The effect of laparoscopic instrument working angle on surgeons' upper extremity workload.
BACKGROUND
Laparoscopic surgery may be kinder to the patient, but it is more demanding on the surgeon. Fixed trocar positions often require the surgeon to work with instruments at awkward angles to their body. We studied the effect of horizontal and vertical laparoscopic instrument working angle on the surgeon's thumb, forearm, and shoulder muscle work.


METHODS
Electronyographic (EMG) signals were collected from the thenar compartment (TH), flexor digitorum superficialis (FDS), and deltoid (DEL) muscles of the dominant arm of eighth surgeons while they were closing a standard pistol-grip disposable laparoscopic grasper against a fixed resistance of 3 N. With the aid of a special testing bench, the instruments' position was randomly changed among 15 degrees, 45 degrees, and 75 degrees of horizontal angulation relative to the surgeons' sagital plane, and 15 degrees, 45 degrees, and 75 degrees degrees of vertical angulation relative to a horizontal plane. EMG signals were rectified and smoothed using analogue circuitry and digitally sampled at l0 Hz using a National Instruments DAQCard-700 connected to a Macintosh PowerBook 5300c running LabVIEW software. Statistical analysis was carried out by analysis of variance (ANOVA).


RESULTS
The effects of vertical and horizontal working angles on the muscle effort were as follows: TH (horizontal, N.S.; vertical, N.S.), FDS (horizontal, p 45 degrees to the surgeon's sagital plane significantly increases the workload of the flexor digitorium superficialis and deltoid muscles. The deltoid muscle is also adversely affected by vertical angulation of the instrument. The instrument working angle has no effect on the thenar muscles. Whenever possible, laparoscopic surgeons should strive to place their instruments and trocars so as to minimize extreme horizontal or vertical displacement of their hands away from a resting position of comfort.
Berguer
R
R
School of Medicine, University of California-Davis and VA Northern California Health Care System, 150 Muir Road (112), Martinez, CA 94553, USA.
Forkey
D L
DL
Smith
W D
WD
D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000706:statistics & numerical data; D004867:Equipment Design; D006804:Ergonomics / Q000379:methods; D013502:General Surgery / Q000295:instrumentation / Q000706:statistics & numerical data*; D006801:Humans; D010535:Laparoscopy / Q000379:methods* / Q000592:standards; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D013525:Surgical Instruments / Q000592:standards; D016526:Workload / Q000706:statistics & numerical data*