MRI Appearance of Posterior Cruciate Ligament Tears

Transcription

1 Musculoskeletal Imaging Clinical Observations Musculoskeletal Imaging Clinical Observations William Rodriguez, Jr. 1 Emily N. Vinson 1 Clyde. Helms 1 lison P. Toth 2 Rodriguez W Jr, Vinson EN, Helms C, Toth P Keywords: knee injury, MRI, posterior cruciate ligament DOI: /JR Received July 23, 2007; accepted after revision pril 29, Presented at the 2006 annual meeting of the merican Roentgen Ray Society, Vancouver, C, Canada. 1 Department of Radiology, Duke University Medical Center, ox 3808, Durham, NC ddress correspondence to E. N. Vinson (vinso003@mc.duke.edu). 2 Division of Orthopaedic Surgery, Duke University Medical Center, Durham, NC. WE This is a Web exclusive article. JR 2008; 191:W155 W X/08/1914 W155 merican Roentgen Ray Society MRI ppearance of Posterior Cruciate Ligament Tears OJECTIVE. There is little in the radiology literature regarding the MRI appearance of a torn posterior cruciate ligament (PCL). The purpose of this study was to describe the MRI appearance of surgically proven PCL tears and to emphasize previously unreported signs. CONCLUSION. The PCL is usually injured as the result of stretching deformation; on MRI, the ligament maintains continuity as a single structure with apparent thickening. On sagittal T2-weighted images, an anteroposterior diameter of 7 mm or more is highly suggestive of a torn PCL. Increased intrasubstance signal intensity in the PCL on proton-density images with lower signal intensity on T2-weighted images is another common feature. s orthopedic surgeons gain more experience with posterior cruciate ligament (PCL) reconstruction and acquire better understanding of the long-term effects of PCL deficiency, it becomes increasingly important for radiologists to identify PCL tears [1, 2]. Knowledge of the diagnosis and management of PCL tears lags behind that of anterior cruciate ligament (CL) tears. Inexperience with this injury is compounded by difficulty in clinical identification of tears. In the acute phase of a tear, physical examination of the PCL can be difficult because of the presence of a hemarthrosis, pain, and concomitant ligamentous injuries [3]. It is not unusual for the findings at physical examination to be normal after acute tear of the PCL [4], and patients rarely describe hearing the pop common with CL tears [1]. s a result, many PCL tears remain undiagnosed at the initial clinical evaluation [5, 6]. In this setting, radiologists may be in a position to make the index diagnosis. There is relatively little in the radiology literature regarding the MRI appearance of PCL tears [7 9]. The purpose of this study was to describe the MRI appearance of surgically proven PCL tears and to emphasize previously unreported signs. Materials and Methods Institutional review board approval was obtained for this study. The records of 34 patients with a postoperative diagnosis of PCL tear and available preoperative MR images of the knee were identified in a search of surgical and imaging databases. The patient group consisted of 23 men (68%) and 11 women (32%) with an average age of 35.2 years (range, years). Sixteen of the injuries (47.1%) were the result of a motor vehicle collision, seven (20.6%) were the result of a sports injury, and four (11.8%) were the result of falls. Two patients (5.9%) were pedestrians injured by moving vehicles. One patient (2.9%) fell from a moving vehicle, one twisted his knee on a wet floor, one was injured walking on a beach, and one was injured descending stairs. One patient had an unknown mechanism of injury. The average time from date of injury to imaging was 54.8 days (range, days) for 33 of the patients. The date of injury was unknown for one patient. The average time from imaging to surgery was 60.1 days (range, days). ll imaging studies were performed over a 4- year period on a 1.5-T unit (Signa, GE Healthcare) according to our standard knee MRI protocol: sagittal fat-suppressed spin-echo proton-density images (TR/TE, 1,500 2,000/20) and sagittal, axial, and coronal fat-suppressed fast spin-echo T2- weighted images (2,000 5,000/57 80). The number of signals acquired was two for fast spin-echo sequences and one for proton-density sequences. The echo-train length was 8 10 for the fast spinecho sequences. slice thickness of 4 mm with a 0.4-mm interslice gap was used. The field of view was 16 cm 2, and the matrix size was Images from the preoperative MRI examinations of the knee were retrospectively evaluated in consensus by three musculoskeletal radiologists. The PCL was assessed on the sagittal T2-weighted JR:191, October 2008 W155

2 and proton-density images for anteroposterior diameter, intrasubstance signal intensity, and the presence or absence of complete disruption of the ligament, defined on the basis of fluid signal intensity traversing the full thickness of the PCL on sagittal T2-weighted images. In cases of disruption or avulsion of the PCL, the site was noted. The anteroposterior diameter of the vertical segment of the PCL between the tibial attachment and genu of the PCL was measured on the sagittal T2-weighted images. The measurement perpendicular to the fibers of the PCL was obtained. The images of a group of control patients (108 men, 92 women; average age, 42.5 years; range, years) without a history of trauma who underwent 200 consecutive MRI examinations of the knee over a 2-month period were retrospectively evaluated for signal intensity of the PCL on proton density and T2-weighted images and for anteroposterior diameter of the vertical segment of the PCL measured on sagittal T2-weighted images. ll observations and measurements of the study and control patients were made in consensus by unblinded observers. lthough axial and coronal T2-weighted images were available for review, the assessments of PCL thickness, continuity, and signal characteristics were made on the sagittal proton density and T2-weighted images. Results In the 200 consecutive control MRI examinations of the knee, 184 PCLs (92%) measured 6 mm or less in anteroposterior diameter (Fig. 1). The range was 4 8 mm. The signal intensity of the PCL in these patients was low on the T2-weighted and proton-density images. In the 34 patients with surgically documented PCL tears, 32 PCLs (94%) measured 7 mm or more in anteroposterior diameter on sagittal T2-weighted images. The average thickness was 9.6 mm, with a range of 4 15 mm (Fig. 2). lso, in 32 of the 34 cases, the anteroposterior diameter of the distal half of the ligament increased with no relation to the location of the tear. In 30 of the 34 PCL tears (88%), the PCL intrasubstance signal intensity on the protondensity images was higher than that on T2- weighted images. ll 34 patients had abnormal intermediate intrasubstance or fluid signal intensity on proton-density images (Fig. 3). The differences in distribution of PCL thicknesses between the control group and the group of patients with PCL tears was statistically significant (p < 0.001, Wilcoxon s test). The estimated sensitivity and specificity of several PCL thicknesses (7 mm and greater, 8 mm and greater, and 9 mm and greater) in the diagnosis of PCL tear are summarized in Table 1. The 95% CIs were based on the Wilson score test. In 21 of 34 cases (62%), the PCL was not completely disrupted or avulsed. Five of the 13 ligaments (15% of the total) that appeared Fig year-old man with normal posterior cruciate ligament (arrows)., Sagittal fat-suppressed proton density weighted MR image (TR/TE, 1,800/17) shows smooth, thin, continuous band of low signal intensity typical of normal posterior cruciate ligament., Sagittal fat-suppressed T2-weighted MR image (3,500/52) in same plane as shows smooth, thin band of low signal intensity. nteroposterior measurement of vertical segment is 4 mm, which is within range of normal. Fig year-old woman with knee pain after injury sustained while playing softball., Sagittal fat-suppressed proton-density MR image (TR/TE, 2,000/20) shows abnormally thickened posterior cruciate ligament (PCL) (arrows) with increased signal intensity within ligament., Sagittal fat-suppressed T2-weighted MR image (3,500/69.1) shows abnormally thickened PCL (arrows) with anteroposterior measurement of 10 mm, which appears to maintain continuity as one structure. Signal intensity of PCL is relatively low in contrast to appearance in. C, Coronal fat-suppressed T2-weighted MR image (3,000/69.2) shows markedly thickened PCL (arrows) in region of genu. t surgery, PCL was present and intact to probing though lax on posterior drawer test performed during arthroscopy. One operative diagnosis was PCL tear. completely disrupted or avulsed were avulsed from the femoral attachment, five (15%) tears were midsubstance, and three ligaments (9%) were avulsed from the tibial attachment. Two of the three avulsions at the C W156 JR:191, October 2008

3 C Fig year-old girl with knee pain after motor vehicle crash., Sagittal fat-suppressed proton density weighted MR image (TR/TE, 2,000/20) of posterior cruciate ligament (PCL) near femoral attachment shows abnormal thickening (arrow) with intrasubstance fluid signal intensity., Sagittal fat-suppressed proton density weighted MR image (2,000/20) of PCL one image plane lateral to reveals abnormal thickening (arrows) with longitudinally oriented striations of fluid signal intensity. C, Sagittal fat-suppressed proton density weighted MR image (2,000/20) of PCL tibial attachment immediately lateral to shows abnormal thickening with intrasubstance striations (arrows) of fluid signal intensity. Lack of complete ligamentous disruption of this torn PCL is evident. D, Sagittal fat-suppressed T2-weighted MR image (3,500/69) of PCL in same imaging plane as reveals abnormal thickening with striations (arrows) of intermediate signal intensity. Intrasubstance signal intensity appears relatively lower than in. nteroposterior measurement of this vertical segment is 10 mm, which is abnormal. t surgery, this PCL was described as torn. Patient underwent anterior cruciate ligament, PCL, and posterolateral corner reconstructions. tibial attachment were tibial avulsion fractures in which a small fragment of cortical bone was distracted proximally from the tibia (Fig. 4). Of the 21 cases without complete disruption, intrasubstance fluid signal intensity within the PCL on the T2-weighted images was present in only four cases (19% of the 21). nother relatively common feature of the torn PCL was a striated appearance, somewhat similar to the normal CL appearance, with longitudinally oriented lines of increased intrasubstance signal intensity. Twenty-four of the 34 tears (71%) had this striated appearance on proton density or T2-weighted images. The characteristics of this striation were variable with regard to location, signal intensity, thickness of lines, and length of area of signal intensity within the ligament. Laxity or a wavy appearance of the PCL was apparent in eight of the 34 cases (24%). Two PCLs that appeared as one continuous structure at MRI were described as completely disrupted at surgery. Only two of the 34 PCL tears were described as isolated injuries in the operative notes; in most of the cases, multiple ligament injuries were reported. The most common associated injuries were CL tears in 20 of the patients (59%), medial collateral ligament tears in 12 patients (35%), and injuries D to one or more structures in the posterolateral corner in 17 patients (50%). Discussion The incidence of PCL injuries is difficult to assess because of the large percentage that remain undiagnosed in the acute setting, a reported 1 44% [10]. Schultz et al. [5] retrospectively studied the epidemiologic characteristics of 494 cases of PCL insufficiency. Those investigators found that most of the injuries were related to traffic accidents (45%) and sports injuries (40%). The mechanism of injury was dashboard type in 35%, fall on a flexed knee (blow to the anterior proximal tibia) with the foot plantar-flexed in 24%, and hyperextension in 12% of cases. Hyperflexion injury has been described as a less-common mechanism of PCL injury [3, 11]. Sports-related PCL injuries are significantly more likely to be isolated and more likely to be diagnosed in the acute phase [5, 11]. Overall, more than 50% of patients presented more than 1 year after injury [5]. ecause the PCL is the primary restraint to posterior tibial translation relative to the femur [12], PCL tears are diagnosed and graded clinically with the posterior drawer test, which is used to evaluate the degree of posterior translation of the tibia relative to the femur with the knee flexed 90. Tears therefore are defined on the basis of functional competency of the ligament rather than the presence or absence of complete disruption. Laxity to probing at arthroscopy is diagnostic of a tear. The normal appearance of the PCL on MR images is a well-defined continuous band of low signal intensity in all pulse sequences. s found in our evaluation of 200 consecutive MR examinations of the knee without a known diagnosis of a PCL tear, a normal PCL usually measures no more than 6 mm in anteroposterior diameter on sagittal T2-weighted images, with the measurement perpendicular to the fibers of the vertical segment. torn PCL typically becomes abnormally enlarged. To our knowledge, abnormal thickening of a torn PCL on MR images has not been previously described. In 94% of our 34 patients with PCL tear, the PCL measured 7 mm or greater. On the basis of a sensitivity of 94% and specificity of 92%, we advocate using 6 mm as the upper limit of normal PCL thickness, thicknesses of 7 mm and greater being suggestive of a tear. This finding corroborates those of Cho et al. [13] in a sonographic investigation. Those investigators measured the distal half of the PCL (vertical JR:191, October 2008 W157

4 TLE 1: Sensitivity and Specificity of Posterior Cruciate Ligament Thicknesses in Diagnosis of Tear Thickness (mm) Sensitivity (%) Specificity (%) 7 94 (81 98) 92 (87 95) 8 82 (67 92) 99 (96 100) 9 71 (54 83) 100 (98 100) Note Values in parentheses are 95% CI. Fig year-old woman with knee pain after motor vehicle crash. Sagittal fat-suppressed T2- weighted MR image (TR/TE, 4,000/70) of posterior cruciate ligament (PCL) shows tibial avulsion fracture. Thin piece of cortical bone (arrow) is avulsed from tibia at insertion of PCL. PCL is redundant and retracted proximally. segment) and evaluated the ligament in the sagittal plane. Using the other knee as a control, they found that the normal PCL measured less than 6 mm (range, 4 6 mm). The mean measurement of torn PCLs in that study was 15.6 mm (range, mm). The thickness of the distal half of the PCL increased whether the tear occurred proximally or distally. Cho et al. concluded that the increase in thickness of the ligament is the most important criterion among the sonographic findings of torn PCL. s we found in this investigation, an acutely torn PCL usually maintains continuity as a single structure and is typically injured as a result of stretching deformity. In 62% of the 34 cases of PCL tear in this study, the PCL maintained continuity as a single structure on images. Similar findings of ligament continuity were discussed by kisue et al. [14], who evaluated acutely torn PCLs clinically and with MRI. In 75% (36 of 48) of their cases of torn PCL, the PCL maintained continuity as one structure on MRI. Those investigators concluded that a high percentage of acutely injured PCLs are likely to develop somewhat slack but continuous ligamentlike tissue. It has been suggested that continuity of the torn PCL on MR images has a favorable prognosis for nonoperative treatment [1]. Surgeons, however, consider many variables when evaluating PCL injuries for possible reconstruction, such as associated ligament, chondral, and meniscal injuries and subjective instability [11]. We found the proton-density (short TE) sequence extremely important in the diagnosis of PCL injuries. With reliance on T2- weighted images alone, one may not recognize subtle pathologic changes in the PCL, resulting in lower sensitivity. In all of our cases of torn PCL, the ligament had abnormally increased intrasubstance signal intensity on proton-density images. In 88% of our cases, the signal intensity on proton-density images was increased relative to the signal intensity on T2-weighted images. If the ligament has homogeneously low signal intensity on proton-density images, acute PCL injury is highly unlikely. In evaluation of the PCL, the negative predictive value of MRI performed with a short-te sequence is reported to approach 100% [9]. The proton-density sequence, however, should not be used for obtaining the anteroposterior measurement of the ligament because the intrasubstance signal intensity of the torn PCL on the protondensity images often approximates that of the adjacent edematous soft tissues, making the margins of the ligament difficult to discern. For this reason, sagittal T2-weighted images should be used for measuring the PCL. Unlike other ligament tears, PCL tears rarely have intrasubstance fluid signal intensity on T2-weighted images. In the 13 cases in this study labeled as discontinuous at imaging, increased T2 signal intensity was present in the expected course of the torn ligament. Eight of these patients had avulsion of the ligament from either the femur or the tibia. However, of the 21 cases in this study in which the PCL appeared as one continuous structure, only four exhibited intrasubstance fluid signal intensity within the PCL on T2-weighted images. The cause of this observation is not certain. Perhaps proteinaceous fluid within the torn PCL has increased signal intensity on proton-density images, whereas the T2 relaxation time is not particularly lengthened owing to the relatively restricted environment of the protons within the contiguous, though functionally torn, fibers of the PCL. lthough we did not assess bone marrow contusions in this study, other authors have described contusion patterns that can lead radiologists to suspect PCL injury. Mair et al. [15] evaluated the bone contusion pattern related to acute PCL tears and found that 83% of their 35 patients had a contusion in at least one location. contusion involving the anterior proximal tibia is a known common finding related to a direct blow [16, 17]. Hyperextension injury resulting in kissing contusions with focal bone marrow edema on the anteroinferior femoral condyle and proximal anterior tibia also may be seen on MR images [16]. The PCL usually is injured as a result of a stretching deformation, whereby the ligament maintains continuity as a thickened structure, rather than frank rupture. pparent ligamentous continuity was seen in 62% of our cases of surgically proven tears. bnormally increased signal intensity within the PCL on proton-density images is highly suggestive of PCL tear and was seen in all of the patients in this study who had a surgical diagnosis of PCL tear. With use of sagittal T2-weighted images, a 7-mm or greater anteroposterior measurement of the vertical portion of the PCL can be considered evidence of a torn PCL with a high degree of certainty. Recognition of these findings should improve radiologists ability to diagnose PCL tears preoperatively. cknowledgment We thank David M. DeLong for assistance with statistical analysis. References 1. Wind WM Jr, ergfeld J, Parker RD. Evaluation and treatment of posterior cruciate ligament injuries: revisited. m J Sports Med 2004; 32: Strobel MJ, Weiler, Schulz MS, Russe K, Eichhorn HJ. rthroscopic evaluation of articular cartilage lesions in posterior-cruciate-ligament-deficient knees. rthroscopy 2003; 19: Margheritini F, Mariani PP. Diagnostic evaluation of posterior cruciate ligament injuries. Knee Surg Sports Traumatol rthrosc 2003; 11: urger RS, Larson RL. cute ligamentous injury. W158 JR:191, October 2008

5 In: Larson RL, Grana W, eds. The knee: form, 9. Grover JS, assett LW, Gross ML, Seeger LL, Radiology 2001; 219: function, pathology, and treatment. Philadelphia, Finerman G. Posterior cruciate ligament: MR 14. kisue T, Kurosaka M, Yoshiya S, Kuroda R, Mi- P: Saunders, 1993: imaging. Radiology 1990; 174: zuno K. Evaluation of healing of the injured pos- 5. Schulz MS, Russe K, Weiler, Eichhorn HJ, 10. Shelbourne KD, Davis TJ, Patel DV. The natural terior cruciate ligament: analysis of instability Strobel MJ. Epidemiology of posterior cruciate history of acute, isolated, nonoperatively treated and magnetic resonance imaging. rthroscopy ligament injuries. rch Orthop Trauma Surg 2003; posterior cruciate ligament injuries: a prospective 2001; 17: : Dandy DJ, Pusey RJ. The long-term results of unrepaired tears of the posterior cruciate ligament. J one Joint Surg r 1982; 64: Sonin H, Fitzgerald SW, Friedman H, Hoff FL, Hendrix RW, Rogers LF. Posterior cruciate ligament injury: MR imaging diagnosis and patterns of injury. Radiology 1994; 190: Niitsu M, nno I, Fukubayashi T, Shimojo H, Kuno S, kisada M. Tears of cruciate ligaments and menisci: evaluation with cine MR imaging. Radiology 1991; 178: study. m J Sports Med 1999; 27: Shino K, Horibe S, Nakata K, Maeda, Hamada M, Nakamura N. Conservative treatment of isolated injuries to the posterior cruciate ligament in athletes. J one Joint Surg r 1995; 77: mis, Gupte CM, ull M, Edwards. natomy of the posterior cruciate ligament and the meniscofemoral ligaments. Knee Surg Sports Traumatol rthrosc 2006; 14: Cho KH, Lee DC, Chhem RK, et al. Normal and acutely torn posterior cruciate ligament of the knee at US evaluation: preliminary experience. 15. Mair SD, Schlegel TF, Gill TJ, Hawkins RJ, Steadman JR. Incidence and location of bone bruises after acute posterior cruciate ligament injury. m J Sports Med 2004; 32: Sanders TG, Miller MD. systematic approach to magnetic resonance imaging interpretation of sports medicine injuries of the knee. m J Sports Med 2005; 33: Ross G, Chapman W, Newberg R, Scheller D Jr. Magnetic resonance imaging for the evaluation of acute posterolateral complex injuries of the knee. m J Sports Med 1997; 25: JR:191, October 2008 W159