BIOMECHANICAL EFFECTS OF TRANSTHORACIC MICRODISCECTOMY

Study Design. Nondestructive flexibility testing was performed to quan tify biomechanical parameters of human cadaveric thoracic spines befor e and after microdiscectomy. Objectives. To assess the biomechanical d ifferences between the normal thoracic spine and the thoracic spine af ter microdiscectomy and to determine whether microdiscectomy results i n spinal instability. Summary of Background Data. Previous studies hav e investigated thoracic disc properties and the biomechanical effects of thoracic ligament or bone trauma. No studies were found assessing t he effects of thoracic discectomy. Methods. Eight motion segments (T4- T5 to T11-T12) from five human cadaveric thoracic spines were studied before and after microdiscectomy. Three-dimensional motion was recorde d in response to nondestructive, nonconstraining pure moments. Paramet ers measured included the neutral zone, elastic zone, range of motion, rotational flexibility, and instantaneous axis of rotation. Results. The neutral zone, elastic zone, and range of motion increased a small but significant (average P = 0.02 for range-of-motion increase) amount in all directions after thoracic microdiscectomy (mean bilateral rang e of motion increase, 2.1 degrees; range, 0.5-4.2 degrees). Flexibilit y increased slightly during lateral bending and flexion. The instantan eous axis of rotation location usually did not change, but sometimes s hifted slightly away from the discectomy site after microdiscectomy. C onclusions. Thoracic microdiscectomy had small effects on the immediat e mechanics and kinematics of the thoracic spine and did not overtly d estabilize the motion segments.