Anterior Cruciate Ligament Tear

The anterior cruciate ligament resists anterior tibial translation and rotatory stress through its anteromedial and posterolateral bundles. Rupture affects about 30 to 80 per 100,000 people a year, concentrated in pivoting sports at ages 15 to 35. Female athletes carry a 2 to 8 times higher risk than males. About 70% of tears are non-contact, from deceleration, landing or a pivot with the knee near full extension and valgus.

Tears are graded 1 (sprain), 2 (partial) and 3 (complete). Associated injuries:

• Lateral meniscal tear in the acute setting and medial meniscal tear in chronic instability
• Bone bruises of the lateral femoral condyle and posterolateral tibial plateau
• Medial collateral ligament injury
• Segond fracture (lateral capsular avulsion of the tibia, which signals an anterior cruciate tear)

Osteoarthritis develops in 20 to 50% within 10 to 20 years whether or not the knee is reconstructed. After reconstruction, graft re-rupture occurs in 5 to 10% and contralateral rupture in 5 to 10%.

• A pop, immediate swelling (hemarthrosis within 2 hours in about 70%), inability to continue play, and later giving way
• Lachman test is the most sensitive (over 85%). Translation of 3 to 5 mm is grade 1, 5 to 10 mm grade 2, over 10 mm grade 3, with a soft endpoint.
• The anterior drawer test is less sensitive acutely.
• The pivot shift is highly specific (about 98%) but is often impossible acutely because of guarding.
• Red flags: a locked knee (bucket handle meniscal tear), cool or pulseless foot (knee dislocation), tibial spine avulsion in a child, and open physes.

• Clinical examination with the Lachman test.
• Radiographs (anteroposterior and lateral) for fracture, Segond fragment, tibial spine avulsion and lipohemarthrosis.
• MRI (sensitivity 90 to 95%): ligament discontinuity, empty notch sign, a bone bruise pattern, and meniscal and collateral injury.
• Arthrometer: side-to-side difference over 3 mm supports rupture.

Differentials: posterior cruciate tear, medial collateral injury, meniscal tear, patellar dislocation, tibial plateau fracture, osteochondral fracture.

Acute phase:

• Rest, ice, compression and elevation, with weight bearing as tolerated on crutches.
• Aspirate a tense hemarthrosis under aseptic technique.
• Ibuprofen 400 mg orally every 8 hours with food for up to 7 days, with paracetamol 1 g orally every 6 hours (maximum 4 g/day). Avoid ibuprofen in peptic ulcer, renal impairment and asthma triggered by NSAIDs. Children: ibuprofen 10 mg/kg/dose every 8 hours and paracetamol 15 mg/kg/dose every 6 hours.
• Prehabilitation until swelling resolves, full extension returns and quadriceps control is regained (3 to 6 weeks).

Non-operative: low demand patients without giving way. Structured rehabilitation for 12 weeks with neuromuscular and strength training.

Surgical reconstruction: young active patients, pivoting sport, recurrent instability, repairable meniscal tear and multiligament injury.

• Arthroscopic anatomic single bundle reconstruction.
• Autograft options: bone patellar tendon bone (anterior knee pain, patellar fracture), four strand hamstring (aim for 8 mm or wider diameter), or quadriceps tendon. Allograft carries 3 to 4 times the failure rate in patients under 25.
• Cefazolin 2 g IV (3 g if over 120 kg) 30 to 60 minutes before incision. Children 30 mg/kg (maximum 2 g).
• Skeletally immature patients: physeal sparing or transphyseal techniques with small tunnels.
• Complications: infection (0.3 to 0.5%), arthrofibrosis (2 to 4%), venous thromboembolism (under 1%), graft failure, saphenous neuralgia, cyclops lesion.

Rehabilitation: full extension in the first 2 weeks, running at 3 to 4 months, pivoting sport at 9 to 12 months once strength and hop tests exceed 90% of the other limb and there is no effusion.

Prevention: neuromuscular training programs of 15 to 20 minutes, 2 to 3 times weekly, reduce injury by about half. Counsel on osteoarthritis risk.