Cedera Ligamen Lutut

01Pathophysiology

The knee joint is stabilized by four primary ligaments that work in pairs to control movement in two planes. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) form the cruciate pair within the intercondylar notch, controlling anteroposterior translation and rotational stability. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) form the collateral pair on the sides of the knee, resisting valgus and varus forces respectively.

The ACL originates from the posteromedial aspect of the lateral femoral condyle and inserts on the anterior tibial plateau. Its primary function is to prevent anterior translation of the tibia relative to the femur and to resist internal rotation. The classic injury mechanism involves a non-contact pivoting motion with the foot planted, a sudden deceleration, or a cutting maneuver. The ACL has poor intrinsic healing capacity due to its intra-articular, extrasynovial location and limited blood supply. This is why patients hear a "pop," develop rapid hemarthrosis (within 2 hours due to the middle genicular artery), and experience recurrent instability rather than spontaneous healing.

The PCL is the strongest ligament in the knee, originating from the medial femoral condyle and inserting on the posterior tibial plateau. It prevents posterior translation of the tibia. The classic mechanism is a direct blow to the anterior proximal tibia with the knee flexed, the so-called "dashboard injury" in motor vehicle collisions. Because the PCL is stronger and has better vascular supply than the ACL, isolated PCL injuries can sometimes be managed non-operatively.

The MCL runs from the medial femoral epicondyle to the proximal medial tibia and is the primary restraint against valgus stress. It is injured by a blow to the lateral knee (valgus force). The MCL has an excellent blood supply from surrounding soft tissues, which is why even Grade III MCL tears can heal without surgery when treated with protective bracing.

The LCL runs from the lateral femoral epicondyle to the fibular head and resists varus stress. Isolated LCL injuries are uncommon; they are frequently associated with injury to the posterolateral corner (PLC) structures, including the popliteus tendon and the arcuate ligament complex. When the LCL and PLC are disrupted together, the knee exhibits combined varus and rotational instability, which generally requires surgical repair.

Understanding the mechanism directly predicts the exam findings: anterior force on the tibia stretches the ACL (positive Lachman), posterior force stretches the PCL (positive posterior drawer), lateral blow produces valgus and injures the MCL, and medial blow produces varus and injures the LCL.

02Classification and Clinical Manifestation

Ligament Sprain Grading

Ligament-by-Ligament Clinical Features

The "Unhappy Triad" (O'Donoghue Triad)

This classic combination involves simultaneous injury to the ACL + MCL + medial meniscus (historically described) or, as more recent data shows, the ACL + MCL + lateral meniscus. This occurs from a valgus and external rotation force applied to the knee. Exam questions presenting a football player hit from the lateral side with medial knee pain and a positive Lachman are testing your recognition of this triad.

03Diagnostic Workup

Physical examination is the best initial diagnostic tool for all knee ligament injuries. In the acute setting, the exam may be limited by pain and guarding, but certain tests remain reliable even with swelling.

For ACL evaluation, the Lachman test is the single most sensitive physical exam maneuver (sensitivity 85-95%). It is performed with the knee at 20-30 degrees of flexion, applying an anterior force to the proximal tibia while stabilizing the femur. A soft or absent endpoint confirms the tear. The anterior drawer test (performed at 90 degrees of flexion) is less sensitive because the hamstrings and menisci can mask laxity. The pivot shift test is the most accurate for functional rotational instability but is difficult to perform on an awake, guarded patient and is best assessed under anesthesia.

For PCL evaluation, the posterior drawer test is the primary maneuver, performed at 90 degrees of flexion by pushing the tibia posteriorly. The posterior sag sign (Godfrey test) is observed with the patient supine, hips and knees flexed to 90 degrees: the injured tibia sags posteriorly compared to the uninjured side under gravity alone.

Plain radiographs should always be obtained first to exclude fractures. The Segond fracture, a small avulsion off the lateral tibial plateau from the anterolateral ligament, is pathognomonic for an ACL tear and is a classic exam image.

MRI is the gold standard for confirming ligament tears and evaluating associated soft tissue injuries. It has greater than 95% sensitivity and near-equal value for identifying meniscal tears, cartilage damage, and bone bruise patterns. The characteristic MRI bone bruise pattern for ACL tears involves the lateral femoral condyle and posterolateral tibial plateau, reflecting the pivot shift mechanism.

In the setting of multiligament injury or suspected knee dislocation, vascular evaluation with CT angiography or the ankle-brachial index (ABI) is mandatory. A knee dislocation (even if spontaneously reduced) carries a 20-40% risk of popliteal artery injury, which can lead to limb loss if not identified promptly. An ABI less than 0.9 necessitates immediate CT angiography.

04Management and Treatment

Acute Stabilization

The immediate management of any acute knee ligament injury follows the RICE protocol: Rest, Ice, Compression, Elevation. NSAIDs such as ibuprofen (400-600 mg every 6-8 hours) or naproxen (250-500 mg twice daily) provide analgesia and reduce inflammation. A knee immobilizer or hinged brace is applied for comfort and protection. Crutches for partial or non-weight-bearing are used until the patient can bear weight without significant pain. If a large tense effusion is present, aspiration provides symptomatic relief and diagnostic information.

ACL Management

The decision between operative and non-operative management depends on the patient's activity level, age, degree of instability, and associated injuries. Young, active patients and athletes are generally recommended for ACL reconstruction because the ACL does not heal on its own and recurrent instability leads to secondary meniscal and cartilage damage. The preferred graft options include:

• Bone-patellar tendon-bone (BPTB) autograft: considered the gold standard for high-demand athletes due to bone-to-bone healing and rigid fixation. The trade-off is anterior knee pain and risk of patellar fracture.

• Hamstring tendon autograft (semitendinosus with or without gracilis): lower donor-site morbidity, but slightly higher re-tear rate in young athletes.

• Quadriceps tendon autograft: increasingly favored; good graft strength with less anterior knee pain than BPTB.

Rehabilitation after ACL reconstruction follows a structured protocol over 6-9 months, emphasizing early range of motion, progressive quadriceps and hamstring strengthening, neuromuscular training, and sport-related functional drills before return to play. Patients are typically cleared for full sport at 9 months with objective strength and functional testing.

For older, low-demand patients who do not participate in pivoting or cutting activities, non-operative management with physical therapy focusing on quadriceps and hamstring strengthening can be sufficient, with activity modification to avoid instability episodes.

PCL Management

Isolated Grade I-II PCL injuries are managed non-operatively with a structured rehabilitation program emphasizing quadriceps strengthening (the quadriceps acts as a dynamic antagonist to posterior tibial sag). A brace locked in extension may be used in the early phase to minimize posterior tibial translation under gravity.

Surgical reconstruction is indicated for Grade III injuries (>10 mm posterior translation), combined ligament injuries, or patients with persistent functional instability despite rehabilitation. Graft options include Achilles tendon allograft or quadriceps tendon autograft.

MCL Management

The MCL is unique among knee ligaments because it has excellent healing capacity owing to its extrasynovial position and rich blood supply. Even complete Grade III tears are generally managed non-operatively with a hinged knee brace allowing progressive range of motion and a physical therapy program over 6-8 weeks. Surgery for the MCL is typically reserved for chronic valgus instability that fails conservative treatment, or when MCL repair is performed concurrently during ACL reconstruction in combined injuries.

LCL and Posterolateral Corner Management

Isolated LCL injuries (Grade I-II) can be managed conservatively. However, Grade III LCL tears, particularly when combined with posterolateral corner (PLC) disruption, require early surgical repair or reconstruction (ideally within 2-3 weeks of injury). Delayed repair of PLC injuries yields poor outcomes because the tissues retract and scar, making anatomic repair impossible. This is a high-yield testing point: PLC injuries are treated surgically and early.

Multiligament Injuries and Knee Dislocation

A knee dislocation (disruption of two or more ligaments) is a surgical emergency not because of the ligaments but because of the risk to the popliteal artery and peroneal nerve. The sequence of management is:

1. Reduce the dislocation immediately.

2. Assess distal pulses and perform ABI measurement.

3. If ABI < 0.9 or pulses are absent, obtain emergent CT angiography or proceed to surgical exploration.

4. If vascular injury is confirmed, vascular repair within 6-8 hours (ischemia time beyond this results in high amputation rates).

5. Ligament reconstruction is staged after vascular repair and soft tissue recovery (typically 2-4 weeks later).

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on knee ligament questions is by confusing the physical exam tests or applying them to the wrong ligament. Remember that the Lachman test, not the anterior drawer test, is the most sensitive test for ACL injury. If a vignette describes a patient with acute hemarthrosis and a soft endpoint on Lachman, the answer is ACL tear regardless of what the anterior drawer shows.

A classic trap involves PCL tears mimicking ACL tears. When the posterior tibial sag goes unrecognized, bringing the tibia from its posteriorly displaced position back to neutral can appear as a "positive anterior drawer," leading to a false diagnosis of ACL injury. The test-writer will present a dashboard injury, describe a positive anterior drawer, and offer both ACL tear and PCL tear as answer choices. The key is the mechanism (dashboard = PCL) and checking the resting position of the tibia.

Another frequently tested concept is the Segond fracture. When a radiograph shows a small avulsion fragment off the lateral tibial plateau, the answer is ACL tear, not just "lateral capsular avulsion." This is a pathognomonic radiographic sign.

The unhappy triad remains a testing favorite. A football player receiving a lateral blow to the knee with resultant medial pain, a positive Lachman, and valgus instability has ACL + MCL injury with likely meniscal involvement.

Regarding management, students often incorrectly select surgery for isolated MCL tears. The key pearl is that MCL heals without surgery even in complete tears, while ACL does not heal and typically requires reconstruction in active individuals. In contrast, LCL and posterolateral corner injuries should be repaired early because delayed reconstruction has poor results.

Finally, never forget the vascular emergency: any multiligament knee injury or knee dislocation demands immediate assessment of the popliteal artery. The test question will present a reduced knee dislocation with diminished pulses, and the next best step is ABI measurement or CT angiography, not MRI or orthopedic referral.