CASE 145

By: Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 35-year-old football player twisted his knee during a football match.

What are your findings?

What is the mechanism of this injury?

FINDINGS:

Sagital T1(A) demonstrates a flipped lateral meniscal tear lying anterior to the PCL in the intercondylar notch giving the double PCL sign. Note the absence of the ACL consistent with its tear.

Sagital T2 (B) shows a large defect in the lateral meniscus consistent with a tear (Absent bow tie sign) which has now flipped into the intercondylar notch.

Coronal STIR (C) shows the empty lateral meniscus at the region of the body of the lateral meniscus with evidence of a flipped fragment in the intercondylar notch.

DIFFERENTIAL DIAGNOSIS:

·        Bucket handle tear of the meniscus.

·        Accessory meniscofemoral ligament.

·        Medial oblique meniscomeniscal ligament.

MECHANISM OF INJURY:

Damage to the meniscus is due to rotational forces directed to a flexed knee (as may occur with twisting sports) is the usual underlying mechanism of injury. A valgus force applied to a flexed knee with the foot plantar flexed and the femur rotated externally can result in a lateral meniscus tear. A Varus force applied to the flexed knee when the foot is plantar flexed, and the femur rotated internally results in a tear of the medial meniscus.

DIAGNOSIS:

Torn ACL with a bucket handle tear of the lateral meniscus which is flipped giving the double PCL sign and absent bow tie sign.

PEARLS AND DISCUSSION:

The double PCL sign seen on MRI happens when a bucket handle tear of usually medial meniscus (80%) but in this case lateral meniscus happens. The meniscus flips toward the center of the knee to lie in the intercondylar notch.

It usually happens with an intact ACL, but in a minority of patients can happen with ACL tear.

The double PCL sign has a high specificity (98-100%) for detecting a displaced bucket handle tear but variable sensitivity (27-53%).

Be aware that there is a double ACL sign which can also happen in bucket handle tears of the medial meniscus.

FURTHER READING:

1.      Wright DH1, De Smet AA, Norris M. AJR Am J Roentgenol. 1995 Sep;165(3):621-5.

2.      Bucket-handle tears of the medial and lateral menisci of the knee: value of MR imaging in detecting displaced fragments.

3.      Takayama K1, Matsushita T, Matsumoto T, Kubo S, Kurosaka M, Kuroda R. The double ACL sign: an unusual bucket-handle tear of medial meniscus. Knee Surg Sports Traumatol Arthrosc. 2011 Aug;19(8).

4.      Camacho MA. The double posterior cruciate ligament sign. Radiology. 2004;233 (2): 503-4