Improved Bone Ingrowth Research Articles

Cortical bone ingrowth in growth hormone-loaded grooved implants with calcium phosphate coatings in goat femurs

Dental implants are succesfully used for tissue-integrated protheses, but the long-term survival in the maxilla is shorter than in the mandible [Cune MS, Thesis, University of Utrecht, 1993; Jaffin RA, Berman CL. J Periodontol 1991;62:2–4]. However, by adding growth hormone at implantation, increased bone apposition may be expected, since it is known that growth hormone has a stimulating effect on the differentiation and proliferation of osteoblastic cells [Ernst M, Froesch ER. Biochem Biophys Res Commun 1988;151:142–47; Scheven BAA et al. Growth Regul 1991;1:160–67; Stracke H et al. Acta Endocrinol 1984;107:16–24]. We studied bone ingrowth and bone contact of grooved implants impregnated with growth hormone in the cortex of femurs of female goats. We compared the effect of growth hormone on grooved implants with or without calcium phosphate coatings at the bottom of the grooves. The coatings used were hydroxyapatite, fluorapatite and heat-treated hydroxyapatite. The implants had both small and large grooves. The implants were positioned in the cortex of one femur and were treated with recombinant human growth hormone, while the implants on the opposite femur served as controls. After 6 weeks, the implants and surrounding tissues were dissected and evaluated histomorphologically and morphometrically by light microscopy. The bone ingrowth and the bone contact in the grooves were quantified by digital image analysis. Calcium phosphate coating at the bottom of the grooves resulted in a significant increase of bone ingrowth and bone contact. Small grooves had significantly more bone ingrowth and bone contact than the larger grooves. However, all implants impregnated with growth hormone showed inhibition of bone contact and bone ingrowth. We conclude that recombinant human growth hormone inhibits bone formation in the grooves coated with calcium phosphate. Without the addition of growth hormone, the calcium phosphate coatings improved bone ingrowth and bone contact in the grooves. Further studies are required to determine whether growth hormone could also possibly act as a bone growth promoting factor in these implants.

Hydroxylapatite coating of porous implants improves bone ingrowth and interface attachment strength.

The effect of a plasma-sprayed hydroxylapatite (HA) coating on the degree of bone ingrowth and interface shear attachment strength was investigated using a canine femoral transcortical implant model. Cylindrical implants were fabricated by sintering spherical Co-Cr-Mo particles 500-710 microns in diameter; the nominal implant dimensions were 5.95 +/- 0.05 mm diameter by 18 mm in length. One half of each implant was coated with hydroxylapatite, 25-30 microns in thickness, by a plasma-spray technique. Using strict aseptic technique, the implants were placed through both femoral cortices into defects approximately 0.05 mm undersized. After 2, 4, 6, 8, 12, 18, 26, and 52 weeks, the implants were harvested and subjected to mechanical pullout testing and undecalcified histologic evaluation. The application of the HA coating to porous implants enhanced both the amount of bone ingrowth and the interface attachment strength at all time periods. These differences were statistically significant for the percent of bone ingrowth at the 4-, 6-, 12-, 18-, 26-, and 52-week time periods, and interface shear strength values were significantly different at the 6-, 8-, 12-, 18-, and 26-week time periods. The rate of development of interface strength and bone ingrowth was also more rapid for the HA-coated implants. No evidence of any disruption, mechanical failure, or biologic resorption of the HA coating was observed. The results of the present study--demonstrating a beneficial effect of the HA coating at all time periods--are believed to be due to the use of paired comparisons, which allow assessment of subtle differences that might otherwise have been obscured by normal biological variability.

Morphological and numerical studies of the stress compatibility of patella implants

Failure of total knee arthroplasty is relatively often caused by problems of the patellofemoral replacement. The purpose of this study was to analyze the distribution of stresses within an anatomical patella and the changes in stress distribution after patellar resurfacing with a Miller-Galante I patellar implant using two- and three dimensional finite element models (FEM). To assess validity, FEM results were compared with morphological findings from contact radiographs and densitographs. Internal orientation of bone trabeculae is in good agreement with the orientation of theoretically calculated principal stresses. Almost unchanged principal tensile stresses after implantation, together with the lack of extreme stress peaks within the cancellous bone ensure stress compatibility of the implant. In the case of a firmly seated implant with good bone ingrowth, increased von Mises stresses are found near the fixation peg/plate junction. Their relevance for improved bone ingrowth near this part of the interface is emphasized. At the same time, material failure at the peg/plate junction can be better understood. An analysis of the early postoperative period assuming nonlinear interface conditions failed to demonstrate an uniform distribution of normal and tangential interface forces.

A Double-Blind Study on the Effects of a Capacitively Coupled Electrical Field on Bone Ingrowth Into Porous-Surfaced Canine Total Hip Prostheses

The effect of a capacitively coupled electrical field on bone ingrowth into titanium fiber mesh porous-surfaced canine total hip arthroplasties (THAs) was investigated in a double-blind experiment. The electrical field was induced by an external source delivering a 60-kHz 5-6-V peak-to-peak sinusoid voltage through skin electrodes. No significant increase in the ingrowth of bone into the porous coating occurred at the end of six weeks of electrical stimulation. The amount of bone that grew into the porous surface, the areal density of bone within the available pore space, and the extent of the prosthesis surface area with bone ingrowth or apposition were not significantly different in the control and stimulated groups. This particular form of electrical stimulation does not improve bone ingrowth into porous-surfaced canine THAs by six weeks.