Clinical Tests Used to Diagnose Anterior Cruciate Ligament Tears Are Less Sensitive in Obese Patients

A Retrospective Cohort Study

Sravya P. Vajapey, MD, MBA; Timothy L. Miller, MD


Curr Orthop Pract. 2021;32(1):6-10. 

In This Article

Abstract and Introduction


Background: Anterior cruciate ligament (ACL) rupture is a common athletic injury. Multiple clinical studies have evaluated the sensitivity and specificity of physical examination tests that are used to diagnose ACL injury. We sought to determine if the sensitivity of these clinical tests is affected by a patient's body habitus. We hypothesized that sensitivity of the Lachman, anterior drawer, and pivot shift tests is lower in obese patients than in patients with a normal body mass index (BMI).

Methods: We compared the sensitivity of three clinical tests, the Lachman, anterior drawer, and pivot shift, in a group of obese patients with a group of nonobese patients. A total of 181 adult patients who had undergone ACL reconstruction by a single surgeon were included in the study.

Results: Sensitivity of the Lachman test was 87.3% in obese patients versus 94.1% in the nonobese control group. Sensitivity of the anterior drawer test was 76.3% in obese patients compared to 88.2% in the nonobese control group. Sensitivity of the pivot shift test could not be accurately assessed because pain and swelling prevented the physician from performing this test in most patients on their initial presentation.

Conclusions: The sensitivity of common clinical tests used to diagnose ACL tear, the Lachman, anterior drawer, and pivot shift, is decreased in obese patients compared with the nonobese control group. This study suggests that a clinician may need to have a lower threshold to perform advanced imaging in an obese patient with a suspected ligamentous injury of the knee even if the physical examination is not fully indicative of ligamentous injury.

Level of Evidence: Level III.


Anterior cruciate ligament (ACL) rupture is a debilitating injury that can lead to functional disability, secondary meniscal tears, chondral injuries, and posttraumatic arthritis if left untreated.[1] Although some of these secondary injuries can persist and cause residual disability with ACL reconstruction, research has shown that it has the potential to prevent further meniscal damage and may even delay degeneration of the knee joint.[2] Furthermore, several studies have shown that athletes with delayed ACL reconstruction have higher incidences of medial meniscal tears and articular cartilage lesions.[3] Therefore, prompt diagnosis and treatment of this condition is important for preventing further damage to the knee.

There are several well-known clinical tests that are commonly used to diagnose an ACL rupture: the Lachman, anterior drawer, and pivot shift. In the original description, the modified Lachman test was performed with the patient placed supine and the injured knee flexed at 30 degrees. The examiner places one hand on the patient's distal femur for stabilization and the other hand on the proximal tibia, pulling the proximal tibia anteriorly. More than 3 mm of displacement of the tibia on the femur with a soft endpoint is considered abnormal and positive.[4] In the anterior drawer test, the patient is supine and the injured knee is flexed at 90 degrees with the foot stabilized. The examiner places his or her thumbs on the proximal tibia with the tibia starting in an anatomically aligned position and attempts to translate the tibia anteriorly on the femur. Increased translation, especially when compared to the normal contralateral knee, is considered positive.[5] In the pivot shift test, the examiner places one hand on the distal tibia with the knee in extension. The examiner places the other hand over the fibular head and brings the knee from extension to flexion when applying a valgus force and internally rotating the tibia. This subluxes the tibial plateau anterior to the lateral femoral condyle, preventing easy reduction when the knee is flexed. At approximately 30 degrees of flexion, the subluxed anterior tibial plateau will suddenly reduce, producing a palpable shift or "clunk." This is considered a positive pivot shift test.[6]

Though there are many other tests to diagnose an ACL rupture, these three are the most common and do not require special equipment like the KT-1000 test. There have been several studies evaluating the sensitivity and specificity of each test. A recent review article demonstrated that the anterior drawer test has sensitivity values ranging from 0.18 to 0.92, the Lachman test from 0.63 to 0.93, and the pivot shift test from 0.18 to 0.48.[7] Although there is no clear consensus as to the most accurate test, combining all three tests can produce high diagnostic accuracy.[8]

There has been extensive research comparing the sensitivity and specificity of clinical tests that are used to diagnose an ACL rupture. However, there are no data that assess the effect of patients' body habitus on the sensitivity of these tests. Obesity is a pandemic in United States of America (USA), with 37.9% of the American population meeting BMI criteria for "obese" in the most recent Centers for Disease Control and Prevention (CDC) data brief published in 2017.[9] The clinical tests for diagnosis of ACL rupture were described in the late 1900s, when the composition of the American patient population was quite different compared to the current population. Some of the clinical tests can be physically taxing on the examiner and even more so when performed on a heavier, more robust limb. The purpose of this study was to determine if the sensitivity of these tests decreases in patients with elevated BMI. We hypothesized that it is more difficult to perform these clinical tests in obese patients and, therefore, the sensitivity of the tests is also lower in this patient population compared to nonobese patients.