Chapter 71 Spinal Injuries in Sports
Section One
Sports-Specific Epidemiology
Each year, approximately 10,000 cases of SCI occur in the United States.1 Participation in sporting activities accounts for nearly 10% of these and is the fourth most common cause of SCI (after motor vehicle accidents, violence, and falls).2,3 Sports-related SCIs also occur at a younger mean age of 24 and are the second most common cause of SCI in the first three decades of life.4,5
Spinal injuries are more common in nonorganized sports such as diving and surfing than in organized sports.1,6 The challenge in this population is that rules, supervision, and training are limited. These limitations make it difficult to improve injury patterns by enforcing safety guidelines and manufacturer standards. Although less frequent, spinal injury in organized sports have a much higher public profile. Several organized sports, including football, ice hockey, rugby, skiing, snowboarding, and equestrian sports, have been identified as placing the participant at high risk for SCI.7–10
Sport-Specific Risks to the Spine
American Football
American football involves approximately 1.4 million athletes at the junior/senior high school level, 75,000 in college, and 1000 in professional play.11 This total contrasts roughly with 60,000 rugby players in the United States. With the innumerable high-velocity collisions incurred during practice and games, it is the most dangerous sport for SCI in terms of exposure and is responsible for the highest risk of cervical spine trauma among organized sports participants. Although American football has a lower per participant rate of catastrophic cervical spine injuries than ice hockey or gymnastics, the huge number of participants translates into the largest overall number with catastrophic cervical spine injuries.11
Notably, a significant increase in catastrophic cervical trauma coincided with the development of the modern football helmet. However, rule changes in 1976 prohibiting playing techniques that used the top of the helmet as the initial point of contact for blocking and tackling (spearing) have significantly reduced this trend. From 1976 to 1987, the rate of cervical injuries decreased 70%, from 7.72 per 100,000 to 2.31 per 100,000 at the high school level.12 Traumatic quadriplegia decreased approximately 82% over the same period.13 Since most football players are injured during tackling, defensive players (defensive backs, members of the kickoff teams, and linebackers) are at the highest risk of injury. Almost all cervical spine injuries occur when a player strikes an opponent with high velocity using the vertex of the helmet or with the head down. This action results in a significant axial load, often with a degree of flexion. The cervical musculature that is responsible for maintaining extension is much stronger than that used in maintaining flexion. Thus, a player who lowers his head in blocking or tackling increases his vulnerability to cervical injury by placing his cervical spine in a position that is less able to absorb the consequent energy.
Baseball and Softball
Minor spinal injuries are fairly common in baseball and softball, but catastrophic injuries do occur. Participants who slide headfirst into a base have the most risk of catastrophic SCI. If the hands of the runner separate, the top of his head can collide with the leg of the defensive player, creating a great deal of axial load transmission to the vertebral column. Although the use of breakaway bases substantially decreases the risk for occurrence of sliding-related injuries, serious injuries can still occur. The use of even lower profile bases and the outlawing of sliding have also been suggested.14
Basketball
Basketball involves rapid changes in direction and explosive movements, causing repeated stresses to the spinal vertebrae. Thus, it is not surprising that the most common neurologic risk in basketball is to the player’s spine. A variety of acute back injuries, such as lumbosacral sprains, contusions, and facet joint and pars interarticularis injuries, are common.15,16 In addition, this sport is a leading cause of sports-related disc disease and has been reported to be the second most common cause of disc herniation among athletes.17 Herniated discs usually arise dorsally or dorsolaterally and occur as a consequence of numerous microtraumas to the intervertebral disc compounded by chronic overstraining. Cervical cord neurapraxia has also been reported in basketball players.
Cycling
Neck and back pain are common complaints in cyclists, occurring in over half of participants. The odds of female cyclists developing neck and shoulder overuse problems have been reported to be 1.5 and 2.0 times greater, respectively, than for their male counterparts.18 Neck pain is partially the result of a combination of increased load on the arms and shoulders required to support the cyclist and hyperextension of the neck in the horizontal, bent forward position of riding. These stresses are compounded in bicycles improperly fitted to the cyclist. Lower back pain often results from hyperextension of the angle between the spine and pelvis, which increases stress at the promontorium.
Equestrian Sports
Approximately 20% of the injuries sustained by an equestrian involve the CNS. One study found that 13% of the patients had injury to the spinal cord, with the cervical region most commonly involved.19 There does not seem to be any correlation between risk of injury and the participant’s age, gender, or experience.20 Equipment failure has been shown to be a common cause of injury. Although jumping events have garnered the majority of attention in the past decade due to catastrophic injuries to celebrities such as Christopher Reeves, the particular type of equestrian activity with the most risk to the spinal cord is unequivocally rodeo rough-stock riding (bull, bareback bronco, and saddle bronco riding).21 Common spinal injuries include cervical and lumbar sprain, acute torticollis secondary to being thrown, and cervicothoracic strain secondary to missing the animal in the steer wrestling competition.
Gymnastics
Gymnasts are a group of athletes with perhaps the greatest risk of back injury. A National Registry of Gymnastic Catastrophic Injury was established in 1978, and 20 gymnasts injured the cervical spine in its first 4 years. Of these, 17 remained quadriplegic and 3 died secondary to their injury. Notably, most of the injuries occurred in experienced gymnasts during practice.22 The sport accounts for a significant proportion of all sports-related SCIs, and an 18-month study of elite and subelite female gymnasts reported a back injury rate of 14.9%.23 Injuries are commonly to the cervical spine, and the sport is by far the leading cause of quadriplegia in women’s sports.
Ice Hockey
The sport of ice hockey has experienced a marked increase in the occurrence of cervical spine injuries through its history.24 Major vertebral column injury occurred at an increased rate between 1982 and 1993, with a mean of 16.8 fracture-dislocations per year during that period. Checking an opponent from behind, which typically produces a headfirst collision of the checked player with the boards, has been identified as an important causative factor in cervical spine trauma in hockey. Changes in the rules that prohibit checking from behind and checking of an opponent who is no longer controlling the puck seem to be decreasing the incidence of these injuries, and data suggest that fewer cases of complete quadriplegia have been caused by these playing techniques since the rule changes have been instituted.24
Mixed Martial Arts
Mixed martial arts (MMA) is a full-contact sport combining elements of boxing, kickboxing, and wrestling. It has evolved since 2001 to become a mainstream sport with improved regulations to minimize injury.25 Most competitions now forbid head butting; stomping or kneeing on an opponent on the ground; and striking the throat, spine, or back of the head. Also, athletes must fight within a predetermined weight class. Despite the dramatic impacts that a participant receives during competition, the overall injury rate in MMA competitions has been determined to be similar to other combat sports, including boxing.25,26 While no catastrophic spinal injury has been reported during competition in the past decade, many of the maneuvers seem to be particularly risky.
Maneuvers known as “spinal locks” are often employed in competition. A spinal lock is performed by forcing the spine beyond its normal ranges of motion and is typically accomplished by bending or twisting the opponent’s head or upper body into abnormal positions. These maneuvers can be separated into two categories based on their primary area of effect on the spinal column: spinal locks on the neck are called neck cranks, and locks on the lower parts of the spine are called spine cranks. Spine cranks are less commonly performed in competition than neck cranks because they are more difficult to apply. These can commonly strain the spinal soft tissue and musculature and if forcefully and/or suddenly applied could theoretically result in ligament damage, bony fracture or displacement, and SCI.
Four of the most commonly utilized maneuvers in the sport are the O goshi (judo), in which the fighter uses his shoulders to swing the opponent over his hips; the suplex (jujitsu), in which the fighter grabs the opponent around the waist and lifts him up over his shoulder to fall forward onto his face; the souplesse, a variant of the suplex, in which the opponent is rotated and slammed down onto his back; and the guillotine drop (a choke hold). A detailed kinematic and biomechanical analysis of these maneuvers showed that the forces involved are of the same order as those involved in whiplash injuries and of the same magnitude as compression injuries of the cervical spine.27
Rugby
Spinal injuries, especially to the cervical region, are common in the traditional tackle games of rugby union, rugby league, and Australian rules football. A retrospective study of SCIs in rugby from 1960 through 1989 identified 117 catastrophic neck injuries. It was also reported that for every serious rugby-associated SCI, 10 severe neck injuries occurred that did not involve the cord.28
Three specific activities during the game of rugby—the tackle, tight scrum, and loose play (ruck and maul)—result in the majority of injuries to the cervical spine.29 Cervical spine injury often results from impact between the tackler’s head and the ground or the body of the opponent (usually the thigh). The immediate halt of the head’s forward progress results in compression fractures of the vertebral bodies from axial forces transmitted down the spine. These forces are increased significantly if the player’s neck is flexed, which eliminates the normal lordosis of the cervical spine. An injury during a high tackle from behind often results from hyperextension secondary to the head being pulled back and down. If the tackle is from the side, hyperflexion injury often results. Rotational forces are also a factor in these injuries, especially if the tackle is performed with only one arm. Double tackles, often referred to as “sandwich” or high-low tackles, are more common near the goal with a concentration of defenders merging on the ball carrier. They can cause injury to both the offensive and defensive player. If the defensive players miss their target, they can collide into each other with considerable force at unexpected angles. If the tackle is successful, the offensive player’s body is forced in two directions. This inhibits the player from moving with either force completely, increasing rotational and shearing stresses to the spine.
Water Sports
The water sport with the most risk for spinal injury is by far recreational diving. Mishaps have been reported to account for up to 75% of all recreation-related spinal cord injuries.30–32 These injuries tend to occur in teenage males involved in unsupervised activities during the summer months. The most common cause of injury is the participant striking his head on the bottom of a pool, lake, or ocean after having miscalculated the depth of the water. Diving injuries occur almost exclusively to the cervical spine and often result in quadriplegia. Forward flexion, often with axial compression, is the usual mechanism of injury. The C5 level is most commonly involved, likely attributable to the wide range of motion and the relatively smaller size of the vertebral canal at this level.33
Wrestling
The sport of wrestling has been associated with spinal injury, most commonly in the cervical region.34 Although the intervertebral discs, joints, and ligaments are somewhat resistant to compression stresses, they are very susceptible to injury by rotational and shearing forces. Most injuries result from landing with the body twisted on the head and neck and occur during takedowns and sparring. Various combinations of thoracolumbar spine abnormalities, such as spondylolysis, are also prevalent in this population of athletes.
Section Two
Cervical Spine and Brachial Plexus
Cervical Sprains, Strains, and Contusions
One of the most common causes of neck pain in the athlete is the constellation of cervical strain, sprain, and contusion. A strain is defined as a stretch injury at the musculotendinous junction or within the muscle itself. If the ligamentous structures of the spine are more involved, it is termed a sprain. Contusions are blunt-force injuries to soft tissue. Injuries in this group most often occur when a force is applied to a contracting muscle. This creates an eccentric contraction resulting in some degree of tensile failure. The most vulnerable area for this injury is at the myotendinous junction as well as areas of greater type II (fast-twitch muscle fibers) concentration.35 Most injuries involve an overlap of all three components, with the severity of injury being a consequence of the magnitude and direction of the applied forces.
The natural course of these injuries is a gradual resolution of pain and muscle spasm with conservative treatment. Obviously, an athlete who presents with pain and limited cervical range of motion should undergo a complete clinical and radiographic examination. At a minimum, this imaging should include dynamic (flexion-extension) plain radiographs in at least two orthogonal planes of the entire cervical spine (occiput to C7-T1 junction). If the injury only appears to be a strain, sprain, or contusion, a cervical collar may be continued until any severe muscle spasm has resolved, which usually takes 7 to 10 days. Use of a cervical collar for longer than this length of time has been demonstrated to result in significant deconditioning and weakening of the cervical musculature.35 Repeat dynamic radiographs can then be taken to ensure that the athlete does not have any delayed instability that could present after the splinting effect of muscle spasm has resolved. If these tests are negative, the collar can be discontinued and physical therapy begun. This should include gentle range-of-motion and isometric strengthening exercises, followed by a more sport-specific regimen.
The athlete may return to play when he or she is asymptomatic, has full range of motion, and has baseline sport-specific neck function. After returning to competition, the athlete should continue stretching and strengthening exercises in an attempt to reduce the incidence and severity of any future injury. The use of a sport-specific protective orthosis (e.g., a “horse collar” in American football) to prevent further injury may be employed, although significant data on their actual benefit are limited. Such orthoses used in American football have been shown to limit hyperextension of the cervical spine while allowing enough extension to prevent axial loading injury.36
Brachial Plexus Neurapraxia
Brachial plexus neurapraxia (also known as stinger-burner or transient brachial plexopathy or nerve root neurapraxia) is a transient neurologic event characterized by pain and paresthesia in a single upper extremity following a blow to the head or shoulder. This condition is one of the most common occurrences in collision sport participation and is not the result of an SCI. It was first described in 1965 by Chrisman et al.37 Because the mechanism was thought to be direct force applied to the shoulder with the neck flexed laterally away from the point of contact, the condition has also been referred to as “cervical pinch syndrome.”38 The symptoms most commonly involve the C5 and C6 spinal roots. The affected athlete can experience burning, tingling, or numbness in a circumferential or dermatomal distribution.38 The symptoms may radiate to the hand or remain localized in the neck. These athletes often maintain a slightly flexed cervical spine posture to reduce pressure on the affected nerve root at the neural foramen or may hold or elevate the affected limb in an attempt to decrease tension on the upper cervical nerve roots.
Weakness in shoulder abduction, external rotation, and arm flexion is a reliable indicator of the injury.39 If weakness is a component, it usually involves the C5-6 neurotome. The radiating arm pain tends to resolve first (within minutes), followed by a return of motor function (within 24–48 hours). Although the condition is usually self-limiting and permanent sensorimotor deficits are rare, a variable degree of muscle weakness can last up to 6 weeks in a small percentage of cases.
As mentioned previously, this injury is most commonly the result of downward displacement of the shoulder with concomitant lateral flexion of the neck toward the contralateral shoulder. This is thought to result in a traction injury to the brachial plexus. The condition may also result from ipsilateral head rotation with axial loading resulting in neural foramen narrowing and compression-impaction of the exiting nerve root within the foramen.40,41 Direct blunt trauma at the Erb point, located superficially in the supraclavicular region, has also been reported to be a cause.42 This can occur when an opponent’s shoulder or helmet drives the affected athlete’s shoulder pad directly into this area.
Stingers with prolonged neurologic symptoms are the most common reason for high school and college athlete cervical spine evaluations in an emergency department.43–45 The athlete commonly demonstrates a full, pain-free arc of neck motion with no midline palpation tenderness on examination. If tenderness is present or unilateral neurologic symptoms persist, a paracentral disc herniation with associated nerve root compression should be considered. This is usually accompanied by the sudden onset of dorsal neck pain and spasm. Monoradiculopathy characterized by radiating pain, paresthesias, and/or weakness in the upper extremity also occurs secondary to compression and inflammation of the cervical root.
Although this injury is usually considered benign, an athlete that suffers an episode of brachial plexus neurapraxia should be immediately removed from competition until symptoms have fully resolved. On-field evaluation should include palpation of the cervical spine to determine any points of tenderness or deformity. Sensation and muscle strength should be evaluated using the unaffected limb as a point of reference. Weakness in the muscles innervated by the upper trunk of the brachial plexus is often observed. These include the deltoid (C5), biceps (C5-6), supraspinatus (C5-6), and infraspinatus (C5-6) muscles.46,47 The shoulder of the affected limb should also be evaluated, paying particular attention to the clavicle, acromioclavicular joint, and supraclavicular and glenohumeral regions. Percussion of the Erb point can be performed in an attempt to elicit radiating symptoms. Obviously, the athlete should be evaluated for other serious injuries such as cervical spine fractures and dislocations. It is unusual to find lower brachial trunk injury patterns involving the C7 or C8 nerve roots. It is also uncommon to see persistent sensory deficits involving either the lower or upper extremities. This condition is always unilateral and has never been reported to involve the lower extremities. If bilateral upper extremity deficits are present, SCI should be at the top of the differential diagnosis. Localized neck stiffness or tenderness with apprehension to active cervical movement should alert the examiner to a potentially serious injury and the subsequent initiation of full spinal precautions, including spine board immobilization and transport for imaging.
If the player does not complain of neck pain, decreased range of motion, or residual symptoms, he or she can usually return to competition. If symptoms do not resolve or there is persistent pain, prompt imaging of the brachial plexus via MRI is recommended. If the symptoms persist for over 2 weeks, electromyography can be performed to establish the distribution and degree of injury.48 Residual muscle weakness, cervical anomalies, or abnormal electromyographic studies are exclusion criteria from return to play.44
By definition, brachial plexus neurapraxia is a transient phenomenon. It usually does not require formal treatment. The athlete should be followed closely with repeat neurologic examinations since although the condition usually resolves in minutes, motor weakness may develop hours to days following the injury.39,45 Repeated injury may result in long-term muscle weakness with persistent paresthesias, resulting in permanent removal from competition.49 Options in participants to decrease the risk of future occurrences are to change their field positions or modify their playing techniques.
Central Cord Syndrome
Burning hand syndrome is considered to be a variant of central cord syndrome. It is characterized by burning dysesthesia in both upper extremities and is likely the result of vascular insufficiency affecting the medial aspect of the somatotopically arranged spinothalamic tracts.50,51 The lower extremities may occasionally be involved and weakness may occasionally be evident. Cervical spine fracture or soft tissue injury is frequently associated with these syndromes, and any athlete exhibiting this condition should be initially treated as having an SCI (see section titled On-Site Evaluation and Management of Spinal Cord Injury).52
Cervical Cord Neurapraxia and Transient Quadriplegia
Neurapraxia of the cervical spinal cord (CCN) resulting in transient quadriplegia has been estimated to occur in 7 per 10,000 football players.53 This alarming injury is characterized by a temporary loss of motor or sensory function and is thought to be the result of a physiologic conduction block without true anatomic disruption of neuronal tissue. The affected athlete may complain of pain, tingling, or loss of sensation bilaterally in the upper and/or lower extremities. A spectrum of muscle weakness is possible, varying from mild quadriparesis to complete quadriplegia. The athlete has a full, pain-free range of cervical motion and does not complain of neck pain. Hemiparesis or hemisensory loss is also possible.
The condition is thought to result from a pincer-type mechanism of compression of the cord between the dorsocaudal portion of one vertebral body and the lamina of the vertebra below.54 Although this can also occur during hyperflexion, it is more commonly the sequela of extension movements with infolding of the ligamentum flavum, which can result in a 30% or more reduction of the anteroposterior diameter of the spinal canal.55 The spinal cord axons become unresponsive to stimulation for a variable period of time, essentially creating a “postconcussive” effect.56
CCN is described by the neurologic deficit, the duration of symptoms, and the anatomic distribution. A continuum of neurologic deficits that range from sensory only, sensory disturbance with motor weakness, or episodes of complete paralysis may occur. These may be described as paresthesia, paresis, or plegia. An injury is defined as grade 1 if the CCN symptoms do not persist for longer than 15 minutes. Grade 2 injuries are defined as lasting from 15 minutes to 24 hours. Grade 3 injuries persist for 24 to 48 hours. All four extremities may be involved; this is considered a “quad” pattern. Upper- and lower-extremity patterns may also be observed.57
By definition, CCN is transient, and complete resolution generally occurs within 15 minutes but may take up to 48 hours. Steroid administration in accordance with the Bracken protocol58 in this population is controversial. No controlled studies have reported that the administration of steroids has altered the natural history of athletes with CCN.44 In players who return to football, the rate of recurrence has been reported to be as high as 56%.57
A considerable amount of controversy exists regarding whether the presence of cervical stenosis makes an athlete more prone to sustaining CCN and even permanent neurologic injury.59,60 This controversy is compounded by the imprecise methods of objectifying whether an individual suffers from stenosis. The anteroposterior diameter of the spinal canal (measured from the dorsal aspect of the vertebral body to the most ventral point on the spinal laminar line) determined from lateral cervical spine radiographs is considered normal if there is more than 15 mm between C3 and C7. Cervical stenosis is considered to be present if the canal diameter is less than 13 mm. However, this measurement varies widely secondary to variations in landmarks used for measurement, changes in target distances for making the radiographs, patient positioning, differences in the triangular cross-sectional shape of the canal, and magnification of the canal because of a patient’s large body habitus. In an effort to eliminate this variability, Torg and Pavlov designed a ratio method for determining the presence of cervical stenosis, comparing the sagittal diameter of the spinal canal with the sagittal midbody diameter of the vertebral body at the same level.61 A ratio of 1:1 was considered normal, and less than 0.8 was indicative of significant cervical stenosis. This ratio was found to mislabel many athletes with adequately sized canals but large vertebral bodies as being stenotic. This observation, as well as an unprecedented ability to image the vertebral column, intervertebral discs, spinal canal, cerebrospinal fluid (CSF), and spinal cord directly, have made MRI, and not boney landmarks, the currently preferred method of choice for assessing “functional spinal stenosis.” MRI assessment of CSF signal around the spinal cord, termed the functional reserve, can be determined, and the visualization of the CSF signal, its attenuation in areas of stenosis, and changes on dynamic sagittal flexion-extension MRI studies are now the standard in diagnosing this condition. An absent CSF pattern on axial and, particularly, sagittal MRI is diagnostic of functional stenosis.
It had been previously accepted that young athletes who suffered an episode of CCN were not predisposed to permanent neurologic injury.60,62 This assumption has recently been called into question now that a player who experienced a CCN subsequently sustained a quadriplegic injury.63
Traumatic Intervertebral Disc Herniation
Acute herniation of an intervertebral disc can occur during participation in sports and in the athletic population. Those involving the cervical spine are less common than lumbar disc injuries and usually involve the older athlete. Compared with the overall incidence of disc herniation in the general public, the incidence is likely increased in the high-performance athlete competing in contact sports such as football and wrestling.64,
