Determinants of rib motion in flail chest

[Biomechanics of thoracic wall instability]

Traumatic injuries of the thorax can entail thoracic wall instability (flail chest), which can affect both the shape of the thorax and the mechanics of respiration; however, so far little is known about the biomechanics of the unstable thoracic wall and the optimal surgical fixation. This review article summarizes the current state of research regarding experimental models and previous findings. The thoracic wall is primarily burdened by complex muscle and compression forces during respiration and the mechanical coupling to spinal movement. Previous experimental models focused on the burden caused by respiration, but are mostly not validated, barely established, and severely limited with respect to the simulation of physiologically occurring forces. Nevertheless, previous results suggested that osteosynthesis of an unstable thoracic wall is essential from a biomechanical point of view to restore the native respiratory mechanics, thoracic shape and spinal stability. Moreover, in vitro studies also showed better stabilizing properties of plate osteosynthesis compared to intramedullary splints, wires or screws. The optimum number and selection of ribs to be fixated for the different types of thoracic wall instability is still unknown from a biomechanical perspective. Future biomechanical investigations should simulate respiratory and spinal movement by means of validated models.

Rib Fracture Fixation Restores Inspiratory Volume and Peak Flow in a Full Thorax Human Cadaveric Breathing Model

Background:

Multiple rib fractures cause significant pain and potential for chest wall instability. Despite an emerging trend of surgical management of flail chest injuries, there are no studies examining the effect of rib fracture fixation on respiratory function.

Objectives:

Using a novel full thorax human cadaveric breathing model, we sought to explore the effect of flail chest injury and subsequent rib fracture fixation on respiratory outcomes.

Patients and Methods:

We used five fresh human cadavers to generate negative breathing models in the left thorax to mimic physiologic respiration. Inspiratory volumes and peak flows were measured using a flow meter for all three chest wall states: intact chest, left-sided flail chest (segmental fractures of ribs 3 - 7), and post-fracture open reduction and internal fixation (ORIF) of the chest wall with a pre-contoured rib specific plate fixation system.

Results:

A wide variation in the mean inspiratory volumes and peak flows were measured between specimens; however, the effect of a flail chest wall and the subsequent internal fixation of the unstable rib fractures was consistent across all samples. Compared to the intact chest wall, the inspiratory volume decreased by 40 ± 19% in the flail chest model (P = 0.04). Open reduction and internal fixation of the flail chest returned the inspiratory volume to 130 ± 71% of the intact chest volumes (P = 0.68). A similar 35 ± 19% decrease in peak flows was seen in the flail chest (P = 0.007) and this returned to 125 ± 71% of the intact chest following ORIF (P = 0.62).

Conclusions:

Negative pressure inspiration is significantly impaired by an unstable chest wall. Restoring mechanical stability of the fractured ribs improves respiratory outcomes similar to baseline values.

A case study of a multiply injured patient

Initial evaluation of severely injured patients requires an organized, rapid, and thorough evaluation of the patient where life-threatening injuries are identified and treated simultaneously. A case study provides the basis for discussion of the management of the multiply injured trauma patient. The ultimate goal in rehabilitation of a multiply injured patient is to return each patient to as much independent function and ability to contribute to society as possible.

The management of flail chest

Flail chest is an uncommon consequence of blunt trauma. It usually occurs in the setting of a high-speed motor vehicle crash and can carry a high morbidity and mortality. The outcome of flail chest injury is a function of associated injuries. Isolated flail chest may be successfully managed with aggressive pulmonary toilet including facemask oxygen, CPAP, and chest physiotherapy. Adequate analgesia is of paramount importance in patient recovery and may contribute to the return of normal respiratory mechanics. Early intubation and mechanical ventilation is paramount in patients with refractory respiratory failure or other serious traumatic injuries. Prolonged mechanical ventilation is associated with the development of pneumonia and a poor outcome. Tracheotomy and frequent flexible bronchoscopy should be considered to provide effective pulmonary toilet. Surgical stabilization is associated with a faster ventilator wean, shorter ICU time, less hospital cost, and recovery of pulmonary function in a select group of patients with flail chest. Open fixation is appropriate in patients who are unable to be weaned from the ventilator secondary to the mechanics of flail chest. Persistent pain, severe chest wall instability, and a progressive decline in pulmonary function testing in a patient with flail chest are also indications for surgical stabilization. Open fixation is also indicated for flail chest when thoracotomy is performed for other concomitant injuries. There is no role for surgical stabilization for patients with severe pulmonary contusion. The underlying lung injury and respiratory failure preclude early ventilator weaning. Supportive therapy and pneumatic stabilization is the recommended approach for this patient subset.