True Graft Research Articles

Predicting Autologous Hamstring Graft Diameter in the Pediatric Population Using Preoperative Magnetic Resonance Imaging and Demographic Data

Background: Anterior cruciate ligament (ACL) reconstruction before 18 years of age has been linked with an increased risk for failure when the graft diameter is <8 mm. Purpose/Hypothesis: The purpose of this study was to determine whether autologous hamstring graft size can be reliably predicted with the use of preoperative magnetic resonance imaging (MRI) measurements. We hypothesized that the average of multiple axial cross-sectional area MRI measurements for the semitendinosus tendon and gracilis tendon would alone accurately predict graft diameter. Additionally, factoring in specific demographic data to the MRI cross-sectional areas would provide a synergistic effect to the accuracy of graft diameter predictions. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: We retrospectively reviewed 51 pediatric patients undergoing ACL reconstructions (age <18 years) performed using either a quadruple-strand semitendinosus tendon or combined double-bundle semitendinosus tendon–gracilis tendon autograft. Preoperative axial MRI scans at multiple points along the craniocaudal axis—specifically, at the level of the joint line, 3 cm cephalad to the medial tibial plateau, and 5 cm cephalad to the medial tibial plateau—were used to determine the combined cross-sectional area of the semitendinosus and gracilis tendons. The MRI measurements were analyzed using Pearson correlation as well as regression analysis to evaluate strength of correlation between measurements. Binomial linear regression was used to analyze the same predictive variables assessed by multiple regression. Results: The predicted graft diameter was within 0.5 mm of the intraoperative graft size in 37 of 51 (72.5%) patients and within 1 mm of the intraoperative graft size in 49 of 51 (96.1%). With the addition of demographics, the accuracy of predictions increased to 78.4% within 0.5 mm and 98% within 1 mm of the actual graft size. Additionally, 38 of 42 patients whose true graft diameter was ≥8 mm were correctly classified, giving a sensitivity of 90.4%. For those whose true graft diameter was <8 mm, 8 of 9 patients were correctly classified; therefore, the specificity was 88.9%. Conclusion: The results of our study suggest that taking the average of multiple preoperative MRI measurements can be used to accurately predict autologous hamstring graft size when approaching pediatric patients undergoing ACL reconstruction.

283. In Vivo Selection of MGMT(P140K) Gene Modified Hematopoietic Cells in the Nonhuman Primate Unmasks a Dormant Pool of Repopulating Clones with Progenitor Cell Ontology

Previously published gene modified cell transplantation studies in nonhuman primate models have described several key features of hematopoietic reconstitution (Kim, S. et al., 2014 and Wu, C. et al., 2014). These studies applied either retrovirus integration site analysis (ISA) or DNA barcode sequencing (DBS) to identify hematopoietic clones in bone marrow or peripheral blood cells. However, these distinct methods detected long-term clones at different time points (1 year after transplant by ISA; ~3 months after transplant by DBS), and neither evaluated reconstitution in the context of selective advantage, which is often the case in gene therapy. Here, we tracked tens of thousands of unique clones in 8 pigtail macaques for up to 10 years following myeloablative transplantation with autologous, lentivirus (LV) gene-modified CD34+ cells. Seven animals received cells gene modified with the P140K mutant methylguanine methyltransferase transgene, conferring resistance to O6- benzylguanine (O6BG) and bis-chloroethylnitrosourea (BCNU) chemotherapy. In two animals, MGMT(P140K)-expressing LVs were DNA barcoded, permitting simultaneous ISA and DBS tracking. Gene marking in peripheral blood cells ranged from 2.3% to 66%. Direct comparison of ISA and DBS demonstrated that abundant clones (&gt 1% of sequence reads) are readily detected by both methods, but DBS captures up to 2-fold more lower abundance clones. Before in vivo selection with O6BG/BCNU, we observed a cell dose-dependent, successive pattern of hematopoietic reconstitution by ISA analysis, with short-term clones declining within 100 days after transplantation. Long-term clones were observed as early as 1 month after transplant. In the first year after transplant, persistent clones ranged from 8% to 54% of clones detected at a &gt 1% frequency, and remained stable in the absence of selective pressure. Importantly, when O6BG/BCNU was administered we observed novel clonal patterns, which directly correlated with transplanted cell dose and time of chemotherapy administration after transplant. In all animals, chemotherapy induced emergence of previously undetected clones. In animals receiving cell doses exceeding 35×106 CD34+ cells/kg (n = 2), chemotherapy more than 1 year after transplant induced a completely novel clonal repertoire. Gene ontology analysis of integration loci among early, long-term and dormant clonal populations identified the greatest functional overlap between early and dormant pools. These data suggest that some short-term repopulating clones revert to a dormant phase within the first year after transplant. Additionally, these data indicate that transplant of excess CD34+ cell numbers results in early dormancy of a large proportion of early repopulating clones. Together, these findings suggest that previous estimates of short- and long-term clonal frequency are an underestimate of true graft repopulation potential.

In Vivo Selection Unmasks a Dormant Pool of Repopulating Hematopoietic Clones

Long-term clonal tracking studies utilizing hematopoietic stem and progenitor cells (HSPCs) in nonhuman primates receiving myeloablative transplantation demonstrate a successive pattern of repopulation: short-term repopulating cells are succeeded by long-term clones. However, the duration of short-term repopulation and the numbers of clones contributing to either short or long-term repopulation are unclear. Here, we tracked >11,000 unique clones in 8 pigtail macaques for up to 9 years following myeloablative transplantation with autologous, lentivirus gene-modified CD34+ HSPCs. Seven of these animals received cells expressing the P140K mutant methylguanine methyltransferase transgene, which is resistant to the combination of O6-benzylguanine (O6BG) and bis-chloroethylnitrosourea (BCNU) chemotherapy, thus conferring a selective advantage to gene-modified cells in vivo. After transplantation and before in vivo selection with O6BG/BCNU, we observed a successive pattern of hematopoietic reconstitution, with short-term clones declining within 100 days after transplantation. Within the first year after transplant, the percent of persistent clones varied from animal-to-animal, ranging from 8% to 54% of clones detected at a >1% frequency, and remained stable in the absence of selective pressure. Importantly, when animals engrafted with P140K-expressing cells were administered O6BG/BCNU we observed novel clonal patterns, which directly correlated with transplanted cell dose and time of chemotherapy administration after transplant. In all animals, chemotherapy induced emergence of previously undetected clones. In animals receiving ≤12x106 CD34+ cells/kg at the time of transplant (n = 4), chemotherapy also induced a re-emergence of previously declined short-term repopulating clones or a stabilization (i.e. decreased fluctuation) of repopulating clones identified between 100 days and 1 year after transplant. However, in animals receiving robust cell doses, ≥35x106 CD34+ cells/kg (n = 2), chemotherapy more than 1 year after transplant induced a completely novel clonal repertoire. In one animal receiving 22x106 CD34+ cells/kg at transplant, chemotherapy administration beginning <1 year (253 days) after transplant induced clonal stability, which was maintained through two additional chemotherapy treatments. These data suggest that some short-term repopulating clones may have long-term repopulation ability, but revert to a dormant phase within the first year after transplant. Additionally, these data indicate that transplant of excess repopulating cells results in early dormancy of a large proportion of repopulating clones. Together, these findings suggest that previous estimates of HSPC frequency based on clone tracking are an underestimate of true graft repopulation potential. DisclosuresNo relevant conflicts of interest to declare.

Sirolimus Conversion Regimen Versus Continued Calcineurin Inhibitors in Liver Allograft Recipients: A Randomized Trial

A large prospective, open-label, randomized trial evaluated conversion from calcineurin inhibitor (CNI)- to sirolimus (SRL)-based immunosuppression for preservation of renal function in liver transplantation patients. Eligible patients received liver allografts 6-144 months previously and maintenance immunosuppression with CNI (cyclosporine or tacrolimus) since early posttransplantation. In total, 607 patients were randomized (2:1) to abrupt conversion (<24 h) from CNI to SRL (n = 393) or CNI continuation for up to 6 years (n = 214). Between-group changes in baseline-adjusted mean Cockcroft-Gault GFR at month 12 (primary efficacy end point) were not significant. The primary safety end point, noninferiority of cumulative rate of graft loss or death at 12 months, was not met (6.6% vs. 5.6% in the SRL and CNI groups, respectively). Rates of death at 12 months were not significantly different, and no true graft losses (e.g. liver transplantation) were observed during the 12-month period. At 52 weeks, SRL conversion was associated with higher rates of biopsy-confirmed acute rejection (p = 0.02) and discontinuations (p < 0.001), primarily for adverse events. Adverse events were consistent with known safety profiles. In conclusion, liver transplantation patients showed no demonstrable benefit 1 year after conversion from CNI- to SRL-based immunosuppression.

WALL SHEAR AND CIRCUMFERENTIAL STRESS CHANGES IN A PORCINE DOUBLE-LAYER VEIN GRAFT

This study aimed to evaluate short-term changes of wall shear stress and circumferential stress in a self-designed double-layer vein graft in a porcine vein graft model. In this study, left and right hind femoral arteries of 40 white pigs were randomly divided into an experimental group (double-layer vein graft) and a control group (single-layer vein graft). At one hour and then at one, two and four weeks after venous bypass grafting, sets of ten animals underwent Doppler-ultrasonic and electromagnetic flowmeter examinations to calculate wall shear stress in middle sections of the vein grafts. Then, the vein grafts were excised and subjected to mechanical tests to assess the circumferential stress. As a result, the double-layer vein grafts showed an increase in wall shear stress by 43.5% compared with the control group at one hour after venous bypass grafting. With time wall shear stress gradually increased, the intimal circumferential stress gradually decreased in the two groups. Intimal circumferential stress in the experimental group was significantly lower than that in the control group at each observational time-point. Hence, the double-layer support of the vein graft may have contributed towards a rise in wall shear stress and reduction in circumferential stress in the true vein graft over the four-week period after venous bypass grafting, and thus conferring some protection to the true vein graft.

The Incidence and Clinical Relevance of Graft Hypertrophy After Matrix-Based Autologous Chondrocyte Implantation

Background: Graft hypertrophy is the most common complication of periosteal autologous chondrocyte implantation (p-ACI). Purpose: The aim of this prospective study was to analyze the development, the incidence rate, and the persistence of graft hypertrophy after matrix-based autologous chondrocyte implantation (mb-ACI) in the knee joint within a 2-year postoperative course. Study Design: Case series; Level of evidence, 4. Methods: Between 2004 and 2007, a total of 41 patients with 44 isolated cartilage defects of the knee were treated with the mb-ACI technique. The mean age of the patients was 35.8 years (standard deviation [SD], 11.3 years), and the mean body mass index was 25.9 (SD, 4.2; range, 19-35.3). The cartilage defects were arthroscopically classified as Outerbridge grades III and IV. The mean area of the cartilage defect measured 6.14 cm2 (SD, 2.3 cm2). Postoperative clinical and magnetic resonance imaging (MRI) examinations were conducted at 3, 6, 12, and 24 months to analyze the incidence and course of the graft. Results: Graft hypertrophy developed in 25% of the patients treated with mb-ACI within a postoperative course of 1 year; 16% of the patients developed hypertrophy grade 2, and 9% developed hypertrophy grade 1. Graft hypertrophy occurred primarily in the first 12 months and regressed in most cases within 2 years. The International Knee Documentation Committee (IKDC) and visual analog scale (VAS) scores improved during the postoperative follow-up time of 2 years. There was no difference between the clinical results regarding the IKDC and VAS pain scores and the presence of graft hypertrophy. Conclusion: The mb-ACI technique does not lead to graft hypertrophy requiring treatment as opposed to classic p-ACI. The frequency of occurrence of graft hypertrophy after p-ACI and mb-ACI is comparable. Graft hypertrophy can be considered as a temporary excessive growth of regenerative cartilage tissue rather than a true graft hypertrophy. It is therefore usually not a persistent or systematic complication in the treatment of circumscribed cartilage defects with mb-ACI.

Synthesis and characterization of dextrin-grafted polypropylene

We carried out the graft copolymerization of the water-soluble natural polymer dextrin onto preirradiated polypropylene (PP) in an aqueous medium using benzoyl peroxide (BPO) as the radical initiator. PP was irradiated by γ rays from a Co60 source at a constant dose rate of 3.40 kGy/h to introduce hydroperoxide linkages, which served as the sites for grafting. The graft copolymerization was studied as a function of different reaction parameters, and the maximum percentage grafting (Pg; 55%) of dextrin onto PP was obtained at optimum conditions of [BPO] = 5.165 × 10−2 mol/L, temperature = 60°C in 120 min with 15 mL of water. Different grafting parameters, such as the percentage apparent grafting, percentage grafting, and percentage true grafting have been evaluated. The graft copolymers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Swelling studies were carried out in pure, binary, ternary, and quaternary solvent systems composed of water, ethanol (EtOH), dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF) at different ratios. The maximum swelling percentage PP-g-dextrin (both composite and true graft) was observed in pure DMSO and DMF followed by EtOH and water. Water-retention studies of PP and PP-g-dextrin (both composite and true graft) were investigated at different time periods, temperatures, and pH values. The maximum percentage water retention of PP-g-dextrin (composite, 124%) was observed at 8 h and 50°C in a neutral medium (pH 7). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Starch‐grafted polypropylene: Synthesis and characterization

AbstractGraft copolymerization of starch has been carried out onto preirradiated polypropylene (PP) in an aqueous medium using benzoyl peroxide (BPO) as the radical initiator. The maximum percentage of grafting (115%) of starch onto PP was obtained at optimum conditions of BPO concentration, 1.239 × 10−3 moles; temperature, 65°C; in 120 min. using 30 mL of water. Swelling studies were carried out in pure, binary, ternary and quaternary solvent systems comprising of water, ethanol (EtOH), dimethylsulphoxide (DMSO), and N,N‐dimethylformamide (DMF) in different ratios. Maximum swelling is observed in DMSO and DMF, followed by EtOH and least in water for true graft. Water retention studies of pristine PP and PP‐g‐Starch (both composite and true graft) were investigated at different time periods, temperature and pH. The composite contains grafted PP, unreacted starch and unreacted PP whereas true graft is the product from which both unreacted polymers have been removed. Maximum % water retention of PP‐g‐Starch (composite) (110%) was observed in 8 h at 50°C in neutral medium (pH = 7). The graft copolymers were characterized by FTIR, DTG, DTA, TGA, and SEM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis and characterization of polypropylene‐grafted gelatin

AbstractModification of polypropylene (PP) has been successfully carried out by graft copolymerization of gelatin, by chemical method using benzoyl peroxide (BPO) as radical initiator. PP was preirradiated by gamma rays at a constant dose rate of 3.40 kGy/h before grafting to introduce hydroperoxide groups. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage of grafting of gelatin (115%) was obtained at BPO concentration = 4.132 × 10−2 mol/L in 120 min at 70°C using 30 mL of water. Characterization of PP‐g‐gelatin was carried out through FTIR, thermogravimetric analysis, and scanning electron microscopy. Swelling studies were carried out in pure, binary, ternary, and quaternary solvent systems comprising distilled water, ethanol, dimethylsulphoxide (DMSO), and N,N‐dimethylformamide (DMF) in different ratios. Maximum swelling of PP‐g‐gelatin (both composite and true graft) was observed in pure solvents that is, DMSO followed by DMF, ethanol, and water and was higher than that observed in the mixed solvent system. Water retention studies of unmodified PP, that is, pristine PP and PP‐g‐gelatin (both composite and true graft) were investigated at different time periods, temperatures and pH. Maximum % water retention for PP‐g‐gelatin (composite; 170%) was observed in 8 h at 50°C in neutral medium (pH = 7). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Can pre-operative measures predict quadruple hamstring graft diameter?

The use of autologous grafts such as the quadrupled semitendinosus and gracilis tendon is very common in anterior cruciate ligament (ACL) reconstruction. The diameter of such grafts can be variable and thus unpredictable prior to surgery. In this study, we hypothesized that parameters such as gender, height, age, and body mass index (BMI) can be used pre-operatively to reveal the true graft diameter. All hamstring ACL reconstructions from 1994 to 2002 were reviewed. 536 cases (302 females, 234 males) met the inclusion criteria. Quadruple hamstring constructs and femoral tunnel diameters were measured using 1 mm increment graft sizers. Pre-operative measures of height, weight, body mass index, gender, and age were obtained. Multiple regression analysis was used to build a predictive model of the quadruple hamstring graft diameter. The results of the study demonstrated that males had significantly larger grafts than females (8.1 ± 0.8 vs. 7.5 ± 0.6 mm). Multiple regression analysis on the entire group showed that pre-operative height ( p < 0.0002) and gender ( p < 0.0047), but not age ( p < 0.06) or weight ( p < 0.019) were significant predictors of graft diameter. Height ( p < 0.0001) was a specific predictor solely in men. In females, none of the pre-operative measures were predictive of graft diameters. Patient height and gender can be used as pre-operative indicators of in vivo quadrupled hamstring graft diameter. Regardless of other variables, 42% of females will have tunnel diameters of 7 mm or less. An alternative graft choice should be discussed pre-operatively if graft sizes may be of concern for the tall and large female patients.

130 Apligraf Heals a Recalcitrant Pressure Ulcer of 28 Years Duration

Background: Apligraf, a bioengineered living skin construct, has been shown to accelerate the healing of venous leg and diabetic foot ulcerations. It appears to function as cell-based therapy (e.g., delivering growth factors), rather than as a true graft. Given this mechanism of action, its use could be expanded to areas in which traditional skin grafting is not routinely employed. Methods: A 64-year-old wheel-chairbound Caucasian male presented to the wound clinic with a grade III left trochanteric pressure ulcer which had been present since 1976. He had been seen by numerous physicians and treated with debridement, topical antimicrobials, negative pressure therapy, growth factors, and a variety of dressings. We spent several months preparing the wound bed: maintaining adequate moisture balance, performing serial debridement, utilizing offloading surfaces and reducing the bacterial burden. His nutritional status was optimized. The wound bed developed a healthy granulating base but failed to close. Results: A single unit of Apligraf was meshed at a 1:1.5 ratio and applied to the wound. It was fixed in place using a nonstick silicone dressing, foam, and a self-adhesive covering. The dressing was changed weekly in the wound clinic. The initial response was a decrease in wound depth followed by steady epithelialization. Complete closure occurred 17 weeks after grafting. The wound has not recurred. Conclusion: This single case study suggests that bilayered cell therapy may have application in difficult wounds, such as pressure ulcerations. Further study into the efficacy of Apligraf in pressure ulcerations is ongoing.

Occlusion of a Giant Saphenous Vein Graft Aneurysm Using Distal Coil Embolisation and a Proximal Vascular Plug

An asymptomatic giant true saphenous vein graft aneurysm was successfully occluded by percutaneous distal coil embolisation combined with deployment of a proximal Amplatzer vascular occlusion plug. The aneurysm cavity was excluded from both antegrade flow via the aortosaphenous anastamosis and retrograde flow via the distal left anterior descending coronary artery (supplied by a left internal mammary artery graft), to reduce the risk of subsequent aneurysm rupture.

Modification of polypropylene through intercrosslinking graft copolymerization of poly(vinyl alcohol): Synthesis and characterization

AbstractModification of polypropylene (PP) has been successfully carried out through intercrosslinking of poly(vinyl alcohol) (PVA), by chemical graft copolymerization method using benzoyl peroxide (BPO) as radical initiator. Prior to grafting, PP was irradiated by gamma rays at a constant dose rate of 3.40 kGy/h to introduce hydroperoxide groups. Optimum conditions pertaining to maximum percentage of grafting were evaluated as a function of different reaction parameters. Maximum percentage ofgrafting of PVA (75%) was obtained at [BPO] = 5.51 × 10−2 mol/L in 120 min at 70°C using 15 mL of water. Characterization of pristine PP and PP‐g‐PVA was carried out by FTIR, thermogravimetric analysis, and scanning electron micrography. Swelling studies were carried out in pure, binary, ternary, and quaternary solvent systems comprising of water, ethanol (EtOH), dimethylsulfoxide (DMSO) and N, N‐dimethylformamide (DMF) in different ratios. Maximum swelling values of PP‐g‐PVA (both composite and true graft) was observed in pure DMSO followed by DMF, EtOH, and water and it was also higher than that observed in mixed solvent system. Water retention studies of pristine PP and PP‐g‐PVA (both composite and true graft) were investigated at different time periods, temperature, and pH. Maximum % water retention of PP‐g‐PVA (composite) (108%) was observed in 8 h at 50°C in neutral medium (pH = 7). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Graft Copolymerization on to Cellulose Using Binary Mixture of Monomers

The graft copolymerization of acrylonitrile (AN) and ethyl acrylate (EA) comonomers onto cellulose has been carried out using ceric ammonium nitrate (CAN) as an initiator in the presence of nitric acid at 35±0.1°C. The addition of ethyl acrylate as comonomer has shown a significant effect on overall and individual graft copolymerization of acrylonitrile on cellulose. The graft yield (%GY) and other grafting parameters viz. true grafting (%GT), graft conversion (%CG), cellulose number (Ng) and frequency of grafting (GF) were evaluated on varying the concentration of comonomers from 6.0–30.0×10−1 mol dm−3 and ceric (IV) ions concentration from 2.5–25×10−3 mol dm−3 at constant feed composition (fAN 0.6) and constant concentration of nitric acid (7.5×10−2 mol dm−3) in the reaction mixture. The graft yield (%GY) and other grafting parameters were optimal at 15×10−1 mol dm−3 concentration of comonomers and at 10×10−3 mol dm−3 concentration of ceric ammonium nitrate. The graft yield (%GY) and composition of grafted chains (FAN) was optimal at a feed composition (fAN) of 0.6. The energy of activation (Ea) for graft copolymerization has been found to be 16 kJ mol−1. The molecular weight (Mw) and molecular weight distribution (Mw/Mn) of grafted chains was determined by GPC and found to be optimum at 15×10−1 mol dm−3 concentration of comonomer in the reaction mixture. The composition of grafted chains (FAN) determined by IR method was used to calculate the reactivity ratios of monomers, which has been found to be 0.62 (r1) and 1.52 (r2), respectively for acrylonitrile (AN) and ethyl acrylate (EA) monomers used for graft copolymerization. The energy of activation for decomposition of cellulose and grafted cellulose was determining by using different models based on constant and different rate (β) of heating. Considering experimental observations, the reaction steps for graft copolymerization were proposed.

Kinetic Study of the Al‐Schiff's Base Initiated Polymerization of ε‐caprolactone and Synthesis of Graft Poly(methylmethacrylate‐g‐caprolactone)

AbstractGraft copolymers of polycaprolactone (PCL) on polymethacrylate (PMMA) backbone have been successfully synthesized and characterized by SEC, 1H and 13C NMR spectroscopy. The strategy used consisted of polymerizing ε‐CL, followed by end‐functionalization of the resulting PCL using methacryloyl chloride. Free radical polymerization of the methacryl double bond lead to the C‐C polymer backbone and an overall graft copolymer. The polymerization of ε‐caprolactone was achieved using Al‐Schiff's base isopropoxide (HAPENAlOiPr) in DCM at ambient temperature. SEC and MALDI analysis of the polymers confirmed that mostly linear chains were obtained with the Al initiator, up until high monomer conversion. The low molar mass PCL was then end‐capped with a methacryloyl group, in a quantitative manner, as evidenced by 1H NMR. The macromonomer thus obtained was copolymerized in small proportions with methyl methacrylate by conventional free radical polymerization and atom transfer radical polymerization (ATRP). Analysis of the products by NMR and SEC showed the presence of true graft copolymers and the absence of homopolymers.

A new method to determine graft angles after knee ligament reconstruction

In posterior cruciate ligament (PCL) reconstruction, the acute angle of the graft at the tibial tunnel (‘the killer curve’) has been implicated as a cause of graft failure. Similar acute angles also occur at the entrance to the femoral tunnel. We describe a method to determine the true graft angle, based on measurements taken from two orthogonal radiographs in a cadaveric model, analysed using three-dimensional geometry. The true angles for the tibial and femoral tunnels are presented for a variety of tunnel positions. The effect on these angles of knee flexion and extension is analysed. Resultant graft-tunnel forces at a constant ligament tension are described. Based on these results, drilling the femoral tunnel from outside-in and lateral placement of the tibial tunnel are theoretically advantageous.

Graft Polyether Polyols Based on α-Methylstyrene and Acrylonitrile for Flexible Polyurethane Foams

The radical grafting copolymerisation reaction of α-Methylstyrene (α-MeSt) and Acrylonitrile (AN) as compared with the usual grafting copolymerisation reaction of Styrene (St) and AN on the polyetheric chains of polyether polyols for polyurethanes, homopolymers of propyleneoxide (PO) or copolymers PO-ethyleneoxide (EO), has been studied. The effect of St substitution by α-MeSt, another cheap and accessible vinylic monomer, has been investigated, concerning the properties of the resultant graft polyethers and the physico-mechanical properties of the resultant flexible polyurethane foams. Special attention was paid to the solid fractions isolated from the polymer polyols proving that the the synthesized products are true graft copolymers and not a physical mixture between vinyl copolymers and polyether polyols. The substitution of St by MeSt leads to graft polyether polyols having a lower degree of grafting but with excellent stability and lower viscosity as compared with the corresponding products based on St-AN. The flexible polyurethane foams based on α-MeSt-AN graft polyethers have very good properties, comparable with those derived from St-AN graft polyethers, but the compression set has an unexpected lower value, better than those of the flexible foams derived from classical St-AN graft polyethers.

The Assessment of Homogeneous Grafting of Cellulose Nitrate

Abstract The homogeneous grafting of polymethyl methacrylate onto cellulose nitrate has been assessed by the techniques of spectroscopy and microscopy combined with chemical procedures. FTIR spectroscopic and electron microscopic evidence confirmed the existence of a true graft copolymer. Homogeneous grafting took place in both the surface layer and the interior of the supermolecular structure of cellulose nitrate. X-ray diffraction provided further evidence that the grafting reaction also occurred in certain ordered domains of cellulose substrate. It is suggested that the free radical graft copolymerization for cellulose nitrate could be performed via a mechanism of denitration and enolization rather than dehydrogenation.

Value of polydirectional tomography in the assessment of the postoperative spine after anterior decompression and vertebral body autografting.

With the growing number of orthopedic reconstructive spinal procedures, the use of bone grafting has steadily increased in the past decade. An understanding of the biology of bone grafting is essential for both the clinician and radiologist. Despite the advent of computed tomography and magnetic resonance imaging, conventional polydirectional tomography remains an important tool in the evaluation of vertebral body autografts. Trispiral or hypocycloidal tomography plays a valuable role in the assessment of bone graft fusion and possible complications, especially in the presence of metallic fixation devices. We present our imaging experience derived from 375 patients with cervical, thoracic, or lumbar anterior spinal fusion. True graft complications occurred in 27 patients (7%) and consisted of fracture (4%), malpositioning (3%), and infection (less than 1%).

Radiation modification of semicrystalline polymers

AbstractThree problems of the radiation modification of polymers are dealt with. Different methods of grafting are compared with respect of the formation of true graft copolymer and homopolymer in the polyethylene‐styrene system; the prevention of the penetration of monomer by grafting polytetrafluoroethylene is shown; the mechanical properties of crosslinked ethylene polymers below and above the melting point are discussed.