Do your knees feel wobbly or are your legs giving way? If you answered yes to either one of these questions, then you might be experiencing a condition known as Arthrogenic Muscle Inhibition. That's a fancy way to say that the muscle weakness is caused by joint arthritis, injury and pain.
As a protective mechanism, the nervous system has reflexes that shut down muscle activity in order to protect the injured body part. In the case of an injured knee, ankle or other joint, doctors have observed significant muscle deactivation in response to joint swelling, pain, and arthritis.1
In response to knee injury, surgery or arthritis, the quadriceps muscles become very weak. Even the hamstring and buttocks muscles are weakened in order to protect the knee. In response to an ankle injury or other painful process, the lower leg muscles in the calf start to lose their power. Researchers are even able to duplicate this arthrogenic muscle response by simulating joint swelling and triggering pain.2,3
This phenomenon presents a significant barrier to rehabilitation, which is why people are researching the causes and solutions.
If the muscles stop working, then the joint is vulnerable to further injury and possibly prolonged recovery. Therapists try to help facilitate muscle activation by using cryotherapy after a recent injury or neuromuscular electrical stimulation after joint replacement surgery. Short-circuiting this protective reflex using electrical stimulation or cold temperatures can allow for quicker recovery times.4,5
Short-circuiting the reflexes that lead to arthrogenic muscle weakness can also help someone with an arthritic joint prolong the need for joint replacement surgery because muscle strength helps to support the joints. Muscles are needed to support the joint during daily activities. The stronger the muscles are the less likely the person will experience pain during these activities. And muscle strength is dependent on the strength of the signals being sent from the nerves. Nerves, muscles, joints; this three-legged joint stability stool relies on each of its three legs to keep from wobbling.6
If your knees are feeling wobbly or your legs are giving way, consider seeing a physical therapist to help stabilize your joint and help to short-circuit a protective reflex that weakens the muscles. Because of the relationship between muscle weakness and arthritis, exercise should be an important part of your arthritis treatment plan.
- Semin Arthritis Rheum. 2010 Dec;40(3):250-66
- Foot Ankle Int. 2005 Dec;26(12):1055-61
- J Athl Train. 2010 Jan-Feb;45(1):87-97
- J Athl Train. 2002 Mar;37(1):25-31
- J Orthop Res. 2012 Nov 8. doi: 10.1002/jor.2226
- Sports Health. 2012 Jul;4(4):284-92