Philippe Poitras

Internal plate fixation of fractures: short history and recent developments

Metal plates for internal fixation of fractures have been used for more than 100 years. Although initial shortcomings such as corrosion and insufficient strength have been overcome, more recent designs have not solved all problems. Further research is needed to develop a plate that accelerates fracture healing while not interfering with bone physiology.The introduction of rigid plates had by far the greatest impact on plate fixation of fractures. However, it led to cortical porosis, delayed bridging, and refractures after plate removal. These unwarranted effects were said to be caused by bone–plate contact interfering with cortical perfusion. Consequently, further plate modifications aimed to reduce this contact area to minimize necrosis and subsequent porosis.The advocates of limited-contact plates have not published measurements of the contact area or proof of the temporary nature of the porosis. Moreover, clinical studies of newer plate types have failed to show a superior outcome. Histomor-phometric measurements of the cortex showed no difference in the extent of necrosis under plates having different contact areas. Necrosis was predominant in the periosteal cortical half, whereas porosis occurred mostly in the endosteal cortical half. No positive correlation was found between either.The scientific evidence to date strongly suggests that bone loss is caused by stress shielding and not interference with cortical perfusion secondary to bone–plate contact. Consequently, an axially compressible plate (ACP) incorporating polylactide (PLA) inserts press-fit around screw holes was designed. The bioresorbable inserts should allow for (1) increased micromotion in the axial plane to promote healing during the union phase and (2) gradual degradation over time to decrease stress shielding during the remodeling phase.Results of ongoing experimental results are encouraging. Only plates allowing dynamic compression in the axial plane can lead to a revolution in fracture fixation.

Genipin Cross-Linked Fibrin Hydrogels for in vitro Human Articular Cartilage Tissue-Engineered Regeneration

Our objective was to examine the potential of a genipin cross-linked human fibrin hydrogel system as a scaffold for articular cartilage tissue engineering. Human articular chondrocytes were incorporated into modified human fibrin gels and evaluated for mechanical properties, cell viability, gene expression, extracellular matrix production and subcutaneous biodegradation. Genipin, a naturally occurring compound used in the treatment of inflammation, was used as a cross-linker. Genipin cross-linking did not significantly affect cell viability, but significantly increased the dynamic compression and shear moduli of the hydrogel. The ratio of the change in collagen II versus collagen I expression increased more than 8-fold over 5 weeks as detected with real-time RT-PCR. Accumulation of collagen II and aggrecan in hydrogel extracellular matrix was observed after 5 weeks in cell culture. Overall, our results indicate that genipin appeared to inhibit the inflammatory reaction observed 3 weeks after subcutaneous implantation of the fibrin into rats. Therefore, genipin cross-linked fibrin hydrogels can be used as cell-compatible tissue engineering scaffolds for articular cartilage regeneration, for utility in autologous treatments that eliminate the risk of tissue rejection and viral infection.

Fibrin Sealants from Fresh or Fresh/Frozen Plasma as Scaffolds for In Vitro Articular Cartilage Regeneration

Our objective was to evaluate human CryoSeal fibrin glue derived from single units of plasma as scaffolds for articular cartilage tissue engineering. Human articular chondrocytes were encapsulated into genipin cross-linked fibrin glue derived from individual units of fresh or frozen plasma using the CryoSeal fibrin sealant (FS) system. The constructs were cultured for up to 7 weeks in vitro under low (5%) or normal (21%) oxygen. Chondrocyte viability was >90% within the fibrin gels. Hypoxia induced significant increases in collagen II and Sox9 gene expression and a significant decrease in collagen I. A significant increase in collagen II was detected in fresh plasma-derived cultures, while only collagen I was significantly increased in frozen plasma cultures. Significant increases in total glycosaminoglycan and collagen were detected in the extracellular matrix secreted by the encapsulated chondrocytes. A significant increase in compression modulus was only observed for fresh plasma-derived gels, which is likely explained by a greater amount of collagen type I detected after 7 weeks in frozen compared to fresh plasma gels. Our results indicate that CryoSeal fibrin glue derived from fresh plasma is suitable as a tissue engineering scaffold for human articular chondrocytes, and therefore should be evaluated for autologous articular cartilage regeneration.

Dual cryogenic fixation for mechanical testing of soft musculoskeletal tissues

Mechanical testing of soft musculoskeletal structures like tendons and ligaments are essential to medical advances. A long-standing limitation for testing these structures in isolation has been the ability to solidly fix both ends of the tendon. Cryogenic fixation technology was leveraged into the development of a dual cryogenic fixation (DCF) device. Results of the study show that the DCF allows tendons to be tested in isolation, at physiologic temperatures, with excellent reproducibility.

Contents Vol. 190, 2009

F. Beck, Leicester A.L. Boskey, New York, N.Y. R.C. Burghardt, College Station, Tex. G. Burnstock, London F. Eckstein, Salzburg A.C. Enders, Davis, Calif. C. Farnum, Ithaca, N.Y. R.H.W. Funk, Dresden N.E. Fusenig, Heidelberg A. Gibson, Phoenix, Ariz. M. Glickstein, London J.W. Hermanson, Ithaca, N.Y. C.J. Kirkpatrick, Mainz P. Köpf-Maier, Berlin W. Kummer, Giessen J.W. Lichtman, Cambridge, Mass. K.G. Marra, Pittsburgh, Pa. O. Ohtani, Toyama P.J. Reier, Gainesville, Fla. R. Roy, Los Angeles, Calif. R. Segal, Chapel Hill, N.C. F. Sinowatz, Munich M. Sittinger, Berlin T. Skutella, Tübingen G.B. Stark, Freiburg i.Br. E. Th ompson, Melbourne C.G. Widmer, Gainesville, Fla. in vivo, in vitro