Experienced Laparoscopic Surgeons are Automated to the “Fulcrum Effect”: An Ergonomic Demonstration

Introduction

Minimal access surgery (MAS) is one of the most exciting advances in contemporary surgical practice. Since its introduction in gynaecology and general surgery it has developed rapidly in both application and complexity, with many forms of abdominal surgery now being performed by this route [1]. Indeed, laparoscopic cholecystectomy, considered an advanced surgical technique when introduced in 1987, now represents the “gold standard” treatment for the removal of the gallbladder, and is the surgical procedure most commonly used to investigate the benefits of MAS to the patient and health care system [2] [3].

Despite its advantages, MAS is also associated with many problems, and has been labelled as “an expensive luxury rather than a surgical revolution” [4]. From an ergonomic perspective, the visual and tactile information available in laparoscopic surgery is of a lower grade, and thus this approach makes more demands on the surgeon and requires more concentration than traditional open surgery. In many cases operation time is also comparatively longer [4], with increased surgical fatigue and stress arising from the ergonomic constraints of the approach. This “surgical fatigue syndrome” is characterized by mental exhaustion, increased irritability, impaired surgical judgement and reduced dexterity [5].

The greater surgical complexity of the laparoscopic procedure is also associated with an increased complication rate. For example, with laparoscopic cholecystectomy the bile duct injury rate is 0.41 - 1.1 % [6], compared with 0 - 0.4 % for open surgery [7]. This relatively high rate of bile duct injury in laparoscopic cholecystectomies presents a significant financial problem to the health care system [3].

From a psychological perspective, many of the problems encountered during MAS arise from perceptual and psychomotor difficulties. For example, the degradation of tactile information leads to a deterioration in the quality of proprioceptive feedback (defined as an integration of vestibular and kinaesthetic sensory information about the body) compared with that from open procedures. Similarly, the surgeon must interpret three-dimensional information from a two-dimensional monitor image. This loss of binocular information leads to problems in hand-eye coordination, and in cognitive mapping [5].

An additional problem in developing MAS skills is the perceived inversion of movement from the handles to the working end of the surgical instrument. This perceived inversion of movement is caused by the “fulcrum effect” of the abdominal wall [8]; for example, an external movement to the right by the surgeon's hand is displayed as a movement to the left on the monitor. This inversion affects both horizontal and vertical movements, and is the normal laparoscopic condition under which all MAS operations are conducted. Thus, MAS creates discordance between the visual and proprioceptive systems. This causes an incorrect sequencing of psychomotor output that requires a significant period of compensatory change.

The detrimental effect of image inversion on various perceptual tasks has been well documented [9]. Specifically, the detrimental nature of the “fulcrum effect” on the performance of a simple laparoscopic task has also been shown by Gallagher et al. [8]. They demonstrated that for inexperienced individuals, simple laparoscopic cutting tasks performed under normal MAS viewing conditions resulted in a significantly poorer performance than when the monitor image was inverted around the Y-axis to correct for the fulcrum effect.

The significant role of experience in the performance of laparoscopic surgery is illustrated by the finding that the rate of operative injuries is reduced as laparoscopic experience is acquired [2] [10]. For example, it was found that 93 % of bile duct injuries occurred during the first ten cases performed by trainee surgeons [9].

With respect to the fulcrum effect, it has been shown that inverting the normal laparoscopic image around the Y-axis accelerates the learning of novice subjects. However, the effect of such an inversion on the performance of experienced surgeons was unknown.

Therefore, the aim of the study reported in this paper was to investigate the effect of Y-axis-image inversion on the performance and learning curves of experienced laparoscopic surgeons. It was hypothesized that under normal laparoscopic viewing conditions the experienced surgeons would perform significantly better than novice participants, and that the inverted Y-axis viewing condition would be associated with a significantly poorer performance by the surgeons compared with novices.

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