A flawless diagnosis of meniscal injury is necessary when considering its diverse consequences for the patient. Logically, the correct diagnosis is even more so important when considering the treatment of athletes.
Thomas Muellner MD, Ajsa Nikolic MS, Vilmos Vécsei Prof. MD
University Clinic of Traumatology, University of Vienna Medical School
It has always been difficult to concoct a method of evaluating knee injuries correctly and, in turn, devising an appropriate rehabilitation process. A flawless diagnosis of meniscal injury is necessary when considering its diverse consequences for the patient. Logically, the correct diagnosis is even more so important when considering the treatment of athletes, bearing in mind the intensified demands they place on their bodies. There is no doubt that an accurate, concise, clinical evaluation of patients with injuries to the knee is the basis of an exact diagnosis and successful treatment. Noninvasive methods such as magnetic resonance imaging are additionally recommended because of their high accuracy and negative predictive value. The use of invasive methods, such as arthroscopic operations should be restricted to treatment instead of diagnosis.
The knee is a common site of injury and functional disability. It can often be damaged as a result of direct blows during contact sports and, frequently also, indirect mechanisms. Over the years, many factors (e.g. the increase in the number of sports participants, the enhanced awareness of physical education, the increase in competitiveness, the positive image athletes portray) have caused the number and severity of injuries related to sports activities to increase. The highest incidence of knee injuries can be found notably in certain sports where a change of the direction, cutting, or pivoting, often occurs. Such sports include football, basketball, soccer, racquet sports, skiing, and track and field. [1-5]
However, as reflected in literature, the establishment of an accurate diagnosis in acute injuries of the knee may be difficult. [1, 6-19] Any delay in diagnosis could cause muscular atrophy thereby setting the athlete back in his programmed training. Furthermore, a prolonged period of disuse reduces the speed, agility and strength of the muscles involved. Therefore the activity level, the motivation, and the desires of the athlete must be considered in the diagnostic and therapeutic approach to management of the injury. [4, 6, 17, 20, 21] There is also the cost aspect of the treatment that needs to be contemplated when establishing the diagnostic and rehabilitation procedures. It would be optimal to devise a cost effective procedure that could be implemented for both athletes and the average patient. The aspects that need to be considered are similar for both groups of patients. Although, the professional athlete will be more sensitive to any type of radical surgery that will require an increased immobility of the joint, for reasons previously stated.
This article reviews anatomical and biomechanical considerations of the meniscus, and summarises recommendations for the diagnosis of meniscal tears in athletes.
1. THE MENISCUS
1.1 Anatomy and Function
The menisci of the knee are C-shaped and interposed between the condyles of the femur and the tibia. Anteriorly and posteriorly the menisci are attached to the tibia. The transverse ligament connects the anterior horns of the medial and the lateral meniscus. The peripheral area of the medial meniscus is firmly attached to the joint capsule throughout its length and in the middle a condensation of the joint capsule, known as the deep medial collateral ligament, strengthens the fixation to the tibia and femur. The lateral meniscus only has a loose attachment to the joint capsule, and the anterior and the posterior meniscofemoral ligaments run from the posterior horn of the lateral meniscus to the medial femoral condyle. 
The importance of the meniscus, in load transmission, joint stability, articular cartilage nutrition, and joint lubrication is well documented in literature. [23-25] Biomechanical studies have demonstrated that at least 50% of the compressive load of the knee joint is transmitted through the meniscus in extension, and approximately 85% of the load is transmitted in 90° of flexion. [26-28] An increased occurence of osteoarthritis described by Fairbank  and many other investigators [30-35] was found in relation to partial or total menisectomy after injuries to the knee.
1.2 Epidemiology of meniscal tears
Any activity that can cause injury to a knee ligament can also cause meniscal tears. Injuries to the healthy meniscus are usually produced by a compression force coupled with a rotation of the flexed knee as it starts to move into extension. The final meniscal tear type and location is determined by the direction and the magnitude of the force that acts on the knee and the position the knee is in at that point in time. Any abnormal mechanical axis in the knee joint, either primarily or secondary to a ligamentous injury, may lead to a greater incidence of meniscal injury. [36, 37] The sports with the highest prevalence of meniscal injuries are soccer, football, basketball, and baseball. [1-5] (FIGURE 1) The incidence of meniscal injuries that result in menisectomy is 61 per 100,000 population.  The ratio of the frequency of medial to lateral tears ranges from 2:1 to 5:1. According to literature, the type of sports activity and the presence of additional ligamentous injuries influence this distribution. [10, 38, 39] (FIGURE 2,3) The jeopardizing effect of ACL deficiency was shown by Irvine and Glasgow  who found only 14 knees with intact menisci in 100 patients with functional instability.
2. DIAGNOSTIC ASSESSMENT
In all areas of medicine, the practitioner uses two basic and informative steps to help diagnose the patients main problem. A meticulous patient history and a skilled clinical examination are only of use if they are performed with much care and routine practice. Patient histories require a good working knowledge of anatomy and internal medicine while, the physical examination often depends on the acquired practice of the physician. These two steps are crucial in the accurate diagnosis and therefore the correct rehabilitation process of the patient, after injury.
2.1 General History
After routine questions such as family history, social status, and vegetative anamnesis an important question is whether there were any previous injuries or surgeries of the involved joint. Not only is anatomy an important basic, but also the knowledge of statistical information such as the fact that there are age related injures.The exact progression of the injury is of vital importance for the prediction of the type of injury (traumatic vs. degenerative). Often a patient's recount of the story can specify a certain type of injury (i.e. an audible "pop" is characteristic for ACL tears). Furthermore, post injury happenings, such as swelling, may also give clues. The occurrence of swelling, secondary to a hemarthrosis, is approximately 70% as a result of an ACL tear, in approximately 20% by a peripheral meniscal tear, in 5% by an osteochondral fracture. [6, 12, 17, 41] There are certain characteristics that can be used as a guideline, (e.g. the presence of chronic recurrent swelling is most likely an indicator of an irritant in the joint, i.e. meniscal tear, loose body) in order to further reduce the number of possibilities. Some seemingly obvious indicators cannot be used as such (e.g. the severity of an injury cannot be judged by the presence or absence of hemarthrosis). A common complaint after injury, knee locking, is more likely to be caused by meniscal lesions in a younger patient and must not be confused with hamstring spasms, which often occur shortly after knee injury and are usually related to injuries of the medial collateral ligament. On the other hand, instability of the knee (i.e. giving way) also often occurring after knee injuries, may be due to pain reflex rather than instability within the knee. (TABLE 1)
2.2 General Physical Examination of the Knee
A certain order of operations, common for all areas of medicine, simplifies the routine and makes diagnosis easier. When the patient is being led into the examining room, attention should be paid to his/her walk and positioning of the injured limb. Attention should be given to the uninjured limb first, enabling the doctor to get familiar with what should be normal, as well as allow the patient to relax. The injured limb is inspected for the presence of wounds, ecchymosis, swelling, effusions, or muscle atrophy, taking further note of any other abnormalities. Then the limb is tested for its range of motion, both actively and passively. Following this, palpation of the knee (collateral ligaments, their attachments, bony prominences and the joint line) and other parts of the extremity (hip and ankle) is performed. Special interest is paid to areas of tenderness and/or discoloration. The doctor should work his way to specific testing of the affected areas. In all cases, attention should first be focused on both legs noting the alignment of the knee (varus vs. valgus) and thrust due to chronic ligament instability or osteoarthritis, while the patient stands, walks or performs squats. In an acute injury the squats can be avoided if insidious pain is felt. There are several tests that can be performed to help specify the type of injury that might have occurred. The diagnosis of ligamentous injuries, patellofemoral problems, anterior knee pain syndromes, and overuse injuries, are not the focus of this paper, and therefore will not be discussed. In one of the following sections a group of six examinations used to detect meniscal injuries will be introduced briefly.
3. SPECIFIC TESTS AND/OR SIGNS FOR MENISCAL TEARS
The evaluation of the general history and a general physical examination should already give the physician clues to lead the diagnosis towards that of a meniscal lesion. In 20% of the knees with acute traumatic hemarthrosis an isolated meniscal tear will be present. [6, 12, 17, 41] Patients with already preexisting functional instability of the knee are highly suspect for the occurrence of meniscal tears.  An additional common symptom is locking of the knee, caused either by the dislocated torn meniscus or by pain related to other pathologies. The extent of the flexion deficit does not correlate to the extent of the meniscal tear. There are several differential diagnosis, depending on acute or chronic meniscal tears, which have to be considered before establishing an accurate diagnosis. (TABLE 2)
In literature there is a great number of tests and signs for the diagnosis of a meniscal tear offered. However, only routine practice and up to date recommendations can help establish an accurate clinical diagnosis of a meniscal tear. The number of tests and signs used to diagnose meniscal tears and the combination of all the possible tests should, with practice, become routine. There are six tests, which allow the most accurate clinical diagnosis of meniscal tears in a trained practitioner's hands.
3.1. Tenderness on palpation of the joint line: Probably the most important finding in patients with a meniscal tear is localized tenderness along the joint line. In 60-80 % of the patients with meniscal lesions, this test will produce pain.  The reported sensitivity is about 75%. 
3.2. Boehler Test: This test  is performed in the same way one tests the stability of the collateral ligaments. Valgus stress should result in pain in a patient with a lateral meniscus lesion, and varus stress should result in pain in a patient with a medial meniscus lesion.
3.3. McMurray´s Test: In this test, the knee is flexed and, at various stages of flexion, internal and external rotation of the tibia are performed.  The medial meniscus is tested in external rotation, and the lateral meniscus in internal rotation. The presence of pain and a palpable "clunk" is a positive McMurray test. In case of a meniscal tear this test is positive in 45% to 50%. [44, 45]
3.4. Steinmann Test 1: This test is performed with the patient supine.  Internal and external rotation of the tibia are performed in various degrees of flexion. The presence of pain is regarded as positive finding. The reported sensitivity is about 40%. 
3.5. Apley Grinding Test: This test is performed with the patient in the prone position.  The hip is extended and the knee is flexed to more than 90°. The examiner places downward pressure on the foot, and the joint surfaces are than rotated and compressed. The reported sensitivity is about 45%. 
3.6. Payr Test: In this test the knee is flexed in 90°.  A varus stress leads to compression of the posterior horn of the medial meniscus. If there is a meniscal tear pain will result. The reported sensitivity is about 40%. 
Several factors help improve the accuracy of the above mentioned tests. For instance, the test should be performed in combination with each other, considering that they will be less precise when performed solely (FIGURE 4). It has also been shown that tears of the medial meniscus are diagnosed more accurately than tears of the lateral meniscus. Furthermore, the time between the injury and the clinical examination, and the epidemiology play a significant role for the accuracy of the clinical examination (FIGURE 5). [4, 46]
4. IMAGING TECHNIQUES
4.1 Radiography, Arthrography, Computed Tomography (CT), Ultrasound (US), Radionuclide Imaging (RI)
Radiographic examination of the knee is fundamental to the evaluation of patients with knee disorders to rule out fractures, osteochondritis dissecans, free bodies, and degenerative changes. With the introduction of non-invasive and non-radiation exposing imaging techniques, arthrography, CT, and RI are not performed anymore at our institution. US investigations for the diagnosis of meniscal tears are also not performed, and therefore, can not be recommended.
4.2 Magnetic Resonance Imaging (MRI)
The introduction of MRI has revolutionized the diagnostic imaging of the musculoskeletal system. When considering the diagnosis of meniscal tears, MRI was shown to be almost equal to arthroscopic evaluation (FIGURE 6). Therefore the time of diagnostic arthroscopies should have long been forgotten. The major limitations continue to be the high cost involved in this purchase, the availability in certain areas, and the experience with MRI knee interpretation. There are several studies considering economical aspects, and it is the decision of the physician whether an MRI investigation is necessary or not to establish an accurate diagnosis. [15, 46-49]
In a previous study we found that MRI did not improve the diagnostic accuracy of the clinical examination alone for detection of meniscal tears in high level athletes.  However, the advantages of the MRI are the visualization of the extent of the meniscal tear, and the detection of occult chondral and osseous injuries by using normal imaging techniques or by doing MRI arthrography with gadolinium complex. [50-53] In our opinion not only should the radiologist interpret the MRI but also the physician, especially when the decision to operate is made. Furthermore, the surgeon always has to decide if the clinical findings in patients with knee complaints coincide with the results of MRI.  In an investigation of asymptomatic professional basketball and collegiate football players Brunner et al. found that 50% of these asymptomatic athletes had significant baseline MRI abnormalities that could have adversely affected scan interpretation in the context of an acute injury.  Casscells pointed out by that not all meniscal tears cause symptoms. 
Based on the principles described earlier, an algorithm for the diagnosis and treatment of meniscal lesions in athletes can be recommended. It is justifiable to say that when the clinical symptoms clearly imply a meniscal tear, arthroscopy should be the next step. We do not recommend a conservative treatment for four to six weeks to wait and see if symptoms subside, if there are some questions about the actual diagnosis. Obviously, athletes will insist on receiving a definite diagnosis and therapy in order to be able to plan delay in sports activities or their return to them. An MRI investigation is a helpful and recommended step if certain aspects of the correct diagnosis remain unclear. Clearly athletes, interested in evading unnecessary operations, will demand an MRI scan. This will logically then have to be considered.
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