AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Based on statements found in the Orthopaedic Knowledge Update 7 regarding the increased incidence of knee ligament injuries, the author proposes that this incidence may be associated with the current emphasis on fitness. These injuries are most often a result of low-velocity, noncontact, deceleration injuries and contact injuries with a rotational component. Contact sports also may produce injury to the anterior cruciate ligament (ACL) secondary to twisting, valgus stress, or hyperextension all directly related to contact or collision.

When matched for activities, a greater prevalence for ACL injury is found in females compared with males. Approximately 50% of patients with ACL injuries also have meniscal tears. In acute ACL injuries, the lateral meniscus is more commonly torn; in chronic ACL tears, the medial meniscus is more commonly torn. The only study on the prevalence of ACL injuries in the general population has estimated the incidence as 1 case in 3,500 people, resulting in 95,000 new ACL ruptures per year. 

The importance of the ACL has been emphasized in athletes who require stability in running, cutting, and kicking. The ACL-deficient knee has also been linked to an increased rate of degenerative changes and meniscal injuries. For these reasons, approximately 60,000-75,000 ACL reconstructions are performed annually in the United States.

For restoration of activity and stability, the expected long-term success rate of ACL reconstruction is between 75-95%. The current failure rate is 8%, which may be attributed to recurrent instability, graft failure, or arthrofibrosis.

Treatment options must be tailored to a patient's preoperative level of activity. The following activity levels are based on the International Knee Documentation Committee:

• Level I includes jumping, pivoting, and hard cutting.



• Level II is heavy manual work or side-to-side sports.



• Level III encompasses light manual work and noncutting sports (eg, running, cycling).



• Level IV is sedentary activity without sports.

Nonsurgical treatment may be considered for patients who participate in level III or IV activities; all others should be considered as candidates for surgery. In addition, consider surgical consultation on any young athlete due to potential complications from recurrent instability.

Frequency

United States

An estimated 200,000 ACL-related injuries occur annually in the United States, with approximately 95,000 ACL ruptures. Approximately 100,000 ACL reconstructions are performed each year. The incidence of ACL injury is higher in people who participate in high-risk sports such as basketball, football, skiing, and soccer. When the frequency of participation is considered, a higher prevalence of injury is observed in females over males, at a rate 2.4-9.7 times greater for females.

International

No international incidence is reported in the literature.

Functional Anatomy

The knee joint develops as a cleft between mesenchymal rudiments of the femur and the tibia. This occurs around the eighth week of fetal development. The cruciate ligaments appear as condensations of vascular synovial mesenchyme at the same time.

By fourteen weeks gestation, the ACL and posterior cruciate ligament have divided; both have a functional blood supply, which is mainly derived from the middle geniculate artery. The inferomedial and lateral genicular arteries also provide blood supply through the fat pad.

The ACL is composed of densely organized, fibrous collagenous connective tissue that attaches the femur to the tibia. The ACL is composed of 2 groups, the anteromedial and posterolateral bands. During flexion the anterior band is taught while the posterior is loose; during extension, the posterolateral band is tight, while the anterior band is loose.

The ACL attaches to bone through a transitional zone of fibrocartilage and mineralized cartilage. On the femur, the ACL is attached to a fossa on the posteromedial edge of the lateral femoral condyle. The tibial insertion is located in a fossa that is anterior and lateral to the anterior tibial spine. The tibial attachment is noted to be somewhat wider and stronger than the femoral attachment.

The ACL is intracapsular and extrasynovial. It courses anteriorly, medially, and distally as it runs from the femur to the tibia.

The ACL receives nerve fibers from the posterior branch of the posterior tibial nerve. The main function is believed to be proprioception, providing the afferent arc for postural changes during motion and ligament deformation.

Sport Specific Biomechanics

The ACL is the primary (85%) restraint to limit anterior translation of the tibia. The greatest restraint is in full extension.

The ACL also serves as a secondary restraint to tibial rotation and varus/valgus angulation at full extension. Since the relationship between the tibia and femur provides little bony stability, the ligamentous structures must provide stability. When the ACL is injured, a combination of anterior translation and rotation occurs.

The average tensile strength for the ACL is 2160 N. This is slightly less than the strength of the posterior cruciate ligament and approximately half as strong as the medial collateral ligament (MCL).

CLINICAL

Section 3 of 11  

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History

Most ACL injuries may be diagnosed through a careful history emphasizing mechanism of injury coupled with a good physical examination. Remember that a previous ligamentous injury may be the cause of instability. When discussing the history, be sure to document mechanism of injury for this episode and any previous episodes.

• Noncontact injury
• • An audible pop often accompanies this injury, which often occurs while changing direction, cutting, or landing from a jump (usually a hyperextension/pivot combination).
  
  
  
  • Within a few hours, a large hemarthrosis develops.
  
  
  
  • Patients usually are unable to return to play, secondary to pain, swelling, and instability or giving way of the knee.
     
• Contact and high-energy traumatic injuries
• • These injuries often are associated with other ligamentous and meniscal injuries.
  
  
  
  • The classic "terrible triad" (ACL, MCL, and medial meniscus tears) involves a valgus stress to the knee with resultant acute injury to the ACL and MCL; however, the medial meniscus tear is now thought to occur later, as a result of chronic ACL deficiency.

Physical

An organized, systematic physical examination is imperative when examining any joint. Immediately after the acute injury, the physical examination may be very limited due to apprehension and guarding by the patient. The basic examination should include the following:

• The examiner should begin with inspection, looking for any gross effusion or bony abnormality. An immediate effusion indicates significant intra-articular trauma. According to Noyes et al, in the absence of bony trauma, an immediate effusion is believed to have a 72% correlation with an ACL injury of some degree.
• Assess the patient's range of motion (ROM), especially looking for lack of complete extension, secondary to a possible bucket-handle meniscus tear or associated loose fragment.
• Palpation of bony structures may suggest an associated tibial plateau fracture.
• Palpation of the joint lines to evaluate a possible associated meniscus tear. Palpation over the collateral ligaments to suggest any possible injury (sprain) of these structures. Up to 50% of ACL ruptures have associated meniscal injuries; acute injuries are likely to have associated injuries of the MCL and meniscus.
• Ligamentous laxity may be difficult to detect in the acute situation. The Lachman test is the most sensitive test for acute ACL rupture. Since the Lachman test must be performed when the patient is relaxed, it is often better to conduct this test prior to manipulating the painful knee.
• • The knee is placed in a position of 20-30° of flexion. The femur is stabilized with a nondominant hand, and an anteriorly directed force is applied to the proximal calf.

  • The amount of displacement (in mm) and the quality of endpoint are assessed (eg, firm, marginal, soft). Asymmetry in side-to-side laxity or a soft endpoint is indicative of an ACL tear. Although difficult to measure, a side-to-side difference of greater than 3 mm is considered abnormal.

• Other ligamentous tests are less reliable especially for primary care providers who may not have as much experience in using these maneuvers. The pivot shift test is performed by extending an ACL-deficient knee, which results in a small amount of anterior translation of the tibia in relation to the femur. During flexion, the translation reduces, resulting in the "shifting or pivoting" of the tibia into its proper alignment on the femur.
• • The pivot shift test is performed with the leg extended, the foot in internal rotation, and a valgus stress is applied to the tibia.

  • Flexion causes a reduction of the anteriorly subluxed tibia at approximately 20-30°

• The anterior drawer test may be influenced by hamstring spasm in the acutely injured knee; thus, this test is considered the least reliable.
• • This test is performed with the patient supine and the knee flexed to 90°

  • The examiner can sit on the patient's foot and grasp around the patient's calf with both hands.

  • An anterior force is applied, and tibial excursion is compared to the unaffected knee.

Causes

Associated risk factors include the following:

• High-risk sports
• • Based on a study performed by Kaiser Permanente, football, baseball, soccer, skiing, and basketball account for up to 78% of sports-related injuries.
  
  
  
  • Hewson and associates found a 100-fold increase in the incidence of ACL injury in college football players when compared to the general population.
     
• Sex
• • Female athletes are more susceptible to ACL injuries. Studies have shown a 2-fold increase in collegiate soccer players and a 4-fold increase in basketball compared with their male counterparts.
  
  
  
  • Differences may be due to experience, differences in training, different strength-to-weight ratios, limb alignment, joint laxity, muscle recruitment patterns, and notch index but further studies to document a definitive cause are ongoing. A recent study has determined that ACL laxity does not vary with the menstrual cycle, thus dismissing this possible etiology.
     
• Femoral notch stenosis (the ratio of the femoral notch width to the width of the femoral condyles)
• • A notch width index of less than 0.2 is defined as notch stenosis.
  
  
  
  • Individuals with notch stenosis have a higher risk of noncontact ACL injuries.
     
• Footwear: Cleats, which have a predominant grip on the periphery, have a higher coefficient of friction on artificial turf and may result in a higher incidence of ACL injuries.

DIFFERENTIALS

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Other Problems to be Considered

Tibial spine fracture
Tibial plateau fractures
Osteochondral fracture
Knee dislocation
Patella dislocation
Meniscal tear

WORKUP

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Lab Studies

• Arthrocentesis
• • Blood with fat globules are indicative of an osteochondral or tibial fracture.

  • Tapping of the knee is rarely performed with the advent of other less invasive and more specific diagnostic tests (MRI).

Imaging Studies

• Plain radiographs
• • Radiographic findings are usually negative.
  
  
  
  • Anteroposterior, lateral, merchant, sunrise, and notch views may be used by the physician to diagnose certain radiographic findings that are associated with ACL ruptures.
  
  
  
  • Oblique radiographs may be helpful to exclude tibial plateau fractures.
  
  
  
  • The Segond fracture (lateral capsular avulsion fracture) may be visualized on an anteroposterior view.
    
    
    • This is an avulsion fracture of the lateral tibial plateau, located near the joint line and posteriorly to the Gerdy tubercle.
    
    
    
    • The Segond fracture represents a disruption of the meniscotibial portion of the lateral capsule.
    
    
    
    • Segond fracture is direct evidence of a lateral capsule injury and indirect evidence of an ACL injury.
       
  • The lateral notch fracture (lateral view) is located in the lateral femoral condyle.
    
    
    • This type of fracture is more commonly seen in chronic ACL-deficient knees, resulting from anterior subluxation of the lateral tibial plateau.
    
    
    
    • The physician must differentiate lateral notch fractures from osteochondral defects or fractures.
       
• Arthrograms
• • These studies generally been replaced by MRI.
  
  
  
  • Arthrograms are mostly of historical interest, having occasionally been used by physicians to diagnose ACL ruptures; they must be performed by a radiologist who is highly skilled in double-contrast arthrography.
     
• MRI
• • MRI has a sensitivity of 90-98% for ACL tears. MRI also may identify bone bruising, which is present in approximately 90% of ACL injuries.
  
  
  
  • An MRI allows the physician to confirm an ACL tear, but it should not be used as a substitute for a good history and physical examination.

Other Tests

• Instrumented ligament testing
• • KT-1000 compares the difference in tibial excursion between the injured and the unaffected knee of a patient.

  • An excursion greater than 3 mm as measured by the KT-1000 is classified as pathologic.

TREATMENT

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Acute Phase

Rehabilitation Program

Physical Therapy

Before any treatment, encourage strengthening of the quadriceps and hamstrings, as well as ROM exercises. Performance of ROM helps reduce the amount of effusion and regain motion and strength.

Surgical Intervention

When deciding whether to perform reconstructive surgery, the physician should consider the following factors:

• Preinjury activity level



• Desire to return to high-demand sports (eg, basketball, football, soccer)



• Associated injuries



• Abnormal laxity



• Patient's expectations

Generally, the recommendation is that surgical intervention be delayed at least 3 weeks following injury to prevent the complication of arthrofibrosis. The methods of surgical repair may be categorized into 3 groups, primary repair, extra-articular repair, and intra-articular repair.

• Primary repair is not recommended except for bony avulsions, which are mostly seen in adolescents. Because the ACL is intra-articular, the ligamentous ends are subjected to synovial fluid, which does not support ligamentous healing.



• Extra-articular repair generally involves a tenodesis of the iliotibial tract. This may prevent a pivot shift but has not been shown to decrease anterior tibial translation.



• Intra-articular reconstruction of the ACL has become the criterion standard for treating ACL tears.
  
  
  • Bone-patella-bone autografts are currently popular because they yield a significantly higher percentage of stable knees with a higher rate of return to preinjury sports. The major pitfall of these grafts is their association with postoperative anterior knee pain (10-40%).
  
  
  
  • Hamstring tendon grafts are associated with a faster recovery and less anterior knee pain. Critics believe that these are more susceptible to graft elongation.
  
  
  
  • Recent literature has supported a greater tensile strength with the use of braided quadruple hamstring grafts. However, this finding has not been confirmed in vivo, and the graft may be limited by the type of fixation.
  
  
  
  • Allografts have also been very popular because of their efficiency, their ability to provide bony fixation, and the lack of associated patella morbidity. However, they are associated with a risk of viral transmission. Allografts are best used in revisions. These have also fallen out of favor by some because several deaths linked to clostridial infections from inadequate sterilization techniques have been reported, which led to increased research into sterilization techniques to ensure safety. In addition, concerns exist regarding what effects the immunologic response and delayed revascularization and remodeling may have on clinical outcomes. Although allografts are generally accepted as having less associated morbidity, no proof of this is present in the literature.
  
  
  
  • Synthetic grafts and ligament augmentation devices have also been used. Synthetic grafts are no longer acceptable, because of their high rate of complications, including failure and aseptic effusions.
  
  
  
  • Intra-articular reconstruction may be performed through a 2-incision technique or a single-incision endoscopic technique; the latter is currently more popular. This procedure requires graft stabilization with some type of fixation hardware for all of the graft options. The stabilization may be performed with metal interference screws, bioabsorbable screws, endobuttons, and cross pins. Each device has its own benefits.
  
  
  
  • Double-tunnel ACL reconstructions attempt to reproduce stability in internal rotation and valgus torque applied to the knee. Investigations into the benefits of such surgical treatment versus the increased level of difficulty and operative time are currently ongoing. Studies at this time have been limited to animal models.

Other Treatment

Nonoperative treatment may be considered in elderly patients or in less active athletes who may not be participating in any pivoting type of sports (eg, running, cycling). The goal is to obtain a full ROM and strength compared with the uninjured knee. This modality of treatment requires modification of activity levels and avoidance of physically demanding occupations. Arthroscopy may also be considered for persons who are poor candidates for reconstruction but have a mechanical block to ROM. The goal of this procedure is to debride the remaining stump to increase motion. Patients with significant arthritis are also thought to be poor candidates unless they are experiencing recurrent instability. See below for bracing information.

Recovery Phase

Rehabilitation Program

Physical Therapy

Postoperative treatment is discussed.

• Closed-chain exercises are used to emphasize early and long-term maintenance of full extension.



• Therapy protocols may be divided into the following 4 categories per Shelbourne and Nitz:
  
  
  • Phase I: This is the preoperative period when the goal is to maintain full ROM.
  
  
  
  • Phase II (0-2 wk): The goal is to achieve full extension, maintain quadriceps control, minimize swelling, and achieve flexion to 90^o.
  
  
  
  • Phase III (3-5 wk): Maintain full extension and increase flexion up to full ROM. Stair-climbers and bicycles may be used.
  
  
  
  • Phase IV (6 wk): Increase strength and agility, progressive return to sports. Return to all sports without activity may take 6-9 months and should be closely monitored by the surgeon and physical therapist.

Other Treatment (Injection, manipulation, etc.)

The use of knee braces remains a highly controversial topic; braces are well accepted by patients, but most biomechanical studies do not support their use. Studies have shown that functional bracing can limit anterior translation of the tibia at low loads. Furthermore, most braces have been found to decrease the reaction time of the hamstring muscles.

Maintenance Phase

Rehabilitation Program

Physical Therapy

Open-chain exercises are initiated. The patient's timeframe for returning to sports depends on his/her strength, ROM, and the type of fixation that was performed.

MEDICATION

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Medication for ACL injuries mainly consists of analgesics. Preoperative drugs may include cyclooxygenase-2 (COX-2) inhibitors and opioid analgesic agents. Postoperatively, the patient may obtain pain relief through nonsteroidal anti-inflammatory drugs (NSAIDs) and opioid analgesics. NSAIDS have been shown to decrease bone formation in spine fusions and rotator cuff surgery. Although this has not been seen clinically in ACL reconstructions with bone-patella tendon-bone grafts, it is plausible to think that this may be the case. Therefore, long-term postoperative use may not be beneficial.

Drug Category: Nonsteroidal anti-inflammatory drugs

Have analgesic and anti-inflammatory activities. Their mechanism of action is not known, but may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation and various cell membrane functions.

Drug Category: Cyclooxygenase-2 inhibitors

Although increased cost can be a negative factor, the incidence of costly and potentially fatal GI bleeds is clearly less with COX-2 inhibitors than with traditional NSAIDs. Ongoing analysis of cost avoidance of GI bleeds will further define the populations that will find COX-2 inhibitors the most beneficial.

FOLLOW-UP

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Return to Play

Once quadriceps strength reaches 65% of the opposite leg, sports-specific activities may be performed; this usually occurs within 5-8 weeks postsurgery. This may be tested using a Cybex machine. The athlete may return to activity when the quadriceps strength has reached 80%, which is usually after at least 3-4 months of sports-specific therapy.

Complications

The current failure rate for ACL reconstruction is approximately 8%. The 3 major categories of failure in an ACL reconstruction are (1) arthrofibrosis (due to inflammation of the synovium and fat pad), (2) pain that limits motion, and (3) recurrent instability, secondary to significant laxity in the reconstructed ligament. These factors may be related to the surgical procedure (eg, malpositioned tibial or femoral tunnels, misplaced hardware, inadequate notchplasty).

• Anterior placement of a tibial tunnel may result in graft impingement. If a tunnel is placed too posteriorly on the femoral side, the posterior cortex of the femur may be violated.

• A graft also may fail due to a lack of incorporation, secondary to rejection or stress shielding.

• Trauma from re-injury or aggressive rehabilitation also may cause graft failure. The incidence of graft re-rupture is approximately 2.5%.

Other complications include patella fractures and patella-tendon ruptures. Reflex sympathetic dystrophy, postoperative infection, and neurovascular complications are rare (each accounting for less than 1% of complications). The rate of postoperative deep venous thrombosis is approximately 0.12%.

Prognosis

Patients treated with surgical reconstruction of the ACL have long-term success rates of 82-95%. Recurrent instability and graft failure is seen in approximately 8% of patients.

Knee scores of those treated nonoperatively have fair/poor results up to 50% of the time. As many as 40% of patients treated nonoperatively had no episodes of giving way. The knee scores in this group may be too sensitive, not accurately representing the clinical situation.

Patients with ACL ruptures, even after successful reconstruction, are at risk for osteoarthrosis. The goal of surgery is to stabilize the knee, decrease the chance of future meniscal injury, and delay the arthritic process.

MISCELLANEOUS

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Special Concerns

• ACL ruptures in the skeletally immature
• • This group presents a difficult dilemma to the orthopedic surgeon. Those who go untreated do poorly, and the current treatment options risk growth disturbances.

  • Surgical reconstruction options vary according to the injury and skeletal maturity.
    • Rare tibial eminence fractures may be fixed by open reduction internal fixation. Midsubstance tears are fixed either transphyseally or nontransphyseally, depending on the skeletal maturity of the patient.

    • If the patient is determined to have more than 1 cm of growth remaining, try to delay the surgery. If the growth plates are closing, these individuals may be treated the same as adults.

MULTIMEDIA

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Media file 1:  Proper technique for the Lachman test.
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Media file 2:  Anterior drawer test: Note the anterior excursion of the tibia in relationship to the femur.
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Media file 3:  The pivot shift test.
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Media file 4:  MRI displaying a ruptured anterior cruciate ligament.
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Media type:  MRI

REFERENCES

Section 11 of 11

• Authors and Editors
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• Belanger MJ, Moore DC, Crisco JJ 3rd, Fadale PD, Hulstyn MJ, Ehrlich MG. Knee laxity does not vary with the menstrual cycle, before or after exercise. Am J Sports Med. Jul-Aug 2004;32(5):1150-7. [Medline].
• Beynnon BD, Johnson RJ, Abate JA, Fleming BC, Nichols CE. Treatment of anterior cruciate ligament injuries, part I. Am J Sports Med. Oct 2005;33(10):1579-602. [Medline].
• Cosgarea AJ, Sebastianelli WJ, DeHaven KE. Prevention of arthrofibrosis after anterior cruciate ligament reconstruction using the central third patellar tendon autograft. Am J Sports Med. Jan-Feb 1995;23(1):87-92. [Medline].
• Daniel DM, Malcom LL, Losse G, Stone ML, Sachs R, Burks R. Instrumented measurement of anterior laxity of the knee. J Bone Joint Surg Am. Jun 1985;67(5):720-6. [Medline].
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• Miyasaka KC, Daniel DM, Stone ML. The incidence of knee ligament injuries in the general population. Am J of Knee Surg. 1991;4:3-8.
• Montgomery KD, Herschman EB, Nicholas S. Anterior cruciate ligament injuries. In: Arendt EA, ed. Orthopaedic Knowledge Update: Sports Medicine 2. Rosemont, Ill: American Academy of Orthopaedic Surgeons; 1999:307-316.
• Noyes FR, Bassett RW, Grood ES, Butler DL. Arthroscopy in acute traumatic hemarthrosis of the knee. Incidence of anterior cruciate tears and other injuries. J Bone Joint Surg Am. Jul 1980;62(5):687-95, 757. [Medline].
• Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am. Mar 1984;66(3):344-52. [Medline].
• Shelbourne KD, Gray T. Anterior cruciate ligament reconstruction with autogenous patellar tendon graft followed by accelerated rehabilitation. A two- to nine-year followup. Am J Sports Med. Nov-Dec 1997;25(6):786-95. [Medline].
• Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports Med. May-Jun 1990;18(3):292-9. [Medline].
• Stanitski CL. Anterior Cruciate Ligament Injury in the Skeletally Immature Patient: Diagnosisand Treatment. J Am Acad Orthop Surg. May 1995;3(3):146-158. [Medline].
• Watson JT. Knee and leg: bone trauma. In: Beaty JH, ed. Orthopaedic Knowledge Update 6. Rosemont, Ill: American Academy of Orthopaedic Surgeons; 1999:521-32.

Article Last Updated: Mar 7, 2006