Medial collateral ligament injuries of the knee

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Anatomy

The MCL consists of the deep and superficial portions.The superficial medial collateral ligament (sMCL) (aka the tibial collateral ligament) has one femoral and two tibial attachments. The femoral insertion occurs in a depression approximately 3.2mm proximal and 4.8 mm posterior to the medial epicondyle . There are two separate tibial attachments, one just anterior to the posteromedial crest of the tibia and the other located witin the pes anserine bursa. The posterior aspect to the sMCL blends in with the distal portion of the semimembranosus tendon insertion. The sMCL has been reported to provide 57% of valgus retraint at 5 degrees flesion and 78% at 25 degrees of flexion .

The deep MCL (dMCL) is a thickening of the medial joint capsule. It is most distinct anteriorly and blends in with the posterior oblique ligament posteriorly. It consists of distinct meniscofemoral and meniscotibial portions .

The three layers of medial knee include :

  1. Deep Fascia
    1. Gracilis and semitendinosus tendons are found between layers I and II.
  2. Superficial MCL, semimembranosus tendon sheath
  3. Deep MCL (deep capsular ligament) and capsule

Function

Primary stabiliter to valgus force. Secondary stabilizer to anterior translation.

Combined injuries to ACL and MCL often result in anteromedial rotatory instability. Loss of either either the MCL or ACL creates increased increased forces on the other ligament (MCL or ACL).

Diagnosis

Mechanism of injury:

Isolated valgus force

Clinical exam:

Palpation along the course of the MCL. Injuries typically occur at the proximal insertion site on the feumur.

Valgus stress with the knee in  full extension tests the capsular structures, cruciates, and MCL. Valgus stress with knee at 30 degress of flexion isolates the MCL.

Imaging:

Although daignosis should be made by clinical exam, radiographs can identify bony avulsions and stress radiographs can identify joint space widening. If a pediatric patient is tender near the growth plate, physeal injuries should be ruled out with stress radiographs.

MRI assists in identifying the location and degree of injury.

Treatment

Grade I and II injuries can typically be treated nonoperatively. Rehab protocol usually entails weight bearing as tolerated with crutches (as needed), range of motion exercises, RICE, and NSAIDS. Protective braces may be used for atheletes who perform cutting maneuvers.

Isolated grade III injuries can be initially treated nonoperatively. Femoral-sided lesions typically heal more reliably than midsubstance or tibial-sided lesions. Immobilization in a brace may be required intially as swelling subsides. ROM exercises are began once swelling allows. If valgus instability persists at 4 to 8 weeks, surgical reconstruction should be considered.

Management of MCL injuries with associated ACL rupures is controversial. However, many clinical studies have reported good outccomes with nonoperative treatment of the MCL injury, including a randomized prospective study comparing operative versus nonoperative managment of the MCL in the setting of ACL reconstruction . Additionally, early reconstruction of both the MCL and ACL may lead to arthrofibrosis. During nonoperative treatment, the medial side is rehabilitiated and ROM is restored prior to ACL reconstruction. 

MCL - PCL combined injury: less common than MCL - ACL injuries. If significant posterior laxity exists, both the MCL and PCL should be reconstructed acutely. If valgus laxity persists in patients who have undergone conservative therapy, both the MCL and PCL should be reconstructed.

Chronic MCL injuries - At this time (typically 3 - 4 mo after the injury) the potential for spontaneous healing is lost. These injuries can result in secondary limb malalignment or secondary ligamentous injuries.

Surgical Technique

Repair

Proximal bony avulsions can be reattached to the femoral epicondyle.

Primary repair of  tears is possible if the midsubstance of the ligament is not significantly stretched.

Reconstruction

The distal semitendinosus tendon can be dissected out and attached to medial femoral condyle while leaving the distal insertion point intact. The musculotendinous junction can be divided or left intact.

Achilles tendon allograft - Calcaneal bone block is fixated at the femoral epicondyle and the tendon is stapled to the tibia 2 - 4 cm distal to the joint line.

Double-bundle technique using tibialis anterior tendon allograft .

Complications

Stiffness - more commonly seen in acute injuries and combined ACL/MCL injuries. Fixation of the ligament reconstruction/repair too close to the joint line can result in capture of the knee.

Pelegrini-Stieda lesions - A form of myositis ossificans involving the proximal MCL. Early disease can be managed with antiinflammatories or steroid injections.

References:

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