Massachusetts General Hospital surgeons have proposed the development of a screening measurement to determine the likelihood of prospective National Football League (NFL) players suffering a potentially career-ending degree of cervical stenosis. This research was presented by Mark Callanan (Massachusetts General Hospital and Harvard Medical School, Boston, USA) at the American Academy of Orthopaedic Surgeons 2018 Meeting (6–10 March, New Orleans, USA).
The NFL Scouting combine is a week-long showcase occurring every February at Lucas Oil Stadium in Indianapolis, USA, where college football players perform physical and mental tests in front of NFL coaches and scouts. As part of the assessment process, all prospective athletes undergo a medical history review by physicians. This informs decisions that are hugely impactful for the young players: which athletes are picked, where they are selected, and ultimately what type of sporting careers they will have.
Having spinal stenosis, a narrowing of the spinal canal, increases the risk of damaging nervous structures from a collision, potentially leading to paralysis, so can be especially detrimental for an athlete, as they are at more risk of experiencing a traumatic collision. Thomas Cha (Massachusetts General Hospital and Harvard Medical School, Boston, USA), study co-author, comments, “It comes into play a lot more with athletes, because obviously they are in a higher risk environment. This particular [hypothetical] athlete might not have a nerve injury or nerve problem now, but that next fall or that next collision, they could, and they end up neurologically compromised, so the effects are catastrophic. It is therefore very important to get as accurate a prediction as possible.”
For common sporting injury sites, such as the knee and shoulder, certain injuries or radiographic findings can guide the physician to decide whether, “this person’s shoulder is too far gone, or it is able to be rehabilitated, and they can keep a functional career”, explains Cha. In this study, the aim was to develop this type of analysis for cervical spine injuries, and to see if it was possible to use an X-ray screening method to demonstrate stenosis.
According to the study investigators, the measurement and clinical interpretation of cervical stenosis in high-level collision athletes remains an ongoing debate. The current best estimate is that there are 0.6 catastrophic cervical spine injuries per 100,000 player exposures, with previous studies determining that it was the location most frequently injured, as well as most likely to be symptomatic in young retired NFL athletes.
Despite this, there are currently no widely accepted criteria for the optimal measurement of cervical stenosis, nor an established value of measured stenosis that reliably correlated to injury risk in elite level contact athletes to serve as a screening tool.
Cha and colleagues therefore set out to apply previously described methods of measuring and calculating cervical stenosis to radiographs and magnetic resonance imaging (MRI) scans in a cohort of NFL-calibre collision athletes, and determine their utility for predicting injury or stenosis in this population. The study involved a retrospective analysis of an NFL combine injury database from 2009–2015, reviewing data for all 382 patients with previous documented cervical spine injury.
Calculating the ratio of lateral mass/canal diameter (LM/ CD) at the C5 vertebrae was evidenced to be a more optimal screening measurement for determining cervical stenosis in NFL-calibre athletes, and did not require the use of MRI. Cha explains why an X-ray is preferable as a screening study to an MRI: “An MRI study takes much longer, and is more expensive. Also, it is difficult to use an MRI for screening more generally as not every hospital has an MRI machine, so it is not widespread in terms of availability and usage—it is a much more involved procedure. An X-ray is more readily available, and can yield study results more quickly.”
In addition to the LM/CD ratio, the measurements the investigators used were mid sagittal canal diameter and the Torg ratio. The mid sagittal canal diameter demonstrated no significant sensitivity or specificity for revealing stenosis measurements, and so would not be a suitable screening tool. However, there was a non-statistically significant correlation between a having a smaller mid sagittal canal diameter and a cervical disc herniation. The LM/ CD ratio is able to predict when a smaller canal diameter is potentially a cause for concern, and when it is ample enough to not cause stenosis.
The Torg ratio is the spinal canal-tovertebral body ratio, and is determined by dividing the sagittal diameter of the spinal canal by the sagittal diameter of the vertebral body. It has been used for assessing the presence of developmental spinal canal stenosis and/ or likelihood for spinal cord compression when interpreting an MRI since it was first described in the twentieth century. A ratio of <0.7 indicates significant spinal stenosis and increased risk for neurological injury.
However, Cha describes the results of this study as, “Another example of the poor performance of the Torg ratio as a screening measurement for developmental stenosis.” He expands: “There have been recent studies showing that the Torg ratio is perhaps not as sensitive or specific at predicting canal stenosis as previously thought, so that is one of the reasons why we looked into comparing other methods [of predicting spinal canal stenosis] to the Torg ratio, to see if there could be something a little bit better.”
In this particular study, the Torg ratio underestimated the amount of cervical stenosis, so was not effective as a screening tool, despite its historical use in this capacity. This has been demonstrated already in the general population, but this is the first time that the Torg ratio’s ineptitude as a screening measure for stenosis has been proved in NFL combine athletes.
Speaking to Spinal News International, Cha also reported a correlation between certain types of cervical injury diagnoses and the compression ratio. The compression ratio is a comparison of the anterior and posterior sagittal diameters with the transverse (side-to side) measurement of the canal. This is therefore a measure of canal shape: two patients could have a similar canal area, but different compression ratios, if the spinal canal was, for example, more oblong in one individual. The results show that this more oblong shape, where the spinal cord is squeezed slightly in the front to back axis, more frequently occurs in people with stingers. A stinger is felt as a burning sensation, and is caused by restriction of the nerves leading to the brachial plexus, a nesting of nerves in the shoulder.
Cha cited a downside of the study as the fact that it was retrospective: “It is very difficult to make that next leap and use this kind of data to predict [spinal stenosis], but that is ultimately how it is going to be used, but you have got to be careful about basing predictions off of these study results.”
Though this screening measurement is a step towards improved predictive power for athletes with potentially damaging spinal stenosis, Cha cautions, “There is no absolute value where we can say with certainty ‘this is a no go here’. This is all guided expert opinion: people are making these decisions all across the country, so we have tried to colour these decisions a bit with some data, but there isn’t a hard and fast number where we would say ‘absolutely not’. We take it on a case by case basis.”
“The goal is that, if an athlete comes in with a history of this type of [cervical] injury, we can tell them they have a lower probability of having a long career because of this injury. Our findings help to inform what we eventually want to be able to do: to predict life changing stenosis in NFL athletes.”