OTA 1999 Posters

The Effect of Hemorrhagic Shock on Closed Tibia Fracture Healing

Adam J. Starr, MD; Robert W. Welch, DVM, PhD; Brian J. Eastridge, MD; William Pierce; Hong Zhang, University of Texas Southwestern Medical Center, Dallas, TX

Introduction: The effect of transient hemorrhagic shock on fracture healing is not known. Most multiply injured patients will sustain a fracture, so the possible effect of shock on fracture healing is important. Transient hemorrhagic shock has been shown to increase osteocyte necrosis at tibia fracture sites in rats, (1) but it is not known if hemorrhagic shock has an effect on fracture healing beyond this apparent effect within the first few days. The purpose of this study was to assess the radiographic, biomechanical, and histologic effects of hemorrhagic shock on fracture healing.

Materials and Methods: Eight adult male goats were assigned to one of two groups: a "tibia fracture with hemorrhagic shock" group (FS), or a "tibia fracture without hemorrhagic shock" control group (FC). The study protocol was approved by the Institutional Animal Care and Research Advisory Committee.

Under general endotracheal anesthesia standardized bilateral, midshaft, transverse tibia fractures were created using a three-point bending press. A standard AO (Synthes, Paoli, PA) external fixator was placed across each fracture using a specially designed jig, to ensure uniform pin placement. The fixators were placed with the aid of a C-arm image intensifier to ensure accurate placement and reduction. All the fixators were double stacked.

Swan Ganz catheters were placed in each goat to record cardiac output (CO). An arterial catheter was placed in the left carotid artery, and arterial blood was sampled to determine base deficit values for the FS goats after hemorrhage.

In the FS group, 30% of each goat's estimated blood volume was removed via the arterial catheter, to induce hemorrhagic shock. The shock state was maintained for 30 minutes, at which point the animals were resuscitated with a volume of normal saline equal to twice the shed volume of blood.

AP and ML radiographs were obtained weekly. After four weeks, the goats were killed using an overdose of barbiturate. The tibias were harvested and non-destructively tested in torsion using an MTS 858. Immediately following mechanical testing, the tibiae were processed for undecalcified histological analysis. Standard histomorphological indices including total bone volume (TV/BV%), osteoblasts surfaces (Ob/BS%), osteoid surface (OS/BS%), osteoclasts surfaces (Oc/BS%), mineral apposition rate (MAR), and bone formation rate (BFR) were determined for each specimen.

Results: Complications: One goat in the FS group became agitated upon emergence from anesthesia and dislodged two of his external fixator pins. This animal was killed, and was not included in the analysis of results. One goat that would have been entered into the FC group was switched to the FS group, leaving four goats in the FS group, and three in the FC group. One goat in the FS group developed a non-union of his left tibia fracture. The non-united bone was not included in the analysis of results. The animal's right tibia healed uneventfully.

Hemorrhage uniformly resulted in shock. In the FS goats, average CO on induction of anesthesia was 3.7. Average CO dropped to 1.3 after hemorrhage, and rose to 6.6 after fluid resuscitation. The average base deficit for the FS goats was -9.9. The FC goats had minor drops in average CO, >from 4.5 on induction of anesthesia, to 4.3 on emergence from anesthesia.

Radiographic analysis showed no apparent differences in healing between groups when comparing callus area and density. With the exception of the nonunion, all other tibiae were considered to be healing normally radiographically. Biomechanical testing showed no statistical difference between the FC and the FS groups; maximum torque (p=0.4), stiffness (p=0.06), and energy absorbed at failure (p=0.7). Histomorphological results indicated there were no qualitative or quantitative differences between groups. Shock did not appear to influence bone formation rate or callus remodeling compared with controls (p=0.6). No evidence of osteocyte necrosis was observed.

Discussion: In this study, no significant was found between the FC and FS groups in any of the parameters measured. Transient hemorrhagic shock does not appear to adversely affect closed tibia fracture healing.

Reference:

1. Wichmann MW, Arnoczky SP, DeMaso CM, et al., Depressed osteoblast activity and increased osteocyte necrosis after closed bone fracture and hemorrhagic shock, J Trauma, 41: 628-633, 1996.