Knee ligament injuries

Last updated: June 27, 2022

Summary

Knee ligament injuries are often the result of rotational movement of the knee joint (e.g., cutting and pivoting movements in sports). Injuries to the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) result in knee pain and instability. Various maneuvers aid in demonstrating knee instability and are usually sufficient for the diagnosis of collateral ligament tears. An MRI is the best confirmatory test for cruciate ligament tears. Isolated ligament injuries are usually treated conservatively, but surgery is recommended for complex injuries, severe knee instability, and patients with physically demanding occupations.

Anatomical overview

ACL and PCL connect the femur to the tibia.
The MCL merges with the joint capsule of the knee.
The LCL connects the femur and the fibula; It does not merge with the joint capsule of the knee.

Ligaments and menisci of the knee Physiological knee joint motion in three dimensions

Anterior cruciate ligament injury

Epidemiology

Most commonly injured knee ligament ^[1]^[2]
Higher incidence in female individuals

Mechanism of injury

Low-energy noncontact: sports injuries with a twisting mechanism, e.g., football, soccer, basketball, baseball, alpine skiing, and gymnastics ^[3]
High-velocity contact injuries (less common): direct blows to the knee causing forced hyperextension or valgus deformity of the knee

Clinical features

History: Patients often report a popping sound shortly before the onset of symptoms.
Physical examination findings
- Knee swelling (e.g., due to hemarthrosis), pain, and instability
- Positive Lachman test (most sensitive test)
  - With the knee joint at 20–30° flexion, the examiner stabilizes the femur and pulls the tibia anteriorly.
  - Increased tibial anterior gliding (compared to the opposite knee) and a soft endpoint indicate an ACL tear.
- Positive anterior drawer test
  - With the knee joint at 90° flexion, the examiner fixes the foot on the table and pulls the proximal tibia forward.
  - Increased tibial anterior gliding (compared to the opposite knee) and a soft endpoint indicate an ACL tear.
- Positive pivot shift test
  - With full extension of the knee joint, the examiner slowly flexes the knee while applying valgus stress with one hand and internally rotating the tibia with the other.
  - If the ACL is torn, the tibial plateau jerks backward at 30° of knee flexion.
Commonly associated injuries
- Most commonly lateral meniscus damage (often together with acute ACL and MCL injury)
- Unhappy triad: simultaneous injury of the ACL, MCL, and medial meniscus (the medial meniscus is attached to the MCL)
  - Usually caused by valgus stress (lateral force) applied to the knee while the foot is fixed (e.g., during contact sports)
  - Clinical features: pain, instability, tender medial joint line, poor knee extension

Lachman test Drawer tests Unhappy triad Lachman Test - Clinical Examination Drawer Test - Clinical Examination Pivot Shift Test - Clinical Examination

Diagnostics

Joint aspiration (in severe joint effusions): hemarthrosis
MRI (confirmatory test)

Anterior cruciate ligament injury

Treatment

Conservative treatment: for mild knee instability, less physically demanding occupations, premorbid inactivity, or postoperatively
Arthroscopic surgery: for multiligament injuries, chronic knee instability, and for highly competitive athletes
- Allograft from Achilles tendon or patellar tendon
- Postoperative care: knee brace, crutches, physical therapy ^[4]
- Double-bundle ACL graft using the semitendinosus and/or gracilis tendons (hamstring muscles)
- ACL graft from the patellar tendon

Complications

Meniscal degeneration
Osteoarthritis
Patella fracture
Patella tendon rupture
Reflex sympathetic dystrophy
Postoperatively: graft failure, graft impingement

Posterior cruciate ligament injury

Mechanism of injury
- Noncontact injury involving hyperflexion of the knee with a plantarflexed foot (seen in athletes)
- Direct posterior blow to a flexed knee, seen in motor vehicle accidents (dashboard injury) or athletic contact injury
- Rotational injury involving hyperextension of the knee (rare)
Clinical features
- Initially vague symptoms: minimal (or absent) posterior knee pain, swelling, decreased functional range of motion
- Positive posterior drawer test
  - With the patient lying supine and the knee at 90° flexion, the examiner fixes the foot on the table and pushes the proximal tibia backward.
  - Increased tibial posterior gliding (compared to the opposite knee) and a soft endpoint indicate PCL injury.
- Positive posterior sag sign
  - The patient lies down with both hips and knees flexed and aligned together.
  - In this position, the tibia on the side of the torn PCL will appear to fall backwards under the influence of gravity.
- Positive quadriceps active test
  - The patient is placed in supine position with the knee flexed at 90° with the foot flat on the bed.
  - The patient is asked to contract the quadriceps which, if there is PCL injury, should move the tibia forward.
  - If the tibia moves forward by more than 2 mm, then the test is positive.
- Positive posterolateral drawer test
  - The patient is sitting on the edge of the examining table (thighs supported) with the legs hanging over the floor.
  - A posterior drawer test is performed which moves the lateral tibial plateau posteriorly around the axis of the PCL.
Diagnostics
- X-rays initially: bony avulsions and posterior sag of the tibia
- MRI (confirmatory test)
Treatment
- Conservative therapy for isolated injuries
- Surgery for multiligament injuries, chronic knee instability, and for highly competitive athletes

Drawer tests Posterior sag sign (knee joint) Bony tear of the posterior cruciate ligament Posterior cruciate ligament tear MRI image of suprapatellar joint effusion and intact posterior cruciate ligament of the knee Drawer Test - Clinical Examination Posterior Sag Test - Clinical Examination

Collateral ligament injury

Overview of collateral ligament injuries
	Medial collateral ligament injury	Lateral collateral ligament injury
Mechanism of injury	Valgus stress with possible external rotation	Varus stress with possible external rotation
Associated injuries	Frequently associated with medial meniscal tear	Usually associated with a tear of the anterior and/or posterior cruciate ligaments, as well as the posterolateral corner (PLC) Isolated LCL injury is very rare.
Clinical features	Knee swelling with ecchymosis, pain, deformity, and instability Increased medial/lateral joint laxity on full knee extension Suggests (additional) cruciate ligament injury The degree of joint laxity is graded based on the size of lateral joint space during the valgus/varus stress test: ^[5] Grade I: 3–5 mm (mild instability) Grade II: 6–10 mm (moderate instability) Grade III: > 10 mm (severe instability; other knee ligaments may be injured)
Clinical features	Medial joint line tenderness Valgus stress test With the patient in supine position and the knee either in extension or at 20–30° flexion, the examiner gently abducts the tibia by pushing on the knee from the lateral side (valgus force). Widening of the medial joint space when the knee is slightly flexed indicates MCL injury.	Lateral joint line tenderness Varus stress test With the patient in supine position and the knee either in extension or at 20–30° flexion, the examiner gently adducts the tibia by pushing on the knee from the medial side (varus force). Widening of the lateral joint space when the knee is slightly flexed indicates LCL injury.
Diagnostics	An isolated collateral ligament tear is a clinical diagnosis. X-rays and MRI can be used to rule out associated injuries.
Treatment	Conservative (functional brace and physical therapy) for isolated tears Surgery if associated injuries are present.

MCL injuries are more common than LCL injuries.

Collateral ligament injuries

Tibiofemoral joint dislocation

Location: knee joint (tibiofemoral articulation)
Mechanism of injury: usually caused by high-energy trauma, e.g., dashboard injury, fall from a height; low-energy trauma possible (especially in obese individuals)
- Anterior dislocation (tibia is anterior to the femur condyles): hyperextension of the knee joint driving the femur posterior to the tibia
- Posterior dislocation (tibia is posterior to the femur condyles): direct impact to the proximal tibia displacing the tibia posterior to the femur
- Medial/lateral dislocation (tibia is medial or lateral to the femur condyles): due to varus or valgus force
Clinical features
- Abnormal position of the knee joint (see “Mechanism of injury” above)
- Swelling of the knee
- Ecchymosis
- Dimple sign (in posterolateral dislocation): indentation of the skin at the medial femoral condyle provoked by the invagination of soft tissue into the intercondylar notch
Diagnostics
- Immediate evaluation (due to potential severe neurovascular injuries), which includes:
  - Assessment of the popliteal and distal pulses
  - Assessment of the sensory and motor function of the knee, lower leg, and foot
- Reevaluation after immediate treatment, which includes:
  - Ankle-brachial index
  - X-ray of the knee joint and the lower leg
  - Duplex ultrasound
Treatment
- Isolated anterior or posterior dislocation: immediate closed reduction
- Posterolateral dislocation: immediate open reduction
Complications
- Injury of ACL, MCL, LCL, PCL, or PLC
- Popliteal artery injury
- Common peroneal or tibial nerve injury
- Compartment syndrome
- Deep vein thrombosis

Knee dislocation Rotatory anterolateral knee dislocation Posterior knee dislocation

Knee dislocations are frequently associated with severe neurovascular injuries and should be treated immediately.

Reference:^[6]

References

Mohseni M, Simon LV. Knee Dislocation. StatPearls. 2021 .
Mall NA, Chalmers PN, Moric M, et al. Incidence and Trends of Anterior Cruciate Ligament Reconstruction in the United States. Am J Sports Med. 2014; 42 (10): p.2363-2370. doi: 10.1177/0363546514542796 . | Open in Read by QxMD
Musahl V, Karlsson J. Anterior Cruciate Ligament Tear. N Engl J Med. 2019; 380 (24): p.2341-2348. doi: 10.1056/nejmcp1805931 . | Open in Read by QxMD
Dordevic M, Hirschmann MT. Injury Mechanisms of ACL Tear. Springer Berlin Heidelberg ; 2014 : p. 49-53
Bousquet BA, O'Brien L, Singleton S, Beggs M. POST-OPERATIVE CRITERION BASED REHABILITATION OF ACL REPAIRS: A CLINICAL COMMENTARY.. International journal of sports physical therapy. 2018; 13 (2): p.293-305.
Phisitkul P, James SL, Wolf BR, Amendola A. MCL injuries of the knee: current concepts review.. Iowa Orthop J. 2006; 26 : p.77-90.

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