature this results in a deviation between handle and femoral axis. Therefore, this study aimed to prove the influence of different handles' curvatures on the preparation of implant site and acting forces and moments in this process. Five femoral models attached to different handles (double-curved, single-curved, straight) were locked in a drop-weight device with standardize implantation forces and moments and five strokes were measured for each possible combination. Distribution of force and moment components was dependent on the handle's curvature, where the lowest variation from the standard force values was by the straight one (av:15.2% ± 0.5%) and the strongest discrepancies were exhibit by the double-curved one (av:54.3% ± 0.1%.). Moment values have also shown this trend with the lowest variation (12.4%-23.3%) by the straight one and the highest discrepancies (56,6%-90.9%) by the double-curved one. Results show that unguided axial impact introduces unwanted transverse forces and moments into the femur. Therefore, broach handles should be modified accordingly so that minimally invasive surgery remains feasible but unwanted forces or moments can still be compensated.

Comparison of Short Stems Versus Straight Hip Stems: A Biomechanical Analysis of the Primary Torsional Stability.

Cementless straight stems show very good survival rates. However, the more distal force application of straight stems may lead to release-related proximal stress-shielding. Nevertheless, this technical brief had the objective of conducting a biomechanical in vitro analysis comparing short stems with established straight stems with respect to their primary torsional stability. Two cementless short hip stems and three cementless straight hip stems were implanted in n = 5 synthetic femora each. Torsional torques were applied into the hip stems at a continuous interval of ±7 Nm. Micromotions were measured by six inductive extensometers on four different measurement levels. At the proximal measuring point, significantly smaller relative micromotions of the CLS® prosthesis could be detected compared to all other stem models (p < 0.05). In all stem models, smallest relative micromotions were found at the metaphyseal/diaphyseal measuring point. Only at the measuring point of the distal tips of the straight stems, statistically significantly lower relative micromotion of the CLS® stem compared to the Trendhip® stem could be found (p < 0.01). All the investigated stems generally display a rather comparable anchoring pattern and an almost physiological force application. Since the comparatively long straight stems present an anchoring pattern nearly identical to that of the examined short stems, a shortening of the established straight stems could be taken into consideration. This would offer the advantage of minimally invasive surgery and bone-saving resection as well as preservation of cancellous bone in case a revision would become necessary.

How screw connections influence the primary stability of acetabular cups under consideration of different bone models.

INTRODUCTION: Good osteointegration of implants requires sufficient primary stability. Aim of this study was to examine the influence of screw fixation on the primary stability of press-fit cups. METHODS: Two press-fit acetabular cups were tested with regard to the influence and number of screws and their primary stability. RESULTS: For the relatively thin-walled Allofit®-S cup, an influence of the number of screws on the different forms of movement could be demonstrated. CONCLUSIONS: We see a clear influence of the cup wall thickness on the elastic deformability and accordingly on the primary stability of the examined cups.

Outcome of short- to medium-term migration analysis of a cementless short stem total hip arthroplasty using EBRA-FCA: a radiological and clinical study.

INTRODUCTION: Stress shielding may lead to aseptic loosening which is a common reason for implant failure. An established method to identify implants with risk of implant failure caused by aseptic loosening is to measure early migration of the stem with the "Ein Bild Roentgen Analyse" femoral component analysis (EBRA-FCA). Therefore, the aim of this study was to measure the migration of a cementless short stem prosthesis via EBRA-FCA to predict the future performance. MATERIALS AND METHODS: A total collective of 71 patients were treated with a cementless short hip stem prosthesis. Indications for surgery were primary coxarthrosis, dysplasia coxarthrosis or femoral head necrosis. After surgery, the patients were followed-up immediately after 3, 6, 12, 24, 36, and 48 months and X-ray images for EBRA-FCA measurements were taken. Axial caudal migration as well as the varus/valgus tilting of the prosthesis was determined. Possible influencing factors like BMI, age, diagnosis, gender or Harris Hip Score (HHS) on the migration of the stem were assessed. RESULTS: HHS increased significantly direct postoperatively (p < 0.001). At the second follow-up the average caudal migration was 0.42 ± 0.52 mm (range: 0.00-2.85 mm) (p < 0.001). A total of 14 patients underwent a caudal migration greater than 1.5 mm until 48 months. The initial varus and valgus tilts within the first 3 months were significant (p < 0.001). No correlations between BMI, age, diagnosis, gender or HHS and the migration as well as the tilting of the cementless short hip stem prosthesis were found. CONCLUSIONS: Although initial axial caudal migration as well as tilting tendencies in varus or valgus position can be detected, there is no marked migration of the examined prosthesis after the first 48 months. Likewise, no aseptic early loosening was detected throughout the study period, which indicates good osseointegration of the short stem prosthesis.

In vitro examination of the primary stability of three press-fit acetabular cups under consideration of two different bearing couples.

BACKROUND: For preclinical statements about the anchoring behavior of prostheses, the primary stability of the prosthesis is of special importance. It was the aim of this study to examine and compare the relevant relative micromotions of three different acetabulum prostheses by introducing three-dimensional torques. METHODS: The cups were implanted under standard conditions into an anatomical artificial bone model. Three-dimensional torques were applied to the acetabular cups. Taking into account the resulting frictional moments of two different bearing couples, ceramic-on-ceramic and ceramic-on-polyethylene, the relative micromotions of the cups were recorded as maximum total micromotion, translational and rotational micromotion, and the primary stability values of the three cups were compared. RESULTS: Relative micromotion of all cup models was always significantly smaller with the CoC bearing couples than with the CoP bearing couples (p < 0.001). The rotational micromotion was always lower (p < 0.001) than the translational micromotion, and the rotational as well as the translational micromotions were each always lower than the maximum total micromotion (p < 0.001, p < 0.010). The thinnest-walled cup system always showed the largest relative micromotions. CONCLUSION: The results of our study can be interpreted as indicating that the low relative micromotions of all cups - irrespective of the use of CoC or CoP bearing couples - are within an acceptable range favoring secondary osseointegration of the implants. Furthermore, we were able to show that the cup wall thickness and the surface quality of the cup systems have an influence on the primary stability and the elastic deformability of the examined cup systems.

The Effect of Dexamethasone, Adrenergic and Cholinergic Receptor Agonists on Phospholipid Metabolism in Human Osteoarthritic Synoviocytes.

Phospholipids (PLs) possess the unique ability to contribute to synovial joint lubrication. The aim of our study was to determine for the first time the effect of dexamethasone and some adrenergic and cholinergic agonists on the biosynthesis and release of PLs from human fibroblast-like synoviocytes (FLS). Osteoarthritic human knee FLS were treated with dexamethasone, terbutaline, epinephrine, carbachol, and pilocarpine, or the glucocorticoid receptor antagonist RU 486. Simultaneously PL biosynthesis was determined through the incorporation of stable isotope-labeled precursors into PLs. Radioactive isotope-labeled precursors were used to radiolabel PLs for the subsequent quantification of their release into nutrient media. Lipids were extracted and quantified using electrospray ionization tandem mass spectrometry or liquid scintillation counting. Dexamethasone significantly decreased the biosynthesis of phosphatidylcholine, phosphatidylethanolamine (PE), PE-based plasmalogen, and sphingomyelin. The addition of RU 486 abolished these effects. A release of PLs from FLS into nutrient media was not recognized by any of the tested agents. None of the adrenergic or cholinergic receptor agonists modulated the PL biosynthesis. We demonstrate for the first time an inhibitory effect of dexamethasone on the PL biosynthesis of FLS from human knees. Moreover, our study indicates that the PL metabolism of synovial joints and lungs are differently regulated.

Development of periprosthetic bone mass density around the cementless Metha® short hip stem during three year follow up-a prospective radiological and clinical study.

PURPOSE: The purpose of this study was to check the concept of the cementless Metha® short hip stem in order to find out whether proximal physiological load transfer can be achieved. METHODS: Fourty-three patients were included. Epidemiological factors were established. The Harris Hip Score was determined and measurement of bone mass density as well as osteodensitometric and radiological measurements was carried out pre-operatively, post-operatively, and after six, 12, 24, and 36 months. RESULTS: Harris Hip Score improved from 55.9 ± 12.4 pre-operatively to 94.8 ± 8.2 after 36 months (p < 0.001). After initial reduction of bone density in zones 1 and 7 up to six months post-operatively, there was a steady approximation of bone density to the initial values (p < 0.05). CONCLUSION: The Metha® short hip stem shows good clinical results. Furthermore, there is an increase of bone density in the proximal zones 1 and 7 between six and 36 months serving as a sign of physiological load transfer.

Age-related osseointegration of a short hip stem: a clinical and radiological 24 months follow-up.

PURPOSE: The purpose of this study was to examine potential differences between patients under and over 60 years who underwent a total short hip stem arthroplasty in a 24-month follow-up in a clinical setting. METHODS: Sixty seven patients were included in this prospective study and divided in two groups. In the younger cohort 39 patients ≤ 59 years and in the older cohort 28 patients ≥ 60 years were included. Clinical and radiological examinations of the patients took place preoperatively, postoperatively and after 3, 6, 12 and 24 months. The Harris Hip Score (HHS) was raised as clinical examination. Changes of bone mass density (BMD), stress shielding, reactive lines, spot welds and sclerosing were examined as radiological analysis. RESULTS: The HHS improved from 53.6 ± 8.2 preoperative to 93.2 ± 9.6 in the younger cohort and for the older cohort from 57.6 ± 14.8 to 94.1 ± 7.6 after 24 months. BMD growth was detectable in regions of interest (ROI) 3 and 6 for both groups. Different results between the cohorts could only be detected in ROIs 4 and 5. The older cohort showed a loss of BMD of 5.95% in ROI 4 and 3.17% in ROI 5 after 24 months, whereas the younger cohort showed no loss of BMD in both ROIs. CONCLUSIONS: No significant differences or any influences of osseointegration and clinical outcome of the short hip stem for both groups were detectable. Lower losses (ROIs 1 and 2) and higher growths (ROIs 3, 4, 5) were discovered in younger patients and the HHS improved in both groups. Reasons for this result could be age, sex or the level of activity of the patients, but in both groups the short hip stem shows comparable results in clinical as well as in radiological examination. We conclude that the short hip stem seems to be an adequate treatment also for older patients.

Comparative Analysis of Peptide Composition and Bioactivity of Different Collagen Hydrolysate Batches on Human Osteoarthritic Synoviocytes.

Collagen hydrolysates (CHs) are heterogeneous mixtures of collagen peptides that are often used as nutraceuticals for osteoarthritis (OA). In this study, we compared the peptide composition and pharmacological effects of three different CH preparations (CH-Alpha®, Peptan® B 2000 and Mobiforte®) as well as their production batches. Our biochemical analysis using MALDI-TOF mass spectrometry and the ICPL™-isotope labelling method revealed marked differences between different CH preparations and even between some production batches of the same preparation. We also investigated the pharmacological effects of these CHs on human fibroblast-like synoviocytes (FLS). No significant effects on cultured FLS could be demonstrated for either production batch of CH-Alpha®, Peptan® B 2000, and Mobiforte® analyzing a small number of pharmacological relevant targets. Thus, our study already shows for the first time that different production batches of the same CH preparation as well as different CH preparations can differ significantly in their peptide composition. In this line, further studies are also needed to verify equal pharmacological efficacy of CH batches on a much broader range of (patho)physiological relevant targets. If OA patients are to be offered a safe and effective nutraceutical a better knowledge about all potential effects as well as ensuring the same active-substance levels are a prerequisite.

Effect of bearing friction torques on the primary stability of press-fit acetabular cups: A novel in vitro method.

Aseptic loosening is the main reason for revision of total hip arthroplasty, and relative micromotions between cementless acetabular cups and bone play an important role regarding their comparatively high loosening rate. Therefore, the aim of the present study was to analyze the influence of resulting frictional torques on the primary stability of press-fit acetabular cups subjected to two different bearing partners. A cementless press-fit cup was implanted in bone-like foam. Primary stability of the cup was analyzed by determining spatial total, translational, and rotational interface micromotions by means of an eddy current sensor measuring system. Torque transmission into the cup was realized by three synchronous servomotors considering resultant friction torques based on constant friction for ceramic-on-ceramic (CoC: µ = 0.044; max. resultant torque: 1.5 Nm) and for ceramic-on-polyethylene (CoP: µ = 0.063; max. resultant torque: 1.9 Nm) bearing partners. Rotational micromotion of CoC was 8.99 ± 0.85 µm and of CoP 13.39 ± 1.43 µm. Translational micromotion of CoC was 29.93 ± 1.44 µm and of CoP 39.91 ± 2.25 µm. Maximum total relative micromotions were 37.10 ± 1.07 µm for CoC and 51.64 ± 2.18 µm for CoP. Micromotions resulting from CoC were statistically lower than those resulting from CoP (p < 0.05). The described 3D-measuring set-up offers a novel in vitro method of measuring primary stability of acetabular cups. We can therefore conclude, that primary stability of acetabular cup systems can be observed using either the lower friction curve (CoC) or the higher friction curve (CoP). In future studies different cup designs or cup fixation mechanisms may be tested and compared in vitro and assessed prior to implantation. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2745-2753, 2018.

Analysis of the elastic bending characteristics of cementless short hip stems considering the valgus alignment of the prosthetic stem.

BACKGROUND: The resultant hip force causes a varus torque which must be compensated by a shear force couple depending on the stem alignment of the prosthesis. Since the prosthesis is substantially less flexible than the bone, the interior of the femur is stiffened over the entire prosthesis length. The present study thus aims at analyzing short-stem prostheses for its elastic bending characteristics, considering inappropriate valgus alignment of the prosthetic stem. METHODS: Five short stem prostheses were implanted each in synthetic femora in a standardized manner - in neutral and valgus stem alignments. Bending movements were recorded applying a tilting torque MX of ±3.5 Nm in medio-lateral direction. Variance analyses and Friedman tests were used. A P-value <.05 was considered statistically significant. FINDINGS: Bending movements b1-b6 showed significant differences (P < .05). It could be shown that different stem alignments (P < .05) and different measuring points had a highly significant influence (P < .001) on the relative movements. Compared to the AIDA®, the MiniHip™ as well as the Metha® stiffened the femur to a higher degree (P < .001). INTERPRETATION: Regarding the elastic bending behavior we see a relevant influence of the stems´ design. We conclude that the short-stem principle does not necessarily require the shortest possible prosthesis but rather a long and thin extending stem tip to optimize the lever ratios, ensuring a more physiological bending behavior of the femur. In addition, without sufficient anchoring of the prosthesis, the valgus stem alignment could favor tilting of the implant and should therefore be avoided.

Growth factors regulate phospholipid biosynthesis in human fibroblast-like synoviocytes obtained from osteoarthritic knees.

Elevated levels of growth factors and phospholipids (PLs) have been found in osteoarthritic synovial fluid (SF), although the metabolic regulation of PLs is currently unknown. This study aimed to determine the effects of growth factors on the biosynthesis of PLs by fibroblast-like synoviocytes (FLS) obtained from human osteoarthritic knee joints. Electrospray ionization tandem mass spectrometry was applied to analyse the newly synthesized PLs. In the presence of stable isotope-labelled PL precursors, cultured FLS were treated with either transforming growth factor-ß1 (TGF-ß1), bone morphogenetic protein (BMP)-2, BMP-4, BMP-7 or insulin-like growth factor-1 (IGF-1) alone or in combination with specific inhibitors of cell signalling pathways. TGF-ß1 and IGF-1 markedly stimulated the biosynthesis of phosphatidylcholine (PC) before sphingomyelin (SM) and lysophosphatidylcholine (LPC) species were stimulated. BMPs elaborated less pronounced effects. The BMPs tested have different potentials to induce the biosynthesis of phosphatidylethanolamine (PE) and PE-based plasmalogens. Our study shows for the first time that TGF-ß1 and IGF-1 substantially regulate the biosynthesis of PC, SM and LPC in human FLS. The functional consequences of elevated levels of PLs require additional study. The BMPs tested may be joint protective in that they upregulate PE-based plasmalogens that function as endogenous antioxidants against reactive oxygen species.

Effect of thermodisinfection on mechanic parameters of cancellous bone.

Revision surgery of joint replacements is increasing and raises the demand for allograft bone since restoration of bone stock is crucial for longevity of implants. Proceedings of bone grafts influence the biological and mechanic properties differently. This study examines the effect of thermodisinfection on mechanic properties of cancellous bone. Bone cylinders from both femoral heads with length 45 mm were taken from twenty-three 6-8 months-old piglets, thermodisinfected at 82.5 °C according to bone bank guidelines and control remained native. The specimens were stored at -20 °C immediately and were put into 21 °C Ringer's solution for 3 h before testing. Shear and pressure modulus were tested since three point bending force was examined until destruction. Statistical analysis was done with non-parametric Wilcoxon, t test and SPSS since p < 0.05 was significant. Shear modulus was significantly reduced by thermodisinfection to 1.02 ± 0.31 GPa from 1.28 ± 0.68 GPa for unprocessed cancellous bone (p = 0.029) since thermodisinfection reduced pressure modulus not significantly from 6.30 ± 4.72 GPa for native specimens to 4.97 ± 2.23 GPa and maximum bending force was 270.03 ± 116.68 N for native and 228.80 ± 70.49 N for thermodisinfected cancellous bone. Shear and pressure modulus were reduced by thermodisinfection around 20 % and maximum bending force was impaired by about 15 % compared with native cancellous bone since only the reduction of shear modulus reached significance. The results suggest that thermodisinfection similarly affects different mechanic properties of cancellous bone and the reduction of mechanic properties should not relevantly impair clinical use of thermodisinfected cancellous bone.

Influence of cerclages on primary stability of tumor megaprostheses subjected to distal femur defects.

BACKROUND: Purpose of this experimental study was to investigate the influence of cerclages on the primary stability of the MUTARS system using distally fractured synthetic femora. METHODS: 4 MUTARS prostheses were implanted in synthetic femora respectively. Groups consisted of 4 intact bones, 4 fractured with cerclages and 4 fractured bones without cerclages. Spatial micromovements were measured with a high-precision rotational setup. FINDINGS: The order from the weakest to the strongest torque transmission of the intact bones was rm1-rm4-rm2-rm3 (p=0.011) and of the fractured bones with cerclages rm4-rm1-rm3-rm2 (p=0.013). The MUTARS stems broke out of the fractured femoral shaft by removing cerclages (p<0.001) and by the influence of bone defect A (p<0.001). Overall micromovements of the intact bones were lower than those of the fractured bones without cerclages (p<0.001) and overall micromovements of the fractured bones with cerclages were lower than those of bones without cerclages (p<0.001). INTERPRETATION: Due to high press-fit at the proximal and distal isthmus region fissural fractures of the femur may occur. This should always be taken into account. It is advisable to secure them and provide a prophylaxis for these fissural fractures by means of cerclages.