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10 Articles in Volume 9, Issue #6
Cytokine Testing in Clinical Pain Practice
Effective Monitoring of Opiates in Chronic Pain Patients
Ethics, Pain Care, and Obama’s Policy Intentions
Interventions for Radiating Upper Extremity and Cervical Facet Pain
Long-Acting Opioids for Refractory Chronic Migraine
Need for More Accurate ER Diagnoses of ACL Injuries
Neural Therapy and Its Role in the Effective Treatment of Chronic Pain
Screening Blood Panel to Evaluate New Chronic Pain Patients
Spinal Pain and Neuromuscular Deficiency
Thermal Imaging Guided Laser Therapy: Part 1

Need for More Accurate ER Diagnoses of ACL Injuries

Recognition of ACL injury by emergency room physicians is essential to optimize outcomes through early and appropriate treatment.

It is a generally held belief that pain is the number one reason why patients visit the emergency room. There are many causes of pain. Some causes are:

  • Illness
  • Injury
  • Infection
  • Idiopathic pain from prior treatment

In 2006, there were approximately 119.2 million visits to the emergency room in the United States.1 General symptoms such as fever, fatigue and pain accounted for 15.6% of visits, followed by musculoskeletal symptoms (13.8%), digestive symptoms (13.7%), and respiratory symptoms (10.7%).2 According to the CDC, knee pain is the second most common musculoskeletal complaint and the most common sports-related injury (32.3%) seen in the emergency room.3

The anterior cruciate ligament (ACL) is the most commonly injured ligament in the knee. Each year, there are nearly 100,000 to 200,000 ACL tears in the US alone, making its incidence 1:3,500.4 With such prevalent numbers, it could be assumed that emergency room physicians would be proficient at diagnosing ACL tears. However, a recent study showed just the opposite.

Guillodo, et al looked at patients 15-55 years old who presented to the emergency room at a teaching hospital over a 5-month period with a chief complaint of knee pain. The results of a standard physical examination conducted by emergency room physicians were compared to findings by a sports medicine specialist. Of the 79 included patients, 27 (34.2%) had a diagnosis of an ACL rupture established by the specialist and confirmed by MRI.5 Of the 27 ACL ruptures, only seven were correctly diagnosed by the emergency room physicians.

Knee injuries, most notably ACL tears, create a public health burden related to their high incidence, association with disability and considerable cost.6 Early recognition of ACL injury is essential to optimize outcomes through early and appropriate treatment. In this article, ACL injuries will be discussed beginning with the anatomy of the knee, mechanism of injury, signs and symptoms, physical exam and diagnostic testing, risk factors associated with ACL injury and, finally, treatment.

Anatomy of the Knee

The knee is a hinge joint comprised of the femur, tibia and patella. The knee is stabilized by four ligaments (see Figure 1): the medial collateral ligament (MCL), the lateral collateral ligament (LCL), the posterior cruciate ligament (PCL), and the anterior cruciate ligament (ACL). The collateral ligaments provide the knee with lateral stability. The MCL runs along the medial aspect of the knee and prevents the knee from bending inward. The LCL runs along the lateral aspect of the knee and prevents the knee from bending outward. It is important to note that the knee has two menisci (medial and lateral) which act as a cushion to disperse force in the knee. The medial meniscus is contiguous with the MCL while the lateral meniscus is a separate entity from the LCL. This explains why in many MCL injuries there is also damage to the medial meniscus.

Figure 1. Posterior view demonstrating the ligaments of the knee: medial collateral ligament, lateral collateral ligament, anterior cruciate ligament, and posterior cruciate ligament.

While the collateral ligaments stabilize the lateral movements of the knee, the cruciate ligaments stabilize the anterior and posterior glide of the knee. The PCL runs from the posterior intercondylar area of the tibia to the medial condyle of the femur and prevents the posterior glide of the tibia on the femur. Originating at the posteromedial aspect of the femoral condyle, the ACL prevents the anterior glide of the tibia on the femur. The ACL courses distally in an anterior and medial fashion to the anteromedial aspect of the tibia between the condyles. The ACL is comprised of two bundles: an anteromedial bundle that is tight in flexion and a posterolateral bundle that is tight in extension. The blood supply of the ACL is from branches of the middle geniculate artery, while a branch of the tibial nerve—the posterior articular nerve—innervates it. 7

Mechanism of ACL Injury

ACL injuries can occur by a variety of mechanisms including contact and noncontact mechanisms. Noncontact injuries are more common, accounting for 70% of ACL tears.8 The typical mechanism for a noncontact ACL injury involves a running or jumping person who suddenly decelerates and changes directions in a way that involves rotation or lateral bending. When a person moves their leg forcefully into this valgus position with the knee extended and tibia rotated, much stress is put on the ACL. Examples of sports where this pivoting motion is common are alpine skiing, soccer, gymnastics, basketball and tennis. On the other hand, contact-related ACL injuries usually occur from a lateral to medial blow causing hyperextension or valgus stress to the knee. This is commonly seen in football when a player’s foot is planted and an opponent strikes him on the lateral aspect of the leg.

ACL injuries are classified by “grades” with 1 being the least severe and 3 being the most severe. A grade 1 sprain is defined as pain with minimal damage to the ligaments. A grade 2 sprain has more ligamentous damage and mild looseness of the joint. In a grade 3 sprain, the ligament is completely torn and the joint is very loose or unstable.9

Signs and Symptoms

Most patients who sustain an ACL injury complain of feeling or hearing a “pop” in their knee at the time of injury. Many patients then experience acute swelling within 6 hours of injury and a feeling of knee instability. After the initial swelling improves, patients are often able to bear weight but continue to complain of knee instability. Movements such as squatting, pivoting and stepping laterally may cause the knee to give out. In addition, any activity where the entire body weight is transferred to the injured leg, such as walking down stairs, will illicit this instability.

Physical Exam and Diagnostic Tests

A thorough physical exam is essential in the diagnosis of an ACL injury. As with all medical evaluations, a comprehensive history and physical exam is crucial. In patients with a possible ACL injury, the physician should inquire about the timing of the injury, the mechanism, joint swelling, functional ability, joint instability and any associated injuries. The physician must remember the basics and inspect, palpate, test mobility of the knee joint, strength of the quadriceps and hamstrings as well as perform special tests to determine the integrity of the ACL. The physician must not forget to examine the unaffected knee for comparison since many individuals have increased laxity that is not pathologic.

The most sensitive and specific special tests used to exam the integrity of the ACL is the Lachman test. The Lachman test has a sensitivity of 85% and a specificity of 94% for an ACL rupture.10 With the patient supine, the knee is placed in 30 degrees of flexion (see Figure 2). The physician then stabilizes the distal femur with one hand while pulling the proximal tibia anteriorly with the other hand in a scissoring motion. A negative test is one in which there is a distinct endpoint and implies an intact ACL. A positive test has a vague endpoint and implies an ACL injury. Again, it is imperative that both the affected and unaffected knee are examined.

Figure 2.The Lachman test: with the patient supine, the knee is placed in 30 degrees of flexion. The physician then stabilizes the distal femur with one hand while pulling the proximal tibia anteriorly with the other hand in a scissoring motion.

Historically the anterior drawer test was used to evaluated ACL integrity. While useful in chronic conditions, with a sensitivity of 92% and a specificity of 91%, the anterior drawer test is not accurate in acute injury.10 Often with an acute injury, the patient will guard their knee by contracting their hamstring and thus resulting in a false negative. The anterior drawer test is performed with the patient supine and the knee flexed at 90 degrees. The proximal tibia is gripped with both hands and pulled anteriorly checking for any anterior translation. Often the physician will sit on the patient’s foot to provide stability (see Figure 3). A test is positive if there is anterior translation.

Figure 3.The anterior drawer test is performed with the patient supine and the knee flexed at 90 degrees. The proximal tibia is gripped with both hands and pulled anteriorly checking for any anterior translation.

After a thorough physical exam, an MRI is often used to aid in the diagnosis of ACL injury as the sensitivity and specificity are both very high. Lee et al performed a retrospective study in which MRIs of the knee were reviewed to evaluate their ability to demonstrate ACL tears previously diagnosed via arthroscopy. The study also compared MRIs to the Lachman and anterior drawer tests. Lee et al found the sensitivity of MRIs to be 94%, compared with 89% for the Lachman test and 78% for the anterior drawer test.11 While highly sensitive, the MRI does have shortcomings. Not only is it less accurate in differentiating complete tears from partial tears, but MRI has been found to be less accurate in detecting chronic tears.12

Risk Factors

It remains unclear what factors predispose athletes to ACL injury. A number of factors ranging from playing surface to genetics may predispose some to ACL injury. ACL injuries are most commonly seen in gymnastics, soccer and basketball. Overall, females sustain significantly more ACL injuries than their male counterparts. One study looked at male and female ACL injury rates in soccer and basketball. It was reported that females sustained 3.5% and 2.7% more ACL injuries for each sport respectively.13 Researchers have proposed a number of theories to try to explain this gender disparity.

Several biomechanical studies have examined the muscles used in deceleration in both men and women. The studies showed that women rely on their quadriceps muscles to decelerate as compared with men who contract their hamstring muscles first.14 The quadriceps muscles are less effective at preventing the anterior tibial glide which increases the tension put on the ACL.

Other biomechanical studies have shown that women are more likely to place their knees in positions of increased valgus angulation when changing direction.15 When the knee is abducted or placed in a valgus position more stress is placed on the ACL. Several collegiate athletic programs have implemented the PEP program (Prevent Injury and Enhance Performance) which acts as a neuromuscular training program to prevent athletes from putting their knee in the valgus position. The PEP program requires 10 minutes to perform and consists of a warm up followed by several strength, agility, plyometric and flexibility exercises. There have been significant reductions in ACL injury rates among members of soccer teams assigned to perform the PEP program before each training session instead of their usual warm-up.16

Other theories revolve around the anatomy of the female body. It is well known that women tend to have a large Q-angle (see Figure 4). The Q-angle is made by drawing a line from the anterior superior iliac spin to the patella and a second line from the patella to the tibial tubercle. The Q-angle tends to be increased in females due to a wide pelvis and short femur. Some researchers claim that an association exists between a larger Q-angle and increased risk of ACL tears, however no evidence exists to substantiate this claim.13

Figure 4.The Q-angle is made by drawing a line from the anterior superior iliac spin to the patella and a second line from the patella to the tibial tubercle.


ACL injuries can be managed non-operatively or operatively. Patients who opt out of having a surgical repair are referred to a physical therapist who helps the patient decrease the joint effusion and strengthen the stabilizing muscles of the knee. If a patient decides to treat a complete ACL rupture non-operatively, it is important to understand the possible consequences. The ACL deficient knee may place the patient at increased risk for further injury such as meniscal tears, chronic pain and decreased level of activity. Fewer than 50% of patients treated non-operatively return to their pre-injury level of sports participation.17 Many studies suggest that the ACL injury alone, regardless of the treatment, predisposes the patient to developing osteoarthritis.16

Most active, young patients and high level athletes opt for surgical reconstruction. The decision to have surgery is based upon several factors including age, level of activity, functional demands and the presence of associated injuries (e.g. meniscal tear.) Patients with associated injuries must have surgical reconstruction. ACL reconstruction is generally performed with arthroscopy using a graft to replace the ruptured ACL. An orthopedic surgeon drills a tunnel in the tibia and femur in order to secure the graft.

Graft selections tend to be a source of debate among orthopedic surgeons. The three most common grafts include the patellar tendon, the allograft and the semitendonosus graft. While each surgeon has their own preference, no particular graft has demonstrated superior functional outcome, and each has it’s own advantages and disadvantages.18

Advantages of the patellar graft include increased initial strength and stiffness compared with the normal ACL and potential bone-to-bone healing in the femoral and tibial tunnels made during surgery. This promotes earlier graft fixation.19 Patellar tendon grafts produce greater anterior knee pain compared with other grafts.20 The semitendonosus graft has several advantages. The use of the hamstring tendon eliminates the anterior knee pain experienced with the patellar graft.

One study found that hamstring donor site pain usually resolved by three months, with normal hamstring strength by 12 months.20 The hamstring graft is also stronger and stiffer when quadruple strands of semitendonosus or gracillis muscle are used.20 Hamstring grafts are composed of the entire tendon as compared to patellar tendon grafts which include a portion of bone at either end. The need for healing between a tendon and an osseous tunnel can pose a potential disadvantage. As a result, the initial fixation may be slower and not as strong as the bone-to-bone healing of a patellar tendon graft.

Allografts are commonly used for ACL reconstruction. The advantages include reduced surgical time, reduced harvest site morbidity and availability of a range of sizes. Possible disadvantages include potential disease transmission (hepatitis C, HIV).

The best time to undergo ACL reconstruction remains unclear. The knee must exhibit full range of motion with no significant effusion as well as adequate strength at the time of surgery. Studies have shown that surgery performed prematurely increases the risk of arthofibrosis in 70% of patients who have knee swelling and inflammation at the time of surgery.21

It is important to realize that the surgery is just the beginning of the healing process. An extensive rehabilitation program is necessary for patients undergoing ACL reconstruction. While the protocol varies from doctor to doctor, most rehabilitation programs range anywhere from 6 to 12 months.


The ACL is the most commonly injured ligament. Most often the injury occurs from a non-contact mechanism when a person decelerates and changes direction causing a lateral or valgus strain on the knee. Patients usually complain of hearing or feeling a popping sound, experiencing acute swelling, and having a feeling of joint instability thereafter. A careful history and physical exam is necessary especially given the amount of ACL diagnoses missed in the emergency room. The Lachman test is the best physical exam test and, when followed by an MRI, is the gold standard to confirm the diagnosis.

ACL injuries may be managed operatively or non-operatively, depending on the patient’s activity level, age, and concurrent injuries. Regardless of the treatment, an extensive rehabilitation program is imperative. As stated in the opening paragraph, ACL injuries are common among emergency room visits. In terms of outcomes, it is crucial that emergency room physicians understand the history and mechanism associated with the ACL and perfect their ability to diagnose ACL injuries using the Lachman test.

Last updated on: October 2, 2012
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