THORACOLUMBAR BURST FRACTURE - A BIOMECHANICAL INVESTIGATION OF ITS MULTIDIRECTIONAL FLEXIBILITY

Assessment of clinical instability of thoracolumbar burst fractures re mains controversial and subjective. The purpose of the study was to ob tain objective measures of acute instability of these fractures. Thirt een fresh cadaveric human spine specimens (T11-L1) were subjected to h igh-speed axial trauma, resulting in burst fractures in 10 specimens. Multidirectional flexibilities were measured when the specimen was int act and after the trauma. The average ranges of motion of the burst fr actures, measured as percentages of the corresponding intact values at 7.5 Newton-meters, were 202%, 403%, 266%, and 462% for flexion/extens ion, axial rotation, lateral bending, and tension/compression, respect ively. For the neutral zone motion parameter, the motions of the burst fracture were even greater: 670%, 1650%, 779%, and 650%, respectively . All of the increases were significant (P < 0.05). The clinical signi ficance of the study lies in its finding of high multidirectional acut e instability of the thoracolumbar burst fracture, especially in axial rotation.