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What is Posterolateral Instability?

Posterolateral instability, also known as posterolateral rotatory instability (PLRI), is a common pattern of knee instability that results from injuries to the structures that support the outside of the knee joint, the posterolateral corner. When individuals injure the knee ligaments, they are most likely to injure the structures of the posterolateral corner. These structures include the popliteus tendon, lateral collateral ligament, and the knee joint capsule. The knee instability mostly occurs along with other ligamentous injuries, in particular, damage to either the ACL (anterior cruciate ligament), the PCL (posterior cruciate ligament), or both.

Causes of Posterolateral Instability

Posterolateral instability of the knee usually results from a sports-related injury that occurs when the knee is forcefully twisted or hyperextended. This usually occurs with an abrupt directional change when the foot is fixed on the ground or when the deceleration force crosses the knee. Other causes of posterolateral instability include:

  • Changing direction rapidly
  • Stopping suddenly
  • Slowing down while running
  • Landing from a jump incorrectly
  • Direct contact or collision with a bent knee
  • Overuse injury

Symptoms of Posterolateral Instability

Some of the common symptoms of posterolateral instability of the knee include:

  • Pain
  • Swelling
  • Tenderness
  • Numbness
  • Sensation of the knee giving out
  • Stiffness

Diagnosis of Posterolateral Instability

The diagnosis of posterolateral instability is made by reviewing your symptoms and medical history and performing a physical examination of the knee by a critical test called Dial test. This test helps to check for posterolateral rotatory instability by determining the rotation of the knee by turning the foot outwards and comparing this with the opposite knee. If there is an excessive rotation, this would signify an injury to the posterolateral corner. By examining the degree of rotation at various levels of knee flexion, your physician can determine which structures are likely damaged.

Treatment for Posterolateral Instability

Treatment options may include non-surgical and surgical treatment.

Non-surgical treatment consists of rest, ice, compression and elevation (RICE protocol); all assist in controlling pain and swelling. Physical therapy may be recommended to improve knee motion and strength. A knee brace may be needed to help immobilize your knee. Crutches may be recommended to protect your knee and avoid bearing weight on your leg.

Surgery is employed for high-grade posterolateral corner injuries that usually result in rupture of one or both cruciate ligaments causing significant instability in the knee joint. Surgery involves reconstructing the torn ligament using a tissue graft taken from another part of your body or a deceased donor. Surgery is usually carried out with an arthroscope using small keyhole incisions around the knee joint. The major advantages of this technique include minimal postoperative pain, short hospital stay, and a fast recovery.

Following surgical reconstruction of the structures, a rehabilitation program will be started to help you resume a wider range of activities.

  • University of Arizona
  • Cal Poly Pomona
  • American Academy of Orthopaedic Surgeons
  • American Board of Orthopaedic Surgery
  • U.S. Ski & Snowboard
  • American Orthopaedic Society for Sports Medicine
  • University of California, Los Angeles
  • Stanford University
  • Biological Association
  • AANA Advancing the Scope