Up to 5 percent of physician visits are related to knee pain. An evaluation is necessary to determine if the pain is the result of a musculoskeletal injury or part of a systemic problem. Evaluation of an injured knee may be difficult because of pain, edema, or underlying disease. Solomon and colleagues reviewed the physical examination of the knee to determine whether it is possible to diagnose certain local musculoskeletal knee injuries on the basis of the examination.
Some local injuries, such as a torn meniscus or a ligament injury, need prompt repair, and therefore require early diagnosis. Knowledge of knee anatomy is essential. Knee joint stability derives from the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial and lateral collateral ligaments (MCL and LCL, respectively), the menisci, and the muscles.
Damage to the ACL is associated with abnormal forward movement of the tibial plateau and internal rotation of the tibia during the end of extension. The patient may perceive the knee to be “buckling” or sense a loss of stability in the joint. ACL injuries often occur if the joint is twisted traumatically, especially when the foot is planted. The tibia may move forward on the femur, and a valgus stress to the joint may be described. The patient may experience a “popping” sensation at the time of the injury.
PCL damage also decreases the stability of the joint and may cause hyperextension of the knee and posterior movement of the tibia when the knee is flexed. Here, too, the knee may buckle. A PCL injury may occur in a similar manner to an ACL injury (i.e., with the foot planted), with the tibia pushed posteriorly while the knee is flexed.
Collateral ligament injuries usually occur when abduction and external rotational forces are applied to the knee while in an extended or slightly flexed position. The menisci provide joint stability and shock absorption. Because it is fixed in place, the medial meniscus is more likely to be injured. If the tibia is rotated internally while the knee is flexed, the meniscus may be torn from its peripheral attachment. Pain occurs when there is bleeding into the attachment (because the menisci have no pain fibers). Some studies have shown that as many as 36 percent of patients older than 45 years have evidence of meniscal injury on magnetic resonance imaging but no pain. A meniscal tear that extends anteriorly beyond the MCL (a “bucket-handle tear”) may cause the knee to lock in a flexed position.
|Where exactly is the knee pain? (“Point to it with one finger.”)|
|What is the duration of the pain?|
|Before the pain started, had there been a change in activities?|
|Was there an injury to the lower extremity and, if so, what was the direction of the force?|
|Was there a “pop” at the time of injury?|
|Was the knee swollen at the time of injury or anytime since?|
|Is the knee giving way or buckling?|
|Is the knee locking or catching in extension or flexion?|
|Is there pain in the hip, thigh, or back?|
|Physical examination tests|
|Alignment: are the femur, tibia, and patella in normal alignment during standing and walking?|
|Range of motion: can the patient actively and/or passively flex and extend the knee?|
|Effusion: is there a fluid wave or does ballottement of the patella produce a tapping sensation?|
|Joint line tenderness: is the patient tender along the medial and/or lateral joint lines?|
|Lachman test: is there a discrete end point when the tibia is anteriorly subluxed on the femur?|
|Anterior drawer test: is there anterior subluxation of the tibia on the femur?|
|Posterior drawer test: is there posterior sag or translation of the tibia on the femur?|
|Lateral pivot shift test: does the tibia “jump” anteriorly when extended or flexed with a valgus stress?|
|McMurray test: is there a “popping” at the joint line when the knee is extended and rotated?|
The examination should start with the patient in a comfortable position and, after the history is obtained, should begin with the less affected knee. If possible, the patient's gait should be observed. Muscular atrophy should be looked for because it may occur after ligamentous injury. Effusion, often most evident with the patient supine, may be seen first in the peripatellar groove. Swelling over the medial or lateral aspects of the joint may be associated with collateral ligament injury. Patellar movement, crepitus, and joint line tenderness should be noted. Specific maneuvers to assess the ACL include the Lachman test, the anterior drawer test, and the lateral pivot shift test. The PCL is evaluated with a posterior drawer test. Other specific maneuvers are recommended to evaluate other components of the knee joint. The accompanying table describes components of the history and physical examination of a patient with a suspected knee injury.
The authors performed a MEDLINE search to evaluate the reliability of knee joint examinations. No published articles discussed a physical examination of the MCL or LCL. If positive, ACL examinations were very predictive of ACL injury (likelihood ratio [LR], 25.0). For the individual maneuvers (i.e., not a composite examination), the anterior drawer sign had a specificity of 23 to 100 percent (mean, 67 percent); the Lachman test had an LR of 42.0 for a positive test and 0.1 for a negative test. For PCL injuries, the composite LR was 21.0 for a positive examination and 0.05 for a negative examination. Meniscal examinations were reviewed in nine studies that used arthroscopy as the reference standard. For composite examination, the sensitivity was 77 percent, and the specificity was 91 percent, with an LR of 2.7 for a positive examination and 0.4 for a negative examination. When divided into specific tests, examination for joint line tenderness had a sensitivity of 79 percent and a specificity of 15 percent. The McMurray test had a sensitivity of 53 percent and a specificity of 59 percent.
Although there are few published evaluations of the accuracy of the physical examination in diagnosing knee injury, the authors conclude that a complete examination for ACL, PCL, and meniscal injuries offers a fairly reasonable sensitivity and specificity and may help the patient avoid unnecessary diagnostic imaging or even referral.