Bodyexamination

Posterior drawer test (knee)

Written by manual therapists Thomas T. Ødegaard and Roar Syltebø

The posterior cruciate ligament (PCL) of the knee is mentioned less often in the literature, and injured less frequently, than the anterior cruciate ligament. PCL injuries account for approximately 8–15% of all cruciate ligament injuries. The posterior drawer test has been described to detect this type of injury, which occurs most often in road traffic accidents and in sport. In the modern literature, Hughston and colleagues were the first to describe the posterior drawer test, in 1976 (Hughston et al., 1976).

Indication

The posterior drawer test is indicated in all acute knee injuries, particularly high-energy injuries, and if the patient has a sensation of instability.

Procedure

The patient lies relaxed in a supine position, with the hip flexed to 45° and the knee flexed to 80–90°. Hughston and colleagues (1976) describe the test performed with the patient’s foot resting on the table and the examiner sitting so that the examiner’s thigh fixes the patient’s foot against the table. The examiner’s hands are placed on the proximal tibia, with the index fingers on the hamstrings to confirm that the muscles are relaxed. The thumbs are placed on, and palpate, the joint line of the knee. The examiner pushes the tibia posteriorly. Hughston and colleagues (1976) emphasise that the push should be gentle. They also describe that the test should be performed with the tibia in external rotation, then internal rotation and finally in neutral. As with the anterior drawer test, it is important to compare with the uninjured side (Hughston et al., 1976).

Solberg and Kirkesola (2007) describe a variant of the test in which a firm, quick push is applied to move the tibia posteriorly.

Posterior drawer test (knee), procedure

Interpretation

The posterior drawer test is positive if there is increased posterior translation, or instability or giving way, compared with the opposite knee. Increased laxity and a complete tear of the ligament will give different end-feels. Posterior instability occurs with an injury to, or complete tear of, the PCL, manifested by the tibial condyles subluxing equally posteriorly without rotation. Anterior instability may also occur as a result of a PCL injury or tear. The work of Hughston and colleagues (1976) covers 50 acute tears of the medial compartment, including 18 patients with a medial ligament injury associated with a PCL injury. The degree of instability can be graded as 1+, indicating 0–5 mm of translation, 2+, indicating 6–10 mm, and 3+, indicating 11 mm or more (Hughston et al., 1976). In this material, the test was negative in 14 and positive in 4 of the 18 patients, which the authors explain by the injuries being examined in the acute phase. The authors state that they have never seen a chronic PCL injury without a positive posterior drawer test (Hughston et al., 1976).

Rubinstein and colleagues (1994) proposed a different way of grading the injuries, based on the position of the tibial plateau relative to the ipsilateral femoral condyle during the test. Grade 1+ is given if the anteromedial edge of the tibia remains anterior to the medial femoral condyle. Grade 2+ is given if there is posterior translation of the tibia with the anterior tibia flush with the femoral condyles, that is, without a step. Grade 3+ is given if the tibial plateau translates posteriorly so that a subluxation and a step relative to the femoral condyles occur (Rubinstein et al., 1994).

Clancy and colleagues (1983) found less translation during the posterior drawer test with the foot in internal rotation in patients with isolated PCL tears. These findings differ from, and are the opposite of, Hughston’s description. One possible explanation that has been suggested is secondary increased tension in one or both meniscofemoral ligaments, which were found to be intact in these patients (Clancy et al., 1983; Feltham & Albright, 2001).

In their study of the PCL, the well-known Finnish researcher Pekka Kannus and colleagues (Kannus et al., 1991) cover everything from anatomy and injury mechanism to rehabilitation protocols. They establish that the PCL is the strongest ligament in the knee, approximately twice as strong as the ACL. They describe the posterior drawer test at 90° of flexion as sensitive but non-specific, while also noting that false-negative findings are frequent, especially in acute knee injuries. On this basis, they consider a positive “sag sign” to be the most characteristic clinical finding in patients with isolated PCL injuries. Kannus and colleagues believe that, where necessary, the clinical diagnosis of a PCL injury should be confirmed by MRI, examination under anaesthesia, arthroscopy or a combination of these (Kannus et al., 1991).

In 1994, Rubinstein and colleagues (Rubinstein et al., 1994) carried out a study to determine which clinical tests are most accurate for diagnosing PCL laxity. This was a blinded, randomised, controlled study of the accuracy of PCL tests among a group of sports medicine orthopaedic surgeons. Thirty-nine volunteers took part: 19 with chronic, isolated PCL injuries, and as controls 9 patients with ACL injuries and 12 subjects with normal knees. All examiners were blinded to the patients’ history, identity and diagnosis. The overall clinical accuracy for all the orthopaedic surgeons was 96%, and the accuracy for detecting a PCL injury was also 96%. The orthopaedic surgeons found that the posterior drawer test, including palpation of the tibiofemoral step-off, was the most sensitive and specific test. The results were:

Sensitivity 90%
Specificity 99%
Negative likelihood ratio 0.1
Positive likelihood ratio 90

In the same material, the accuracy was highest for grade 2 and 3 injuries, while grade 1 injuries were detected less well. For grade 1 laxity, the test was no more than 70% sensitive. The five orthopaedic surgeons agreed on the grading of the PCL injury in 81% of cases. The study concludes that a good history and a careful clinical examination with a combination of several tests provide a sound basis for detecting an isolated PCL injury (Rubinstein et al., 1994).

A German group, Hochstein and colleagues (Hochstein et al., 1999), evaluated the incidence of PCL injuries and, on that basis, carried out a general review of the examination of PCL injuries. They report that approximately 8–10% of all serious ligament injuries of the knee involve the PCL, corresponding by their estimate to around 4,000–5,000 Germans with a PCL injury each year. Most of these injuries occur in road traffic accidents, while the number of PCL injuries in sport is increasing. In their experience, 90% of PCL injuries are high-energy injuries, often combined with other injuries, frequently fractures. This, they suggest, explains why PCL injuries tend to be detected late, as a PCL injury is mainly a clinical diagnosis and is not seen on plain radiographs. The instability after a PCL injury can often appear in the same way as after an ACL injury, and it can be difficult to judge whether it is the anterior or the posterior drawer test that is positive.

On this basis, the German group argues that the posterior drawer test alone is not good enough and has too many sources of error. To make the diagnosis as reliable as possible, Hochstein and colleagues recommend performing several PCL tests. They also point out that various bony abnormalities may be present, which underlines the importance of radiographs in the assessment of complex chronic unstable knees. The research group considers arthroscopy to be the gold standard for diagnosing cruciate ligament injuries (Hochstein et al., 1999).

In 2003, Jackson and colleagues (Jackson et al., 2003) published an article reviewing the literature on the evaluation of acute knee pain in primary care, including the accuracy of clinical tests. The posterior drawer test is not mentioned specifically in the article. The authors report that, when the history suggests a meniscal or ligament injury, the clinical examination has a sensitivity of 0.81 and a specificity of 0.95 for PCL injury (Jackson et al., 2003).

In a systematic review, Kopkow et al. (2013) searched MEDLINE, Embase and other databases up to April 2012 for studies comparing clinical tests with a reference standard such as arthroscopy or MRI in PCL injuries. Of 1,307 articles identified, only 11 met the inclusion criteria, and together they studied 11 different clinical tests. Because of differences between the studies, a meta-analysis was not possible. The authors conclude that most clinical tests for PCL injuries have not been studied well enough for us to be confident that they can confirm or rule out a PCL tear, and that there is a strong need for further research (Kopkow et al., 2013).

Solberg and Kirkesola (Solberg & Kirkesola, 2007) describe the posterior drawer test performed with a firm, quick push to test the PCL. A firm push often makes it easier to assess the end-feel. The book also points out that various structures in the knee may give a positive test.

Cook and Hegedus (2012) give the posterior drawer test a utility score of 2, meaning that the evidence moderately supports its use in the diagnosis of PCL injuries (on a scale from 1, strong support, to 3, minimal or no support). This assessment reflects the literature up to 2012 and rests largely on a study of chronic injuries examined by experienced orthopaedic surgeons (Rubinstein et al., 1994). The later systematic review by Kopkow et al. (2013) calls this score into question, as it concluded that the research base for clinical PCL tests is too limited to say with confidence whether they can confirm or rule out a PCL tear.

Body Examination is aware that there are some further studies of the PCL than those mentioned here, but they are of lower methodological quality. These studies are characterised by few patients and by being unblinded and retrospective.

Body Examination suggests the following interpretation of the posterior drawer test:

  • Increased posterior translation of the tibia compared with the opposite knee suggests a PCL injury.
  • Body Examination considers the posterior drawer test to be a very simple test to perform that all clinicians should master. The interpretation can be challenging, and careful technique and comparison with the opposite side are important.
  • Both the original test and its modifications show that the degree of tibial rotation can be decisive.
  • Body Examination suggests testing posterior translation both with a slow movement and with a quicker push, to make it easier to distinguish between increased laxity and the type of end-feel.
  • In chronic injuries, the posterior drawer test appears to be both sensitive and specific, but it is less reliable in acute injuries, and the research base for PCL tests as a whole is limited.
  • The posterior drawer test is a simple test for the PCL. Body Examination nevertheless recommends supplementing it with other PCL tests, as it is not good enough on its own, particularly in acute injuries.

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.

References

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