Can you rebuild knee cartilage?
I worked with a Marine coming off a long deployment with poor gym access. An avid lifter with all things barbell, he mentioned that he had started to develop dull, achy pain behind both kneecaps upon return to regular gym workouts. He also reported that his knee joints felt “swollen” the day after a heavy lifting session.
“I had X-rays, and they said I had some arthritis, that my knees had lost some cartilage. Can we do anything about that? I miss lifting like I used to,” he said.
What does cartilage do?
Knee cartilage is a network of tightly packed cells and water molecules that form a thick, dense cushion over the ends of bones. Strong cartilage is firm, smooth, and slick, like the surface of an ice rink. Strong cartilage protects the underlying bone tissue and provides a greased surface for the motion of two adjacent bones.
Weak cartilage is soft and pliable, like a squishy rubber floor mat. It lacks a tight bond between the cells and water molecules, making it less able to withstand force (termed chondromalacia). Over time, tiny pieces may wear off (osteoarthritis).
When the cartilage layer is compromised, the bone underneath may become irritated and painful from a lack of protection. In the knee, weak cartilage can cause pain when the forces between bones exceed cartilage strength, such as running and squats.
Can you rebuild knee cartilage?
Yes! But not in the ways you might think. While there is no current method or technology to make the existing cartilage layer thicker, research shows that cartilage responds to pressure and movement by adapting and growing stronger. And strong cartilage is what’s necessary for active, pain-free knees.
What works: exercise that applies consistent, progressive, moderate loads to your knee surfaces. With slow and steady forward progress a hallmark of knee joint rehab programs, the process of cartilage rebuilding really embraces a “1% better every day” attitude.
What doesn’t work: strength training your quads with exercises that hurt (such as squats and step-ups). First, it’s nearly impossible to strengthen muscles when pain is on board. Pain actually shuts down muscle force as a protective mechanism to prevent damage to the underlying bones and joints. Second, the forces needed to train muscles far exceed the load tolerance of a weakened joint. Step-ups, for example, produce forces 2-3 times your body weight with each rep. Add a couple of dumbbells and a few hundred reps, and you’ll be doing a severe disservice to a knee joint in trouble.
As a teacher of mine, Doug Kelsey PT, Ph.D., once said, “weak joints need to be nudged to get stronger, not pushed.”
Cartilage training, at a glance.
Though he was just 36 years old, our lifter admitted that he had had knee pain for over a year, even with everyday tasks such as standing up from a chair or getting out of his car. This was important information: after all, standing puts much less force on the knees compared to back squats. He completed a Load Tolerance Test to determine how much force we could safely apply to each knee for 5-10 reps without pain. Armed with the numbers, we designed a program to get him back into lifting without knee pain.
We started with exercises using a variable incline plane (e.g., The Total Gym of Chuck Norris infomercial fame). Later, as his load tolerance improved, he progressed to supported squats (e.g., TRX suspension straps), lunges with a slider/slideboard, and finally back to barbell squats. Power and impact came next (a missing link in his training for years) and started with medicine ball throws against a wall and simple jump rope intervals. Within about 4 months, he had progressed back to a regular running program, with jumping and sprints added in later stages.
But how will I know? My x-rays don’t look any different…
Indeed, most x-rays and MRI images aren’t sensitive enough to identify a change in cartilage strength. Though technology is improving, most images use cartilage thickness as an indicator of its health.
However, those of us in sports medicine have learned that, in most cases, cartilage thickness does not equal strength. The ability to handle heavy loads over multiple workouts without knee pain is the most meaningful metric to most lifters. A person can be completely free of knee pain – despite having thinned cartilage on imaging – because their cartilage is strong.
- Strong cartilage is necessary for active, pain-free knees.
- Cartilage thickness does not equal cartilage strength.
- You can strengthen cartilage, but not with the same methods used for muscles.
- Cartilage will grow stronger with training, just like other body parts do. You just need to give it the respect it deserves. The right amount of workload and time to adapt can produce impressive results.
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- Sophia Fox AJ, Bedi A, Rodeo SA. The basic science of articular cartilage: structure, composition, and function. Sports Health. 2009;1(6):461-468.
- Wang Y, Ding C, Wluka AE, et al. Factors affecting progression of knee cartilage defects in normal subjects over 2 years, Rheumatology. 2006;45(1):79–84.
- Kelsey D. (2019).The Runner’s Knee Bible: A Comprehensive Guide to Beating Knee Pain in Runners. [Kindle eBook]
- Pritzker KP, Gay S, Jimenez SA, et al. Osteoarthritis cartilage histopathology: grading and staging. Osteoarthritis Cartilage. 2006;14(1):13-29.