Osteoarthritis leads to articular cartilage destruction.

The treatments reduce pain and improve function by using physical therapy, anti-inflammatory drugs, and surgical intervention, when necessary.

Several studies suggest that 30% of patients undergoing knee replacement are not satisfied with results, thus highlighting a possible correlation with quadriceps strength and activities of daily living performance.

Some authors studied the connection between clinical and radiological variables and quadriceps thickness, measured by ultrasound in patients with knee replacement.

We conducted a cross-sectional study, enrolling 28 patient submitted to the same rehabilitation protocol (4 weeks), after knee arthroplasty, evaluated at admission (T0) and discharge, (TF), using ultrasound for measurement of vastus medialis thickness, and functional scales for abilities and pain.

We noted that patients with a cross-sectional diameter of vastus medialis larger than 10 millimetres at the admission manifested less pain and improved their function and abilities values at TF compared to patients with a cross-sectional diameter smaller than 10 millimetres, and showed a better recovery process.

Our study demonstrates that the weakness of vastus medialis could be an independent factor which can impact the outcome of patients submitted to arthroplasty of knee, and that it can be evaluated using ultrasound.