Diagnosis of Anterior Cruciate Ligament Tear




Abstract


Acute ACL tear is perhaps the most under-diagnosed orthopedic condition that usually requires surgery because most tears present to emergency rooms or primary care providers who can not necessarily be expected to make the diagnosis. The history, examination, and diagnostic tests are less reliable than commonly thought, and the presentation is often not classic. This chapter reviews the important elements of history, examination and diagnostic tests and their usefulness in diagnosing ACL complete and partial tears.




Keywords

complete ACL tear, Diagnosis, KT-1000, Lachman test, MRI, Partial tear, Pivot test

 




Introduction


The overwhelming majority of orthopaedists are very skilled in the diagnosis of anterior cruciate ligament (ACL) tears. However, acute ACL tear is perhaps the most underdiagnosed orthopaedic condition that usually requires surgery because most tears present to emergency rooms or primary care providers who cannot necessarily be expected to make the diagnosis. The history, examination, and diagnostic tests are less reliable than commonly thought, and the presentation is often not classic . Failure to refer to an orthopaedist in these cases, or failure of the patient to actually see the referred-to orthopaedist, results in underdiagnosis, with delays in diagnosis that can extend over months or years.


Marked underdiagnosis of ACL tears has been found in numerous studies in primary care and emergency departments. One study found that only 7 of 27 ACL tears were detected in an emergency department. Even in multidisciplinary sports medicine clinics the diagnostic accuracy has been found to be surprisingly low. This underdiagnosis has, in turn, been shown to result in an increased incidence of meniscal tears.




Keywords

complete ACL tear, Diagnosis, KT-1000, Lachman test, MRI, Partial tear, Pivot test

 




Introduction


The overwhelming majority of orthopaedists are very skilled in the diagnosis of anterior cruciate ligament (ACL) tears. However, acute ACL tear is perhaps the most underdiagnosed orthopaedic condition that usually requires surgery because most tears present to emergency rooms or primary care providers who cannot necessarily be expected to make the diagnosis. The history, examination, and diagnostic tests are less reliable than commonly thought, and the presentation is often not classic . Failure to refer to an orthopaedist in these cases, or failure of the patient to actually see the referred-to orthopaedist, results in underdiagnosis, with delays in diagnosis that can extend over months or years.


Marked underdiagnosis of ACL tears has been found in numerous studies in primary care and emergency departments. One study found that only 7 of 27 ACL tears were detected in an emergency department. Even in multidisciplinary sports medicine clinics the diagnostic accuracy has been found to be surprisingly low. This underdiagnosis has, in turn, been shown to result in an increased incidence of meniscal tears.




Diagnosis in the Acute Versus the Chronic Setting


Diagnosis of complete ACL tears differs in some respects in the acute versus the chronic state regarding the history, physical exam, and diagnostic tests. This chapter will discuss the acute versus chronic diagnostic dichotomy for each of these diagnostic modalities. In the acute setting, the diagnosis is primarily of the ACL tear itself, whereas in the chronic setting, the diagnosis more often includes the signs and symptoms of secondary damage. Because the most important aspect of ACL reconstruction is the prevention or mitigation of subsequent meniscal and articular damage to the knee, it is paramount that ACL tears are diagnosed and treated acutely before such further damage occurs.




Partial Tears


This chapter deals primarily with complete ACL tears. Traditionally, partial tears have been found to produce a smaller degree of anteroposterior (AP) laxity than complete tears on Lachman or instrumented Lachman testing, as described later. Until the present time, the only alternatives have been nonoperative treatment or complete reconstruction, which would necessitate ablation of the remaining ligament. Given these alternatives, nonsurgical treatment has been the usual alternative if less than 50% of the ligament was torn. With more awareness of ACL double-bundle anatomy, single-bundle repairs that preserve the remaining ligament have been developed. These repairs have been used in some cases of single-bundle partial ACL tear. Lachman testing and arthrometer testing in these cases appear to show 2- to 3-mm asymmetry in anteromedial bundle tears and 1- to 2-mm asymmetry in posterolateral bundle tears. Arthroscopy is required for definite anatomical diagnosis. The pivot shift is of much greater value in the anesthetized versus the fully conscious patient. Diagnostic criteria as well as surgical indications and techniques in these cases continue to evolve.




History


Acute


The history and mechanism of ACL tear are familiar to all orthopaedists. The history most commonly entails twisting, landing, or a valgus blow to the knee. However, almost any history of knee trauma can be associated with ACL tear. These atypical histories may represent unusual mechanisms or inaccurate remembrances by the patient. The important point is never to eliminate ACL tear from the differential diagnosis based on the history. Classically, swelling is marked within a few hours. However, some ACL tears never produce more than minimal swelling, even acutely. Patients often hear or feel a pop , but many do not. Similarly, patients may have felt the knee go out of place or felt their leg go one way and the body another , but often they do not even feel these sensations. Pain may be severe and persisting or may be mild and transient.


Nonorthopaedists are aware that ACL tear is a serious injury and are often misled into thinking that the injury is only a sprain , because the history and exam are much less dramatic than they are expecting for such a serious injury. Team physicians should therefore perform a Lachman test on any knee injury during a game, because ACL tears in the heat of competition are often not obvious by the athlete’s historical account and sometimes produce little pain initially before swelling sets in. This underdiagnosis is very common in emergency rooms (ERs), where the diagnosis of ACL tear may not be made by the emergency physician. Patients will often feel that the injury is not serious, especially if they do not have a concomitant meniscal tear, which would have produced its own set of symptoms. This is particularly true if the injury is called a sprain , such that the patient in many cases feels that there is no need for orthopaedic follow-up. Because magnetic resonance imaging (MRI) will usually not be ordered in this instance, the diagnosis is easily missed.


Patients with meniscal or articular cartilage damage will usually have continued symptomatology from their cartilage damage and are more likely to follow up. Patients with bucket-handle tears and locked knees will virtually always seek further care and be diagnosed accurately by the exam or MRI, or at arthroscopy.


Chronic


Chronic ACL tears often present because of pain from a meniscal tear or articular cartilage damage. Patients may or may not give a history of instability. Classically, instability will occur during pivoting, but the symptoms can take almost any form. It can be confused with patellar instability, particularly in adolescents, as well as meniscal tear. Any symptom of instability should cause the orthopaedist to rule in or rule out ACL tear.




Physical Exam


Pivot Shift


The pivot shift is a specific but very insensitive test for ACL tear in the unanesthetized patient. It is also subject to great interobserver error. Because the pivot shift is often quite painful when positive, has low sensitivity, and usually adds nothing beyond the Lachman test, the lead author (C. Prodromos) uses it only rarely for the diagnosis of ACL tear in the office. However, it is the gold standard for complete ACL tear in the anesthetized patient.


Lachman Test


The Lachman test, the anterior drawer test in approximately 20 degrees of flexion, is the most reliable exam test for ACL tear but is far more reliable in the chronic case, when secondary restraints have stretched and there is less hamstring spasm, than in the acute case. After 30 years of sports medicine practice, the lead author still finds the Lachman test inconclusive with some frequency in the acute setting, particularly in regard to the differential between partial and complete tear, because of persisting hamstring spasm. The firmness of the endpoint may be particularly difficult to evaluate. The examiner may or may not be successful in relaxing the hamstrings. Palpating them posteriorly and simultaneously while asking the patient to relax them is often effective. It is important that the patient is in the supine, not sitting, position, and he or she should be instructed to relax the entire body to help relax the knee. The Lachman test should be considered definitive only if it is clearly negative with a firm endpoint. It is important that the examiner be able to differentiate between a negative Lachman test and a false negative caused by this hamstring spasm to avoid missing a torn ACL.


Anterior Cruciate Ligament Versus Posterior Cruciate Ligament Tear


A posterior cruciate ligament (PCL) tear produces increased AP laxity and can mimic an ACL tear. Classically, there will be increased AP laxity, but with a firm anterior endpoint, with a PCL tear. However, this can also be seen with a healed partial ACL tear. If there is a question of ACL versus PCL tear, then MRI or the quadriceps active test should be used to differentiate the two. In addition, it is wise to always arthroscopically inspect the knee before any graft harvesting takes place to make certain that the ACL is, in fact, completely torn.


Valgus Laxity


In patients with coexisting medial collateral ligament insufficiency, and hence valgus laxity, the Lachman test can be false positive. Rotation of the lax proximal medial tibial plateau can mimic translation of the entire proximal tibia if rotation is not carefully controlled by the examiner during the exam. Thus when the examiner is aware that valgus laxity exists, he or she should pay particular attention to controlling tibial rotation during the test to minimize this possibility. This can be challenging in patients with large-girth lower extremities.


Locking


Pseudolocking may be seen classically with partial tears. However, a knee with a 20-degree or so persisting flexion contracture (i.e., pseudolocking) can occasionally be seen with isolated complete ACL tear from hamstring spasm alone—especially in adolescent patients. True locking is seen with ACL tear in combination with displaced bucket-handle meniscal tears. In these cases, the locking is actually reflex hamstring spasm in response to extension in the presence of the displaced meniscal tear. Thus the Lachman test is always difficult to perform and frequently false negative because of the hamstring spasm.


Hemarthrosis


The presence of a large hemarthrosis is much more highly associated with ACL tears in adults than in children. Patellar dislocation and fracture are other leading causes of hemarthrosis. The former can usually be accurately diagnosed by physical exam, and the latter by radiography. Arthrocentesis is usually not indicated. Its only diagnostic value is in determining whether a large effusion is a hemarthrosis. In most of these cases, an MRI will be ordered, which will provide much more information and spare the patient the pain of the arthrocentesis. If the effusion is sufficiently tense, hemarthrosis may be indicated for pain relief. If MRI is unavailable and the exam is equivocal, then arthrocentesis may be useful. A 16-gauge needle is preferable, but an 18-gauge needle may be used.


Patellofemoral Injury


Although concomitant ACL tear and patellar dislocation or injury are unusual, this combination does occur. The presence of physical exam signs of acute patellar instability should not cause the examiner to fail to test for ACL instability.


KT-1000 or Other Instrumented Lachman Test


The KT-1000 ( Figs. 9.1 and 9.2 ) maximum manual examination is a highly accurate method for definitive diagnosis of ACL tear that is heavily relied on in our clinic. When it indicates a complete ACL tear, we generally do not order an MRI scan. A side-to-side difference of more than 4 mm, particularly with an absolute value of 10 or more, is nearly 100% specific for complete ACL tear if the examiner is experienced in its use. The more difficult differential may be between complete and partial ACL tear. We have found partial ACL tears to usually have a laxity of 2 or 3 mm. When it is greater, a complete tear has almost always existed. Others have found a slightly larger range. Larger differences, up to 4 and perhaps 5 mm, can be seen after ACL reconstruction without graft discontinuity. It is important to point out that the maximum manual test is more reliable than other methods. A 20-lb pull in particular will understate the amount of laxity. The 30-lb pull will as well, but to a lesser extent. Other arthrometers are in use, particularly in Europe, with reportedly good results. We have no experience with them.


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Aug 21, 2017 | Posted by in ORTHOPEDIC | Comments Off on Diagnosis of Anterior Cruciate Ligament Tear

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