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Selected Orthopedic Stress Tests for the Knee
Selected tests are shown that are commonly performed by physicians to test the stability of the knee
and evaluate ligamental injury. Consider each test in terms of the restraints offered by a normal,
intact ligament and the excessive motion that would be allowed if injury occurred. In A, the hands are
positioned to apply a valgus stress to a slightly bent knee to evaluate the integrity of the medial col-
lateral ligament. When the medial collateral ligament is torn, excessive “opening up” of the inside of
the knee is evident. In B, the hands are positioned to apply a varus stress to evaluate the integrity of
the lateral collateral ligament. When the lateral collateral ligament is severely torn, excessive “opening
up” of the outside of the knee may occur. In C, the hands are positioned to pull the tibia forward to
evaluate the integrity of the anterior cruciate ligament (ACL). When the ACL is torn, excessive anterior
displacement of the tibia relative to the femur is evident. In D, the hands are positioned to carefully
press the tibia backward to evaluate the integrity of the posterior cruciate ligament. When the poste-
rior cruciate ligament is torn, excessive posterior displacement of the tibia occurs; and even before
the posterior pressure is applied, the tibia will appear farther back than normal (“posterior sag”) as
evidenced by a concavity beneath the patella.