Knee injuries involving the meniscus (cartilage) are well-known in adults, especially athletes. But meniscal tears in children are becoming almost as common. And there are two reasons for that. One is the increased sports participation among young children and young adolescents and two is the presence of a discoid meniscus. The first reason probably comes as no surprise to you and needs no explanation. But discoid meniscal tears aren’t something you read about in the daily news.
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. 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 and create instability that can result in injury from trauma.
Usually, the menisci are even, symmetrical and about the same thickness and width throughout. But 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 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 causing a snapping, popping, or clicking sensation called the snapping knee syndrome.
In this article, orthopedic surgeons specializing in sports medicine (and in particular, children’s sports medicine), provide a very thorough discussion of meniscus injuries in young athletes. They provide a review of the normal anatomy of the meniscus as well as the unusual changes present in discoid menisci. With colorful drawings, photos taken during arthroscopic surgery, and MRIs, the reader gets a clear view of the normal anatomy as well as the what-can-go-wrong depiction of discoid menisci and menisci damaged from injuries.
A second focus of the article is the diagnosis and treatment of these conditions. The patient’s history comes first. In many of the nondiscoid meniscal tears, there is a twisting injury during sports participation that traumatizes the knee. Bleeding into the joint, meniscal tears, and ruptures of the anterior cruciate ligament (ACL) are the most common patterns reported.
The examiner will then perform several special tests to assess the integrity of the soft tissue structures. The exam may be limited by the child’s pain and swelling. Whenever possible, two tests: the McMurray maneuver and the Lachman test are done. McMurray’s maneuver helps show the status of the menisci, while the Lachman test is used to find ACL tears.
Imaging studies such as X-rays and MRI scans are useful to look for fractures, dislocation, loose fragments of bone or cartilage, and bleeding into the joint. MRIs are less reliable in children under the age of 12 because of the immature bone and soft tissues. What looks like a meniscal tear may just be the extra blood supply to the area normally present in a growing child.
Once the diagnosis has been made, then the decision about what to do comes next. Unlike adults, children have a much greater chance of healing from a meniscal tear (even large tears), again because of the increased blood supply to the area. Even surgery in children is likely to be more successful because the meniscus is not degenerating with age like it is in older adults. When necessary, the meniscus is sewn back in place. Surgical removal of the meniscus called a meniscectomy may be needed if the meniscus just can’t be saved. Surgeons avoid removing any part of the meniscus as much as possible because studies show that the loss of the meniscus results in continued pain and early arthritic changes even in children.
The authors provide surgeons with a detailed discussion of repair techniques for meniscal tears as well as repair or reconstruction of any other damage that occurred at the time of the injury. The advantages and disadvantages of various meniscal repair systems used during surgery are also presented. Special considerations for the surgeon along with guidelines for postoperative care (both based on type and extent of the meniscal tear) are also reviewed.
Discoid menisci that aren’t injured or that do not cause pain and/or instability are left alone. When surgical repair is advised, 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.
What can these children expect after surgery? As mentioned, younger children seem to have the best success rate. Actual studies of results based on age have not been published yet. It’s difficult to compare results when there is such a wide range of injury types — some children just have meniscal tears but others have additional soft tissue damage. Failure to recognize and repair other ligamentous injuries is the biggest reason why surgical results to repair torn menisci fail or are less successful than hoped for. And long-term studies have not been done to show if younger, more active patients with meniscal injuries that are repaired will develop arthritic changes later like adults do.
The authors conclude that results are good-to-excellent for most children (75 to 87 per cent) with any type of meniscal injury following repair. They suggest there is plenty of room for further research in the area of meniscal tears in young athletes. Until it’s clear the best approach to take, surgeons are advised to conduct a careful history and exam in order to accurately diagnose knee injuries and plan treatment accordingly.