Special Tests for Patellar Ligamentous Instability (Anterior Cruciate Ligament)

Patellar Ligamentous Instability
We often hear ” Oh, I tore my ACL” and we wonder it’s something about the knee. But, what does ACL stand for and how can we test its instability.

What are the ligaments of the knee?

  • Medial Collateral Ligament (tibial collateral ligament) – limits valgus (knocked knee) motion of your knee.
  • Lateral Collateral Ligament (fibular collateral ligament) – limits varus (bowed legs) motion of your knee.
  • Anterior cruciate ligament – attaches the tibia and the femur in the center of your knee; it’s located deep inside the knee and in front of the posterior cruciate ligament. It limits rotation and anterior motion of the tibia.
  • Posterior cruciate ligament – is the strongest ligament and attaches the tibia and the femur; it’s also deep inside the knee behind the anterior cruciate ligament. It limits the posterior motion of the tibia.
  • Patellar ligament – attaches the kneecap to the tibia.

“Patellar instability – is a cluster of conditions affecting movement of the patella. It includes patellar dislocation and patellar subluxation which can be of various types.”

The mechanism of Injury can include:

  • Sudden change of direction while foot is caught on the ground
  • Uncontrolled landing

The Special Tests are:

  • Anterior Drawer Test
  • Lachman’s Test

Anterior Drawer Test

  • The patient is supine with the knee flexed to 90 degrees so that the foot is flat.
  • The examiner sits on the patient’s foot and grasps behind the proximal tibia with thumbs palpating the tibial plateau and index fingers palpating the tendon of the hamstring medially and laterally.
  • An anterior tibial force is applied.

Lachman’s Test

  • The patient is in supine with the knee flexed to 15 degrees
  • The examiner stabilizes the distal femur with one hand and grasps behind the proximal tibia with the other hand.
  • The examiner then applies an anterior tibial force to the proximal tibia.

A positive result for the Anterior Drawer Test, and Lachman’s Test, is indicated by greater anterior displacement on the affected side when compared to the unaffected side.

How effective are they?

Sensitivity and Specificity

Sensitivity- the probability of a positive test results in someone with the pathology.

Specificity- the probability of a negative test results in someone without the pathology.

Lachman’s Test
Sensitivity- 63%- 99%
Specificity-50%-100%

Anterior Drawer Test
Sensitivity- 18%-95%
Specificity- 55%-100%

By: Rhia Vista, PTA

Tagged with: , ,

Posted in: Knee

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