The Other Side of Knee OA | The Role of Subchondral Bone and Inflammation
Knee osteoarthritis is characterized by cartilage wear and tear (or cartilage loss). This explanation – although important, as damage to the cartilage is an element of the condition – is too simplistic. In real life, knee osteoarthritis does not only affect the cartilage surface but also the entire joint environment.
Cartilage, synovium, synovial fluid, subchondral bone, meniscus, ligaments and surrounding muscles, as well as inflammatory signals and pain pathways, contribute to the described molecular networking in the knee joint. If these structures are out of balance, patients may experience knee pain, swelling, stiffness, limited range of motion, difficulty walking, and pain with stair climbing.
This explains why the use of UC-MSCs expanded in osteoarthritis of the knee, which is not as easy to reduce as just a matter of “regrowing cartilage.”
Synovial inflammation and the role of synovium
The synovium is the cushy lining in your knee joint. It also aids in the production of synovial fluid, which lubricates and supports smooth joint movement.
In knee osteoarthritis, the synovium can become irritated or inflamed. This condition itself is referred to as synovial inflammation, synonymously known as synovitis. In b, when the synovium is inflamed, it can secrete inflammatory mediators that induce joint hypersensitivity or hyperalgesia, inflammation, and hence swelling and stiffness (not shown), which increases pressure on the cartilage environment.
Hence, addressing inflammation homeostasis within the knee joint should be an integral part of the management of knee osteoarthritis, and should go beyond cartilage thickness.
Joint Fluid and Smooth Movement
Synovial fluid (joint fluid in the context of the knee) also increases flexibility by reducing friction and allowing for smooth movement between the two ends of a joint. The quality of this fluid might change with the course of osteoarthritis. It will be less useful as a lubricant, and the knee may feel stiff, dry, painful, or hard to move.
Patients may experience pain while walking, bending, standing, or going upstairs when the balance of joint fluid is disturbed. The joint microenvironment, which should involve the quality of the joint fluid, therefore justifies a whole-joint approach.
Subchondral Bone, Meniscus and Stress Load
The subchondral bone (the bone below the cartilage) is also involved in knee osteoarthritis. Repetitive trauma, poor alignment, and joint degeneration over time can create stress in this area.
The meniscus is also believed to play an important role in shock absorption and load distribution. When the meniscus is damaged, torn, or thin, pressure within the knee may rise. This is not exactly going to help with the stress on cartilage and only adds to pain.
Mechanical load is another key factor. Various factors can impact how much load the knee sustains, including body weight, leg positioning, walking pattern, muscle strength in areas such as the pelvis, trunk, and leg muscles, hip joint stability, and level of activity. If the mechanical load is high, treatment may be ineffective.
Pain Signaling in Knee Osteoarthritis
Knee osteoarthritis pain does not always correlate with X-ray or MRI findings. In some cases, patients will have only mild imaging changes yet terrible pain, while others may be severely degenerated but have far less symptomatology.
One reason is pain signaling. Certain factors seem to dictate how much of this pain the patient is aware of: inflammation, tissue irritation, synovial stress, ligament strain, muscle tension, and nerve sensitivity. This means that a target for effective knee osteoarthritis care would not be limited to structure, but would also include inflammation and pain sensitivity.
UC-MSCs and Joint Microenvironment Support
In the field of regenerative medicine, studies on umbilical cord-derived mesenchymal stem cells (UC-MSCs) have received much attention due to their favorable properties and potential as therapeutic agents: they are multipotent and can release biological signals. They can be growth factors, cytokines, extracellular vesicles, and other signaling molecules.
For knee osteoarthritis, it is wrong to describe UC-MSCs as a “step and repeat process” that “regrows new cartilage.” A more plausible explanation of the aforementioned is that UC-MSCs might maintain the microenvironment around the joint and inflammation balance by modulating cellular signaling.
In selected patients, these would seem to play a role in assisting with tissue crosstalk, dampening inflammation and stress responses, and tilting the balance back toward homeostasis within the joint.
What Patients Need to Know Before Getting UC-MSCs
Patients should be wary — UC-MSCs are not a panacea, and their role in cartilage regeneration should not be marketed as an absolute. Outcomes may be contingent on stage of arthritis, body weight, leg alignment, meniscus status, degree of inflammation, muscle strength or conditioning, or other comorbidities.
A good plan should include a medical checkup, imaging, movement assessment, load management, and strengthening and rehab when necessary.
Conclusion
Knee osteoarthritis and UC-MSCs in a whole-joint perspective: Osteoarthritis of the knee is more than loss of cartilage. In addition, synovial inflammation, joint fluid, subchondral bone, meniscus, pain signaling, and mechanical load also play a role.
For certain patient populations, UC-MSCs may play an additional role in a medically framed supportive care plan to maintain the joint microenvironment and balance spinal and systemic inflammation, while emphasizing comfort, mobility, and realistic expectations.
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