Bioactive porous coating
Plasmapore® coated orthopaedic implants have been used successfully in joint replacement arthroplasty since 1986. The cementless implants are coated with a layer of fine titanium powder applied in a plasmaspray process under vacuum. The Plasmapore® pore sizes range from 50 to 200 μm with a microporosity of 35 % and a thickness of 0.35 mm.
These characteristics are optimal for bone ingrowth. Plasmapore® is a very rough surface and supports primary stability better than alternative coatings.
All cementless Aesculap hip stem systems and acetabular cup systems are offered with this coating.
Highly crystallized calcium phosphate (CaP) is used as the bioactive material for Plasmapore® μ-CaP. The Plasmapore® surface is combined with a very thin CaP layer of 20 μm, which is applied electrochemically. This Plasmapore® μ-CaP surface accelerates direct bone-implant contact and resorbs without giant cell reactions within 8-12 weeks.
The modular Prevision® revision hip stem and the short hip stem Metha® are coated exclusively with Plasmapore® μ-CaP.
Plasmapore® with Dicalcium Phosphate
The well-known characteristics of calcium phosphates such as HAC (hydroxylapatite) and TCP (tricalcium phosphate), and various HAC/TCP combinations led to Aesculap’s selection of dicalcium phosphate dehydrate (CaHPO4 x 2H2O) for use with Plasmapore®.
Dicalcium phosphate dehydrate (DCPD) is very soluble in vivo, and dissolves into calcium and phosphate ions. During the acellular dissolving process, calcium and phosphate ions are continuously released in a ratio of 1:1, which are then available for bone modeling.
In contrast, the poorly soluble hydroxyapatite (HAC) releases only calcium ions from non-HAC calcium compounds (CaO) resulting from the manufacturing process, but almost no phosphate ions.
The resorbable tricalcium phosphate (TCP) stimulates giant cell reactions, and is therefore not optimal for use with orthopaedic implants. In orthopaedic implants the transition between primary and secondary implant stability is a continuous process of bone remodeling, characterized by apposition and resorption at the implant surface. The DCPD layer supports the continuous release of calcium and phosphate ions and encourages the formation of new bone structures at the bone-implant interface. Due to the continuous dissolving process of the calcium phosphate, the pores of the Plasmapore® coating remain open for bony ingrowth.
Improved bone contact
The features of thin calcium phosphate surfaces are important in the short postoperative term. The dicalcium phosphate μ-CaP layer is resorbed within 8-12 weeks in vivo. The dissolving process takes place without any giant cell activity. Simulation tests of the solution behavior of HAC and μ-CaP show a different ion release of μ-CaP in comparison to hydroxylapatite ceramic surfaces. HAC surfaces do not release phosphate ions but in the initial solution phase, calcium ions are released from non-HAP calcium compounds (CaO) resulting from certain manufacturing processes. In contrast, μ-CaP dicalcium phosphate releases phosphate and calcium ions during the entire resorption period with a ratio of 1:1. These ions are available for bone synthesis. Due to the osteoconductive characteristics of calcium phosphate, the bone is brought into direct contact with the implant surface.