DOI: 10.1148/radiol.2393040273
(Radiology 2006;239:914-915.)
© RSNA, 2006
The Anterior Tibial Translocation Sign1
Sonny Sau-hin Chiu, MBChB
1 From the Department of Radiology, Kwong Wah Hospital, 25 Waterloo Rd, Hong Kong. Received February 12, 2004; revision requested April 20; revision received May 3; accepted May 24.
Address correspondence to the author (e-mail: sc723{at}yahoo.com).
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APPEARANCE
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The anterior tibial translocation sign (1) is seen on sagittal magnetic resonance (MR) images of the lateral femoral condyle. This sign occurs when there is 7-mm or greater anterior translocation of the tibia relative to the femur (2,3) (Figs 1, 2).
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Figure 1: Degree of anterior tibial translocation is measured by drawing vertical lines tangent to the posterior margins of the lateral femoral condyle and tibia. Sagittal intermediate-weighted, fast spin-echo (3150/17, repetition time msec/echo time msec) MR image of the knee through the midpoint of the lateral femoral condyle in a patient with complete anterior cruciate ligament (ACL) tear shows abnormal anterior tibial translocation of 9 mm. The tangent line of the posterior margin of the tibia passes through the posteriorly displaced posterior limb of the lateral meniscus.
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Figure 2: Sagittal intermediate-weighted, fast spin-echo (3150/17) MR image through the midpoint of the lateral femoral condyle in a different patient with an intact ACL shows no anterior translocation of the tibia. The tangent line of the posterior cortex of the tibia does not pass through the posterior limb of the lateral meniscus.
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EXPLANATION
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The ACL attaches to the inner aspect of the lateral femoral condyle proximally and fans out to attach to the anterior aspect of the intercondylar eminence of the tibia distally. It runs from the femur to the tibia anteriorly, medially, and distally within the intercondylar notch. It is intraarticular and extrasynovial throughout its course. The primary role of the ACL is to provide stability to the knee joint. It resists anterior translocation and internal rotation of the tibia over the femur. The ACL also limits hyperextension and both valgus and varus forces on the knee (4).
ACL injury is associated with anterolateral instability of the knee. Deficiency of the ACL allows the tibia to undergo anterior subluxation relative to the femur, thus producing the anterior tibial translocation sign. The degree of anterior subluxation of the tibia can be measured directly at MR imaging. This is analogous to the anterior drawer test (5) elicited during physical examination, in which the tibia moves anteriorly as the leg is pulled forward.
Along the midsagittal plane of the lateral compartment of the knee, the distance between two lines drawn tangent to the posterior of the lateral femoral condyle and the proximal tibia indicates the degree of anterior tibial translocation. Two methods of drawing the tangent lines were described by Vahey et al (1). In the first method, the tangents were drawn perpendicular to the tibial plateau. In the second methods, the tangents were vertical and parallel to the image frame. The measured tibial displacement would be greater for the second method.
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DISCUSSION
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The ACL is the most commonly disrupted ligament of the knee (6), especially among athletes who participate in sports that involve rapid starting, stopping, and pivoting over a planted leg, such as soccer, basketball, tennis, and snow skiing. ACL tears typically occur in the middle portion of the ligament, although they can also occur at the proximal or distal attachments. Avulsion of the tibial attachment may be seen in younger patients. Injuries of the ACL are often caused by external rotational forces of the femur, occurring at abduction and flexion of the knee.
The integrity of the ACL may be difficult to assess when the ACL is not depicted in its entirety in a single sagittal image. In addition to direct visualization of the ACL defect, MR imaging can also demonstrate misalignment of the knee joint as a result of ACL tear. Anterior translocation of the tibia is one of the secondary signs of ACL tear that can be seen at MR imaging. Various other names have been given to this sign, including anterior drawer sign or anterior displacement of the tibia (7,8), anterior translation of the tibia (9) and anterior subluxation of the tibia (10).
In the study conducted by Chan et al (10), anterior translocation of 5 mm or more was shown to have a sensitivity of 86% and a specificity of 99% for ACL tear. According to Vahey et al (1) in another study, when measured at the midsagittal plane of the lateral femoral condyle, anterior translocation of the tibia was a specific indicator of ACL tear. Subluxation of 5 mm or more had 58% sensitivity and 93% specificity for ACL tear. In this study, all knees with subluxation of 7 mm or more had a torn ACL.
Secondary signs of ACL tear on MR images have high specificity and moderate to low sensitivity in both adult and pediatric patients (7). The presence of secondary signs of ACL tear increases the confidence of the diagnosis. The absence of secondary signs, however, does not exclude the possibility of ACL tear (1). Secondary signs can be used to diagnose ACL tear even when the ACL itself cannot be visualized (9). Both chronic and acute ACL tears may demonstrate the anterior tibial translocation sign (11). The degree of anterior displacement is greater in chronic ACL tears than acute ACL tears, with mean values of 8.7 mm and 5.4 mm, respectively (8). Chan et al (10) showed that anterior tibial subluxation greater than 5 mm was a simple objective measurement that served as an adjunctive sign in the diagnosis of complete tear of the ACL.
Anterolateral instability of the tibia relative to the femur is associated with ACL tear. A related finding of anterior tibial translocation occurs when the posterior horn of the lateral meniscus is subluxed relative to the posterior cortical margin of the lateral tibial condyle. As a result, the vertical line tangent to the posterior margin of the tibia passes through the posteriorly displaced posterior horn of the lateral meniscus. Abnormal forward displacement of the tibia may also manifest itself as bowing of the posterior cruciate ligament (12). ACL injury can be associated with medial collateral ligament injury and medial meniscal tear. The association is termed the O'Donoghue triad (3).
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FOOTNOTES
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Author stated no financial relationship to disclose.
| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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References
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- Vahey TN, Hunt JE, Shelbourne KD. Anterior translocation of the tibia at MR imaging: a secondary sign of anterior cruciate ligament tear. Radiology 1993;187(3):817–819.[Abstract/Free Full Text]
- Moore SL. Imaging the anterior cruciate ligament. Orthop Clin North Am 2002;33(4):663–674.[CrossRef][Medline]
- May DA, Disler DG. Trauma. In: Manaster BJ, Disler DG, May DA, eds. Musculoskeletal imaging: the requisites. 2nd ed. St Louis, Mo: Mosby, 2002; 344.
- Dienst M, Burks RT, Greis PE. Anatomy and biomechanics of the anterior cruciate ligament. Orthop Clin North Am 2002;33(4):605–620.[CrossRef][Medline]
- Solomon DH, Simel DL, Bates DW, Katz JN, Schaffer JL. The rational clinical examination: does this patient have a torn meniscus or ligament of the knee? value of the physical examination. JAMA 2001;286(13):1610–1620.[Abstract/Free Full Text]
- Chew FS, Bui-Mansfield LT, Kline MJ. In: The core curriculum: musculoskeletal imaging. Philadelphia, Pa: Lippincott Williams & Wilkins, 2003; 114.
- Lee K, Siegel MJ, Lau DM, Hildebolt CF, Matava MJ. Anterior cruciate ligament tears: MR imaging-based diagnosis in a pediatric population. Radiology 1999;213(3):697–704.[Abstract/Free Full Text]
- Gentili A, Seeger LL, Yao L, Do HM. Anterior cruciate ligament tear: indirect signs at MR imaging. Radiology 1994;193(3):835–840.[Abstract/Free Full Text]
- Brandser EA, Riley MA, Berbaum KS, el-Khoury GY, Bennett DL. MR imaging of anterior cruciate ligament injury: independent value of primary and secondary signs. AJR Am J Roentgenol 1996;167(1):121–126.[Abstract/Free Full Text]
- Chan WP, Peterfy C, Fritz RC, Genant HK. MR diagnosis of complete tears of the anterior cruciate ligament of the knee: importance of anterior subluxation of the tibia. AJR Am J Roentgenol 1994;162(2):355–360.[Abstract/Free Full Text]
- Robertson PL, Schweitzer ME, Bartolozzi AR, Ugoni A. Anterior cruciate ligament tears: evaluation of multiple signs with MR imaging. Radiology 1994;193(3):829–834.[Abstract/Free Full Text]
- Tung GA, Davis LM, Wiggins ME, Fadale PD. Tears of the anterior cruciate ligament: primary and secondary signs at MR imaging. Radiology 1993;188(3):661–667.[Abstract/Free Full Text]
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