Knee Ligament Injuries

Knee ligament injuries are commonly seen in young athletes as well as in middle-aged adults. Although the clinical presentation varies for each injured ligament, all of these injuries present with joint instability, pain, and difficulty bearing weight. Diagnosis is based on clinical exam and confirmed with diagnostic imaging or direct visualization (arthroscopy). Management can be conservative or surgical, depending on the severity of the injury.

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Anterior Cruciate Ligament (ACL) Injury

Definition

An anterior cruciate ligament (ACL) injury causes structural damage to the ligament whose functions are to control anterior translation of the tibia and restrain tibial rotation and varus/valgus stress.

Anatomy

  • Originates at the posteromedial aspect of the lateral femoral condyle, posterior to the longitudinal axis of the femur
  • Runs inferiorly, medially, and anteriorly 
  • Attaches to the anteromedial aspect of the tibia between the condyles

Epidemiology

  • Incidence: 68.6 per 100,000/year in the United States
    • Peak incidence in men: between 19 and 25 years; related to sports
    • Peak incidence in women: 14–18 years 
  • Most commonly injured ligament in the knee
  • Athletes and trauma patients are the most commonly affected.

Etiology

  • Noncontact mechanism (rotational forces): 
    • Skiers
    • Baseball players
    • Soccer players
    • Basketball players
  • Contact mechanism (direct blunt trauma to the knee): football players

Clinical presentation

Patients with an ACL injury present with pain and report recent high-energy blunt trauma to the knee.

History:

  • Patient reports hearing or feeling a “pop” and that the affected knee “gave out” at the time of injury.
  • Also important to delineate:
    • Timing 
    • Mechanism of trauma
    • Site of injury
    • Further details of the specific situation

Physical examination:

  • Antalgic gait
  • Tenderness to palpation along the joint line
  • Edema around the knee joint
  • Decreased range of motion
  • Knee instability tests:
    • Anterior drawer maneuver: 
      • The patient lies supine with hips flexed to 45 degrees, knee at a 90-degree angle, and feet flat on the exam table. 
      • The clinician stabilizes the leg by sitting on the patient’s toes and holds the proximal tibia with both hands and pulls anteriorly. 
      • Positive test: Proximal tibia will slide anteriorly, like a drawer being opened.
    •  Pivot shift test: 
      • The patient lies supine.
      • The tibia is rotated internally as the knee is flexed.
      • The test is positive if the knee becomes unstable and subluxated. 
    • Lachman test:
      • The patient lies supine with the affected knee at a 30-degree angle. 
      • The clinician stabilizes the distal femur with the left hand and pulls on the tibia toward themselves.
      • Positive test: anterior displacement

Diagnosis

Diagnosis is made clinically and confirmed by imaging.

  • MRI is the preferred imaging method:
    • Primary signs:
      • Hyperintensity of the ACL (usually at the midportion)
      • Discontinuity of ligament fibers
      • Alteration of Blumensaat’s line
      • Edema
    • Secondary signs:
      • Bone marrow edema
      • Associated medial collateral ligament injury
      • Anterior tibial translation > 7 mm
  • X-ray is useful only to rule out fractures.
  • Arthroscopy: uses an instrument (arthroscope) inserted into the joint through a small incision
    • Gold standard for diagnosis
    • Minimally invasive surgical procedure used for diagnosis; may also be used for the treatment of meniscal tears

Management

  • Conservative management: in patients with low functional demand 
    • Rest, Ice, Compression, and Elevation (RICE)
    • No weight-bearing (use crutches or wheelchair)
    • NSAIDs for pain relief
  • Orthopedic surgery consultation and surgical management for reconstruction using a tissue graft is done in:
    • Athletes 
    • Young, active patients
    • Significant knee instability
    • Injury to multiple structures of the knee
  • Rehabilitation with physical therapy: 
    • Improves functionality 
    • Increases knee stability
  • Prognosis: 90% of patients will return to normal functioning after repair.
Anatomic ACL reconstruction with bone-patellar tendon-bone (BTB) graft

Anatomic anterior cruciate ligament (ACL) reconstruction with bone–patellar tendon–bone (BTB) graft

Image: “BTB reconstruction” by Branch T, Lavoie F, Guier C, Branch E, Lording T, Stinton S, Neyret P. License: CC BY 4.0, cropped by Lecturio.

Differential diagnosis of ACL tear

  • Meniscal tear: injury to the meniscus caused by rotational or shearing forces across the tibiofemoral joint. Clinical presentation includes a history of a twisting or rotational injury followed by joint line pain associated with a small effusion. Some patients may also present with mechanical symptoms, such as joint locking, clicking, or catching.
  • Posterior knee dislocation: pathologic loss of articulation of the knee joint due to high-energy trauma such as that due to motor-vehicle collisions or low-energy trauma such as that seen in athletic training.
  • Fracture of the tibial spine or femoral or tibial epiphysis: diagnosed on X-ray and managed by an orthopedic specialist.
  • Medial collateral knee ligament injury: causes structural damage to the ligament, whose function is to provide valgus stability to the knee.
Menisci and articular surfaces of the knee

Image displaying the menisci, ligaments, and bony surfaces and their relation to one another

Image by Lecturio. License: CC BY-NC-SA 4.0

Medial Collateral Ligament (MCL) Injury

Definition

A medial collateral ligament (MCL) injury causes structural damage to the ligament whose function is to provide valgus stability to the knee.

Unhappy triad: simultaneous injury of the MCL, ACL, and the medial meniscus

Anatomy

  • Originates from the medial epicondyle of the femur and runs to the medial condyle of the tibia 
  • Attaches in 2 places on the tibia

Epidemiology

  • 40% of all knee injuries
  • 60% of knee injuries while skiing involve the MCL.

Etiology

  • Sudden, high-energy twisting or turning motions (rotational forces):
    • Skiers
    • Baseball players
    • Soccer players
    • Basketball players
  • Blunt trauma (direct blow to the knee) 

Clinical presentation

Patients with MCL injury present with pain and report recent trauma to the knee. The exam is ideally done in the 1st 20–30 minutes, before swelling interferes with the exam.

History:

  • Patient reports hearing or feeling a pop and that the affected knee feels unstable.
  • Also important to delineate:
    • Timing 
    • Mechanism of trauma
    • Site of injury
    • Further details of the specific situation

Physical examination:

  • Antalgic gait
  • Pain on palpation along the course of the MCL
  • Edema/ecchymosis on the medial aspect of the knee
  • Decreased range of motion
  • Knee instability valgus stress test:
    • The patient lies supine with the affected limb abducted off the examination table and the knee fully extended.
    • The clinician holds the ipsilateral ankle with 1 hand and applies valgus pressure on the knee.
    • The test is positive if joint opening and pain are detected. 
  • Grades of instability in MCL injuries:
    • Grade I: pain along the course of the MCL with no joint opening
    • Grade II: partial opening of the joint
    • Grade III: significant joint opening
Valgus and varus stress tests

Valgus and varus stress tests

Image: “Valgus and varus stress tests” by Rossi R, Dettoni F, Bruzzone M, Cottino U, D’Elicio DG, Bonasia DE. License: CC BY 2.0

Diagnosis

Diagnosis is made clinically and later confirmed by imaging studies.

  • MRI is the preferred imaging method: allows for examination of neighboring structures
  • Ultrasonography may be a more accessible alternative to MRI.
  • X-ray is useful only to rule out fractures.

Management

  • Conservative management: in patients with low functional demand 
    • RICE
    • No weight-bearing (use crutches or wheelchair)
    • NSAIDs for pain relief
  • Orthopedic surgery consultation and surgical management: 
    • Indicated in all cases for evaluation and treatment options
    • Surgical management is performed in grade III injuries with or without concomitant injuries.
  • Rehabilitation with physical therapy:
    • Return-to-play protocol: progressive increase in the difficulty of exercises
    • Program must be as comprehensive as possible to ensure maximal recovery of functionality.
  • Prognosis: 98% of patients with grade I and II injuries will experience a full recovery with conservative management. 
    • Grade I injuries: typically can return to athletic activity in 10–14 days.
    • Grade II and III injuries: variable recovery times

Differential diagnosis of MCL tear

  • Slipped capital femoral epiphysis: orthopedic disorder of early adolescence characterized by the pathologic “slipping,” or displacement, of the femoral head, or epiphysis, on the femoral neck. Slipped capital femoral epiphysis is considered a type I Salter-Harris growth plate fracture, and it affects boys twice as often as girls. 
  • Osteoarthritis: most common form of arthritis due to cartilage destruction and changes of the subchondral bone. The risk of developing osteoarthritis increases with age, obesity, and repetitive joint use or trauma. Patients develop gradual joint pain, stiffness lasting < 30 minutes, and decreased range of motion.
Image displaying the menisci and their relation with other articular surfaces that compose the knee joint

Image displaying the menisci and their relation with other articular surfaces that compose the knee joint

Image by BioDigital, edited by Lecturio

Lateral Collateral Ligament (LCL) Injury

Definition

A lateral collateral ligament (LCL) injury causes structural damage to the ligament whose function is to prevent varus angulation of the knee.

Anatomy

  • Originates from the lateral epicondyle of the femur and runs on the outside of the knee
  • Attaches on the fibular head
  • Is narrower than the MCL and is not fused with the capsular ligament or lateral meniscus
  • Is more flexible than the MCL and is less susceptible to injury

Epidemiology and etiology

  • Least common of all ligamentous knee injuries
  • Rarely seen in isolation; usually accompanies other injuries of the knee
  • Women and athletes are considered at increased risk:
    • Tennis
    • Gymnastics
  • Can also be due to direct blunt trauma to the anteromedial aspect of the knee, causing extreme hyperextension and varus stress

Clinical presentation

History: 

The patient reports trauma to the medial aspect of the knee followed by varus bending.

Physical examination:

  • Antalgic gait
  • Pain on palpation along the joint line
  • Lower limb weakness and/or foot drop
  • Edema around the knee joint
  • Decreased range of motion
  • Knee instability tests:
    • Varus stress test: 
      • The patient lies supine with the affected knee at a 30-degree angle. 
      • The clinician stabilizes the distal femur with 1 hand and applies varus pressure on the ankle. 
      • The test is positive if there is lateral compartment gaping. 
    • External rotation recurvatum test: 
      • The patient lies supine with the affected knee extended.
      • The clinician stabilizes the distal femur with 1 hand and externally rotates the tibia.
      • Positive test: hyperextension of the knee
  • Grades of instability in LCL injuries:
    • Grade I:
      • Clinical signs of sprain (pain)
      • No instability
    • Grade II:
      • More signs of sprain (pain and edema)
      • Ligament laxity is observed, but with an end point.
    • Grade III:
      • Severe clinical signs of sprain (pain, edema, ecchymosis)
      • Noticeable knee instability
External rotation recurvatum test

External rotation recurvatum test

Image: “External Rotation Recurvatum Test” by Rossi R, Dettoni F, Bruzzone M, Cottino U, D’Elicio DG, Bonasia DE. License: CC BY 2.0

Diagnosis

Diagnosis is made clinically and confirmed by imaging studies.

  • Bedside ultrasonography in minor LCL injuries
  • X-ray is useful only to rule out fractures.
  • MRI indicated if:
    • History of significant trauma 
    • Ultrasound findings suggest major injury to the LCL and other structures: 
      • Cruciate ligament
      • Meniscal tear

Management

  • Conservative management for grade I and II injuries:
    • RICE
    • No weight-bearing (use crutches or wheelchair)
    • NSAIDs for pain relief
    • Bracing for 3–6 weeks
  • Orthopedic surgery consultation and surgical management:
    • Consultation in all cases to discuss treatment options
    • Surgery is indicated in grade III injuries.
    • Caution to avoid injury to the common peroneal nerve and neurologic complications
  • Rehabilitation with physical therapy 6 weeks after grade I and II injuries:
    • Joint instability and pain must be resolved and range of motion restored.
    • Grade I: return to activity after 4 weeks
    • Grade II: return to activity after 10 weeks
  • Grade III injuries: immobilization and non–weight-bearing for 6 weeks postoperatively
    • Rehabilitation starts 4 months after reconstruction. 
    • Criteria for return to full activity:
      • Fully restored range of motion 
      • Recovered quadriceps and hamstring strength
      • Resolution of joint pain
      • Resolution of joint laxity and instability
      • Able to complete normal physical activities without pain
  • Complications:
    • Chronic knee pain
    • Knee instability
    • Neurologic, due to common peroneal nerve injury:
      • Long-term foot drop
      • Lower limb weakness
      • Decreased sensation
  • Prognosis: The majority of patients return to normal functioning after treatment.

Differential diagnosis of LCL tear

  • Posterior knee dislocation: pathologic loss of articulation of the knee joint due to high-energy trauma such as that due to motor-vehicle collisions or low-energy trauma such as that seen in athletic training. 
  • Meniscal tear: injury to the meniscus caused by rotational or shearing forces across the tibiofemoral joint. Clinical presentation includes a history of a twisting or rotational injury followed by joint line pain associated with a small effusion. Some patients may also present with mechanical symptoms, such as joint locking, clicking, or catching.
  • ACL injury: causes structural damage to the ligament whose functions are to control anterior translation of the tibia and restrain tibial rotation and varus/valgus stress.

Posterior Cruciate Ligament (PCL) Injury

Definition

The posterior cruciate ligament (PCL) is the largest and strongest ligament in the knee. Injury to the PCL causes structural damage resulting in loss of stabilization with resultant posterior translation of the tibia.

Epidemiology

  • Seen in approximately 3% of knee injuries due to trauma
  • 95% of PCL tears occur in combination with other ligament tears; isolated PCL injuries are uncommon.

Etiology

  • High-energy trauma such as motor-vehicle accidents, in association with damage to other knee structures
  • Sports injuries: 2nd most common cause of PCL injury

Clinical presentation

Isolated PCL injuries are relatively uncommon, and athletes with such injuries may continue to function at a high level.

History:

  • Pain in the back of the knee (especially with squatting or kneeling)
  • Slight limp 
  • Chronically injured PCL-deficient knee may present with generalized anterior knee pain localized to the medial compartment or patellofemoral joint.

Physical examination: 

  • Mild to moderate knee effusion
  • Loss of terminal knee flexion (final 10–20 degrees)
  • Posterior drawer test:
    • The patient lies supine with the affected knee at a 90-degree angle. 
    • The clinician stabilizes the leg by sitting on the patient’s toes and grasps the proximal lower leg at the upper tibia and tries to displace the lower leg posteriorly. 
    • Positive test: excessive posterior translation
  • Muller’s test, also called the quadriceps active test:
    • The patient lies supine as above and is asked to raise the foot off the table.
    • Positive test: anterior translation of the proximal tibia prior to the foot leaving the table while attempting to elevate the foot
Quadriceps active test

Muller’s test, also called the quadriceps active test

Image: “Quadriceps Active Test” by Rossi R, Dettoni F, Bruzzone M, Cottino U, D’Elicio DG, Bonasia DE. License: CC BY 2.0

Diagnosis

  • X-ray to rule out fractures
  • MRI for suspected PCL injury

Management

Referral to orthopedic surgeon is needed.

  • Grade III PCL injuries: demonstrated by the anterior border of the medial tibial plateau being displaced posteriorly > 10 mm
  • Additional significant soft tissue injuries 
  • PCL disruption involving avulsion fracture at the ligamentous insertion at the tibia
  • Isolated PCL injuries, as multiligament trauma typically requires surgical intervention. 

Differential diagnosis of PCL tear

  • Posterior collateral ligament injury: Other injuries are often sustained in combination with PCL injury.
  • Proximal tibial fracture: may result from similar injuries causing a PCL tear. A tibial fracture typically presents clinically with a hemarthrosis, larger than the effusion seen with a PCL injury. There is associated pain and guarding that limit clinical examination. Diagnosis is made with X-ray, and management is by an orthopedic specialist.
  • Tibiofemoral dislocation: may occur following significant trauma and is a potentially limb-threatening injury if there is circulatory compromise. Tibiofemoral dislocation requires emergency evaluation. Clinical presentation is with severe pain and swelling and gross instability of the knee. There may be obvious deformity, and management is an urgent reduction if the dislocation does not reduce spontaneously.
  • Bone contusion: may occur at the same time as PCL injury; however, posterior drawer test would be negative in a patient with an isolated bone contusion.
  • Quadriceps tendon and patellar tendon tears: also may occur due to an injury involving falling with the knee flexed. With tendon tears, patients often report feeling a popping sensation in the knee and are immediately unable to bear weight, whereas patients with a PCL injury usually can bear weight. On X-ray, patients with tendon tears may have altered height of the patella or signs of a patellar avulsion injury.

References

  1. Jagodzinski, M., Weber-Spickschen, T. S., & Guenther, D. (2020). Dislocations and Soft Tissue Injuries of the Knee. In Browner, B., Jupiter, J., Krettek, C., Anderson, P. (Eds.), Skeletal Trauma: Basic Science, Management, and Reconstruction. pp. 2146–2180. Philadelphia: Elsevier.
  2. Evans, J., Nielson, J. (2021). Anterior cruciate ligament knee injuries. StatPearls. Retrieved June 9, 2021, from http://www.ncbi.nlm.nih.gov/books/NBK499848/
  3. Naqvi, U., Sherman, A. (2021). Medial collateral ligament knee injuries. StatPearls. Retrieved June 9, 2021, from http://www.ncbi.nlm.nih.gov/books/NBK431095/
  4. Yaras, R. J., O’Neill, N., Yaish, A. M. (2021). Lateral collateral ligament knee injuries. StatPearls. Retrieved June 9, 2021, from http://www.ncbi.nlm.nih.gov/books/NBK560847/
  5. Martin, S.N., DeWeber, K. (2019). Lateral collateral ligament injury and related posterolateral corner injuries of the knee. UpToDate. Retrieved June 10, 2021, from https://www.uptodate.com/contents/lateral-collateral-ligament-injury-and-related-posterolateral-corner-injuries-of-the-knee
  6. MacDonald, J., Rodenberg, R. (2019). Posterior cruciate ligament injury. UpToDate. Retrieved June 10, 2021, from https://www.uptodate.com/contents/posterior-cruciate-ligament-injury

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