Thermal effects of polymerization of methyl-methacrylate on small tubular bones

Development of polyurethanes for bone repair

The purpose of this paper is to review recent developments on polyurethanes aimed at the design, synthesis, modifications, and biological properties in the field of bone tissue engineering. Different polyurethane systems are presented and discussed in terms of biodegradation, biocompatibility and bioactivity. A comprehensive discussion is provided of the influence of hard to soft segments ratio, catalysts, stiffness and hydrophilicity of polyurethanes. Interaction with various cells, behavior in vivo and current strategies in enhancing bioactivity of polyurethanes are described. The discussion on the incorporation of biomolecules and growth factors, surface modifications, and obtaining polyurethane-ceramics composites strategies is held. The main emphasis is placed on the progress of polyurethane applications in bone regeneration, including bone void fillers, shape memory scaffolds, and drug carrier.

Nano-Hydroxyapatite Bone Substitute Functionalized with Bone Active Molecules for Enhanced Cranial Bone Regeneration

The aim of this study was to synthesize and characterize a nano-hydroxyapatite (nHAP) and calcium sulfate bone substitute (NC) for cranioplasty. The NC was functionalized with low concentrations of bone morphogenetic protein-2 (BMP-2) and zoledronic acid (ZA) and characterized both in vitro and in vivo. In vitro studies included MTT, ALP assays, and fluorescent staining of Saos-2 (human osteoblasts) and MC3T3-E1 (murine preosteoblasts) cells cultured on NC. An in vivo study divided 20 male Wistar rats into four groups: control (defect only), NC, NC + ZA, and NC + ZA + rhBMP-2. The materials were implanted in an 8.5 mm critical size defect in the calvarium for 12 weeks. Micro-CT quantitative analysis was carried out in vivo at 8 weeks and ex vivo after 12 weeks. Mineralization was highest in the NC + ZA + rhBMP-2 group (13.0 ± 2.8 mm³) compared to the NC + ZA group (9.0 ± 3.2 mm³), NC group (6.4 ± 1.9 mm³), and control group (3.4 ± 1.0 mm³) after 12 weeks. Histological and spectroscopic analysis of the defect site provided a qualitative confirmation of neo-bone, which was in agreement with the micro-CT results. In conclusion, NC can be used as a carrier for bioactive molecules, and functionalization with rhBMP-2 and ZA in low doses enhances bone regeneration.

Injectable PolyMIPE Scaffolds for Soft Tissue Regeneration

Injury caused by trauma, burns, surgery, or disease often results in soft tissue loss leading to impaired function and permanent disfiguration. Tissue engineering aims to overcome the lack of viable donor tissue by fabricating synthetic scaffolds with the requisite properties and bioactive cues to regenerate these tissues. Biomaterial scaffolds designed to match soft tissue modulus and strength should also retain the elastomeric and fatigue-resistant properties of the tissue. Of particular design importance is the interconnected porous structure of the scaffold needed to support tissue growth by facilitating mass transport. Adequate mass transport is especially true for newly implanted scaffolds that lack vasculature to provide nutrient flux. Common scaffold fabrication strategies often utilize toxic solvents and high temperatures or pressures to achieve the desired porosity. In this study, a polymerized medium internal phase emulsion (polyMIPE) is used to generate an injectable graft that cures to a porous foam at body temperature without toxic solvents. These poly(ester urethane urea) scaffolds possess elastomeric properties with tunable compressive moduli (20-200 kPa) and strengths (4-60 kPa) as well as high recovery after the first conditioning cycle (97-99%). The resultant pore architecture was highly interconnected with large voids (0.5-2 mm) from carbon dioxide generation surrounded by water-templated pores (50-300 μm). The ability to modulate both scaffold pore architecture and mechanical properties by altering emulsion chemistry was demonstrated. Permeability and form factor were experimentally measured to determine the effects of polyMIPE composition on pore interconnectivity. Finally, initial human mesenchymal stem cell (hMSC) cytocompatibility testing supported the use of these candidate scaffolds in regenerative applications. Overall, these injectable polyMIPE foams show strong promise as a biomaterial scaffold for soft tissue repair.

Functional and radiographic evaluation of 214 aggressive benign bone lesions treated with curettage, cauterization, and cementation: 24 years of follow-up

PURPOSE

Treatment with curettage, cauterization, and methylmethacrylate of aggressive benign bone lesions is a method now widely accepted in most orthopedic oncology centers. However, one of the controversies regarding this technique is the possible complications that may arise from the use of methylmethacrylate, which has caused some authors to remove it 2 years after the surgery and replace it with bone graft. The objective of this paper is to present a functional and radiographic evaluation of 214 patients presenting with aggressive benign bone lesions treated with curettage, cauterization, and methylmethacrylate from 1974 to 1998, with some of them having 24 years of follow-up. These patients were clinically and radiographically evaluated for the incidence of late osteoarthrosis, range of motion, and pain in the involved joint.

METHOD

This study comprised 214 patients, with an average follow-up duration of 10.6 years (range: 2 to 24 years. All cases involved aggressive benign lesions. The patients were evaluated according to the Musculoskeletal Tumor Society Score (MSTS) functional evaluation system, and the complications are described.

RESULTS

The MSTS functional evaluation was excellent in 166 cases (78%), good in 26 (12%), fair in 11 (5%), and poor in 11 (5%). The following complications were observed: late osteoarthrosis, 25 cases (12%); infection, 12 (6%); pathologic fracture, 11 (5%); and local recurrence, 19 (9%).

CONCLUSION

Based on clinical assessment, no significant deleterious effects directly related to the use of methylmethacrylate were observed. The functional evaluation performed in 1998 (up to 24 years of follow-up) did not show significant change when compared to the evaluation performed in 1985.

Glenoid cementing may generate sufficient heat to endanger the surrounding bone

Glenoid loosening is a common complication of shoulder arthroplasty. One possible cause is bone necrosis from the exothermic reaction of polymethylmethacrylate. The relationship between the amount of cement used in glenoid fixation and the risk of thermal injury to bone was examined. Glenoid arthroplasty was done on 17 fresh cadaver scapulas, recording the amount of cement used. The bone surface temperature during cement curing was measured using infrared thermography. Using these data and published thresholds for thermal necrosis, the frontal plane area of bone that would be at risk for necrosis in vivo was estimated. The average weight of cement implanted was 5.35 g (2.65-8.08 g). The maximum temperature recorded averaged 64.7 degree C (48.2 degree-76.8 degree C). The area of bone at risk correlated with the amount of cement used. This study indicates that potentially dangerous amounts of heat may be generated during cementing of glenoid components.

Theoretical prediction and experimental determination of the effect of mold characteristics on temperature and monomer conversion fraction profiles during polymerization of a PMMA-based bone cement

The present work is concerned with applications of a kinetic model for free-radical polymerization of a polymethylmethacrylate-based bone cement. Autocatalytic behavior at the first part of the reaction as well as a diffusion control phenomenon near vitrification are described by the model. Comparison of theoretical computations with experimental measurements for the temperature evolution during batch casting demonstrated the capacity of the proposed model to represent the kinetic behavior of the polymerization reaction. Temperature evolution and monomer conversion were simulated for the cure of the cement in molds made of different materials. The maximum monomer conversion fraction was markedly influenced by the physical properties of the mold material. The unreacted monomer acts as a plasticizer that influences the mechanical behavior of the cement. Hence, the same cement formulation cured in molds of different materials may result in different mechanical response because of the differences in the amounts of residual monomer. Standardization of the mold type to prepare specimens for the mechanical characterization of bone cements is recommended. Theoretical prediction of temperature evolution during hip replacement indicated that for cement thickness lower than 6 mm the peak temperature at the bone-cement interface was below the limit stated for thermal injury (50 degrees C for more than 1 min). The use of thin cement layers is recommended to diminish the risk of thermal injury; however, it is accompanied by an increase in the amount of unreacted monomer present in the cured material.

Effects of synthetic craniofacial materials on cerebral microcirculation

Four groups were studied to look at effects of synthetic materials on the pial vasculature. Using Sprague-Dawley rats, an open pial window approach was used in which there was a control group, a hydroxyapatite cement group mixed with sodium phosphate, a methylmethacrylate slow-set, and a methylmethacrylate fast-set group. There were 10 animals with 20 vessels studied within each group. The permeability leakage outside the vessel was evaluated to determine the vascular albumin leakage, and the number of rolling and adherent leukocytes was studied within each group. It was seen that the control group was significantly different compared with the fast-set methylmethacrylate group during a 2-hour period in regard to the percentage leakage, as well as a number of rolling and adherent leukocytes. This is one of the first studies to demonstrate the effects of synthetic craniofacial materials on the underlying pial vasculature.

Implant arthroplasty of the hand: retrospective and prospective considerations

Small joint arthroplasty has lagged behind the development of that in large joints because of their small sizes, different shapes, presence within kinetic chains, complex soft tissue investments, presence of adjacent rays, secondary displacement and contracture, and the differing requirements of degenerative and rheumatoid arthritis. Prosthetic development must take into consideration range of motion, stability, tendon moment arms, fixation, ease of implantation, biocompatibility, wear and strength characteristics, and soft tissue reconstruction. The metacarpophalangeal, interphalangeal, and trapeziometacarpal joints each present different problems in the design of kinematic equivalent prostheses. One-piece polymeric designs have advantages in cost, adaptability, and known performance but show degradation of function with time. Total joint designs have the potential of better simulating normal joint function but have shown tendencies to subsidence, loosening, and breakage. The rigidity of hinge joints limits the damping of out-of-plane forces and places greater stress on bone-stem interfaces, whereas global designs have poor constraint features.

The effects of methylmethacrylate's hyperthermic polymerization on cerebral vascular permeability

This study was undertaken to analyze the effects of significant hyperthermia (> 100 degrees C) associated with the polymerization of polymethlymethacrylate (PMM) on the permeability of the cerebral vasculature in rats. The method used to visualize the pial vasculature included the open pial window technique and epifluorescence microscopy. Results indicated that there is a significant increase in cerebral vascular permeability following in situ polymerization of PMM over the craniectomy site.

Design of a non-constrained, non-cemented, modular, metacarpophalangeal prosthesis

A non-constrained, non-cemented, modular prosthesis for replacement of the metacarpophalangeal joints of the fingers has been developed. The prosthesis is of a surface design which is modular in construction and is implanted into the bones with a press fit. The prosthesis is designed to be implanted into patients with traumatic injuries, post-traumatic osteoarthritis and into patients with rheumatoid arthritis at an early stage in the disease where the muscles and ligaments that surround the joint are still functional and can provide joint stability.

Metacarpophalangeal joint prostheses: a review of past and current designs

The anatomy and biomechanics of the metacarpophalangeal (MCP) joint are briefly described. Hinge, flexible and surface designs of past and current MCP prosthetic joints are reviewed, outlining their respective advantages and disadvantages. Although existing prostheses can restore cosmetic appearance and relieve pain, none can equal the stability and versatility of the natural joint. Delayed reconstructive surgery may be partly responsible for the mediocre results experienced, since the later the surgery the worse will be the condition of the muscles and ligaments surrounding the joint. These are the structures responsible for strength, movement and stability of the joint. From a mechanical viewpoint it may be desirable to operate at an earlier stage of the disease than is currently indicated, but this is a clinical decision. Some design aspects, namely fixation and wear, require a different approach when designing an MCP prosthesis from that adopted in the case of prosthetic hips and knees.

Fixation of a surface replacement endoprosthesis of the metacarpophalangeal joint

Surface replacement of the metacarpophalangeal joint would provide many benefits over current conservative treatment or the use of hinged spacers in excision arthroplasty. One of the main problems in surface replacement is securing adequate fixation of the prosthesis, especially if cement is not to be used. The direction and size of the forces that cause loosening have been described and a series of experiments in cadaveric bone have been used to elucidate the best shape of the component and stem to resist these forces. A 5 mm square section stem of 30 mm length gave the best overall result when combined with a flat on the palmar aspect of the inner bearing surface.

Compressive behavior of human bone-cement composites

Current surgical practice in the implantation of cemented total joint arthroplasties generally creates a zone of variable thickness in which polymethylmethacrylate (PMMA) is intermixed with trabecular bone. The authors' objectives in these experiments were to characterize the compressive mechanical properties of this bone-cement composite material. They found that the mechanical properties of bone-cement composite specimens, fabricated under in vitro conditions that would promote nearly complete cement filling, are closer to the properties of trabecular bone than to those of cement. For both low-viscosity cement (LVC) and PMMA specimens, with the cement introduced by either hand-packing or pressurized injection at periods of 2 and 7 minutes, the compressive strengths ranged from 29 MPa to 50 MPa and the compressive moduli from 539 MPa to 1,210 MPa. Cement volume fractions achieved using different filling methods ranged from 76% to 87%. In contrast to previous studies of bone-cement composites using high-density bovine bone, neither mechanical properties nor filling parameters correlated significantly with bone porosity measured prior to filling. The authors expect that the mechanical properties of bone-cement regions created at surgery under less than these ideal in vitro filling conditions will only approach their values as an upper limit. Thus, bone-cement composites created in situ at surgery will also exhibit mechanical properties well below previously assumed values.

Histological features of the interface membrane of failed isoelastic cementless prostheses

The interface membranes of both components from two isoelastic cementless hip arthroplasties, which were revised for aseptic loosening, were examined histologically. The membranes consisted of densely structured fibrous tissue interspersed with giant cell granulomas, sheets of histiocytes and chronic inflammatory infiltrates. The granulomas and the histiocytes contained polymeric and metallic wear products, respectively. The morphological features of these membranes were compared with those of cemented joint replacements. Apart from the deposits of acrylic cement bordered by macrophages, there were no distinctive differences between the membranes of failed cementless and cemented arthroplasties. The release and deposition of wear products, of whatever nature, are apparently responsible for the formation of exuberant interface membranes.