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Collateral Ligament Sprain

Collateral Ligament Sprain of the knee is caused due to sudden thrust being applied to the knee joint along the frontal plane commonly from the lateral side.
The medial and lateral collateral ligaments of the knee are very important structures that predominantly prevent valgus and varus forces, respectively. As with other ligamentous injuries, knee collateral ligament sprains can be classified in three grades of injury.

With a first-degree sprain, there is localized tenderness without frank instability. Anatomically, only a minimal number of fibers are torn. On physical examination, the joint space opens less than 5 mm.
With a moderate, or second-degree sprain, there is more generalized tenderness without frank instability. Grade 2 sprains can cover the gamut from a few fibers torn to nearly all fibers torn. The joint may gap 5 to 10 mm when force is applied.
A severe or grade 3 sprain is a complete disruption of all ligamentous fibers with the joint space gapping greater than 10 mm upon stressing the ligament.

Medial collateral ligament and Resultant Instability

The medial collateral ligament (MCL) also known as the tibial collateral ligament is the most commonly injured ligament of the knee. Usually this ligament is injured when valgus forces are applied to the knee. Contact injuries often produce grade 3 MCL deficits, whereas noncontact MCL injuries typically result in lower-grade injuries. Although MCL injury can occur in isolation, valgus forces typically instigate injury to other medial structures.

Findings of a rotational component to medial joint instability indicate cruciate ligament injury or meniscal or posterior oblique ligament involvement.

Lateral collateral ligament and Resultant Instability

The lateral collateral ligament (LCL) also known as the fibular collateral ligament is much less commonly injured than the MCL. True isolated injury to the LCL is very rare. True straight lateral instability requires a large vector force. Thus, a complete knee dislocation with possible damage to neurovascular structures should be suspected if straight lateral instability is present.

Posterolateral rotatory instability appears to be a more common cause of lateral instability than straight lateral instability. It is generally believed that posterolateral rotatory instability requires disruption of the arcuate complex, posterior cruciate ligament, and the LCL. The mechanism of posterolateral rotatory instability usually occurs when the knee is forced into hyperextension and external rotation.

Collateral ligaments of the knee
Collateral ligaments of the knee


  • Medial or lateral knee pain is the most common symptom related to knee collateral ligament injury. Grade 1 and 2 injuries cause more pain than grade 3 injuries.
  • Pain is often accompanied by a sensation of knee locking. This may be due to hamstring spasm or concomitant meniscal injury. Though more common with anterior cruciate ligament injuries, patients may also report an audible pop.
  • A give-way sensation or a feeling of instability is often reported with high-grade injuries.
  • Patients with high-grade injuries may also have neurovascular damage. Consequently, these patients may complain of a loss of sensation or strength underneath the knee.

Treatment of collateral ligament sprain

Initial Phase

  • All grades of collateral ligament injuries are treated initially in the same manner. The basic principles of PRICE (pressure/protection, rest, ice, and elevation) apply.
  • Patients with grade 2 and 3 injuries may need crutches and/or a hinged knee brace locked between 20 to 60 degrees to provide additional support for an unstable knee.
  • Allowable brace range of motion (ROM) should be increased as tolerated to prevent arthrofibrosis
  • Nonsteroidal anti-inflammatory medications may be prescribed to provide pain relief and reduce local inflammation associated with acute injury.


  • The goals of rehabilitation for the knee with a collateral ligament injury are to restore range of motion, increase stability, and return to pain-free activity.
  • Within the first 24 to 48 hours after injury, static quadricep contractions and electrical stimulation can be instituted to reduce local tissue swelling and retard muscular atrophy.
  • ROM and gentle stretching activities are introduced after the first day. Early weight bearing should also be encouraged.
  • Aerobic conditioning can be maintained by utilizing upper body ergometry, stationary bicycle, or swimming with gentle flutter kicks.
  • Maintenance phase rehabilitation should emphasize exercises in multiple planes.
  • Rehabilitation should eventually progress to functional or sport-specific activity.
  • A combination of closed and open kinetic chain exercises is utilized.
  • Typically, individuals with mild collateral ligament injuries return to activity after 3 to 4 weeks, whereas patients with severe injuries typically return to activity after 8 to 12 weeks.
  • Prophylactic hinged knee brace use has been advocated, although its effectiveness remains controversial
  • Upon achieving full strength and pain-free ROM in the lower extremity, the athlete can be cleared to return to their sport, most often without any brace or external support.

Surgical Intervention

  • Isolated MCL tears rarely require operative repair, while treatment of severe combined ruptures of the MCL and ACL or PCL would require reconstruction