Adam Bartsch, Edward Benzel, Vincent Miele and Vikas Prakash
Concussion is the signature American football injury of the 21st century. Modern varsity helmets, as compared with vintage leather helmets, or “leatherheads,” are widely believed to universally improve protection by reducing head impact doses and head injury risk for the 3 million young football players in the US. The object of this study was to compare the head impact doses and injury risks with 11 widely used 21st century varsity helmets and 2 early 20th century leatherheads and to hypothesize what the results might mean for children wearing similar varsity helmets.
In an injury biomechanics laboratory, the authors conducted front, oblique front, lateral, oblique rear, and rear head impact tests at 5.0 m/second using helmeted headforms, inducing near- and subconcussive head impact doses on par with approximately the 95th percentile of on-field collision severity. They also calculated impact dose injury risk parameters common to laboratory and on-field traumatic neuromechanics: linear acceleration, angular acceleration, angular velocity, Gadd Severity Index, diffuse axonal injury, acute subdural hematoma, and brain contusion.
In many instances the head impact doses and head injury risks while wearing vintage leatherheads were comparable to or better than those while wearing several widely used 21st century varsity helmets.
The authors do not advocate reverting to leather headgear, but they do strongly recommend, especially for young players, instituting helmet safety designs and testing standards, which encourage the minimization of linear and angular impact doses and injury risks in near- and subconcussive head impacts.
Adam J. Bartsch, Edward C. Benzel, Vincent J. Miele, Douglas R. Morr and Vikas Prakash
In spite of ample literature pointing to rotational and combined impact dosage being key contributors to head and neck injury, boxing and mixed martial arts (MMA) padding is still designed to primarily reduce cranium linear acceleration. The objects of this study were to quantify preliminary linear and rotational head impact dosage for selected boxing and MMA padding in response to hook punches; compute theoretical skull, brain, and neck injury risk metrics; and statistically compare the protective effect of various glove and head padding conditions.
An instrumented Hybrid III 50th percentile anthropomorphic test device (ATD) was struck in 54 pendulum impacts replicating hook punches at low (27–29 J) and high (54–58 J) energy. Five padding combinations were examined: unpadded (control), MMA glove–unpadded head, boxing glove–unpadded head, unpadded pendulum–boxing headgear, and boxing glove–boxing headgear. A total of 17 injury risk parameters were measured or calculated.
All padding conditions reduced linear impact dosage. Other parameters significantly decreased, significantly increased, or were unaffected depending on padding condition. Of real-world conditions (MMA glove–bare head, boxing glove–bare head, and boxing glove–headgear), the boxing glove–headgear condition showed the most meaningful reduction in most of the parameters. In equivalent impacts, the MMA glove–bare head condition induced higher rotational dosage than the boxing glove–bare head condition. Finite element analysis indicated a risk of brain strain injury in spite of significant reduction of linear impact dosage.
In the replicated hook punch impacts, all padding conditions reduced linear but not rotational impact dosage. Head and neck dosage theoretically accumulates fastest in MMA and boxing bouts without use of protective headgear. The boxing glove–headgear condition provided the best overall reduction in impact dosage. More work is needed to develop improved protective padding to minimize linear and rotational impact dosage and develop next-generation standards for head and neck injury risk.
Adam Bartsch, Edward Benzel, Vincent Miele and Vikas Prakash
Prasath Mageswaran, Robert F. McLain, Robb Colbrunn, Tara Bonner, Elijah Hothem and Adam Bartsch
This study compared the fixing strength and stability achieved by a unilateral plate and screw configuration against a standard cervical fixation plate using a single-level corpectomy and allograft strut graft model.
Multidirectional in vitro flexibility tests were performed using a robotic spine testing system. Human cadaveric spines were assessed for spinal stability after vertebral corpectomy and anterior instrumentation. Specimens were mounted cranially and caudally on custom jigs that were then attached to load cells on the robotic system's end effector and base pedestal. C2–T1 spine specimens (n = 6) were tested intact; then after C-5 corpectomy (the vertebral body was excised), allograft placement and anterior plate fixation were performed. The surgeons performed a uniform corpectomy and reconstruction of each specimen in a protocol fashion. Two plates were compared: a unilateral 4-hole cervical plate designed to obtain rigid fixation using 4 convergent fixation screws all placed unilateral to the vertebral midline, and a standard cervical plate with bilateral plate screw configuration. The plate testing sequence was selected at random to limit bias. Fixation screws were matched for length and diameter. Pure moments were applied under load control (maximum 1.8 Nm) in flexion, extension, left/right lateral bending, and left/right axial rotation. Vertebral motion was measured using an optoelectronic system. The mean relative range of motion between C-4 and C-6 was compared among groups using repeated-measures ANOVA (significance level of 0.05).
In comparing the intact construct and 2 different plates in all planes of motion, only motion in extension (intact vs unilateral plate, p = 0.003; intact vs standard plate, p = 0.001) and left axial rotation (intact vs unilateral plate, p = 0.019) were significantly affected. In terms of immediate cervical stability after 1-level corpectomy and placement of an allograft reconstruction, the unilateral plate showed comparable stiffness to the standard plate in all 3 motion planes (flexion [p = 0.993], extension [p = 0.732], left lateral bending [p = 0.683], right lateral bending [p = 0.546], left axial rotation [p = 0.082], and right axial rotation [p = 0.489]). The unilateral plate showed a trend toward improved stiffness in axial rotation. In no direction did the unilateral configuration prove significantly less stiff than the traditional configuration.
The unilateral plate design proposed here requires minimal dissection and retraction beyond the midline of tissues susceptible to scar, postoperative pain, and swelling. The authors' study suggests that a unilateral plate can be configured to provide comparable fixation strength and torsional stiffness compared with traditional, widely accepted plate designs.
Robert Cantu, Pat Bishop, Stefan Duma, Tom Gennarelli, Richard M. Greenwald, Kevin Guskiewicz, Frederick O. Mueller, P. Dave Halstead, Thomas Blaine Hoshizaki, Albert I. King and Margot Putukian