Tissue ingrowth into titanium and hydroxyapatite‐coated implants during stable and unstable mechanical conditions

Abstract

Summary: Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. TO study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)-coated implants, a loaded unstable device producing movements of 500 pm during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight-bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA-coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p < 0.01). However, shear strength values of unstable HA-coated implants were significantly greater than those of unstable 'l'i implants (p < 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA-coated implants, which was threefold stronger as compared with the stable Ti implants (p < 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA-coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of iibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth. Key Words: Bone ingrowth-Fibrous membraneHydroxyapatite-Micromotion-Porous ingrowth-Titanium. Porous coated prostheses were designed to obtain permanent fixation by ingrowth of bone into the porous implant surface. However, recent histological analyses of cementless tibia1 components (1 1,16) and total hip replacements (10,12) retrieved 285

Locally delivered TGF-β1 and IGF-1 enhance the fixation of titanium implants: A study in dogs

“…Our previous work with gap implants has consistently shown abundant ongrowth of fibrous tissue, inferior bony ongrowth, and poor mechanical fixation (Soballe et al 1990, Elmengaard et al 2005. In previous studies, the titanium implant surface has been shown to be similar to that of commercially available prostheses with a plasma spray titanium coating (Soballe et al 1992(Soballe et al , 1993. We hypothesized that the combination of TGF-β1 and IGF-1 in PDLLA would enhance the osseointegration and mechanical fixation of unloaded cylindrical porous-coated titanium implants surrounded by a gap.…”

Lower periprosthetic bone loss and good fixation of an ultra-short stem compared to a conventional stem in uncemented total hip arthroplasty

“…Shorter femoral stems, aimed at giving a more physiological load pattern in the proximal femur, have become popular lately because of expectations of reducing stress shielding. Absence of a diaphyseal engaging stem is a key factor to prevent off-loading of the proximal femoral bone, but at the same time it will challenge the primary stability necessary for bone osseointegration of the femoral implant (Søballe et al 1992). …”

Compacted cancellous bone has a spring-back effect

“…Moreover, experimental studies have shown that initial implant stability is essential to bone ingrowth (Cameron et al 1973, Ducheyne et al 1977, Pilliar et al 1986, Søballe et al 1992, Bragdon et al 1996, Jasty et al 1997, Heck et al 1986. It is therefore important to create initial implant stability during surgery so as to ensure the latter stability achieved by bony ingrowth.…”