EUROSPINE 2016 FULL PAPER AWARD: Wire cerclage can restore the stability of the thoracic spine after median sternotomy: an in vitro study with entire rib cage specimens

Abstract

The influence of the anterior rib cage on the stability of the human thoracic spine is not completely known. One of the most common surgical interventions on the anterior rib cage is the longitudinal median sternotomy and its fixation by wire cerclage. Therefore, the purpose of this in vitro study was to examine, if wire cerclage can restore the stability of the human thoracic spine after longitudinal median sternotomy. Six fresh frozen human thoracic spine specimens (C7-L1, 56years in average, range 50-65), including the intact rib cage without intercostal muscles, were tested in a spinal loading simulator and monitored with an optical motion tracking system. While applying 2 Nm pure moment in flexion/extension (FE), lateral bending (LB), and axial rotation (AR), the range of motion (ROM) and neutral zone (NZ) of the functional spinal units of the thoracic spine (T1-T12) were studied (1) in intact condition, (2) after longitudinal median sternotomy, and (3) after sternal closure using wire cerclage. The longitudinal median sternotomy caused a significant increase of the thoracic spine ROM relative to the intact condition (FE: 12°±5°, LB: 18°±5°, AR: 25°±10°) in FE (+12%) and AR (+22%). As a result, the sagittal cut faces of the sternum slipped apart visibly. Wire cerclage fixation resulted in a significant decrease of the ROM in AR (-12%) relative to condition after sternotomy. ROM increased relative to the intact condition, in AR even significantly (+8%). The NZ showed a proportional behavior compared to the ROM in all loading planes, but it was distinctly higher in FE (72%) and in LB (82%) compared to the ROM than in AR (12%). In this in vitro study, the longitudinal median sternotomy resulted in a destabilization of the thoracic spine and relative motion of the sternal cut faces, which could be rectified by fixation with wire cerclage. However, the stability of the intact condition could not be reached. Nevertheless, a fixation of the sternum should be considered clinically to avoid instability of the spine and sternal pseudarthrosis.