Quadriceps Weakness After a Total Knee Replacement
Injury Care & PreventionWellness Feb 28, 2019
Quadriceps Weakness After a Total Knee Replacement

After a total knee replacement, physical therapy will often begin within the same day as surgery. One of the first priorities is to get your new knee moving – to regain the range of motion. Other items high on the priority list are achieving quadriceps activation and strength.

First – let’s talk about the quads. The quadriceps is a group of muscles on the front of your thigh. The function of the quads is to extend, or straighten, your knee. Having good quad control and strength is important for a normal walking pattern and stability of the knee. The quads are also involved during other functional activities like getting up from a chair, squatting, or climbing stairs.

Now, given the activities listed above, you can see why the quadriceps are an important muscle group. But what you may not know – and what patients often ask – is why the quads get so weak after a total knee replacement. A study conducted by Mizner and colleagues investigated that question.

The researchers tested 20 patients about 10 days before having a total knee replacement surgery and 27 days after. They looked at several factors including quad strength, voluntary muscle activation, cross-sectional area of the muscles, pain, and function. After all the data were collected, they compared the pre-surgery numbers to the post-surgery numbers, and ran statistics to see which variables had the biggest impact on quad strength post-surgery.

To make a long story short, they found that the loss of quad strength was most attributed to impaired voluntary muscle activation (the ability to contract, or tighten, your muscles with control) and decreased cross-sectional area (atrophy, or loss of muscle mass).

So, what does all of this have to do with physical therapy? In addition to exercises that focus on increasing your knee range of motion, your PT will include exercises for quadriceps activation and light strengthening in the early phases of rehab. After these exercises are demonstrated or explained, many patients are surprised at how difficult it can be to get their quads to activate when they first try.

But as we just discussed, the loss of voluntary muscle activation of the quads is a common and significant impairment that results after a total knee replacement. So, don’t be discouraged, but definitely work hard on your exercises to regain that activation and control. Once you master that step in the process, strengthening will come next.

Recovery from a total knee replacement surgery is often a long process and needs to be progressed appropriately based on your body’s response to exercise and how well it heals after surgery. Thankfully, your PT has the tools and knowledge necessary to help guide you – from range of motion and quad activation to strength to getting back to doing what you love.