Cervical Pain and Disability - Part One
The amount of neck pain and disability suffered by patients varies greatly from very low pain levels and virtually no disability to high pain levels which interfere significantly with activities of daily living. The underlying reasons for this are likely to be related to the pathological and neurological mechanisms at work in the differing neck pain syndromes. Initial focus was on identifying pathology in the cervical spine which could be responsible but this approach has not led to a complete understanding. Attention has moved towards the underlying pain mechanisms potentially responsible.
The first step towards targeting more specific and accurate e.g. whiplash treatment at someone with neck pain is to understand which neck pain syndrome is dominant in the patient''s presentation. Repetitive minor events, sustained postural stresses or a defined incident such as a whiplash injury may all contribute to trauma suffered by the neck. If inflammatory changes are present due to these factors then this is understood to have profound effects on the way pain is processed in the local area of tissue damage and in the spinal cord and brain, the central nervous system. Animal research work provides most evidence but can be interpreted to understand human pain.
The central nervous system can be pushed into a state of heightened sensitivity and overreact to incoming stimuli as a result of the chain reaction caused by the injury in the locally injured part and in the spinal cord and brain. On investigation of patients with whiplash syndrome and also with more non-specific neck pain the presence of a reduced pain threshold and a reduced pain tolerance has been established. Hyperalgesia is the medical term for this increase in pain response to a normally painful stimulus.
All whiplash injuries, whatever their severity, show some degree of hyperalgesia, but those who have mild symptoms or recover completely show a decrease over 2 or 3 months. In patients with chronic and with more severe pain presentation this hyperalgesia persists. As whiplash patients are known to exhibit damaged neck and head structures after their injury, this could cause localised areas of sensitisation. A second explanation is that there has been sensitisation of the central nervous system which then overreacts to incoming stimuli, interpreting them as pain and being responsible for pain maintenance.
The internal nerve mechanisms of the central nervous system are very likely important in neck pain problems but there is evidence of ongoing pain sources in the shape of damaged neck structures. Investigation of the facet joints of the neck by injection blocks has indicated they are a pain source in some chronic whiplash pain patients. Referred pain is also a typical phenomenon, with pain being perceived away from the site of its generation. This may be because the nervous system interprets pain inputs from bodily structures such as joints and discs as related to other areas linked with the same sensory nerve pathways.
The neck segments from cervical vertebra three upwards can refer head pain whilst those from there down to the first thoracic can give arm pain. There can be an increased pain response on testing in parts of the body where there are no reports of pain symptoms from the patients. Hyperalgesia, an increased response to mechanical inputs, is common to both whiplash patients and those with general neck pain. Whiplash patients however, may exhibit more complicated neurological disturbance with increased reactions to cold, heat and pressure but these results are not well explained.
With more widespread symptoms and a higher pain level also comes a wider sensitivity response to incoming stimuli, typical findings in patients with chronic neck and arm pain from nerve root problems and with whiplash. Whiplash and cervical radiculopathy (a condition where the nerve root in the spinal cord is compromised by for example compression as it exits the spinal canal) may both cause complex excitation changes in the way the nervous system processes incoming pain signals. But this may not be the only mechanism as it might be maintained by incoming pain from damaged or injured neck muscles, joints, ligaments or discs in the neck.