Why Does My Knee Feel Like it is Giving Out and Getting Weak?

Orthopaedic & Spine Center
Image of Dr. Boyd Haynes

Boyd W. Haynes III, MD

A very common complaint I hear in the office, especially from my older patients, is “my knee is feeling weaker and weaker and sometimes it just gives out when I’m walking.  Why is that happening to me?”

When arthritis of the knee progresses, the cartilage in the joint space erodes.  Cartilage acts as a cushion and a glider against which the bones move.  When the cartilage goes away, the bones of the knee start to shift and rub against one another.  We call this “bone-on-bone” arthritis.  Because this erosion typically doesn’t happen in an even pattern, one side of the knee tends to worsen more quickly than the other. 

Very often, pain accompanies this cartilage degeneration, and the patient will start to compensate by walking differently and putting more weight on their less affected leg. They will begin using their painful knee and leg less and less.  As a result, the muscles surrounding their painful knee, and in the leg, will start to atrophy. Your legs are made of many muscles, tendons, and ligaments and some of the larger ones that will be affected will be the quadriceps, the gastrocnemius, the anterior tibialis, the rectus femoris and the patellar tendon.

This is often easily visualized when comparing the two legs, especially when looking at the calf muscles.  You may be able to see that one is larger and fuller, while the other on the affected leg may appear shrunken and the skin over it may be loose and shriveled.

Over time, the muscles in the surrounding the arthritic knee can become so weak that when called upon to work, they just can’t function well.  This can result in the knee “giving out” or collapsing.  Another consideration is that the cartilage in the knee can often tear, and a small piece can become caught in the joint during movement, causing pain and dysfunction.

Unfortunately, bone-on-bone arthritis is a condition that can only be remedied by a joint replacement.  We can delay surgery by treating with physical therapy to improve strength, cortisone shots, or viscosupplementation, but we can’t replace cartilage at this time.