Mechanical stability analysis of reference clamp fixation in computer-assisted spine surgery.

BACKGROUND

Pedicle screw misplacement is a common complication, while 7% may result in neurological complications. Computer-assisted navigation improves the rate of ideally placed screws. Inappropriate reference marker attachment can cause major problems in the outcome and duration of surgery.

OBJECTIVE

To improve fixation of reference bases by comparing different designs of spine clamps and measuring their stability against the relevant thoracic and lumbar anatomy.

METHODS

Force needed to dislocate the clamp from the processus spinosus using defined fixation of 0.79, 0.90 and 1.02 Nm torque was evaluated. Force transmission from clamp to the processus spinosus was also examined. Artificial thoracic and lumbar vertebral bodies were used for attaching spine clamps of three different designs. An instrument transmitted linear force onto the reference clamp and recorded the force when dislocation occurred. Another device determined transmitted force for each clamp utilizing 0.79, 0.90, 1.02, 1.13 and 1.24 Nm torque.

RESULTS

L-clamp had the most stable fixation in lumbar section for every torque and developed the greatest forces. These transmitted forces were similar to the less stable Y-design. I-design created the smallest forces and had the most stable fixation for thoracic spine. The Y- and the L-design caused a notably high number of fractures.

CONCLUSION

Great force leads to great stability, but also creates more fractures, favoring the use of smaller forces. Specific anatomy adaptation is important. Different clamp designs create different forces, while still differing in stability depending on their application in the thoracic or the lumbar spine.