Final answer:
Magnetic resonance imaging (MRI) is the most sensitive and specific exam for diagnosing an ACL injury, by providing clear images of the ACL. Clinical tests such as the Lachman test are also sensitive and specific for initial assessment.
Step-by-step explanation:
When considering the most sensitive and specific exam for diagnosing an ACL injury, magnetic resonance imaging (MRI) is typically regarded as the gold standard. MRI is a non-invasive imaging technique that provides high-resolution images of soft tissues like the anterior cruciate ligament (ACL). Its sensitivity and specificity allow for a clear visualization of ACL integrity. If there is an ACL tear, an MRI will often show it clearly. However, physical examination maneuvers like the Lachman test, pivot-shift test, or anterior drawer test can also be highly sensitive and specific, especially when performed by experienced clinicians. These clinical tests are typically used as first-line assessment tools due to their convenience and the immediate feedback they provide regarding ligamentous stability. It is essential to have a thorough clinical examination complemented by an MRI for a conclusive diagnosis.