Abduction stress test

To primarily detect pain and/or laxity of the medial collateral ligament (MCL).

The MCL is the most commonly injured knee ligament and the valgus stress test is the primary tool for assessing the integrity of its deep and superficial fibres. In addition the posteromedial capsule, posterior oblique ligament, PCL and ACL will also be subject to stress during this manoeuvre.

In the acute injury, full physical assessment may not be possible because of pain, apprehension and swelling, so diagnosis may depend on assessment of the force and mechanism of injury, the degree of pain, the rapidity of swelling (immediate, significant swelling suggesting haemarthrosis) and the degree of disability.

Assessment of the subacute or chronic lesion allows the MCL injury to be graded (Bulstrode et al 2002, Kesson & Atkins 2005):

Imaging with stress X-rays and/or MRI may help grade the injury more specifically and determine the presence of concurrent damage to other structures.

Although valgus stress is the most frequently used test in assessing injury to the MCL, the absence of an appropriate reference standard against which to measure the accuracy of mild injury or rupture has resulted in little evidence to support its use. Only one study reported a sensitivity of 86% for MCL tears using arthroscopy as a reference standard (Malanga et al 2003).

Ensuring that the hip is internally rotated prevents extraneous movement of the leg during testing and allows the application of selective stress on the structures responsible for stabilizing the medial aspect of the knee. A positive test in slight knee flexion incriminates the MCL and/or posterior capsule, as this position takes tension off the ACL which provides a secondary restraint to valgus in full extension. When repeated in full extension, a positive test suggests damage not only to the MCL and posterior capsule but also to one or both cruciate ligaments.

Tibial rotation has an opposite effect on the collateral and cruciate ligaments. In external rotation the MCL/lateral collateral ligament are more taut and the ACL/PCL more lax and in internal rotation the opposite is true. The degree of MCL stress during this test can therefore be increased by adding external rotation of the tibia.

EXPERT OPINION	COMMENTS
	Valgus test
	Used in every patient as a screening test for medial knee stability and pain.

To primarily detect pain and/or laxity of the lateral collateral ligament (LCL).

Lateral or posterolateral knee injuries are relatively uncommon as the mechanism of injury usually requires an external impact (e.g. being hit by a car or a rugby tackle) to force the knee into an extreme varus position. In contrast to the MCL, the ligament is quite independent of the lateral capsule and meniscus which makes the structure less vulnerable to injury. The normal degree of varus is variable (usually around 7°) and should be compared to the normal knee if laxity is suspected. Stress X-ray showing a lateral opening of more than 8 mm is suggestive of a grade III injury (see ligament injury table, p. 184) and the likelihood of injury to the other posterolateral structures (cruciate ligaments, posterolateral capsule, arcuate–popliteus complex, iliotibial band) increases with the degree of abnormal varus movement detected (LaPrade & Terry 1997, Larsen & Toth 2005). Lateral instability, though much less common, is potentially more disabling than medial instability.

Fig. 6.2 Varus test.

Varus stress tests the integrity of the LCL ligament. Although laxity noted on this test may indicate one-plane lateral instability, it is more likely to be positive where there has been injury to the other structures that contribute to posterolateral stability (Malanga et al 2003). If this is suspected, the posterolateral drawer test (see p. 205), dial test (see p. 209) or external recurvatum test (see p. 211) are considered to be more accurate in detecting posterolateral rotational instability (PLRI; Baker et al 1983). Conversely, a negative varus test does not rule out PLRI as an intact PCL contributes to varus stability in full extension and may limit varus excursion. In one large study, the LCL was found to be involved in only 23% of PLRI injuries (LaPrade & Terry 1997).

There is little evidence on the accuracy of any of the tests for the lateral structures of the knee primarily due to the absence of an appropriate reference standard. The clinical findings for lateral and posterolateral injuries of the knee are often subtle and, as a result, are more frequently misinterpreted (Hughston et al 1976).

To maximize stress on the LCL, the tibia needs to be positioned in slight flexion and as much external rotation as possible as this reduces stress on the cruciates and leaves the iliotibial band lying centrally over the lateral joint line.

The test can be repeated with the knee in full extension and if instability is still detected, major disruption of the knee has occurred and injury to either the cruciates, popliteus or other lateral structures should be suspected along with injury to the LCL (Larsen & Toth 2005, Malanga et al 2003).

EXPERT OPINION	COMMENTS
	Varus test
	Used in every patient as a screening test for lateral knee instability.

To detect posterior (one-plane) instability and posterior cruciate ligament (PCL) laxity.

In a complete PCL tear, the average extent of posterior excursion of the tibia is 9.2 mm although incomplete tears will produce varied degrees of laxity (Hewett et al 1997). Injury of other stabilizing structures (i.e. arcuate–popliteus complex, posterior oblique ligament, iliotibial band) should always be considered as a potential source of pain and/or instability. Posterior excursion can be assessed and graded by measuring the amount of ‘step-off’ between the anterior tibial plateau and the femoral condyles (Larsen & Toth 2005).

The posterior drawer test is considered to be the most accurate test for diagnosing isolated PCL injuries but this has not been verified in studies examining its use as an isolated test. A high degree of sensitivity and specificity has been recorded where it is used as part of a composite assessment to determine PCL injury, particularly when complemented by other tests such as the posterior sag test (Malanga et al 2003); analysing the test in this context is helpful as it mirrors usual clinical practice.

Perhaps unsurprisingly, increased inter-examiner reliability has been noted in the presence of more significant grade II and III injuries (Rubenstein et al 1994).

TABLE 6.1 POSTERIOR DRAWER TEST

With an isolated tear of the PCL, the greatest degree of tibial excursion is noted at 90° flexion. Where the injury is located to the posterolateral corner, most excursion is found when the test is performed in 30°. In a combined posterolateral corner and PCL injury, increased posterior tibial movement will be noted when the test is repeated at both 30° and 90° flexion (Larsen & Toth 2005) and injury to other lateral stabilizers will be likely.

If the PCL is ruptured, the tibia, having lost some posterior restraint, tends to gravitate backwards (posterior sag sign). This false starting position can lead an inexperienced clinician to incorrectly record an increase in anterior tibial translation when in fact there is PCL insufficiency. Observing for a posterior sag of the tibia on the femur and performing the posterior drawer test prior to ACL assessment should guard against this (see related tests).

EXPERT OPINION	COMMENTS
	Posterior drawer test
	A standard test used in all patients which accurately identifies PCL tears.

The posterior sag sign/gravity drawer test/Godfrey’s test is a useful adjunct to the posterior drawer test. The patient lies supine with the hips and knees flexed to 90° and the lower legs supported by the clinician. If posterior instability is present, a posterior ‘sag’ appears and additional backward pressure will increase this posterior displacement.

The active drawer test/quadriceps active test can be helpful in confirming PCL insufficiency. In the drawer test position with the foot stabilized, the patient is asked to attempt to extend the knee. The backwards sag of the tibia will be reduced with this isometric contraction of the quadriceps (bringing the tibia back into its normal position) and increased with hamstring isometric contraction. This positions the tibia in its fully displaced position and provides a good starting position for maximum anterior translation to occur when the quadriceps contract again.

To detect anterior (one-plane) instability and anterior cruciate ligament (ACL) laxity.

In an evaluation of the evidence around physical tests at the knee, a composite assessment (which included the anterior drawer test) was found to be more accurate than any one single test in diagnosing ligament and meniscal lesions (Solomon et al 2001). The test has also demonstrated a high degree of specificity (Jackson et al 2003) although doubts over its degree of sensitivity led other studies to conclude that the test should be secondary to the more sensitive Lachman (see p. 194) or pivot shift test (see p. 201) (Benjaminse et al 2006, Jackson et al 2003, Ostrowski 2006, Scholten et al 2003). It is an easier test to perform, however, and for the less experienced practitioner, the findings may be more helpful than trying to detect abnormalities with the pivot shift test. The sensitivity of all these tests improves when testing in the acute stages is avoided and they are used either when the patient is anaesthetized or in the subacute/chronic stage of the condition.

In the test position of 90° knee flexion, the MCL and posterior capsule provide secondary restraints to anterior tibial translation. If these structures are intact and the ACL is injured in isolation, the drawer test will be normal, leading to a false negative result. Other factors that can lead to a false negative result are hamstring spasm, a bucket-handle meniscal tear which blocks anterior translation of the tibia, or a partial ACL tear which has attached to the PCL during the healing process (Kim & Kim 1995). A false positive test can occur (increased anterior translation even when the ACL is intact) if the medial coronary (meniscotibial) ligament has been disrupted (Magee 2008). Increased anterior excursion of the medial tibial condyle should lead the clinician to conduct further multiplanar tests (see Slocum AMRI, p. 198) to establish the extent of the rotational instability. If a click or sudden shift accompanies a positive drawer test, suspicion of a concurrent meniscal tear should be aroused. The sudden movement or jerk is known as Finochietto’s jump sign (Magee 2008).

TABLE 6.2 ANTERIOR DRAWER TEST

If the posterior cruciate ligament has been injured it can be difficult to establish the normal starting position for this test. PCL laxity or rupture will cause the tibia to drop backwards (posterior sag sign, see p. 191) which then falsely leads to an apparent increase in anterior drawer. It is therefore necessary to eliminate a positive sag sign before recording an increase in anterior drawer.

EXPERT OPINION	COMMENTS
	Anterior drawer test
	Useful as a secondary test if Lachman’s test is equivocal.

To detect anterior (one-plane) instability and anterior cruciate ligament (ACL) laxity.

This is a test for one-plane anterior instability and is the most sensitive physical test for diagnosing an isolated ACL injury. It was originally described by Torg but he named the test after his boss, Lachman (Torg et al 1976).

In studies using arthroscopy as the ‘gold standard’ for ACL diagnosis (Jackson et al 2003, Ostrowski 2006) Lachman’s test has been shown to be both more sensitive and specific compared with the anterior drawer (see p. 191) and pivot shift (see p. 201) tests. The Lachman test has also been found to be more accurate than MRI in the diagnosis of ligamentous injury (Kocabey et al 2004, Liu et al 1995, Rose & Gold 1996), a negative test thereby effectively ruling out complete ACL rupture (Scholten et al 2003).

The test is less sensitive where there is complex or acute injury (Frobell et al 2007, Yoon et al 1997) and, as with all ligament tests at the knee, is more sensitive when performed under anaesthesia (Kim & Kim 1995, Katz & Fingeroth 1986). Torg’s original study (Torg et al 1976) examined its use on patients with combined ACL and meniscal lesions and reported high levels of sensitivity, largely unaffected by the presence of bucket-handle tears. False negative results have been reported however, in cases where there is only a partial tear of the ACL, in chronic lesions where the injured ACL has adhered to the PCL, or where there is a concurrent meniscal injury sufficiently significant to prevent anterior translation of the tibia (Kim & Kim 1995).

In the test position, maximum tension is found in all portions of the ACL (Kim & Kim 1995). If instability is detected, stress X-rays can assist in grading the degree of injury (see below) although, in practice, clinicians are more likely to use their findings on examination to subjectively grade the degree of tibial translation.

In the larger patient, the knee can be supported in the required flexed position over the clinician’s knee, making handling a heavy leg easier. The degree of anterior drawer can be palpated if the fingers of the outside hand are placed over the joint line while the tibia is drawn forwards.

TABLE 6.3 LACHMAN’S TEST

The knee must be maintained in a degree of flexion throughout the test to reduce tension on the medial and lateral collateral ligaments and the iliotibial band, thereby minimizing their ability to restrain anterior movement of the tibia (Magee 2008). Lerat et al (2000) suggested that sensitivity of the test was improved by positioning the tibia in slight external rotation with the anterior translatory force coming from a posteromedial direction, as anterior translation of the medial compartment is thought to be a better indication of ACL deficiency in chronic tears than translation of the lateral compartment.

EXPERT OPINION	COMMENTS
	Lachman’s test
	Extremely helpful, with a positive test confirming an ACL tear, but the range must be compared with the unaffected knee as this varies considerably in the normal population.

To detect anteromedial rotatory instability (AMRI) of the knee.

AMRI occurs as a result of a forceful external rotation injury to the flexed knee while the foot is planted (e.g. pivoting on the weight-bearing foot while running or jumping); the injury is therefore often sustained during sporting activities.

The sequence of injury originally described by Slocum & Larson (1968) started with rupture of the medial collateral ligament and medial joint capsule followed by the posterior oblique ligament. If the knee continues to rotate into further external rotation, especially if accompanied by a valgus force, strain then falls on the anterior cruciate ligament which will ultimately rupture if the force is great enough. With this degree of instability, abnormal loading of the medial meniscus over time will predispose the knee to further injury. Given the structures implicated in AMRI, other physical tests should be used to fully assess the stability of the knee (see Lachman’s test, p. 194; valgus test, p. 183).

The degree of instability can be graded with stress X-rays by measuring the extent of anterior subluxation of the tibia (Magee 2008) (see below) although, in practice, clinicians are more likely to use their findings on examination to subjectively grade the degree of tibial translation.

The tibia must not be fully rotated as this will tension the surrounding structures and could lead to a false negative finding. If abnormal external rotation is noted when placing the leg into the pre-test position, major disruption of the medial capsule and deep portion of the medial ligament should be suspected. Greater degrees of instability would also implicate injury to the more superficial layer of the medial ligament and ACL (Slocum & Larson 1968).

EXPERT OPINION	COMMENTS
	Slocum (AMRI) test
	There is a lack of evidence to determine relative sensitivities and specificities for this test and it is considered by clinicians to be insufficient, if used in isolation, to diagnose AMRI with confidence. It should therefore be employed alongside other instability tests.