Conclusions and outlook
Impact hypotheses for the carbon pin
The basic healing mechanisms are assumed to be induced by penetration of the subchondral bone, i.e. bone-marrow stimulating techniques. There is a clear shift of quantity towards the application of carbon pins.
The fibrin plug that is created after the drilling is very fragile and is mechanically stabilised by means of the pin. With its large porous surface the pin can be integrated into the fibrin mesh and protects it against outer mechanical influences, especially against compressive loads. Furthermore, it acts as a basis for the newly created cartilage replacement tissue.
The replacement cartilage tissue that is formed over the drilling and covers the defect presumably originates from precursor cells that migrate from the bone marrow through the drilling into the joint surface. In case of a drilling without pin, the hole is filled with bone in the course of time and migration is stopped. In case of the pin, a layer of fibrous connective tissue remains between bone and pin, as bone does not grow directly onto the carbon surface. This layer enables migration of cells from the bone marrow even over a longer period. Results of histological and electron microscopic investigations support this thesis (9,31).
Guidance-effect for cell migration
Oriented fibrous structures are known to influence cell migration (so-called contact guidance (8)). Carbon fibre pins have a textile woven structure with clearly oriented fibres (axial orientation at certain angles). When cells migrate from the fibres, they have a clear migration direction due to the orientation of the fibres and concentration gradient of cells (contact inhibition (16)).
Carbon fibre pins are inert, non-toxic, non-allergenic, and have excellent mechanical properties.
Clinical studies show consistently good to excellent results.
No serious complications have been observed associated with the implantation of the carbon pin, such as increased infection, loosening, or implant failure. Fortunately, other synovial joints of the human body, such as the metatarsophalangeal or upper ankle joint, have also been treated successfully.
The application of carbon fibre pins is technically easy and does not present a problem for the experienced surgeon.