Pathology – a tear that has developed gradually in the meniscus. Considered a feature of knee osteoarthritis.
Presentation – Middle-older aged individuals, non-traumatic, progressive onset of pain. Pain is typically medial and activity-related (e.g. pivoting).
Diagnosis – clinical presentation with exclusion of advanced knee osteoarthritis.
Treatment – education, exercise therapy, weight management.
Where to refer – physiotherapy.
There are two menisci in each knee. The medial (inner) and lateral (outer) meniscus are located between the thigh (femur) and shin bones (tibia) (figure 1), are ‘C’ shaped when viewed from above but wedge shaped in cross section (figure 2). In the first decade of life, the whole meniscus has a blood supply but as the menisci mature the blood supply recedes and is limited to the outer third (figures 2-3 red zone). The nerve supply to the meniscus follows the blood supply and may provide information to the nervous system regarding knee joint position (proprioception).
Figures 1-2: front, bird’s eye and cross section views of the menisci.
Figure 3: zones of the menisci
50-70% of load placed on the knee is transmitted away from the joint cartilage by the menisci. This protects the cartilage from excessive pressures but is dependent on the menisci, and their attachments to the bones, being intact. The menisci also nourish the joint cartilage, lubricate the joint and provide stability to the knee. The medial meniscus is particularly important for knee joint stability in anterior cruciate ligament injured knees.
Meniscal tears can be categorised as traumatic or degenerative. It is important to differentiate these two separate presentations to ensure appropriate treatment is provided.
Degenerative meniscus tears usually develop gradually and are often found in individuals with no symptoms. Substantial evidence suggests that degenerative tears should be considered a feature of knee osteoarthritis rather than a separate condition; in individuals with no X-ray evidence of knee osteoarthritis, a degenerative tear is thought to represent early degenerative changes within the joint.
Occupations that involve frequent kneeling, squatting or stair use (more than 30 flights) are risk factors for developing a degenerative meniscus tear, most likely due to the increased mechanical load that is placed on the menisci during these activities.
Degenerative meniscus tears are more common in the middle-older aged population and more prevalent with increasing age. Since degenerative tears are considered part of a degenerative process within the knee (i.e. knee osteoarthritis), individuals typically present with a gradual onset of arthritic symptoms, as described below. It is important to note that the torn meniscus itself is unlikely to be the source of the individual’s symptoms; the symptoms are likely to be caused by other degenerative changes within the knee. If the individual can recall a specific injury that corresponded with the onset of their symptoms, this will be a trivial incident (e.g. standing from a low chair, squatting down) rather than a significant, traumatic injury that is associated with traumatic meniscal tears.
The main complaint in symptomatic individuals with early degenerative changes is pain in the knee joint. The pain is related to certain activities (e.g. kneeling, squatting) and usually improves with rest. The pain can be felt over the entire knee or confined to a specific area, depending on which knee compartments are involved.
As the degenerative process progresses, the individual may experience additional symptoms including early morning joint stiffness, a grating sensation (crepitus) or catching/locking. Please click for more information regarding established knee osteoarthritis.
Various tests are performed clinically in an attempt to diagnose meniscal tears, including joint line tenderness (video 1), McMurray’s test (video 2) and the Thessaly test (video 3). However, the diagnostic accuracy of these individual tests for meniscal tears is poor; for details on the diagnostic accuracy of individual tests, please visit the statistics section.
Since degenerative meniscus tears are considered a feature of knee osteoarthritis, the clinical criteria for diagnosing knee osteoarthritis are more relevant for identifying individuals with knee symptoms of a degenerative nature.
Magnetic resonance imaging (MRI) has high diagnostic accuracy for identifying degenerative meniscal tears but these tears are also seen in individuals with no symptoms. If an individual has already had an MRI scan performed, the presence of a tear does not confirm that the tear is the source of their symptoms. Degenerative tears are typically seen in the medial meniscus and occur in a horizontal direction (figures 4-5); these are called horizontal cleavage tears and a displaced horizontal cleavage tear is referred to as a flap tear. Degenerative tears that consist of multiple directions are described as complex tears. An MRI scan simply confirms the presence of degenerative changes within the knee (i.e. knee osteoarthritis), does not influence treatment, and is therefore not indicated.
Figures 4-5: back and side views of a horizontal cleavage tear on MRI (white arrows).
High quality evidence has shown that surgical removal of meniscal tissue (arthroscopic partial meniscectomy) (figures 7-8) is no more effective than sham surgery in patients with a degenerative meniscal tear and knee symptoms (pain, catching/locking). This suggests that a degenerative meniscus tear is unlikely to be the source of a patient’s symptoms and any improvements gained following surgery can be attributed to the placebo effect or a natural resolution of symptoms.
It has been proposed that specific sub-groups of patients benefit more from surgery than others, but there is currently a lack of strong evidence to support this notion. Arthroscopic partial meniscectomy is also associated with rare but potentially serious risks (DVT, infection, death), increases the risk for knee replacement surgery three-fold, and is therefore not recommended for most individuals with degenerative meniscal tears and knee symptoms. According to a recent clinical practice guideline, future research should investigate whether partial meniscectomy benefits patients that are unable to straighten their knee, or who have persistent, severe, and frequent mechanical symptoms.
Figures 7-8: partial and sub-total meniscectomy.
Exercise therapy is an effective intervention for individuals with degenerative meniscal tears and knee symptoms, without the associated risks of surgery. A recent high-quality study found that exercise therapy not only provided the same improvement in symptoms as surgery, but also increased thigh muscle strength. Quadriceps muscle weakness is a risk factor for knee osteoarthritis, therefore exercise therapy may be particularly important for individuals with degenerative meniscal tears and no X-ray evidence of significant arthritic changes.
Exercise therapy is therefore recommended as the most appropriate treatment for individuals with degenerative knee symptoms. Video 4 and 5 summarise the relevant initial exercises.
In overweight or obese patients with knee symptoms of a degenerative nature, losing at least 5-10% body weight has been shown to improve pain and/or function. Pain is a complex topic that is influenced by an individual’s beliefs, therefore patients should be offered accurate information regarding the disease process and management of degenerative meniscal tears, addressing any misconceptions they may have.
Improvements in symptoms and function are likely to be noticeable within 12 weeks of initiating the appropriate exercise. Continuing with exercise is important to sustain improvements gained for knee symptoms of a degenerative nature.
Individuals with knee symptoms of a degenerative nature should be assessed and managed by a physiotherapist.
Written by: Richard Norris, The Knee Resource.
Reviewed by: Jonas Bloch Thorlund, Professor, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark.
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