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Child Orthopedics
Spine - Cervical
Spine - Lumbar
Spine - Thoracic

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Have you ever heard of the snapping knee syndrome? I'm trying to find out more about it.

Snapping knee syndrome refers to a snapping, popping, or clicking that occurs when the meniscus (knee cartilage) is pulled out of place inside the knee. To understand this better, a little review of meniscus anatomy might be helpful. Most of the time, knee meniscus (menisci is the plural form of the word) has a standard C-shape. Placed on either side of the knee (medial for the inside/lateral for the outside), it forms two horseshoe-like structures to support the joint and provide smooth movement. Usually, the menisci are even, symmetrical and about the same thickness and width throughout. But like all things in the human body, there can be differences in the size, shape, and structure of the menisci. Unusual meniscal shapes in the knee are called discoid meniscus. They are most common in the lateral meniscus seen in young children and they can be present in one or both knees. They can create instability that can result in injury from trauma. And it's the child or teenager with a discoid meniscus who seems to end up with snapping knee syndrome most often. The discoid meniscus, instead of being a curved crescent shape, tends to be block-shaped. The discoid meniscus is thicker than normal but the fibers that form the meniscus tend to be disorganized and form more of a haphazard pattern. They are larger than usual -- large enough to cover the entire lateral side of the joint (the normal lateral meniscus covers up to 80 per cent of the surface). Usually, the normal meniscus is held in place by a series of ligaments. But in the discoid meniscus, the absence of some of these ligaments allows the meniscus to move around. That excess movement called hypermobility pulls the meniscus out of place, creating an unstable joint and causing a snapping, popping, or clicking sensation called the snapping knee syndrome. At first the snapping or popping seems to occur off and on -- usually when the knee is moving from a flexed or bent position to an extended or straight position. Pain with movement and/or activity accompanies the snapping as the child gets older (around eight to 10 years of age). Discoid menisci that aren't injured or that do not cause pain and/or instability are left alone. But if an injury occurs and surgical repair is advised, then an arthroscopic approach is possible. The meniscus is reshaped and smoothed down, a procedure called saucerization. The goal is to create a stable, yet functional, meniscus. There is some concern that the remaining discoid meniscus won't function properly because of its abnormalities, but studies done so far have shown that children seem to adapt. Long-term studies are needed to see what happens over time.


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