Approximately 10,000 acute cervical spine injuries occur annually in the United States,1 occasionally resulting in permanent neurologic deficits.2 These injuries can occur at any level of participation, ranging from unsupervised to professional levels of activity, and in a variety of sports, ranging from collision (football) to noncontact (gymnastics).3
For professional athletes, return to play (RTP) after a cervical spine injury is a controversial topic. Although a single-level anterior cervical diskectomy and fusion (ACDF) for cervical disk herniation is a potentially career-threatening procedure, most athletes successfully RTP at baseline performance.4 However, subtle differences in range of movement after fusion can lead to altered performance in elite athletes dependent on sport-specific demands and position.4
Currently, a 2-level cervical fusion is a relative contraindication for many professional sports because of theoretically additional restricted range of movement and stress on adjacent levels,5 but case series and anecdotal evidence of successful RTP after this surgery suggest decisions should be made on a case-by-case basis. Finally, there is often little agreement for RTP after a finding of cervical stenosis.6 This review presents a putative systematic framework to help guide decision-making in common cervical conditions in athletes.
Cervical Disk Herniation
Cervical disk disease in collision sport athletes, such as American football players, has a higher incidence compared with the general population.7,8 Athletes can return to their sport after both nonoperative and operative treatments for single-level cervical disk herniation after they become asymptomatic.2,9 Meredith et al10 cleared 11 of 13 professional football players to RTP after conservative treatments, and multiple studies across a variety of sports, such as football, rugby, wrestling, and baseball, have displayed the benefits of single-level ACDF for the treatment of cervical disk herniation in professional athletes.4,11–14
In 2011, the authors' research group examined NFL athletes who underwent single-level spine surgery for cervical disk herniation and found that players treated surgically vs nonsurgically returned to their sport at a higher rate (72% compared with 46%, respectively).4 Among this group, defensive backs experienced significantly shorter careers after treatment compared with other positions, which may be explained by the position's unique physical demands, such as the instinctive reactions to a football or offensive player requiring uninterrupted cervical range of motion. Not surprisingly, age also was a factor, with older athletes experiencing significantly shorter careers after cervical disk herniation.
Mai et al8 compared RTP in professional athletes who underwent either single-level ACDF (n=86) or posterior foraminotomy (n=13) and found players who underwent posterior foraminotomy returned to their sport at a significantly higher rate (92.3% vs 70.9%) and in a significantly shorter amount of time (238 vs 367 days). However, the reoperation rate for posterior foraminotomy was significantly higher (46.2% vs 1.2%) within that time period. Tumialán et al15 conducted a study comparing the effectiveness of posterior foraminotomy with ACDF in a military population, which faces similar physical demands.8,16 Similarly, the time to return to active duty in those who underwent posterior foraminotomy (n=19) compared with those who underwent ACDF (n=19) was significantly shorter. The shorter recovery time after foraminotomy may affect decision-making depending on the point in the season that the injury is sustained. Furthermore, data from the authors' research group suggest that performing a 1-level ACDF after a failed posterior foraminotomy leads to similar outcomes to a virgin ACDF (ie, a neck not previously operated on).8
Although the use of cervical disk arthroplasty (CDA) has grown in the general population during the past decade,17–19 its widespread applicability to professional athletes remains unknown.20 Small case series of professional lugers and baseball players who underwent a 1-level CDA and successfully returned to sport have been reported.8,21 Data on return to active duty in the military population after CDA suggest successful outcomes in the elite athlete.22,23 In 2010, Tumialán et al24 compared clinical outcomes in military personnel who underwent single-level CDA and ACDF. The CDA group, which included 7 Navy SEALS and 1 marine, all returned to unrestricted active duty and in a significantly shorter amount of time (10.3 vs 16.5 weeks) compared with the ACDF group. Long-term outcomes after CDA in professional athletes are currently unknown.6
Although a number of authors have opined that a 2-level ACDF is considered a contraindication to RTP for collision sports,2,3,9,10,25–29 there is a paucity of objective data supporting this view. Furthermore, some have advocated for RTP to football after 2-level fusion.6 A professional rugby player and 2 military servicemen have been reported to return to full active duty after undergoing a 2-level fusion.14,15 The authors believe the criteria for RTP after such an operation should depend on a number of factors including collision vs contact sports, position, symptoms, and physical examination. For example, a 2-level ACDF may not be compatible with successful RTP for a defensive back but may be for an offensive lineman in American football. Further study is required to delineate this conundrum.
Critical cervical stenosis increases an athlete's risk for spinal cord injury after spine trauma.30–32 However, many associated factors can affect its impact including the clinical symptoms, severity of stenosis, and cord pathology. When this diagnosis is found incidentally, there is little guidance in the evidence-based literature for RTP recommendations. This often leads to challenges among team physicians regarding the relative risk of neurologic deficit with repeated collision events. The following 4 critical factors should be considered in determining RTP in athletes with cervical stenosis: (1) sport played, (2) imaging characteristics, (3) clinical symptoms, and (4) physical examination. Each of these aspects adds additional information regarding the state of neurologic dysfunction and future risks to the spinal cord.
Athletes who participate in noncontact (eg, golf, swimming, and tennis), contact (eg, basketball, baseball, and soccer), and collision sports (eg, American football, hockey, and lacrosse) should be evaluated differently because of the relative physical demands required to participate at a high level for each respective activity. Collision sports put athletes at risk for head and neck trauma on a routine basis, whereas athletes in noncontact sports avoid this risk. The relative requirements of the spinal canal in these situations should be different based on the goals of the athlete.
The imaging characteristics of cervical stenosis in the athlete should be evaluated thoroughly. Absolute stenosis on imaging has been defined in the literature as a relationship to the diameter of the cervical spinal canal.31 One of the initial methods for interpreting cervical stenosis was a ratio method that used the relative length of the vertebral body and spinal canal distance measured on plain radiographs.33 However, this method has been proven to be unsatisfactory due to inherent magnification errors and standardization of images associated with this modality.34–36 With the advent of advanced imaging of the cervical spine, the reproducibility of measurement as well as the definition of stenosis has evolved. The most common method described in the literature is to measure the sagittal diameter of the cervical spinal canal on a mid-sagittal T2-weighted magnetic resonance image (MRI) (Figure 1).
Sagittal T2-weighted magnetic resonance image showing the diameter (red) of the cervical spinal canal at different levels.
In 1986, Ladd and Scranton37 first defined stenosis as a diameter of the cervical spinal canal in the sagittal plane less than 15 mm, with critical stenosis being less than 12 mm. Since then, there has been some disagreement as to the exact thresholds of a stenosis diagnosis ranging from 10 to 14 mm, which has been based mainly on expert opinion.9,38–40 These values provide some framework for an absolute definition, but none of the values are based on clinical symptoms or injuries, which greatly limits their use.
Schroeder et al31 first described a case series of professional American football players (n=10) with successful careers (approximately 5 years in the sport) and a cervical spinal canal diameter less than 10 mm at one or more levels measured on MRI without spinal cord injury. None of these athletes were symptomatic, and they did not have prior episodes of transient quadriplegia. In a study conducted by Bailes,38 professional athletes (n=3) who had canal diameters less than 8 mm experienced more severe clinical symptoms compared with athletes who had larger (>10 mm) canal diameters.
Aebli et al32 studied the risk of spinal cord injury after minor trauma in the general population and concluded that a canal diameter of 8 mm or less measured on sagittal T2-weighted MRI had the highest predictive value for spinal cord injury compared with canal diameters of 8.5, 9.0, and 9.5 mm. The risk of spinal cord injury can be impacted by the relative diameter of the spinal canal vs the spinal cord. Ulbrich et al41 demonstrated the average spinal cord diameter is 7.6 mm at C3 and decreases to 7.1 mm at C6. An 8-mm spinal canal may have a different risk profile compared with an individual with a smaller spinal cord.
Because of the inherent variations in cord anatomy, experts recently have been using a more qualitative assessment of the spinal canal, defined as functional stenosis. This condition has been referred to as a lack of cerebrospinal fluid reserves around the spinal cord on MRI, myelography, or contrast computed tomography and has been used as a contraindication to RTP in contact sports (Figure 2).28,34,38,39,42–44 The theory behind this is that these patients do not have a cushioning cerebrospinal fluid buffer between the spinal cord and the vertebral bodies, which could lead to direct contact to the spinal cord after head or neck trauma. Bailes38 reported on a case series of 3 athletes who were diagnosed with a lack of reserves on MRI and experienced severe episodes of transient quadriplegia; the athletes were advised to retire from sport, which has been supported by other authors.42
Sagittal T2-weighted magnetic resonance image showing a lack of cerebrospinal fluid reserves around the spinal cord (arrow) indicating the presence of functional stenosis.
Subsequently, Paulus and Kennedy29 reported most cases of cervical cord neurapraxia, when analyzed retrospectively, happen in the context of functional stenosis. Cantu et al28 further reported that in the National Center for Catastrophic Sports Injury Research database, the only cases of documented athletes with quadriplegia who did not present with spine fracture had functional stenosis. In the near future, new technologies such as functional MRI (fMRI) potentially could allow physicians to assess spinal cord function and better understand stenosis.45 Based on the current literature, the authors believe athletes who have functional stenosis should not return to collision sports.
The authors' research group46 recently defined congenital cervical stenosis as a canal diameter less than 10 mm measured on mid-sagittal MRI at 2 or more subaxial cervical levels in a patient population younger than 50 years and concluded this was a posterior-based anatomic anomaly. Based on the authors' experience in this patient population, this may be a more common condition in symptomatic high-level athletes than in the general population. Recent expert opinion6 suggests the presence of congenital stenosis should not prevent asymptomatic athletes or athletes with no prior episodes of transient quadriplegia from returning to a contact sport. However, the authors' believe that if the absolute diameter is less than 8 mm at 1 of the subaxial cervical levels, then athletes should not return to a contact sport.
A player's history and clinical presentation need to be assessed to shed light on the state of current neurologic function.47 Transient quadriparesis is diagnosed when a player suffers symptoms similar to a spinal cord injury immediately after head and neck trauma that recovers over time. This condition sometimes can be confused with a “burner/stinger,” acute radiculopathy, or a concussion. Delineating the exact symptoms and history surrounding the trauma is important in identifying risk of future injury. Although most experts have opined that athletes who have had multiple episodes of transient quadriparesis in the setting of cervical stenosis should not be allowed to return to contact sports,2,25,30,36,38,48,49 the fate of a player who has experienced a single episode has been debated.6
Guidelines offered by Torg36 and Torg and Ramsey-Emrhein25 suggest that a single episode with critical stenosis should serve as a relative contraindication to RTP., In a review article of the available literature on the topic, Kepler and Vaccaro2 concluded that even after one incidence of transient quadriplegia, depending on the severity of the stenosis, an athlete might not be able to RTP. Similarly, Cantu50 stated that a stenotic athlete should not RTP after a single episode of transient quadriplegia because the risk for subsequent injury is too high. In the authors' opinion, the severity of the clinical episode of transient quadriparesis should impact RTP decisions on a case-by-case basis. For example, a single, isolated, mild episode of transient quadriplegia with mild symptoms that resolve within 10 seconds may not preclude an athlete from RTP, whereas an episode that results in hospitalization or paralysis, requires up to 24 hours to resolve, or has residual symptoms should serve as a contraindication to RTP.
Finally, an athlete's physical examination may demonstrate signs of impending neurologic issues that may not manifest as symptoms. Physical examination findings such as hyperreflexia, weakness or numbness of the hands, subtle gait abnormalities, and loss of hand dexterity could lead to an active diagnosis of cervical myelopathy, which should preclude RTP to contact sports.6,47 These signs may indicate a sick spinal cord that would not withstand the forces imparted from a contact or collision sport. In addition, other physical examination findings such as cervical range of motion, focal neurologic deficits, or pain with manipulation are important to consider for RTP decision-making. For example, professional league guidelines mandate that players have painless cervical range of motion before RTP.3
There is a fair amount of controversy surrounding the significance of signal changes in the cervical spinal cord, or myelomalacia, in the professional athlete population. Because this finding may indicate swelling and damage to the spinal cord parenchyma,51 some experts have opined that this should prevent an athlete from returning to a contact sport.6 Although many physicians would tolerate RTP to contact activities if the cord changes resolved after successful treatment, there is disagreement in postinjury protocols if the myelomalacia persists despite the player having a full recovery, a normal neurologic examination, and no pain after cervical insult.6
Meredith et al10 performed single-level ACDF on 3 NFL players who had cord signal change as a result of cervical disk herniation and reportedly cleared all 3 to RTP after surgery (1 actually returned to sport). In a subsequent study, Tempel et al52 cleared 3 of 4 professional contact athletes with cord signal change on T2-weighted MRI to RTP; unstable fusion, not cord signal change, prevented the fourth athlete from returning to play. The authors believe the finding of persistent myelomalacia alone should not preclude an athlete from returning to collision sports as long as there is adequate area for the spinal cord and no neurologic symptoms.
Although the best clinical outcomes after cervical spine fusion are achieved after successful bone healing fusion,53,54 the incidence of pseudarthrosis in the general population can be as high as 50%, with approximately 30% being asymptomatic54 and more commonly diagnosed in younger patients.55 Subsequently, professional athletes with significant physical demands could be at higher risk for developing a symptomatic pseudarthrosis after surgery.
There is no consensus regarding how to approach a nonunion after cervical fusion in the professional athlete.6 Some experts believe the incidence of symptoms after contact is too high, whereas others believe pseudarthrosis after a 1-level cervical fusion does not impart additional risk to the spinal cord. One important consideration is the presence of a stable fibrous union, in which there is documented stability at the index segment without full bony bridging. This finding is in contrast to an unstable pseudarthrosis, which can manifest as screw loosening or breakage, local kyphosis, or spondylolisthesis. Tempel et al52 reported stable fibrous union after ACDF in a professional collision athlete who was not cleared to RTP. The authors believe RTP protocols should differ depending on the sport played, physical examination findings, and full informed consent. It is reasonable that a stable fibrous union may be compatible with repetitive collision activities, whereas an unstable cervical pseudarthrosis is not. More data are required to address this controversy.
There are many considerations that deserve attention when making decisions regarding cervical spine conditions for an elite athlete's career. Only in the past decade have the authors seen case-control and cohort clinical studies that can help guide treatment in this patient population. For example, for a single-level cervical disk herniation, which was a controversial topic 20 years ago, the evidence-based literature now demonstrates there are different options for treatment that can lead to excellent clinical outcomes. The diagnosis of certain conditions, such as cervical stenosis, also is evolving. With the advent and further development of advanced imaging, there is the potential for additional value in the characterization of neural elements in a stenotic cervical canal. The authors believe there are critical criteria, including type of sport, imaging characteristics, patient history, and physical examination, that should be used to determine RTP in elite athletes on a case-by-case basis.
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