In the United States approximately 7% of all new cases of spinal cord injury are related to athletic activities . Sports injuries are the second most common cause of spinal cord injury in the first 30 years of life . Permanent spinal cord injury is much more likely to result from cervical spinal injury than thoracic or lumbar injury. In a 3-year nationwide survey of all sports in Japan the incidence of spinal injury was 1.95 per 1 million per year, with a mean age at injury of 28.5 years, and 88% occurring in males . Sports identified as placing the participant at high risk for spinal cord injury include football, ice hockey, wrestling, diving, skiing and snowboarding, rugby, cheerleading, and baseball. Information on catastrophic injuries in athletes is provided by the National Center for Catastrophic Sports Injury Research (NCCSIR), the National Spinal Cord Injury Statistical Center, the United States Consumer Product Safety Commission (CPSC), and other organizations (Table 1).
Catastrophic Cervical Spine Injuries
The spectrum of catastrophic cervical spine injuries in sports include unstable fractures and dislocations, cervical cord neuropraxia (transient quadriplegia), and intervertebral disk herniation . Unstable fractures and dislocations are the most frequent causes of catastrophic cervical spine trauma in the athlete and typically occur in the lower cervical spine, especially at the C5-C6 level. The mechanism associated with most catastrophic cervical injuries is an axial force to the top of the head with the neck slightly flexed [5•]. When the neck is in a neutral position, the cervical spine is in a lordotic or extended position and most energy is dissipated by the paravertebral muscles and the intervertebral discs. However, when the neck is flexed 30°, the cervical spine becomes straight, and the forces are transmitted to the segmented cervical column. Once the maximum compressive deformation is reached, the spine fails in either a flexion (flexion teardrop) or pure compression (burst fracture) mode with a resultant fracture, dislocation, or subluxation. Spinal fragments or the intervertebral disc may retropulse into the spinal canal causing spinal cord damage.
Although football has a lower rate of catastrophic injuries than other sports, the large number of participants has resulted in football being associated with the highest number of severe neck injuries per year for all high school and college sports in the United States [6•]. Although the incidence of head-related fatalities started to decline in the early 1970s the number of cases of permanent cervical quadriplegia continued to rise. This is likely due to the improved helmets allowed tacklers to strike an opponent using the crown of the head with less fear of self-induced injury. Torg et al.  were instrumental in reducing the rate of quadriplegic events by demonstrating that spearing or tackling a player with the top of the head is the major cause of permanent cervical quadriplegia. In 1976 spearing was banned and the rate of catastrophic cervical injuries dramatically dropped [7,8]. From 1976 to 1987 the rate of traumatic quadriplegia decreased approximately 80% . Current data indicate a plateau in the incidence of traumatic quadriplegia.
Cervical cord neuropraxia (CCN) is an acute, transient neurologic episode associated with sensory changes with or without motor weakness, or complete paralysis in the arms, legs, or both [9,10•]. The prevalence has been estimated to be seven per 10,000 football participants [5•]. Complete recovery usually occurs within 10 to 15 minutes but may take up to 2 days. Cervical stenosis is believed to be the primary causative factor predisposing to CCN. The hypothesized mechanism is either hyperflexion or hyperextention of the neck causing a pincer-type compression injury to the spinal cord.
An episode of CCN is not an absolute contraindication to return to football. It is unlikely that athletes who experience CCN are at risk for permanent neurologic sequelae with return to play. Rather playing technique in which the athlete employs the top of the head for tackling is the primary factor resulting in cervical quadriplegia. The overall risk of a recurrent CCN episode with return to football is just over 50% and is correlated with the canal diameter size; the smaller the canal diameter the greater the risk of recurrence [10•]. Athletes with ligamentous instability, neurologic symptoms lasting more than 36 hours, multiple episodes, or MRI evidence of cord defect, cord edema, or minimal functional reserve should not be allowed to return to contact sports [6•].
Although the number of catastrophic injuries in ice hockey is low compared with other sports, the incidence per 100,000 participants is high [6•]. A Canadian survey from 1966 to 1993 reported a total of 241 spinal fractures and dislocations in ice hockey [11•]. The majority of spinal injuries in ice hockey are reported to occur to the cervical spine, especially between levels C5 and C7 . The most common mechanism of injury is checking from behind and being hurled horizontally into the boards [11•,12] (Fig. 1). Contact with the boards typically occurs to the crown of the player's head subjecting the neck to an axial load . The frequency and severity of cervical spinal injuries may be reduced in ice hockey by enforcing current rules against pushing or checking from behind. Padding the boards is an alternative preventive strategy that may be effective. Although it has been implicated that head and facial protection leads to an increased risk of catastrophic spinal injuries, this has never been substantiated . Aggressive play and fighting in hockey should also be discouraged.
Cervical fractures or major cervical ligament injuries constitute the majority of traumatic catastrophic wrestling injuries . There is a trend toward more spine injuries in the low- and middle-weight classes. Most injuries occur in match competitions, where intense, competitive situations place wrestlers at a higher risk . The position most frequently associated with spinal injury is the defensive posture during the takedown maneuver, followed by the down position (kneeling), and the lying position . There is no clear predominance of any one type of takedown hold that contributes to wrestling injuries. The athlete is typically injured by one of three scenarios: 1) the wrestler's arms are in a hold such that he is unable to prevent himself from landing on his head when thrown to the mat; 2) the wrestler attempts a roll but is landed on by the full weight of his opponent, causing a twisting, usually hyperflexion, neck injury; and 3) the wrestler lands on the top of his head, sustaining an axial compression force to the cervical spine.
General prevention strategies for catastrophic spine injuries in wrestling rely on the referees and coaches. Referees should strictly enforce penalties for slams and gain more awareness of dangerous holds. There is particular vulnerability for the defensive wrestler who may be off balance, have one or both arms held, and then have his opponent land on top of him. Stringent penalties for intentional slams or throws are encouraged. The referee should have a low threshold of tolerance to stop the match during potentially dangerous situations. Coaches can prevent serious injuries by emphasizing safe, legal wrestling techniques such as teaching wrestlers to keep their head up during any takedown maneuver to prevent axial compression injuries to the cervical spine. Proper rolling techniques, with avoidance of landing on the head, need to be emphasized in practice sessions.
Most catastrophic spinal swimming injuries are related to the racing dive into the shallow end of pools [6•]. The injury occurs when a swimmer dives head first into the shallow end of a pool and sustains an axial compression injury to the cervical spine. The national high school and collegiate associations have implemented rules to prevent injuries during the racing dive. At the high school level, swimmers must start the race in the water if the water depth at the starting end is less than 3.5 feet. If the water depth is 3.5 feet to less than 4 feet at the starting end, the swimmer may start in the water or from the deck. If the water depth at the starting end is 4 feet or more the swimmer may start from a platform up to 30 inches above the water surface. College rules require a minimum water depth of 4 feet at the starting end of the pool. During practice sessions in which platforms may not be available, swimmers are advised to only dive into the deep end of the pool or to jump into the water feet first.
Many recreational diving injuries go unreported, hampering attempts at improved awareness and water safety. In a retrospective review of traumatic spinal cord injuries presenting to a trauma center in Germany, 7.7% were caused by diving accidents ; 97% of the injured patients were male. Inadequate supervision, alcohol use, shallow water, and inexperienced divers are all risk factors for injury . Diving head first into shallow or unknown waters was the reported cause in most cases. Many recreational aquatic centers have removed the high-board in favor of a water slide to reduce the incidence of spinal cord injuries.
Downhill Skiing and Snowboarding
Although the accident rate in skiing is 1.5 to 4 per 1000 skier-days, the incidence of serious spinal cord injury is 0.01 injuries per 1000 skier-days . The location of spinal injuries is fairly evenly distributed between the cervical, thoracic, and lumbar levels . Spinal injuries appear to be increasing among skiers over the past 20 years and tend to occur predominantly in young men. The primary causes of injury are falls caused by poorly groomed slopes, equipment failure, unfavorable weather conditions, overcrowding with skier-skier or skier-snowboarder collisions, skier error, or high speeds with loss of control. The injury rates increase at the end of the day suggesting a link with skier fatigue. Fatality rates for downhill skiers have been estimated to be one death per 1.5 million skier-days . Most fatalities result from reckless skiers colliding with a stationary object, especially a tree . Although most fatalities are caused by severe head injuries, spinal injuries have also been documented . Enforcement of responsible safe skiing by the ski patrol is an important factor in preventing injuries.
The incidence of spinal injury in snowboarding has been reported to be fourfold higher than skiing [19•]. Jumping is the primary cause of injury in snowboarding contributing up to 80% of the injuries, most occurring in the thoracolumbar region [18,19•]. Prevention strategies include regulating the downhill runs so snowboarders don't overcrowd the slopes or keeping snowboarders on separate slopes from skiers. Snowboarders should also be made aware of the potentially deleterious effects of high-risk jumping practices.
The lack of protective gear and aggressive style of play in rugby has resulted in a high rate of cervical injury. Scher [20,21] reported that 10% of serious injuries in rugby involve the cervical spine, with spinal cord contusions constituting 25% of the spinal injuries. Cervical spine injuries most frequently occur during the scrum when the opposing packs of tightly bound players come together (engagement) . The hooker or central player on the front row suffers the most injuries. During engagement the eight-person scrum may generate forces up to 1.5 tons; the hooker may encounter almost 50% of this force. If engagement does not occur properly or the hooker employs his or her head as a weapon with the neck flexed during contact a severe cervical injury may result. Preventive methods include avoiding a mismatch in physical size of the hookers, not allowing unskilled players to participate on the front row, and changing the rules of engagement. Sequential engagement or having the front rows engage separately from the pack prevents the second and third rows from thrusting unprepared front-row players into their opponents. An uncontested scrum in which there is no pushing or shoving and the offensive team always wins the scrum has also been shown to be an effective preventive strategy . There are insufficient data to determine if protective headgear changes the rate of cervical spine injury.
Over the past 20 years cheerleading has evolved into an activity demanding high levels of skill, athleticism, and complex gymnastics maneuvers. Compared with other sports, cheerleading has a low overall incidence of injuries, but a high risk of catastrophic injuries. At the college and high school levels cheerleaders account for more than half of the catastrophic injuries that occur in female athletes [6•]. College athletes are more likely to sustain a catastrophic injury than their high school counterparts, which is likely due to the increased complexity of stunts at the college level [23•]. In 2000 the CPSC estimated a total of 1814 neck injuries in cheerleaders of all ages, 76 as cervical fractures.
The most common stunts resulting in catastrophic injury are the pyramid with the cheerleader at the top of the pyramid most frequently injured, or the basket toss [23•]. A basket toss is a stunt where a cheerleader is thrown into the air, often between 6 and 20 feet, by either three or four tossers. Less common mechanisms include advanced floor tumbling routines, participating on a wet surface, or performing a mount. The majority of injuries occur when an athlete lands on an indoor hard gym surface [23•].
The high school and college associations have attempted to reduce pyramid injuries by limiting the height and complexity of a pyramid, and specifying positions for spotters. Height restrictions on pyramids are limited to two levels in high school and 2.5 body lengths in college. The top cheerleaders are required to be supported by one or more individuals (base) who are in direct weight-bearing contact with the performing surface. Spotters must be present for each person extended above shoulder level. The suspended person is not allowed to be inverted (head below horizontal) or to rotate on the dismount.
Safety measures have also been instituted for the basket toss such as limiting the basket toss to four throwers, starting the toss from the ground level (no flips), and having one of the throwers behind the top person during the toss. The top person (flyer) is trained to be directed vertically and not allow the head to drop backwards out of alignment with the torso or below a horizontal plane with the body. Because several injuries have been reported during rainy weather, all stunts should be restricted when wet conditions are present. Floor tumbling routines can be prevented by proper supervision, progression to complex tumbling only when simple maneuvers are mastered, and spotters as necessary. Mini trampolines, springboards, or any apparatus used to propel a participant have been prohibited since the late 1980s.
Cheerleading coaches need to place equal time and attention on the technique and attentiveness of spotters in practice compared with the athletes' performing the stunts. Pyramids and basket tosses should be limited to experienced cheerleaders who have mastered all other skills and should not be performed without qualified spotters or landing mats [23•].
Similar to cheerleading, baseball has a low rate of noncatastrophic injuries, but a relatively high incidence of catastrophic injuries compared with other sports. Severe head injuries are more frequent than spine injuries. The most common mechanism of catastrophic spine injury in baseball is a collision between a base runner and a fielder [24•]. Collisions between base runners and fielders often involve the catcher. A typical scenario is a base runner who dives head first into a catcher and sustains an axial compression cervical injury [24•]. Baseball rules state that the runner should avoid the fielder who has the right to the base path. Unfortunately, this rule is not always enforced when a base runner is racing toward home plate. Because the risk of injury from collisions of a base runner and catcher is significant, and the speed of head-first sliding has been shown not to be statistically different from feet-first sliding, the authors believe that the head-first slide needs to be reassessed at the high school and college levels . In Little League baseball head-first sliding is not allowed at any base.
It has been clearly documented that physical activity has numerous health-related benefits. Nonetheless, there is an extremely low risk of catastrophic spine injuries in certain organized sports. The cost to the injured athlete and to society can be tremendous. In addition to the decreased quality of life for the patient, the lifetime cost for a complete quadriplegic individual can easily surpass $2 million . It has been estimated that the annual aggregate cost of treatment of spinal cord injuries due to sports in the United States in 1995 was close to $700 million . Prevention is the most effective means of reducing the incidence and costs associated with catastrophic spine injuries in sports. Continued research of the epidemiology and mechanisms of catastrophic spine injuries is critical to prevent these injuries.
References and Recommended Reading
Papers of particular interest, published recently, have been highlighted as: • Of importance, •• Of major importance
1. Mueller FO: Introduction.Catastrophic Injuries in High School and College Sports.
Edited by Mueller FO, Cantu RC, VanCamp SP. Champaign: HK Sport Science Monograph Series; 1996:1–4.
2. Nobunga AI, Go BK, Karunas RB: Recent demographic and injury trends in people served by the model spine cord injury care systems.Arch Phys Med Rehabil
3. Katoh, S, Shingu H, Ikata T, et al.
: Sports-related spinal cord injury in Japan (From the nationwide spinal cord injury registry between 1990 and 1992).Spinal Cord
4. Banerjee R, Palumbo MA, Fadale PD: Catastrophic cervical spine injuries in the collision sport athlete, part 1: epidemiology, functional anatomy, and diagnosis.Am J Sports Med
5.• Torg JS, Guille JT, Jaffe S: Current concepts review: injuries to the cervical spine in American football players.J Bone Joint Surg Am
Comprehensive review of pathomechanics of cervical injuries in football players.
6.• Mueller FO, Cantu RC: National Center for Catastrophic Sports Injury Research: Twentieth Annual Report, Fall 1982–Spring 2002.
Chapel Hill: National Center for Catastrophic Sports Injury Research; 2002:1–25.
Web site review of 20 years of catastrophic injuries reported to the NCCSI research.
7. Torg JS, Vegso JJ, O'Neill MJ, Sennett B: The epidemiologic, pathologic, biomechanical, and cinematographic analysis of football-induced cervical spine trauma.Am J Sports Med
8. Torg JS, Gennarelli TA: Head and cervical spine injuries.Orthopaedic Sports Medicine: Principles and Practice.
Edited by DeLee JC, Drez Jr D. Philadelphia: WB Saunders; 1994:417–462.
9. Torg JS, Pavlov H, Genuario SE, et al.
: Neuropraxia of the cervical spinal cord with transient quadriplegia.J Bone Joint Surg Am
10.• Torg JS, Naranja Jr RJ, Pavlov H, et al.
: The relationship of developmental narrowing of the cervical spinal canal to reversible and irreversible injury of the cervical spinal cord in football players. An epidemiological study.J Bone Joint Surg Am
Article discusses risk of recurrent cervical cord neuropraxia with return to football.
11.• Tator CH, Carson JD, Edmonds VE: Spinal injuries in ice hockey.Clin Sports Med
Canadian registry reports on 117 cases of spine or spinal cord injury sustained in ice hockey.
12. Molsa JJ, Tegner Y, Alaranta H, et al.
: Spinal cord injuries in ice hockey in Finland and Sweden from 1980 to 1996.Int J Sports Med
13. Stuart MJ, Smith AM, Malo-Ortiguera SA, et al.
: A comparison of facial protection and the incidence of head, neck, and facial injuries in junior A hockey players: a function of individual playing time.Am J Sports Med
14. Boden BP, Lin W, Young M, Mueller FO: Catastrophic injuries in wrestlers.Am J Sports Med
15. Schmitt H, Gerner HJ: Paralysis from sport and diving accidents.Clin J Sports Med
16. Truitt-Cooper M, McGee Kevin M, Anderson DG: Epidemiology of athletic head and neck injuries.Clin Sports Med
17. Morrow PL, McQuillen EN, Eaton Jr LA, et al.
: Downhill ski fatalities: the Vermont experience.J Trauma
18. Levy AS, Smith RH: Neurologic injuries in skiers and snowboarders.Semin Neurol
19.• Tarazi F, Dvorak MF, Wing PC: Spinal injuries in skiers and snowboarders.Am J Sports Med
Authors review incidence and causes of spinal injuries in skiers and snowboarders.
20. Scher AT: Rugby injuries to the cervical spine and spinal cord: a 10 year review.Clin Sports Med
21. Scher AT: Rugby spinal cord concussion in rugby players.Am J Sports Med
22. Wetzler MJ, Akpata T, Laughlin W, et al.
: Occurrence of cervical spine injuries during the rugby scrum.Am J Sports Med
23.• Boden BP, Tacchetti R, Mueller FO: Catastrophic cheerleading injuries.Am J Sports Med
Review of mechanisms and prevention strategies for catastrophic cheerleading injuries.
24.• Boden BP, Tacchetti R, Mueller FO: Catastrophic injuries in high school and college baseball players.Am J Sports Med
Recent review of mechanisms and prevention strategies for catastrophic baseball injuries.
25. Kane SM, House HO, Overgaard KA: Head-first versus feet-first sliding: A comparison of speed from base to base.Am J Sports Med
26. DeVivo MJ: Causes and costs of spinal cord injury in the United States.Spinal Cord