In part 2 of our blog series, we summarize which types of tissue are frequently affected by orthopedic and trauma-related complaints and how their varying metabolic activities influence the healing process.
Note: The compiled information does not constitute medical or professional advice and does not claim to be complete.
Tissue Regeneration Times and Types
In orthopedic and medical training, the following tissue types are primarily affected:
- Bone
- Muscle
- Tendons, ligaments, capsules
- Cartilage
The different tissues not only consist of different structures but also vary in their metabolic activity: active versus sluggish. Depending on the level of activity, the adaptation and healing process differs. Metabolically active tissue can adapt faster to stimuli and thus heals faster.
Why is this the case?
Some tissue types, like skin tissue, are richly supplied with blood vessels and well-vascularized. Other tissues, such as hyaline joint cartilage*, can only be nourished through diffusion processes**.
The length of rehabilitation phases is based on the knowledge of the following tissue regeneration times (cf. Freese, 2001). The longer the regeneration time, the slower the adaptation process, and the more carefully training stimuli should be applied:
- Skin tissue: 2 days
- Joint fluid: 7-10 days
- Muscle tissue: 3-4 weeks
- Nucleus pulposus (inner core of the intervertebral disc): 2-4 weeks
- Bone tissue: 4-6 months
- Lymphatic vessel tissue: 4-6 months
- Anulus fibrosus (outer ring of the intervertebral disc): 1-1.5 years
- Tendon/capsule/ligament tissue: 1-1.5 years
- Cartilage tissue: 200-400 years
The Types of Tissue
Bone is part of the passive musculoskeletal system and forms the support framework of the human body. Bone is in a constant remodeling process involving osteoblasts*** and osteoclasts****. Bone structure is spongy and aligns with the tensile forces acting upon it. Along the tensile lines, trabeculae (spicules) in the bone form to make the structure more resilient.
In medical training, cases often involve trauma, usually injuries to joints from various types of accidents. In the context of degenerative diseases, bones may become a focus in the medium term – for instance, when surgery becomes necessary. Examples include bone tendon tears and joint replacements.
Muscle is part of the active musculoskeletal system and is a highly metabolically active tissue type. It is affected in medical training therapy when sports injuries and surgical interventions have occurred.
Tendons are the transitional connection from muscle to bone and are often affected in sports accidents. Tendon tissue can be damaged due to overexertion caused by repetitive, unfamiliar movement patterns or incorrect training with an increase in load too quickly. The cause lies in the different regeneration times of tissues: muscles adapt faster to stimuli than tendons or the more mineralized tendon-to-bone junction.
This manifests as tendon insertion inflammation.
Bone attachment issues can also occur with ligaments. Ligaments, attached to bones, are responsible for support and stabilization. Most ligaments consist of dense, parallel-fibered connective tissue that contains Type 1 collagen fibers. Some ligaments also have elastic properties. Joint capsules have a similar structure, being made up of collagenous, tightly interwoven fiber structures.
In synovial joints, the two bony joint partners are covered with hyaline cartilage. Cartilage acts as a shock absorber, protects the bone, and compensates for irregularities between joint surfaces. The larger the contact area between the joint partners, the less pressure and strain on the joint.
Since cartilage is no longer supplied directly by blood vessels after the growth plates close in adolescence, it can only be nourished through diffusion processes. This task is mainly carried out by synovial fluid (joint lubricant), produced by the cells of the inner capsule wall.
Bone is supplied with nerve endings and blood vessels. If arthritic changes occur in the joint, joint pain can be related to this bone zone.
In part three, we will introduce the most common signs of inflammation.
* Hyaline cartilage is highly pressure-resistant, which is why it is found where primarily compressive forces occur (e.g., most joint surfaces).
** Diffusion: A phenomenon of substance transport where random thermal motion of particles causes a self-mixing of a solution, distributing the dissolved substance within the solvent.
*** Osteoblasts are specialized bone cells originating from embryonic mesenchyme. Their primary function is the synthesis of the collagenous bone matrix (mainly collagen type 1).
**** Osteoclasts are multinucleated giant cells formed by the fusion of mononuclear precursor cells from bone marrow. They belong to the mononuclear phagocyte system (MPS). Their main function is the resorption of bone tissue.