Nathan Dau

On the accuracy of the Head Impact Telemetry (HIT) System used in football helmets

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturers fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on the Hybrid III produced average pressures greater than the 99th percentile volunteer pressure level. Linear impactor tests were conducted using a large and medium helmet on the Hybrid III. Testing was conducted by two independent laboratories. HIT data were compared to data from the Hybrid III equipped with a 3-2-2-2 accelerometer array. The absolute and root mean square error (RMSE) for HIT were computed for each impact (n=90). Fifty-five percent (n=49) had an absolute error greater than 15% while the RMSE was 59.1% for peak linear acceleration.

Comparison of Pullout Strength between 3.5-mm Fully Threaded, Bicortical Screws and 4.0-mm Partially Threaded, Cancellous Screws in the Fixation of Medial Malleolar Fractures

Displaced medial malleolus fractures are considered unstable and typically require open reduction and internal fixation for anatomic reduction and early joint range of motion. These fractures are usually fixated with either compression lag screws or tension band wiring depending on the fracture pattern, size of the distal fragment, and bone quality. When fracture fixation fails, it is typically in pullout strength. Failure of primary bone healing can result in nonunion, malunion, and need for revision surgery. The current study wished to explore a potentially stronger fixation technique in regard to pullout strength for medial malleolar fractures compared with traditional cancellous screws. This was a comparative study of the relative pullout strength of 2 fully threaded 3.5-mm bicortical screws versus 2 partially threaded 4.0-mm cancellous screws for the fixation of medial malleolar fractures. Ten fresh-frozen limbs from 5 cadavers, mean age 79 years (range of 65-97 years), were tested using the Instron 8500 Plus system. The median force recorded at 2 mm of distraction using unicortical partially threaded cancellous screws was 116.2 N (range 70.2 to 355.5N) compared with 327.6 N (range 117.5 to 804.3 N) in the fully threaded bicortical screw (P = .04). The unicortical screw fixation displayed only 64.53% of the median strength noted with the bicortical screw fixation at clinical failure. The current study demonstrated statistically significantly greater pullout strength for 3.5-mm bicortical screws when compared with 4.0-mm partially threaded cancellous screws used to fixate medial malleolar fractures in a cadaveric model.

Biomechanical Comparison of Internal Fixation Techniques for the Akin Osteotomy of the Proximal Phalanx

The Akin osteotomy is performed at the proximal phalanx for correction of an abducted great toe in a hallux abducto valgus deformity. Several internal fixation techniques have been widely advocated; however, their respective stabilities have not been compared. A biomechanical analysis was performed comparing 5 commonly used fixation techniques for the Akin osteotomy to determine the strongest method in simulated weightbearing in sawbone models. An Akin osteotomy was uniformly performed on 25 sawbones and fixated with 5 different internal fixation types, including a 2-hole locking plate and locking screws, a heat-sensitive memory staple (8 mm × 8 mm), a 28-gauge monofilament wire, 2.7-mm bicortical screws, and crossed 0.062-in. Kirschner wires. The results of simulated weightbearing load to failure rates with an Instron compression device demonstrated the following mean load to failures: crossed Kirschner wire, 57.05 N; 2-hole locking plate, 36.49 N; monofilament wire, 35.69 N; heat-sensitive memory staple, 34.32 N; and 2.7-mm bicortical screw, 13.66 N. Statistical analysis demonstrated the crossed Kirschner wire technique performed significantly better than the other fixation techniques (p < .007); the 4 other techniques were found not to be significantly different statistically (p = .041) from each another. Our study results suggest a crossing Kirschner wire construct significantly increases the stability of the Akin osteotomy in a sawbone model. This might be clinically extrapolated in an effort to improve patient outcomes because these osteotomies can undergo nonunion and malunion, resulting in postoperative pain and swelling.

Protecting Our Children From the Consequences of Chest Blows on the Playing Field: A Time for Science Over Marketing

Commotio cordis is the devastating consequence of otherwise innocent-appearing chest-wall blows, with sudden cardiac death often resulting from projectiles striking the precordium.1,2 This phenomenon occurs most commonly in sports when a baseball, lacrosse ball, or hockey puck strikes the chest directly over the cardiac silhouette and triggers ventricular fibrillation.3 During the past several years, the number of documented commotio cordis events reported to our registry has risen to almost 200, more likely a result of enhanced awareness rather than a true increase in incidence. Commotio cordis has now been cited as the second leading cause of sudden death in young athletes4 and is a uniquely pediatric problem, with an average age of only 14 years for the victims (Fig 1). FIGURE 1 Age at which commotio cordis occurred in cases reported to the Commotio Cordis Registry. The median age was 14 years; 90% of case-patients were younger than 21 years. (Reproduced with permission from Maron BJ, Gohman TE, Kyle SB, Estes NAM III, Link MS. JAMA . 2002;287(9):1143.) Among the reported commotio cordis cases, nearly 50% occurred during competitive sports.1,2 Of particular note, some form of chest-wall protection was worn by almost 40% of the athletes who incurred fatal or nonfatal events.5 In these cases, sudden death resulted directly from chest blows as a result of either inadequate chest-barrier composition (ie, with direct precordial impact) or inadequate design (ie, failure to cover the precordium during all bodily movements). In some circumstances, such as with those chest protectors used in lacrosse and baseball, the ball struck the chest barrier … Address correspondence to Mark S. Link, MD, Tufts Medical Center, NEMC Box 197, 750 Washington St, Boston, MA 02111. E-mail: mlink{at}tufts-nemc.org

Ballistic Fractures: Indirect Fracture to Bone

BACKGROUND Two mechanisms of injury, the temporary cavity and the sonic wave, have been proposed to produce indirect fractures as a projectile passes nearby in tissue. The purpose of this study is to evaluate the temporal relationship of pressure waves using strain gauge technology and high-speed video to elucidate whether the sonic wave, the temporary cavity, or both are responsible for the formation of indirect fractures. METHODS Twenty-eight fresh frozen cadaveric diaphyseal tibia (2) and femurs (26) were implanted into ordnance gelatin blocks. Shots were fired using 9- and 5.56-mm bullets traversing through the gelatin only, passing close to the edge of the bone, but not touching, to produce an indirect fracture. High-speed video of the impact event was collected at 20,000 frames/s. Acquisition of the strain data were synchronized with the video at 20,000 Hz. The exact time of fracture was determined by analyzing and comparing the strain gauge output and video. RESULTS Twenty-eight shots were fired, 2 with 9-mm bullets and 26 with 5.56-mm bullets. Eight indirect fractures that occurred were of a simple (oblique or wedge) pattern. Comparison of the average distance of the projectile from the bone was 9.68 mm (range, 3-20 mm) for fractured specimens and 15.15 mm (range, 7-28 mm) for nonfractured specimens (Students t test, p = 0.036). CONCLUSIONS In this study, indirect fractures were produced after passage of the projectile. Thus, the temporary cavity, not the sonic wave, was responsible for the indirect fractures.

Stability of Midface Fracture Repair Using Absorbable Plate and Screw System Pilot Holes Drilled and Pin Placement at Angles Other Than 90

IMPORTANCE Conventional plating systems use titanium plates for fixation of fractures, with benefits of strength and biocompatibility. However, titanium plates require that screws be placed at a 90° angle to the pilot holes. In the midface, this becomes extremely difficult. Today, a variety of craniomaxillofacial osteosynthesis systems are available, including resorbable plating systems. Specifically, the KLS Martin Sonic Weld system ultrasonically fuses the plate and the head of the pin when placed and will fill the pilot hole grooves completely even at less than 90° angles, which provides a tremendous advantage in midface fracture repair. OBJECTIVE To determine if the KLS Martin Sonic Weld system provides plate-screw construct stability in human heads even when placed at acute angles at the midface buttresses. DESIGN, SETTING, AND SPECIMENS: Twenty cadaveric head specimens with the mandible removed were prepared by creating osteotomies in the midface buttresses bilaterally. Specimens were defleshed and placed in a 2-part testing rig to hold and position the head for testing in a standard material testing system. Testing was performed at the Wayne State University Bioengineering test laboratories, Detroit, Michigan, using an Instron device and high-speed camera. Specimens were plated on one side of the midface using the KLS Martin Sonic Weld system with pilot holes and pins placed at 90° angles. On the contralateral side, the buttresses were plated with the KLS Martin Sonic Weld system at 60°, 45°, and 30° angles. Data were collected using the TDAS data acquisition system and were compared with matched pairs within each specimen. MAIN OUTCOMES AND MEASURES Ultrasonically vibrated pins placed into absorbable mini-plates at less than 90° angles with the KLS Martin Sonic Weld system were compared with the same amount of stress as the system placed at a 90° angle before demonstrating plate-screw construct failure. RESULTS Fifty-seven paired tests were collected, with 114 total tests. Twenty failures were due to bone breakage, and 94 fixations failed as a result of the plate-screw construct breaking. Fractures fixated with the ultrasonic absorbable plating system placed with screws at all tested angles failed at similar loads to our control plates with pins placed at 90° angles. These results lend the surgeon to successfully reduce fractures in the midface fragments in difficult-to-reach areas and possibly cut down on operative time while improving the chance of achieving a long-lasting adequate reduction. CONCLUSIONS AND RELEVANCE Although there is a measured difference in the laboratory, no clinical difference is observed because the maximum force is not usually encountered. Overall, the clinical scenario indicates absorbable plates to be a viable option in less accessible areas. LEVEL OF EVIDENCE NA.

Correlation of Impact Force and Left Ventricular Pressure for Chest Impacts in an Animal Model for Evaluation of Commotio Cordis Protection

Commotio cordis (CC) is defined as sudden cardiac death from a chest impact without any observable physical damage. This phenomenon is most prevalent in the youth population, especially during sporting events. Over 85% of those affected do not survive [1].Copyright

Evaluation of Lower Limb Injury Mitigation Techniques for High Velocity Impacts With the Mil-LX

Improvised Explosive Devices (IED) and landmines present a significant threat to mounted troops currently serving in Iraq and Afghanistan. As a result of these threats, a substantial number of lower limb injuries are sustained by service members. Due to this reality, a critical factor in military vehicle design is the mitigation of lower limb trauma. Past studies have shown that the standard Hybrid III and THOR-LX are not biofidelic in military axial loading conditions (up to 12 m/s). Both of these surrogates over predict axial forces compared to Post Mortem Human Specimens (PMHS) [1]. As a result, a new surrogate was developed, Mil-LX (Military Lower Extremity), that matches the PMHS response for axial loading of the lower leg up to 12 m/s [2,3]. While injury mitigation techniques, such as energy absorbing mats, foot rests, and isolation floors, have been effective in reducing lower extremity injuries in live fire test events, there are several variants of each of these methods. Additionally, it has also been suggested that the positioning of the lower limbs may affect the load sustained by these extremities [4].Copyright