ACL Injury



  • The anterior cruciate ligament (ACL) is a primary knee stabilizer that serves to prevent excessive anterior translation and internal rotation of the tibia on the femur.
  • The ACL and posterior cruciate ligament (PCL) work together to stabilize the knee during dynamic movement.
  • ACL injuries are common and can occur through multiple mechanisms.
  • >70% of ACL injuries are caused by noncontact forces, usually low velocity, sudden deceleration, with a rotational component.
  • Although partial tears occur, complete ACL tears are more common.
  • Due to differences in pelvic architecture, lower extremity alignment, and hormone fluctuations, female athletes are at 2 to 5 times higher at risk of ACL tear.
  • ACL injury is associated with early onset of knee osteoarthritis (OA).
  • Surgery is often indicated to restore function.



  • 250,000 ACL injuries annually in the United States
  • >175,000 ACL reconstructions in United States yearly
  • Female incidence 2- to 5-fold > male (1)
  • Greater incidence of noncontact ACL injuries in sports requiring cutting, pivoting, and rapid deceleration, such as basketball, football, skiing, and soccer (1)


  • Young athletes (15 to 25 years) sustain >50% of all ACL injuries (1)[B].
  • >2/3 of patients with complete ACL tear have associated meniscal and/or articular cartilage injury.

Pediatric Considerations

  • Rule out physeal injuries in skeletally immature patients.
  • The incidence of ACL tears in patients with open physes has increased in recent years.
  • ACL injury rates increase for both boys and girls after age 11 years.

Etiology and Pathophysiology

  • Noncontact mechanisms: Torsional or hyperextension forces creates anterior translation of the tibia relative to the femur. This creates excessive stress across the ACL with resultant rupture.
  • Direct trauma: most often, a valgus blow to the knee with resultant trauma to ACL, medial collateral ligament (MCL), and lateral meniscus (“unhappy triad”)

Risk Factors

Female athletes have increased 1.6 times risk.

  • Hormonal influence
    • Alterations in hormonal balance hypothesized to increase risk, but no conclusive evidence linking menstrual phase to ACL injury risk.
  • Anatomic gender differences
    • Increased Q angle, increased genu valgum, narrower femoral notch size, smaller ACL
    • Neuromuscular imbalances (increased quadriceps activation, decreased hamstring activity during landings)

General Prevention

  • Neuromuscular training with proprioceptive, plyometric, and strength exercises significantly reduces noncontact ACL injuries in female athletes if performed several times a week for >6 weeks.
  • Prophylactic knee bracing does not prevent ACL injury.

Commonly Associated Conditions

  • Meniscal tear
  • Collateral ligament tear
  • PCL tear
  • Tibia or femur fractures
  • Osteochondral injury
  • Early-onset degenerative joint disease



Describe mechanism.

  • Noncontact
    • Sudden deceleration
    • Cutting, sudden change in direction
    • Landing from a jump with the knee in extension
  • Contact with player, object
  • May recall sudden pop or snap
  • Sudden pain and giving way
  • Marked effusion/hemarthrosis within 4 to 12 hours
  • “Pop” with deceleration or twisting movement associated with early effusion and inability to continue with participation are highly suggestive of ACL tear.

Physical Exam

  • Inspect for malalignment (fracture, dislocation).
  • Palpate for effusion.
  • Assess range of motion (ROM).
    • Deficits may be secondary to pain, effusion, mechanical blocks (meniscal tear, loose body, torn ACL stump).
  • Joint instability, difficulty bearing weight
  • Evaluate integrity of extensor mechanism.
  • Special maneuvers: Test ligament/meniscal integrity.
  • Lachman test: most sensitive, highly specific diagnostic test for ACL injury in acute setting (2)[B]
    • 20 to 30 degrees of knee flexion. Tibia is translated anteriorly with femur stabilized by the opposite hand. Increased anterior translation compared with uninjured knee indicates injury. Lack of a solid end point indicates rupture.
  • Pivot shift test: less sensitive, but more than Lachman test: specific for ACL tear (2)[B]
    • Knee is placed in extension. Knee is flexed while valgus and internal rotation stress is applied. A positive test is anterior subluxation at 20 to 40 degrees of flexion.
  • Anterior drawer (2)[B]
    • Low sensitivity for ACL integrity, especially in acute setting (limited by swelling)
  • Posterior drawer test assesses PCL integrity.
  • McMurray test assesses for meniscal tears.
  • Valgus/varus stress test for MCL/lateral collateral ligament (LCL) integrity

Differential Diagnosis

  • Fracture
  • Meniscal injury
  • Patellar dislocation/subluxation
  • Tendon disruption/PCL/collateral ligament injury

Diagnostic Tests & Interpretation

Initial Tests (lab, imaging)

  • Radiographs to rule out associated bony injury
  • Anterior-posterior (AP), lateral, and tunnel views
    • Segond fracture: avulsion fracture of the lateral capsular margin of the tibia
    • Tibial eminence avulsion fracture
    • Fracture of proximal tibia or distal femur
    • Osteochondral injuries

Follow-Up Tests & Special Considerations

  • MRI is the gold standard for imaging ligamentous and intra-articular structures.
  • Sensitivity of MRI is 87–94%, specificity 88–93% (3).
  • Secondary signs of ACL injury on MRI include contusion of the anterior femoral condyle and/or posterior tibial plateau, anterior translation of the tibia, an uncovered or displaced posterior horn of the lateral meniscus, PCL buckling, or a Segond fracture (an avulsion fracture of the lateral tibial condyle).
  • Ultrasound is an emerging technique that is fast and noninvasive.

Diagnostic Procedures/Other
Surgical management should be considered in the active population, young or old.


General Measures

  • Acute injury: protection, relative rest, ice, compression, elevation, medications, modalities (PRICEMM) therapy
  • Crutches may be useful until patient is able to ambulate without pain.
  • Locked knee brace may be used initially for comfort. Use with caution and transition to a hinged knee brace as soon as possible to avoid quadriceps atrophy and stiffness.
  • Aspiration of large effusion may alleviate pain and increase ROM.


First Line

  • Nonsteroidal anti-inflammatory drugs (NSAIDs)
    • Acute ligament sprains
      • Ibuprofen: 200 to 800 mg TID
      • Naproxen: 250 to 500 mg BID
      • Acetaminophen: 3 g/day divided TID
  • Opioids for severe pain (e.g., acetaminophen-hydrocodone)

Issues For Referral

The decision to manage ACL tears surgically or nonsurgically (“conservatively”) can be difficult. Consider surgical management in active patients or if the injury interferes with activities of daily living.

  • Physical therapy is essential whether an athlete chooses nonsurgical or surgical treatment. Proper rehabilitation is time-consuming (6 to 12 months) and hard work. Physical therapy restores ROM, strength, and proprioception.
  • Preoperative phase
    • Increase ROM and quadriceps strength; minimize inflammation with preoperative physical therapy.
  • Early postoperative phase: weeks 2 to 4
    • ROM 0 to 90 degrees: Full passive extension is main goal.
    • Control postoperative pain/swelling.
    • Rehabilitation begins immediately.
    • Early progressive to full weight-bearing
  • Intermediate postoperative phase: weeks 4 to 12
    • ROM: full flexion, hyperextension
    • Quadriceps and hamstring strengthening proprioceptive training normalize gait.
    • Able to progress when able to demonstrate unilateral weight-bearing without pain with full ROM (4)
  • Late postoperative phase: >3 months postoperative
    • Straight-line running
    • Increase speed, duration over 6 to 8 weeks.
    • Progress to cutting and sport-specific drills.
    • Strength and proprioceptive training

Geriatric Considerations
Management is based on anticipated activity level, associated injuries, coexisting medical conditions, and acute versus long-standing ACL deficiency.

Surgery/Other Procedures

  • The decision for surgery depends on patient’s activity level, age, associated injuries, and presence of OA.
  • Recent evidence suggests higher than previously reported second ACL injury rates, lower return to sport rates, and a high incidence of OA, despite ACL reconstruction (4).
  • Annually, >200,000 ACL injuries occur in the United States with the majority of these patients electing to undergo ACL reconstruction (4).
  • There is an insufficient evidence to recommend surgery over conservative management in skeletally immature patients.
  • No significant difference in patient-reported knee function or muscle strength between surgical and nonsurgical management (2)[B]
  • Reconstruction techniques
    • Bone–patella tendon–bone autograft
    • Hamstring autograft
    • Allograft tendon (from cadaver)
  • No consistent significant differences in outcome between patellar tendon and hamstring tendon autografts
  • Concomitant meniscal tears are repaired at the time of ACL reconstruction.

Admission, Inpatient, and Nursing Considerations


Ongoing Care

Follow-up Recommendations

  • ROM exercises to regain full flexion and extension
  • Advance activity as tolerated

Patient Monitoring
Assess functional status, rehabilitative exercise compliance, and pain control at follow-up visit.


  • Athletes typically are out of competitive play for 6 to 9 months after injury for reconstructive surgery and rehabilitation.
  • High prevalence of OA, even in those with early ACL reconstruction
  • Delaying surgical repair of torn ACL increases risk of secondary meniscal injury.


  • Instability
  • Secondary meniscal and articular cartilage injury
  • Early-onset degenerative arthritis
  • Surgical risks
    • Infection, pulmonary embolism (PE), subsequent ACL graft rupture, laxity due to failure of graft remodeling

Additional Reading

  • Dufka FL, Lansdown DA, Zhang AL, et al. Accuracy of MRI evaluation of meniscus tears in the setting of ACL injuries. Knee. 2016;23(3):460–464. [PMID:26917035]
  • Frobell RB, Roos EM, Roos HP, et al. A randomized trial of treatment for acute anterior cruciate ligament tears. N Engl J Med. 2010;363(4):331–342. [PMID:20660401]
  • Grindem H, Eitzen I, Engebretsen L, et al. Nonsurgical or surgical treatment of ACL injuries: knee function, sports participation, and knee reinjury: the Delaware-Oslo ACL cohort study. J Bone Joint Surg Am. 2014;96(15):1233–1241. [PMID:25100769]
  • Grzelak P, Podgórski MT, Stefańczyk L, et al. Ultrasonographic test for complete anterior cruciate ligament injury. Indian J Orthop. 2015;49(2):143–149. [PMID:26015601]
  • Hewett TE, Di Stasi SL, Myer GD. Current concepts for injury prevention in athletes after anterior cruciate ligament reconstruction. Am J Sports Med. 2013;41(1):216–224. [PMID:23041233]
  • Koga H, Muneta T, Yagishita K, et al. Mid- to long-term results of single-bundle versus double-bundle anterior cruciate ligament reconstruction: randomized controlled trial. Arthroscopy. 2015;31(1):69–76. [PMID:25242512]
  • Mohtadi NG, Chan DS, Dainty KN, et al. Patellar tendon versus hamstring tendon autograft for anterior cruciate ligament rupture in adults. Cochrane Database Syst Rev. 2011;(9):CD005960. [PMID:21901700]
  • Silvers HJ, Mandelbaum BR. Prevention of anterior cruciate ligament injury in the female athlete. Br J Sports Med. 2007;(41 Suppl 1):i52–i59. [PMID:17609222]
  • White K, Di Stasi SL, Smith AH, et al. Anterior cruciate ligament- specialized post-operative return-to-sports (ACL-SPORTS) training: a randomized control trial. BMC Musculoskelet Disord. 2013;14:108. [PMID:23522373]

See Also

Algorithm: Knee pain



  • M23.611 Oth spon disrupt of anterior cruciate ligament of right knee
  • M23.612 Oth spon disrupt of anterior cruciate ligament of left knee
  • M23.619 Oth spon disrupt of anterior cruciate ligament of unsp knee
  • S83.511A Sprain of anterior cruciate ligament of right knee, init
  • S83.512A Sprain of anterior cruciate ligament of left knee, init
  • S83.519A Sprain of anterior cruciate ligament of unsp knee, init


  • 717.83 Old disruption of anterior cruciate ligament
  • 844.2 Sprain of cruciate ligament of knee


  • 11861761000119103 Rupture of anterior cruciate ligament of right knee (disorder)
  • 11861801000119106 Rupture of anterior cruciate ligament of left knee (disorder)
  • 127292004 sprain of anterior cruciate ligament of knee (disorder)
  • 202110002 Old anterior cruciate ligament disruption (disorder)
  • 202121006 Old partial tear anterior cruciate ligament (disorder)
  • 202122004 Old complete tear anterior cruciate ligament (disorder)
  • 209520004 partial tear, knee, anterior cruciate ligament (disorder)
  • 209629006 complete tear, knee, anterior cruciate ligament (disorder)
  • 239725005 Rupture of anterior cruciate ligament (disorder)
  • 444470001 Injury of anterior cruciate ligament

Clinical Pearls

  • Lachman test is the most sensitive and specific physical examination maneuver for diagnosing acute ACL injury.
  • Bone contusion of the anterior femoral condyle and/or posterior tibial plateau on MRI is highly suggestive of ACL tear.
  • 2/3 of complete ACL tears have associated meniscal or articular injuries.
  • The decision for surgical repair is based on patient’s age, activity level, and associated symptoms.


Caitlin G. Waters, MD
J. Herbert Stevenson, MD


  1. Beynnon BD, Vacek PM, Newell MK, et al. The effects of level of competition, sport, and sex on the incidence of first-time noncontact anterior cruciate ligament injury. Am J Sports Med. 2014;42(8):1806–1812. [PMID:25016012]
  2. Jain DK, Amaravati R, Sharma G. Evaluation of the clinical signs of anterior cruciate ligament and meniscal injuries. Indian J Orthop. 2009;43(4):375–378. [PMID:19838388]
  3. Gornitzky AL, Lott A, Yellin JL, et al. Sport-specific yearly risk and incidence of anterior cruciate ligament tears in high school athletes: a systematic review and meta-analysis. Am J Sports Med. 2016;44(10):2716–2723. [PMID:26657853]
  4. Paterno MV. Non-operative care of the patient with an ACL-deficient knee. Curr Rev Musculoskelet Med. 2017;10(3):322–327. [PMID:28756525]

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