Medial collateral ligament sprain of the knee

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Pathology

A sprain of the medial collateral ligament is a disruption of the connection between the medial femur and the medial tibia. Like all other ligament injuries, these are graded one, two, and three, corresponding to mild injuries with no objective laxity, those with some laxity, with the ligaments still in continuity, and those with complete disruption respectively.

Pathophysiology

A disruption of the medial collateral ligament will lead to valgus instability of the knee, that is, medial gaping when a valgus force is applied. This can be associated with a sense of instability, pain (some of the ligament is still intact), and altered biomechanics leading to posttraumatic arthrosis.

Presentation

A patient with a medial collateral ligament injury will report pain following a non-contact twisting injury or a direct valgus blow to the lateral knee. Perhaps paradoxically the higher grade injuries are associated with less pain (probably on the basis of no ongoing tension, as the two ends are "flapping in the breeze.")

An effusion may be present (typically signifying an intra articular injury), however, rupture of the medial capsule can allow the effusion fluid to trickle out of the knee, and thus the knee may appear (falsely) dry on your exam.

The objective physical examination will show pain on valgus stress for a grade I injury; grade II and III there will be objective laxity noted.

A detailed examination must rule out concomitant injuries. (See differential diagnosis below.) It may be difficult to exclude a medial meniscal injury in the setting of an MCL sprain, as the location of pain right over the medial joint line is similar to both. X-rays should be obtained to exclude other diagnoses.

In an isolated MCL injury the x-rays can be normal. An MRI is often obtained to rule out a secondary injury. The MRI not only can confirm the presence of a medial collateral ligament injury, but its location, that is, avulsions off the femur versus intra substance damage.

Etiology

Medial collateral ligament injuries occur in response to a direct valgus load applied on the lateral knee or twisting mechanisms. The direct blow is more apt to cause a higher grade injury.

Epidemiology

Medial collateral ligament sprains are thought to be the most common sprains about the knee. Precise numbers are difficult to obtain.

Prevention

Theoretically, strengthening the muscles that course across the medial knee - the pes specifically, but also the knee flexors in general - could prevent medial collateral ligament injuries. There are no data to prove this, however.

Differential diagnosis

The key aspect of making a diagnosis of a medial collateral ligament injury is not so much to confirm the presence of this condition (which is usually not difficult to do), but rather to exclude other associated injuries. A direct blow that completely tears the medial collateral ligament could also injure the cruciate. A twisting injury could rupture the anterior cruciate ligament as well. A patellar injury may appear like a medial collateral ligament injury, especially if the patient is too tender for a good stress examination.

Of note, medial compartment arthrosis with joint space narrowing may present with "pseudo laxity" of the medial collateral ligament. Indeed, the medial collateral ligament is perfectly normal, however, there is a sense of valgus laxity as the knee is taken out of the acquired varus position to a more normal alignment. This condition is differentiated on the basis of x-rays, establishing the presence of arthrosis, the absence of pain with valgus load, and the firmness of the end point. Note that medial collateral ligament laxity is present with the knee flexed 30 degrees. If there is laxity in full extension as well, the posterior medial capsule is likely to have been disrupted. The physical examination must be performed in both 30 degrees of flexion and in full extension to make this differential diagnosis.

Treatment

Isolated medial collateral ligament injuries, regardless of severity, are typically treated non-operatively. Mild injuries may need only gentle protection with gradual advancement of activities as tolerated. Complete isolated ruptures should be treated with immobilization to allow healing of the ligament with the correct length and absence of laxity. The knee should be immobilized in 30 degrees of flexion to maintain the minimum distance between the femur and the tibia. Surgical repair has been frowned upon, as the results are rarely better than what would be achieved with non-operative treatment. The rationale for this, the thought, is that there is no single isometric point for the medial collateral ligament. Thus, if the knee is made adequately "tight," then range of motion will be restricted; and if adequate motion is allowed, the ligament would be too lax.

Miscellaneous

The Pellegrini-Stiada lesion is a calcification within the medial collateral ligament seen on x-rays. It is a sign of a chronic injury. Although a verbal description of this may suggest an osteochondroma, the characteristic appearance of this lesion leaves no doubt what it is.

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