Description

• The anterior cruciate ligament (ACL) is one of the major stabilizers of the knee:
  • It prevents excessive anterior translation and internal rotation of the tibia in relation to 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 noncontact or contact mechanisms. >70% of ACL injuries are caused by noncontact forces (1).
• Partial tears of the ACL can occur, but complete tears are far more common.
• Female athletes are at 2–5 times higher risk of ACL tear, particularly in soccer, basketball, and skiing.
• ACL injury is associated with early onset of knee osteoarthritis, regardless of surgical or nonsurgical treatment (2)[B].

Epidemiology

• 250,000 ACL injuries annually in the US (1)
• Female athletes incidence 2–5-fold > male athletes
• Greater incidence of noncontact ACL injuries in sports requiring cutting, pivoting, and rapid deceleration, such as basketball and soccer

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

• Must be concerned about physeal injuries in the skeletally immature
• The incidence of ACL tears in patients with open physes has increased in recent years.
• ACL injury rates increase for both boys and girls beginning at age 11 years.

Risk Factors

• No single risk factor correlates directly with higher ACL injury rates in female athletes. Likely multifactorial etiology:
  • Sex hormones:
    • Increased rate may be due to monthly hormonal fluctuations.
    • No conclusive evidence linking a menstrual cycle 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)

Genetics
Familial tendency has been identified.

General Prevention

• Neuromuscular training with proprioceptive, plyometric, and strength exercises may reduce noncontact ACL injuries by 72% in female athletes if performed > once per week for >6 weeks (1,3)[B].
• No evidence that prophylactic knee bracing prevents ACL injuries
• Educate the patient about possible risk factors for ACL injury and provide instruction on neuromuscular training exercises.

Etiology

• Noncontact mechanisms (torsional or hyperextension forces)
• Direct trauma (player, object on playing field), most often a valgus blow to the knee

Commonly Associated Conditions

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

History

May recall mechanism:

• Noncontact:
  • Sudden deceleration
  • Cutting, sudden change in direction
  • Landing from a jump in extension
  • Combination of mechanisms
• Contact with player, object
• May recall sudden pop or snap
• Sudden pain and giving way
• Marked effusion/hemarthrosis within 4–12 hours

Physical Exam

• Pain
• Effusion
• Decreased range of motion (ROM)
• Joint instability
• Difficulty bearing weight
• Inspect for malalignment (fracture, dislocation)
• Palpate for effusion
• Evaluate extensor mechanism integrity
• Evaluate ROM:
  • Deficits may be secondary to pain, effusion, mechanical blocks (meniscal tear, loose body, torn ACL stump).

Diagnostic Tests and Interpretation

• Lachman test: Most sensitive and highly specific diagnostic test for ACL injury, especially in acute setting (4)[A]:
  • Knee placed in 20–30° flexion. Tibia is translated anteriorly while the femur is stabilized with the opposite hand. Increased anterior translation compared with uninjured knee indicates injury. Lack of a solid endpoint indicates rupture.
• Pivot shift test: Lower sensitivity, but more specific for ACL tear than Lachman test (4)[B]:
  • Knee placed in extension. Knee is flexed while applying a valgus and internal rotation stress. A positive test is subluxation at 20–40° of flexion.
• Anterior drawer test:
  • Low sensitivity for ACL integrity, especially in acute setting (4)[A]
• 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

• 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

• MRI is the gold standard for imaging ligamentous and intra-articular structures; MRI may show secondary signs of ACL injury. The sensitivity of MRI is 87–94%, specificity 88–93% (5).
• Secondary signs include: Bone 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).

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

Differential Diagnosis

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

Medication (Drugs)

• NSAIDs:
  • Acute ligament sprains:
    • Ibuprofen: 200–800 mg t.i.d.
    • Naproxen: 375–500 mg b.i.d.
    • Indomethacin: 25–50 mg t.i.d.
• Acetaminophen
• Narcotics for severe pain (e.g., acetaminophen-hydrocodone)
• Contraindications/Precautions/Interactions: Refer to the manufacturer’s profile of each drug.

Additional Treatment

• Acute injury: PRICEMM therapy: Protection, Relative rest, Ice, Compression, Elevation, Medications, Modalities
• Crutches may be indicated until patient is able to ambulate without pain.
• Knee brace may be used initially for comfort. Use with caution.
• Aspiration of large effusion may be indicated to alleviate pain and increase ROM.

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

Issue for Referral
Surgical management should be considered in the active population.

• Physical therapy is recommended if an athlete chooses nonsurgical or surgical treatment. Nonsurgical physical therapy is focused on restoring ROM, strength, and proprioception.
• Preoperative phase:
  • Increase ROM, minimize inflammation
• Early postoperative phase: Weeks 2–4:
  • ROM: Full extension is the most important goal. Rehabilitation begins immediately.
  • Progress to full weight bearing.
• Intermediate postoperative phase: Weeks 4–12:
  • ROM: Full flexion, hyperextension
  • Quadriceps and hamstring strengthening proprioceptive training, normalize gait
• Late postop phase: 2–3 months postop:
  • Straight-line running
  • Increase speed, duration over 6–8 weeks.
  • Progress to cutting and sport-specific drills.
  • Strength and proprioceptive training

Surgery/Other Procedures

• Surgical vs. conservative management depends on patient’s activity level, age, associated injuries, and presence of osteoarthritis.
• Insufficient evidence for ACL reconstructive surgery vs. conservative management in the skeletally immature patient
• Insufficient evidence from randomized trials comparing surgical vs. nonoperative management of ACL injuries in adults based on studies in the 1980s (6)[A]
• 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 rehab alone failed. In fact, the latter strategy led to an overall reduction of ACL reconstructions (7)[A].
• 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 (8)[A]
• Concomitant meniscal tears are repaired at the time of ACL reconstruction.

In-Patient Considerations

Initial Stabilization
Outpatient

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.

Prognosis

• Athletes typically are out of competitive play for 6–9 months after injury to undergo ACL reconstructive surgery and rehabilitation.
• High prevalence of OA, even in those with early ACL reconstruction (2)[B]
• Delay of surgical reconstruction of torn ACL raises risk of secondary meniscal injury

Complications

• 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

See Also

Algorithm: Knee pain

ICD-9

844.2 Sprain of cruciate ligament of knee

ICD-10

• S83.519A Sprain of anterior cruciate ligament of unsp knee, init
• S83.519D Sprain of anterior cruciate ligament of unsp knee, subs
• S83.519S Sprain of anterior cruciate ligament of unsp knee, sequela
• S83.511A Sprain of anterior cruciate ligament of right knee, init
• S83.511D Sprain of anterior cruciate ligament of right knee, subs
• S83.511S Sprain of anterior cruciate ligament of right knee, sequela
• S83.512A Sprain of anterior cruciate ligament of left knee, init
• S83.512D Sprain of anterior cruciate ligament of left knee, subs
• S83.512S Sprain of anterior cruciate ligament of left knee, sequela

SNOMED

• 444470001 Injury of anterior cruciate ligament
• 127292004 sprain of anterior cruciate ligament of knee (disorder)
• 239725005 Rupture of anterior cruciate ligament (disorder)
• 209520004 partial tear, knee, anterior cruciate ligament (disorder)
• 209629006 complete tear, knee, anterior cruciate ligament (disorder)