David's Discoid Meniscus

David R. is an 8 year old with an audible clunk and snap in his knee. It has been symptomatic for several years but noticeably louder and more painful in the last several months. The clunk seems to be originating from the lateral joint line and occurs with walking, running and twisting.

Here's David's MRI scan:

This is a front view of David's knee with the lateral meniscus on the right side of this image. Note that the meniscus extends all the way across the compartment in contrast to the short triangular shape of the medial meniscus seen on the left side of this image. A discoid meniscus is a congenital condition that has existed since birth, however the tear itself has occurred more recently.

There is a horizontal tear going across nearly the entire discoid meniscus. It essentially splits the meniscus into upper and lower portions.

This is a side view of the lateral discoid meniscus. Again, the white line representing a horizontal meniscal tear can be seen splitting the meniscus into two pieces.

David underwent subsequent arthroscopy of the knee and the discoid meniscus indeed had a horizontal tear in the posterior aspect. Unfortunately the size and location of the tear demanded that the meniscectomy include more than just the abnormal redundant discoid tissue; a portion of the posterior horn itself had to be removed.

Arthroscopic view of the left discoid lateral meniscus looking from the front of the knee towards the rear. The dotted line represents where the border of a normal lateral meniscus would be. This view shows the top surface of the meniscus and no tear is visible at this point.

A probe has been inserted to examine the meniscus further. Looking underneath the posterior portion reveals a horizontal cleavage tear about 2/3rds of the way back into the tissue.

This view shows the meniscus after treatment. Not only was the abnormal redundant discoid tissue removed, but the horizontal tear itself had to be taken out as well. Only then did the audible joint clunking cease.