Bone reaction to a biomimetic third-generation hydroxyapatite coating and new surface treatment for the Symax hip stem

Four uncemented Symax hip stems were extracted at three weeks and nine, 13 and 32 months, respectively, for reasons other than loosening. The reasons for implant removal were infection in two cases, recurrent dislocation in one and acetabular fracture in one. They were analysed to assess the effect and behaviour of an electrochemically deposited, completely resorbable biomimetic BONIT-hydroxyapatite (HA) coating (proximal part) and a DOTIZE surface treatment (distal part) using qualitative histology, quantitative histomorphometry and scanning electron microscopy (SEM). Early and direct bone-implant bonding with signs of active remodelling of bone and the HA coating were demonstrated by histology and SEM. No loose BONIT-HA particles or delamination of the coating were observed, and there was no inflammation or fibrous interposition at the interface. Histomorphometry showed bone-implant contact varying between 26.5% at three weeks and 83.5% at 13 months at the HA-coated implant surface. The bone density in the area of investigation was between 24.6% at three weeks and 41.1% at 32 months. The DOTIZE surface treatment of the distal part of the stem completely prevented tissue and bone apposition in all cases, thereby optimising proximal stress transfer. The overall features of this implant, in terms of geometry and surface texture, suggest a mechanically stable design with a highly active biomimetic coating, resulting in rapid and extensive osseo-integration, exclusively in the metaphyseal part of the stem. Early remodelling of the HA coating does not seem to have a detrimental effect on short-term bone-implant coupling. There were no adverse effects identified from either the BONIT-HA coating or the DOTIZE surface treatment

Improving peri-prosthetic bone adaptation around cementless hip stems: A clinical and finite element study

This study assessed whether the Symax™ implant, a modification of the Omnifit® stem (in terms of shape, proximal coating and distal surface treatment), would yield improved bone remodelling in a clinical DEXA study, and if these results could be predicted in a finite element (FE) simulation study. In a randomized clinical trial, 2 year DEXA measurements between the uncemented Symax™ and Omnifit® stem (both n = 25) showed bone mineral density (BMD) loss in Gruen zone 7 of 14% and 20%, respectively (p < 0.05). In contrast, the FE models predicted a 28% (Symax™) and 26% (Omnifit®) bone loss. When the distal treatment to the Symax™ was not modelled in the simulation, bone loss of 35% was predicted, suggesting the benefit of this surface treatment for proximal bone maintenance. The theoretical concept for enhanced proximal bone loading by the Symax™, and the predicted remodelling pattern were confirmed by DEXA-results, but there was no quantitative match between clinical and FE findings. This was due to a simulation based on incomplete assumptions concerning the yet unknown biological and mechanical effects of the new coating and surface treatmen

Bone response adjacent to calcium phosphate electrostatic spray deposition coated implants: an experimental study in goats.

Item does not contain fulltextBACKGROUND: A new technique to deposit calcium phosphate (CaP) coatings onto titanium substrates has been developed recently. This electrostatic spray deposition (ESD) technique seems to be very promising. It appears to have clinical advantages such as an inexpensive and simple set-up, high deposition efficiency and the possibility to synthesize layers with a defined surface morphology. OBJECTIVE: The aim of this study was to examine biological properties and osteoconductivity of ESD CaP coatings when inserted into the femoral condyle of a goat. MATERIAL AND METHODS: Twenty-four implants with two gaps, i.e. 1 or 2 mm, were inserted into the femoral condyles of six goats. The implants were coated on one side with either a commercially available plasma-sprayed hydroxyapatite (HAPS) coating or an ESD carbonate apatite (CAESD) coating. The other side of the implant was always left uncoated (Ti). Twelve weeks after implantation the animals were sacrificed and the characteristics of bone ingrowth and bone contact were evaluated. Results: At 3 months, histological and quantitative histomorphometrical measurements demonstrated more bone ingrowth and bone contact for coated sites as compared with uncoated sites. Statistical testing revealed that for both the 1 and 2 mm gaps HAPS (plasma-sprayed hydroxyapatite) as well as CAESD (ESD carbonate apatite) -coated surfaces always had a significantly higher (P<0.05) amount of bone contact than uncoated Ti surfaces. On HAPS surfaces always significantly more bone was present than on CAESD surfaces. Further statistical testing revealed a significant difference in bone ingrowth between the HAPS as well as CAESD and Ti 1+2 mm gap specimens (P<0.05). Further, HAPS 1 mm gaps showed more bone ingrowth than CAESD 1 mm gaps. No significant difference existed between HAPS and CAESD 2 mm gaps. CONCLUSION: On the basis of our observations, we conclude that the used ESD technique is a promising new method to deposit CaP coatings onto titanium substrates. On the other hand, plasma-spray HA-coated implants have a still more favourable effect on the bone response