Assessment and Diagnosis of Anterior Cruciate Ligament Injuries

Injuries to the anterior cruciate ligament (ACL) are common injuries of the knee. There are approximately 200,000 injuries of the ACL in the United States annually. Of these injuries, surgical reconstructions are involved in the rehabilitation process of around 100,000. It is important for health care professionals to have the ability to confidently and accurately assess these injuries when they occur to allow individuals to begin proper treatment as soon as possible. Knowledge of mechanism of injury, signs and symptoms, and diagnostic tests for ACL injuries are all important assessment tools for a health care professional when diagnosing ACL injuries. Current researches in these areas are important to consider ensuring that the best examination process is being used for accurate diagnosis of ACL injuries.

The ACL, along with the Posterior Collateral Ligament, is one of two intracapsular cruciate ligaments in the knee. The ACL is comprised of collagen – mostly Type I – and is arranged in multiple bundles of fibers. The ACL is innervated by the posterior tibial nerve and receives its blood supply from the middle and inferior genicular arteries. Jarbo et al. (2017) state that the ACL has two separate portions, “the anteromedial bundle and the posterolateral bundle, named for their respective insertion sites from the tibia to the femur”. One group of researchers argues that these bundles have less of an anatomical separation, but more of a functional differentiation. Markatos et al. (2013) explain, “An anteromedial bundle becomes taut at 90 degrees of flexion, and a posterolateral bundle becomes tight as full extension is approached”. This allows the knee to maintain stability at various joint angles that may occur through everyday movements.

The function of the ACL involves the maintenance of stability at the knee joint. Jarbo et al. (2017) describe the role of the ACL as follows: “The ACL is responsible for preventing anterior translation of the tibia relative to the femur and also acts as a secondary restraint to tibial rotation and varus/valgus rotation”. This means that the ACL has more than one responsibility to help maintain knee stability, with the main function being the resistance to anterior motion of the tibia.

The importance of the role of the ACL in preventing this motion is described by Markatos et al. (2013) who claim that “the ACL…accounts for up to 86% of the total force resisting anterior draw”. Total knee stability, including resistance to rotational movement, is further aided by the surrounding musculature. However, the body is not always able to maintain this stability, especially during athletics. When the ACL is exposed to a load greater than it is able to handle, it causes injury varying from small tears to a full rupture. Athletes of all levels are at an increased risk for an ACL rupture. The risk for those in basketball, handball soccer and skiing is even higher than other sports.

ACL injuries can occur from both contact and non-contact mechanisms of injury, however, non-contact mechanisms make up the majority of ACL ruptures. Kiapour et al. (2015) state that over 70% of all ACL injuries occur from a non-contact mechanism. The most common forms of non-contact mechanisms for ACL injuries are related to a change in speed or “the generation of multidirectional force across the knee joint while bearing weight”. According to Wetters et al., the individual’s knee is typically in the range of “early flexion to hyperextension at the moment of injury”. They go on to explain that when the knee is in this range, the tensile properties of the ACL are higher. An athletic movement when the knee is often in this range is during deceleration. Therefore, deceleration is described as a frequent mechanism for ACL injuries. This can be explained by the fact that when decelerating, “the quadriceps forces required to stop the athlete are increased and thus contractions can place significant stresses on the ACL”. Other mechanisms include landing from a jump or performing a sideways cutting motion. Wetters et al. (2015) add that twisting and pivoting movements can also lead to non-contact ACL injuries. Overall these injuries tend to be caused by a combination of movements and forces at the knee.

One group of researchers describe that “sagittal and coronal load, in combination with imbalanced muscle contraction forces of the quadriceps and hamstrings muscle groups, can lead to significant stresses on the ACL”. When the stresses of these forces are too high within the knee, the ACL ruptures. Diagnosing ACL injuries start from recognition of the mechanism of injury. Knowing the mechanism of injury can give clues as to whether or not an ACL injury should be considered as an index of suspicion while performing an assessment. Furthermore, it is important to recognize common signs and symptoms of ACL injuries to assist in a correct diagnosis. One author suggests it is important to make sure to ask the affected individual is they heard any auditory cues, such as a snap or a pop. Complete ACL tears often create a sound loud enough for the individual or those around to hear. This can be a good indication of a potential ACL tear. The patient will often describe feeling unstable or that the knee will give out. They may be apprehensive to stand up or walk initially following the injury. Upon inspection, ACL tears commonly “produce rapid swelling at the joint line”. While it is important to recognize these signs and symptoms of ACL injuries, the most important diagnostic tool is the use of special tests for ACL tears.

There are a variety of special tests that can be used to diagnose ACL injuries. According to Jarbo et al. (2017), “The 3 most widely accepted clinical tests to diagnose an ACL tear include the anterior drawer, Lachman, and pivot shift tests, all of which were initially described in the 1970s”. Recently, a new test has been proposed, called the “Lever Sign”. It is important to study the literature when new tests are released to ensure that the clinical examination tools being used in practice are the most appropriate for the condition. Additionally, it is important to consider that in the clinical setting, “the accuracy of these examinations may be affected by patient factors such as swelling, pain, protective muscle action and examiner experience”. Therefore, selection of a special test for diagnostic needs to be based on evidence as well as current patient presentation. The Anterior Drawer tests is a simple test for ACL injury. This simplicity makes it one of the most commonly used ACL tests. To perform this test, the practitioner has the patient in a supine position with their foot flat on the assessment table, hip flexed at 45 degrees and knee flexed at 90 degrees. The foot is stabilized as the practitioner applies an anterior translation to the tibia. Two different scenarios can be a positive test result; if there is no end-feel or if there is increased tibial translation compared to the uninjured side it is considered positive for an ACL injury. For this test to be completed correctly, the practitioner needs to ensure that the tibia is aligned with the medial condyle of the femur before initiating test. Rossi et al. (2011) explain that failing to do this could cause a false positive if there is a damaged PCL, because it can cause a more posterior tibial starting position, making it seem like there is an increased anterior translation compared to the other side.

Another point to consider is that pain and inflammation may make it uncomfortable or impossible for the patient to obtain 90 degrees of knee flexion to properly perform this test. The Lachman test is proposed to be the most valid ACL examination test as it typically has high sensitivity and specificity. This test is also performed with the patient in a supine position, but it only requires 20-30 degrees of knee flexion to perform. For this test, “the examiner stabilizes the patient’s femur with one hand while translating the tibia in an anterior direction with the other hand. As with the Anterior Drawer test, it is important to consider the end feel when this test is performed. Rossi et al. (2011) explain that a soft end feel is indicative of a complete ACL tear, whereas a firm end feel would be a negative test. The pivot shift test is one that does not require the examiner to consider an end feel. This test is performed with the patient in a supine position and 40 degrees of hip flexion and slight adduction of the hip. The examiner has the patient’s knee slightly flexed and applies slight valgus and internal rotation forces. The knee is then passively flexed by the practitioner while maintaining these forces. Lichtenberg et al. (2018) describe a positive test as follows: “there is an anterior subluxation of the lateral tibial plateau that reduces spontaneously beyond 30 degrees of knee flexion”.

The newest ACL diagnostic test is Lever sign test. This test is also performed with the patient in a supine position, but with the knee fully extended. The examiner then “places a closed fist under the proximal third of the calf [which] causes the knee to flex slightly”. This will act as the fulcrum of the lever in this test. Next, the examiner provides an anterior to posterior force on the patient’s quadriceps, about one third proximal to the knee. This test looks for “discontinuity of the ACL”. A negative test would be if the knee joint performs full extension and the heel of the affected leg rises off the table. This would mean that an uninjured ACL is creating an intact lever at the knee, which allows the heel to lift off the table from the force applied at the quadriceps. Conversely, a positive test would have a missing part of the lever system; this means that a damaged ACL will not be able to assist in lifting the heel off the table. Therefore, a positive Lever Sign test is one in which the knee does not move into flexion and the heel remains on the table.

Various studies have been completed to compare the efficacy of this new Lever Sign test compared to the three other, more traditional, ACL diagnostic tests. Measures of the efficacy of special tests include sensitivity and specificity. Sensitivity is defined by Fritz & Wainner (2001) as “the ability of the test to recognize the condition when present. A highly sensitive test has relatively few false negative results”.

Conversely, “specificity is the ability of the test to identify the absence of disease”. This means that “a highly specific test has relatively few false positive results”. Ideally, a test will have both high sensitivity and high specificity, however, Fritz & Wainner (2001) argue that few tests fall into this category. Ideally, a test will have both high sensitivity and high specificity, however, Fritz & Wainner (2001) argue that few tests fall into this category. In their study, Lelli et al. (2016) performed a prospective study over an 8 month period. They evaluated a total of 400 patients in 4 different categories. These categories were based on their stage of healing post-injury – acute or chronic – and their MRI results – complete or partial ACL rupture. In this study, acute was defined as “less than 20 days from injury”. The patients in this study were 29.8% female and 70.2% male with an average age of 26.4 years old. All of the patients were tested by the same examiner who was blinded to the results of the MRI. Each participant was evaluated using “the Lachman test the Anterior Drawer test, the Pivot Shift test and Lever Sign test”. The uninjured leg of each participant was used as a control for this study, but only for the Lever Sign test. This test showed that the sensitivity and specificity of the Lever Sign test were both 1.0, meaning that the test was always correct compared to the results of the MRI. The mean sensitivity of the other three tests were 62% for the Lachman test, 72% for the Anterior Drawer test, and 47% for the Pivot Shift test. Because these tests were not compared to the uninjured side, the specificity was not calculated.

A study conducted by Jarbo et al. (2017) also looked at the new Lever Sign test and it’s efficacy as a diagnostic test. Their study looked at 102 patients with acute knee injuries. Acute injuries were defined as less than or equal to 4 weeks old. There were 44 females included in the study, 28 in the surgical group and 16 in the nonsurgical group, and 58 males in the study, 26 in the surgical and 32 in the nonsurgical. Those included in the study had an average age of 23 years old. All the patients were assessed in the clinic setting for ACL integrity using all 4 diagnostic tests – the Lachman test, the Anterior Drawer, the Pict Shift and the Lever Sign test. The patients in the surgical group were also tested with all 4 tests under anaesthesia. The surgical group had their ACL integrity, or lack thereof, confirmed by MRI and arthroscopic surgery, while the ACL injury status of the nonsurgical group was confirmed by MRI only; however, the results were only compared to MRI results to calculate sensitivity and specificity. Having the testing results from the clinical and surgical settings allowed the researchers to compare the accuracy of the tests in awake patients and those under anaesthesia. When under anaesthesia, the Anterior Drawer, Lachman and Pivot Shift tests were all more accurate, but the difference in Lever Sign test results were not statistically significant.

Furthermore, when compared to the MRI, the sensitivity values for all 4 tests were as follows: 88% for the Anterior Drawer test, 90% for the Lachman test, 59% for the Pivot Shift, and 63% for the Lever Sign. Additionally, the sensitivity of the tests were 94% for the Anterior Drawer test, 96% for the Lachman test, 98% for the Pivot Shift test, and 90% for the Lever Sign test. The authors add that the overall accuracy for the Lachman test was the highest of all 4 tests at 93%, and the Lever Sign test was the lowest at 77%. The same four assessment tests were compared in a study by Lichtenberg et al. (2018). This study looked at 94 patients who had a knee injury with indications for arthroscopic knee surgery. There were 57 males and 37 females with an average age of 34 years old. The researchers had three steps to their design, with the first step being a test-retest routine to test interrater reliability. To perform this portion of their study, they had the same tests performed by an orthopaedic or trauma surgeon and a physical therapist and the results were compared. The tests were always performed in the same order “(1) the lever sign test, (2) the anterior drawer test, (3) the Lachman test, and (4) the pivot-shift test”. The interrater reliability results were considered almost perfect, which is defined as “kappa values exceeding 0.80”, for both the Lever Sign test and the Pivot Shift test. The Anterior Drawer test and Lachman test had an interrater reliability qualification of “substantial”, indicating that they “had kappa values between 0.61 and 0.80”. Altogether this indicates that the Lever sign and the pivot shift are more likely to yield identical results when different practitioners perform the same test. The four tests were also compared to arthroscopic diagnostic surgery to calculate the diagnostic value, including the sensitivity and specificity, of each test. The results showed a high percentage of specificity for each, with 94% for the Anterior Drawer test, 91% for the Lachman test, 98% for the Pivot Shift test, and 100% for the Lever Sign test.

On the other hand, the sensitivity of these tests were more varied; the Anterior Drawer test was 71% sensitive, the Lachman test was 87%, the Pivot-shift test was 50%, and the Lever Sign test was only 39%. The first study described was performed by Lelli et al. (2016) and was the first to evaluate the new Lever Sign test. The results were promising for this test as a new diagnostic tool for practitioners as the sensitivity and specificity were both 100%. The other benefits of this test is that it is relatively simple for examiners to learn and perform. Jarbo et al. (2017) also suggest that the gentle motion of the Lever Sign test may also decrease any potential “pain and inhibition” that may arise from performing the test.

Overall, these studies show similar results for the 3 original ACL assessment tools; the Lachman test has the highest sensitivity and specificity when all three studies are considered together, and the Pivot Shift test had lower sensitivity but high specificity. However, where the studies differ is the accuracy of the Lever Sign test. The study by Lelli et al. (2016) shows that the Lever Sign test has a sensitivity and specificity of 100%. Lichtenberg et al. (2018) were able to confirm the specificity of 100% for this test, but the sensitivity of the Lever Sign test was only 39% in their study. Furthermore, the study by Jarbo et al. (2017) showed a sensitivity of 63% and specificity of 90% for the Lever Sign test. One factor that may have played into these differences was described by Lichtenberg et al. (2018) and that was that the lead author of the first study was also the inventor of the Lever Sign test, which may have contributed to bias when conducting the study. Because Dr. Leilli himself was the only one performing the tests in the study by Lelli et al. (2016), it could either mean that there was bias, as was suggested, or it could mean that the examiners in the other studies were not performing the test as well as Dr. Lelli. However, the test by Lichtenberg et al. (2018) considered the interrater reliability for this test and the results showed that the Lever Sign test had an almost perfect interrater reliability; this suggests that this explanation is less likely. Another factor to consider is that the study by Lichtenberg et al. (2018) was the only one to calculate sensitivity and specificity compared to arthroscopic surgery, while the others compared the tests to MRI results. Jarbo et al. (2017) explains that they used MRI for the confirmation of their tests as current literature suggests its sensitivity and specificity ranges from 94% to 98%. However the gold standard for confirming ACL ruptures is considered to be arthroscopic surgery. This difference in comparative tests is something to consider when evaluating these tests, but the difference it causes is likely minimal; Jarbo et al. (2017) compared the arthroscopic results with the MRI results and they only found one test that was different out of 54 surgical patients.

This indicates that their results, which were compared to the MRI results, would be close but not perfect. The evaluation of an ACL injury begins with the mechanism of injury and ends with the use of special diagnostic tools. The potential of a new ACL diagnostic test is promising for health care practitioners as it gives another method of assessment to ensure they are making the correct diagnosis. While the evidence of the accuracy of the Lever Sign test is still new and emerging, it is a promising new technique to consider, with current studies yielding similar results to the widely accepted Pivot Shift test. Further research is needed into the biomechanical mechanism of this test so that it can be better understood and more accurately researched.

In conclusion, accurate diagnosis of ACL injuries is something that all health care practitioners strive for, and therefore new literature should be examined frequently to ensure the use of evidence-based practice.