Anterior cruciate ligament (ACL) tears are the most common knee ligament injury encountered in radiology practice.
The ACL is the most commonly disrupted ligament of the knee, especially in athletes who participate in sports that involve rapid starting, stopping, and pivoting (e.g. soccer, basketball, tennis, netball and snow skiing).
An avulsion of the tibial attachment may be seen in younger patients.
- deep lateral sulcus sign
- anterior tibial translocation sign
- Segond fracture
- arcuate fracture
- joint effusion
Considered to have high specificity and sensitivity in detecting ACL disruption 6. CT is helpful in characterising the avulsion bone fragment when it is present.
Imaging of ACL tears should be divided into primary and secondary signs.
Primary signs are those that pertain to the ligament itself. Secondary signs are those which are closely related to ACL injuries.
- increased signal on T2 or PD FS
- fiber discontinuity
- change in the expected course of ACL: ACL angle that is less steep than Blumensaat's line: when drawing a line in the course of a normal ACL on the sagittal image the angle should be as steep or steeper than the intercondylar roof, so the apex is pointing posteriorly. If the ACL is less steeper than the intercondylar roof (i.e. the apex of the angle points anteriorly) means that ACL is completely torn and collapsed
ACL tears typically occur in the middle portion of the ligament and appear as discontinuity of the ligament or abnormal contour. The signal of the ACL can be more hyperintense on T2. If the angle is still normal and there is a hyperintense signal, a partial rupture is more likely than a complete rupture.
Secondary signs include:
- bone contusion in lateral femoral condyle and posterolateral tibial plateau 7
- >7 mm of anterior tibial translation also known as anterior tibial translocation sign or anterior drawer sign 7
- uncovered posterior horn of the lateral meniscus
- Segond fracture, and to a lesser degree arcuate sign
- reduced PCL angle due to buckling of PCL 7
- positive PCL line 7
- MCL or ACL injury
- 1. Chiu SS. The anterior tibial translocation sign. Radiology. 2006;239 (3): 914-5. doi:10.1148/radiol.2393040273 - Pubmed citation
- 2. Brandser EA, Riley MA, Berbaum KS et-al. MR imaging of anterior cruciate ligament injury: independent value of primary and secondary signs. AJR Am J Roentgenol. 1996;167 (1): 121-6. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Petersen W, Zantop T. Partial rupture of the anterior cruciate ligament. Arthroscopy. 2006;22 (11): 1143-5. Pubmed citation
- 4. Petersen W, Zantop T. Anatomy of the anterior cruciate ligament with regard to its two bundles. Clin. Orthop. Relat. Res. 2007;454: 35-47. doi:10.1097/BLO.0b013e31802b4a59 - Pubmed citation
- 5. Vande Berg BC, Lecouvet FE, Poilvache P et-al. Anterior cruciate ligament tears and associated meniscal lesions: assessment at dual-detector spiral CT arthrography. Radiology. 2002;223 (2): 403-9. doi:10.1148/radiol.2232011024 - Pubmed citation
- 6. Lee W, Kim HS, Kim SJ et-al. CT arthrography and virtual arthroscopy in the diagnosis of the anterior cruciate ligament and meniscal abnormalities of the knee joint. Korean J Radiol. 2004;5 (1): 47-54. Free text at pubmed - Pubmed citation
- 7. Lee K, Siegel MJ, Lau DM et-al. Anterior cruciate ligament tears: MR imaging-based diagnosis in a pediatric population. Radiology. 1999;213 (3): 697-704. doi:10.1148/radiology.213.3.r99dc26697 - Pubmed citation
The knee is a complex synovial joint that can be affected by a range of pathologies:
- bone and cartilage
- distal femoral condyle fracture
- tibial plateau fracture (classification)
- patella fracture
avulsion fractures of the knee
- Segond fracture
- reverse Segond fracture
- anterior cruciate ligament avulsion fracture
- posterior cruciate ligament avulsion fracture
- arcuate complex avulsion fracture (arcuate sign)
- biceps femoris avulsion fracture
- iliotibial band avulsion fracture
- semimembranosus tendon avulsion fracture
- Stieda fracture (MCL avulsion fracture)
- patella fracture
- chronic avulsion injuries
- chondromalacia patellae
- osteoarthritis of the knee
- osteochondral defects
- osteochondritis dissecans of the knee
- pattern of bone contusion in knee injuries
- knee fractures
- meniscal lesions
- synovial lesions
- fat pad
- popliteal fossa