Pathology – injury to a structure on the medial aspect of the knee, specifically the superficial medial collateral ligament, deep medial collateral ligament and/or posterior oblique ligament.
Presentation – frequently caused by a contact mechanism, medial knee pain with possible valgus or rotational instability in higher grade injuries.
Diagnosis – combining history with clinical tests, stress X-Rays or MRI if required.
Clinical tests – local tenderness, valgus stress test, anteromedial drawer test, dial test. The diagnostic ability of tests are either limited or not reported.
Treatment – isolated medial knee injuries are often managed without surgery. Multi-ligament injuries have better outcomes with surgery.
The superficial medial collateral ligament (sMCL), deep MCL (dMCL) and posterior oblique ligament (POL) are considered the three most important stabilisers of the medial knee (figures 1-2), with the bony configuration, medial meniscus, joint capsule and surrounding muscles/tendons also contributing to joint stability.
The sMCL originates just superior (above) and posterior to (behind) the medial epicondyle of the femur. The proximal division of the sMCL attaches to the tibia, just below the joint line, while the distal division inserts more distally on the tibia.
The dMCL is a thickening of the medial joint capsule, attaching the medial meniscus to the femur (meniscofemoral division) and the tibia (meniscotibial division). The POL is located posterior to the sMCL, is an extension of the semimembranosus tendon and reinforces the posteromedial joint capsule.
Together, the sMCL, dMCL, POL, oblique popliteal ligament (OPL) and posterior horn of the medial meniscus are considered the main structures of the posteromedial corner (figure 3).
Figure 1-3: anatomy of the medial and posterior aspect of the knee. With permission Laprade et al (2007) and Wijdicks et al (2010).
The proximal division of the sMCL is a primary constraint to valgus stress, while the distal division has a primary role in resisting both external and internal rotation of the tibia. The meniscofemoral division of the dMCL provides primary constraint to internal rotation of the tibia, with both divisions of the dMCL acting as secondary constraints to knee valgus. The POL provides resistance to valgus and rotation force, particularly when the knee is in full extension. Therefore, any forceful movements into knee valgus, tibial rotation, or combinations of these positions, can injure the medial structures.
Data collected from elite European football teams indicates that approximately three-quarters of MCL injuries are caused by a contact injury, typically when a player is tackling or being tackled.
In the early stages following injury, the individual will complain of pain on the medial aspect of the knee with tenderness on palpation (poking) of the medial knee structures. The proximal third of the sMCL is the most common site of injury, followed by the middle third and less commonly the distal third.
Infrequently, the distal insertion of the sMCL may avulse (pull away) from the tibia (figure 4). If the pes anserinus structures become interposed between the ligament and bone, healing of the ligament back to the bone may be compromised; this is known as a Stener-like lesion.
Figure 4: distal avulsion of the sMCL
The sMCL is an extra-articular structure (located outside the joint), therefore injury to this ligament can result in localised medial knee swelling or bruising. Approximately 90% of MCL injuries occur in isolation but a large proportion of grade III medial knee injuries occur in combination with a cruciate ligament rupture, causing additional swelling within the knee joint (haemarthrosis/effusion).
Injury to the medial knee can result in valgus and/or anteromedial rotatory instability (AMRI), which is often described by the individual as a ‘giving way’ sensation in the knee. In chronic presentations, patients may demonstrate a valgus thrust, where the knee ‘thrusts’ inwards during the weight bearing phase of walking. AMRI occurs when there is excessive anterior translation and lateral rotation of the medial tibial plateau.
The infrapatellar and sartorial branches of the saphenous nerve transmits signals from the skin to the central nervous system for sensation. This nerve may be involved in medial knee injuries, presenting as altered sensation on the lateral aspect of the knee or medial aspect of the shin and ankle.
90% of MCL injuries are isolated, but 78% of grade III injuries occur in combination with anterior cruciate ligament or posterior cruciate ligament ruptures. A diagnosis of grade III medial knee instability should therefore raise suspicion of concomitant cruciate ligament injury.
Clinical tests that quantify abduction (valgus) or anteromedial rotation of the tibia have been recommended to assess the integrity of the medial knee structures. For details on the diagnostic accuracy of clinical tests for medial injury, please visit the statistics section.
Valgus Stress Test
This test is performed with the knee semi-flexed (20-30°) and in full extension (0°), assessing for medial joint gapping/laxity and an end point (video 1).
Video 1: valgus stress test with the knee semi-flexed.
Medial knee pain with no or minimal laxity is classified as a grade I injury. Valgus laxity at 20-30°, but not at 0°, suggests the MCL is injured but the POL is likely intact (grade II injury). Valgus gapping at both 20-30° and 0° suggests the MCL and POL are both injured (grade III medial knee injury), with likely additional involvement of a cruciate ligament.
The Hughston grading scale is often used to classify medial knee injuries.
Table 1: Hughston grading scale
|Increased medial knee gapping||0-5mm||5-10mm||>10mm|
It is important to note that this scale is based on the perceived amount of gapping and the actual values, as measured with X-ray (valgus stress radiographs), are less than proposed.
External Rotation 'Dial' Test
This test is performed with the patient supine (on their back) or prone (on their front) and knees together. The tibia is externally rotated as far as possible with the knee at 30° and 90° of knee flexion. The amount of external tibial rotation is compared between sides at both angles, using the medial borders of the feet for reference (video 2).
Video 2: prone dial test at 30° and 90°.
A side-to-side difference of greater than 10° is considered a positive test at 30° of knee flexion. For the test to be positive at 90°, the side-to-side difference should be the same, or greater, than that noted at 30°.
Anteromedial rotary instability, secondary to a medial knee injury, can result in a positive dial test at both 30° and 90° of knee flexion.
Care must be taken when interpreting a dial test that is positive at both 30° and 90° as these findings may also represent an isolated posterolateral corner (PLC) injury or combined PLC and posterior cruciate ligament (PCL) injury. To differentiate these three injury patterns, the dial test findings should be used in combination with other clinical tests for the medial knee and PCL.
Anteromedial Drawer Test
This test is performed with the patient supine, knee flexed to 80° and tibia externally rotated 15°. An anteromedial force is then applied to the tibia, assessing for a side-to-side difference in anteromedial laxity.
Video 3: anteromedial drawer test.
Increased anteromedial laxity is suggestive of a medial knee injury, with or without concomitant ACL injury.
Imaging is not typically required for acute medial knee injuries but may be required to differentiate medial and lateral knee laxity in chronic presentations.
The valgus stress test can be performed during X-ray (valgus stress radiographs) to objectively measure the side-to-side difference in medial joint gapping (figure 5). Isolated sectioning of the sMCL has been shown to result in >3.2mm side-to-side difference during valgus stress with the knee slightly flexed and >1.7mm with the knee fully extended. Sectioning of all the main medial knee structures (sMCL, dMCL and POL) results in >9.8mm and >6.5mm side-to-side difference with the knee slightly flexed and fully extended respectively.
In patients with significant pain at the upper third of the sMCL, X-rays may show evidence of a Pellegrini-Stieda lesion (figure 6), which is ossification near the proximal insertion of the ligament to the femur.
Figures 5-6: valgus stress radiograph and Pellegrini-Stieda lesion (white arrow).
Figures 7-8: MCL injury with bone marrow oedema lateral tibial plateau.
The optimal management of isolated medial knee injuries is not clear as little evidence exists investigating conservative (non-surgical) and surgical interventions. Dislocated knees, which often involve the medial structures, have been shown to have superior outcomes in function, knee stability, return to work and return to sport following surgical intervention.
Isolated medial knee injuries (grade I-III) are usually managed without surgery. There is no consensus regarding bracing but grade III medial knee injuries are usually placed in a long lever brace with restricted weight bearing to protect the structures during the early stages of healing. Protocol 1 is based on expert opinion and published studies.
Surgical repair/reattachment of avulsed medial structures, or reconstruction of the medial knee structures in chronic instability may be required; the procedure of choice is often dependent on surgeon preference and patient presentation.
Limited evidence exists regarding rehabilitation after medial knee surgery; rehabilitation is often inadequately described regarding the number of sets/repetitions of exercises and criteria for progression. Protocol 2 is based on expert opinion and published literature.
Protocol 1 and 2: conservative and surgical management of medial knee injury. Please click images to access the full protocols.
Recovery following isolated medial knee injury is dependent on the grade of injury, use of a brace and whether surgery has been performed. Recent evidence in elite footballers found that the average lay-off time was 24 days for all MCL injuries (10 and 23 days for grade I and II injuries respectively), with return to sport for grade II injuries being delayed by 10 days on average in those that were braced.
Written by: Richard Norris, The Knee Resource
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