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Anterior Cruciate Ligament Injury

  • The ACL is critical for knee function in athletes who require knee stability in activities such as running, cutting, jumping, and kicking.
  • The ACL originates on the posteromedial aspect of the lateral femoral condyle and inserts anterior to and between the intercondylar eminences of the tibia.
  • The ACL is composed of 2 bundles, an anteromedial bundle and a posterolateral bundle.
  • The ACL functions as the primary restraint to limit anterior tibial translation and as a secondary restraint to internal rotation of the tibia.
  • In the skeletally immature patient, injury to the ACL most often occurs at the bone ligament interface, as an avulsion of the tibial spine.
  • In the adult patient, rupture of the midsubstance of the ligament is more common.
ACL injuries commonly are associated with sports such as football, hockey, basketball, lacrosse, gymnastics, wrestling, and volleyball.
Risk Factors
ACL injury rate is 6 times higher in females than males in competitive sports.
  • Etiologic factors include anatomic features, such as an elevated Q angle, notch stenosis, a narrower than normal ACL, and neuromuscular factors (landing with decreased knee flexion and increased knee valgus).
  • ACL injuries often are the result of a noncontact injury that occurs while decelerating, changing direction, or landing from a jump.
  • Direct contact to the knee with a valgus load and external rotation of the tibia, such as a clipping injury, is another common mechanism.
Associated Conditions
  • Bone bruises (trabecular microfractures), which occur in >50% of acute ACL injuries, typically are located on the posterior portion of the lateral tibial plateau and near the sulcus terminalis on the lateral femoral condyle.
  • Meniscal injuries (>50%) :
    • Acutely, lateral meniscal injuries are more common than medial.
    • In patients with chronic ACL deficiency, medial meniscal injuries are more common than lateral.
  • Collateral ligamentous injuries in the knee
  • Articular cartilage injuries
Signs and Symptoms
  • The injury often is associated with immediate pain and an audible pop
  • Swelling of the knee is noted within a few hours (acute hemarthrosis).
  • The patient often states that the knee feels too unstable to continue playing and that weightbearing is difficult.
Physical Exam
  • A careful physical examination can diagnose most ACL injuries.
  • The results of the physical examination of the injured knee must be compared with those of the normal knee.
  • Inspection usually reveals a moderate to severe effusion.
  • Typically, full knee extension is limited secondary to pain, effusion, hamstring spasm, and ACL stump impingement.
  • Flexion often is limited by effusion.
  • Care should be taken to observe that anterior translation or drawer testing is not reducing a posteriorly sagged tibia (OSD injury) from a subluxated position.
  • The Lachman test is the most sensitive examination for acute ACL injuries.
    • The knee is placed in 30° of flexion, the femur is stabilized, and an anteriorly directed force is applied to the proximal calf.
    • The examiner assesses the magnitude of anterior translation and the firmness (firm versus soft) of the endpoint.
    • Differences between the injured and uninjured knees are clinically significant.
  • The pivot shift test is used to assess the anterior subluxation of the lateral tibial plateau on the femoral condyle.
    • It is difficult to perform this test in an awake patient in the acute setting, but it is helpful in evaluating an ACL-deficient knee.
    • This test is especially helpful when the patient is anesthetized.
    • Procedure:
      • Patient supine, knee extended
      • With the tibia internally rotated, apply a valgus force to the knee as it is passively flexed.
      • If, at approximately 20-40° of knee flexion, the patient experiences a sudden jerk as the iliotibial band reduces the anteriorly subluxated tibia, the test is considered positive.
  • The anterior drawer test is the least reliable test for acute ACL injuries .
    • The hip is flexed at 45°, and the knee is flexed to 90°.
    • An anterior force is directed by the examiner to the proximal calf.
    • The examiner assesses the magnitude of anterior translation and the firmness (firm versus soft) of the endpoint.
    • Differences between the injured and uninjured knee are clinically significant.
  • Instrumented knee laxity measurements can be performed using a device such as the KT-1000.
    • These devices are useful for quantifying knee laxity objectively, but they are not necessary for diagnosis.
    • A difference of >3 mm of anterior tibial translation between the injured and uninjured knee is considered pathologic.
  • Radiography:
    • Evaluation should include AP, lateral, and tunnel views of the knee.
    • Plain radiographic findings suggestive of an ACL injury include a tibial spine avulsion fracture, a Segond fracture (lateral capsule avulsion fracture of the tibial plateau), or a deepened sulcus terminalis.
  • MRI is the imaging modality of choice for evaluating the ACL and associated bony contusions and ligamentous or meniscal injuries.
    • MRI has an overall accuracy of 95% in diagnosing ACL injuries .
    • On sagittal MRI, an ACL tear is visualized as a discontinuity in the ligament.
Differential Diagnosis
  • Osteochondral fracture
  • Tibial plateau fracture
  • Meniscal injury
  • Cartilage injury
  • MCL or LCL injury
  • OSD injury
Initial Stabilization
  • The initial treatment of the acutely injured ACL is splinting and the use of crutches for comfort and early active ROM. The goal is to obtain full ROM.
  • Ice, elevation, and analgesics are prescribed in the initial postinjury period.
General Measures
  • Treatment decisions should be based on many factors, including patient age, activity level, type of sporting activity (especially jumping, cutting, and pivoting sports), degree of instability, and associated knee pathology.
  • Treatment options in the skeletally mature patient include nonoperative interventions and intra-articular ligamentous reconstruction.
  • Nonoperative treatment is preferred for elderly patients or those with sedentary lifestyles (see Physical Therapy section).
  • For the skeletally immature patient with a midsubstance ACL injury:
    • Some clinicians favor nonoperative treatment and rehabilitation measures until skeletal maturity is reached .
    • Others favor physeal sparing surgical reconstructive procedures .
  • Nondisplaced and minimally displaced tibial spine avulsion fractures in skeletally immature individuals are treated with closed reduction.
  • Patients should be counseled concerning high-risk activities, such as cutting, pivoting, and jumping.
  • Regardless of treatment modality, functional knee bracing after ACL injury is controversial.
Special Therapy
Physical Therapy
  • Preoperative, postoperative, and nonoperative rehabilitation emphasizes early ROM (especially full extension of the knee) and early weightbearing.
    • For patients treated nonoperatively or surgically, strengthening is achieved by using closed-chain weightbearing exercises.
    • The goal is to return the function of the hamstring and quadriceps muscles to within 90% of that of the contralateral limb.
    • In patients treated surgically, agility and strengthening exercises typically are started 6 weeks after surgery.
First Line
  • In the acute period:
    • NSAIDs
    • Acetaminophen
    • Mild narcotic analgesics
  • Before surgery, the patient should undergo physical therapy to regain full ROM and minimize swelling.
  • Intra-articular ACL reconstruction currently is favored for:
    • Those with active lifestyles but acute ACL deficiency
    • Those with chronic ACL deficiencies that result in functional instability that endangers the menisci
  • Intra-articular ACL reconstruction with grafting can be performed effectively via either open or arthroscopic techniques.
  • Graft selection depends on patient factors and surgeon preference.
    • Autograft: Bone patellar tendon bone, strand hamstrings, or quadriceps tendon
    • Allograft: Fascia lata and Achilles, quadriceps, patellar, hamstring, and anterior and posterior tibialis tendons
    • Allograft is associated with lessened donor-site morbidity, but it has the potential for viral transmission .
  • Primary repair is favored for a displaced tibial spine avulsion fracture but is not recommended for a midsubstance ACL rupture.
  • In the skeletally immature patient with a midsubstance ACL injury, a variety of reconstructive procedures may be performed based on the maturity of the patient.
    • Tanner stage 1 patients: Physeal-sparing procedures
    • Tanner stage 2 patients: Partial transphyseal techniques
    • Tanner stage 3 and above (those approaching skeletal maturity): Complete transphyseal reconstructions
  • In the ACL-deficient knee, meniscal tears, cartilage damage, and possibly degenerative arthrosis may ensue.
  • Prognosis is excellent for appropriately selected patients who have undergone ACL reconstruction.
  • Nonoperative-related (i.e., the chronic ACL-deficient knee):
    • Higher incidence of complex meniscal tears than in surgically treated patients
    • Possibly more prone to development of late osteoarthritis (controversial)
  • Surgery-related:
    • Graft failure, graft impingement, quadriceps weakness, patellofemoral pain, infection, arthroscopic fluid extravasation and compartment syndrome, deep vein thrombosis, reflex sympathetic dystrophy (<1%), nerve and vascular injuries (<1%), and arthrofibrosis.
    • Harvesting bone patellar tendon bone autograft is associated with anterior knee pain, kneeling pain, and (rarely) patellar fracture and patellar tendon rupture  .
Patient Monitoring
Patients should be followed carefully at  6-week intervals to ensure that they regain ROM and strength of the quadriceps and hamstrings.
  • 717.83 Old disruption of the anterior cruciate ligament
  • 844.2 Acute sprain of cruciate ligament of knee
Patient Teaching
Most patients do not return to their previous level of activity if they were high-performance athletes, but most patients can return to sports.
Q: If I choose not to undergo ACL reconstruction, what activity modifications will I have to make?
A: Patients permanently should avoid high-impact or cutting motions and contact sports. Straight-away running and closed-chain exercises are excellent for conditioning and strengthening.
Q: If I undergo ACL reconstruction, how long will I be out of sports?
A: In uncomplicated cases and depending on the sport, athletes can expect to return to full sports participation in approximately 6-9 months after ACL reconstruction.
Q: What is the role of bracing to prevent ACL injuries?
A: Although the issue is controversial, use of knee braces during aggressive athletic activity, such as football, has not been shown to decrease incidence of knee injuries and may give the player a false sense of security.

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