SUMMARYThe derived proportions of the human hand may provide supportive buttressing that protects the hand from injury when striking with a fist. Flexion of digits 2-5 results in buttressing of the pads of the distal phalanges against the central palm and the palmar pads of the proximal phalanges. Additionally, adduction of the thenar eminence to abut the dorsal surface of the distal phalanges of digits 2 and 3 locks these digits into a solid configuration that may allow a transfer of energy through the thenar eminence to the wrist. To test the hypothesis of a performance advantage, we measured: (1) the forces and rate of change of acceleration (jerk) from maximum effort strikes of subjects striking with a fist and an open hand; (2) the static stiffness of the second metacarpophalangeal (MCP) joint in buttressed and unbuttressed fist postures; and (3) static force transfer from digits 2 and 3 to digit 1 also in buttressed and unbuttressed fist postures. We found that peak forces, force impulses and peak jerk did not differ between the closed fist and open palm strikes. However, the structure of the human fist provides buttressing that increases the stiffness of the second MCP joint by fourfold and, as a result of force transfer through the thenar eminence, more than doubles the ability of the proximal phalanges to transmit ʻpunchingʼ force. Thus, the proportions of the human hand provide a performance advantage when striking with a fist. We propose that the derived proportions of hominin hands reflect, in part, sexual selection to improve fighting performance.

When humans fight hand-to-hand the face is usually the primary target and the bones that suffer the highest rates of fracture are the parts of the skull that exhibit the greatest increase in robusticity during the evolution of basal hominins. These bones are also the most sexually dimorphic parts of the skull in both australopiths and humans. In this review, we suggest that many of the facial features that characterize early hominins evolved to protect the face from injury during fighting with fists. Specifically, the trend towards a more orthognathic face; the bunodont form and expansion of the postcanine teeth; the increased robusticity of the orbit; the increased robusticity of the masticatory system, including the mandibular corpus and condyle, zygoma, and anterior pillars of the maxilla; and the enlarged jaw adductor musculature are traits that may represent protective buttressing of the face. If the protective buttressing hypothesis is correct, the primary differences in the face of robust versus gracile australopiths may be more a function of differences in mating system than differences in diet as is generally assumed. In this scenario, the evolution of reduced facial robusticity in Homo is associated with the evolution of reduced strength of the upper body and, therefore, with reduced striking power. The protective buttressing hypothesis provides a functional explanation for the puzzling observation that although humans do not fight by biting our species exhibits pronounced sexual dimorphism in the strength and power of the jaw and neck musculature. The protective buttressing hypothesis is also consistent with observations that modern humans can accurately assess a male's strength and fighting ability from facial shape and voice quality.

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Audience: This edible cricothyrotomy trainer is designed to teach residents and faculty the procedure of cricothyrotomy.Introduction: Cricothyrotomy is an essential procedure for any provider in the emergency department where the estimated incidence of a failed airway leading to surgical airway is 0.5%. 1,2,3 It is challenging to obtain cost-effective and realistic models to train clinicians and provide further opportunities for practice and skills maintenance.We created a novel edible cricothyrotomy (EC) model that is made entirely of edible materials, other than the trachea, which is represented by a piece of ventilator tubing. There is a tortilla base layer, with great vessels represented by colored licorice, thyroid cartilage made from Hershey's chocolate, cricoid from gummy worm, and fruit leather platysma topped with an additional tortilla to complete the skin layer.Objectives: At the end of this educational session, learners will be able to: 1) list the steps involved in performing a cricothyrotomy, 2) identify the laryngeal landmarks necessary to perform a successful cricothyrotomy, 3) successfully perform a cricothyrotomy, 4) deliberately practice to perform the procedure quickly and safely.Method: An edible cricothyrotomy model was built for each participant from the ingredients listed above. An educational session was developed to test the EC in comparison to the more traditional pig trachea (PT) and plastic model (PM). A pre-and post-survey was administered to participants to assess the usability and realism of the models as well as the learners' comfort with the procedure. During the session, a lecture was given, and then participants rotated to all three models and were videotaped and timed performing a scalpelfinger-bougie cricothyrotomy. Times to successful completion, participant satisfaction with the models, and cost of the models were compared. Section breakResults: 43 participants completed the educational session. All completed the pre-survey and 40 of 43 completed the post-surveys (93% response rate). Times to complete a cricothyrotomy were faster for PT (median 32 sec, Interquartile Range [IQR] 24-41 sec) and PM (median 33 sec, IQR 28-39 sec) than on the EC (44 sec, IQR 35-63). There was a statistically significant divergence in preference (p=0.0001) with participants rating the PT first (median rank 1, IQR 1-1), the EC second (median rank 2, IQR 2-2), and the PM third (median rank 3, IQR 2.5-3). Cost of the models at the time of analysis (October, 2104) was $2.77 for EC and $7.64 for PT. The plastic model was built from materials obtained in the emergency department (ventilator tubing, 4inch white foam tape, ½ inch white tape, and Coban.) These materials were not purchased, so cost per plastic model was not calculated. Conclusion:A novel, edible cricothyrotomy training model is a suitable and cost-effective alternative to a pig trachea and has a role for learners seeking multiple attempts at the procedure for skills maintenance and retention.

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