Removal of free light chains in hemodialysis patients without multiple myeloma: a crossover comparison of three different dialyzers.

BACKGROUND: Immunoglobulin light chains are classified as middle molecule uremic toxins able to interact with B lymphocyte membranes leading to the activation of transmembrane signaling. The ensuing impairment of neutrophil function can contribute to the chronic inflammation state of uremic patients, and the increased risk of bacterial infections or vascular calcifications. The aim of this crossover observational study was to assess the difference in free light chain removal by three different hemodialysis filters in patients not affected by multiple myeloma. METHODS: Free light chain removal was compared in the polymethylmethacrylate (PMMA) membrane Filtryzer BK-F, the polyphenylene HFR17 filter and the conventional polysulfone filter F7HPS. Twenty chronic hemodialysis patients were enrolled: mean age was 67.7 ± 17.0 years, M/F = 14/6, dialysis vintage (months) 25.5 ± 32.0. The patients were randomized into two groups of treatment lasting 6 weeks each. The dialysis sessions checked were the midweek sessions and the blood was drawn at times 0, 120' and 240'. Kappa (k) and lambda (λ) light chain levels, ß2microglobulin (ß2M), C reactive protein (CRP) and albumin were checked. RESULTS: K light chain levels were 345.0 ± 100.0 mg/L, λ light chains were 121.4 ± 27.0 mg/L. The values of k light chains at times 120' and 240' were significantly lower with PMMA and HFR17 than those obtained with F7. The reduction ratio per session (RRs) for k light chains was 44.1 ± 4.3% with HFR17, 55.3 ± 3.4% with PMMA, 25.7 ± 8.3% with F7 (p = 0.018). The RRs for λ light chains was 30.3 ± 2.9% with HFR17, 37.8 ± 17.3% with PMMA, 14.0 ± 3.9% with F7 (p = 0.032). As to ß2M, RRs was 42.4 ± 3.2% with HFR17 vs. 33.9 ± 2.8% with PMMA vs. 6.3 ± 1.9% with F7 (p = 0.022). The three filters tested showed no differences in CRP or albumin levels. CONCLUSION: In terms of light chain and ß2M removal, the PMMA and on-line HFR filters are similar and both are significantly more effective than the F7 filter in chronic dialysis patients. TRIAL REGISTRATION: The present trial was registered retrospectively ( NCT02950389 , 31/10/2016).

Complicação tardia de preenchimento cutâneo após facelift: relato de caso / Late complication of cutaneous filling after a facelift: a case report

Os autores apresentam o caso de uma paciente submetida 7 anos após aplicação de polimetilmetacrilato (PMMA) a um facelift com implante de prótese mentoniana, o qual evoluiu com granuloma por corpo estranho em região distante da aplicação do preenchimento. Após quase um ano de tratamento, a paciente evoluiu com resolução do caso.

The authors present the case of a patient who underwent a facelift with a chin implant 7 years after polymethylmethacrylate (PMMA) implantation, which evolved with foreign body granuloma in a region distant from the filling application. After nearly a year of treatment, the patient evolved with resolution of the granuloma.

Effect of storage temperature and equilibration time on polymethyl methacrylate (PMMA) bone cement polymerization in joint replacement surgery.

BACKGROUND: In cemented joint arthroplasty, the handling characteristics (doughing, working, and setting times) of polymethyl methacrylate (PMMA) bone cement is important as it determines the amount of time surgeons have to optimally position an implant. Storage conditions (temperature and humidity) and the time given for PMMA cement to equilibrate to ambient operating theater (OT) temperatures are often unregulated and may lead to inconsistencies in its handling characteristics. This has not been previously studied. Hence, the purpose of this study was to investigate the effect of storage temperatures on the handling characteristics of PMMA cement and the duration of equilibration time needed at each storage temperature to produce consistent and reproducible doughing, setting, and working times. METHODS: SmartSet® HV cement was stored at three different controlled temperatures: 20 °C (control), 24 °C, and 28 °C for at least 24 h prior to mixing. The cement components were then brought into a room kept at 20 °C and 50 % humidity. Samples were allowed to equilibrate to ambient conditions for 15, 30, 45, and 60 min. The cement components were mixed and the dough time, temperature-versus-time curve (Lutron TM-947SD, Lutron Electronics, Inc., Coopersburg, PA), and setting time were recorded. Analysis was performed using the two-way ANOVA test (IBM SPSS Statistics V.22). RESULTS: At 20 °C (control) storage temperature, the mean setting time was 534 ± 17 s. At 24 °C storage temperature, the mean setting time was 414 ± 6 s (p < 0.001*) with 15 min of equilibration, 446 ± 11 s (p < 0.001*) with 30 min of equilibration, 501 ± 12 s (p < 0.001*) with 45 min of equilibration, and 528 ± 15 (p > 0.05) with 60 min of equilibration. At 28 °C storage temperature, the mean setting time was 381 ± 8 s (p < 0.001*) with 15 min of equilibration, 432 ± 30 s (p < 0.001*) with 30 min of equilibration, 487 ± 9 (p < 0.001*) with 45 min of equilibration, and 520 ± 16 s (p > 0.05) with 60 min of equilibration. CONCLUSIONS: This study reflects the extent to which storage temperatures and equilibration times can potentially affect the handling characteristics of PMMA cement. We recommend institutions to have a well-regulated temperature and humidity-controlled facility for storage of bone cements and a protocol to standardize the equilibration time of cements prior to use in the OT to improve consistency and reproducibility of the handling characteristics of PMMA cement.

[Bone cement adhesion on ceramic surfaces - surface activation of retention surfaces of knee prostheses by atmospheric plasma versus thermal surface treatment]. / Zementhaftung auf keramischen Oberflächen - Oberflächenaktivierung der Retentionsflächen von Knieendoprothesen durch atmosphärisches Plasma vs. thermischer Oberflächenbehandlung.

AIM: CoCrMo alloys are contraindicated for allergy sufferers. For these patients, uncemented and cemented prostheses made of titanium alloy are indicated. Knee prostheses machined from that alloy, however, may have poor tribological behaviour, especially in relation to UHMWPE inlays. Therefore, for knee replacement cemented high-strength oxide ceramic prostheses are suitable for allergy sufferers and in cases of particle-induced aseptic loosening. For adhesion of bone cement, the ceramic surface, however, only exposes inefficient mechanical retention spots as compared with a textured metal surface. Undercuts generated by corundum blasting which in the short-term are highly efficient on a CoCrMo surface are not possible on a ceramic surface due to the brittleness of ceramics. Textures due to blasting may initiate cracks which will weaken the strength of a ceramic prosthesis. Due to the lack of textures mechanical retention is poor or even not existent. Micromotions are promoted and early aseptic loosening is predictable. Instead silicoating of the ceramic surface will allow specific adhesion and result in better hydrolytic stability of bonding thereby preventing early aseptic loosening. Silicoating, however, presupposes a clean and chemically active surface which can be achieved by atmospheric plasma or thermal surface treatment. METHOD: In order to evaluate the effectiveness of silicoating the bond strengths of atmospheric plasma versus thermal surface treated and silicate layered ZPTA surfaces were compared with "as-fired" surfaces by utilising TiAlV probes (diameter 6 mm) for traction-adhesive strength tests. After preparing samples for traction-adhesive strength tests (sequence: ceramic substrate, silicate and silane, protective lacquer [PolyMA], bone cement, TiAlV probe) they were aged for up to 150 days at 37 °C in Ringer's solution. RESULTS: The bond strengths observed for all ageing intervals were well above 20 MPa and much higher and more hydrolytically stable for silicate layered compared with "as-fired" ZPTA samples. CONCLUSION: Silicoating may be effective for achieving high initial bond strength of bone cement on surfaces of oxide ceramics and also suitable to stabilise bond strength under hydrolytic conditions as present in the human body in the long-term. Activation by atmospheric plasma or thermal surface treatment seems to be effective for activation prior to silicoating. Due the proposed silicate layer migration, micromotions and debonding should be widely reduced or even eliminated.

The effect of application time of two types of bone cement on the cement-bone interface strength.

The aim of this study was to investigate whether the application time of bone cement would have an effect on the cement-bone interface strength in two types of commercially available bone cements. CMW1 Radiopaque(®) (CMW1) and SmartSetHV(®) (SmartSet) were applied to bovine cancellous bone specimens at 2 and at 4 min. Specimens were loaded to failure and the shear strength of the cement-bone interface was calculated. The mean shear strength (±standard deviation) of the cement-bone interface was 2.79 ± 1.29 MPa for CMW1 applied at 2 min; 1.35 ± 0.89 MPa for CMW1 applied at 4 min; 2.93 ± 1.21 MPa for SmartSet applied at 2 min and 3.00 ± 1.11 MPa for SmartSet applied at 4 min. Compared to all other groups, the cement-bone interface strength was significantly lower when CMW1 was applied to the bone specimens at 4 min (p < 0.05). There was no significant difference in the cement-bone interface strength when SmartSet was applied to bone at 2 and at 4 min. Under these testing conditions, the cement-bone interface strength was not affected by the time of application of SmartSet to bone. However, it was significantly lower when CMW1 was applied to bone at 4 min.

A cadaver study to compare vertebral augmentation with a high-viscosity cement to augmentation with conventional lower-viscosity cement.

STUDY DESIGN: Comparison of extravasations in fractured cadaver vertebrae augmented with commercial low-viscosity versus high-viscosity cements. OBJECTIVE: Use of high-resolution, 3-dimensional (3D) imaging to test the hypothesis that high-viscosity cements can reduce the type and severity of extravasations after vertebral augmentation procedures. SUMMARY OF BACKGROUND DATA: Cement extravasations are one of the primary complications of vertebral augmentation procedures. There is some evidence that high-viscosity cements might reduce extravasations, but additional data are needed to confirm the early findings. METHODS: A range of vertebral fractures were created in fresh human cadavers. One group was then augmented with a low-viscosity polymethylmethacrylate (PMMA)-based cement and the other group injected with high-viscosity PMMA-based cement. High-resolution computerized tomography exams were obtained, and extravasations were assessed using 3D volume renderings. The type and severity of extravasations were recorded and analyzed. RESULTS: The proportion of vertebrae with any type of extravasation through the posterior wall to the spinal canal, into small vessels laterally or anteriorly, through the endplates, or anywhere around the body was not significantly different between the high-viscosity and low-viscosity groups. There was significantly less severe extravasation through the endplates (P=0.02), and a trend toward less severe extravasation through vessels (P=0.06) with the high versus low-viscosity cements. CONCLUSIONS: In agreement with previous research, high-viscosity PMMA-based cement may help to reduce the more severe forms of extravasations after vertebral augmentation procedures in newly fractured vertebrae.

Comparative assessment of sacral screw loosening augmented with PMMA versus a calcium triglyceride bone cement.

STUDY DESIGN: A calcium triglyceride bone cement (CTBC) was compared with the gold-standard polymethylmethacrylate (PMMA) to assess the stability of augmented sacral screw fixation under cyclic loading. OBJECTIVE: To determine whether CTBC augmentation of a pedicle screw would provide a similar level of fixation in the S1 pedicles compared with PMMA augmentation. SUMMARY OF BACKGROUND DATA: Numerous studies have shown the advantages of using PMMA to augment screw fixation; however, its biomechanical properties are not ideal. CTBC offers potential benefits such as being low exothermic, a modulus of elasticity closer to bone, and the potential for osteoconductivity, but its comparative performance in this situation has not been previously evaluated. METHODS: Six cadaveric sacra were used in this study; 3.0 mL volumes of PMMA (Simplex P) and CTBC (Kryptonite™ Bone Cement) were injected into contralateral screw tracts, with the screw immediately inserted after cement injection. After a 12-hour setting period, the sacrum was potted in a custom fixture and mounted to the frame of a materials testing machine. Alternating flexion and extension bending moments were applied at 1 Hz. Flexion moments were applied starting at 0.5 Nm and increased by 1 Nm after every 1000 cycles until the screw had reached 6° of rotation relative to its starting position. Extension moments were maintained at 0.5 Nm. Screw rotation relative to bone was determined in real time by a custom optical tracking system and was analyzed using two-way repeated-measures analyses of variance (ANOVAs) and post hoc Student-Newman-Keuls tests (α = 0.05). RESULTS: To reach 6° of screw rotation, the PMMA-augmented screw required more loading cycles (15,464 ± 2526 vs. 10,277 ± 1762 cycles; P = 0.006) and a larger applied moment (15.3 ± 2.2 vs. 10.5 ± 1.7 Nm; P = 0.010) than CTBC-augmented screw. CONCLUSION: The PMMA augmentation provided increased resistance to cyclic loading compared with the CTBC augmentation for sacral pedicle screw fixation, but both augmentations well exceeded previously published findings for nonaugmented screws.

Bending characteristics of polymethylmethacrylate columns, connecting bars of carbon fiber, titanium, and stainless steel used in external skeletal fixation and an acrylic interface.

OBJECTIVE: To (1) mechanically evaluate polymethylmethacrylate (PMMA) columns of various sizes and compare them to connecting bar materials (carbon fiber composite, titanium, stainless steel) and (2) compare the properties of an intact PMMA column to those of an acrylic interface. STUDY DESIGN: Experimental mechanical study. SAMPLE POPULATION: Experiment 1: 6 groups of 6 specimens each; experiment 2: 2 groups of 12 specimens each. METHODS: All specimens were tested in 3-point bending. Stiffness, yield strength, and ultimate strength values were calculated for each specimen. RESULTS: PMMA 1 columns (23.25 mm) compared favorably to titanium or stainless-steel bars. PMMA 3 columns (30.15 mm) and carbon fiber bars had similar yield strength but PMMA 3 columns were less stiff than carbon fiber bars. PMMA 3 columns had lower bending modulus and a higher variability in their mechanical properties than PMMA 1 or PMMA 2 (25.64 mm) columns. Acrylic interface specimens were less strong but as stiff as intact specimens. CONCLUSION: An acrylic interface was easily created and had acceptable biomechanical characteristics. CLINICAL RELEVANCE: PMMA 2 and PMMA 3 columns are not recommended for clinical use at this time. Further tests are needed to analyze an acrylic patch in a more clinically relevant loading model.

Torsional stability of interference screws derived from bovine bone--a biomechanical study.

BACKGROUND: In the present biomechanical study, the torsional stability of different interference screws, made of bovine bone, was tested. Interference screws derived from bovine bone are a possible biological alternative to conventional metallic or bioabsorbable polymer interference screws. METHODS: In the first part of the study we compared the torsional stability of self-made 8 mm Interference screws (BC) and a commercial 8 mm interference screw (Tutofix). Furthermore, we compared the torsional strength of BC screws with different diameters. For screwing in, a hexagon head and an octagon head were tested. Maximum breaking torques in polymethyl methacrylate resin were recorded by means of an electronic torque screw driver. In the second part of the study the tibial part of a bone-patellar tendon-bone graft was fixed in porcine test specimens using an 8 mm BC screw and the maximum insertion torques were recorded. Each interference screw type was tested 5 times. RESULTS: There was no statistically significant difference between the different 8 mm interference screws (p = 0.121). Pairwise comparisons did not reveal statistically significant differences, either. It was demonstrated for the BC screws, that a larger screw diameter significantly leads to higher torsional stability (p = 9.779 x 10(-5)). Pairwise comparisons showed a significantly lower torsional stability for the 7 mm BC screw than for the 8 mm BC screw (p = 0.0079) and the 9 mm BC screw (p = 0.0079). Statistically significant differences between the 8 mm and the 9 mm BC screw could not be found (p = 0.15). During screwing into the tibial graft channel of the porcine specimens, insertion torques between 0.5 Nm and 3.2 Nm were recorded. In one case the hexagon head of a BC screw broke off during the last turn. CONCLUSIONS: The BC screws show comparable torsional stability to Tutofix interference screws. As expected the torsional strength of the screws increases significantly with the diameter. The safety and in vivo performance of products derived from xenogeneic bone should be the focus of further investigations.

Acrylic bone cements: influence of time and environment on physical properties.

Acrylic bone cements are in extensive use in joint replacement surgery. They are weight bearing and load transferring in the bone-cement-prosthesis complex and therefore, inter alia, their mechanical properties are deemed to be crucial for the overall outcome. In spite of adequate preclinical test results according to the current specifications (ISO, ASTM), cements with inferior clinical results have appeared on the market. The aim of this study was to investigate whether it is possible to predict the long term clinical performance of acrylic bone cement on the basis of mechanical in vitro testing. We performed in vitro quasistatic testing of cement after aging in different media and at different temperatures for up to 5 years. Dynamic creep testing and testing of retrieved cement were also performed. Testing under dry conditions, as required in current standards, always gave higher values for mechanical properties than did storage and testing under more physiological conditions. We could demonstrate a continuous increase in mechanical properties when testing in air, while testing in water resulted in a slight decrease in mechanical properties after 1 week and then levelled out. Palacos bone cement showed a higher creep than CMW3G and the retrieved Boneloc specimens showed a higher creep than retrieved Palacos. The strength of a bone cement develops more slowly than the apparent high initial setting rate indicates and there are changes in mechanical properties over a period of five years. The effect of water absorption is important for the physical properties but the mechanical changes caused by physical aging are still present after immersion in water. The established standards are in need of more clinically relevant test methods and their associated requirements need better definition. We recommend that testing of bone cements should be performed after extended aging under simulated physiological conditions. Simple quasistatic and dynamic creep tests seem unable to predict clinical performance of acrylic bone cements when the products under test are chemically very similar. However, such testing might be clinically relevant if the cements exhibit substantial differences.

The effect of screw length and bone cement augmentation on the fixation strength of iliac screws: a biomechanical study.

STUDY DESIGN: Comparison of the biomechanical fixation strengths offered by 3 iliac screw fixation techniques: short screw, short screw augmented with cement, and long screw. OBJECTIVE: Evaluate the effect of screw length and bone cement augmentation on the fixation strength of iliac screw upon fatigue loading. SUMMARY OF BACKGROUND DATA: Iliac screws have been used in treating spinal disorders such as spinal deformity, spondylolisthesis, and sacral tumor. In clinical practices, both short screws and long screws are being used. It has been reported that short iliac screws have a higher rate of loosening. Therefore, short iliac screws are being used with bone cement augmentation to improve fixation. To date, no biomechanical study has compared the strengths of these 3 different iliac screw fixation techniques. METHOD: Fresh, frozen human cadaveric pelvis specimens (n = 18, 12 males, 6 females, average age 61 y) were used. Bone density was measured to characterize bone quality. The specimens were randomly divided into 2 groups. In group 1 (n = 8), short screws of 7.0-mm diameter and 70 + or - 4 mm length (as the length of exceeding over ischial notch) and long screw of 7.0-mm diameter and 120 + or - 4 mm length were placed on either side of the pelvis (left and right). In group 2 (n = 10), short iliac screws were placed after augmentation with polymethyl methacrylate bone cement on 1 side of the pelvis and long iliac screw were placed on the other side (left and right). Cyclic loading ranging from 20 to 200 N was applied to each screw at a frequency of 2 Hz up to 5000 cycles. Pullout tests were then conducted at the rate of 5 mm/min after the fatigue test, and the maximum pullout strength for each screw was recorded and analyzed. RESULTS: The maximum pullout strength of the long screw and short screw groups after fatigue conditioning were 2386 + or - 1470 and 833 + or - 681 N respectively. Significant difference was found between the 2 groups (P < 0.05). The short iliac screw had a higher loosening rate. The pullout force of the short screw fixation with augmentation and the long screw fixation after cyclic loading were 2436 + or - 915 and 2529 + or - 1055 N, respectively. No significant difference was found between the 2 groups (P > 0.05). CONCLUSIONS: Short iliac screws are susceptible to loosening after cyclic loading. Bone cement augmentation of short screws has demonstrated a significant increase in the fixation strength of short screws to an extent similar to that of long iliac screws. Thus, short iliac screw fixation after augmentation with bone cement will be a viable clinical option for spino-pelvic reconstruction.

The effect of pulsed jet lavage in vertebroplasty on injection forces of PMMA bone cement: an animal study.

Percutaneous vertebroplasty, comprising of the injection of polymethylmethacrylate (PMMA) into vertebral bodies, is an efficient procedure to stabilize osteoporotic compression fractures as well as other weakening lesions. Besides fat embolism, cement leakage is considered to be one of the major and most severe complications during percutaneous vertebroplasty. The viscosity of the PMMA during injection plays a key role in this context. It was shown in vitro that the best way to lower the risk of cement leakage is to inject the cement at higher viscosity, which is requires high injection forces. Injection forces can be reduced by applying a newly developed lavage technique as it was shown in vitro using human cadaver vertebrae. The purpose of this study was to prove the in vitro results in an in vivo model. The investigation was incorporated in an animal study that was performed to evaluate the cardiovascular reaction on cement augmentation using the lavage technique. Injection forces were measured with instrumentation for 1 cc syringes, additionally acquiring plunger displacement. Averaged injection forces measured, ranged from 12 to 130 N and from 28 to 140 N for the lavage group and the control group, respectively. Normalized injection forces (by viscosity and injection speed) showed a trend to be lower for the lavage group in comparison to the control group (P = 0.073). In conclusion, the clinical relevance on the investigated lavage technique concerning lowering injection forces was only shown by trend in the performed animal study. However, it might well be that the effect is more pronounced for osteoporotic vertebral bodies.

Cumulative effect of disinfection procedures on microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin.

Microwave irradiation has been used for disinfection of dentures instead of chemical solutions; yet, its effect on resin properties after repeated procedures still is unclear. This study evaluated the cumulative effect of two disinfection methods on Knoop microhardness and tridimensional stability of a poly(methyl methacrylate) denture base resin. For the microhardness measurement, 24-resin discs received mechanical polishing and were submitted to the following treatments: (1) control (no disinfection), (2) chemical disinfection (immersion in 100ppm chloride solution for 24h), or (3) microwave disinfection (irradiation at 690 W for 6 min). Disinfection procedures were performed twice (T1, T2) with a 7-day interval. Knoop microhardness was recorded after polishing (T0) and after T1 and T2. For the dimensional stability test (measured by the adaptation of the denture bases), 36-maxillary denture bases were obtained from type III dental stone casts duplicated from a metallic master model and submitted to the disinfection treatment. Adaptation of denture bases was measured at baseline (T0) and after T1 and T2 by weighing a vinyl polysiloxane film reproducing the gap between resin base and master model. Data were analyzed by ANOVA GLM for repeated measures and Bonferroni's test, alpha = 0.05. Knoop microhardness was not modified by any disinfection procedure but decreased over time. Denture resin bases submitted to microwave disinfection had gradual increase of distortion over time, while bases immersed in chloride solution did not differ from the control group and remained dimensionally stable from T1 to T2.

[Mechanical in vitro testing of fifteen commercial bone cements based on polymethylmethacrylate]. / Mechanische In-vitro-Prüfung von fünfzehn kommerziellen Knochenzementen auf der Basis von Polymethylmethacrylat.

UNLABELLED: INTRODUCTION The long-term stability in cemented hip arthroplasty depends not only on the mechanical properties of the acrylic bone cements but also on an improvement of cementing techniques. MATERIAL AND METHODS: The bending strengths of 15 commonly used bone cements (CMW 3 Gentamycin; CMW 3; Refobacin Palacos R; Palacos R; Palamed G; Palamed; Cerafixgenta; Cerafix; Duracem; Simplex Tobramycin; Simplex P; Versabond; Sulcem; Sulcem 3 Genta; Copal) have been mechanically tested in a standardised in vitro four-point bending test (ISO 5833). The fatigue fracture surfaces were morphologically analysed with light microscopy. RESULTS: The highest values of bending strength were found in vacuum mixed specimens cured under pressure. The lowest values of strength were seen in with blood contaminated specimens. Fatigue cracks were often initiated from air bubbles or other inclusions such as antibiotics or blood in the bone cement. CONCLUSIONS: The present in vitro study highlights the supposition that the quality of the cementing technique is of eminent importance in determining the long-term stability of cemented hip arthroplasties.

Segmental polymethylmethacrylate-augmented pedicle screw fixation in patients with bone softening caused by osteoporosis and metastatic tumor involvement: a clinical evaluation.

OBJECTIVE: Instrumentation of the osteoporotic spine may result in bone failure because of pedicle screw loosening and pullout. A clinical evaluation of a novel fenestrated bone tap used in pedicle screw augmentation was performed to determine the performance and safety of this technique. METHODS: Over a 2.5-year period, the clinical and radiographic results of 119 consecutive patients who underwent instrumented arthrodesis were reviewed. Of these patients, 23 had bone softening secondary to osteoporosis and/or metastatic spinal tumor involvement. These patients underwent surgical decompression and spinal instrumentation. RESULTS: Six patients (26%) had metastatic spine disease (squamous cell lung carcinoma, renal cell carcinoma, bladder carcinoma, breast, prostate, and uterine adenocarcinoma); five patients (22%) had a degenerative spondylolisthesis; and 12 patients (52%) had burst fractures, eight as a result of benign causes and four as a result of metastatic disease. Four (17%) patients underwent revision surgery of previous pedicle screw failure resulting from bone softening and pseudarthrosis. A total of 98 levels were fused using 158 polymethylmethacrylate-augmented screws. None of the patients experienced operative death, myocardial infarction, hypoxemia, intraoperative hypotension, radiculopathy, or myelopathy. Asymptomatic anterior cement extravasation was observed in nine patients (39%). There was one asymptomatic polymethylmethacrylate pulmonary embolus and one wound infection. There was no significant relationship between cement extravasation and the quantity used, levels augmented, or location (P > 0.05). There were no construct failures. CONCLUSION: Polymethylmethacrylate-augmented pedicle screw fixation reduces the likelihood of pedicle screw loosening and pullout in patients with osteoporosis requiring instrumented arthrodesis.

Adjacent vertebral failure after vertebroplasty: a biomechanical study of low-modulus PMMA cement.

PMMA is the most common bone substitute used for vertebroplasty. An increased fracture rate of the adjacent vertebrae has been observed after vertebroplasty. Decreased failure strength has been noted in a laboratory study of augmented functional spine units (FSUs), where the adjacent, non-augmented vertebral body always failed. This may provide evidence that rigid cement augmentation may facilitate the subsequent collapse of the adjacent vertebrae. The purpose of this study was to evaluate whether the decrease in failure strength of augmented FSUs can be avoided using low-modulus PMMA bone cement. In cadaveric FSUs, overall stiffness, failure strength and stiffness of the two vertebral bodies were determined under compression for both the treated and untreated specimens. Augmentation was performed on the caudal vertebrae with either regular or low-modulus PMMA. Endplate and wedge-shaped fractures occurred in the cranial and caudal vertebrae in the ratios endplate:wedge (cranial:caudal): 3:8 (5:6), 4:7 (7:4) and 10:1 (10:1) for control, low-modulus and regular cement group, respectively. The mean failure strength was 3.3 +/- 1 MPa with low-modulus cement, 2.9 +/- 1.2 MPa with regular cement and 3.6 +/- 1.3 MPa for the control group. Differences between the groups were not significant (p = 0.754 and p = 0.375, respectively, for low-modulus cement vs. control and regular cement vs. control). Overall FSU stiffness was not significantly affected by augmentation. Significant differences were observed for the stiffness differences of the cranial to the caudal vertebral body for the regular PMMA group to the other groups (p < 0.003). The individual vertebral stiffness values clearly showed the stiffening effect of the regular cement and the lesser alteration of the stiffness of the augmented vertebrae using the low-modulus PMMA compared to the control group (p = 0.999). In vitro biomechanical study and biomechanical evaluation of the hypothesis state that the failure strength of augmented functional spine units could be better preserved using low-modulus PMMA in comparison to regular PMMA cement.

The polymethyl methacrylate cervical cage for treatment of cervical disk disease Part III. Biomechanical properties.

BACKGROUND: In a previous article, we used the PMMA cervical cage in the treatment of single-level cervical disk disease and the preliminary clinical results were satisfactory. However, the mechanical properties of the PMMA cage were not clear. Therefore, we designed a comparative in vitro biomechanical study to determine the mechanical properties of the PMMA cage. METHODS: The PMMA cervical cage and the Solis PEEK cervical cage were compressed in a materials testing machine to determine the mechanical properties. RESULTS: The compressive yield strength of the PMMA cage (7030 +/- 637 N) was less than that of the Solis polymer cervical cage (8100 +/- 572 N). The ultimate compressive strength of the PMMA cage (8160 +/- 724 N) was less than that of the Solis cage (9100 +/- 634 N). The stiffness of the PMMA cervical cage (8106 +/- 817 N/mm) was greater than that of the Solis cage (6486 +/- 530 N/mm). The elastic modulus of the PMMA cage (623 +/- 57 MPa) was greater than that of the Solis cage (510 +/- 42 MPa). The elongation of PMMA cage (43.5 +/- 5.7%) was larger than that of the Solis cage (36.1 +/- 4.3%). CONCLUSIONS: Although the compressive yield strength and ultimate compressive strength of the PMMA cervical cage were less than those of the Solis polymer cage, the mechanical properties are better than those of the cervical vertebral body. The PMMA cage is strong and safe for use as a spacer for cervical interbody fusion. Compared with other cage materials, the PMMA cage has many advantages and no obvious failings at present. However, the PMMA cervical cage warrants further long-term clinical study.

Validation of the small-punch test as a technique for characterizing the mechanical properties of acrylic bone cement.

This paper examines the validity of using the small-punch test technique as a means of quantifying the mechanical properties of acrylic bone cement under different test conditions. The elastic moduli calculated using the small-punch test method were compared with data measured using the international standard for acrylic bone resin, ISO 5833. Conclusions from the study indicate that the small-punch test is a reproducible miniature specimen test method that can be used to characterize the mechanical properties of retrieved acrylic bone cement as used in total joint replacement surgery. Moreover, the test conditions were found to influence the elastic modulus of acrylic bone cement. The test temperature had a greater effect on the elastic behaviour of the bone cement than the test medium.