The inevitable wearing away of cartilage on the ends of our bones presents a significant problem to the aging/athletic population, and to the medical world. It is the natural aging process, but many factors can accelerate its degeneration. Cartilage protects our joints and as it wears away, the bones grate on each other causing inflammation within the joint which is what arthritis is. As with anything, there are varying degrees and varying factors that contribute to it. It is an extremely common problem and nine percent of the U.S. population over 30 has osteoarthritis of the hip or knee and over 400,000 knee replacements are performed each year in the U.S. alone (Grande, et al 2013). It gets worse as we age if nothing is done about it. It can occur in the spine and is termed “spondylosis” rather than osteoarthritis.
So what exactly is cartilage? It is smooth elastic tissue that protects bones and joints, and allows joints to glide and roll on each other without abrasion. It has an extracellular matrix comprised mostly of aggregans and collagen. Within the aggregans are glycosaminoglycans which attract water, and proteoglycans which act as lubricants. The type 1 collagen found in the extracellular matrix functions to resist compressive forces which is the main function of cartilage.
Despite the fact that arthritis is the most common joint disease, it is not well understood. It is considered to be multifactorial and aging, trauma, genetic predisposition, obesity, inflammation, and the metabolic syndrome are all contributors. Inflammatory factors can lead to the breakdown of cartilage (Bricca, et al 2017). Acute inflammation is a natural part of the healing process, but chronic inflammation leads to a cascade of destructive changes to the cartilage, synovial tissue, and underlying bone (Grande et al, 2013). Injury of a joint frequently leads to instability which can compound the situation (Jimenez et al, 2018). Perhaps most importantly, the way you move plays a significant role in the vitality of cartilage.
Muscles hold the skeleton together and if there is a relative weakness surrounding a joint, the way the joint operates will be altered. This can lead to compression on one side of the joint. The knee is a good example as it one of the least complicated joints:
If you are knock-kneed (genu valgum), you will have more compression on the outside of your knee. Conversely, if you are bow-legged (genu varum), you will have more compression on the out inside of your knee.
What about running? This has been a well debated topic for years. A meta-analysis in 2017 (Bricca et al), found that a high dose of exercise may have negative impacts on cartilage on the knee joint, while a low dose had positive impacts. However, these studies were performed on dogs and rats. This idea of the right dosage brings us to Wolff’s law which states that tissue will respond to load applied, or not applied. So in other words, weight-bearing stimulates bone growth, and sitting on the couch stimulates bone depletion. This is why astronauts return from space with significant bone density loss; it is difficult for them to apply load to their joints without gravity.
So it would follow that applying load to cartilage may stimulate cartilage growth. However, for all tissue, there is a tipping point. Apply enough load to a bone, and it will break. What we see clinically is that people that go from being sedentary to a sudden increase in exercise volume without a ramp period get injured.
What’s the bottom line? We don’t officially know where the line is for what is too little and too much, and I doubt we ever will as each person is unique. I tell my patients to slowly progress the load to your joints, don’t do the weekend warrior routine. Watch your technique; learn how to step, squat, jump and land correctly. Do you have flat feet that and tight calves that cause your foot to turn out and make your knee collapse? Or maybe weak hip abductors that are unable to support your body weight in each step you take? This is where a thorough exam will tease out the culprit to poor running or stepping mechanics. Fix your mechanics, and progressively load the joints.
What if it’s too late and you have severe arthritis? What are the options? Below is summary of current concepts in cartilage repair.
This is a ‘cleaning up’ of the joint. Any loose fragments are removed along with excessive fluid and is best suited for patients in the beginning stages of arthritis. When someone says they had a ‘knee scope’, this is what they are talking about.
Marrow stimulation techniques (microfracture)
This is also an arthroscopic procedure but the difference is that holes are drilled into the underlying bone. Cartilage has poor blood supply but bone has good blood supply and drilling into it causes blood to flood the joint, stimulating healing. The only problem is that fibrocartilage forms which is rougher than the original cartilage.
Marrow stimulation augmented with hydrogel implant
This is a new technique and is being studied in Europe. It involved the same drilling into subchondral bone, but then a hydrogel is implant on the joint surface. The gel is designed to act as a scaffolding to promote hyaline cartilage formation.
Marrow stimulation augmented with peripheral blood stem cells
This is an area that is exciting and shows significant promise. This procedure combines microfracture and peripheral blood stem cells injections. In 2011 Saw et al, confirmed the regrowth of hyaline cartilage in 5 patients. This is significant as it is usually the rougher fibrocartilage that grows.
Osteochondral autografts and allografts
This procedure takes a section of bone and cartilage from a cadaver and is implanted, typically in the knee. As with any transplant from a donor, the risk is rejection of the tissue.
Cell based repair
This procedure requires two surgeries. First, healthy cartilage is taken from non-loadbearing regions. Then it is grow and replicated in a laboratory. Once the cell population has grown to an adequate amount, usually a month and a half, it is transplanted to the target area.
Platelet rich plasma is a technique where the patient’s own blood is drawn and put into a centifuge to concentrate the platelets. It is then injected into an affected area to facilitate healing. One study by Spakova et al (2012), found that 3 PRP injections improved outcomes compared to 3 injections of hyaluronic acid.
Grande, D. A., Schwartz, J. A., Brandel, E., Chahine, N. O., & Sgaglione, N. (2013). Articular Cartilage Repair. Cartilage, 4(4), 281-285. doi:10.1177/1947603513494402
Bricca, A., Juhl, C., Grodzinsky, A., & Roos, E. (2017). Impact of a daily exercise dose on knee joint cartilage – a systematic review and meta-analysis of randomized controlled trials in healthy animals. Osteoarthritis and Cartilage,25(8), 1223-1237. doi:10.1016/j.joca.2017.03.009
Jiménez, G., Cobo-Molinos, J., Antich, C., & López-Ruiz, E. (2018). Osteoarthritis: Trauma vs Disease. Osteochondral Tissue Engineering Advances in Experimental Medicine and Biology, 63-83. doi:10.1007/978-3-319-76735-2_3