What is the Varus stress test?
The varus stress test at 20-30 ° knee flexion is the real workhorse test to perform when evaluating posterolateral knee instability. This test isolates the function of the collateral ligament of the fibula. Indeed, there should be no increased varus separation of the knee at 20-30 ° of flexion when the fibula collateral ligament is intact. When other structures are simultaneously injured with a fibula collateral ligament tear, such as the popliteal tendon or the peroneal popliteal ligament, there will be a greater amount of varus space present.
Evaluation of varus instability can be quite accurate in the hands of an experienced practitioner. Generally, subtle increases in varus separation can be evaluated to determine the degree of instability. Stress radiographs have found that 2.7 mm increases in lateral compartment space are indicative of a complete tear of the fibula collateral ligament, whereas 4 mm increases in lateral compartment space are indicative of a complete injury of the posterolateral corner.
To perform the varus stress test at 30 ° of knee flexion, the leg is placed on the examination table with the knee flexed between 20 °-30°. The fingers are then placed on the joint line while the distal femur is stabilized. Then a varus tension is applied to the knee while supporting the foot and ankle. Then the fingers can assess the amount of space. As with the medial side of the knee, it is important not to grab the distal tibia when applying this test and apply tension across the foot and ankle to determine the amount of increased rotational instability and determine the actual amount of lateral compartment gaps.
Use of varus stress test
To measure the integrity of the sideways collateral ligament and other structures that prevent lateral instability of the knee.
Procedure for the varus stress test
Client in supine position; stabilize the tibia in neutral while applying varus tension to the knee; act again with the knee slightly bent
Tibia will move away from the femur (laterally), excessively. Pain is also an indicator.
LCL, ACL, PCL, ITB, lateral gastrocnemius, joint capsule, or biceps femoris ligament may have been damaged.
LCL, ITB, biceps femoris tendon or joint capsule may be damaged
To evaluate the integrity of the LCL.
Performing the varus stress test
The patient’s leg must be relaxed for this test. The inspector should inertly bend the affected leg to about 30 degrees of flexion. Though palpating the lateral joint line, the examiner should apply a varus strength to the patient’s knee. A positive test occurs when there is pain or excessive spaces (some space is normal at 30 degrees). Be sure not to include hip rotation in your application of force. The examiner should then repeat the test with the knee in the neutral position (0 degrees of flexion). A positive test occurs when pain or space occurs. There should be no gaps at 0 degrees.
Compassion: 0.25 (“Evaluation of knee instability in acute ligamentous injuries”).
Importance of varus stress test
The lateral collateral ligament is significant in fighting varus force on the knee due to its attachments along the femur and the head of the fibula. Meanwhile, the peroneal nerve is also situated around the head of the fibula, any injury with a varus force mechanism to the knee could potentially stress the peroneal nerve as well. Other tissues at risk for these injuries contain the PCL and arcuate complex, particularly if the varus force of the injury is combined with extension.
At 0 degrees, generally, no gap occurs when varus stress is applied, so if a gap occurs during testing, serious injury is suspected, i.e. ACL, PCL, LCL, Capsule. At the 30-degree position, some space is produced, because the LCL and other structures are no longer under maximum stress. The LCL is a very thick fibrous tendon that can be palpated with positional tension in the position in figure 4 (just think about the accessories!). Due to the trouble that varus forces are a mechanism of damage (due to the shielding of the opposite lower extremity), isolated injuries to the LCL are relatively rare.