Simulation of low-energy impacts on the human hand for prediction of peak reaction forces and bone fracture.

Hands of workers in extractive and heavy-duty industries are susceptible to suffering injuries of varying severity. Improved safety procedures and new technologies for production and maintenance tasks have contributed to reducing the severity of injuries. However, manual tasks with high-risk factors can still lead to hand injuries. Hand bone fractures and dislocations can be caused by relatively small objects impacting a region of the hand at velocities in the range of 1.3 to 1.6 m per second. This impact can produce significant functional, physical, and psychological consequences in those affected and result in high costs derived from medical care. This study presents the results of a finite element simulation study conducted to reproduce impacts with energies in the range of 7 to 10 Joules of an object on the dorsal region of the hand. Simulation results are compared to previous experimental results obtained from controlled impact tests performed using cadaveric hand specimens. The vertical peak reaction force (PRF) as a function of the impact position was used as a primary outcome for comparisons. Simulation results for all impact positions were within the standard deviation measured experimentally, with differences in the PRF values in the range of -5.3% to 4.9%. Bone stress analyses at the position of impacts showed the locations where the maximum principal stress exceeded the bone strength, as well as the variability in the correspondence between the stress distribution predicted by the FE models and the fracture rate distribution observed experimentally.

Experimental evaluation of impact-resistant gloves using surrogate hands.

Injuries to the hand and fingers with varying degrees of severity are widespread in industries such as mining and oil and gas production. This study presents the results of tests carried out to measure the impact performance for commonly used impact-resistant gloves (metacarpal gloves). Sets of surrogate hands made out of a 3D-printed skeletal structure and soft tissues represented by synthetic gel were manufactured and subjected to controlled impact tests. The calibration and validation of the surrogates were based on impact response data reported previously for cadaveric specimens. Calibrated surrogate hand specimens were tested to assess the impact protection of typical metacarpal gloves. Each type of metacarpal glove provided different levels of protection measured by the decrease in the peak impact reaction force and the fractures detected after the impacts. Results indicated that surrogate specimens suffered fractures in 77% and 33% of the impacts for unprotected and protected hands, respectively.

Mechanical Characterization of Synthetic Gels for Creation of Surrogate Hands Subjected to Low-Velocity Impacts.

The development of human body simulators that can be used as surrogates for testing protective devices and measures requires selecting synthetic materials with mechanical properties closely representative of the human tissues under consideration. For impact tests, gelatinous materials are often used to represent the soft tissues as a whole without distinguishing layers such as skin, fat, or muscles. This research focuses on the mechanical characterization of medical-grade synthetic gels that can be implemented to represent the soft tissues of the hand. Six grades of commercially available gels are selected for quasi-static hardness and firmness tests as well as for controlled low-velocity impact tests, which are not routinely conducted by gel manufacturers and require additional considerations such as energy level and specimen sizes relevant to the specific application. Specimens subject to impacts represent the hand thicknesses at the fingers, knuckles, and mid-metacarpal regions. Two impact test configurations are considered: one with the gel specimens including a solid insert representing a bone and one without this insert. The impact behavior of the candidate gels is evaluated by the coefficient of restitution, the energy loss percentage, and the peak reaction force at the time of impact. The resulting values are compared with similar indicators reported for experiments with cadaveric hands. Relatively softer gels, characterized by Shore OOO hardness in the range of 32.6 ± 0.9 to 34.4 ± 2.0, closely matched the impact behavior of cadaveric specimens. These results show that softer gels would be the most suitable gels to represent soft tissues in the creation of surrogate hands that can be used for extensive impact testing, thus, minimizing the need for cadaveric specimens.

Experimental evaluation of protected and unprotected hands under impact loading.

Hand injuries are a significant problem in many industries with relatively high incidence rates and injury severity. Many workers are required to wear impact protective gloves to protect their hands from impact-related hazards. This research presents the results of an experimental quantification of metacarpal gloves performance subjected to controlled impacts. Thirteen cadaveric hands were used to conduct a set of controlled impact tests on protected and unprotected hands. The controlled impacts targeted the proximal interphalangeal (PIP) joints, the metacarpophalangeal (MCP) joints, and the middle section of the metacarpal bones. Two types of metacarpal gloves commonly used in mining and oil and gas operations were selected for the tests. These gloves include different material and protection configurations on the dorsal side of the hand. The performance of selected gloves was quantified using the maximum reaction force to the impact and number of bone fractures. A total of 191 impacts produced 108 fractures, from which 71% corresponded to the unprotected hands and 40% to the protected hands. Depending on the impact position and type of glove used, the effect of protection ranged from no change up to a 23% reduction in peak reaction force.

Effects of wearing of metacarpal gloves on hand dexterity, function, and perceived comfort: A pilot study.

Metacarpal gloves are commonly used in heavy-duty industries such as mining and are typically thicker and bulkier than manufacturing or assembly industrial gloves. This pilot study investigates the impact of wearing metacarpal gloves on hand dexterity, functional capabilities, and perceived comfort. Four types of commercially available metacarpal gloves were selected for evaluation in a randomized controlled trial. Evaluations included turning and placing tests, also grip, pinch, and screwdriver tests, and rating of the perceived level of effort. Dexterity test results showed that metacarpal gloves significantly reduced the ability to perform motor tasks requiring coordination compared to bare hands. Hand functions such as gripping, pinching, and forearm rotations were not significantly affected. However, the perceived level of effort needed to complete those hand functions increased as the metacarpal glove's bulkiness increased. High levels of mechanical protection typically offered by metacarpal gloves can inversely affect hand dexterity and hand exertion.