SYMPTOMS OF MENISCAL TEARS
A basic ability to identify meniscal tear symptoms is essential for diagnosis and treatment of injury (see Table 1). The first symptom typically indicative of a meniscal tear is pain. In the case of a traumatic tear, pain may present immediately at the time of injury and is often accompanied by an audible pop. In a degenerative tear, the onset of pain may be more gradual, with no definite moment of injury. In both cases, pain may be accompanied by swelling and subsequent limitation in range of motion. Another hallmark of meniscal tears is clicking, popping, or locking in the knee joint. These symptoms are mostly likely a result of a torn flap of meniscal tissue which catches in the joint during movement. Instability and weakness are also both common symptoms because a damaged meniscus—as well as damaged ligaments and tendons—inhibits normal mechanical function.
| Table 1. Symptoms of meniscus tears. |
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The severity of initiating trauma, as well as the nature and characteristics of the tear, plays an important role in the meniscus’ ability to heal (see Table 2). Tears that are shorter, partial thickness, and located in the vascular red zone have a much better chance of healing than extensive, complete thickness tears located in the white zone.24,25 When other cartilages and ligaments are injured in the knee, this can also have a detrimental effect on the meniscus’ ability to heal on its own. Because of the interdependence of each of the knee’s mechanisms, meniscal injuries often occur in conjunction with other internal ligament damage. The most common example of this is O’Donoghue’s “unhappy triad,” the correlated injury of the meniscus (debatably either medial or lateral), tibial collateral ligament, and ACL.26-28 The severity of meniscal lesions has been found to increase in direct proportion to ACL injury and/or laxity, and create less favorable conditions for repair.29 Furthermore, previous injury to either the meniscus or any other ligament inside the knee can increase the risk of future injury to the meniscus, even if the injury has healed or been surgically repaired.
| Table 2. Factors affecting the healing of a torn meniscus. |
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DISCOID MENISCUS CONDITION
Another condition which can be both a cause and complication of meniscal tears is a discoid meniscus (see Figure 6). A discoid meniscus occurs when the lateral meniscus takes on the shape of a disc rather than a crescent and is most often manifested in adolescence.30 Although the cause has never been officially determined, the repercussions of a discoid meniscus have been widely documented. Often referred to as “snapping knee syndrome,” this condition is identified with its only symptom, snapping on extension. The “snap” is caused when the femur and the meniscus are not able to move in sync with each other and the femur either slips over a ridge in the meniscus or off of the meniscus altogether.31 Unlike the normal meniscus, which is shaped to fit the condyle of the femur, a discoid meniscus lacks the configuration to serve as a stable surface for motion. This abnormal tracking adds stress to the meniscus, increasing the probability of lateral meniscus tears.32 Unfortunately, discoid menisci often remain undetected when no symptoms present prior to injury, and the only other way to identify a discoid meniscus is by magnetic resonance imaging (MRI).
| Figure 6. Discoid meniscus of right knee. |
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IMAGING
For decades, MRI has been used as a primary determinant for meniscal injuries but the fact that it is more sensitive to some tissues than others, however, can prevent it from producing a completely accurate picture of an injured area. This can cause injured tissues to remain undetected, or other “abnormalities” on the MRI may be misread as actual injuries (“false-positive”). One study that brought these issues into the spotlight was performed on college basketball players at Duke University who displayed no clinical symptoms of knee abnormality. Internal irregularities of the knee including cartilage defects, joint effusions, bone marrow edema, and even discoid menisci were found on the MRI’s of 75% of subjects, who never displayed any symptoms of meniscal abnormaility.33 More distressing is the fact that in another study on children with a mean age 12.2 years, 66% showed a high signal intensity within the menisci.34 A high signal intensity is one of the criterion to diagnose degenerative menisci (see Figure 7).
| Figure 7. False-positive MRIs of the knee in teenagers. Because significant abnormalities show up in the menisci on MRI in teenagers, when no true injury exists, relying on this modality to make a diagnosis is a scary proposition, especially if surgery is contemplated. Used with permission of Beulah Land Press © 2001 Oak Park, IL. Prolo Your Sports Injuries Away!, fig. 16-10. |
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Just as MRIs can lead to false-positive readings, they may also produce falsenegative findings by failing to detect an actual meniscal injury. This was the case in one study of 254 human knees, where the researchers found patients presenting with normal MRIs, despite exhibiting symptoms of meniscal injury confirmable on arthroscopy.35 Another study published in the Journal of Arthroscopic Surgery reported that 35% of their patients would have undergone unnecessary surgery if the examiner had relied on just MRI findings of meniscal tear alone, leading the researchers to conclude that MRIs are “an expensive, unnecessary procedure”35 (see Figure 8). Stanitski found that 71% of his patients were given inaccurate MRI readings, with 24% showing false-positive evidence of meniscal tears, while actual ACL, meniscal, and cartilage injuries went undetected in half of the patients.36 Part of the reason there are so many MRI “abnormalities” in the menisci in asymptomatic individuals is because structures that attach to the menisci can cause an increased signal and produce the false appearance of a meniscal tear.
| Figure 8. MRI of the right knee without contrast. Noted are changes in the medial meniscus. See how even the radiologist cannot determine whether this represents a recurrent meniscal tear or is just post surgical changes. |
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Perhaps the best study to date to document abnormal meniscal MRI findings in asymptomatic individuals was published in the New England Journal of Medicine in 2008.37 In this study MRI scans on 991 knees were taken and compared to patients’ responses about pain and disability in those knees. The MRIs in these patients (aged 50 to 90) showed that over 60% had meniscal tears documented on MRI and that sixty-one percent of subjects who had meniscal tears did not have any pain, aching, or stiffness in their knees.
As seen by these and numerous other studies, MR imaging often disagrees with patients’ clinical symptoms or arthroscopic findings, making it a poor tool for diagnosis. Rushing to surgery based on an MRI alone, therefore, can cause unnecessary surgery resulting in premature degenerative changes and may not solve the pain complaints of the patient.
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