Posterolateral Rotatory Instability of the Knee

Posterolateral rotatory instability occurs when there is damage to the structures that support the outside of the knee joint, the posterolateral corner. These structures are critical to preventing symptoms of knee instability. When patients injure the knee ligaments, it is possible to injure the structures of the posterolateral corner.

Until recently, not much attention was paid to the structures of the posterolateral corner. These structures include the lateral collateral ligament, the popliteus tendon, and the knee joint capsule. Recent evidence has shown that these structures can be injured when the knee sustains ligament damage including ACL tears and PCL tears. If the structures of the posterolateral corner are not assessed and are damaged, persistent knee problems can occur despite treatment of the rest of the knee.

Injuries to the posterolateral corner most often occur along with injuries to the cruciate ligaments, the ACL, and the PCL. Posterolateral corner injuries often occur with knee dislocations. About 70% of posterolateral corner injuries occur in the setting of an injury to the ACL and/or PCL. In about 20-30% of patients, there is an isolated injury to the posterolateral corner.

Symptoms of posterolateral corner injuries include sensations that the knee is going to give out. Pain and swelling are over the outside of the knee joint, more toward the back of the knee. About 15% of patients who sustain an injury to the posterolateral corner will also injure the peroneal nerve, an important nerve that can cause numbness down the outside of the leg and foot.

When examining your knee for posterolateral rotatory instability, the critical test is known as the Dial Test. Your doctor will determine the rotation of the knee (by turning the foot outwards) and compare this to the opposite knee. If there is an excessive rotation, this is indicative of an injury to the posterolateral corner. By checking the degree of rotation at different levels of knee flexion, your doctor can determine which structures are likely injured.

Treatment of the posterolateral corner depends on the degree of instability. The primary reason the posterolateral corner has become an interesting subject in orthopedics is that it has been thought to be the reason why many people who had a failure of ACL reconstruction surgery, may have had unrecognized posterolateral corner injuries.

When posterolateral corner injuries cause significant instability in the knee joint, the structures are surgically repaired. This requires an incision along the outside of the knee joint. Recent injuries can often be repaired, whereas chronic injuries may require the use of donor tissue to reconstruct the damaged structures. More severe injuries also generally require some donor tissue to augment the repair along the outside of the knee.

Rehabilitation after posterolateral reconstruction will depend on the structures repaired in the knee. Rehab is similar to recovery from other knee ligament surgery, but you should discuss specific variations with your surgeon.