Session II - Basic Science

*Overexpression of Bone-Related Growth Factors after Traumatic Brain Injury

Uwe F. Scherbel, MD; William G. DeLong, Jr., MD; Christopher T. Born, MD; Jasvir Khurana, MD; Peter Riess, MD, University of Pennsylvania, Philadelphia, PA (all authors ­ a-Howmedica Osteonics, Smith-Nephew)

Purpose: Clinically, increased bone formation is characterized as an accelerated rate of normal fracture healing and/or bone formation in ectopic sites and is referred to as heterotopic ossification (HO). Although the etiology of HO is unknown, there are certain requisite conditions for it to occur. Patients with brain injury are known to have an increased tendency to form ectopic bone and are given corticosteroids, nonsteroidal anti-inflammatory drugs, disphosphonates, and radiotherapy as a preventative measure. Our goal was to create an animal model of upregulated bone formation and investigate the role of potential chemical mediators known to be involved in the regulation of bone growth. In summary, we used brain injury as a tool to get new insights into bone formation.By using a well established brain-injury model in rats (fluid percussion) we also looked at the systemic response to traumatic brain injury (TBI). In polytraumatized patients traumatic brain injury often goes along with compromised lung function. There still is an ongoing discussion as to whether methods like nailing of a femur can be used in brain-injured patients to avoid worsening expected pulmonal complications.

Methods: Rats were subjected to severe experimental lateral fluid percussion (FP) injury (3.0-3.6 atm). We used a reliable tibia-fracture model for rats. One group (n = 5) of rats was exposed to TBI, another group (n = 5) of rats was exposed to TBI and an experimental fracture, the third group was only exposed to experimental fracture (n = 5) and sham animals (n = 5) were subjected to anesthesia without injury. Animals were sacrificed 3 days and 1 week after injury, and the lungs were removed. Muscle specimens around the hip as well as the whole area of the fractured tibia were taken and processed. Immunostaining for c-fos and c-jun as well as RT-PCR was performed. The lungs were fixed and cut and then stained with hematoxylin and eosin.

Results: In four out of five brain-injured animals and animals with brain injury and fracture lymphocytic infiltration could be found in the lungs. There was no sign of cellular infiltration in the fracture group alone or in uninjured but anesthetized animals. Immunostaining showed an upregulation of c-fos and c-jun in all brain-injured animals. RT-PCR showed an upregulation of BMP 2/4, FGF, and NGF in muscle around the hip of all brain-injured animals. BMP2/4 and FGF were also expressed in the muscle and bone of the fractured tibia. There was no upregulation of BMP2/4 or FGF in uninjured animals. There was also no upregulation of BMP2/4, FGF, or NGF around the hip in rats that had only been exposed to experimental fracture.

Discussion: Creation of an animal model that mimics human clinical scenarios is necessary for investigators to understand the biochemical mechanisms underlying certain phenomena. We developed an animal model with use of brain injury as a tool to get new insights into bone formation. Mediators like BMP2/4, FGF, and NGF have been found upregulated in brain-injured animals. Also genes like c-fos and c-jun, which are closely related to the early stages of enchondral ossification, have been found to be upregulated. Further studies using this animal model (with brain injury as a tool) have to be conducted to see if fracture healing can be enhanced and which factors are responsible for the enhancement. Brain-injured rats showed lymphocytic infiltration in their lungs 1 week after injury. When planning an operation in brain-injured patients, the surgeon might take their expected compromised lung function into account.