Pistol Grip Tools Research Articles

Impact of novel shift handle laparoscopic tool on wrist ergonomics and task performance.

Laparoscopic tool handles causing wrist flexion and extension more than 15° from neutral are considered "at risk" for musculoskeletal strain. Therefore, this study measured the impact of laparoscopic tool handle angles on wrist postures and task performance. Eight surgeons performed standard and modified Fundamentals of Laparoscopic Surgery (FLS) tasks with laparoscopic tools. Tool A had three adjustable handle angle configurations, i.e., in-line 0° (A0), 30° (A30), and pistol-grip 70° (A70). Tool B was a fixed pistol-grip grasper. Participants performed FLS peg transfer, inverted peg transfer, and inverted circle cut with each tool and handle angle. Inverted tasks were adapted from standard FLS tasks to simulate advanced tasks observed during abdominal wall surgeries, e.g., ventral hernia. Motion tracking, video analysis, and modified NASA-TLX workload questionnaires were used to measure postures, performance (e.g., completion time and errors), and workload. Task performance did not differ between tools. For FLS peg transfer, self-reported physical workload was lower for B than for A70, and mean wrist postures showed significantly higher flexion for in-line than for pistol-grip tools (B and A70). For inverted peg transfer, workload was higher for all configurations. However, less time was spent in at-risk wrist postures for in-line (47%) than for pistol-grip (93-94%), and most participants preferred Tool A. For inverted circle cut, workload did not vary across configurations, mean wrist posture was 10° closer to neutral for A0 than B, and median time in at-risk wrist postures was significantly less for A0 (43%) than for B (87%). The best ergonomic wrist positions for FLS (floor) tasks are provided by pistol-grip tools and for tasks on the abdominal wall (ventral surface) by in-line handles. Adjustable handle angle laparoscopic tools can reduce ergonomic risks of musculoskeletal strain and allow versatility for tasks alternating between the floor and ceiling positions in a surgical trainer without impacting performance.

The effect of ergonomic laparoscopic tool handle design on performance and efficiency

Many factors can affect a surgeon's performance in the operating room; these may include surgeon comfort, ergonomics of tool handle design, and fatigue. A laparoscopic tool handle designed with ergonomic considerations (pistol grip) was tested against a current market tool with a traditional pinch grip handle. The goal of this study is to quantify the impact ergonomic design considerations which have on surgeon performance. We hypothesized that there will be measurable differences between the efficiency while performing FLS surgical trainer tasks when using both tool handle designs in three categories: time to completion, technical skill, and subjective user ratings. The pistol grip incorporates an ergonomic interface intended to reduce contact stress points on the hand and fingers, promote a more neutral operating wrist posture, and reduce hand tremor and fatigue. The traditional pinch grip is a laparoscopic tool developed by Stryker Inc. widely used during minimal invasive surgery. Twenty-three (13 M, 10 F) participants with no existing upper extremity musculoskeletal disorders or experience performing laparoscopic procedures were selected to perform in this study. During a training session prior to testing, participants performed practice trials in a SAGES FLS trainer with both tools. During data collection, participants performed three evaluation tasks using both handle designs (order was randomized, and each trial completed three times). The tasks consisted of FLS peg transfer, cutting, and suturing tasks. Feedback from test participants indicated that they significantly preferred the ergonomic pistol grip in every category (p < 0.05); most notably, participants experienced greater degrees of discomfort in their hands after using the pinch grip tool. Furthermore, participants completed cutting and peg transfer tasks in a shorter time duration (p < 0.05) with the pistol grip than with the pinch grip design; there was no significant difference between completion times for the suturing task. Finally, there was no significant interaction between tool type and errors made during trials. There was a significant preference for as well as lower pain experienced during use of the pistol grip tool as seen from the survey feedback. Both evaluation tasks (cutting and peg transfer) were also completed significantly faster with the pistol grip tool. Finally, due to the high degree of variability in the error data, it was not possible to draw any meaningful conclusions about the effect of tool design on the number or degree of errors made.

Ergonomic analysis of fastening vibration based on ISO Standard 5349 (2001)

Hand-held power tools used for fastening operations exert high dynamic forces on the operator's hand-arm, potentially causing injuries to the operator in the long run. This paper presents a study that analyzed the vibrations exerted by two hand-held power tools used for fastening operations with the operating exhibiting different postures. The two pneumatic tools, a right-angled nut-runner and an offset pistol-grip, are used to install shearing-type fasteners. A tri-axial accelerometer is used to measure the tool's vibration. The position and orientation of the transducer mounted on the tool follows the ISO-5349 Standard. The measured vibration data is used to compare the two power tools at different operating postures. The data analysis determines the number of years required to reach a 10% probability of developing finger blanching. The results indicate that the pistol-grip tool induces more vibration in the hand-arm than the right-angled nut-runner and that the vibrations exerted on the hand-arm vary for different postures.

Fastening ergonomics study based on state-space modelling of hand-arm system

The aim of this study is to model the hand-arm as a rotational single-degree-of-freedom system during fastening operations with shear-type fasteners using state-space representation. The values of the model parameters are estimated by determining the characteristic state-space matrices from the measured tool rotation and torque data collected during the fastening operation and then using a parameter extraction algorithm to derive the model parameters in the state-space matrices. The identified parameter values are used to determine the response and the dynamic reaction force, which are used to assess the dynamic effects of tool operation on the hand-arm. The effect of posture, grip-force and tool-type variation is analysed using the dynamic reaction force. Strong agreements are observed between the predicted and measured responses. The model parameter values increase with an increase in grip force and vary significantly for the two tools and four postures studied. The pistol-grip tool generates larger reaction force than the right-angled tool.

Exposures and Physiological Responses in Power Tool Operations: Fastening vs. Unfastening Threaded Hardware

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders. This study examined and compared the kinetic and physiological impacts on operator upper extremities between the fastening and unfastening operations. Thirty-two healthy, right-handed male operators used four tools on two joint simulators at different working heights and distances in the laboratory. Three work configurations were simulated: pistol grip tools on a vertical and horizontal surface, and right angle tools on a horizontal surface. Grip force was measured on an instrumented handle attached to each tool. Muscle activity was monitored at the wrist flexor and extensor and the upper trapezius of the right arm. Paired comparisons showed that when pistol grip tools were used, the peak torque to unfasten a joint (3.7 Nm) was significantly less than to fasten the same joint (5.7 Nm). However, the exposure time was longer for unfastening cycles (98 ms more on the horizontal surface, and 107 ms more on the vertical surface). The average grip force scaled to corresponding peak tool torque revealed that the effort to react against torque was greater in unfastening cycles than in fastening cycles for all work configurations. It also showed that as a proximal stabilizer, the upper trapezius muscle had a greater activity in unfastening cycles. The kinetic and physiological responses demonstrated that unfastening fasteners, which has been neglected in the literature, have the potential to increase risk for musculoskeletal disorders and should be considered in ergonomics assessment in the workplace.

Effect of a Manual Screwdriver with a Pistol-Grip Handle on Maximum Torque and Muscle Activity

Electric utility power plant electricians use a conventional manual screwdriver to loosen and tighten small fasteners on a day-to-day basis, which may expose them to risk of musculoskeletal disorders (MSDs) affecting the wrist and upper extremity. Using a screwdriver handle that requires less muscle activity to exert the same level of torque can reduce the risk of MSDs. Maximal forearm torque in both supinating and pronating directions and at 3 forearm positions (supinated, neutral and pronated) were tested with 2 screwdrivers, a conventional straight-handled tool and pistol-grip screwdriver. Electromyography (EMG) of the finger flexor and extensor muscles and the biceps were monitored while performing maximal forearm torque exertions in the pronating and supinating directions at 3 forearm positions. The torque exerted while using the pistol-grip screwdriver was twice as great as with the straight handle (8.47 and 4.24 Nm, respectively). The turning direction affected maximal torque and interacted with position of the forearm. Normalizing maximal torque data to the muscle activity (Nm / %MVC EMG) revealed that the pistol-grip tool was much more efficient than the straight handle tool.

Predicting subjective perceptions of powered tool torque reactions

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders. In this study, subjective ratings of discomfort and acceptability of reaction forces were collected in an attempt to identify their associations with factors such as work location, and response covariates such as grip force and tool handle displacement. Three work configurations using pistol grip and right angle pneumatic nutrunners on horizontal and vertical surfaces were set up in the laboratory. Twenty healthy right-handed male participants operated four tools at nine locations and the corresponding subjective responses were collected. The results indicate that normalized grip force during the torque buildup period was a significant factor for both subjective ratings. For the unacceptable torque reactions across the three tool configurations, the ratio of hand moment impulse over tool torque impulse was significantly greater than for the acceptable reactions. For pistol grip tools used on the vertical surface, as the working height increased 30 cm, the odds of an unacceptable rating over an acceptable rating increased 1.6 times. Prediction models for subjective ratings of discomfort and acceptability provide insight regarding either workstation design or exposure control. These models can further be used to establish exposure limits based on handle displacement and grip force.

Power grip strength as a function of tool handle orientation and location

Thirty male volunteers participated in a study evaluating the effect of workspace envelope (work height and reach distance) and handle orientation on grip force capacity. Maximum voluntary power grip exertions were recorded using instrumented tool handles under three conditions: a pistol grip tool handle oriented horizontally and vertically and a right angle tool handle oriented horizontally. Significant main effects of handle height and reach location on normalized grip force capacity were observed with the horizontally oriented pistol grip and right angle handles, whereas only an interaction effect was observed with the vertically oriented pistol grip handle. Comparison of results to scores produced with a job assessment tool (RULA) is included as an appendix. The proposed methodology can provide information useful to job, workstation or tool design directed toward best accommodating the physical capacities of workers performing hand tool tasks.

Power Hand Tool Kinetics Associated with Upper Limb Injuries in an Automobile Assembly Plant

This study investigated the relationship between pneumatic nutrunner handle reactions, workstation characteristics, and prevalence of upper limb injuries in an automobile assembly plant. Tool properties (geometry, inertial properties, and motor characteristics), fastener properties, orientation relative to the fastener, and the position of the tool operator (horizontal and vertical distances) were measured for 69 workstations using 15 different pneumatic nutrunners. Handle reaction response was predicted using a deterministic mechanical model of the human operator and tool that was previously developed in our laboratory, specific to the measured tool, workstation, and job factors. Handle force was a function of target torque, tool geometry and inertial properties, motor speed, work orientation, and joint hardness. The study found that tool target torque was not well correlated with predicted handle reaction force (r = 0.495) or displacement (r = 0.285). The individual tool, tool shape, and threaded fastener joint hardness all affected predicted forces and displacements (p < 0.05). The average peak handle force and displacement for right-angle tools were twice as great as pistol grip tools. Soft-threaded fastener joints had the greatest average handle forces and displacements. Upper limb injury cases were identified using plant OSHA 200 log and personnel records. Predicted handle forces for jobs where injuries were reported were significantly greater than those jobs free of injuries (p < 0.05), whereas target torque and predicted handle displacement did not show statistically significant differences. The study concluded that quantification of handle reaction force, rather than target torque alone, is necessary for identifying stressful power hand tool operations and for controlling exposure to forces in manufacturing jobs involving power nutrunners. Therefore, a combination of tool, work station, and task requirements should be considered.

Subjective Perceptions toward Selected Power Nutrunner Torque Reactions

Power hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders (UEMSDs). The reaction forces affect the subjective ratings of perceived exertions associated with tool operations. This paper addresses how operators perceived power nutrunner torque reactions. Two work configurations using pistol grip and right angle tools were tested in the laboratory. Twenty male participants operated four automatic shutoff pneumatic nutrunners on two different task joints using various postures. Handle displacement and the grip force for each torque reaction was monitored. Subjective ratings of discomfort and acceptance toward the given reaction were recorded. The results show that discomfort and acceptance for torque reactions were significantly affected by grip force but not by handle displacement. Odds ratios using grip force as a predictor were calculated. This study can helping setting physical exposure limits encountered in power nutrunner operations.

Handle displacement and operator responses to pneumatic nutrunner torque buildup

The objective of this study is to investigate the workstation and tool effects on the responses of the powered hand tool operator reacting against the impulsive reaction forces that may be associated with upper extremity musculoskeletal disorders. The study demonstrated a means of direct measurement of force at the interface between the tool and the operator. Fifteen experienced male operators performed three independent work configurations: pistol grip and right angle tools used on the horizontal surface and pistol grip tools used on the vertical surface, in the laboratory. A full factorial experiment consisting of 36 conditions was designed to examine the effects of working height, distance, tool, and fastener joint hardness on handle displacement and grip forces. The results indicate that operator responses were affected by different factors depending on the work configuration. When pistol grip tools were used on the vertical surface, the mean handle displacement decreased from 9.9° to 7.3° as the working height increased from 30 cm below shoulder to 30 cm above shoulder. When right angle tools were used, the greatest handle displacement (51.1 mm) and grip force (84.7% MVC) during torque reactions were measured at 30 cm below elbow and 40% forward reach away from the operator. This study provides quantitative information that can be used for workstation design and tool selection to reduce the torque reaction experienced by powered nutrunner operators.

Effect of User Experience on Powered Nutrunner Torque Reactions

Powered tools are widely used in industries and they produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force, and upper limb EMG during impulsive torque reactions due to the effect of operator experience was examined in the study with 15 experienced and 15 novice tool users. The results show that experienced users allowed an average of 7.9° of handle displacement, while novice users allowed 11.5° when pistol grip tools were used on a horizontal surface. Experienced users exerted more grip force than novice users when using right angle tools, but less when using pistol grip tools. Average EMG magnitudes at flexors, extensors, and biceps were greater for experienced users. Recommendations regarding tool selection and workstation design can be derived from the results to minimize physical exposure for both user groups during power tool usage.

Effects of User Experience, Working Posture, and Joint Hardness on Powered Nutrunner Torque Reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. Fifteen experienced and fifteen novice male powered tool users operated pistol grip and right angle nutrunners in a laboratory study. A full factorial experiment examined the effects of operator experience, working height, distance, tool, and fastener joint hardness on handle displacement and grip forces due to torque reactions. The results show that in addition to working height and distance, experience significantly affected tool handle displacement resulting from reaction torque. Experienced users allowed an average of 7.9°, while novice users allowed 11.5° when pistol grip tools were used on a horizontal surface. Experienced users allowed less handle displacement for all working conditions, and exerted more force than novice users when using right angle tools, but less force when using pistol grip tools. Operator experience influences mechanical exposure during power tool usage.

An ergonomic comparison of pneumatic and electrical pistol grip hand tools

The purpose of this study was to compare the ergonomic demands associated with air and DC pistol grip hand tool use. Seven channels of EMG data were collected from 15 male and 15 female subjects to estimate the muscular demands on the forearms, biceps, shoulders and neck. An accelerometer was also used to estimate the torque reaction transmitted to the hand. Subjects performed drilling with five pistol grip tools obtained from two tool suppliers. This resulted in two air tools, one non-transducerized electric (DCNT) and two transducerized electric (DCT) tools. Three types of joints were simulated: (1) 2Nm/720∘, (2) 7Nm/720∘ and (3) 7Nm/30∘. Subjects were asked to drill five joints to completion within a 60s period, and to repeat this five times for each condition (25 joints per condition). Results of a three factor repeated measures ANOVA indicated that, in comparison to air tools, pistol grip DC tools do not pose an additional risk of musculoskeletal injury to the upper limbs. In fact, the data suggest that the use of pistol grip DC tools will reduce the demands on the forearms during horizontal drilling. Relevance to industryPowered hand tools can potentially cause upper limb injuries due to the postures, repetitions, and forces associated with their use. However, while DC tools have engineering advantages (loop monitoring of the tool, and increased quality control) the ability to implement ergonomic strategies also appears to reduce the muscle demands associated with tool use.

Perspectives in Powered Nutrunner Torque Reaction: Handle Displacement and Grip Force

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders (UEMSDs). This paper reports an ongoing study to quantify how operators respond to nutrunner reaction forces, with results from twelve male subjects. Three work configurations using pistol grip and angle tools were tested in the laboratory. Handle displacement due to torque reaction was recorded using a cable potentiometer. Grip force was measured on an instrumented handle attached to each tool. A full factorial experiment was designed considering working height, distance, tool, and fastener joint hardness. The results show that working height significantly affected grip force and handle displacement. The mean displacement was 22.75 mm when using pistol grip tools on a horizontal surface on a soft joint, and was 7.15 mm on the hard joint. This study provides information regarding the workstation design and tool selection that could minimize the torque reaction experienced by nutrunner operators.

Do Handle Design and Hand Posture Affect Pointing Accuracy?

The design of ergonomic tools has focused on reducing the awkward wrist angles during tasks. However, anecdotal evidence shows that the adoption of ergonomic tools has been slow. This may be due, in part, to the ergonomic handles reducing accuracy of the task performed. A pilot study employing 20 subjects (9 men, 11 women) was undertaken to evaluate 4 handles, with two handles being used both in a pistol-grip and an inline-grip. All handles were evaluated while either seeing the target or blindfolded and either using the index finger extended as a guide or not. Each subject performed 24 total trials, which consisted of aiming at a sheet of vertically mounted A3 paper. The center point was marked and positioned such that the subject, when holding a pistol grip tool, had an adducted shoulder, a right angle at the elbow and a neutral wrist position. Each subject was asked to aim and puncture 10 holes in each target paper at a fixed pace. The results of the pilot study show that the dependent variables of the vector distance from the origin and the vector distance from the centroid of the points is affected primarily by the sight condition, but that the handle orientation with the inline condition was significantly better than the pistol grip for accuracy. In addition, the main effects of gender and tool type were significant for the dependent variable of the vector distance from the centroid. The overall implication is that the most ‘ergonomic’ handle may not yield the most accurate cluster or grouping when pointing and that handles held in an ergonomically awkward wrist posture (average 23° ulnar deviation).

A Mechanical Model of Hand Force in Power Hand Tool Operation

A three-dimensional static equilibrium mechanical model of power hand tool operation was developed and used for comparing hand force associated with use of nutrunners having similar operating parameters (i.e. torque and feed force) but different physical parameters (i.e. shape, size, and mass distribution). The model used a Cartesian coordinate system relative to the orientation of the handle grasped in the hand using a power grip. Several important relationships between tool parameters and required hand force were revealed. Resultant hand force associated with different torque and feed force requirements were compared between four pistol grip nutrunners, and between pistol grip and right angle tools used for the same operation. Accessory handles and counterbalancers are also included in the model. Further development and validation of this model will be useful to power hand tool designers and tool engineers.

Quantifying exposure in occupational manual tasks with cumulative trauma disorder potential

A method of describing the musculoskeletal loads in the hand and wrist during manual tasks is presented. A profile of twelve factors is used to quantify the exposure of applicable soft tissues to modes of loading suggested as being related to a number of chronic, work-related musculoskeletal disorders such as chronic muscle strain, tenosynovitis, and carpal tunnel syndrome. These factors include estimates of tendon loads and movement, frictional work done on the tendon sheaths, and muscle activation determined using electromyography. The response of these measures to changes of force, repetition, and posture was studied using eight conditions of a simulated task utilizing a pistol grip tool. Measures of tendon frictional work and dynamic electromyographic activity best paralleled the injury outcomes of an epidemiological study using similar task definitions (Silverstein et al. 1986). This field-usable system is being used currently to investigate the relationship between occupational exposure and musculoskeletal disorders.

Design for a three-fingered hand

This paper describes the construction of a prototype mechanical hand or “end effector” for use on a remotely controlled robot, but with possible application as a prosthetic device. An analysis of hand motions is reported, from which it is concluded that the two most important manipulations (apart from grasps) are to be able to pick up a tool and draw it into a nested grip against the palm, and to be able to hold a pistol-grip tool such as an electric drill and pull the trigger. One of our models was tested and found capable of both these operations.