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Knee Sprain

What is it?

There are four ligaments that are used to stabilize the knee, they are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The MCL provides the primary resistance against lateral to medial stress. The primary responsibility of the LCL is to resist medial to lateral moves. The LCL plays an additional role in limiting external rotation when the knee is flexed.

The MCL is the most commonly injured ligament of the knee and accounts for almost 8% of all athletic injuries. The primary mechanism for MCL injury involves application of sudden lateral to medial valgus stress, which includes a direct hit to the lateral knee while the foot is planted.

The LCL is the least commonly injured ligament of the knee. The primary mechanism of LCL injury involves a medial to lateral varus stress, usually in combination with hyperextension. LCL injuries are typically more complex than MCL injuries and may involve multiple structures such as the cruciate ligaments.

Ligament injuries are traditionally classified as grade I through grade III. Grade I includes a stretch with no microscopic fiber disruption. A grade II usually involves a partial fiber disruption. A grade III is a rupture of the ligament.

A significant knee trauma is capable of producing a multi-ligament injury. In fact, in about ⅔ of grade III MCL sprains result in an ACL disruption as well. A combined injury of the MCL, ACL, and meniscus are termed an “unhappy triad” or “blown knee.”

Clinical Presentation

The typical presentation of collateral ligament sprain includes pain on the medial or lateral aspect of the knee following an acute trauma. Patients will often report hearing a pop with subsequent pain. Complaints may include diminished range of motion from pain and swelling. Patients will notice an increase of pain with activity. Difficulty walking with this injury is common. Some patients may complain of a feeling of weakness and instability. A clicking sound is possible, particularly if there is damage to the meniscus as well.

Clinical evaluation may reveal tenderness and/or localized swelling over the affected collateral ligament. Passive knee flexion and extension are affected in isolated collateral ligament sprains, although terminal motions may be limited due to pain and/or swelling.

The diagnosis of collateral ligament sprain is highly likely when the following findings are present: a history of trauma, localized swelling, reproduction of familiar pain with palpating the injured ligament, and a pain or laxity on valgus and varus stress testing.


Advanced imaging of knee sprains is generally unnecessary, as skilled clinical evaluation may detect knee injury with similar sensitivity to MRI. Advanced imaging should be reserved for pre-operative planning or investigating concomitant injuries like a meniscus tear or ACL tear.


The management of collateral ligament sprains has shifted to a more conservative, non-surgical approach. The rehabilitation of collateral ligament sprain can be divided into three phases.

The initial phase of treatment seeks to promote optimal conditions for healing. The main goal of the first phase is to keep torn fibers in close continuity, implementing controlled motion, and protecting against further stress. The patient has completed phase I if they are able to attain full weight bearing with normal gait.

The goal of the second phase is to restore a full, pain free range of motion while increasing strength.

Phase Three is for the return of functional activity through endurance exercise, proprioceptive training, and agility drills. The patient may progress to the final stage of rehabilitation when they have full range of motion with no visual sign of swelling.

Clinicians should implement controlled motion as soon as possible. Early motion may help accelerate collagen synthesis (the healing process). Range of motion exercises should begin in a gentle non-painful with flexion and extension of the knee.

Strengthening exercises should focus on the quads, hamstrings, gastroc, soleus, and hip abductors. Research has shown that closed kinetic chain exercises are most acceptable. Early aerobic activity could include a stationary bicycle, elliptical stepper, or water aerobics.

Clinicians should consider the use of a double upright hinged knee brace for grade II injuries, and an immobilizer for grade III sprains. Immobilizing grade III injuries should last about 1-6 weeks. Depending on the severity of the tear, crutches may be necessary until the patient is able to walk with a normal gait. The patient should return to weight bearing as soon as tolerated to encourage cartilage nourishment.

Myofascial release and stretching may be appropriate for the hip flexors, quads, hamstrings, and gastroc/soleus muscles. The application of IASTM may be helpful and accelerate healing for grade I and grade II ligament sprains.

Return to full activity is dependent upon the degree of injury, as well as the location of tear, other injuries, age, and activity demands. Most grade I and II injuries can return to play within 1-3 weeks, while grade III injuries require 6 weeks or more to heal. The hinge brace may be necessary to help prevent re-injury.

Surgery is reversed for knees that are functionally unstable or for patients with persistent pain and/or disability, despite conservative management.

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