Clinical, MRI, and arthroscopic findings associated with failure to diagnose a lateral meniscal tear on knee MRI.

OBJECTIVE: We performed this study to determine whether clinical, MRI, or arthroscopic findings are associated with missed lateral meniscal tears to help understand why these tears are missed on MRI.

MATERIALS AND METHODS: We reviewed the medical records of 483 patients who had undergone knee MRI and arthroscopy. We assessed patient age; spontaneous or traumatic onset of knee pain; interval between pain onset and MRI; interval between MRI and arthroscopy; and arthroscopic type, size, and location of lateral meniscal tear for their association with a missed lateral meniscal tear. Each MR examination with a missed lateral meniscal tear was reviewed to determine whether the tear could be seen in retrospect.

RESULTS: Thirty-six of the 189 lateral meniscal tears found at arthroscopy were not diagnosed on the original MR interpretations. There was a significant association between a missed lateral tear and a posterior horn tear or a tear involving only one third of the meniscus. There was no association between a missed lateral meniscal tear and the other variables. Review of the 36 missed tears revealed that 10 tears were visible retrospectively, six of which were longitudinal peripheral tears in the posterior horn.

CONCLUSION: Lateral meniscal tears are more likely to be missed if the tear involves only one third of the meniscus or is in the posterior horn. Longitudinal peripheral tears of the posterior horn were the most commonly missed tears that could be seen in retrospect.