Tissues & Healing

One of the most amazing things about the human body is it's ability to heal itself from injury. When damage occurs, the body begins the process of clean up, repair and remodeling the tissue. Not all tissues heal the same way and some have less of a healing capacity than others. My rule of thumb for the capacity of tissue healing is as follows: A tissue will have less capacity to heal if:

It has less blood flow
It is highly specialized
There is less of it in the body

Therefore, tissues like skin and muscle do quite well in returning to their original states. These tissue have good blood and are generally built for repair as they built for wear and tear. Tissue such as cartilage and nerve have a poorer abilities to heal. They have less blood flow, are highly specialized to a specific job and there is very little of it in the body.

The Role of Inflammation

Inflammation plays a crucial role in tissue repair. While unpleasant because it is associated with pain, it is a natural and necessary response of the body to injury or tissue damage. The following are the steps involved in the role of inflammation in tissue repair:

Recognition: Upon injury, cells release chemical signals that trigger an inflammatory response.
Vasodilation: Blood vessels dilate, allowing more blood flow to the injured area, carrying oxygen, nutrients, and immune cells.
Immune Cell Activation: Immune cells, such as white blood cells, are activated and migrate to the site of injury to clear away damaged tissue and pathogens.
Pro-inflammatory cytokine release: Pro-inflammatory cytokines, such as TNF-α and IL-1, are produced and released to further recruit immune cells and coordinate the immune response.
Tissue Repair: The removal of damaged tissue, combined with increased blood flow and cytokine release, promote tissue repair and healing.
Resolution: Once the repair process is complete, the inflammatory response subsides, and the affected area returns to its normal state.

This is the basic process of tissue healing for skin, but it is also fairly accurate of other tissues that have a good blood supply such as muscle. During the proliferative phase, the tissue will differentiate to the type that was damaged or scar.

How Muscles and Tendons Repair

Muscles and tendons repair themselves through a series of biological processes that involve the following steps:

Inflammation: Upon injury, the body triggers an inflammatory response, which sends immune cells and blood flow to the affected area to remove damaged tissue and debris.

Proliferation: Proliferation of cells and fibroblasts, including satellite cells and tendon cells, help to lay down new tissue in the damaged area.
Matrix Synthesis: The proliferation of cells and fibroblasts is followed by the synthesis of new extracellular matrix, including collagen and glycoproteins, which provides the structural support necessary for tissue repair.
Remodeling: The newly synthesized matrix is gradually remodeled and reorganized, which leads to the formation of stronger, more organized tissue.
Maturation: The repaired tissue matures over time, becoming stronger and more functional, and the inflammation subsides.

What about Cartilage?

Articular cartilage is a type of connective tissue that covers the surfaces of bones in joints and provides a smooth, low-friction surface for movement. It is composed of specialized cells called chondrocytes and a matrix of collagen fibers and proteoglycans. The following are some key characteristics and functions of articular cartilage:

Structure: Articular cartilage has a smooth and consistent surface that provides a low-friction interface for joint movement. It is also relatively thin, allowing for minimal joint space and maximum congruency between bones.
Absorption: Articular cartilage is able to absorb shock and distribute loads evenly, reducing stress on the bones and minimizing damage to the joint. While a tough tissue, cartilage can wear down with repetitive compression and shearing forces.
Lubrication: The matrix of articular cartilage contains synovial fluid, which lubricates the joint and reduces friction, allowing for smooth and pain-free movement.
Limited Healing: Unlike other tissues, articular cartilage has a limited capacity for self-repair and regeneration. This makes it vulnerable to degeneration and injury, which can lead to joint pain and limited mobility. This is due to poor blood supply and inability to differentiate back into new cartilage. Often bone is replaced when cartilage is missing, hence bone spurring.

Cartilage Healing

Articular cartilage, the smooth white tissue that covers the surface of bones and allows them to glide smoothly against each other, has a very limited ability to repair itself. When it is damaged, the body responds by attempting to repair the damaged tissue through a process called "regeneration."

During the regeneration process, the body sends specialized cells called chondrocytes to the site of the damage. These cells produce new collagen fibers and a substance called proteoglycan, which helps to rebuild the cartilage matrix. However, the body's ability to regenerate cartilage decreases with age, and severe damage may not be able to heal on its own.

There are several factors that can affect the success of cartilage regeneration, including the size and depth of the injury, the age of the patient, and the overall health of the joint. In some cases, surgical intervention may be necessary to repair or replace the damaged cartilage.

It is important to note that the healing process for damaged cartilage can take several months or even years, and complete recovery may not be possible in all cases. However, taking steps to protect the joint and reduce the risk of further damage can help to improve overall joint function and reduce pain and discomfort.

Spinal Nerve Roots

Spinal nerve roots are part of the peripheral nervous system and are located along the spinal cord. They serve as the connection between the spinal cord and the rest of the body, transmitting signals from the brain to the muscles and sensory organs.

Each spinal nerve root originates from the spinal cord and exits the spinal column through an opening between the vertebral bodies, known as a spinal foramen. The spinal nerve roots then branch out into peripheral nerves that supply different areas of the body.

Spinal nerve roots play a critical role in motor function, sensation, and pain management. Injury or damage to spinal nerve roots can result in symptoms such as muscle weakness, numbness, tingling, and pain in the affected area. (You can learn more about their role here.)

Inflammation and Spinal Nerves

Most people believe that it is direct compression on nerves that cause most problems. While that is true of spinal stenosis in older patients, most patient experience chemical irritability of nerve root. The nerve reacts to the chemicals in the inflammatory by product and produces changes to the nerve tissue.

Inflammation can affect nerves by causing swelling and pressure on the nerve, leading to nerve damage or impairing its function. Chronic inflammation can also lead to the destruction of the protective myelin sheath surrounding the nerve. Additionally, inflammation-related chemicals can alter nerve signaling and lead to chronic pain. This will result in local pain and in larger cases, myotomal and dermatomal referral depending on the level. (You can see what patches of skin and muscles can be affected here.)

Nerve Repair

The process of nerve healing involves the following steps:

Inflammation: After a nerve injury, an inflammatory response is triggered, causing swelling and increased blood flow to the area.

Formation of a scar: A scar forms around the injured area, providing stability and protection to the nerve.

Axonal regrowth:

Axonal regrowth is the process of regeneration of damaged nerve fibers (axons) in the central nervous system (CNS) and peripheral nervous system (PNS). After a nerve injury, the damaged nerve fibers are triggered to regrow and establish new connections with other nerve fibers and muscles, allowing the restoration of normal nerve function. This process is crucial for recovery from nerve damage, but it can be slow and not always successful, particularly in cases of severe injury or neurodegenerative diseases.

In the PNS, axons have the ability to regenerate naturally, but in the CNS, axonal regrowth is limited due to the presence of inhibitory molecules and limited intrinsic regenerative capacity. Efforts to enhance axonal regrowth and improve nerve repair have been a focus of ongoing research in the field of neuroscience.

Remodeling of the scar: The scar tissue begins to mature and shrink, making room for the regrowing nerve fibers.

Myelination:

Nerve myelination is the process by which nerve fibers (axons) in the peripheral nervous system (PNS) and central nervous system (CNS) are covered by a fatty sheath called myelin. This sheath acts as insulation, improving the conduction of nerve signals and allowing for more efficient and rapid transmission of signals.

Reestablishment of nerve function:

Nerves can reconnect through a process called axonal regrowth, in which damaged nerve fibers regenerate and reestablish connections with other nerve fibers and muscles. This process is crucial for the recovery of nerve function after injury and involves the following steps:

Formation of growth cones: The tips of the regrowing nerve fibers form growth cones that help to guide the regrowth process.
Migration of Schwann cells: In the peripheral nervous system (PNS), Schwann cells migrate to the site of injury and provide support for the regrowing nerve fibers.
Formation of new connections: The regrowing nerve fibers make new connections with other nerve fibers and muscles, allowing for the restoration of normal nerve function.
Remodeling of connections: Over time, the connections between the regrowing nerve fibers and other nerves and muscles are strengthened and refined, further improving nerve function.

This process can take several weeks to several months, (maybe years) and the outcome depends on the extent of the nerve damage. In some cases, the nerve may not be able to fully regrow, and residual weakness or numbness may persist.