Development of force measurement system for clinical use in minimal access surgery.

Background: Analysis of force in minimal access surgery (MAS) is important for instrument design, surgical simulators, and in the understanding of tissue trauma incurred during surgery. The aim of this study is to develop a force measuring system for use with different instruments in clinical practice.

Methods: Strain gauges were connected to both arms of a standard -5 mm interchangeable forceps handle. A rotational sensor was used to indicate the relative position of the handle arms, and consequently the jaws' position. A generic force-direction assembly was manufactured to determine the force direction at the port site. Interface electronics included signal conditioning and patient isolation circuits. Dedicated software was used for data acquisition, display, and analysis. To test their performance after sterilization, repeated force measures were obtained with the instruments after 10 cycles of autoclaving. Graduated weights were used to calibrate the strain gauges and a spring balance was employed to calibrate the force applied at the instrument tip. Calibration tests were also carried out to determine the effect of mounting the force direction assembly onto the access port.

Results: Gripping, dissecting, pushing, and pulling forces, along with the vector sum of forces acting at the port site, were synchronously displayed with the operative video record. Repeated autoclaving caused no deterioration in force sensing or signal transmission. The accuracy of the strain gauge readings was +/-0.05 V for the jaw force and +/-0.1 V for the force at the access port. The additional force created by the force direction assembly force was 7% of the port force alone.

Conclusion: Force measurement system has been developed for clinical use. The system measures the gripping, dissecting, pulling and pushing forces as well as the force vector at port site. It also determines the position of instrument's jaws.