Polymethylmethacrylate Implants Research Articles

Clinicopathologic findings after experimental implantation of synthetic intraocular lenses in dogs

Summary Clinical findings indicate that canine eyes tolerate implantation of polymethylmethacrylate (pmma) intraocular lenses (iol) well, although inflammation and ocular damage attributable to the implants is not known. The use of silicone or polyhydroxyethylmethacrylate (hema) iol has not been reported in dogs. In this study, 15 conditioned, mixed-breed dogs were allotted to 3 groups: 5 received pmma iol; 5 received silicone iol; and 5 received hema iol. The iol optic was inserted into the anterior chamber of the right eye and anchored to the cornea. An identical surgical procedure was done on the left eye, except that no lens optic was inserted. Clinical examination and measurement of corneal thickness were done immediately prior to and after surgery. Aqueous humor samples were collected at the time of surgery and 28 days after surgery. Only mild and transient inflammation was observed in iol-implanted eyes. On several postoperative days, it was found that pmma iol induced significantly greater corneal thickness, aqueous flare, anterior uveal irritation, and corneal edema than did other iol. Significantly more anterior uveal irritation and increased aqueous humor protein concentration was observed with hema iol than with pmma or silicone iol. Silicone iol induced significantly less fibrin deposition than did pmma or hema iol.

Polymethylmethacrylate-induced inflammatory macrophages resorb bone.

Macrophages and their fused products are commonly found at the polymethylmethacrylate cement-bone interface, but it is not known if they contribute directly to the osteolysis associated with loosening of the cemented prosthesis. We isolated mononuclear phagocytes from granulomas formed by subcutaneous implantation of polymethylmethacrylate into mice and incubated them on bone slices in which they formed resorption lacunae after co-culture for seven to 14 days with both marrow stromal cells and osteoblast-like cells (in the presence of 1 alpha,25-dihydroxyvitamin D3 and dexamethasone). Increased numbers of tartrate-resistant acid phosphatase-positive mononuclear and multinucleated cells formed in these cultures. Both in the presence and absence of stromal cells, macrophages produced extensive superficial roughening of the bone surface. Polymethylmethacrylate-induced macrophages are thus capable of low-grade surface and high-grade lacunar osteolysis, the latter requiring the presence of specific hormonal and stromal cell elements. These two forms of bone resorption could account for the pathogenesis and clinical patterns associated with loosening of the cemented prosthesis.

Preparation and characterization of biodegradable poly( l-lactic acid) gentamicin delivery systems

In the last two decades, localized antibiotic therapy has emerged as an important approach to treating orthopedic infections. This paper describes the preparation and in vitro evaluation of biodegradable, poly( l-lactic acid), implants for localized delivery of gentamicin sulfate for the treatment of osteomyelitis. Cylindrical, poly( l-lactic acid) implants containing gentamicin sulfate were obtained by compression of microcapsules prepared by a nonsolvent-induced, coacervation process. Mean particle size distributions of the microcapsules, based on volume, ranged from 278 to 444 μm. The gentamicin sulfate loading of the microcapsules, after a methylene chloride-water extraction procedure, exceeded 95% of the theoretical value. In vitro dissolution studies on microcapsules and implants with drug loading varying from 5 to 67% w/w indicated that the rate of gentamicin sulfate released from both microcapsules and implants increased, while the dissolution half-life ( T 50) decreased, exponentially, with an increase in drug loading. Profiles of amount of drug dissolved at different times followed a square-root-time relationship. All batches of microcapsules and implants released greater than 80% gentamicin sulfate within 3 weeks. In comparison, previous studies in this laboratory have indicated that conventional, nonbiodegradable polymethylmethacrylate implants, containing gentamicin or tobramycin, show incomplete and poorly controlled drug release during the same time period.

Quantitative comparison of the histological effects of particulate polymethylmethacrylate versus polyethylene in the rabbit tibia

Fourteen mature female New Zealand White rabbits underwent implantation of Simplex polymethylmethacrylate (PMMA) powder or particulate (average 67 microns) ultrahigh-molecular-weight polyethylene (UHMWPE) through a drill hole in the proximal right tibia. The left tibia functioned as a prepared but nonimplanted control. Animals were killed after 16 weeks. Histological examination of the bone-implant interface in the particulate PMMA group disclosed a florid foreign-body reaction with the presence of giant cells and histiocytes. The particulate UHMWPE group demonstrated positively birefringent UHMWPE fragments, rimmed by foreign-body giant cells and histiocytes, embedded in a loose connective tissue stroma. UHMWPE interfaces were thicker and contained more histiocytes and fibrocytes; PMMA interfaces contained more marrow cells and lymphocytes. This study underscores the importance of biomaterial debris in the process of aseptic loosening of cemented joint arthroplasties.

Effects on the surrounding tissues and morphological changes of components after implantation of PMMA and heparin surface modified PMMA intraocular lens in rabbit eyes

The aim of this study was to evaluate the cellular response and morphological changes of cells on the intraocular lens(IOL) implanted over a course of time and to identify the basic mechanism of IOL adaptation to tissue reaction in the implanted eye by comparing polymethylmethacrylate (PMMA) IOL with heparin surface modified PMMA IOL. ECCE using Healon was done in 36 eyes of 36 rabbits. A heparin surface modified IOL was implanted in 18 eyes (Group I), while PMMA IOL was implanted into another 18 eyes (Group II). Corneal thickness and endothelial cell density were measured for 3 months. Postoperatively, the eyes were enucleated, and a cytopathologic examination of the cells on the surface of the IOL and their ultrastructural changes were observed with light and scanning microscope at various points of time. The findings of this present study suggested that heparin surface modified PMMA IOL reduced the degree of endothelial cell damage, postoperative tissue reaction, and pigment deposits on the surface of the IOL. These were statistically significant. The most important cell was considered to be the macrophage for the adaptation of IOL in the eye which gradually changed into a fibroblast-like cell, giant cell and finally disappeared after forming an acellular membrane on the IOL.

Advantages and limitations of current soft intraocular lenses

We report our clinical experience with six soft intraocular lenses: (1) STAAB silicone, (2) CooperVision/Schlegel silicone, (3) IOLAB silicone, (4) Allergan Medical Optics (AMO) silicone, (5) Fyodorov silicone, and (6) Alcon hydrogel (IOGEL). We found that these soft intraocular lenses have several common design problems. The singlesize design of five of the six soft lenses can lead to a windshield-wiper decentration effect in lenses too small for larger eyes. We observed several instances in which the one-piece lenses became decentered, subluxed, and vaulted anteriorly against the iris or posteriorly away from the iris as postoperative capsulozonular changes occurred. We found that the insertion methods for these soft lenses need refining to reduce the risk of intraocular damage and wound stretching if the lenses are to be folded and inserted through a small 3.0 mm to 3.5 mm incision. The surface and physical characteristics of these lenses may also require further study. We observed folding grooves, sebacium deposits, and rust from the insertion instrument on some lenses inside the postoperative eye and pigment dispersion associated with hydrogel lenses. We conclude that small diameter polymethylmethacrylate implants are the best choice for small incision cataract surgery at this time.

Release Kinetics of Tobramycin Sulfate from Polymethylmethacrylate Implants

AbstractThe effects of various formulation factors on the in vitro release characteristics of spherical polymethylmethacrylate implants were studied. Physical and mathematical models were proposed to describe observed in vitro release profiles. The in vitro release data could be described by a biexponential equation of the type: fraction of tobramycin remaining in the implant at time t = Ae−αt + Be−βt, where α and β represent the rate constants for the initial rapid and subsequent slow phases of release. The influence of drug loading, volume of dissolution medium, implant size, type of commercial cement and the incorporation of water soluble additives on the release profiles as well as the α and β rate constants is described

The treatment of infection after interlocking nailing

Infection following interlocking nailing should be treated in stages. The infection is controlled with suction irrigation or gentamycin polymethyl methacrylate (PMMA) implants and systemic antibiotics. Medullary reaming removes endosteal sequestrae. If the nail is removed before the fracture is united, an external fixateur can be used to immobilize the fracture. The use of a loop drain for continuous suction irrigation and techniques for antibiotic PMMA implants are described. The goal is a healed fracture without recurrence of infection.

Initial clinical studies with silicone intraocular implants

Initial clinical studies with 117 silicone implants are presented. Techniques of implantation including flat insertion, bar-style folder, and syringe-style inserter are discussed. Visual results were compared wih results after polymethylmethacrylate (PMMA) lens implantantion and were equal if not better. Eliminating patients with preoperative pathology, best corrected visual results of 20/40 or better occured in 96% of eyes with silicone implants and 88% with PMMA implants. Complications included “Z” dislocations because of inadvertent baptic placement in the bag and one case of severe uveitis and common transient pigment in the anterior chamber. In 37.5% of cases, posterior capsular opacities significant enough to require YAG laser capsulotomy occurred.

Multinucleated cells elicited in response to implants of devitalized bone particles possess receptors for calcitonin.

The introduction into soft tissues of particulate materials resistant to digestion results in the induction of a "foreign-body giant-cell reaction." We have examined the relation between osteoclasts and foreign-body giant cells by comparing the tissue responses elicited by subcutaneous implants of devitalized, mineral-containing bone particles (BP), nonresorbable plastics such as polymethylmethacrylate (PMMA), or both. Implantation of BP results in the recruitment of multinucleated cells with features of in osso osteoclasts including tartrate-resistant acid phosphatase activity, contact-mediated resorption of BP, membrane specializations (ruffled borders and clear zones), and inhibition of resorption by calcitonin treatment of animals. In the present study, an autoradiographic technique employing 125I-salmon calcitonin was used to demonstrate the presence of receptors for this hormone on multinucleated cells from BP implants. In contrast, outgrowth cells from PMMA implants lacked calcitonin receptors. Demonstration of features of the osteoclastic phenotype in multinucleated cells elicited in response to BP supports the hypothesis that the mineralized matrix of bone may be a requirement for acquisition of the osteoclast phenotype.

Posterior capsule opacification after silicone lens implantation and its management

The incidence and time of onset of posterior capsular opacification in a consecutive series of 147 silicone lens implants and in 585 polymethylmethacrylate (PMMA) lens implants were compared. Silicone lenses, sulcus and capsular hag fixated, had an opacification rate of 27.9%, while PMMA had a rate of 7.0%. In the silicone lens series, 65.9% of the opaque capsules required YAG laser posterior capsulotomies in the first four months In the PMMA implants, only 28.6% required YAG laser capsulotomies in the first four months. The mean follow-up time was nine months. Management of capsular opacification in silicone lenses required early YAG laser capsulotomy, with focusing posterior to the capsule to avoid pitting the implant.

Clinicopathologic findings after in-the-bag implantation of open-loop polymethylmethacrylate and silicone lenses in the rabbit eye

Two lens models, one all silicone with J-loop haptics, the second with PMMA optics and angled polypropylene C-loop haptics, were implanted in the capsular bag of 36 rabbit eyes following extracapsular lens extraction. Technical ease of implantation, inflammatory response, lens position, and fibrin exudation as well as precipitate formation were examined. Biomicroscopy, light and phase-contrast microscopy were used. Differences in haptic vulnerability, lens position, and fibrin clot formation were found between the two lens types. Lens-specific differences in precipitate formation could not be substantiated.

Complications associated with STAAR silicone implants

We compared the incidence of various complications in consecutive series of cases in which 76 eyes received STAAR silicone intraocular implants and 76 eyes received small incision IOLAB G708G polymethylmethacrylate (PMMA) intraocular implants. All surgeries were performed by the same surgeon employing the same phacoemulsification technique. A higher incidence of lens subluxation, lens repositioning, corneal edema, and elevated intraocular pressure was observed in the eyes receiving STAAR silicone implants than in the eyes receiving IOLAB PMMA implants, In addition, a YAG laser posterior capsulotomy could not be performed through several STAAR silicone RMX 1 model implants. An invasive pars plana posterior capsulotomy was necessary in these eyes. We also found that the STAAR silicone RMX 3 model implants were often pitted by the YAG laser during successful posterior capsulotomies. Despite these problems, the STAAR silicone intraocular lens group achieved corrected vision similar to the PMMA lens group.

The intraneoplastic chemotherapy in a rat brain tumour model utilizing methotrexate-polymethylmethacrylate-pellets.

In an experimental glioma model, using ethylnitrosourea induced and subsequently intracerebrally implanted tumours in BD-IX rats, the effectiveness of intratumoural application of methotrexate (MTX) by stereotactic implantation of polymethylmethacrylate (PMMA) pellets containing MTX, has been studied. Tumour volume 10 days after pellet implantation as well as survival rates of treated, untreated and control animals have been the criteria of the effect of treatment. Tumour volume was significantly smaller in treated compared to untreated animals. The survival rate of untreated to treated animals increased 150 and 233% respectively when compared with the control animals. Thus a positive therapeutic effect of MTX-PMMA pellet implantation in the experimental glioma could be proven. Possible consequences for the treatment of human gliomas are shortly discussed.

The effect of the radial head and prosthetic radial head replacement on resisting valgus stress at the elbow.

Five fresh nonembalmed elbows were tested for resistance to valgus stress in their anatomic state, after radial head resection, and after insertion of Silastic and polymethylmethacrylate (PMMA) radial head replacements. The resistance to valgus stress was found to be reduced an average of 28% after radial head resection. The PMMA and Silastic implants restored valgus stiffness an average of 86% and 78% respectively, as compared to intact elbow values for corresponding flexion angles. Testing in pronation, supination and neutral forearm rotation demonstrated no difference in valgus stiffness. For each elbow, resistance to valgus stress was greatest at full extension and dropped approximately 30% at all other flexion angles as compared to corresponding full extension value. These data support the concept of the radial head as a stabilizer to valgus stress in the in vitro elbow. Further, this data demonstrated the ineffectiveness of current radial head replacement systems in restoring this biomechanical function and suggest that the use of a stiffer implant material may be beneficial in resisting valgus stress. Additional testing is indicated to determine the performance of a stiffer implant at the clinical and biological levels.

Primary mineralization in the interface between bone and methyl methacrylate implants in rat mandibles. A correlative light and scanning and transmission electron microscope study.

Self curing polymethylmethacrylate implants were administered into rat mandibular bone. Tissue reaction was studied after different periods with light microscopy and transmission and scanning electron microscopy. Formation of fibrous tissue in the interface between implant and bone was associated with initial bone resorption and followed by the occurrence of primary calcification in a collagen rich matrix after 4-8 weeks. The features of primary mineralization comprised appearance of hydroxyapatite crystals within matrix vesicles and formation of calcospheritic structures. The occurrence of calcifying fronts after the intraosseous administration of polymethylmethacrylate suggests a favourable relationship between bone and the implant material.

Noninvasive capsulectomy using a new pulsed infrared laser

We evaluated the ocular effect of a new neodymium, yttrium-aluminum-garnet (Nd-YAG) laser (P/V YAG) that emits a 1300 nm wavelength. Corneas were undamaged when they were not placed in the focal point of the beam. The iris and secondary membranes were successfully ruptured. The laser beam did not destroy polymethylmethacrylate (PMMA) implants when they were not placed in the focal point of the beam. In our experimental setting, we could not produce a retinal lesion using this wavelength.