Injury Criteria Used in Evaluating Seats for Whiplash Protection
Injury Criteria Used in Evaluating Seats for Whiplash Protection
A Comparison of Injury Criteria Used in Evaluating Seats for Whiplash Protection
ALLAN F. TENCER A1, SOHAIL MIRZA A1, PHILIPPE HUBER A1
A1 Orthopedic Sciences Laboratory, Department of Orthopedics, University of Washington, Seattle, Washington, USA
Abstract:
A protocol has been proposed for testing seats for whiplash protection, however injury criteria have not yet been chosen. Assuming that whiplash symptoms arise from non-physiological motions of vertebral segments, we determined the ability of proposed criteria to predict peak individual vertebral displacements. Twenty-eight volunteers were subjected to rear impacts while seated in a car seat with head restraint, mounted onto a sled. Accelerometers were used to record head and torso accelerations. The volunteer data was used as a basis for testing post-mortem human specimens (PMHS). The seat was replaced by a platform onto which was mounted each of 11 cervico-thoracic spines. An instrumented headform was mounted to the upper end of the spine. The head restraint, head-to-restraint geometry, sled, and impact pulse remained the same. Head and T1 accelerations were measured and individual vertebral sagittal (XZ) plane rotations and translations were obtained from high speed video. Proposed injury criteria (NIC, Nkm, Nte, Nd) were tested for their ability to predict average, total, and peak intervertebral displacements. PMHS specimens had chest and head X (horizontal) and Z (vertical) linear accelerations similar to volunteers whose heads hit the head restraint. The best predictors were: Nd shear and peak intervertebral posterior translation (r2 = 0.80), Nd extension and peak extension angle (r2 = 0.70), and Nd distraction and peak distraction (r2 = 0.51). Therefore consideration should be given to a displacement based injury criteria such as Nd in assessment of whiplash protection devices.
Abnormal Hand Sensations After a Football Tackle
Abnormal Hand Sensations After a Football Tackle
Abnormal Hand Sensations After a Football Tackle
Jane T. Servi, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 29 - NO.10 - OCTOBER 2001
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In Brief: A high school football player developed bilateral transient abnormal hand sensations after a tackle. He went on to play the remainder of the season without symptoms. The following season, he again reported abnormal sensations in both hands after tackling. An MRI of the spine revealed cervical canal stenosis and spinal cord edema. This case report demonstrates the need to be responsive to symptoms that affect more than one limb simultaneously, however transient they may be. Prompt recognition and restricting patients from contact sports may prevent catastrophic spinal cord injury.
Abnormal upper-extremity sensations or paresthesias, particularly when bilateral, can indicate congenital or acquired cervical pathology. Because of the potential for catastrophic spinal cord injury, an underlying cervical disorder can be a relative or absolute contraindication to participation in contact sports.
Case Report
History. A high school sophomore football player took a hit while tackling and went down on his back during a game. The mechanism of injury was an axial load. He reported no loss of consciousness or neck pain. He noted a "weird feeling" in all 10 fingers that lasted less than 30 seconds and did not feel like numbness or tingling. He had no history of neck trauma, concussion, or similar episodes.
The player's physical exam was normal at the time of injury, but he was held from the rest of the game. He remained asymptomatic, and his exam continued to be normal in the ensuing weeks. He played the rest of the season without problems.
The student returned to play football the following school year. After a practice, he reported that when he tackled using a technique similar to spearing, he experienced transient midline cervical pain and bilateral transient hypoesthesias in his hands and fingers upon cervical impact. His coaches were questioned about his technique and confirmed that he appreciated the risks but continued to tackle this way despite their attempts to revise it.
Physical exam. His neck had full range of motion with tenderness to palpation at midline over C-3. No palpable step-offs to the cervical spinous processes or paraspinous muscle tenderness were noted. There was full strength of the cervical spine. An axial head compression test was positive, as were Spurling's maneuvers to both sides. The upper extremities had full range of motion and strength. There was no atrophy or scapular winging. Sensation and two-point discrimination were intact, and his deep tendon reflexes were normal.
Diagnosis and treatment. Anteroposterior, lateral, and flexion-extension radiographs were initially believed to reveal anterior translation of C-3 on C-4; a later review by a radiologist was interpreted as normal (figure 1). A magnetic resonance image (MRI) of the cervical spine revealed an incidental type 1 Chiari malformation (per neurologist), increased signal (possible bruise) within the spinal cord at C-2 to C-3, and significant spinal stenosis at C-2 to C-3, with a congenitally small canal from C-2 to C-6 (figure 2). The player was diagnosed with cervical stenosis, cervical cord edema, and burning hands syndrome. This diagnosis conferred an absolute contraindication to future participation in football or other contact sports.
Discussion of Neurapraxia
Cervical cord neurapraxia results from an acute mechanical deformation of the spinal cord, often from an axial load placed on a hyperflexed or hyperextended cervical spine, which frequently occurs in combination with a narrowed cervical canal (1,2). (A discussion of Chiari malformations is beyond the scope of this article.) Cervical stenosis, also referred to as cervical spinal stenosis, is defined as the loss of the cerebrospinal fluid cushion surrounding the spinal cord as identified by MRI or computed tomographic (CT) myelogram. Cord compression can occur without evidence of radiologic abnormalities when hyperflexion or hyperextension of the spine in a stenotic cervical canal causes a sudden decrease in the anteroposterior diameter of the canal as the vertebral body and lamina of the subjacent vertebra approximate. This compression of the spinal cord is known as the "pincer's" mechanism (1-3).
Patients typically exhibit neurologic symptoms that are acute and transient in nature. Symptoms and physical findings may involve both upper extremities (burning hands syndrome), both lower extremities, ipsilateral extremities, or all four extremities. Symptoms generally are sensory, but they may be accompanied by motor findings. Neck pain is typically absent. Sensory complaints range from burning pain to numbness, tingling, and loss of sensation; motor findings vary from weakness to complete paralysis (transient quadriplegia) (1). Complete resolution of symptoms and findings usually occurs within 15 minutes but may take up to 48 hours (1).
Burning hands syndrome is a variant of central cord syndrome (1). Edema and vascular insufficiency occur selectively within the medial spinothalamic tract (4,5). Burning dysthesias occur in a glovelike distribution; strength, reflexes, and sensation are preserved (1).
The exact prevalence is not well documented, but Torg and Ramsey-Emrhein (6) reported that 32% of college football recruits sustained moderate cervical spine injuries while in high school and that catastrophic injuries with associated quadriplegia occurred in fewer than 1 in 100,000 participants per season at the high school level (6,7). During the 1984 NCAA season, neurapraxia of the cord was reported in 1.3 per 10,000 players (1,8). Torg and Ramsey-Emrhein (6) studied recurrent episodes in a group of 110 football players who sustained cervical cord neurapraxia; of 63 who returned to play, 35 (56%) had a recurrent episode.
Making the Diagnosis
All patients who experience cervical cord neurapraxia should undergo routine cervical spine x-rays, including anteroposterior, lateral, and flexion-extension views, to identify bony abnormalities such as fracture or instability. Pavlov and Torg ratios (ratios of the segmental diameter of the canal to the width of the vertebral body) have fallen out of favor as predictors of stenosis because of the high number of false positives seen in patients with large vertebral bodies, such as football players. Variations in both measuring technique and anatomy contribute to inaccurate measurements, and radiologic bone measurements fail to account for canal narrowing from soft-tissue elements (1,6). MRI evaluation is considered the standard protocol to determine the presence of a stenotic cervical canal and potential for insult (contusion) to the spinal cord. Because abnormalities are often not evident on x-ray, patients with signs or symptoms of cord injury should undergo MRI evaluation or CT myelogram (1). A CT myelogram can provide sagittal and axial information for determining canal measurements and delineate bony detail better than MRI, but unlike MRI, it does not provide information about intrinsic cord abnormalities or other diagnostic possibilities such as Chiari malformations or spinal cord tumors.
Return to Activity
There is no general consensus concerning criteria for return to play in contact sports after cervical cord neurapraxia. Some guidelines for absolute contraindication to play contact sports do exist, but guidelines remain somewhat more obscure for participation in limited-contact and lower-impact sports. Contraindications vary from relative to absolute between authors. Relative contraindications to participation in contact sports include players who have intervertebral disk disease or degenerative changes. Developmental canal stenosis with MRI evidence of cord compression, recurrent episodes of cervical cord neurapraxia, symptoms lasting longer than 36 hours, or ligamentous instability confer absolute contraindication from participation in contact sports (1,2,6,9).
Points of Emphasis
As with most sports injures, an active role should be taken to prevent injury. Most severe cervical spine injuries result from an axial load placed on the cervical spine, as in spear tackling. Young players need to be instructed in proper tackling technique. This case illustrates the potential injuries that may occur when using the spearing technique and why this technique is illegal.
When cervical spine injury occurs, evaluation and management require particular caution because the nervous system sequelae may confer a catastrophic result. Athletes with congenital or acquired cervical stenosis are predisposed to cord neurapraxia when an axial load is placed on a hyperflexed or hyperextended cervical spine. Even when plain films are negative, athletes who have neurologic symptoms (eg, both arms or hands, or four-limb involvement) should undergo MRI or CT myelogram evaluation. Guidelines for return to play are just that, guidelines. Each patient should be assessed on individual criteria, and clinical judgment concerning return-to-play decisions should always be employed.
References
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Torg JS, Ramsey-Emrhein JA: Cervical spine and brachial plexus injuries: return-to-play recommendations. Phys Sportsmed 1997;25(7):61-88
Penning L: Some aspects of plain radiography of the cervical spine in chronic myelopathy. Neurology 1962;12:513-519
Maroon JC: 'Burning hands' in football spinal cord injuries. JAMA 1977;238(19):2049-2051
Wilberger JE, Abla A, Maroon JC: Burning hands syndrome revisited. Neurosurgery 1986;19(6):1038-1040
Torg JS, Ramsey-Emrhein JA: Management guidelines for participation in collision activities with congenital, developmental, or postinjury lesions involving the cervical spine. Clin J Sport Med 1997;7(4):273-291
Torg JS, Vegso JJ, Sennett B, et al: The National Football Head and Neck Injury Registry: 14-year report on cervical quadriplegia, 1971 through 1984. JAMA 1985;254(24):3439-3443
Torg JS, Pavlov H, Genuario SE, et al: Neurapraxia of the cervical spinal cord with transient quadriplegia. J Bone Joint Surg Am 1986;68(9):1354-1370
Nichols AW: Cervical spine injuries: on-field management, in Sallis RE, Massimino F (eds): American College of Sports Medicine: Essentials of Sports Medicine, St Louis, Mosby, 1997, p 375
