In 1973, physicians Adrian Upton and Alan McComas introduced a concept suggesting that undiagnosed cervical spine problems could increase the incidence of extremity peripheral entrapment syndromes. They referred to this new concept as the:
Double Crush in Nerve-Entrapment Syndromes
Drs. Upton and McComas published their initial study on this Double Crush Nerve-Entrapment Syndrome in the journal The Lancet, August 18, 1973 (1). Since the introduction of this Double Crush Syndrome concept, numerous studies have supported it, and are reviewed below.
In their original article, Drs. Upton and McComas performed a comprehensive electromyographic study of 115 patients with carpal-tunnel syndromes and lesions of the ulnar nerve at the elbow. In 81 cases (70%) they found electrophysiological evidence, often supported by clinical symptoms, of associated neural lesions in the neck. They concluded that the association between carpel-tunnel syndromes, elbow ulnar nerve lesions, and electrophysiological abnormalities of the cervical spine were not “fortuitous, but rather the result of serial constraints of axoplasmic flow in nerve fibers.”
Drs. Upton and McComas note that in carpal tunnel syndrome, fibers of the median nerve are compressed beneath the transverse carpal ligament.
At surgery the median nerve can be seen:
1) To be flattened or narrowed
2) To be swollen and pink
3) To have thickened synovial sheaths around the wrist flexor tendons
Precipitating factors to developing carpal tunnel syndrome include:
1) Heavy manual work
4) Rheumatoid arthritis
5) Prior wrist injury
However, many patients who develop carpal tunnel syndrome have none of these classical precipitating factors. Drs. Upton and McComas note that:
“Many patients with clinical and electromyographic evidence of a carpal tunnel syndrome feel some pain in the forearm, elbow, upper arm, shoulder, and front and back of the chest.”
Upton and McComas make an argument why these symptoms may not be referred from the wrist, as they are commonly believed to be, but rather represent symptoms that are proximal, especially from lesions in the cervical spine. They note:
“Not all patients lose the numbness in their fingers or regain strength in their thenar muscles after surgical decompression of the median nerve” even though the diagnosis was correct and the surgical decompression was adequate.
Additionally, at times, the severity of symptoms is not proportional to the compressive pathology seen at surgery. They cite a surgical study of carpal tunnel syndrome where 29% (61/212) of the nerves showed no evidence of compression.
In their 1973 study, “in no fewer than 81 (70%) of the 115 patients with an electrophysiological-proven entrapment neuropathy there was evidence of a cervical root lesion.”
The evidence for cervical root lesion included:
1) Radiological evidence of cervical spondylosis.
2) Complaints of neck pain and stiffness.
3) “A previous history of neck injury, commonly of the hyperextension ‘whiplash’ type sustained in a rear-end motor vehicle accidents.”
4) “Clinical evidence of a sensory abnormality corresponding to a dermatomal rather than a peripheral nerve distribution.”
5) Electromyographic evidence of denervation of other muscles that are supplied by the nerve root.
Drs. Upton and McComas state:
“Most patients with carpal tunnel syndromes or ulnar neuropathies not only have compressive lesions at the wrist or elbow, but they also have evidence of damage at the level of the cervical roots.”
A cervical lesion would explain the presence of pain in the shoulder and upper arm, the variable nerve pathology seen at the wrist, and the surgical failure of cases with adequate wrist nerve decompression. Neural function is impaired because “single axon compression at one region becomes especially susceptible to damage at another [peripheral] site.” Slight degrees of nerve compression may cause no symptoms, but reduce the axoplasmic flow of trophic substances, so that a slight distal compression may add to the reduction of axoplasmic flow of trophic substances, causing symptoms.
Even though Drs. Upton and McComas refer to such a phenomenon as a “double crush,” they “accept” that “in some patients, especially those with a history of neck injury, the proximal lesion may have been excessive stretch, rather than compression, of the nerve fibers.”
Drs. Upton and McComas end their study by noting:
“Treatment, rather than being directed at a single site, should be applied to all vulnerable points along the course of the nerve—i.e., to both the neck and to the wrist or elbow, depending on the nerve involved.”
The Double Crush Nerve-Entrapment Syndrome is an important concept for all providers that treat peripheral entrapment syndromes, such as carpel tunnel syndrome. It indicates that a majority of such patients may also have proximal neurological lesions that also require treatment, starting at the level of the cervical nerve roots. A summary of the key points from this study by Drs. Upton and McComas include:
1) The DOUBLE CRUSH SYNDROME is: serial constraints of axoplasmic flow in nerve fibers increasing the susceptibility of distal axons, of that nerve, to compression syndromes and symptomatology.
2) Surgical decompression of the wrist clearly does not fix all the patients with carpal tunnel syndrome.
3) In this study, 70% of the patients with an electrophysiological-proven entrapment neuropathy had evidence of a cervical nerve root lesion.
4) The most common history for those with a double crush syndrome is that of “A previous history of neck injury, commonly of the hyperextension ‘whiplash’ type sustained in a rear-end motor vehicle accident.”
5) The most common non-local complaint for those with a double crush syndrome is neck pain and stiffness.
6) The most common examination finding for those with a double crush syndrome is evidence of cervical spondylosis.
7) “Most patients with carpal tunnel syndromes or ulnar neuropathies not only have compressive lesions at the wrist or elbow, but they also have evidence of damage at the level of the cervical roots.”
8) Even though these authors refer to such a phenomenon as a “double crush,” they “accept” that “in some patients, especially those with a history of neck injury, the proximal lesion may have been excessive stretch, rather than compression, of the nerve fibers.”
9) In the treatment of peripheral neuropathies (such as carpal tunnel syndrome) “treatment, rather than being directed at a single site, should be applied to all vulnerable points along the course of the nerve—i.e., to both the neck and to the wrist or elbow, depending on the nerve involved.”
In 1975, the International Conference on the Approaches to the Validation of Manipulation Therapy was held at the University of California, Irvine. •••••• renowned international spinal experts contributed to the conference. The Proceedings from the conference were published in 1977 (2). Chapter 7 of the book is authored by Dr. Adrian Upton, one of the originators of the Double Crush Hypothesis. In his chapter, Dr. Upton restates his Double Crush Hypothesis as follows:
“Serial lesions along the course of nerve axons may predispose to nerve damage more distally, possibly by serial constraints on axoplasmic flow; hence the proximal symptoms in a patient with carpal tunnel syndrome may be due to nerve root impairment which has predisposed them to a distal entrapment neuropathy.”
“Serial constraints on axoplasmic flow may be responsible for increasing the susceptibility of nerve axons to distal impairment.”
In his discussion, Dr. Upton includes not only the median nerve as related to
carpal tunnel syndrome, but also extends his discussion to include the ulnar nerve as well as the sciatic nerve.
More than a decade after the original study of the Double Crush Nerve-Entrapment Syndrome by Drs. Adrian Upton and Alan McComas, a follow-up study was published in the British Journal of Hand Surgery, titled (3):
The relationship of the double crush to carpal tunnel syndrome
(an analysis of 1,000 cases of carpal tunnel syndrome)
In this study, the authors reviewed 1,000 cases of carpal tunnel syndrome and found that in 888 patients (89%), “there is a statistically significant incidence of bilaterality in patients with cervical arthritis.” They note that their findings “lend further support to Upton’s Double Crush hypothesis.”
Additionally, these authors note that in those suffering from the double crush syndrome subsequent to cervical spine lesions, there is an increased probability that the carpel tunnel syndrome will exist bilaterally. They also note that bilateral carpel tunnel syndrome subsequent to cervical spine Double Crush is associated with a worse prognosis for clinical recovery. This may be an explanation for some of the failures following carpal tunnel surgery, and surgeons to look for associated mechanical blocks (Double Crush Syndrome), “when attempting to alleviate recalcitrant symptoms.”
This article also makes a special note of the finding that systemic diseases, especially diabetes mellitus, can predispose an individual to both peripheral entrapment syndromes as well as to “Double Crush Syndromes.”
Three years later, in 1988, Dr. Osterman from the Hospital of the University of Pennsylvania, Philadelphia, published in the journal Orthopedic Clinics of North America an article titled (4):
The Double Crush Syndrome
In this article, Dr. Osterman makes the following points:
This article adds to the literature supporting the existence of a double crush
peripheral nerve entrapment syndrome. Additionally, this author stresses the need to treat the proximal neurological lesion in an effort to achieve maximum benefit of peripheral management, including surgery. In essence, if the cervical spine is involved in a double crush capacity, it should be appropriately treated.
Primary experimental evidence to support the double crush hypothesis was presented in 1991 (5) by Drs. Dellon and Mackinnon from the Division of Plastic Surgery, Johns Hopkins University School of Medicine, Toronto, Ontario, Canada. Their paper was published in the Annals of Plastic Surgery, and titled:
Chronic nerve compression model for the double crush hypothesis
In this article, Drs. Dellon and Mackinnon make the following points:
This experimental animal study is the first to offer viable evidence that there
is a scientific basis for the Double Crush Syndrome that had been used to describe observations on human subjects.
In 1994, Drs. Raps and Rubin from the Department of Neurology, Hospital for Special Surgery, New York, NY, published an article that consisted of two case studies of proximal median neuropathy associated with cervical radiculopathy which they diagnosed in their EMG laboratory. Their paper was published in the journal Electromyography and Clinical Neurophysiology (6), and titled:
Proximal median neuropathy and cervical radiculopathy:
double crush revisited
In their paper, Drs. Raps and Rubin note:
In 1999, Drs. from St. Mary’s Hospital associated with Yale University School of Medicine in Waterbury, CT, presented two cases of nerve compression consistent with the Double Crush Syndrome. Their paper was published in Connecticut Medicine (7), and titled:
The double-crush phenomenon:
an unusual presentation and literature review
As noted, in their review of the literature, the authors made the following points:
Importantly, this 1999 article reiterates the relevance of cervical and/or thoracic spinal problems adversely affecting the nerve roots as contributing to the peripheral double crush phenomenon. It also reiterates the issue of systemic metabolic problems, such as diabetes.
More recently, in 2003, Drs. Pierre-Jerome and Bekkelund from the Department of Radiology, Ulleval University Hospital, Oslo, Norway, published a study in the Scandinavian Journal of Plastic and Reconstructive Hand Surgery (8), and titled: