Anterior Cruciate Ligament (ACL) Knee Injuries


Article Author:
Jennifer Evans


Article Editor:
Jeffery Nielson


Editors In Chief:
Dustin Constant
Donald Kushner


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Frank Smeeks
Kristina Soman-Faulkner
Trevor Nezwek
Radia Jamil
Patrick Le
Sobhan Daneshfar
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Nazia Sadiq
Hajira Basit
Phillip Hynes
Tehmina Warsi


Updated:
3/8/2019 8:11:59 AM

Introduction

The anterior cruciate ligament (ACL) is one of 2 cruciate ligaments which aids in stabilization of the knee joint. It is a strong band made of connective tissue and collagenous fibers that originate from the anteromedial aspect of the intercondylar region of the tibial plateau and extends posteromedially to attach to the lateral femoral condyle. The anteromedial bundle and posterolateral bundle form the 2 components of the ACL.  [1][2][3] The ACL and the posterior cruciate ligament (PCL) together form a cross (or an “x”) within the knee and prevents excessive forward or backward motion of the tibia in relation to the femur during flexion and extension. The ACL additionally provides rotational stability to the knee with varus or valgus stress. ACL sprains and tears are common knee injuries with a reported incidence of 100,000 to 200,000 in the United States every year.

Etiology

The ACL is the most commonly injured ligament in the knee. The annual reported incidence in the United States alone is approximately 1 in 3500 people. However, data may not be accurate as there is no standard surveillance. Most ACL tears occur in athletes by noncontact mechanisms versus contact mechanisms, such as rotational forces versus a direct hit to the knee. The most at risk athletes for noncontact injury include skiers, soccer players, and basketball players, while the most at risk athletes for contact injury are football players.

Epidemiology

There is no age or gender bias; however, it has been suggested that women are at increased risk of ACL injury secondary to a multitude of factors. Some studies suggest that females may have weaker hamstrings and preferential utilize the quadriceps muscle group while decelerating. When engaging the quadriceps musculature while slowing down, this places abnormally increased stress on the ACL, as the quadriceps muscles are less effective at preventing anterior tibial translation versus the hamstring muscles. A second factor that may increase the risk of ACL injury is the increased valgus angulation of the knee. [4] [5]One study utilizing video analysis demonstrated that female athletes are more likely to place their knees in increased valgus angulations when changing directions suddenly, which increased the stress on the ACL ligament. Lastly, it has been suggested that estrogenic effects on the strength and flexibility of tissues such as ligaments may play a role and predispose females to injury; however, this remains controversial and has yet to be proven.

History and Physical

One of the most common knee injuries is an ACL sprain or tear. Typically, injury occurs during activity/sports play that includes sudden changes in the direction of movement, rapid stopping, jumping and landing abnormally, a direct blow to the lateral aspect of the knee, or slowing down while running.

Most patients complain of hearing and feeling a sudden “pop” and feel that their knee “gives out” from under them at the time of injury. Other symptoms include tenderness along the joint line, pain, and swelling, decreased or loss of range of motion, and difficulty ambulating.

The physical exam should include timing of the injury, mechanism of injury, ambulatory status, joint stability, mobility, strength, palpation, and evaluation of possible associated injuries.

Multiple maneuvers are employed to test the ACL and include the anterior drawer, the pivot shift, and the Lachman tests.[6][7] These tests should be performed whenever there is suspicion for injury to the anterior cruciate ligament.

  • The anterior drawer test is performed with the patient lying supine with their affected knee flexed to 90 degrees and the foot in a planted position (Sometimes it is easiest for the clinician to stabilize the patient’s foot by sitting on it). The clinician will grip the proximal tibia with both hands and pull with an anterior motion. If there is excessive anterior motion and instability, then the test is positive. It may also be useful to compare to the unaffected knee as patients may have increased laxity of the ACL that is not pathologic. This test has a sensitivity of 92% and specificity of 91% in chronic injuries, but not acute injuries.

  • The pivot shift test is performed with the patient in the supine position. The clinician should hold the patient’s lower leg and begin with the knee in extension and flexion of the hip to 20 to 30 degrees. Next, the clinician will bring the tibia into the internal rotation with one hand and begin placing valgus stress on the knee using the other hand. While holding this position, the knee should now be flexed. This causes stress, instability, and ultimately subluxation of the ACL of the affected knee. With flexion of the knee, if the tibia subluxes posteriorly and one may feel a “clunk”; this would indicate a positive test. This test can be difficult to perform in patients who are guarding, and some may not allow the clinician to perform the test. This is a highly specific test (98%) when positive, but is insensitive (24%) due to the difficulty in evaluation secondary to patient pain and cooperation.

  • The Lachman test is performed with the patient in the supine position with the knee flexed to about 30 degrees. The clinician should stabilize the distal femur with one hand and with the other hand pull the tibia toward themselves. If there is increased anterior translation, then this is a positive test. Again, comparing to the unaffected side may be helpful. This test has a sensitivity of 95% and specificity of 94% for ACL rupture.

It is important to evaluate for associated injuries such as medial or lateral collateral ligamentous injury, injury to the posterior collateral ligament, or meniscal injuries.

Evaluation

Although ACL injury can be diagnosed clinically, imaging with magnetic resonance (MRI) is often utilized to confirm the diagnosis. MRI is the primary modality to diagnose ACL pathology with a sensitivity of 86% and specificity of 95%. Diagnosis may also be made with knee arthroscopy to differentiate complete from partial tears, as well as chronic tears. Arthrography is considered the gold standard as it is 92% to 100% sensitive and 95% to 100% specific; however, it is rarely used as the initial step in diagnosis as it is invasive and requires anesthesia.

On MR, ACL tears have primary and secondary signs. Primary signs will indicate changes associated directly with the ligamentous injury while secondary signs are changes that are closely related to the ACL injury. Primary signs include edema, an increased signal of the anterior cruciate ligament on T2 weighted or proton density images, discontinuity of the fibers, and a change in the expected course of the ACL (alteration of Blumensaat’s line). Tears usually occur within the midportion of the ligament, and signal changes are most often seen here and appear hyperintense. Secondary signs include bone marrow edema (secondary to bone contusion), Second fracture (as discussed below), associated medial collateral ligament injury, or anterior tibial translation of greater than 7 mm of the tibia relative to the femur (best seen on lateral view).

Radiographs are generally non-contributory for ACL injuries but are helpful to rule out fractures or other associated osseous injuries. In younger patients, avulsion of the tibial attachment may be seen. Other non-specific features that can be seen on radiographs include:

  • Second fracture: An avulsion fracture at the site of the lateral capsular ligaments/IT band insertion on the tibia

  • Arcuate fracture. An avulsion fracture at the proximal fibula at the site of the lateral collateral ligament and/or biceps femoris tendon

  • Joint effusion

  • Deep lateral sulcus sign: A notch on the lateral femoral condyle with a depth of 1.5 mm or more, best seen on the lateral view

Computed tomography (CT) is not generally utilized in evaluating the ACL and is only accurate in detecting an intact ACL.

Treatment / Management

Acute treatment consists of the “RICE” therapy, which includes rest, ice, compression of the affected knee, and elevation of the affected lower extremity. Patients should be non-weight bearing and may utilize crutches, or a wheelchair if necessary. Pain relief can be achieved with over the counter medications such as NSAIDs but is typically at the discretion of the treating physician.

ACL injuries, depending upon their severity, can be managed nonoperatively or operatively. The patient with an anterior cruciate ligament injury should be referred to the orthopedic physician to discuss treatment options and a physical therapist (PT) for rehabilitation.

Nonoperative treatment is typically reserved for those with low functional demands, type and severity of ACL tear, and time of injury and subsequent assessment. Continued monitoring and treatment by an orthopedist and physical therapist is necessary and will only improve their functional status and stability post-injury. Of note, about half of the patients who initially choose the non-operative pathway will later choose to undergo surgical repair.

The decision to undergo operative treatment is based upon a multitude of factors such as patient’s baseline level of physical activity, functional demands, age, occupation, and other associated injuries, if present. [8][9][10]Athletes and individuals who are younger and more active tend to opt for surgical repair and reconstruction. Other candidates for surgical repair/reconstruction are those with significant instability of the knee and/or multiple knee structures injured. Operative treatment is typical with a tissue graft. In a recent systematic review, 81% of those involved treated with ACL reconstruction returned to some athletic activity, 65% returned to the preinjury level of competition, and 55% of high-level athletes returned to normal play and competition. Although, it has been reported that of those who undergo surgical repair, overall 90% return to near normal functioning. The factors that may contribute to a lower percentage of return to play may be secondary to external factors such as fear of reinjury.

Pearls and Other Issues

Return to activity is variable and patient dependent. Average return to full activity and/or sports participation is estimated to be between 6 to 12 months after surgical reconstruction depending upon their progress with PT and the type of sport/activity to which they are returning. However, some studies have shown up to 18 months or more for the graft to become fully functional and incorporated. Early/premature return to activity can lead to reinjury and graft failure.

Enhancing Healthcare Team Outcomes

The diagnosis and management of ACL is made by a multidisciplinary team that includes an emergency department physician, orthopedic surgeon, sports physician, nurse practitioner and a physical therapist. The initial treatment of ACL is RICE therapy. ACL injuries, depending upon their severity, can be managed nonoperatively or operatively. The patient with an anterior cruciate ligament injury should be referred to the orthopedic physician to discuss treatment options and a physical therapist (PT) for rehabilitation. The outcomes for patients with ACL injury are good but the recovery may takes at least 3-9 months of intense physical therapy.[2][11]


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Anterior Cruciate Ligament (ACL) Knee Injuries - Questions

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A 16-year-old female gymnast drops from the high bar. Her right knee buckles and she hears a pop. There is immediate pain, and by the time she is seen an hour later, her knee is swollen. She reports her knee feels "loose." Effusion is noted on exam. What is the most likely isolated injury?



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Which of the following tests is most appropriate for the diagnosis of an anterior cruciate ligament tear?



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A patient presents with a suspected acute anterior cruciate ligament (ACL) tear. She is placed in an immobilizer, given pain medication, and referred to an orthopedic surgeon. She returns with markedly increased pain and effusion. Therapeutic arthrocentesis yields 80 mL of bloody fluid. Joint fluid exam shows blood and fat droplets. What is the most likely diagnosis?



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What diagnosis is indicated by a positive anterior drawer sign?



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Which of the following is not torn as part of the "unhappy triad" of the knee joint?



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Which injury is most likely to cause disruption of the cruciate ligaments?



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Which knee structure is assessed with the anterior drawer sign, the pivot shift, and Lachman test?



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A patient tears his anterior cruciate ligament during a hockey game. What kind of injury is this?



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A 17 year old was skiing when he twisted his left knee, felt a pop and then pain and swelling; on exam his knee is swollen with decreased ROM and positive Lachman and anterior drawer tests; his diagnosis?



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A 17-year-old female is playing soccer when she feels her left knee buckle and hears a pop as she plants her left foot to kick the ball. She complains immediately of intense pain in her left knee. The next morning, she has continued left knee pain and a sensation of instability in the joint. Based on this history alone, the most likely diagnosis is:



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All of the following would help a provider make the diagnosis of (ACL) anterior cruciate ligament tear except for:



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What test is most helpful in making the diagnosis of anterior cruciate ligament tear?



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Which of the following is not true regarding anterior cruciate ligament (ACL) injuries and their assessment?



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A competitive 17 year old female soccer player ruptures her anterior cruciate ligament (ACL). She informs you that she plans on playing competitively in college as well. Which of the following treatments do you suggest?



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Which of the following athletes are at greatest risk for anterior cruciate ligament injuries and hyperextension of the thumb?



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Following a non-contact football injury, a provider examines the knee at 90 degrees of flexion. The examiner appreciates an increased anterior translation of the tibia on the femur. The examiner also notes that the knee does not demonstrate a posterior sag sign and a negative posterior drawer test. What knee ligament is most likely injured?



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A quarterback is tackled simultaneously from the front at hip level and from behind at knee level. What ligament is most likely to be damaged?



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After being tackled heavily on the football field, a patient is unable to weight bear on his right knee. In the emergency room, his knee is swollen and aspiration reveals fresh blood. What orthopedic injury is often associated with an immediate collection of blood in the joint?



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Which is true regarding recovery of quadriceps muscle function after anterior cruciate ligament reconstruction surgery?



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A 17-year-old male sustains an injury while playing soccer. The patient states that during practice he pivoted quickly to try to "steal the ball." He felt like his left knee "gave out" and has felt weak since. The patient's physical exam demonstrates a positive Lachman test. On an initial radiograph, there is a small avulsion fracture involving the lateral aspect of the tibial plateau. What is the most likely associated injury?



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Anterior Cruciate Ligament (ACL) Knee Injuries - References

References

Gupta R,Malhotra A,Sood M,Masih GD, Is anterior cruciate ligament graft rupture (after successful anterior cruciate ligament reconstruction and return to sports) actually a graft failure or a re-injury? Journal of orthopaedic surgery (Hong Kong). 2019 Jan-Apr;     [PubMed]
Hoogeslag RAG,Brouwer RW,Boer BC,de Vries AJ,Huis In 't Veld R, Acute Anterior Cruciate Ligament Rupture: Repair or Reconstruction? Two-Year Results of a Randomized Controlled Clinical Trial. The American journal of sports medicine. 2019 Mar;     [PubMed]
Barfod KW,Rasmussen R,Blaabjerg B,Hölmich P,Lind M, [Return to play after anterior cruciate ligament reconstruction]. Ugeskrift for laeger. 2019 Feb 18;     [PubMed]
Davey A,Endres NK,Johnson RJ,Shealy JE, Alpine Skiing Injuries. Sports health. 2019 Jan/Feb;     [PubMed]
Vaudreuil NJ,Rothrauff BB,de Sa D,Musahl V, The Pivot Shift: Current Experimental Methodology and Clinical Utility for Anterior Cruciate Ligament Rupture and Associated Injury. Current reviews in musculoskeletal medicine. 2019 Mar;     [PubMed]
Eberl R, [Anterior cruciate ligament rupture in children with open growth plate : Diagnostics and treatment]. Der Unfallchirurg. 2019 Jan;     [PubMed]
Palazzolo A,Rosso F,Bonasia DE,Saccia F,Rossi R, Uncommon Complications after Anterior Cruciate Ligament Reconstruction. Joints. 2018 Sep;     [PubMed]
Benjaminse A,Webster KE,Kimp A,Meijer M,Gokeler A, Revised Approach to the Role of Fatigue in Anterior Cruciate Ligament Injury Prevention: A Systematic Review with Meta-Analyses. Sports medicine (Auckland, N.Z.). 2019 Jan 18;     [PubMed]
Losciale JM,Zdeb RM,Ledbetter L,Reiman MP,Sell TC, The Association Between Passing Return-to-Sport Criteria and Second Anterior Cruciate Ligament Injury Risk: A Systematic Review With Meta-analysis. The Journal of orthopaedic and sports physical therapy. 2019 Feb;     [PubMed]
Roth TS,Osbahr DC, Knee Injuries in Elite Level Soccer Players. American journal of orthopedics (Belle Mead, N.J.). 2018 Oct;     [PubMed]
Thoma LM,Grindem H,Logerstedt D,Axe M,Engebretsen L,Risberg MA,Snyder-Mackler L, Coper Classification Early After Anterior Cruciate Ligament Rupture Changes With Progressive Neuromuscular and Strength Training and Is Associated With 2-Year Success: The Delaware-Oslo ACL Cohort Study. The American journal of sports medicine. 2019 Feb 21;     [PubMed]

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