Valgus stress test of the knee

The Valgus stress test of the knee is used to evaluate the integrity of the medial collateral ligament (MCL) of the knee.

How is Valgus Test of the knee Performed?

The Valgus Test of the knee is performed with the patient lies in the supine position. By Placing the affected leg in extension and slight external rotation, the clinician holds the patient’s ankle with one hand, while the other hand is on the lateral condyle of the femur. Then he applies a strong valgus force, with a counterforce applied at the lateral femoral condyle.

To further assess the medial collateral ligament, posterior oblique ligament, and posterior cruciate ligament (PCL), the test is then repeated at 20–30 degrees of flexion.

The posterior fibers of the MCL can be isolated, by placing the knee in 90 degrees of flexion with full external rotation of the tibia. The femur is prevented from rotating by the clinician’s shoulder. The clinician places one hand on the posterior aspect of the foot and the other on the heel, and an external rotation force is applied using the foot as a lever.

What does a positive Valgus stress test of the knee mean?

Valgus Test of the knee is Positive if pain or an excessive amount of motion is detected compared with the other extremity, a hypermobility or instability should be suspected.

With the knee tested in full extension, any demonstrable instability is usually very significant.

Pain with this maneuver is caused by an increase in tension of the medial collateral structures or the connection of these structures with the medial meniscus.

The following structures may be implicated with a positive Valgus Test of the knee:

1. Superficial and deep fibers of the medial collateral ligament.
2. Posterior oblique ligament
3. Posteromedial capsule
4. Medial capsular ligament
5. Anterior Cruciate Ligament (ACL)
6. Posterior Cruciate Ligament (PCL).

Hughston¹ concluded that a valgus stress test positive at 30 degrees and negative at 0 degree indicates a tear limited to the medial compartment ligaments (posterior oblique ligament) and posterior medial capsule, whereas a valgus stress test positive at 0 degree indicates a tear of both the PCL and the medial compartment ligaments.

Notes:

• Normally, there is little or no valgus movement in the knee, and, if present, it should be less than the amount of varus motion.
• Under normal conditions, the end-feel is firm.
• With degeneration of the medial or lateral compartments, varus and valgus motions may be increased, while the end-feels will be normal.

The varus and Valgus Test of the knee can be graded by the following:

• Grade I: The joint space opening is within 2 mm of the contralateral side.
• Grade II: The joint space opens 3–5 mm more than the contralateral side in 20 degrees of knee flexion and less than 2 mm more than the normal knee in full extension.
• Grade III: The joint space opens 5–10 mm more than that of the normal knee in 20 degrees of flexion and full extension.

Related Anatomy

Medial Collateral Ligament

Both the MCL and the LCL are considered to be extra-articular ligaments. The MCL, or tibial collateral ligament, develops as a thickening of the medial joint capsule.

It can be subdivided into a superficial band and a deep band:

1. The superficial band:

• It is a thick, flat band, and has a fan-like attachment proximally on the medial femoral condyle, just distal to the adductor tubercle, from which it extends to the medial surface of the tibia approximately 6 cm below the joint line, covering the medial inferior genicular artery and nerve.
• The superficial band blends with the posteromedial corner of the capsule and, when combined, is referred to as the posterior oblique ligament.
• The superficial band is separated from the deep layer of the ligament by a bursa.
• Since the superficial band is farther from the center of the knee, it is the first ligament injured when a valgus stress is applied.

2. The deep band:

• The deep band (medial capsular ligament) is a continuation of the capsule.
• It blends with the medial meniscus and consists of an upper meniscofemoral portion and a lower meniscotibial portion.

The anterior fibers of the MCL are taut in flexion and can be palpated easily in this position.

The posterior fibers, which are taut in extension, blend intimately with the capsule and with the medial border of the medial meniscus, making them difficult to palpate.

Information regarding the biomechanical function of the collateral ligaments is quite scarce compared with that of the
ACL.

It would appear that the MCL is the primary stabilizer of the medial side of the knee against valgus forces, and external rotation of the tibia, especially when the knee is flexed.

Grood et al.² determined that the MCL was the primary restraint, providing 57% and 78% of the total restraining moment against valgus force at 5 and 25 degrees of flexion.

Reference

1. Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities. Part I. The medial compartment and cruciate ligaments. J Bone Joint Surg Am. 1976 Mar;58(2):159-72. PMID: 1254619.
2. Grood ES, Noyes FR, Butler DL, Suntay WJ. Ligamentous and capsular restraints preventing straight medial and lateral laxity in intact human cadaver knees. J Bone Joint Surg Am. 1981 Oct;63(8):1257-69. PMID: 7287796.
3. Clinical Tests for the Musculoskeletal System, Third Edition book.
4. Mark Dutton, Pt . Dutton’s Orthopaedic Examination, Evaluation, And Intervention, 3rd Edition Book.