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Glass-ceramic coated implants. A simple model for a loaded hip prosthesis with a bioactive interface.

The favorable histological results at the bone-implant-interface of glass ceramic material are well-known. The mechanical properties of the solid material limit it's application for implants. Therefore metallic hip implants had been coated by glass ceramic granules, by a special technique, to transfer the bioactive property of the glass ceramic on to the metal stem. The following loaded experiments in rabbits with a simple model of a hip endoprosthesis showed a direct and tight bonding between implant surface and surrounding new bone formation. These findings demonstrate a possibility to anchor a joint endoprosthesis without the use of bone cement.

Animals↗

[Histological analysis of the bone/prosthesis interface in man after implantation of a hip prosthesis coated with plasma-sprayed hydroxyapatite].

Thin coatings of calcium phosphate hydroxyapatite on metal alloys provide to these materials biological properties of calcium phosphates. We have analysed, using histological techniques or newly developed scanning electronic microscopy techniques, hip prostheses implanted into humans for periods from a few days up to twenty six months. The results of these analyses confirm the good osteointegration of these prostheses observed during clinical studies. Moreover, an active remodeling of the bone in contact with the ceramic-coating was observed. The coating was also concerned by the remodeling process and evolved once implanted.

Bone Matrix↗

Survival of the Lubinus hip prosthesis. An eight- to 12-year follow-up evaluation of 444 cases.

The Kaplan-Meier survival method was used to analyze 444 Lubinus arthroplasties in 398 patients who were observed between eight and 12 years. The indication for arthroplasty was osteoarthrosis in 316 hips, rheumatoid arthritis in 84 hips, and various other conditions for the other 44 hips. Survival was determined for the entire prosthesis, as well as separately for the femoral stem, the acetabulum cup, and their four subgroups. Four patient-related variables (diagnosis, gender, age, and weight) were analyzed. The overall survival of the Lubinus implants was 97.1% at five years and 87.1% at ten years. No significant difference in survival was found between the acetabular and femoral components. Survival was not significantly better with a new anatomic (SP1) stem than with the old curved one (IP). Of the four patient-related variables studied, only diagnosis and age had a significant effect on prosthesis survival. There was no difference in survival between osteoarthrosis and rheumatoid arthrosis hips, but survival was clearly poorer at ten years in the miscellaneous diagnosis group. The authors obtained a significantly lower survival percentage for patients younger than 65 years of age than for those 65 years and older. There were no deep postoperative infections in this series. The revision rate was 11.5%. The wear seen at the lower front edge of cups that were removed is discussed.

Age Factors↗

Stem surface roughness alters creep induced subsidence and 'taper-lock' in a cemented femoral hip prosthesis.

The clinical success of polished tapered stems has been widely reported in numerous long term studies. The mechanical environment that exists for polished tapered stems, however, is not fully understood. In this investigation, a collarless, tapered femoral total hip stem with an unsupported distal tip was evaluated using a 'physiological' three-dimensional (3D) finite element analysis. It was hypothesized that stem-cement interface friction, which alters the magnitude and orientation of the cement mantle stress, would subsequently influence stem 'taper-lock' and viscoelastic relaxation of bone cement stresses. The hypothesis that creep-induced subsidence would result in increases to stem-cement normal (radial) interface stresses was also examined. Utilizing a viscoelastic material model for the bone cement in the analysis, three different stem-cement interface conditions were considered: debonded stem with zero friction coefficient (mu=0) (frictionless), debonded stem with stem-cement interface friction (mu=0.22) ('smooth' or polished) and a completely bonded stem ('rough'). Stem roughness had a profound influence on cement mantle stress, stem subsidence and cement mantle stress relaxation over the 24-h test period. The frictionless and smooth tapered stems generated compressive normal stress at the stem-cement interface creating a mechanical environment indicative of 'taper-lock'. The normal stress increased with decreasing stem-cement interface friction but decreased proximally with time and stem subsidence. Stem subsidence also increased with decreasing stem-cement interface friction. We conclude that polished stems have a greater potential to develop 'taper-lock' fixation than do rough stems. However, subsidence is not an important determinant of the maintenance of 'taper-lock'. Rather subsidence is a function of stem-cement interface friction and bone cement creep.

Aged↗

Results of the Harris-Galante cementless hip prosthesis.

We reviewed 82 primary arthroplasties (in 71 patients) in which cementless porous-coated hip prostheses were used. The mean age of the patients at operation was 52 years (24 to 86); they were followed up for an average of 62.1 months (60 to 66). The diagnosis was avascular necrosis of the femoral head in 35%, fracture of the femoral neck in 24%, primary osteoarthritis in 16% and miscellaneous in 25%. The average preoperative Harris hip score was 56.7 points and the average postoperative score was 83.3 points. Eight hips (10%) had component loosening; four had been revised and four were awaiting revision. In 27 hips (33%) there was a radiolucent line wider than 2 mm in zones 1 and 7. In 55 hips (67%) there was calcar resorption of more than 10 mm. Twenty patients (28%) complained of thigh pain although they had no radiographic evidence of loosening of a component. Factors that may have contributed to the poor clinical and radiographic results were: 1) inadequate surface area for bone ingrowth, particularly on the lateral aspect of the upper part of the prosthesis, 2) poor initial fit of the stem in the metaphysis, which resulted in cantilever motion of the proximal part of the stem about the well-fixed distal stem, and 3) the collar of the prosthesis, which prevented it from subsiding to a naturally stable position and caused damage to the calcar.

Bone Cements↗

The centrometaphyseal femoral hip prosthesis: 8-year follow-up.

The CM-prosthesis is a cementless femoral prosthesis made of titanium alloy. Its surface is coated with HAC (hydroxyapatite ceramic), and it is available in 6 sizes. The CM-prosthesis concept is based on the biogeometrical configurations of the femoral metaphysis.

Biomechanical Phenomena↗