Anterior cruciate ligament tear
Anterior cruciate ligament tear is a noncontact pivoting knee injury diagnosed clinically with the Lachman test and confirmed on MRI, and the central decision is surgical reconstruction versus supervised rehabilitation based on age, activity level, and knee instability.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
The anterior cruciate ligament (ACL) is the primary restraint against anterior translation of the tibia relative to the femur and is the most frequently injured ligament in the knee, composed of an…
- Epidemiology
Most commonly injured knee ligament: the ACL is torn more often than the PCL, MCL, or LCL.
- Risk factors
Sports requiring pivoting, cutting, or jumping: soccer, basketball, football, gymnastics, and skiing carry the highest exposure to the noncontact deceleration-and-pivot mechanism.
- Pathophysiology
Noncontact pivot mechanism: a sudden deceleration, cutting, or landing maneuver generates rotational and anterior shear force on a planted, slightly flexed knee that exceeds the tensile capacity of…
- Clinical features
Acute noncontact pivot or deceleration injury with a felt or heard "pop," followed by pain and rapid swelling: the hallmark presentation.
- Differential diagnosis
Posterior cruciate ligament tear: caused by a posteriorly directed force on the proximal tibia (dashboard injury) or hyperextension; a positive posterior drawer or sag test with a negative Lachman test distinguishes it.
- Diagnosis
ACL tear is diagnosed clinically by the Lachman test: increased anterior tibial translation with a soft or absent end point at 20 to 30 degrees of knee flexion, compared with the contralateral knee…
- Management
First, control pain and swelling and protect the joint: rest, ice, compression, elevation, a knee immobilizer or hinged brace, and crutches with weight bearing as tolerated until quadriceps control returns.
- Complications
Post-traumatic osteoarthritis: the leading long-term complication regardless of whether the ligament is reconstructed, though reconstruction reduces the recurrent instability episodes that accelerate cartilage damage.
- Prognosis
Surgical reconstruction restores mechanical stability and allows most active patients to return to pivoting sport, with timing individualized to strength and functional testing.
- Prevention
Structured preseason and in-season neuromuscular training programs for athletes in pivoting and jumping sports (soccer, basketball), emphasizing landing mechanics, deceleration technique, and…
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.
Related articles
- Meniscal tear
Meniscal tear is diagnosed clinically from a twisting-injury history with joint-line tenderness and a positive McMurray or Thessaly test, and management is conservative first for both acute and degenerative tears, with surgery reserved for persistent mechanical symptoms.
- Patellofemoral pain syndrome
Patellofemoral pain syndrome is a clinical diagnosis of disordered patellar tracking causing poorly localized anterior knee pain with stairs, squatting, and prolonged sitting, requiring no imaging, and its only proven long-term treatment is physical therapy that strengthens the quadriceps, hamstrings, and gluteal muscles.
- Patellar dislocation
Patellar dislocation is an acute lateral displacement of the patella out of the femoral trochlear groove, usually from a twisting non-contact pivot or a direct blow, presenting with a hemarthrosis and a positive apprehension test, and confirmed by plain radiograph with MRI reserved to assess the medial patellofemoral ligament and cartilage before deciding on bracing versus surgical stabilization.
- Iliotibial band syndrome
Iliotibial band syndrome is an overuse friction injury of runners and cyclists causing lateral knee and distal thigh pain, diagnosed at the bedside with a positive Noble compression test and treated first with activity modification, ice, and hip abductor strengthening rather than imaging or surgery.
- Osteoarthritis
Osteoarthritis is a chronic progressive joint disorder of cartilage and subchondral bone degradation with low-grade synovitis, diagnosed clinically from age, activity-related pain, and exam findings, and managed with exercise, weight loss, topical or oral NSAIDs, and joint replacement for refractory disease.
- Popliteal Baker cyst
A popliteal (Baker) cyst is a synovial fluid-filled outpouching of the gastrocnemius-semimembranosus bursa driven by intra-articular knee pressure from osteoarthritis, inflammatory arthritis, or meniscal injury, and is managed by aspirating and injecting the knee joint rather than the cyst itself, since a ruptured cyst can masquerade as deep venous thrombosis.