The effect of hemorrhagic shock in a caprine tibial fracture model

Objectives: The purpose of this study was to assess effects of hemorrhagic shock on fracture healing in a large animal closed fracture model. Design: Prospective randomized trial. Setting: University Medical Center. Study Subjects: Eight skeletally mature neutered male goats. Intervention: Standardized bilateral closed midshaft tibia fractures were created in all the goats. The goats were randomized to a hemorrhage, shock and resuscitation group (shock group), or a control group. Hemorrhagic shock was induced in the four goats in the shock group. The shock state was maintained for thirty minutes. The remaining four goats were used as a control group. All fractures were stabilized with a standardized external fixator. Outcome Measures: Swan-Ganz catheters were used to record cardiac output (CO). Arterial blood was sampled to determine base deficit values for the goats after hemorrhage. Radiographs were obtained weekly. After four weeks the tibias were harvested and nondestructively tested in torsion. Immediately after mechanical testing, the tibias were processed for histologic analysis. Standard histomorphologic indices, including total bone volume (TV/BV%), osteoblast surfaces (Ob/BS%), and osteoid surface (OS/BS%), were measured. Results: One goat in the shock 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 control group was then switched to the shock group, leaving four goats in the shock group and three in the control group. One goat in the shock group developed a nonunion of his left tibia fracture. This nonunion occurred because of loosening of pin fixation in the distal tibia. The nonunited bone was not included in the analysis of results. The animal's right tibia healed uneventfully. Hemorrhage uniformly resulted in shock. In the shock group goats, average CO on induction of anesthesia was 3.7 1/min. Average CO dropped to 0.7 after hemorrhage and rose to 6.6 after fluid resuscitation. The average base deficit for the shock group animals was -9.9. The control group animals 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 tibiae were considered to be healing normally radiographically. Biomechanical testing showed no statistical difference between the shock and control groups in maximum torque (p = 0.95), stiffness (p = 0.64), and energy absorbed at failure (p = 0.91). Histomorphologic results indicated there were no 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. Conclusions: In this study no significant difference was found between the shock and control groups in any of the parameters measured. Transient hemorrhagic shock does not appear to adversely affect closed tibia fracture healing in a goat model.