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A practical application of the translational energy criteria: evaluation of baseball and softball head impact injury potentials
Published September 12, 1990 by International Research Council on Biokinetics of Impact in Switzerland
The development of the Unified Head Injury Theory (UHIT) has been under way at The Ohio State University for the last eight years. The new criteria have two major parts. The first deals with translationsl (rigid impact) head injuries which include skull fracture and brain contusion. The second part deals with rotational (induced brain motion ) head injuries which include diffuse axonal injuries (DAI) and bridging vein tears.
The first criteria of the UHIT is called the Translatinal Energy Criteria (TEC) and is the subject of this paper. The TEC can estimate the severity of brain contusion (Equivalent Abbreviated Injury Scale, EAIS) and the occurrence of skull fracture (Probability of Skull Fracture, POSF). The TEC is based on the response of the Translational Head Injury Model (THIM). The THIM is a collection of one-dimensional, three-degrees-of-freedom, semi-definite lumped parameter models; each model consists of two masses, two dampers, and a spring. The THIM is derived from mechanical impedance experiments conducted on human cadaver heads, and the TEC was validated for use with the Hybrid III head with accident reconstruction data.
A series of 13 softballs of various construction, one baseball, and two ball helmets were evaluated with the TEC, the Severity Index (SI), and the Head Injury Criterion (HIC) at three impact speeds. The softball impacts were to the side of the head, while the baseball impacts were to both the front and side of the head. The helmeted head impacts were only to the side of the head and only with softballs.
The evaluation of the softball tests indicated that in impact squarely over the temple at ball speeds of approximately 17.9, 26.9 and 35.8 meters per second will result in an average EAIS of 2.8, 4.2 and 5.8 respectively. The baseball study, conducted at the University of Michigan, indicated that under the same impact conditions as the softball study a baseball head impact will result in a slightly lower EAIS value. The baseball study very graphically demonstrates that a direct head impact, as opposed to a glancing blow to the head, is a rate event. The helmet study showed that for the helmets tested, very little benefit was realized for direct head impacts above 26.9 meters per second. The HIC and the SI were unable to distinguish the hardness of the softball at all speeds. Also, the HIC and the SI failed to give a realistic or meaningful evaluation of the severity of the impacts, i.e. the HIC of 6,000 has no real world injury severity reference as well as the HIC of 3,000. The TEC was able to distinguish the hardness of all the softballs, and to evaluate the impacts continuously in terms of the Abbreviated Injury Scale (AIS)