Written by manual therapists Thomas T. Ødegaard and Roar Syltebø

Injuries to the medial collateral ligament (MCL) are the most common of all “serious” knee injuries (Kurzweil & Kelley, 2006; Kastelein et al., 2008). These structures are traditionally tested by applying valgus stress to the knee. Hughston and colleagues gave the first good description of the test, which they called the “abduction stress test”, in 1976 (Hughston et al., 1976).

Indication

The valgus stress test is indicated after all knee injuries, particularly when the patient has medial pain or a sensation of instability.

Procedure

The patient lies supine. The leg being tested is slightly abducted at the hip. The examiner grasps the lower leg/ankle of the leg to be tested and places the other hand over the lateral aspect of the knee. The valgus stress test should be performed both in full extension and at 20–30° of knee flexion. For testing in flexion, the knee is flexed approximately 20–30° over the edge of the examination table. In extension, both the thigh and the lower leg rest on the table. With the hand holding the lower leg/ankle, the examiner applies a gentle abduction (valgus) force, while the hand at the knee provides counter-pressure in a medial direction.

The valgus force should be applied through the foot/ankle. Hughston and colleagues note that the hand at the ankle usually rotates the lower leg slightly externally, often without the examiner being aware of it. The test should be performed slowly with a constant force, making it easier to assess pain and instability. It should be repeated several times, gradually increasing the stress up to the point of pain, to obtain an accurate picture of the patient’s knee. Once the test is clearly positive, the knee should not be forced further into valgus (Hughston et al., 1976).

Hughston and colleagues (1976) emphasise that the uninjured side should always be tested first in acute injuries. This shows the patient what to expect, builds confidence and prevents unnecessary tension and fear. Testing the uninjured side also provides an important clinical baseline for assessing the injured knee.

Alternatively, the examiner can stabilise the distal lower leg/ankle under the arm while both hands grasp around the patient’s knee. With this grip, the knee can be flexed and extended, the examiner can palpate the joint line with the thumbs, and varus and valgus stress can be applied by turning the trunk towards or away from the table (Solberg & Kirkesola, 2007; Cook & Hegedus, 2012). In addition to slowly applied forces, this grip allows the examiner to give quick varus and valgus impulses and assess “looseness” in the knee. This is characterised by increased varus and valgus movement and may be felt as a “clunk” in the knee.

Interpretation

The valgus stress test is positive if it reproduces familiar pain on the medial side and/or shows instability with increased medial joint opening (“gapping”) compared with the uninjured side. A positive test at 30° of flexion suggests an MCL injury, while a positive test also at 0° suggests a more extensive injury, which may also involve the cruciate ligaments and/or the posterior joint capsule (Hughston et al., 1976; Simonsen et al., 1984; Solberg & Kirkesola, 2007).

Anatomy and biomechanics

The medial ligament complex of the knee has three parts: the superficial MCL, the deep MCL and the posterior oblique ligament. Together they cross the joint line and stabilise the knee against valgus. The semimembranosus tendon has fibres that blend with the posterior oblique ligament and reinforce the posteromedial joint capsule. The posterior oblique ligament thus forms a functional unit with the semimembranosus and contributes to the control of internal rotation of the knee. This is one reason why major MCL injuries can cause chronic instability, particularly rotational instability (LaPrade et al., 2007; Laprade & Wijdicks, 2012; Kurzweil & Kelley, 2006).

Incidence and mechanism of injury

Traumatic knee injuries (excluding fractures) occur in about 5.3 per 1,000 patients per year in Dutch general practice (Kastelein et al., 2008). Kastelein and colleagues (2008) found an MCL lesion on MRI in 35 of 134 adults (26%) who consulted their general practitioner within five weeks of a knee injury. Sixteen (12%) had an isolated MCL lesion, and 12 (9%) had an MCL lesion combined with a meniscal tear (Kastelein et al., 2008). In an MRI study from the same Dutch general practice cohort, 25.7% of the injured knees had a partial and 0.7% a complete MCL lesion (Boks et al., 2006). The most common mechanism of injury is a fall and/or a force against the outside of a slightly flexed knee, pushing it into valgus. These are often isolated collateral ligament injuries with a partial or complete tear. The patient typically has severe medial pain, and an isolated injury causes local swelling but no joint effusion (Laprade & Wijdicks, 2012).

Scientific properties

To standardise the grading of instability, the Committee on the Medical Aspects of Sports of the American Medical Association published guidelines in 1967/68, so that clinicians would have a common scale (“The team physician”, 1967). Most articles and textbooks use this scale: grade 1+ corresponds to 0–5 mm of joint opening, grade 2+ to 6–10 mm and grade 3+ to 11 mm or more.

Although joint opening is difficult to estimate to the nearest millimetre, the scale gives the clinician a working framework. A complete MCL tear is graded 3+ and may show far more instability than 11 mm (Hughston et al., 1976).

In general, instability during collateral ligament testing is greater when the patient is under anaesthesia, as the muscles are relaxed and the joint can open more. This was confirmed in 68 knees in the work of Hughston and colleagues (Hughston et al., 1976).

Hughston and colleagues compared their clinical findings with the findings at surgery in 68 knees. They concluded that an isolated MCL injury is present when there is increased joint opening corresponding to grade 2+ at 30° of flexion and a negative test at 0°. Grade 3+ instability with the knee straight indicates an additional injury to the posterior cruciate ligament (Hughston et al., 1976). They reported no figures for sensitivity or specificity, but describe the test at 30° of flexion as completely reliable for detecting injuries of the medial compartment (Hughston et al., 1976).

In 1984, a Danish group, Simonsen and colleagues, studied the accuracy of clinical knee tests in 118 patients with an acute knee injury and joint effusion in whom a ligament injury was suspected. All patients were examined both without and under anaesthesia. Fifty-two per cent of the patients had an MCL injury, most of them complete tears. The group found 21 false-positive findings on clinical examination and 5 on examination under anaesthesia. The valgus stress test had a sensitivity of 88% and a specificity of 73% without anaesthesia, and a sensitivity of 94% and a specificity of 88% under anaesthesia (Simonsen et al., 1984).

A weakness of this study is that the procedure for the MCL test is not described, and reliability was not assessed. The authors conclude that an MCL injury is primarily a clinical diagnosis for which arthroscopy is not necessary. Most of the cases in which an MCL injury was missed are explained by major additional injuries, for example to the posterior cruciate ligament (Simonsen et al., 1984).

In 1986, Sandberg and colleagues studied stability tests of the knee, again with and without anaesthesia. The valgus stress test had a sensitivity of 80% without anaesthesia and 100% under anaesthesia. The study has several weaknesses: the patients were tested at 20° and 90° of knee flexion, the description of the procedure is incomplete, and neither reliability nor specificity was assessed (Sandberg et al., 1986).

Harilainen and colleagues published two studies in the mid-1980s (Harilainen et al., 1986; Harilainen, 1987). The studies are of low methodological quality, and the patients were only examined at 20° of flexion. The authors recommend examination under anaesthesia, as an ordinary clinical examination gives many false-negative findings (Harilainen, 1987).

Anatomical studies and several textbooks show that a normal knee with intact ligaments is stable in full extension (Solberg & Kirkesola, 2007). A positive collateral ligament test with the knee straight therefore suggests injury both to the medial structures and to the cruciate ligaments. In slight flexion, the knee is closer to its resting position, and a little side-to-side movement is normal even with intact ligaments. A positive test in flexion may be due to an isolated MCL injury, but also to intra-articular conditions, sprain of ligaments and capsule, or synovitis (Solberg & Kirkesola, 2007).

LaPrade and colleagues (2010) measured joint opening on stress radiographs in a biomechanical cadaver study, with the valgus force applied by a clinician. With a simulated grade III injury of the superficial MCL, medial joint opening increased by 1.7 mm in extension and 3.2 mm at 20° of flexion. With a complete injury of the whole medial ligament complex, it increased by 6.5 mm in extension and 9.8 mm at 20° of flexion. Testing in slight flexion was thus the most sensitive position for isolated MCL injuries, while marked joint opening also in extension suggested a concomitant cruciate ligament injury. The authors suggest that an increase of more than 3.2 mm compared with the uninjured side at 20° of flexion should raise suspicion of a grade III MCL injury, and that clinical grading may underestimate the severity of the injury (LaPrade et al., 2010). As this is a cadaver study, the figures cannot be transferred directly to clinical examination, but they support the traditional interpretation of testing in extension and flexion.

In 2008, Kastelein and colleagues published a comprehensive study of the diagnostic value of history-taking and physical examination in general practice. A total of 134 patients aged 18–65 years who consulted their general practitioner within 5 weeks of a knee injury underwent a standardised physical examination, with MRI as the reference standard. The history findings associated with an MCL lesion were an external force to the leg and rotational trauma. Pain and increased joint opening on valgus stress at 30° of flexion were the findings from the physical examination associated with an MCL lesion. The valgus stress test was assessed both as a pain provocation test and as a test of increased joint opening (Kastelein et al., 2008):

Valgus stress test as a pain provocation test
Sensitivity	78%
Specificity	67%
Positive likelihood ratio	2.3
Negative likelihood ratio	0.3

Valgus stress test for assessment of increased joint opening (laxity)
Sensitivity	91%
Specificity	49%
Positive likelihood ratio	1.8
Negative likelihood ratio	0.2

Each test on its own therefore changed the probability of an MCL lesion only slightly. When the history findings were combined with both pain and increased joint opening on valgus stress, the positive likelihood ratio rose to 6.4. The authors conclude that MCL lesions are common after knee injuries in general practice, and that history-taking has diagnostic value, which increases considerably when combined with physical examination (Kastelein et al., 2008).

The American Physical Therapy Association (APTA) clinical practice guideline for knee ligament sprain (Logerstedt et al., 2017) still relies on the findings of Kastelein and colleagues. The APTA clinical practice guideline for knee ligament sprain lists medial pain and increased joint opening on valgus stress at 30° of flexion, together with a force to the outside of the leg, rotational trauma, and tenderness over the MCL and its attachments that reproduces familiar pain, as findings in MCL injury. The 2017 revision found no new research on the diagnosis of collateral ligament injuries (Logerstedt et al., 2017).

A systematic review of imaging of the MCL found that clinical examination was slightly inferior to stress radiography in detecting MCL injuries, while examination under anaesthesia performed about as well as stress radiography. MRI agreed with the clinical findings in 65–92% of cases and was more sensitive than clinical examination, but was limited in showing where the injury was located and how severe the instability was. Medial joint opening in healthy knees ranged from 3 to 11 mm, which underlines the importance of comparing with the uninjured side (Meyer et al., 2022).

Cook and Hegedus (2012) give the valgus stress test a utility score of 2, meaning that the evidence moderately supports its use (on a scale from 1, strong support, to 3, minimal or no support). This assessment reflects the literature up to 2012. More recent research has not changed this picture substantially: no new clinical studies of the diagnostic accuracy of the test have been published, and the APTA clinical practice guideline for knee ligament sprain still relies on Kastelein et al. (2008) (Logerstedt et al., 2017).

There are few studies, and several of them have major methodological weaknesses. More and better research is needed to establish the diagnostic accuracy and reliability of the valgus stress test. Clinically, however, Body Examination finds the test very useful.

Body Examination suggests the following interpretation of the valgus stress test:

• The valgus stress test is positive if it reproduces familiar pain and/or shows instability with increased medial joint opening.
• Body Examination considers the valgus stress test, based on clinical experience, to be a good clinical test for assessing the medial structures of the knee.
• There is little research on the diagnostic properties of the test. Experience nevertheless indicates that current theory and practice are sound.
• A positive test at 30° of flexion and a negative test in extension suggest an isolated MCL injury. A positive test also in extension suggests a more extensive injury, with possible involvement of the cruciate ligaments and the posterior joint capsule.
• Body Examination considers the valgus stress test to be a relatively simple test to perform, which all clinicians who examine patients with knee complaints should master. The interpretation can be challenging, and careful technique and comparison with the opposite side are very important. Remember that many people have naturally increased laxity in the knee, so increased joint opening on both sides may be normal for the individual.
• Body Examination suggests testing the MCL with slow movements, but also with quicker varus and valgus impulses, to make it easier to assess increased laxity and the type of end-feel.
• Body Examination recommends testing the knee as early as possible after the injury. In this phase, bleeding, hamstring guarding or other injuries may make the procedure and interpretation less certain. The knee should therefore be re-examined in the subacute phase, when swelling and muscle tension have subsided.
• In challenging acute cases, Body Examination recommends testing only with the leg lying straight on the table. In our experience, it is easier for the patient to relax, and a clear impression of pain and instability can still be obtained. A positive test with the knee straight indicates a larger injury than the MCL alone.
• Body Examination has good experience with the modified variant in which the patient’s lower leg/ankle is held between the examiner’s body and arm. It makes the patient feel secure and gives the examiner a favourable lever arm.
• The valgus stress test is not good enough on its own. Body Examination strongly recommends combining it with a thorough history and other tests when a medial injury is suspected.

Literature search, updating and translation were carried out with the assistance of AI (Claude, Anthropic). The professional content has been reviewed and quality-assured by the editor-in-chief, Roar Syltebø.

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