Peripheral nerve injury is an entity that is commonly encountered by physical therapists in their day to day practice. The scope of management would be to rely on the medical model to determine the type and status of the injury depending on the extent of disruption of nerve tissue and the resultant sequelae from a motor and functional perspective. Essentially then diagnostic determinants are based on the classification by Seddon1 and are as follows:
The first category is referred to the physical therapist for the most part and of a lesser prevalence category two. Category three is invariably a surgical referral. In any given situation there is an obvious functional loss by the time the patient is on your treatment table, say a ‘foot drop’ or a ‘wrist drop’. Pain as the main entity, without obvious functional loss may not be considered from a neural perspective. It is usually seen as a global neuroorthopedic entity as in ‘cervical spondylosis with radiculopathy’ or ‘sciatica’.
The bigger focus in this literature review is ‘pain’ and the neural determinants of pain, hence the diagnostic criteria may not follow the Seddon classification. Rather the pathologies of reference are preneuropraxic and ‘pain’ invariably being a bigger factor than ‘motor loss’.
As physical therapists, we are most concerned about movement and we aim to treat pathologic motion. We apply this sound conceptual basis to the musculoskeletal system and call it biomechanics for normal movement and pathomechanics for abnormal motion. Can the peripheral neural system be considered a movable system and can the above concepts be applied to it? Most certainly and the concept long described. The pioneers in this field call it neurodynamics and are principally concerned about the movement of peripheral neural tissue.2
As our body moves, and along with it the extremities, the soft tissue, including muscle fascia and ligaments modify their length to adapt for the movement changes. The peripheral nerves that traverse the extremities will hence also have to modify their length to adapt for the length changes with movement. It is obvious then that a certain amount of gliding occurs in these nerves and this helps to adapt for the changes in length. Hence, the postulation is, from the origin of the nerve in the spinal cord, to its termination, it has to traverse through connective tissue, bone, muscle and fascia which may be in the form of fibroosseous tunnels, and these are the milieu through which they glide. They may hence, due to faulty mechanics and dysfunctional states, be entrapped in these areas that they traverse through and result in pathology. The chemical effusion that results from dysfunctional states of the mileu has also been considered as added predisposition to dysfunction and pain.5 We call this an external entrapment. In addition the nerve can experience entrapment in the individual nerve fascicles which would also result in dysfunction. This would constitute an internal entrapment.
Mechanical extremity nerve pain has been traditionally viewed as originating from abnormal changes in the spinal canal. The commonest described causes are herniations of the nucleus pulposis, degenerative spinal and foraminal stenosis, fractures and spondylolisthesis. The term mechanical implies pathology of a neuromusculoskeletal origin rather than a disease process as in neurilemomas, anerysms, tumors, hematomas, diabetes, etc. However, contemporary research has shown that radicular pain may not necessarily occur secondary to changes within the spine.3 Nerve irritation that occur outside the spine are called extraspinal lesions. When a detail clinical and radiological investigation rules out the possible existence of a nonmechanical cause (tumors, abscesses, nerve disease, etc.) for nerve pain, the situation may leave the clinician to investigate the possible mechanical origin of the pain. Standard examination procedures however, aim at identifying a spinal origin for the symptoms, unfortunately though, a variety of possible extraspinal causes may exist. These extraspinal sites of nerve irritation may be the bone, muscle, fascia, and ligaments that the nerve glides through following its exit at the vertebral foramen. Awareness of this fact is mandatory as mechanical radicular pain in the extremities, by default, are assumed to be of a spinal origin. Indeed, most often it is the case, but what if not. Newer research has made it easier by the application of clinical prediction rules, as in a cluster of tests to identify the presence of pain of a spinal origin.4 If symptoms are not modified or altered by the application of this cluster of tests, then the assumption is made that the pain is not of a spinal origin. However, it is considered astute to prioritize the possibility of a spinal origin of symptoms and hence careful examination is warranted.
A collective description of spinal and extraspinal mechanical causes of radicular pain in the spine and extremity may enable the clinician to make a differential diagnosis and arrive at a more specific conclusion as to the site of irritation. This literature review aims to collectively describe the possible spinal and extraspinal causes of radicular pain which are of a mechanical origin to enable the clinician to make a more accurate diagnosis and help avoid unnecessary and expensive diagnostic and surgical procedures.
- Andrew Kaye. Classification of Nerve Injuries; in Essential Neurosurgery. Churchill Livingstone. 1991. pp. 333-4.
- Nee R J, Butler D. Management of peripheral neuropathic pain: Integrating neurobiology, neurodynamics, and clinical evidence: Physical Therapy in Sport 2006;2(7):36-49.
- Lewis AM, Layzer R, Engstrom JW, et al. Magnetic Resonance Neurography in Extraspinal Sciatica. Arch Neurol 2006;63:1469-72.
- Wainner RS, Fritz JM, Irrgang JJ, Boninger ML, Delitto A, Allison S. Reliability and diagnostic accuracy of the clinical examination and patient self-report measures for cervical radiculopathy. Spine 2003;28(1):52-62.
- Takahashi N, Yabuki S, Aoki Y, Kikuchi S. Pathomechanisms of nerve root injury caused by disk herniation: An experimental study of mechanical compression and chemical irritation. Spine 2003;28(5):435-41.