Understanding the Patellar Grinding Test (Clarks Sign or Zohlen Sign) Assessment
To assess for **Patellofemoral Pain Syndrome (PFPS)** and damage to the **articular cartilage** on the deep surface of the patella.
Watch How It's Done
How do I start?
Patient is supine with the knee fully extended.
What happens?
The examiner places the web space of the hand just superior to the patella and applies a firm, **distally directed pressure** (pushing the patella toward the feet) while instructing the patient to **gently and maximally contract the quadriceps**.
In Plain English
What Does a Positive Result Mean?
The patient reports **pain beneath or around the patella** during the resisted contraction, often accompanied by a **grinding or grating sensation** (crepitus).
Helpful Tip:
This test can be very painful and should be performed carefully. It is highly sensitive for patellofemoral joint irritation.
Safety First
This guide is to help you understand what happens in a clinic. Do not try to diagnose yourself. If you have severe pain, swelling, or cannot put weight on your leg, please visit an urgent care center or your doctor immediately.
Other Knee Tests
Pivot Shift Test
To dynamically assess for **anterolateral rotatory instability** of the knee, which is highly indicative of a **complete ACL tear**.
Posterior Drawer Test of the Knee
To assess the integrity of the **Posterior Cruciate Ligament (PCL)**.
Posterior Sag Sign (Gravity Drawer Test)
To detect a rupture of the **Posterior Cruciate Ligament (PCL)** by observing the effect of gravity.
Slocum Test (Anterolateral Rotatory Instability)
To assess for **anterolateral rotatory instability** and the function of the **Anterolateral Ligament** (a dynamic variant of the Anterior Drawer).