Electromechanical factors in healing cortical bone defects

Abstract

Direct current flowing in the medul la ry canal of bone increases osteoblastie ac t iv i ty around the negat ive electrode. The new bone s t imulated electrically, however, is difficult to differentiate f rom tha t arising solely f rom the presence of an inact ive electrode in the medul lary canal. Fur ther more, new bone around a negat ive electrode within the medul la ry canal serves litt le or no mechanical function. I n order to clarify the role of electrical s t imulat ion, a new model for s tudying osteogenesis in dogs has been developed. Variables in healing response, inherent in different breeds and ages of dogs, were minimized by using a closed colony of l i t t e rmate beagles of known age as a source of exper imenta l animals. In all experiments , the contrala teral femur served as a control. A tota l of 20 beagles were employed in this s tudy and were sacrificed a t 28, 42, and 70 days. In the first phase of the investigation, three cortical defects, two measur ing 4 m m and one measur ing 5 m m in d iameter were produced in the lateral femoral cortex. A teflon ring with an inside d iameter of 4 m m was placed in the 5 m m hole, a solid teflon plug inserted into the second, and the third hole was left empty . React ive new bone filled the control, cortical defects within r weeks and was l imited largely to the axis of the cortices containing the defects. Cells responsible for reorganizat ion seemed to be derived pr imar i ly f rom the medullary canal. At four weeks, the hole containing the teflon ring was filled only with fibrous tissue, a l though there was a mass of young, fiber bone bridging the defect and located in the medul la ry canal a t the base of the ring. Fibrous connective tissue within the teflon was replaced gradual ly over the nex t 6 weeks b y fiber bone in a manne r similar to t ha t observed in Millipore ensheathed, cortical defects (RUEDI and BASSETT, 1967). The teflon ring-lined cortical defect appeared to have the largest endosteal mass of react ive new bone. In older specimens (70 days), the d iameter of the teflon plug was diminished where i t passed through the cortex, bu t not in the medul la ry canal, where i t was surrounded b y the newly formed bone. This teflon ring model had the following characterist ics which were advantageous in subsequent phases of the invest igat ion to s tudy effects of weak electric currents on osteogenesis: 1. substant ia l ly diminished ra te of osseous bridging, 2. a volume appreciably greater than the combined volume of the inserted electrode, together with any react ive bone encapsulating the electrode. I n a second series of experiments , epoxy-" po t t ed ", silicone-encapsulated, b a t t e r y resistor packs were implan ted in animals containing teflon ring-lined cortical defects. These packs combined two ir idium -p la t inum electrodes, of similar polari ty, flanking a center electrode of oppo-

DOI: 10.1007/BF02152381

Cite this paper

@article{Pawluk1970ElectromechanicalFI, title={Electromechanical factors in healing cortical bone defects}, author={Robert J Pawluk and C. Andrew L. Bassett}, journal={Calcified Tissue Research}, year={1970}, volume={4}, pages={120-121} }