Effect of surface topology on the osseointegration of implant materials in trabecular bone.

The importance of surface topology and implant material composition on osseointegration in trabecular bone was investigated using three commericially used implant materials and surface-texturing procedures which included blasting, high temperature acid etching, and hydroxyapatite (HA) coating. Surface roughness and spacing parameters were measured for each implant group with a laser interferometric profilometer. Cylindrical implants were press-fit into trabecular bone sites in the knee of mature miniature pigs. After 12 weeks in situ, osseointegration was evaluated by (1) mechanical pushout tests to measure bone-implant interface strength and (2) quantitative morphometric measurements of the percent implant surface covered by bone. We found that HA-coated implants showed superior osseointegration in terms of both pushout failure load and surface coverage by bone measurements. An excellent correlation (r2 = .90) was found between the average roughness of the implant surface and pushout failure load. New methods for altering the local topologic and/or chemical state of the implant surface (i.e., by acid etching) may provide an important new avenue of research for improving the osseointegrative properties of orthopedic materials.

[Removal torques of small screws of steel and titanium with different surfaces]. / Lösemomente an Kleinschrauben aus Stahl und Titan mit unterschiedlichen Oberflächen.

This study was designed to investigate the relationship between metal surfaces and bone holding strength and the safety margin against breakage available in small screws at implant removal. Small cortical bone screws of 1.5 and 2 mm outer diameter (mini-screws) made of stainless steel or commercially pure titanium have been mechanically and chemically treated to give different surface conditions. They were implanted in randomized groups of four or five speciments into the proximal halves of rabbit tibiae. Tightening was performed with a standardized torque of 10 or 18 Ncm by means of an instrumented screwdriver. The animals were sacrificed after 12 weeks and screw removal torques were measured. Stainless steel screws used as reference screws were found to have loosened their seat by 27% compared with the original tightening torque. Titanium implants, in contrast, revealed improved bone contact with higher removal torques varying from 130% to 160%. No correspondence could be found between these values and the surface roughness of glass-ball-blasted versus polished screws.

A comparative study of the initial stability of cementless hip prostheses.

In the process of prosthetic loosening, the initial motion of the implant relative to the bone is a key element. In order to provide quantitative information, three straight and one curved cementless hip stems were submitted to in vitro tests in autopsy specimens of the femur under dynamic axial and torsional loads with the displacements measured in several directions. The results were compared to those of an additional group of cemented straight stem prostheses providing reference values. Subsidence of cementless implants on the average was significantly higher than the cemented reference, but single implants were comparable to the reference. Rotational motion was distinctly higher than the reference values, with considerable differences between designs. When comparing displacements perpendicular to the main load direction, the sagittal plane motion was found to be at least double the motion in the frontal plane. Micromotions at the prosthesis/bone interfaces under the load case selected were smallest for the curved and highest for one of the straight prostheses.

Experimental method for the in vitro testing of the initial stability of cementless hip prostheses.

Micromotions at the interface between bone and prosthesis are believed to induce bone resorption and ultimately lead to loosening of the implant. Thus the initial stability achieved by a hip prosthesis is an important factor for the long-term function of the implant. Knowing the biological consequences of the mechanical conditions, it appears to be mandatory to measure the extent of these three-dimensional movements. An in vitro dynamic method for measurement of the micromotion of the femoral component of hip prostheses has been developed. Tests in cemented prostheses have confirmed that the use of cement reduces sinkage and rotation manyfold and have yielded reference values for stability. Comparison with two types of cementless prostheses has shown that certain cementless implants may achieve stability comparable to cemented ones in some load directions.

[Biocermics in rat experiments (preliminary report)]. / Biokeramik im Rattenversuch (vorläufige Mitteilung).

Bioactive ceramics in the shape of small plates was implanted into the femoral diaphysis of rats. The specimens were examined 2 months later by optical and mechanical methods for their behaviour of incorporation into the tissues. The composition of materials, the technique of implantation, the methods of histological preparation and the examination of adhesive resistance are described. The inadequacy of current methods of examination and their replacement by better ones is pointed out.