Clip compression model is useful for thoracic spinal cord injuries - Histologic and functional correlates

Study Design. Experimental investigation of an acute thoracic spinal cord injury model in rats involving acute clip compression that simulates human injury. Objective. To assess the dose-response of this model for the relationship between the force of injury on the rat thoracic spinal cord and histological and functional outcome measures. Summary of Background Data. Acute extradural clip compression injury has been a reliable model for producing acute experimental cervical spinal cord injury; however, this model has not been formally evaluated with dose-response curves for acute injury of the thoracic spinal cord. Methods. After laminectomy at T2 in Sprague-Dawley rats, a modified aneurysm clip exerting a closing force of 20, 26, or 35 g was applied extradurally around the spinal cord at T2, and then rapidly released with cord compression persisting for 1 minute. These forces were selected to simulate acute compression injuries of mild to moderate, moderate, and moderate to severe degrees, respectively (n = 8/group). Motor activity was assessed weekly for 4 weeks with the Basso, Beattie, and Bresnahan (BBB) open field locomotor test. The injured spinal cord was then examined histologically including quantification of cavitation. Results. A significant main effect was observed for clip force and BBB score ( F( 2,20) = 5.42, P = 0.013). For 4 weeks after injury, the BBB scores for the 20 g and 35 g clip injury groups were significantly different ( P = 0.05). The cavitation volume at 4 weeks was directly proportional to the severity of injury: the 20 g group had significantly smaller cavities than the 35 g group ( P < 0.05), and the cavitation volume correlated with the BBB scores. Conclusion. The rat thoracic cord clip compression model is a reproducible, clinically relevant spinal cord injury model. This is the first time that the force of clip compression injury in the rat thoracic cord has been correlated with both functional and histologic outcome measures.