Bone implants--a challenge to materials science.

The review paper discusses the conditions for obtaining in vivo a composite from a synthetic, inorganic material and collagen fibres. Bone itself is a composite containing collagen fibres and hydroxoapatite crystals. The crystal size is, however, far smaller than can be made using conventional methods of ceramics technology. The paper discusses therefore the possibilities to synthesize the apatite in a gel. The requirements of initial load bearing can be met by forming the gel on the surface of glass particle, sintered to a porous body. In the pores calcium ions react with the gel to form (= SiO)Ca+ complexes. When the phosphate concentration in the pore is high enough to exceed the solubility product of apatite, the calcium-gel complexes release the calcium and highly dispersed apatite crystallites are precipitated in the gel. These give the gel the osteoconductive properties observed for bioactive glasses. Glass compositions, which give a gel surface enough hydrated to form calcium complexes, are discussed.     

An overview of implant materials

Materials used for implant manufacture may play an important role in implant fixation. The choice of a material influences rigidity, corrosion characteristics, biocompatibility and tissue receptivity. The surface morphology of the implant affects its stability within the skeleton or within the surrounding cement mantle. This paper summarizes materials used in orthopedic implants, including metals and metal alloys, polymers and ceramics.     

Cartilage substitutes: overview of basic science and treatment options

Articular cartilage defects that are symptomatic and refractory to nonoperative treatment represent a clinical management challenge. Although there have been important advances in stimulating intrinsic repair mechanisms, cartilage regeneration, and other substitution techniques, to date none has unlocked the understanding necessary to duplicate normal articular cartilage. The objectives of treatment of cartilage lesions are to obtain pain relief, reduce effusions and inflammation, restore function, reduce disability, and postpone or alleviate the need for prosthetic replacement. As the field of articular cartilage repair continues to evolve rapidly, the most appropriate treatment option for an individual patient should be based on the pathologic characteristics of the lesion and the patient's symptoms and expectations. The orthopaedic surgeon needs to be familiar with both the existing and the newly emerging cartilage treatment techniques in order to best educate patients and meet their expectations for long-term benefits.     

Osteoinductive bone graft substitutes for spinal fusion: a basic science summary.

An understanding of precise biologic mechanisms at work during spinal fusion healing is just beginning to evolve. Current molecular biology research has shown this process to be multifactorial and extremely complex. With the advent of improved animal models to study the biology of spinal fusion, essential information regarding the basic science behind arthrodesis has advanced knowledge of this process. Moreover, with advances in local gene therapy as well as osteoinductive proteins and osteoinductive carrier matrices, the orthopedic surgeon will soon enter into a new era of biologic manipulation for fusion.     

Bone graft substitutes.

A better understanding of the biology of fracture healing and an increasing awareness of the limitations and potential complications of autogenous bone graft harvest have combined to foster a burgeoning interest in the development of bone graft substitutes. A few of these materials have been available for more than a decade, and many more should become available in the near future. The characteristics of the ideal bone graft substitute may vary considerably depending on the intended site of application and the clinical setting in which it is used. Knowledge of the available alternatives is a necessary prerequisite to informed decision making.     

An overview of prosthetic materials for fixation

Total hip component fixation can result from both the intrinsic stability of the implant's macroscopic geometry within the host anatomy and from the implant surface microscopic interaction with the surrounding host tissue. In practice, functionally stable total hip components rely to some extent on both macroscopic and microscopic interaction with the adjacent skeletal structures. Clearly, there is an interdependency between macroscopic and microscopic implant fixation such that they rarely occur in isolation. Both modes of implant fixation are dependent upon the materials chosen for implant construction. The materials used in implant fixation include metals, polymers, and ceramics. Implant fixation has used each of these materials in smooth, textured, and porous surface conditions. The utility of these materials for implant fixation is judged on their biocompatibility, durability, and reception to incorporation by specific tissue types.     

Osteolysis: basic science.

Since the recognition of aseptic loosening by Charnley in the early 1960s, much information has been gained on the basic science of periprosthetic bone loss. Initially termed cement disease, it now generally is accepted that, in most instances, osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris, possibly facilitated by local hydrodynamic effects. Tissue explant, animal, and cell culture studies have allowed us to compile an appreciation of the complexity of cellular interactions and chemical mediators involved in osteolysis. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular responses and effects on bone include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin 6. However, an increasing number of other proinflammatory and antiinflammatory cytokines, prostenoids, and enzymes have been shown to play important roles in this process. The ultimate goal of basic research is to develop novel strategies for evaluation and treatment of patients with osteolysis. Although initial animal studies are promising for possible pharmacologic treatment and prevention of osteolysis, well-controlled human trials are required before agents such as bisphosphonates can be recommended for general clinical use.     

An overture to basic science aspects of nerve injuries

Does the lack of improvement in surgical treatment of nerve injury despite thousands of years of research disturb you? Do you think that basic science has not really contributed to any advancement in the treatment of nerve injury? Have you contributed? Do you think that new molecular biology knowledge in nerve injury and repair is important? Knowing from basic science that the immature nervous system is more fragile would you agree with the view that to be 'aggressive' in surgery of the newborn with a brachial plexus injury could be unscrupulous? As molecular biology of the nervous system has demonstrated that the best conditions for regeneration occur immediately after an injury do you find the approach of postponing surgery until at least 3 months after a closed nerve injury to be ignorant and even negligent? Taking into account the normal occurrence of inhibitory molecules in the uninjured peripheral nerve do you think that functional improvement from end to side nerve repair is a myth? Are the recent attempts to artificially enhance nerve regeneration for instance in synthetical conduits like nature seen 'through a glass darkly'? Do you agree that new concepts in surgical treatment of nerve injury are timely? Do you have the time?     

Bone graft and total hip arthroplasty. A review.

The success of total hip arthroplasty has been well documented. Aseptic loosening remains the major long-term problem that can lead to significant bone loss and structural deficits. Bone graft has been used with increasing frequency to reconstruct these difficult cases. In this review, the authors detail the biology, biomechanics, and banking of bone grafts. A summary of currently available data on the clinical result of autograft and allograft in reconstructive hip surgery is presented.     

Penile prostheses. An overview

Penile prosthesis implantation in selected patients can achieve very gratifying results. Satisfactory surgical results can be obtained in a high percentage of cases, and if the patient and his partner are well informed preoperatively, patient and partner satisfaction can also be very good.     

An in vitro study of the properties influencing Staphylococcus epidermidis adhesion to prosthetic vascular graft materials.

This study examines the influence of the properties of various vascular graft materials on the bacterial adherence process of two different strains of Staphylococcus epidermidis (mucous and normucous producing). Dacron grafts (both knitted and woven), Teflon grafts, and Dacron grafts coated with one and two layers of silicone were studied because these materials differ significantly in porosity, hydrophobicity, and surface charge (zeta potential). Graft segments were immersed in 3H-labeled bacteria solution for periods ranging from 5 to 180 minutes and liquid scintillation techniques were used to quantify bacterial adherence. The porous knitted Dacron material had a significantly higher rate of bacterial adherence than either the woven Dacron or Teflon (p less than 0.05). Silicone coating (either one or two layers) reduced adherence by a factor of four for the knitted Dacron (p less than 0.05) and by a factor of two for woven Dacron (p less than 0.05). The mucous producing strain of S. epidermidis displayed significantly better adherence to woven and knitted Dacron than the normucous producing strain, but only when 0.25% dextrose was added to the bacteria solution. These findings indicate that the highly porous knitted Dacron grafts have the highest propensity for bacterial adhesion. Graft materials with the most negative zeta potentials are more resistant to bacterial adherence. Silicone coating of Dacron material significantly changed adherence characteristics, suggesting that this may be a viable strategy for protecting implantable medical devices containing materials to which bacteria readily adhere.     

Instrumentation of the lumbar spine. An overview

The use of any implant system to promote arthrodesis of any segment of the spine is only as good as the technique of surgical arthrodesis. The success of the implant depends, in short, on the success of the arthrodesis. A successful arthrodesis depends on meticulous soft-tissue debridement, decortication, and copious iliac bone grafting or allograft bone grafting if autogenous graft is deficient. If the anterior approach is used, complete and thorough debridement of the intervertebral disc and cartilaginous end-plates with meticulous bone grafting of the interspace is essential for a successful fusion. A pseudarthrosis in the presence of an implant will eventually lead to implant failure. In implants placed anteriorly, this may lead to severe consequences and complications. If implants are used anteriorly and anterior arthrodesis is not achieved, a posterior spinal fusion should be carried out. All implants used anteriorly should be placed laterally away from great vessels, particularly the femoral artery. If separation from the vessels and the implant is not possible, the implant should either be removed or the vessels should be protected with a Dacron graft placed over any protuberant metal.     

An overview of cardiac surgery.

The scope of cardiac surgery has extended greatly in the last decade, advances being particularly in the areas of perfusion technology, ischaemic heart disease, and congenital defects in the infant. This paper sets out to summarize accepted current practice in the surgery of the heart and great vessels. Principles have been emphasized at the expense of detail, since the aim has been to present information which might be of interest to surgeons in general. Some aspects which have a special reievance to general surgical practice have been grouped separately for the sake of emphasis.