Biochemical features of pseudomembrane at the bone-cement interface of loosened total hip prostheses

An experimental analogue to model the fibrous tissue layer in cemented hip replacements

Fibrous tissue at the bone-cement interface of cemented joint replacements has been reported frequently in cases of revisions made necessary by aseptic loosening. This work describes the development of in vitro specimens suitable for biomechanical modeling of cemented femoral hip replacements with a fibrous tissue layer at the bone-cement interface. In particular, a series of uniaxial compression tests were performed on silicone elastomer specimens to identify a suitable analogue with similar mechanical characteristics to those reported for the fibrous tissue layer. A method was developed to apply the silicone elastomer at the bone-cement interface. This was examined for two types of cemented hip replacements implanted in composite femurs. The selected thickness of the elastomer layers was in the range of those found in clinical cases of aseptic loosening. Specimens produced by these methods could be used in preclinical biomechanical tests (such as stability or stress shielding tests) to assess the effects of a soft-tissue layer, to model in vitro a long-term-implant scenario, and to provide validation for similar finite element studies.

The bone-cement interface: histological observations on the interface of cemented arthroplasties within the immediate and late phases

Undecalcified specimens of cemented arthroplasties obtained during the early and late phases were studied. On the tenth postoperative day, there was excellent interlocking of the cement with the soft and hard tissues of the bone: there was no necrosis of the bed of the implant: a neutrophilic and macrophagic inflammatory response, where present, was mild and focal. Samples of the bone-cement interface of well fixed components obtained (at autopsy or by biopsy) many years after implantation revealed a thin and quiescent fibrous interfacial membrane alternating with bone and osteoid (that is, segmental osseointegration) or a cartilaginous layer abutting on the cement. It is concluded that, firstly, modern cementation techniques are not associated with extensive necrosis of the underlying bone in the immediate postoperative period; secondly, monomeric and polymeric methylmethacrylate as such is not toxic to the tissues; and, thirdly, acrylic cement is osseointegrated when motion at the interface is at its minimum.

Histological patterns of bone and articular tissues after orthopaedic reconstructive surgery (artificial joint implants)

Revision surgery after failures of joint replacements leads to histological studies on joint and bone tissues close to the implanted material. Aspectic loosening is the main complication. The surgical pathologist has to identify wear debris (metal, polyethylene, polymethylmethacrylate, chiefly) which promotes a histiocytic granuloma. Some surgical procedures such as cup or resurfacing arthroplasties create a new articular surface and a bone remodeling or necrosis. Cemented joint prostheses show various membrane structures between bone and the cement mantle while there is an association of bone resorption and formation. Non-cemented, porous-coated joint prostheses induce little bone ingrowth, even in satisfactory clinical results. Mechanical factors are predominant in massive limb prostheses. For silicone elastomer implants or artificial ligaments, wear of material promotes many tissular reactions. Often used bone grafts show little creeping substitution process in case of homografts, even well-incorporated on X-rays. More retrieval specimen studies are necessary to delineate precise topographical histological lesions, including non-loosened joint implants.

Cellular events in the mechanisms of prosthesis loosening

The functional restoration of a joint damaged by trauma or disease is obtained by prosthetic surgery. In particular the implantation of hip prostheses is regarded as routine in orthopedic surgery and thorough research has been developed in this field. The prosthetic replacement of the knee and even more so the ankle and elbow occurs less frequently in clinical practice and has been studied less intensively. The results of artifical hip replacement are generally good, both in terms of pain relief and the restoration of satisfactory joint function. Nevertheless, as time passes, a high rate of failures have been recorded due to prosthesis infections, fracture and wearing of the prosthetic components and prosthesis loosening by various causes. The use of ultra-filtered air and laminar flow in operating theatres and antibiotic prophylaxis have dramatically reduced the incidence of infections in total hip arthroplasty. Thanks to the setting up of new stem configurations and the use of superalloys that are highly resistant to fatigue failure, the fracture of the femoral component has been virtually eliminated as a complication of total hip arthroplasty replacements. Loosening is thus the most frequent complication in total hip replacement.

Femoral lysis after cemented hip arthroplasty

The cause of femoral lysis after cemented total hip arthroplasty is unknown. Clinical aspects are poorly understood, and there have been only a few reports, with small numbers of cases, in the literature. The author analyzed common factors and clinical aspects in 51 cemented hip arthroplasties with lysis around the femoral component, in an effort to understand the cause of lysis. The process frequently starts where metal abuts against bone or where cement is deficient or fractured. Men are more commonly affected than women (4:1). Pain is the only symptom, but lysis can occur without pain. Lysis is progressive and always culminates in implant loosening. Progression is usually slow but can be alarmingly rapid. Twenty-six percent of cases in this series had associated acetabular loosening. After bilateral hip arthroplasty, lysis can be bilateral but usually is not. The major causative factor may be microfragmentation of any of the component parts of the artificial joint complex.

Trabecular bone remodeling around smooth and porous implants in an equine patellar model

The objective of this investigation was to examine the stress-morphology relationships for trabecular bone around implants with different surface characteristics. Stainless steel spheres with either a polished surface or a sintered-bead porous coating were implanted unilaterally into equine patellae and maintained for a 6 month period. Stereological methods were used to quantify the trabecular bone morphology and finite element analyses were performed to predict the trabecular bone stresses. In general, the remodeling response around the smooth implants was greater than that around those porous implants that exhibited bone ingrowth. In accordance with these differences, the finite element models predicted greater changes in the stresses adjacent to the smooth implants due to the nonlinear boundary conditions. However, it did not appear that the trajectorial theory, in its simplest form, was applicable to the remodeling induced by the implants. A linear relationship between the change in bone areal density and the change in von Mises effective stress provides support for the hypothesis that the architecture of trabecular bone corresponds to an optimal structure. The results also demonstrated that, under certain circumstances, small changes in the stress state may result in large changes in the principal material orientation.

A histopathologic comparison of the tissue reaction to prosthetic materials in the knee joint of rats

The five kinds of prosthetic materials: powders of cobalt alloy, stainless steel, alumina ceramic, HDP plastic and bone cement, were injected to the knee joints of 16 rats for each material. Two controls were used, one with saline solution and the other untreated. Some of the rats were sacrificed at one week, being left untreated. Some of the rats were sacrificed at one, four, 12 and 25 weeks after injection. The knee joints of these rats were taken out for a histopathologic study. The main changes were fibrosis and granulation due to foreign bodies, but no remarkable change in the degree of tissue reactions was observed within each material group, nor did the length of period have any effect thereon. Comparing the degree of the above changes caused by each material in the tissue, ceramic powder showed the most significant change, followed by bone cement, HDP, stainless steel and cobalt alloy powder, in that order. No tumorous condition was observed.