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ACL Injury
Jeff Wang, MD, MPH
J. Herbert Stevenson, MD
image BASICS
  • 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.
    • During dynamic movement, the ACL and posterior cruciate ligament (PCL) work together to stabilize the knee.
  • ACL injuries are common and can occur through multiple mechanisms. >70% of ACL injuries are caused by noncontact forces.
  • Although partial tears occur, complete ACL tears are more common.
  • Due to differences in pelvic architecture and lower extremity alignment, female athletes are at 2 to 5 times higher at risk of ACL tear.
  • ACL injury is associated with early onset of knee osteoarthritis.
  • 250,000 ACL injuries annually in the United States
  • 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 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.
  • 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, and lateral meniscus (“unhappy triad”)
A genetic predisposition has been identified. An association has been found between the genes encoding proteoglycans and the risk of ACL tears (7)[B].
  • Female athletes have increased 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)
    • Movement patterns (sudden deceleration, change-of-direction cutting movements, landing from a jump in hyperextension)
  • Neuromuscular training with proprioceptive, plyometric, and strength exercises significantly reduce noncontact ACL injuries in female athletes if performed several times a week for >6 weeks (2)[C].
  • Prophylactic knee bracing does not prevent ACL injury.
  • Meniscal tear
  • Collateral ligament tear
  • PCL tear
  • Tibia or femur fractures
  • Osteochondral injury
  • Early-onset degenerative joint disease
  • Inspect for malalignment (fracture, dislocation).
  • Palpate for effusion.
  • Decreased 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 (Lachman; anterior drawer; pivot shift) to assess ACL integrity
  • Lachman test: most sensitive and highly specific diagnostic test for ACL injury in acute setting (3)[B]
    • Knee is placed in 20 to 30 degrees of 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 (3)[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 test (3)[B]
    • Low sensitivity for ACL integrity, especially in acute setting
  • Posterior drawer test assesses PCL integrity.
  • McMurray test assesses for meniscal tears.
  • Valgus/varus stress test for medial collateral ligament/lateral collateral (MCL/LCL) integrity
  • Fracture
  • Meniscal injury
  • Patellar dislocation/subluxation
  • Tendon disruption
  • PCL injury
  • Collateral ligament injury
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. The sensitivity of MRI is 87-94%, specificity 88-93% (4).
  • 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 (5)[B].
Diagnostic Procedures/Other
Surgical management should be considered in the active population, young or old.
  • 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)
The decision to manage ACL tears surgically or non-surgically (“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.
  • Early postoperative phase: weeks 2 to 4
    • ROM: Full extension is the primary goal. Rehabilitation begins immediately.
    • Progress to full weight bearing
  • Intermediate postoperative phase: weeks 4 to 12
    • ROM: full flexion, hyperextension
    • Quadriceps and hamstring strengthening proprioceptive training, normalize gait
  • Late postop phase: >3 months postop
    • 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.
  • The decision for surgery depends on patient's activity level, age, associated injuries, and presence of osteoarthritis.
  • 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 (6)[B].
  • In young, active adults with acute ACL tears, rehabilitation plus early ACL repair was not superior to a strategy of initial rehabilitation with delayed repair if rehabilitation alone failed. Rehabilitation alone results in an overall reduction of ACL reconstructions (6)[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
  • In the hamstring autograft approach, double bundle is superior to the single bundle (7)[B].
  • Concomitant meniscal tears are repaired at the time of ACL reconstruction.
Admission Criteria/Initial Stabilization
  • 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.
1. Beynnon B, 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.
2. Acevedo RJ, Rivera-Vega A, Miranda G, et al. Anterior cruciate ligament injury: identification of risk factors and prevention strategies. Curr Sports Med Rep. 2014:13(3):186-191.
3. 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.
4. Grzelak P, Podgórski MT, Stefańczyk L, et al. Ultrasonographic test for complete anterior cruciate ligament injury. Indian J Orthop. 2015;49(2): 143-149.
5. Grindem H, Eitzen I, Engbretsen 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 and Joint Surg. 2014;96(15):1233-1241.
6. Koga H, Muneta T, Yagishita K, et al. Mid- to longterm results of single-bundle versus double-bundle anterior cruciate ligament reconstruction: randomized controlled trial. Arthroscopy. 2015;31(1):69-76.
7. Mannion S, Mtintsilana A, Posthumus M, et al. Genes encoding proteoglycans are associated with the risk of anterior cruciate ligament rupture. Br J Sports Med. 2014;48(22):1640-1646.
Additional Reading
  • Christiansen BA, Anderson MJ, Lee CA, et al. Musculoskeletal changes following non-invasive knee injury using a novel mouse model of post-traumatic osteoarthritis. Osteoarthr Cartil. 2012;20(7):773-782.
  • 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.
  • 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.
  • Mohtadi NG, Chan DS, Dainty KN, et al. Patellar tendon versus hamstring tendon autograft for anterior cruciate ligament ruptures in adults. Cochrane Database Syst Rev. 2011;(9):CD005960.
  • Silvers HJ, Mandelbaum BR. Prevention of anterior cruciate ligament injury in the female athlete. Br J Sports Med. 2007;(41 Suppl 1):i52-i59.
  • 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.
See Also
Algorithm: Knee pain
  • S83.519A Sprain of anterior cruciate ligament of unsp knee, init
  • M23.619 Oth spon disrupt of anterior cruciate ligament of unsp knee
  • S83.511A Sprain of anterior cruciate ligament of right knee, init
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 age, activity level, and associated symptoms.