History
Patients often describe a discrete event that caused the injury. A direct blow to the anteromedial aspect of the knee is a common injury mechanism for the PLC. Noncontact varus stresses as well as hyperextension stresses can also cause injuries to these structures.
The severity of injury should be delineated if acutely evaluating a patient. Significant ligamentous injuries to the knee that result in knee instability or dislocation have been associated with vascular injuries that may distally compromise perfusion of the limb.
Symptoms include pain, difficulty on uneven ground, swelling, and ecchymosis. Patients may also describe paresthesias as well as a foot drop if injury to the peroneal nerve has occurred.
A complete history including age, occupation, recreational activities, lifestyle, and interests should be obtained. Previous knee symptoms, injuries, or surgeries should also be elicited.
Physical Examination
The extremity should be evaluated for alignment, ecchymosis, skin abrasions, open wounds, and effusion.
Palpate the joint line, quadriceps insertion, patella, patellar tendon origin and insertion, lateral epicondyle, and fibular head. Palpate the suprapatellar pouch for effusion.
Perform a neurovascular examination that includes evaluation of the dorsalis pedis and posterior tibialis pulses. Evaluate the ankle plantar flexion and dorsiflexion, as well as foot eversion and inversion. (See also the Medscape Reference article Foot Drop.)
If a knee dislocation is suspected, the ankle brachial index should be determined. Values less than 0.9 should warrant an arteriogram and vascular surgery consultation to evaluate for arterial injury.
Examine passive and active range of motion of the knee.
Examine the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and medial collateral ligament (MCL).
To specifically isolate the LCL, apply a varus stress to the knee at 30º of flexion. Evaluate the amount of opening as well as the presence or absence of an endpoint. Ligamentous injuries can be graded as follows [1, 2] :
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Grade 1 – Interstitial injury without laxity is present, but pain occurs varus stress; only microscopic tearing has occurred.
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Grade 2 – A 5-10 mm of joint-space opening with a distinct end point is noted; partial macroscopic tearing has occurred.
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Grade 3 – Complete tearing (>10 mm joint-space opening) has occurred; complete macroscopic tearing is noted.
Compare examination to uninvolved extremity.
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The medial and lateral collateral ligaments of the knee. Courtesy of Randale Sechrest, MD, CEO, Medical Multimedia Group
