Cartilage plays several important roles in the way joints move and function. Joint cartilage provides lubrication, acts as a shock absorber, and helps the joint move smoothly. Joint cartilage is comprised of two substances chondrocytes (i.e. cartilage cells) and extracellular matrix (proteins such as hyaluronic acid, collagen, fibronectin, etc.).
Many conditions can lead to joint cartilage defects. In young people, the most common cause of the joint cartilage defect is an injury. For instance, a football player suffers a hard contact that injures the joint. Another example is a gymnast who repeatedly places substantial impact forces on the knee and other joints of the lower body, resulting in damage. In older people, the most common cause of joint cartilage defects is Osteoarthritis. Over time, the joint cartilage breaks down in the cartilage loses its ability to lubricate, absorb shock, and support the smooth movement of the joint. This leads to stiffness, pain, and “trick” joints, among other symptoms.
Orthopedic surgeons, rheumatologists, and other physicians have attempted to treat these conditions by injecting the damaged joint with one of the two main components of joint cartilage: extracellular matrix. Physicians inject hyaluronic acid (and sometimes related extracellular matrix proteins) to help replace and restore damaged joints. This approach can be helpful for some patients, but it is certainly not a cure.
Only recently, have researchers attempted to replace the other component of joint cartilage: chondrocytes. Specifically, researchers have focused their efforts on mesenchymal stem cells that have the ability to differentiate and become cartilage cells. Li and colleagues injected combinations of bone marrow-derived mesenchymal stem cells and hyaluronic acid into animals with experimental cartilage defects. They showed that hyaluronic acid injections alone modestly repaired the cartilage damage. However, when stem cells plus hyaluronic acid was injected, the joints were almost completely repaired. In other words, stem cells plus hyaluronic acid resulted in much greater improvement in joint cartilage damage than hyaluronic acid alone.
The authors of the study concluded that “bone marrow stem cells plus hyaluronic acid could be a better way to repair cartilage defects.” While additional work is needed, these results are extremely exciting for people who suffer from joint cartilage defects such as osteoarthritis. In the future, people who are candidates for hyaluronic acid injection treatments may instead receive a combination of hyaluronic acid plus stem cells and may enjoy an even greater benefit than hyaluronic acid treatment alone.
Reference: Li et al. (2018). Mesenchymal Stem Cells in Combination with Hyaluronic Acid for Articular Cartilage Defects. Scientific Reports. 2018; 8: 9900.