By Dr. Matt Janzen and Dr. Josh Woggon
This article was originally published in The American Chiropractor in August 2014. Drs. Michael and Matthew Janzen of Janzen and Janzen Chiropractic in Campbell, CA, have a YouTube channel where they demonstrate the Cox sign, as well as the theory behind spinal cord tension in scoliosis. You can access these videos here: https://www.youtube.com/user/janzenandjanzen
Several years ago, a patient came to my office with low back pain. During a routine exam, while performing the Straight Leg Raise, the pelvis lifted off of the table with the leg. Although I was unaware of the significance of this finding, practitioners of the Cox technique may recognize this as the Cox sign, introduced by Dr. James Cox. At the time, I assumed it was caused by tightness in the hamstrings, which correlated with the other signs of pelvic and lumbar dysfunction in this individual. Presuming an uncomplicated case of back pain, I prescribed a six-visit treatment plan. After five visits, the patient discontinued care with no explanation. Following up with him, I learned that his back symptoms had resolved, but numbness, tingling, and weakness had manifested in the lower extremities. He had visited with another chiropractor, who referred him for a surgical consultation.
It’s often said that we learn more from our failures than our successes, and this case was no exception. The feeling that I could have helped this patient if only I had understood more about his condition inspired me to begin studying the Cox Low Back Pain textbook, which is when I came across the Cox sign. According to Dr. Cox,1 “Cox’s sign occurs when, during SLR, the pelvis rises from the table rather than the hip flexing. I have noticed this occurrence in patients with prolapse into the intervertebral foramen – a grave condition.” Due to the circumstances, the Cox sign became a particularly meaningful test for me. There were none of the other classic signs of disc problems in this patient; the Cox sign was the only indicator of underlying disc pathophysiology.
I now recognize that the palpable sense of the Cox sign differs greatly from simple tightness of the hamstring, where there is a gradual increase in muscle tension until it starts becoming uncomfortable. With a Cox sign, there is free range of motion throughout the maneuver, then a sudden lock when the pelvis will lift. This sudden lock, or resistance of the hip to further flexion, is presumed to be due to a neurologic tension (sciatic nerve), rather than a muscular tension (hamstring).
With a positive Cox sign, the transition to resistance is very dramatic and very sudden, and is drastically different from a patient who does not have nerve tension. The Cox sign can be easy to miss when you are not specifically observing for it. To improve sensitivity for detecting the Cox sign, one can elongate the neuroaxis of the patient by placing a fulcrum under the low back along with a large pillow to place the neck in flexion. It may show up at 40 degrees, or as high as 80 or 90.
A few years ago, I began focusing heavily on managing cases of scoliosis. Looking for the Cox sign continued to be a part of my routine procedures, and we began detecting it frequently in this population. Whereas before we would note a positive Cox sign one to three times annually, we were now seeing this in scoliosis patients on a daily basis.
This was merely a curious finding at first. Since the cases observed were children with normal disc signal on MRI, it was assumed that the nerve tension we were observing with the Cox sign was a result of the scoliosis (e.g., we thought the extreme twisting and bending of the spine was probably causing the nerve tension). However, one day we were testing a young adolescent with only an 18 degree scoliosis. Upon straight leg raise, a Cox sign appeared at around 55 degrees of straight leg raise. Such a small curve could not reasonably be the cause of such significant nerve tension. The nerve tension was occurring even before the spine became significantly twisted. This led us to suspect that the Cox sign and the nerve tension might actually be preceding the development of the scoliotic curve.
The concept of nerve tension, specifically tension in the spinal cord, being the cause of scoliosis was first proposed by Dr. Roth in 1968.2 Dr. Roth proposed that a spinal cord that was short relative to the length of the vertebral column may result in a tension that causes the spine to “coil down” around the axis of the spinal cord. Such a theory provides a logical explanation for the paradoxical rotation of the vertebra in a scoliosis, in that the vertebrae rotate opposite to the spinal cord.3 The work of Chu et al supports this hypothesis, namely, “that anterior spinal column overgrowth relative to a normal length spinal cord exerts a stretching tethering force between the two ends, cranially and caudally leading to the initiation and progression of thoracic AIS.”4
This new theory has been termed “Uncoupled Neuro-Osseous Development,” which states according to Porter, “in some patients with scoliosis there is disproportionate neuro-osseous growth – the longitudinal growth of the spinal cord fails to keep pace with the growth of the vertebral column and, as a consequence, the spine buckles into a scoliosis deformity.”5 Porter points out that many abnormalities associated with scoliosis can be explained well in that they may contribute to asynchronous neuro-osseous development and hence spinal cord tension. For example, dysfunction of the pineal gland and melatonin have been implicated in scoliosis. Such dysfunction of the endocrine system is theorized to contribute to an asynchronous neuro-osseous development. Since Porter’s article in 2001, there has been a growing awareness of this theory in the published literature.6,7
Dr. James Cox proposed the Cox sign as an observation of extreme nerve tension caused by more severely entrapped nerve roots. Now we are seeing that same Cox sign in a child-onset condition in which nerve tension is the leading theory for causation. If the Cox sign is truly and reliably indicative of underlying nerve tension in a child, it may help to identify individuals who are at-risk for developing scoliosis.
A personal anecdotal story supporting this theory was the appearance of the Cox sign in my daughter at 6 and ½ years old. I was shocked the evening I first observed this, realizing the potential implication in my own daughter. I followed up with a postural evaluation and scoliometry, yet there was no evidence any curvature or rotation as would occur in scoliosis. However, if the Cox sign was indicative of a nerve tension that can cause scoliosis, it meant that my daughter was at very high risk for a future scoliotic curve. Over the course of a year the Cox sign persisted. When our daughter was 8 years old we performed a standing 3D full spine MRI, which revealed a 13 degree left lumbar scoliosis. Seated MRI revealed a 21 degree scoliosis – a common finding of a true scoliosis for the curve size to increase as the patient sits versus stands.
It must be recognized that idiopathic scoliosis is not a diagnosis but rather a lack of one. Multiple distinct and separate disease entities will fall under the umbrella term of IS, and not every case of idiopathic scoliosis may be caused by nerve tension. However, in the overwhelming majority of IS cases tested in our office, obvious clinical signs of nerve tension are consistently found.
Currently, difficult and time-consuming MRI techniques are being researched to uncover evidence of spinal cord tension in IS cases. Expensive and complex genetics tests are being developed to attempt to predict risk for progression. All of this technology still only catches the problem quite late in the game – only after a scoliosis has had a chance to significantly deform the structure of a spine. If the Cox sign proves to be a reliable predictor of a root-driving force for IS, then detecting scoliosis before it occurs may actually become a reality.
If the Cox Test could prove to be quick, inexpensive early detection test for scoliosis, it could easily be performed routinely by chiropractors and pediatricians to detect scoliosis before it even occurs. While further research is needed to draw conclusions, the chiropractic profession has the opportunity to lead the way in this potentially ground-breaking early scoliosis detection research.