Abstract
Despite biomechanical well established implants and improved operation techniques we still have a too high rate of complications in orthopaedic and trauma surgery like non-union, implant loosening or implant associated infections. The development of bioactive implants could improve the clinical outcome.
Growth factors are important regulators of bone metabolism. During fracture healing many growth factors or cytokines were locally released at the facture site. In several studies, different growth factors demonstrated osteoinductive and fracture stimulating properties.
In vitro and in vivo studies showed a stimulating effect of Insulin-like growth factor-I (IGF-I), Transforming growth factor-A71 (TGF-A71) and Bone morphogenetic protein-2 (BMP-2) on osteo- and chondrogenetic cells. The exact effectiveness and the interaction of these growth factors during fracture healing is not known so far. Further, the local application of these factors for therapeutically use in fracture treatment is still a problem.
A biodegradable poly(D,L-lactide)-coating of implants allows the local and controlled release of incorporated growth factors directly at the fracture site. The coated implant serves on the one hand for fracture stabilization and on the other hand as a drug delivery system. The coating has a high mechanical stability. The incorporated growths factors remain biologically active in the coating and were released in a sustained and controlled manner.
To investigate the effect of locally released growth factors IGF-I, TGF-A71 and BMP-2 and the carrier PDLLA on fracture healing, standardised closed fracture models were developed with a close relationship to clinical situation. Further, possible local and systemic side effects were analysed.
The results demonstrated a significantly higher stimulating effect of IGF-I on fracture healing compared to TGF-A71. The combined application of both growth factors showed a synergistic effect on the mechanical stability and callus remodeling compared to single treatment.
The local release of BMP-2 also enhanced fracture healing significantly – comparable to combination of IGF-I and TGF-A71. However, a higher rate of mineralisation was measurable outside the fracture region using BMP-2 in a rat fracture model.
Using a large animal model on pigs with a 1 mm osteotomy gap, the effectiveness of locally released growths factors could be confirmed. Further, the PDLLA-coating without any incorporated growth factors demonstrated a significantly effect on healing processes in both models. These investigations showed, that the local release of growth factors from PDLLA coated implants significantly stimulate fracture healing without any local or systemic side effects.
Comparing systemic with local stimulation techniques, we found an improvement of fracture healing by systemic administration of growth hormone and local application of IGF-I and TGF-A71. However, the combined use of both simulation techniques did not lead to a further increase of healing processes.
Investigations on the effectiveness and the interaction of growth factors during fracture healing demonstrated an dramatic effect in the early phases of healing processes. The growth factors stimulate the differentiation of osteoblasts with a higher production of collagen I in vitro and increase osteogenesis and vascularisation of the fracture callus in vivo.
Further applications of the coating technology are the use of PDLLA and growth factor coated cages for the stimulation of intervertebral fusion and the use of PDLLA and Gentamicin coated implants in order to prevent implant associated infections.
The first patients with open tibia fractures were treated with PDLLA and Gentamicin coated IM nails.
The abstracts were prepared by Ms Grazia Gliozzi. Correspondence should be addressed to her at the Italian Orthopaedic Research Society, Laboratory for Pathophysiology, Instituti Ortopedici Rizzoli, University of Bologna, Bologna, Italy.
