Journal of Rehabilitation Research and Development Rehabilitation R & D Progress Reports 1986 VII. Wound and Fracture Healing VII . Wound and Fracture Healing Electrical Stimulation for Augmentation of Wound Healing Scott R. Crowgey, M.D., and Steven M. Sharpe Veterans Administration Research and Development, Decatur, GA 30033 Sponsor: VA Rehabilitation Research and Development Service Purpose—This project will attempt to identify ing that could be influenced by electrical stimu- aspects of the wound healing process that may lation. Efforts will then be directed toward de- be augmented by the exogenous influence of veloping mathematical models of the possible electromagnetic fields. A theoretical analysis of electrical interaction of electromagnetic fields the possible effects of electromagnetic fields on with cells and cell structures to determine how wound healing will include analyses of the these interactions could be optimized to im- interaction of electromagnetic fields with cellu- prove wound healing. It is anticipated that the lar structures and of the deposition of heat in literature will not contain all the information damaged tissue via exogenously applied energy necessary to develop these models . Any gaps in fields. This analysis will then be used as a basis necessary information and data will be filled, if for developing a plan for future investigations practical, using tissue phantom modeling mate- into the potential application of electrical stim- rials, blood, and possibly even primitive tissue ulation for the augmentation of wound healing. culture exposed to a variety of known electro- The initial research will involve a review of magnetic environments, using easily construct- the literature to identify aspects of wound heal- ed exposure chambers. Development of a Mathematical Model of Fracture Healing in Long Bones Gary Beaupre, Ph.D., and Dennis Carter, Ph.D. Rehabilitation Research and Development Center, Veterans Administration Medical Center, Palo Alto, CA 94304 Sponsor: VA Rehabilitation Research and Development Service Purpose—When a long bone is fractured, its heals in the presence of different stress states mechanical properties change significantly as and how the mechanical properties change ac- the bone heals. However there is very little cordingly will offer insights into the fracture quantitative information on how mechanical healing process for both normal and pathologi- stresses influence the healing process and on cal healing situations. A better understanding how the mechanical properties of the fracture of fracture biomechanics will provide guidelines site change as the bone regenerates back to its in the design of treatment modalities for frac- original shape and structure. tures and fracture nonunions. Much attention has been given to the de- To date, there have been numerous histo- velopment of fixation devices for fractured long logical and morphological studies on the heal- bones, and many different mathematical ing process of fractured bones. The healing models have been used to evaluate the stress process has been categorized into four basic states and deformations caused by the applica- phases: 1) initial reformation of the vascular tion of these devices. The mechanical properties system with formation of soft callus tissue ; 2) assumed at the fracture site influence the re- formation of cartilaginous callus ; 3) formation sults of these analyses. The development of a of bone tissue; and 4) remodeling of bone tissue. mathematical model to quantify how a bone These sequential phases stabilize and progres- 228 229 Rehabilitation R&D Progress Reports 1986 sively stiffen and strengthen the healing bone. femur. The appropriate loading and boundary Some data are available on the mechanical conditions are obtained from previous studies properties of the tissues involved, but no using: 1) load-sensing implants and prostheses; models exist that can describe or predict this 2) in vitro experiments; and 3) static and dy- healing process. Our hypothesis is that the namic mathematical models of lower limb transition from the initial phases of fractured forces. An iterative mathematical procedure bone to its original structure, in particular that triggers the transformation of cartilage from the cartilaginous stage to the formation of into bone will be used. This procedure will bone tissue, is influenced by the local state of permit the temporal and geometric pattern of stress and strain within the tissues participat- healing to be both predicted and followed. ing in the healing process . As healing proceeds, In this study two- and three-dimensional the material and structural properties of the nonlinear finite element models of an idealized fracture are changed, resulting in a progressive fractured bone are being developed. Initial frac- increase in the structural integrity of the bone. ture callus geometry was determined from pre- vious studies. Preliminary studies suggest that Progress—The finite element method is being the local strain energy density is a likely candi- used to create a mathematical model of a frac- date for the controlling mechanism that trig- tured long bone. The idealized bone is based gers the transformation from cartilage into upon the midshaft geometry of the human bone. Bioelectricity in Fracture Healing John F. Connolly, M .D.; Dennis A. Chakkalakal, Ph.D.; Louis Lippiello, Ph.D. Veterans Administration Medical Center, Omaha, NE 68105, and the University of Nebraska Medical Center, Omaha 68131 Sponsor: VA Rehabilitation Research and Development Service Purpose—To investigate the role of bioelectri- in humans for diagnosis of problem fractures, city in fracture healing, two research projects for choice of the optimum method of treatment, are under way: "Electrical Osteogenesis: Mech- and for prognosis of all fractures. anisms and Causes of Failure," and "Scientific We used both internally fixed and external- Basis for a New Protocol in External Fixation ly fixed long-bone fracture models (radius and of Fractures." The basic knowledge of bioelec- tibia) in dogs that heal normally and those that tricity's role derived from these studies will be are delayed to carry out our studies according used to identify electrical signals that will be to the following two themes: most effective in promoting healing in fractures A) Characterize these long-bone fracture that are difficult to heal . In patients with an os- models through biomechanical, physico-chemi- teoporotic condition, external fixation is pre- cal, vascular, histomorphometric, and biochemi- ferred over internal fixation. However, external cal measurements so that we can understand fixation has a tendency to delay fracture heal- details of the differences between a normally ing. Therefore, we are attempting to identify healing fracture and a delayed-healing one. electrical signals that may be applied to pre- B) Investigate roles of electrical activity vent such a delay. that occur in living systems naturally following injury and of externally applied electricity in Progress—We are developing objective methods altering the various features of these fractures for measuring the rate of return of mechanical revealed from the above study. rigidity, bone blood flow, and skin-surface elec- trical activity toward normal in fracture heal- Preliminary Results—From the studies under ing in dogs so that these can eventually be used theme A, we obtained the following results: 1) a 230 Wound and Fracture Healing method for determining an index of rigidity of microamperes) applied during the first week the fractured bone; 2) a method for measuring after fracture seem to stimulate cell prolifera- the return of the venous flow in bone toward tive activity that leads to a significant accelera- normal; 3) a predictable relationship between tion of bone formation at the fracture site at 7 the patterns (with respect to time) of the rees- weeks after injury; two different cell popula- tablishment of blood flow and mechanical prop- tions or two different mechanisms may be in- erties; and 4) the relationships between biome- volved in this response. 4) Comparison of five chanical and biochemical features and also be- different electrical signals similar to those used tween biomechanical features and calcification clinically in fracture healing, as applied in long in fractures. bones in dogs, demonstrate widely different fea- From the second set of studies, theme B, tures (amplitude, frequency, etc .), even though the results were as follows: 1) There are two they have comparable clinical efficiency. naturally occurring "batteries" in dogs—one as- Our studies under theme B also suggest sociated with the epidermis of skin and the that none of these signals may be the most ef- other with the endosteum of bone—that become fective one for fracture healing . We expect that activated in response to an injury involving the knowledge about the influence of specific both bone and the surrounding tissues. 2) Skin- electrical parameters on the various features of surface measurements of electrical voltage and fracture healing gained from our studies will be current reveal different patterns associated a useful contribution to the development of with normal and delayed-healing fractures more reliable procedures for electrical therapy within the first 3 to 4 weeks after the injury . 3) and prognosis in fracture healing. Two different DC signals (1 microampere and 7 Stimulation of Repair of Cortical Bone Transplants by Implantation of Piezoelectric