Answer: Hemothorax with shifting of the mediastinum
to the left.

Discussion:

The present report documents the occurrence of a hemothorax contralateral to the side of the incision due to penetration of the diaphragm by a screw that protruded too far beyond the margins of the vertebra. We had intended for the screws to project just out of the vertebral bodies and to engage two cortices, thereby providing more stable fixation. We inadvertently left the screw tips protruding too far beyond the cortical margins because of inaccurate measurement of the widths of the vertebral bodies and failure to confirm the position of the screws on radiographs. Continuous irritation of the diaphragm by the sharp device, secondary to respiratory movements, resulted in a laceration that led to the development of a hemothorax.

When performing anterior spinal procedures in the thoracic and thoracolumbar regions, it is important to remember the anatomical features of the diaphragm. This musculotendinous, dome-shaped structure separates the thoracic and abdominal cavities and has a rich blood supply. Depending on the stage of the respiratory cycle, the diaphragm may be situated in a number of different positions in the chest. The central tendon may descend to the level of the ninth rib and migrate superiorly to the level of the fourth rib with each forceful respiration. Because of its unique shape, mobility, and close relationship with the thoracolumbar spine, the diaphragm is vulnerable to injury during a variety of thoracic and anterior spinal procedures.

Bone that has a low mineral density is associated with a higher prevalence of failure of instrumentation. It is possible to obtain stronger and more rigid fixation of such bone with bicortical fixation of the screws.

In the case of our patient, the major concern was the possibility of an unexpected injury of the contralateral vital structures secondary to protrusion of a vertebral screw. The structures that are at risk following fixation at the eleventh thoracic level include the segmental vessels of the vertebra, the azygos and hemiazygos veins, the descending aorta, the lungs, and the diaphragm. Although we do not know the precise amount of protrusion that may endanger a patient, this issue warrants attention in view of the possibility of life-threatening complications.

We emphasize the importance of a correct determination of the appropriate screw length by means of a careful assessment of preoperative images combined with intraoperative measurement of the transverse diameter of the vertebral body with use of calipers. Screws should be inserted parallel to the vertebral end plate, and each screw should just penetrate the contralateral cortex for maximum fixation. The surgeon must confirm that the screw tip is just palpable beyond the cortex of the vertebral body, and the position of the screws must be confirmed on radiographs. The use of low-profile, smooth-tipped screws and the application of a layer of viable soft tissue or a Teflon (polytetrafluoroethylene) sheet over the instrumentation may prevent abrasion and irritation of vital structures by the protruding screw tip. Additional stability of fixation should not be gained at the expense of an increased risk of complications. A rapidly progressive perioperative deterioration in the hemodynamic status of the patient after an anterior spinal procedure should alert the surgeon to the possibility of injury of the contralateral structures so that prompt and appropriate treatment can be provided.

Reference:

Hsieh, P.H.; Chen, W.J.; Chen, L.H. and Niu, C.C.: An unusual complication of anterior spinal instrumentation: hemothorax contralateral to the side of incision. A case report. J. Bone and Joint Surg., 81-A: 998-1001, July 1999.