Pain and Connective Tissue Properties: Tissue Repair Process
Tissue repair process
Following tissue injury, the process that in principle leads to recovery is divided into 3 overlapping phases: Inflammation, repair, and Remodelling. In fact, each part of this process is essential to the structure of the final result. Connective tissue and muscle do not regenerate if damaged, but are replaced by inferior scar tissue. To produce optimal repair tissue, all phases of this process need to be completed in the appropriate time.
Pain and Connective Tissue Properties: Chemical vs. Mechanical Pain
As the cause of pain is an important determinant of the appropriateness of mechanical therapy, it is vital to distinguish between mechanical and chemical sources of nociception. A key characteristic that indicates the possibility of pain of chemical origin is constant pain. Not all constant pain is inflammatory in nature, but chemical pain is always constant.
Key factors in the identification of pain of an inflammatory nature:
- constant pain
- shortly after onset
- cardinal signs may be present (swelling, redness, heat, tenderness)
- lasting aggravation of pain by all movements
- no movement found that reduces, abolishes, or centralises pain.
Key factors in identifying constant pain of mechanical origin:
- certain repeated movements cause lasting reduction, abolition, or centralisation of pain.
- movements in one direction worsens symptoms, whereas movements in another direction improves them
- the mechanical presentation improves with the symptoms
Pain and Connective Tissue Properties: Trauma as a cause of pain
Pain due to trauma is produced by a combination of mechanical deformation and chemical irritation. Initially, mechanical deformation causes damage to soft tissues, and pain of mechanical origin will be felt. Shortly after injury chemical substances accumulate in the damaged tissues. As soon as the concentration of these chemical irritants is sufficient to enhance the activity of the nociceptive receptor system in the surrounding tissues, pain will be felt.
Pain and Connective Tissue Properties:
Chemical Nociception
In this situation pain is produced by the irritation of free nerve endings in the presence of certain chemicals, such as histamine, serotonin, hydrogen ions, substance p and bradykinin. These chemicals are released as a result of cell damage or by cells associated with the inflammatory process. Therefore, except in the case of inflammatory or infective diseases and certain degenerative conditions, chemical pain only occurs following trauma and actual tissue damage.
Pain and Connective Tissue Properties: Activation of Nociceptors
Only three mechanisms are known that can activate nociceptors: thermal, mechanical, and chemical. Let's look at Mechanical Nociception
Mechanical nociception
Pain may be produced in the absence of actual tissue damage by excessive mechanical strain or tension upon collagen fibres. This is thought to be the result of the deformation of collagen networks so that nerve endings are squeezed between the collagen fibres with the excessive pressure perceived as pain. No damage to the tissues need have occurred, and when the stress is removed the pain will abate. Mechanical pain can ensue from normal stresses upon weakneded, damaged, or abnormal tissues. If the excessive strain is so great as to produce actual tissue damage the inflammatory process will be provoked.
Pain and Connective Tissue Properties: Central Pain
Another form of neurogenic pain may arise from cells within the central nervous system, known as central pain. Classic examples of this are phatom limb pain, post-herpetic neuralgia and the the pain from brachial plexus lesion. There is growing speculation that in some musculoskeletal pains, especially chronic conditions, central mechanisms may be more importatn in the maintanence of symptoms than peripheral nociception. Pain in this instance would be the result of abnormalities with the central nervous system.
Pain and Connective Tissue Properties: Combined States
Referred pain is either somatic or radicular in origin. These two states may be combined in one individual. For instance, a patient may have back pain of somatic origin from pressure of the annulus fibrosus, and leg pain of radicular origin, which is caused by involvement of the nerve root.
Pain and Connective Tissue Properties: Radicular Pain
Radicular or neurogenic pain is produced when the nerve root or dorsal root ganglia are involved in symptom production. This is the product of pressure on nerve roots that are already inflammed or irritated, not on normal nerve roots. Although sudden onset of sciatica does occur, experimentally tension or pressure has only reproduced radicular pain on sensitised, not normal nerve roots.
It is different in quality from somatic pain. Radicular pain is severe and shooting in quality, felt along a narrow strip, and this different in quality from the vague, dull aching associated with somatic-referred pain. All nerve root pain will be felt in the leg, and its always referred pain; oftne the leg pain will be worse than any back pain that may be present. However, all leg pain is not nerve root pain. Radicular pain tends to be distributed in dermatomal patterns, with the L4, L5, and S1 nerve roots most commonly affected. Typically pain from the L4 is felt down the anterior aspect of the thigh and leg, L5 is down the lateral aspect and S1 down the posterior aspect--however, variety exists.
Pain and Connective Tissue Properties: Somatic Pain
Somatic Pain
Somatic structures include the intervertebral disc, posterior longitudinal ligament, SIJ, facet joint capsule, etc. Only pain that originates from cutaneous tissue is felt localised to the area; all pain that stems from deep somatic structures is referred pain to a greater or lesser extent. The deeper the structure the more difficult it is to localise the pain source--therefore, most musculoskeletal pain is referred pain to a varying degree. Referred pain simply reflects the lack of localising information available with nociceptor activity from deep structures. the quality of somatic referred pain is deep and aching in quality, vague, and hard to localise.
Pain and Connective Tissue Properties: Types of Pain
Tissue injury pain relates to somatic structures, while nervous system injury pain includes neurogenic or radicular and pain generated with the central nervous system. The other source of pain that occasionally must be considered in the differential diagnosis is visceral pain from organs.
Basic Pain Types
Pain Type Structures Involved
Somatic pain Musculoskeletal tissue
Radicular pain Nerve root/dorsal root ganglion/dura
Central pain Central Nervous System
Visceral pain Visceral organs
