Patellar Grind Test (Zohlen Sign or Clarke sign) is used to evaluate patellofemoral Pain Syndrome (chondromalacia patellae).
How is Patellar Grind Test performed?
The patient is supine with the leg extended.
The examiner applies medial and lateral pressure to the proximal patella to press it into the trochlear groove and asks the patient to extend the leg further or to tense the quadriceps.
In the second phase, the examiner pushes the patella directly downward into the trochlear grove while asking the patient to contract the quadriceps muscle.
What does a positive Patellar Grind Test mean?
The quadriceps exerts a proximal pull on the patella, pressing it tightly against the trochlear groove.
This will cause retropatellar and/or peripatellar pain in the presence of retropatellar cartilage damage.
Sensitivity & Specificity
A Validation study by Scott T Doberstein1 to evaluate the diagnostic value of the clarke sign in assessing Chondromalacia Patella, he found the sensitivity & specificity was:
Sensitivity: 39 %
Specificity: 67 %
As this test is often positive in normal patients, one should repeat the procedure several times, increasing the pressure on the patella each time and comparing the results with those of the unaffected side.
To better localize the retropatellar damage, the knee should be tested in 30°, 60°, and 90° of flexion as well as in full extension.
The term chondromalacia patella has long been a catch-all category of anterior and, specifically, retropatellar knee pain.
The term chondromalacia was first used by Aleman in 1928. He used the term “chondromalacia posttraumatica patellae” to describe lesions of the patella found at surgery and thought to be caused by prior trauma.
With time, chondromalacia became an all-inclusive term with no agreed-on classification system or definitions of terms.
True chondromalacia refers to a softening of the cartilage on the posterior aspect of the patella and is estimated to occur in fewer than 20% of persons who present with anterior knee pain.
The syndrome is most common in the 12–35-year-old age group, and most studies show a predominance in females.
Two types of chondromalacia have been described:
One type involves surface degeneration of the patella that is age dependent and most often asymptomatic.
The other type involves basal degeneration. This type results from trauma and abnormal tracking of the patella and is symptomatic.
Chondromalacia patella Classification:
Chondromalacia is classified into four grades, according to the degree of degeneration noted arthroscopically:
Grade 1: Closed disease. This grade is characterized by an intact joint surface that is spongy. The softening is reversible. A blister or raised portion of the articular surface is seen.
Grade 2: Open disease. This grade is characterized by fissures that may or may not be obvious initially.
Grade 3: Severe exuberant fibrillation or crabmeat appearance.
Grade 4: The fibrillation is full-thickness and the erosive changes extend down to bone, which may be exposed. This is, in effect, OA and its extent depends on the size of the lesion.
Doberstein ST, Romeyn RL, Reineke DM. The diagnostic value of the Clarke sign in assessing chondromalacia patella. J Athl Train. 2008 Apr-Jun;43(2):190-6. doi: 10.4085/1062-6050-43.2.190. PMID: 18345345; PMCID: PMC2267328.