What is the valgus stress test?
The valgus stress test or medial stress test is a test to sense damage to the medial collateral ligament of the knee. It involves placing the leg in extension, with one hand positioned as a pivot on the knee. With the other hand placed on the foot applying an abduction force, an attempt is made to force the leg at the knee into the valgus. If the knee is gotten to open on the medial side, this is indicative of medial collateral ligament damage and may also designate laxity of the capsular or cruciate ligament.
Purpose of valgus stress test
The valgus stress test, also recognized as the medial stress test, is used to measure the integrity of the medial collateral ligament (MCL) of the knee. MCL injuries are common in the athletic population and can occur as isolated injuries or in combination with other structural injuries.
Carrying out the test
The inspector places one hand on the outside of the knee, acting as a pivot point, while the other hand is located on the foot. The medial joint line is palpated while the examiner simultaneously applies a kidnapping force to the foot and a valgus force finished the knee joint.
This test is typically performed at 30 and 0 degrees of knee flexion. When performed at 30 degrees, the MCL is more isolated from other structures in the medial joint, with a sensitivity of .86 to .96 for MCL tears. The second version of the test can then be performed, at 0 degrees of knee flexion, which allows evaluating other medial joint structures.
The two versions are summarized below:
- Knee in valgus at 0°: Together with the MCL, the medial knee joint capsule, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL) are under tension.
- Knee in valgus at 30°: The MCL is the main stabilizer in this position and is, therefore, the main structure evaluated. The medial joint capsule is also harassed in this position.
Diagnostic accuracy of valgus stress test
At 30 degrees: Sensitivity: .86-.96 (“Medial collateral ligament tears: MRI findings and associated injuries”, “Evaluation of knee instability in acute ligament injuries”).
Importance of valgus stress test of the knee
The medial collateral ligament is important in resisting valgus force on the knee due to its attachments along the femur, meniscus, and tibia. The MCL also plays an important role in restricting tibial external rotation. Surgical cutting of the superficial portion of the MCL was shown to increase the tibial external rotation to 90 degrees approximately 3 times (Ellenbecker, 2000). According to Neumann, the MCL attaches to the medial epicondyle proximally and posterior to the distal insertion of the anserinus foot distally on the anteromedial tibia.
The pro-founder fibers of the MCL are shorter than the superficial fibers and also attach to the posteromedial capsule, meniscus, and semimembranous tendon. Because the deeper fibers are shorter than the surface fibers, they are more likely to be injured when a valgus force is applied to them, although the surface fibers provide the primary resistance to the valgus force! On the other hand, the superficial fibers are more likely to be stressed by external rotation of the tibia on the femur (or internal rotation of the femur on the tibia). With the attachment of the MCL to the meniscus, whenever the mechanism of injury affects the MCL, be sure to also check the meniscus for injury.
At 0 degrees, there is usually no space when valgus stress is applied, so if a gap occurs during the test, a serious injury is suspected, i.e., ACL, PCL, MCL, capsule oblique popliteal ligament, and parts of the ACL are tighter in full extension). At the 30-degree position, some clearance is produced, because the MCL and other structures are no longer under maximum stress, but the MCL is the main stabilizer at this position.
The MCL in general is one of the most important ligaments for the stability of the knee. With a hypermobile knee, due to an MCL sprain, it is significant to take extra precautions to decrease the risk of additional injury. With a loose MCL, the ACL becomes increasingly stressed with valgus forces, especially at 45 degrees of flexion (Ellenbecker, 2000). Remember that the MCL is the main valgus restriction on the flexed knee; Without it, the anterior cruciate ligament is prone to injury.
The significance of the valgus stress test in the diagnosis of posterolateral variability of the knee.
The diagnosis of posterolateral knee unpredictability is often based on a typical indirect mechanism of injury, a history of “giving in”, and a positive dial test. Our search of the English literature did not reveal any mention of the inclusion of the valgus stress test in the diagnostic protocol for posterolateral instability.
Hypothesis: Created on our experience, we hypothesized that a medial collateral ligament (MCL) tear will also yield a positive dial test and that a valgus stress test would provide differential diagnostic information.
Methods: The MCLs of 14 fresh cadaveric knees (7 cadavers) were cut to simulate a grade 3 tear, taking care not to damage the medial retinaculum or posteromedial knee stabilizers. The amount of tibial external rotation (the dial test) was measured for each knee before and after the MCL cross-section.
Valgus stress test at 30° knee flexion
The 30 ° valgus stress test is the workhorse test to determine if there is a medical injury to the knee. The main structure that provides valgus stability to the knee at 20-30° of knee flexion is the superficial medial collateral ligament. This is the major and most important structure on the medial aspect of the knee and is best appraised at this flexion angle.
To perform the valgus stress test, the knee is flexed amongst 20° and 30°, and the fingers are placed straight on the joint line. Valgus tension is then applied to the knee by applying the tension across the patient’s foot or ankle. It is important not to apply the test solely through the distal tibia because then the potential rotational instability that is present with a medial knee injury is not isolated and may result in an underestimation of the amount of medial space.
There are many different ways to qualitatively and quantitatively evaluate medial knee injuries. One of the most common ways is through the AMA classification that was devised in 1966. In this classification, pain, but not a significant gap, during the application of a valgus stress test is indicative of a partial tear of degree I into substance. Increased space, but a defined endpoint, is indicative of a grade II tear, whereas space without a definitive endpoint is indicative of a grade III or a complete medial knee injury.
Additional tests have evolved more recently and include the use of valgus stress radiographs, which are more accurate in assessing the degree of a medial knee injury. In general, increasing the medial knee spacing at 20° knee flexion of 3.2 mm is indicative of a complete injury to the superficial medial collateral ligament, while increasing the knee spacing of 9, 8 mm is indicative of a complete injury to the medial knee.