Clinical History: 16 year-old male s/p soccer injury with an ACL tear.
Web Clinic Challenge: Fat-suppressed proton density sagittal images (1a,1b) are provided. Note the meniscofemoral ligament of Wrisberg (arrow) coursing behind the PCL on image (1a). The edematous and lax ACL is readily apparent. In this case, the ACL tear resulted from a tibial attachment avulsion fracture (arrowhead). In (1b), note the posterior horn of the lateral meniscus near the Wrisberg attachment (arrow). Is a meniscal tear present?
Yes, but it’s ok if you said no (explanation to follow).
The Ligament of Wrisberg is the more common of the meniscofemoral ligaments1, and courses posterior to the PCL (2a) as it descends to the posterior horn of the lateral meniscus. Less commonly, a Ligament of Humphrey is present, in which case the ligament runs anterior to the PCL.
If you answered “no tear”, it’s likely because you are aware of the well-known Ligament of Wrisberg pseudo-tear2, caused by the vertical/oblique signal intensity region (3a) that occurs normally at the junction of the Ligament of Wrisberg with the posterior horn of the lateral meniscus.
In the current example, the single sagittal image of the lateral meniscus looks very similar to a Wrisberg pseudo-tear. Therefore, if you said that no tear was present, you could not be blamed for the missed diagnosis. However, here is what was seen on the adjacent sagittal slices: (4a, 4b).
This case demonstrates a particular lateral meniscal tear pattern that we have seen frequently in association with ACL tears. A longitudinal tear is noted within the posterior horn of the lateral meniscus, extending laterally from the Wrisberg ligament attachment to the posterior horn. We believe that this particular tear type occurs as a result of traction from the Ligament of Wrisberg upon the posterior horn of the lateral meniscus in cases of ACL disruption. In fact, we have not seen this particular meniscal tear pattern in the absence of an ACL tear.
Why does this tear pattern occur” Recall that during an ACL disruption the tibia typically translates anteriorly relative to the distal femur. The Ligament of Wrisberg is attached proximally to the lateral aspect of the medial femoral condyle and distally to the posterior horn of the lateral meniscus. With ACL disruption, as the tibia moves anteriorly relative to the femur, the Ligament of Wrisberg thus causes traction on the peripheral rim of the posterior horn of the lateral meniscus (5a). As a result, one may suffer a tear through the posterior horn of the lateral meniscus, originating at the Wrisberg attachment. Because of the unique mechanism of injury involved with this meniscal tear, we have named this tear the “Wrisberg Rip”.
The Wrisberg Rip is a characteristic longitudinal tear of the posterior horn of the lateral meniscus that may be seen in association with ACL tears. This tear type is important for two reasons. First, many people realize that meniscal tears are common in association with ACL disruption, but tears at the central portion of the posterior horn laterally are among the most frequently missed. The Wrisberg Rip is one of those tears. Second, because the Wrisberg Rip appears to occur only in association with ACL tears, this tear pattern may be used as a secondary sign of ACL disruption.
1 Cho JM, Suh JS, Na JB, et al. Variations in meniscofemoral ligaments at anatomical study and MR imaging. Skeletal Radiol 1999. 28(4): 189-95.
2 De Smet AA, Tuite MJ, Norris MA, Swan SJ. MR diagnosis of meniscal tears: Analysis of causes of errors. AJR 1994; 163: 149-154.