First, What You Should Know About Pain
Pain is perceived by the patient as coming from a particular site; and may indeed arise from a local structure but, equally, it may be referred to that site from a structure some distance away. The best example of this concept occurs in amputees who perceive pain in their amputated limbs, known as ‘phantom limb pain.” Another example occurs when pain is perceived in the neck or arm in patients with angina. An understanding of the concept referred pain is vital for successful treatment of musculoskeletal pain.
There are two types of referred pain. Radicular pain is the pain associated with nerve root compression and has the characteristic quality of sharp, shooting pain in a relatively narrow band. Radicular pain is cuased by nerve root rcompression and must, therefore, be accompanied by other neurological abnormalities, for example, paresthesia corresponding to a dermatomal distribution or muscle weakness. Nerve root compression results in a fairly consistent pattern of pain distribution, known as a dermatome. These dermatomes are mapped out and used to determine the segmental level of the nerve root compression.
The other type of referred pain is somatic pain. Somatic pain perceived in one area that originates from another. Somatic referred pain may be from myofascial trigger points or joints. Pain perceived in the hamstring and buttock, for example, may arise from one of the pain-sensitive structures of the lumbar spine, such as the annulus fibrosus of the intervertebreal disk or the aophyseal joints. Pain felt around the shoulder may originate from structures in the cervical spine. The perception of pain at a point distant to the brain source of the pain is thought to be due to the brain misinterpreting the origin of the painful stimulus. For example, impulses from pain-sensitive structures in the lumbar spine may converge with impulses from the buttock or hamstring. The brain is, therefore, unable to distinguish between the two impulses. It is important to remember that it is possible to have pain at the site distant from the source without pain at the source itself. For example, lumbar spinal structures can be the source of pain the hamstring region without causing low back pain. Local tenderness may occur even when the pain is referred from antoehr source. However, the tenderness associated with referred pain will usually be considerably less than that found when pathology is logical. Pain referred from somatic structures, unlike radicular pain, does not have a consistent distribution. Fields of referred pain from particular segments overlap greatly, both in individuals and between individuals.
Common Sites of Referred Pain
- TrPs: Trigger Points
- Occipital headache: Upper cervical spine, TrPs in upper trapezius, sternocleidomastoid
- Shoulder: Lower cervical, upper thoracic spine TrPs in supraspinatus, infraspinatus
- Lateral elbow: Lower cervical (C5-6), upper thoracic, TrPS in forearm extensor muscles, supinator and triceps
- Chest wall: Throacic spine TrPs in pectoralis major, intercostals muscles
- Sacroiliac region, loin, flank: Thoracolumbar junction (L4-5) TrPs in quadtratus lumborum
- Groin: Sacroiliac joint, thoracolumbar junction, upper lumbar spine TrPs in adductors, gluteal muscles
- Buttock, hamstring: Lumbar spine, sacroiliac joint TrPs in gluteal muscles nad piriformis
- Lateral knee/thigh: Lumbar spine TrPs in tensor fascia lata, gluteus minimus