Review Question - QID 219964

This patient presents with an acute anterior crucial ligament (ACL) injury, which may be suspected on physical exam in the presence of a positive pivot shift test, as described in answer choice 3.

ACL injuries are commonly encountered within orthopedic practice, estimated to account for half of all knee injuries overall. Females playing pivoting sports are at high risk of ACL injuries, due to multiple risk factors (e.g., high-energy pivoting may lead to excessive acute valgus and rotatory load on the knee joint, quadriceps dominance predisposes to increased anterior tibial translation). Although an MRI confirms this diagnosis, a detailed physical exam remains a highly effective method for diagnosis. Commonly utilized clinical exam maneuvers include the anterior drawer test, Lachman test, and pivot shift test. Of these, the Lachman’s test is typically considered the most sensitive, and the pivot shift test is regarded as the most specific, supporting the approach of utilizing both maneuvers as part of a standardized exam to optimize exam accuracy.

Furthermore, the anteromedial (AM) and posterolateral (PL) bundles of the ACL have been shown to provide differential contributions in resistance to tibial anterior translation and internal rotation in relation to the femur. The AM bundle is thought to contribute more significantly to anterior translation, whereas the PL bundle — particularly in knee extension — is considered to play a greater role in resisting tibial rotation. Utilizing both the Lachman test and pivot shift test allows for more specific assessment of these patterns of instability individually, which may improve diagnostic accuracy or assist in surgical planning.

Galway and Macintosh first described lateral pivot shift (LPS) as a form of knee instability arising from ACL insufficiency. They described the characteristic anterior subluxation of the lateral tibial plateau out from beneath the lateral femoral condyle. They concluded that this form of instability is the most common etiology for patients reporting complaints of “giving way” of the knee, and highlight the chronic consequences of this mechanism—namely, meniscal tears, articular cartilage damage, and eventual osteoarthritis of the knee.

Lopomo et al. reviewed the literature on quantifying the pivot shift test for assessing ACL injury, identifying 68 studies that used at least one quantitative parameter beyond clinical grading. They found that while 25 different parameters have been used, most studies focused on anterior-posterior tibial translation, internal-external rotation, and acceleration in the anterior-posterior direction, measured using various technologies including navigation systems, electromagnetic sensors, and accelerometers. They concluded that despite numerous methodologies developed, a standardized "gold standard" for quantifying dynamic knee laxity during the pivot shift test is still lacking, and further development and adoption of standardized methods are needed for objective comparison of ACL reconstruction outcomes.

Benjaminse et al. reviewed 28 studies to analyze the diagnostic accuracy of the Lachman, pivot shift, and anterior drawer tests for ACL ruptures, comparing clinical examination findings to arthroscopy, arthrotomy, or MRI results. They found the Lachman test to be the most accurate, with a pooled sensitivity of 85% and specificity of 94%, while the pivot shift test demonstrated high specificity (98%) but low sensitivity (24%) without anesthesia. The anterior drawer test showed good sensitivity (92%) and specificity (91%) in chronic conditions but was less accurate in acute settings, and the authors concluded that the Lachman test is the most accurate for diagnosing ACL tears, and the pivot shift test, given its high specificity, should also be performed to aid in diagnosis, particularly in chronic cases.

Figure A demonstrates representative sagittal slices of a knee PD-FSE MRI of an ACL rupture. The top image demonstrates the characteristic lateral distal femur injury often associated with acute ACL injuries, with impaction at the sulcus terminalis and associated bony edema. The bottom image demonstrates discontinuity at the proximal aspect of the ACL.

Incorrect Answers:
Answer choices 1 and 5: These represent positive quadriceps active and reverse pivot shift tests, respectively. These findings would be consistent with a posterior crucial ligament (PCL) injury.
Answer choices 2 and 4: These represent a positive McMurray’s test, with answer choice 2 being more consistent with a lateral meniscus tear and answer choice 4 being more consistent with a medial meniscus tear.