How the body heals following injury. This is long but good!

OK! It's long but it's really good!

The following information is a synthesis of appropriate literature to explain the mechanisms involved in healing post injury.  The mechanism here is the one I try to explain for motor vehicle injuries.  The reference numbers are for the articles I have cited for the paper but I’ve left them out of this blog.  The same mechanism works for most tissues in the body but I’ve written it for spinal based injury.

Here we go….

It is important to know what happens when soft tissue is injured to understand the healing process that the patient has gone through. There are basically two processes- the first is the physical healing with scar tissue and how that affects the tissue; the second is the neurologic consequences from the trauma.

Damaged soft tissue takes approximately one year to heal. Healing occurs in three specific phases. The first phase, called the acute inflammatory phase, will last for approximately 72 hours. (1,3) During this phase there is death of damaged cells and continuous bleeding into and around the damaged tissues. (2,3) Chemicals are released that trigger the inflammatory response which causes fluid to be pumped into the damaged area thereby immobilizing the damaged tissue. (3) This fluid build up and the chemistry from the damaged cells causes pain to be perceived. (1,3) Muscles tighten to protect the damaged area in an attempt to further immobilize it. (3) Therefore, it is not uncommon for the patient to feel worse for the first few days. Normally, within several days the cellular debris is removed from the area and with less debris there is less impetus for the inflammatory response, leading to less muscle spasm and more patient comfort. This process occurs normally over a 10 to 14 day period. (3)

Seventy-two hours following injury, the damaged tissues start to repair.   (1) This begins the second phase of healing called the phase of regeneration when the tears in the damaged muscles, ligaments, and other tissues are repaired. (1,3) Cells called fibrocytes are attracted to the area by the chemical exudates of the damaged cells. (3) These fibrocytes manufacture and secrete collagen protein glues (known as scar tissue or fibrotic tissue) in order to bridge the gap in the torn tissues. (1,3) This phase will last approximately 6-8 weeks. (1,3) At the end of 6-8 weeks the gap in the torn tissues is totally bridged with a strong but inelastic matting of scar tissue fibers. Pain may not be present during the end stage of this phase because the inflammation and subsequent protective muscle spasm are reduced but the diminishment of pain does not mean that healing is finished. 

There is a third and final phase of healing called the phase of remodeling. (1,3)  It starts near the end of the phase of regeneration. The scar tissue that was laid down for repair is remodeled in the direction of stress and strain forces acting upon the tissue. (3) The collagen fibers in the scar will slowly become stronger and will change their orientation from an irregular pattern to a more regular pattern. (3) The goal is to make the repair tissue look and act the same as the original tissue before it was damaged. Scar tissue may never restore the damaged tissue to an original state even in the absence of pain but proper treatment is necessary if we are to get optimal results from healing. Healing takes place as a direct by-product of motion. Chiropractic health care is an ideal method of treatment for this type of injury because it puts motion into tissues in an effort to line the fibers up along the directions of stress and strain, thereby providing a more elastic healing. (5) 

Tissues have three ranges of motion; the active range where a tissue can move without force; the passive range where much more motion is available with an activity like stretching or mobilization; and the periarticular paraphysiological range where the minute amount of motion that is still residual after the passive range is at maximum, and this is achieved through joint manipulation. Chiropractic joint manipulation moves the tissue through the three distinct ranges of its motion. This is a benefit to the patient because most other forms of health care only focus on one or two ranges of motion. Exercise, electric modalities, drugs, and mobilization techniques only allow motion of the joint tissue into a maximum of two of the three ranges. Unlike chiropractic manipulation they do not move the tissues into the periarticular paraphysiological range. When this space is attained there is a tearing of cross bonded and matted scar tissue fibers which, up to this point, were restricting motion. (5)  Therefore, chiropractic osseous joint manipulation is the treatment of choice for the remodeling of periarticular soft tissues that have been injured and scarred. (1,3,6)

There are some problems associated with the healing of injured soft tissues. Microscopic studies show that the repaired tissue is different from the original, adjacent, undamaged tissue. The scarring (fibrosis) of the damaged tissue creates problems which can adversely affect those tissues for years, or even forever. (1,3,6) The fibrosed tissues are functionally different than the adjacent normal tissues. (3) The differences fall into three main categories; (1) the repaired tissue is weaker due to the smaller diameter of the scar tissue fibers, (2) the repaired tissue is stiffer or less elastic because the healing fibers are not aligned identically to the original undamaged tissue, (they are aligned across the plane of motion), and, (3) there are more pain fibers in the repair tissue therefore the repair tissue is more sensitive or sore to pressure. (1,3,24) Due to the fibrous scar tissue rendering the tissues weaker, less elastic and more pain sensitive, the patient will have a history of flare-ups of pain and/or spasm at times of increased use or stress. (12,24) These flare-ups are the rule, not the exception, and are a cause of the patient's problems. (14,17,18,19)   It is likely that the patient will have a need for continuing care subsequent to these episodes.

The health care for the injuries sustained in an accident is designed to change the fibrotic nature of a repairative process that has left the patient with residuals that are weaker, stiffer, more painful, and for some patients, permanent. Patients will have to learn to deal with the occasional episodes of pain and/or spasm and will not necessarily feel better in the prescribed time for healing. (17,18,19)

The “normal” person does a poor job of maintaining optimum tissue motion and elasticity over a lifetime. Degenerative processes (called “wear and tear”) occur due to long term, abnormal mechanical function of the tissues including low grade inflammation of the joint and disc tissues and typically become more pronounced with age. (1,2)  Degeneration can occur in the absence of pain but pain is only perceived when a threshold level is exceeded. (2) The repair process alters the mechanics of the joints and disc and degeneration of the tissues is increased following injury. (1) The patient's motor vehicle accident puts him at a greater risk of degenerative change over time because of the way it has altered his tissues. (1,2)

There is a new model that has been proposed to explain recurrent spinal pain. The issue is one of neurologic control of spinal segments and how loss of that neurologic control has devastating results for the patient. I will summarize some representative current literature and explain how this new model is important in this case.

The spine has been described as having three layers of muscular support. (40) The deep layer consists of vertebrae, discs, ligaments and muscles. (40) The muscles are small and seemingly weak with less of a motion function and more of a neurologic feedback function. (26,27) This deep layer performs the stabilization of the spinal column and provides the central nervous system with information about position sense of every structure in the spine. (26,27,34) Discs, small muscles and ligaments are well innervated with position sense fibers (proprioceptors). (40,52) The finer the movements required by the individual segments of the spine, the more the innervation. (28,54) . The central nervous system requires a huge barrage of information without errors to ensure that coordinated motion occurs properly. (40) When there is damage to the structures in the deep layer, there are corresponding errors made by the central nervous system in controlling motion. (10,34) For example, the cervical spine performs many fine discreet motions of coordination but a motor vehicle accident injury can cause alterations in proprioceptive input in the cervical spine, altering the function of the spine.

The middle layer consists of muscles which function to stabilize and allow the spine to move properly. (40) The multifidus is the muscle most used in extension. (25,25,40) Middle layer muscles are neurologically preactivated before virtually any form of movement. (29,40) Therefore even slight movements of muscles far away from the spine (for example: lifting an arm) will not cause a loss of balance. (29,40) With trauma to the spine, a middle layer muscle called the Transversus Abdominis loses its sequenced firing and is not stabilizing the spine at the right time. (29,30,31) In the lumbar spine this process is the cause of many of the acute spasms of pain experienced with forward flexion. (32) This causes an overuse of the multifidus muscles which are then turned off by the nervous system in order to protect the joint. (30,35) Larger outer layer muscles then compensate by spasm. (13) The multifidus muscles immediately start to atrophy from lack of neurologic control and from disuse as the large muscles take over causing fatty infiltration of the muscles. (25,30,33,34) Larger muscles then take over the responsibility for joint motion but as they are large, they lack the ability to coordinate fine motion. (35) This is a very important piece of the puzzle of spinal pain and we need to restore the neurologic feedback to the middle layer muscles in order for them to stabilize the spine effectively. (10)

 In whiplash type injuries there is damage to the neurologic mechanisms controlling deep and middle layer muscles of the neck. (41) In the neck, the muscles which show fatty infiltration are the rectus capitus posterior major and minor and the multifidus. (36,41) Following injury, the longus colli and longissimus cervicis muscle activity is much less than the large muscles like the scalenes and sternocleidomastoid which are in spasm to limit joint use. (13,42) This alters the normal functional stability of the joints and increases the chance of re-injury which can set up chronic pain patterns and increase the chance of degeneration over the long term. (12,19)
 
The outer layer is made up of the big muscles which create body movement. (40) These muscles are easily seen and because they are big, create such great power. (40) We have tended to pay a lot of attention to them in the gym and certainly have from the perspective of rehabilitating the patient. (40) But results have been disappointing using the old methods of stretch and strengthening the large muscle groups. (39) The new model suggests that treatments which stimulate proper nerve coordination of the small muscles combined with a program designed to strengthen specifically the small muscles of the spine is the best way to restore motion to the patient. (40,48,49)
Manipulation is a logical way to stimulate the nerves in the joint ligaments which can cause activation of the intersegmental muscles. (7,35,46) Stimulating the proprioceptors from an early stage of treatment prevents atrophy of the muscles as well as recruiting resting, unused proprioceptors in surrounding tissues to help with coordinated motion. (55) Spinal manipulation of the joint increases the ability of the nervous system to access the small and middle layer muscles which were turned off following trauma. (35,46) It also decreases muscle spasm of the large outer layer muscles. (7,46) Spinal manipulation increases proprioceptor firing which decreases pain, increases coordinated motion of the segments and also increases balance sense. (10) In the future, rehabilitation will be aimed at the neurologic mechanisms of the deep layer to normalize the output from those structures, and to retrain the sequencing and strength of the deep and middle muscles. (40,45) Patients who get manipulation and do proprioceptor retraining exercises have much better results than those getting manipulation or exercise alone. (43,44,45)
 
Spinal ligaments provide nerve information (proprioception) to the central nervous system about the ability of the particular segment to move. (4,27,51) Muscles, tendons, discs and ligaments all provide position information. (11,27,28,52) With injury there is damage to this information flow. It is either not flowing or is flowing incorrectly. (4,11) If there is a decrease in the information into the spinal cord it causes an inhibition of the deep segmental muscles. (47,53) As well, the proprioceptive input into the spinal cord inhibits pain perception. (56) If the proprioceptive input is diminished, there is no inhibition of pain, which may explain why patients with chronic and recurrent pain continue to have problems, as pain may be more readily experienced. (41) Inflamation also increases firing of pain receptors. (9,24) The literature shows that 80 - 90 percent of patients will have recurrence of their spinal pain, two thirds of them within a year. (15,16,18,52) Neck pain patients have a prevalence of recurrence up to 70% in their lifetime. (18,19,20)

 The goal for the patient is to restore function which can be achieved through several modalities. (17,45) First, the proprioceptive input to the central nervous system must be re-established. Manipulation is an excellent tool for this. (22,35) As well, specific exercise programs are essential. (50) Next, the middle layer muscles must be recruited, sequenced, strengthened, made more dense and increased in size. (37,38) Finally, even though it sounds obvious, the patients will have to be patient because this does not happen overnight. The patient's must attend treatment sessions if they plan on getting optimal results. (22,35,45) They also have to be treated frequently to achieve change and to avoid becoming chronic. (21,22,23,37) Finally they must learn how to continue on their own following treatment.(8,37)

They will no doubt have some residuals from the trauma and left untreated, these will continue to cause compensatory mechanisms to come in to play with the result being recurrence of pain as well as degeneration of motion. (14,17,18,19,33,50) By restoring function the patient should have the painless mobility and coordinated motion that they were born with. (53) The problem though, is that once damage has occurred , the sequella of healing (including inflammation, scar tissue formation, pain supersensitivity, degenerative change, neurologic inhibition of spinal muscle, coordinated motion and pain) is such that full restoration to normal is almost impossible. (14,18,25,33)

It is difficult to accurately view these types of changes in a single patient and many of our tests are far too basic, too expensive for clinical practice, or too time consuming to be practical in determining the exact causes of a patient’s discomforts. (24) It is easy to understand a case based on a gross deficit like a missing limb, but very difficult to assess the future of a patient who has lost subtle neurologic function, who in all likelihood will never fully regain that function, and who is therefore at a much greater risk of degenerative change over time.