The football player in the question stem has an anterior cruciate ligament injury, as indicated by the positive anterior drawer sign. This injury is often accompanied by medial meniscus (MM) injury and medial collateral ligament (MCL) injury to comprise the "unhappy triad" of knee injuries. Lateral meniscus (LM) injuries can also commonly co-occur.
ACL injuries are very common in sports, but can also happen with sudden-stop pivoting on a planted foot. These injuries rarely occur in isolation, and are most commonly associated with LM and MCL tears in greater than 90% of cases.
Cimino et al. report on the demographics and diagnostic sensitivity of ACL injuries. They report that 80,000-100,000 ACL repairs are performed in the United States each year with most tears occuring from noncontact injuries. Demographically, women experience ACL tears 9x more often than men. When performed properly, they assert that a complete knee examination is more than 80 percent sensitive for an ACL injury.
Millett et al. discuss the risk of associated injuries in ACL trauma secondary to delays in repair. They showed that associated injuries are common in young individuals with ACL tears and that a delay in surgical treatment was associated with a higher incidence of medial meniscal tears.
Figure A shows the type hypervalgus displacement of the lower extremity following lateral impact to the knee. Illustration A shows the normal anatomy of the knee.
Answer 1: Although concurrent ACL and lateral cruciate ligament (LCL) tears occur, MCL and lateral meniscus injury are more commonly seen with ACL avulsions.
Answer 3: A tear in the patellar ligament (patellar tendon rupture) would result in migration of the patella superiorly and inability of the patient to extend the knee. This injury is not classically seen in conjunction with ACL injury.
Answer 4: Although medial meniscus tear rather than lateral meniscus tear was part of the original "unhappy triad" described by O'Donoghue, lateral meniscus tears are far more common with ACL and MCL injury. Furthermore, if a medial meniscus tear occurs as part of an "unhappy triad", it is usually in the setting of a concurrent lateral meniscus tear.
Answer 5: Posterior cruciate ligament (PCL) avulsion injury is not generally associated with ACL injury and requires a different mechanism of action (posterior displacement of the tibia in a flexed knee, such as falling on a bent knee or "dashboard injury").
Cimino et al. Am Fam Physician. 2010 Oct 15;82(8):917-922.
PMID:20949884 (Link to Abstract)
Millett et al. Arthroscopy. 2002 Nov-Dec;18(9):955-9.
PMID:12426537 (Link to Abstract)