Pathology – meniscus tear caused during a significant, memorable injury to the knee.
Presentation – typically in younger individuals. Joint line pain, haemarthrosis or effusion, possible mechanical symptoms (clicking, catching, locking or giving way).
Diagnosis – combining history, clinical tests and MRI scan findings.
Treatment – locked knees due to displaced meniscal tissue: surgical repair or excision. Non-locked knees: optimal management is not clear.
Where to refer – locked knees: urgent referral to an orthopaedic surgeon. Non-locked knees: physiotherapist with possible onward referral to orthopaedics.
Anatomy and function
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 zones). 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.
Traumatic meniscus tears are caused by a significant, memorable injury to the knee; this typically occurs whilst twisting on one leg with the knee slightly bent. The force exerted on the knee causes a tear in the meniscus, either in isolation or in combination with injury to other knee structures (e.g. anterior cruciate ligament).
Sports such as football and rugby are a risk factor for developing a traumatic meniscus tear, most likely due to the increased frequency of pivoting and twisting movements that are involved with these activities.
Traumatic meniscal tears occur most often in younger individuals, especially those aged 20-29. The individual may have felt a ‘click’ or tearing sensation with pain along the joint line at the time of injury. The individual is usually unable to continue the activity, or even weight bear, and may notice immediate swelling within the joint (i.e. within 2 hours of injury). Swelling that develops within this time period indicates bleeding within the knee joint (haemarthrosis); traumatic meniscal tears are one of the most common causes of haemarthrosis. However, if the meniscus tear is limited to an area with limited or no blood supply (figures 2-3 pink and white zones), swelling within the joint (effusion) may develop more gradually due to inflammation of the joint lining (traumatic synovitis). The effusion usually persists and the joint line pain is reproduced during certain movements (e.g. twisting when weight bearing or crouching).
Patients with displaced meniscal tissue may experience painful clicking/catching within the knee, or be unable to fully straighten their knee (extension deficit/locked knee) if the torn tissue physically blocks the joint. Patient’s may complain of knee instability, which may be due to unstable meniscal tissue, quadriceps muscle inhibition secondary to pain and/or swelling, or a lack of trust in the knee.
Various tests are used 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 meniscus tears is poor; for details on the diagnostic accuracy of individual tests, please visit the statistics section. It is generally recommended that several different positive tests, in combination with the clinical history and exclusion of other diagnoses, are needed to diagnose a traumatic meniscal tear.
Magnetic resonance imaging (MRI) has high diagnostic accuracy for identifying traumatic meniscal tears, but the presence of a tear does not confirm that the tear is the source of an individual’s symptoms. Vertical tears that occur in a longitudinal direction (longitudinal tears) (figure 4) typically occur in the periphery of the meniscus and therefore have potential to cause pain, but also to heal. Vertical tears that start from the inner edge of the meniscus and extend across the radius (radial tears) (figure 5) or in an oblique direction (oblique or parrot beak tears) (figure 6) are less likely to cause pain, but may not heal.
Figures 4-6: circumferential/longitudinal, radial and oblique tears.
Large meniscal tears can cause a physical block to movement, which may require urgent treatment. If the central portion of a longitudinal tear becomes displaced, the tear is called a bucket handle tear (figure 7), while a displaced oblique tear is described as a flap tear. MRI diagnosis of a meniscal tear is therefore not required unless the knee is locked, as the results of the scan do not influence treatment.
Patients presenting with a locked knee (physical block to extension) (image 1) caused by displaced meniscal tissue are considered appropriate for surgical intervention, and this is often performed on an emergency basis. The physical block is usually a bucket handle tear of the meniscus (image 2), but may be caused by other injuries including a rupture of the anterior cruciate ligament or tibial eminence fracture; it is therefore important to differentiate these different injuries.
Image 1: locked knee
Image 2: MRI bucket handle meniscus tear
During surgery, the torn meniscus is either repaired (figure 8) or removed (arthroscopic partial meniscectomy) (figure 9), depending on the location of the tear, direction of the tear (e.g. longitudinal or radial) and whether the tear can be securely repositioned.
Figures 7-9: bucket handle tear, meniscal repair and partial meniscectomy of a radial tear.
Meniscus repair provides better long-term results for knee function and X-ray evidence of knee osteoarthritis when compared with partial meniscectomy, but the decision to attempt repair can only be made during surgery. Meniscal repair is performed in approximately one quarter of young patients and has a failure rate of 22-24% within 5 years of surgery. Re-operation rates are lower in lateral meniscal repairs, or if a torn anterior cruciate ligament is reconstructed at the same time as meniscal repair, but are still substantially higher than partial meniscectomy.
The optimal management of traumatic meniscal tears (in patients without a locked knee) is not clear. Earlier studies show that meniscal tears can heal without surgery but those that have not healed may not cause symptoms. When comparing patient reported outcomes following partial meniscectomy for traumatic and degenerative meniscal tears, outcomes were similar to patients with degenerative meniscal tears, which are no better than sham (fake) surgery or exercise therapy.
To date, the outcomes of surgical versus non-surgical treatment for this patient group has not been investigated, although Dutch and Danish studies are underway.
Post operative rehabilitation
Restricted weight bearing or range of motion (ROM) does not improve outcomes following isolated meniscus surgery (repair or partial meniscectomy). However, any restrictions associated with other procedures performed at the time of meniscus surgery should be considered during post-operative rehabilitation.
Rehabilitation should be progressed based on the impairments present, the individual’s specific requirements (e.g. running, jumping) and their response to treatment. The following post-operative protocols are based on published literature for vertical meniscal tears.
Limited information exists regarding the recovery timeframe in conservatively managed, traumatic meniscal tears. Future clinical trials will provide important information on the recovery timeframes following conservative and surgically managed traumatic meniscal tears.
Individuals with a physical block to knee extension (locked knee) should be referred to an orthopaedic department as soon as possible. Individuals with a suspected traumatic meniscal tear without a locked knee should be assessed and managed by a physiotherapist. If symptoms do not improve, onward referral to orthopaedics is recommended for further assessment.
Written by: Richard Norris, The Knee Resource.
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