Why do people with knee pain have weak muscles
Full reference: McWilliams DF, Yue B, Smith SL, Stocks J, Doherty M, Valdes AM, Zhang W, Sarmanova A, Fernandes GS, Hall M, Walsh DA. Associations of muscle strength with central aspects of pain: Data from the Knee Pain and related health In the Community cohort. Journal of Personalized Medicine 2023; 13(10)
Knee pain and knee osteoarthritis are common causes of disability in the UK. They become even more common as people get older. People with knee pain often experience muscle weakness, which can increase disability. Knee pain depends not only on osteoarthritis in the joint, but also on how the central nervous system (CNS: spinal cord and brain) processes nerve signals from the joint. In this study, researchers looked at whether joint disease or changes in the central nervous system cause muscle weakness in people with knee pain.
201 people undertook detailed assessment of their pain and muscle weakness. They filled in a questionnaire developed by Pain Centre Versus Arthritis to assess central aspects of pain, and they also underwent some pain sensitivity tests. X-rays of their knees were scored for osteoarthritis and inflammation measured using ultrasound scans. Thigh muscle and hand/wrist weakness were measured. All of these measurements were repeated after 1 year.
We found that measurements of central nervous system aspects of pain predicted muscle weakness 1 year later, whereas x-rays and ultrasound measurements of the knee did not. This was found both for thigh strength and also handgrip strength. This suggests that muscle weakness might be caused by changes in the central nervous system that affect the whole body, and not simply by what is going on in the knee.