Biologische Wertigkeit verschiedener Knochenersatzmittel in der Behandlung von Knochendefekten

In clinical practice, biologic and synthetic substances have been used more and more as bone substitutes during the last few years. Different properties of the implant material are required according to the various fields of application. This implies a precise investigation of the biologic value by adequate experimentations on animals. It has been demonstrated in a bioassay with several synthetic implant materials, especially ceramics made of calcium phosphate, powders and granulated materials of tricalcium phosphate, and hydroxylapatite with different pore sizes and numbers, that there is only poor or even not any biologic activity in these substances which would produce an orthotopic stimulation of osseous formation. The application of these substances as bone substitutes can only be recommended in a adequate transplantation bed. However, all implant materials tested by different experimentations on animals showed an incomplete absorption in the histomorphological investigation even after twelve months. The various biologic bone substitutes (autologous and homologous spongiosa, demineralized homologous spongiosa, different forms of bone gelatin) show different degrees of biologic activity. Hitherto an inducing heterotopic effect could be demonstrated for bone gelatin in rats, dogs, and sheep. The inducing effect of bone gelatin combined with soluble calcium phosphate ceramics in rats was increased as compared with autologous spongiosa. Regarding our own results as well as various communications in literature, we consider it absolutely necessary to give more attention to the objectifying criteria when describing the biologic activity of “biologic and synthetic bone substitutes”.     

Considerations in the use of biologic grafts and alloplastic implants in facial plastic and reconstructive surgery

Surgical changes in the contour of soft tissue and bone of the craniomaxillofacial structures may require use of a biologic graft or alloplastic implant. Autologous materials are preferred; however, the harvesting procedure, donor site, and its associated morbidity are the disadvantages of using autografts. There are numerous types of alloplastic implants and they all differ in how they interact with host tissues. Factors such as implant texture, ability to integrate with host tissues, and rate of resorption all influence the overall success of different implants. In this article, we discuss some considerations in the use of biologic grafts and alloplastic implants in facial plastic and reconstructive surgery.     

Soft tissue infection around a skin penetrating osseointegrated implant. A case report

A case is reported where a female patient with bilateral otosclerosis received a bone-anchored and skin-penetrating titanium implant on which a hearing aid was mounted to improve conductive hearing loss. The patient developed an infection that did not cease despite intensive local treatment and skin-grafting. Eventually the implant was removed. The histological examination of the interface between implant and surrounding bone and soft tissues showed an inflammatory reaction in the superficial parts of the soft tissues whereas the deeper portions of the soft tissues and all of the bone tissue were free of inflammation. It is concluded that it is possible to maintain osseointegration in spite of an aggressive soft tissue infection around the implant.     

The restoration of resected mandibles in children without the use of bone grafts

Following resection of the mandible for various types of neoplastic disease, six patients between the ages of 5 and 14 were followed for a period of 8 to 12 years after osseous surgical reconstructive surgery. It was found in children of this age group that a surgical technique may be employed which will effect complete bone regeneration without the use of bone graft materials. All six of the patients spontaneously regenerated large segments of the mandible from full-body ostectomy to hemimandibulectomy defects. The surgical procedure involves the use of a titanium mesh implant between the ostectomized bone fragments to maintain the surrounding soft tissues in a distracted position. It is found that if the soft tissues of the growing child are surgically prepared using the described technique, a new periosteum and bone will be formed along the titanium mesh implant. The titanium mesh may be removed at a later date or, depending on its method of placement, may be allowed to remain as the child grows, regenerating additional bone structure. It was found that in only one case was additional grafting necessary to obtain osseous union between the spontaneously regenerated mandibular bone and the host-bone ostectomized fragments. The technique is advocated for bone restoration in cases of large osseous discontinuity defects of the mandible in children.     

The scientific basis of cement versus cementless fixation.

The arguments for and against three implant materials (polymethylmethacrylate, cobalt-chrome alloy, and titanium aluminium vanadium alloy) when used as interfaces between a loaded implant and bone are reviewed from mechanical and biologic standpoints. It is concluded that there is neither an overwhelming advantage nor a disadvantage for any one of them.     

Unalloyed titanium for implants in bone surgery

Commercially pure (c.p.) titanium has proven its suitability as an implant material in bone surgery over many years in the fields of osteosynthesis, oral implantology, and in certain applications in joint prosthetics. Excellent biocompatibility and corrosion resistance are outstanding features. Furthermore, c.p. titanium is known for not causing allergic reactions. The different grades of c.p. titanium and their minimum mechanical properties are specified in ISO and ASTM standards for implant materials. Typical mechanical properties are given for AO ASIF implant applications. The properties and clinical performance of c.p. titanium are discussed and compared to those of implant stainless steel and titanium alloys. In brief some specific features relating to c.p. titanium implant material are treated, including biocompatibility and soft tissue and bone response and taking into account the effects of implant surface configurations at the same time. In addition, issues are addressed which arise from frequent inquiries from clinics.     

Positive cytokine production in failed metal-on-metal total hip replacements

Tissues surrounding failed conventional total hips have been shown to produce inflammatory cytokines that can induce osteoclastic bone resorption. We evaluated the cytokine profiles of tissues from 5 failed metal-on-metal total hip replacements. Serial frozen sections were stained using immunohistochemical and in situ hybridization techniques. Inflammatory and osteoclast-stimulating cytokines were noted in the tissues. As compared to a group of 5 metal-polyethylene hip tissues, we found fewer CD68 positive macrophages, and lower levels of TGF-beta and TNF-alpha, but no differences in CD3 positive lymphocytes, IL-1beta, IL-6 and PDGF-alpha in the metal-on-metal tissues. This may be due, in part to the presence of wear particles from sources other than the bearing surfaces. Thus, cytokines associated with bone resorption and implant loosening may occur in total hips despite the use of alternative bearing materials.     

Wear particulate and osteolysis

Total joint replacements of the hip and knee are generally highly successful, with satisfactory longevity and clinical results. Using modern biocompatible materials, optimal component design, and meticulous surgical technique, survivorship of cemented or cementless joint replacements is approximately 15 years with more than a 90% probability. The host's biologic response is critical to implant longevity. Particulate disease refers to the host's adverse biologic response to wear debris and byproducts generated from the prosthesis. Initially, emphasis was placed on particulate polymethylmethacrylate (cement disease), but more recently polyethylene wear debris has been underscored. Debris from several materials in sufficient quantities and physicochemical forms, however, can generate an inflammatory cascade resulting in periprosthetic bone destruction (osteolysis), jeopardizing long-term success of the implant.     

The role of bioprosthetics in abdominal wall reconstruction

In several common situations, bioprosthetic materials may have distinct advantages over synthetic mesh and autologous flap or graft techniques for abdominal wall reconstruction. These off-the-shelf materials entail no donor site morbidity and are used successfully in contaminated wounds owing to their ability to resist infection, become revascularized and incorporated into host tissue, and reduce visceral adhesions. Fibrovascular incorporation into surrounding tissues and implant remodeling reduce the risks associated with a persistent foreign body, such as chronic infection, enterocutaneous fistulae, and cutaneous exposure. Disadvantages of bioprosthetic materials include higher implant cost relative to synthetic mesh, limited size of individual sheets in some cases, and risk of seroma formation. Bioprosthetic mesh has been used for abdominal wall reconstruction for approximately 5 years, so long-term studies are not available. Current laboratory and clinical evidence suggests that these materials provide a strong, durable musculofascial repair when used for abdominal wall repair. Further studies and ongoing clinical experience will be important in determining the indications for which bioprosthetic mesh will have the greatest impact. Currently available commercial products have distinct differences that result in varied clinical biologic and physiologic activity. New products and modifications to existing products may further enhance the benefits of bioprosthetic mesh, particularly in challenging cases. The use of bioprosthetic mesh has attracted interest in a relatively short period of time, with rapidly increasing indications and volume of cases successfully performed. Bioprosthetic mesh likely will play a progressively greater role in trunk reconstruction in the future.     

The optimal fixation of the cementless acetabular component in primary total hip arthroplasty.

The optimal fixation of the acetabular component in primary total hip arthroplasty remains controversial. Long-term follow-up studies show that significant loosening rates occur with cemented acetabular components and that these problems persist despite attempts to improve cementing technique. Cementless acetabular components that rely on biologic fixation can have lower rates of radiographic loosening at 10 years compared with cemented acetabular components. Although revision rates for both modes of fixation are largely equivalent at 10 years, the superior radiographic performance of cementless acetabular components at 10 years suggests that biologic fixation through bone ingrowth may provide more durable long-term implant survival compared with cemented fixation. Osteolysis is the major obstacle to long-term cementless acetabular component survival. Potential future options that may inhibit osteolysis include decreasing bone resorption that results from debris-stimulated foreign body response through the use of medications; decreasing the number of particles generated by using alternative bearing surfaces; and improving bone ingrowth, particularly through the use of growth factors and improved implant materials and designs.     

Properties of biomaterials

Metallic biomaterials, including iron-, cobalt-, and titanium-based systems, have a long history of applications for surgical implant devices. The mechanical properties of these alloys (modulus, strength, and ductility) have been used to make devices to replace skeletal structures with long-term in vivo stabilities. In addition, the passive surface oxide layers have provided chemical inertness within biologic environments. Recent trends to provide porous metallic conditions for biologic ingrowth and fixation have introduced questions with regard to the relative strength and biodegradation properties. Some biomaterial strengths have been reduced to magnitudes less than 50% of the nonporous alloys, which emphasizes the criticality of design. Surface area increases of 3-10 times has emphasized biocorrosion magnitudes, the elements released to the tissues, and the biologic consequences of these products. This article provides a brief review of these issues with emphasis on mechanical-biomechanical and chemical-biochemical properties of metallic alloys.     

Effects of material properties of femoral hip components on bone remodeling.

Bone loss around femoral hip stems is one of the problems threatening the long-term fixation of uncemented stems. Many believe that this phenomenon is caused by reduced stresses in the bone (stress shielding). In the present study the mechanical consequences of different femoral stem materials were investigated using adaptive bone remodeling theory in combination with the finite element method. Bone-remodeling in the femur around the implant and interface stresses between bone and implant were investigated for fully bonded femoral stems. Cemented stems (cobalt-chrome or titanium alloy) caused less bone resorption and lower interface stresses than uncemented stems made from the same materials. The range of the bone resorption predicted in the simulation models was from 23% in the proximal medial cortex surrounding the cemented titanium alloy stem to 76% in the proximal medial cortex around the uncemented cobalt-chrome stem. Very little bone resorption was predicted around a flexible, uncemented "iso-elastic" stem, but the proximal interface stresses increased drastically relative to the stiffer uncemented stems composed of cobalt-chrome or titanium alloy. However, the proximal interface stress peak was reduced and shifted during the adaptive remodeling process. The latter was found particularly in the stiffer uncemented cobalt-chrome-molybdenum implant and less for the flexible iso-elastic implant.     

The significance of wear and material fatigue in loosening of hip prostheses

Particles created by wear and disintegration of implant materials give rise to foreign body reactions in the tissue surrounding joint endoprostheses. Histiocytes and foreign body giant cells phagocytize the particles released and form granulomas, which lead in turn to remodelling and resorption of the bone at the interface between implant and bone. As a consequence of this, osteolysis develops, which may lead to loosening and complete failure of fixation of the implant. Radiographically, the areas of osteolysis appear as localized, round, oval or oblong scalloping defects or as radiolucent lines in the endosteal sections of the bone immediately adjacent to the implants. This paper reports on 21 hip joint endoprostheses in which polyethylene and bone cement particles induced large areas of osteolysis at the bone/cement interface. In 8 cases the polyethylene particles originated from the convex joint surfaces of ball heads in "soft-top" endoprostheses (with or without simultaneous replacement of the acetabulum by a metal cup), and in 5 cases they originated from the anchoring surfaces of non-cemented cone-shaped screw-in sockets (Endler type); osteolysis and loosening of these endoprostheses appeared on average 48.2 and 76.6 months after implantation, respectively. The bone cement fragments came from the bone cement mantle of the femur, which had become fractured, disrupted and crushed, in 8 cases of total hip replacement with cemented prostheses; osteolysis appeared on average 87 months after primary implantation in these cases. Tissue samples taken at revision surgery from the joint capsule, the bone/cement interface and the osteolytic areas were processed into histological sections for microscopy and examined in the usual way. The type and amount of phagocytized material were subjected to semiquantitative analysis. We were able to show that osteolysis at the bone/cement interface can be induced by foreign body reactions to abraded polyethylene particles alone as well as by reactions to fragmented bone cement. The morphology of the tissue reaction to particles of the different materials is quite similar. The effect of the foreign body granulomas depends less on the type of the polymer than on the amount of abrasion and fragmentation products released into the surrounding tissue. This again proves that the life-time of joint endoprostheses depends essentially on factors influencing the wear rate. Polymer materials, with low wear resistance, are unsuitable for convex joint surfaces and for direct fixation to bone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Antiprotrusio cages for acetabular revision

The purpose of this review was to explore the results of antiprotrusio cages and present indications for these devices. The role of antiprotrusio cages has had several reassessments in North America during the past decade. Currently, the primary indication for antiprotrusio cages are: (1) circumstances in which a stable, uncemented hemispheric acetabular component cannot be gained; and (2) circumstances in which there is so little remaining host bone that biologic fixation of a porous implant is very unlikely. Antiprotrusio cages have been reported to have a mechanical failure rate between 0% and 15% at midterm followup but most series do not report selective results of using cages only for the most severe bone defects. Key technical points when using antiprotrusio cages include: (1) wide exposure of the acetabular bone while protecting surrounding neurovascular structures; (2) positioning the antiprotrusio cage so as to span from host bone to host bone, thereby bridging acetabular defects; (3) appropriate bone grafting of acetabular bone deficiencies; and (4) secure fixation of the cage with good dome and posterior column support.     

Gap healing enhanced by hydroxyapatite coating in dogs.

During prosthetic implantation, gaps between the implant surface and the surrounding bone may occur resulting in reduced implant stability. In these instances bone-conductive materials might augment the formation of hosting bone into the pores of the implant and insure earlier implant stabilization and fixation by bony ingrowth. Titanium-alloy cylinders with a porous-titanium-alloy plasma spray coating were implanted into the medial femoral condyles in six mature dogs. In another group of six dogs, matched in age, weight, and gender, hydroxyapatite (HA) coated implants were used. All implants were surrounded by a 1-mm gap. Unilateral osteopenia of the knee, with a 20% reduction of bone density as judged by computed tomography scanning, was induced by 12 weekly intraarticular injections of carrageenin into the right knee before surgery. Four weeks after implantation, the HA-coated implants were compared to the parent porous-titanium implants by mechanical testing and histomorphometry. A marked positive influence of HA coating on bone mineralization and the strength of the interfacial bone between the bone and implant was found. The increment in interface shear strength and shear stiffness was three- to fivefold in osteopenic bone and two-fold in control bone. Coating of an unloaded porous-titanium-coated implant with HA accelerates the rate of bone ingrowth and thereby provides relatively high, early interfacial shear strengths in the presence of an initial gap between bone and implant even in the presence of osteopenic host bone.     

Constructive soft tissue remodelling with a biologic extracellular matrix graft: overview and review of the clinical literature

The extracellular matrix directs all phases of healing following trauma or disease and is therefore nature's ideal scaffold material. When used strategically to induce the repair and restoration of soft tissues following surgery, exogenous extracellular matrix scaffolds interact with surrounding tissues and cells to form a permanent repair without leaving behind a permanent material that can result in chronic inflammation or infection. Biomaterials derived from natural extracellular matrix, such as Surgisis (Cook Medical Incorporated, Bloomington, IN, USA), provide the extracellular components necessary to direct the healing response, allow for the reconstruction of new, healthy tissue and restore mechanical and functional integrity to the damaged site. The 3-dimensional organization of these extracellular components distinguishes the Surgisis mesh from synthetic materials and is associated with better long-term repairs. The tissue response to this biologic mesh is discussed in the context of recent reports on successful clinical applications.     

Madreporische Hydroxylapatitgranulate zur Füllung ossärer Defekte

Two macrocrystalline madreporic granular hydroxyapatite implants of different size range (single crystal size within both implants 1-3 microns) were implanted for 7, 28, 84 and 168 days into the trabecular bone of the distal femur epiphysis of rabbits. Both materials were investigated histologically. For testing of granular materials a new animal model has been developed. The drill hole was closed by reimplantation of an autologeous chondrocortical tissue slice to prevent loss of particles into the knee-joint. Both of the granular materials tested developed increasing bone bonding from the 7th day on to outer surfaces and pore surfaces. The degradation of both of the materials affected the superficial implant layers in soft-tissue interfaces exclusively and was mainly due to passive processes, e.g. leaching, fragmentation of granules after crack-production, particulate degradation and subsequent phagocytosis of liberated implant particles by macrophages and foreign body giant cells. Zones of superficial implant degradation were bonded partially to bone a second time. A possible low-degree, active superficial degradation by foreign body giant cells is discussed. Osteoclasts of typical morphology as being observed on other hydroxyapatite implant surfaces were not demonstrated. This was related to the low degradation rate of the implants. Both of the granular materials tested are useful in filling bone defects. A guided tissue regeneration due to partial implant degradation and subsequent bone formation seems to be impossible since the degradation rate of the materials is too low.     

Biologic fixation and bone ingrowth

Total hip arthroplasty has provided thousands of patients with pain relief and has improved their quality of life. Advances in orthopaedic surgical techniques and implant biomaterials now allow predictable surgical results in most patients. Despite the overwhelming success of this surgical procedure, the debate continues surrounding the optimal choice of implants. Femoral and acetabular implants with varying geometries and fixation methods are currently available. Acrylic bone cement has been used extensively in the past for acetabular and femoral fixation. This mode of component fixation currently remains the technique used most frequently throughout Europe and has shown excellent long-term results. Problems inherent with acrylic bone cement, however, have encouraged other surgeons to use alternative surfaces to allow biologic fixation.     

Collagen modifications

Collagen, the major structural protein found in all animal tissues, has a variety of uses in the armamentarium of the plastic surgeon. This article discusses the biologic characteristics of collagen that determine its behavior as an implant material. Clinical applications discussed include hemostatic collagen fleece, collagen sponge wound dressing, composite tissue tendon allografts, injectable collagen, and manipulation of scar collagen.     

Coralline bone graft substitutes.

Coralline porous ceramics are biocompatible and osteoconductive implants. They have proven to be effective as bone graft substitutes in large animal models and in humans. Bone and supporting soft tissue grow into and throughout their porosity if the implant is placed in direct apposition to viable bone and the interfaces are stabilized. The bone within the implant remodels in response to Wolff's law. Both the implant properties (chemistry and porosity) and the biologic environment modulate the rate of implant resorption. Composite technology with resorbable polymers can improve the mechanical properties of these ceramics.