MR imaging of the postoperative knee: a pictorial essay.

Magnetic resonance (MR) imaging of the postoperative knee has become more common because more arthroscopic repair procedures are being performed. The most common procedures include partial meniscectomy and meniscal repair, anterior cruciate ligament (ACL) reconstruction, and cartilage repair procedures. Specific findings of a retorn meniscus following meniscal repair or partial meniscectomy are increased signal intensity extending through the site of repair on T2-weighted images, displaced meniscal fragments, and abnormal signal intensity at a site distant from the repair. Findings of ACL graft disruption on T2-weighted MR images include absence of intact graft fibers and increased signal intensity similar to that of fluid within the expected region of the graft. Partial tears of the graft appear as areas of increased signal intensity affecting a portion of the graft with some intact fibers still present. An impinged ACL graft may appear to be draped over the anterior inferior edge of the intercondylar roof or be posteriorly bowed. Localized anterior arthrofibrosis appears on T1-weighted MR images as a focal nodular lesion of low signal intensity that is anterior to the ACL graft in the intercondylar notch and is indistinguishable from adjacent joint fluid. On T2-weighted images, the nodule is well differentiated from high-signal-intensity joint fluid. Finally, MR imaging has been shown to be accurate in the evaluation of cartilage repair tissue. Knowledge of the normal MR imaging appearance of the knee after the more common repair procedures will allow radiologists to recognize complications associated with such procedures.     

前交叉韧带部分断裂的诊治

目的 :探讨前交叉韧带 (anteriorcruciateligament,ACL)部分断裂的诊断方法和治疗方式。方法 :2 0 0 0年 3月～ 2 0 0 2年 6月收治ACL部分断裂患者 2 4例 ,其中 7例以前内束断裂为主 ,17例以后外束断裂为主。所有病例均经关节镜检查确诊 ,其中行关节镜下ACL重建者 16例。结合症状、体征和MRI进行诊断 ,并比较前内束断裂和后外束断裂临床表现的差异。术后随访 9～ 13个月 ,平均 11个月。对手术前后膝关节Lysholm评分结果进行统计分析。结果 :本组病例出现关节不稳的 ,ACL前内束断裂者占 2 8 6 % ,后外束断裂者占 98 2 % ;体检前抽屉试验 (ADT)、Lachman试验和轴移试验 (PST)阳性率 ,前内束断裂者分别为 71 4 %、14 3%和 0 ;后外束断裂者分别为 17 6 %、98 2 %和 76 5 %。ACL重建术后Lysholm评分平均为 93 4 7± 2 6 2 ,较术前 (6 3 5 3± 8 11)明显提高(P <0 0 1)。结论 :ACL部分断裂根据损伤部位的不同临床表现也存在差异。后外束断裂者出现关节不稳较前内束常见 ,前内束断裂主要表现为前抽屉试验阳性 ,而后外束断裂常表现为Lachman试验和轴移试验阳性。对于伴有关节不稳的 ,手术重建ACL效果良好。     

前交叉韧带斜冠状面薄层解剖断面与MRI表现对照研究

目的对冰冻膝关节前交叉韧带（ACL）斜冠状面薄层解剖断面与正常人膝关节MRI特点进行对照研究，为ACL损伤分级诊断建立基础。方法1例（1只）膝关节标本行斜冠状面MRI确定角度，冰冻后沿斜冠状面1mm层厚铣切，观察ACL薄层解剖特点。选择50名正常人对其ACL进行MR斜冠状面扫描，观察ACL的MRI特点。结果1只膝关节标本的ACL在斜冠状面薄层断面清晰显示其全程走行，清晰地显示ACL前内束与后外束，前内束从股骨髁附着点后上方区自后向外侧及前内侧走行，止于髁间棘附着区前内侧方，后外侧束从股骨髁附着点前下方区，自后外侧及外下走行，止于髁间棘附着区后外侧方。斜冠状面MRI能够显示50名正常人ACL全程，显示率为100％。MRI能够区分ACL前内束与后外束结构，显示前内束自后外侧向前内走行，止于髁间棘附着区前内侧方，后外束自后外侧向外下走行，止于髁间棘附着区后外侧方。MRI显示ACL走行与薄层断面显示的走行一致。结论斜冠状面是观察ACL的最佳方位，临床对怀疑ACL损伤的患者必要时行MR斜冠状面扫描。     

Anterior cruciate ligament reconstruction: evaluation with MR imaging

Fifty magnetic resonance (MR) imaging examinations were performed in 37 patients after arthroscopic anterior cruciate ligament (ACL) reconstruction with patellar bone-tendon-tibial bone autografts. T1-weighted sagittal and axial images were obtained. In 34 patients with clinically stable ACL autografts, 43 of 47 MR examinations demonstrated a well-defined, intact ACL autograft. All three patients with ACL laxity failed to demonstrate a well-defined autograft, for an overall correlation between MR imaging and clinical examination results of 92%. Of the 12 patients who underwent second-look arthroscopy, 100% correlation was present between MR imaging and arthroscopic results. As in the nonreconstructed knee, buckling of the posterior cruciate ligament was suggestive of ACL laxity. MR imaging also documented optimum placement of bone tunnels in the femur and tibia. MR imaging has proved to be an excellent noninvasive imaging modality for evaluating ACL reconstruction, while also providing ancillary information about the postoperative knee.     

膝关节前十字韧带撕裂的MRI诊断价值

目的：评价MRI诊断前十字韧带撕裂的价值。方法：对临床拟诊为膝关节前十字韧带撕裂的12例患者，对照分析其MRI资料及手术结果。结果：MRI矢状面9例，冠状面7例显示前十字韧带撕裂。12例中8例前十字韧带内有不规则高信号，4例前十字韧带前缘呈不规则波浪状，1例前十字韧带不连续。12例中6例伴后外侧胜分平台分析。MRI确诊11例。结论：MRI诊断前十字韧带撕裂是有价值的，膝关节后外侧胜管平台分析高度提示急性前十字韧带撕裂。     

Grading of anterior cruciate ligament injury. Diagnostic efficacy of oblique coronal magnetic resonance imaging of the knee

OBJECTIVE: This study was undertaken to evaluate the diagnostic efficacy of additional oblique coronal magnetic resonance (MR) imaging of the knee for the grading of anterior cruciate ligament (ACL) injury. METHODS: We retrospectively reviewed MR images of the knee in 169 patients. The MR examinations included routine sequences and oblique coronal T2-weighted images, which oriented in parallel to the course of the femoral intercondylar roof. Two independent readers evaluated the status of the ACL by routine knee MR imaging and then by additional oblique coronal imaging. The severity of the ACL injury was graded using a 4-point system from MR images, namely, intact, low-grade partial tear, high-grade partial tear, and complete tear, and results were compared with arthroscopic findings. Weighted kappa statistics were used to analyze the diagnostic accuracy of routine knee MR imaging with and without additional oblique coronal imaging. RESULTS: The weighted kappa scores (kappaws) were 0.752 (reader 1) and 0.784 (reader 2) by routine knee MR imaging only; with additional oblique coronal imaging, the kappaws increased to 0.809 (reader 1) and 0.843 (reader 2). Interobserver agreements for routine knee MR imaging and additional coronal imaging were considered to be "very good" (kappaw = 0.851, 0.868, respectively). CONCLUSION: Additional use of oblique coronal MR imaging of the knee improves diagnostic accuracy in the grading of ACL injury.     

The diagnostic accuracy of ruptures of the anterior cruciate ligament comparing the Lachman test, the anterior drawer sign, and the pivot shift test in acute and chronic knee injuries

Eighty-five patients with knee injuries were included in a 4 month retrospective study that compared the relative accuracy of the Lachman test, the anterior drawer sign, and the pivot shift test. All examinations were performed under anesthesia and followed by arthroscopy, which confirmed 22 injuries. Of all ACL injuries occurring within 2 weeks of arthroscopy (N = 9), the pivot shift test was the most sensitive (88.8%), followed by the Lachman test with a 77.7% sensitivity. The anterior drawer sign was the least sensitive at 22.2%. All had specificities more than 95%. For all injuries of more than 2 weeks (N = 13), the Lachman and pivot shift tests were 84.6% sensitive, while the anterior drawer sign increased to a sensitivity of 53.8%. Again, all were specific to more than 95%. For all ACL injuries, irrespective of age, the Lachman test was 81.8% sensitive and 96.8% specific; the anterior drawer sign was 40.9% sensitive and 95.2% specific; and the pivot shift was 81.8% sensitive and 98.4% specific. The data support an accurate preoperative diagnosis in ACL deficient knees when the Lachman and pivot shift tests are positive, and essentially rules out this type of injury when these tests are negative. The anterior drawer sign, although widely used, is a poor diagnostic indicator of ACL injuries, especially in the acute setting.     

A comparison of acute anterior cruciate ligament examinations. Initial versus examination under anesthesia

The preoperative examination, the examination under anesthesia, and the findings at surgery were compared for acutely injured knees that were found at surgery to have anterior cruciate ligament (ACL) tears. The pivot shift was initially positive in only 35% of the knees; however, under anesthesia 98% were positive. The Lachman test was initially positive in 99% of the knees, and under anesthesia, 100%. The anterior drawer sign was present initially in 70% of the knees, and under anesthesia this increased to 91%. Of the 37 patients with isolated ACL tears, only 20 (54%) had initially positive anterior drawer signs. In the knees in which secondary restraints to anterior-posterior motion were injured, this percentage increased to 69% in medial meniscus injury, 82% in lateral meniscus injury and 89.5% in rupture of the medial collateral ligament (MCL). The Lachman test seems relatively unaffected by associated ligamentous or meniscal injuries, but the end point in the Lachman test is absent in all complete ACL tears. The pivot shift phenomenon, which was demonstrable in 98% of patients when tested under anesthesia, may be diminished when there is a MCL injury or absent in partial ACL tears. Experience in performing the Lachman test and in appreciating the quality of the end point will give the examiner a high degree of accuracy in making the diagnosis of an ACL tear without resorting to anesthesia, arthroscopy, or arthrography in most patients.     

Comparison of clinical tests and the KT1000 in the diagnosis of anterior cruciate ligament rupture.

A prospective study was undertaken to compare the accuracy of the Lachman test, anterior drawer test and jerk test with the KT1000 knee arthrometer in patients with proven anterior cruciate ligament deficiency. The Lachman and anterior drawer tests were found to be the most accurate indicators of anterior cruciate ligament deficiency. The KT1000 knee arthrometer was found to be totally inaccurate, which precludes its use as an objective measure of anteroposterior laxity of the knee.     

Evaluation of anterior knee laxity on MRI

Purpose

Evaluation of the ACL and anterior knee laxity on MR during anterior tibial translation.

Patients and methods

Three groups were identified based on clinical and arthrometric (KT-1000) data: normal ACL (n = 12), complete tear (n = 10) and partial tear (n = 20). MRI was performed without and with anterior tibial translation (pneumatic device) with morphological and laximetric analysis: drawer tests and dynamic evaluation of ligamentous tension.

Results

Intra- and inter-observer reproducibility was excellent, correlated to arthrometric data and clinical tests (Lachman, pivot shift). The difference between the drawer signs of normal subjects and patients with ACL tear was significant for a threshold value of 1,1 mm for the anterior drawer (sensitivity: 93,33%, specificity: 91,7%) and 2,8 mm for the posterior drawer (sensitivity: 86,7%, specificity: 100%). Dynamic evaluation of ligamentous tension was also reproducible, statistically correlated to the MR drawer tests and reliable for the diagnosis of ACL lesions. In this preliminary study, the distinction between complete and partial ACL tears could not be detected.

Conclusion

Anterior cruciate ligament function can be demonstrated on MR. The predictive value of this morphological and functional association should be determined in the management of patients with partial tears.     

Anomalous insertion of the medial meniscus into the anterior cruciate ligament: the MR appearance

The aim of this study was to determine the characteristic MR findings of the anomalous insertion of the medial meniscus (AIMM) into the anterior cruciate ligament (ACL), and to document potential pitfalls in its interpretation. We reviewed 1326 consecutive knee arthroscopic studies to identify patients with an AIMM. 30 knees of 26 patients (4 females, 22 males; average age, 31.3 years; range, 14-50 years) were included in this study. We evaluated the presence of an AIMM and analysed the MR findings, including the ACL attachment sites of the AIMMs, the absence of the transverse ligament, meniscal tears and a discoid meniscus. AIMMs were detected by MR imaging in 16 knees of 18 patients (60%, 18/30). The AIMMs showed a linear band with low signal intensity on T2 weighted sagittal images running parallel to the ACL. The AIMMs were inserted into the lower portion of the ACL in eight knees, the middle portion in five knees, and the intercondylar notch in five knees. Meniscal tears (10 medial, 10 lateral) were found in 20 knees of 16 patients. Six knees of five patients showed a discoid meniscus. 15 knees of 14 patients showed no transverse ligament on MR imaging. An AIMM has the potential to be misinterpreted as a meniscal tear, ACL tear or infrapatellar plica on knee MR imaging. Familiarity with the characteristic MR findings can aid in the detection of an AIMM into the ACL.     

Knee stability after articulated external fixation

BACKGROUND: Articulated external fixation has been proposed as a method to protect ligament reconstructions while allowing aggressive and early postoperative rehabilitation after knee dislocation. However, the ability of these fixators to protect and stabilize the knee joint has not been clearly determined. HYPOTHESIS: Articulated external fixation can reduce anteroposterior translation in the cruciate-deficient knee and reduce cruciate ligament strain in cases of intact or reconstructed ligaments. STUDY DESIGN: Controlled laboratory study. METHODS: Knee stability was assessed by 3 standard clinical stability tests (Lachman, anterior drawer, and posterior drawer) on 7 human cadaveric lower extremities. Instrumented forces of 100 N were applied to the tibia to measure cruciate ligament forces and tibiofemoral displacement in intact and cruciate-deficient specimens with and without articulated external fixation to determine the degree to which a fixator can protect cruciate ligaments and stabilize the knee. Articulated external fixation was applied using monolateral and bilateral fixators to comparatively analyze the effectiveness of each construct. Statistical analysis was performed using 2-tailed, paired Student t tests. RESULTS: Application of the monolateral articulated external fixator to specimens with intact ligaments significantly reduced cruciate ligament forces by 1.0 N (P = .011), 1.7 N (P = .046), and 1.4 N (P = .009) for Lachman, anterior drawer, and posterior drawer tests, respectively. In the cruciate ligament-deficient knees, the application of a monolateral fixator significantly reduced tibiofemoral translation by 49%, 70%, and 46% for Lachman, anterior drawer, and posterior drawer tests, respectively. No significant differences between the monolateral and bilateral fixator frames, in terms of ligament protection and joint stabilization, were observed.Conclusion and CLINICAL RELEVANCE: Articulated external fixation of the knee can reduce stress in the cruciate ligaments after multiligament reconstructions and can decrease anteroposterior translation in the cruciate-deficient knee.     

The function of the anterior cruciate ligament during anterior drawer and Lachman's testing. An in vivo analysis in normal knees

In order to clarify the function of the anterior cruciate ligament (ACL) during clinical testing an in vivo arthroscopic method of assessing the tension of ACL was developed. Twenty young adult patients with normal knee ligaments and menisci were selected. A spring mechanism in the handle of the specially designed probe allowed the surgeon to apply a known perpendicularly directed force to the ligament while the amount of displacement was observed and recorded. Tension was determined in the anteromedial central and posterolateral portions of ACL before and during an anterior drawer test (knee flexed 90 degrees) and before and during a Lachman's test (knee flexed 15 degrees). The results were consistent in all 20 knees. Baseline tension was greater at 15 degrees of flexion than at 90 degrees. A Lachman's test produced maximal tension in the majority of the ligaments. The anterior drawer did not produce maximal tension in any portion of the ligament. Tension within the anteromedial and central portion of the ligament predominated during both uses. This analysis confirms the specificity of Lachman's test as an indicator of ACL integrity. The concept of two reciprocally functioning ACL "bands" by either anterior drawer or Lachman's test is not supported by our data.     

MRI of anterior cruciate ligament reconstruction.

Eleven asymptomatic patients 1-9 months after arthroscopic assisted anterior cruciate ligament (ACL) reconstruction with autogenous semitendinosus and gracilis tendons as a "neoligament" were studied by MR. Each neoligament was clinically intact. Examinations were performed at 1.5 T with T1- and T2-weighted sagittal and oblique spin echo images in the plane of ACL repair. On MR in 9 of the 11 patients (82%) the ACL neoligament appeared as a smooth well-defined band of low signal intensity along its entire course. In two patients (18%) the integrity of the neoligament could not be determined by MR. Ligaments in which integrity could not be determined demonstrated irregularity or a wavy contour, high signal intensity change within the ligament, or discontinuity of the ligament. We conclude that, contrary to previous reports, MR can demonstrate an intact ACL reconstruction.     

An in vivo strain gage study of elongation of the anterior cruciate ligament

The purpose of this paper is to study the load-elongation characteristics of a Grade II sprain of the anterior cruciate ligament (ACL) at the time of local anesthesia arthroscopy. The data may be used to increase diagnostic and prognostic accuracy when evaluating Grade II ACL sprains and to structure properly a rehabilitation program following ACL injury. This report is based on the data from two in vivo strain gage studies of Grade II ACL sprains. Following instrumentation of the ligament, several events common to physical examination and rehabilitation programs were tested. The Lachman test produced greater elongation of the anteromedial fibers than did the anterior drawer or pivot shift test. A fairly high force of 80 pounds may be required by the examiner's hands to test satisfactorily the anteromedial fibers in the acutely injured large athlete. The proper order for a rehabilitation program should be crutch walking, cycling, walking, slow running, and faster running. Patients should be cautioned to run on a perfectly level surface. Cycling produced 7% as much elongation as an 80 pound Lachman test, and the one leg half squat 21% as much. Quadriceps rehabilitation can be done more safely using these exercises. Quadriceps exercises by knee extension against a 20 pound weight boot in the range of full extension to 22 degrees flexion created peak elongation of the anteromedial fibers ranging from 87 to 121% of that produced by an 80 pound Lachman test. We recommend that quadriceps exercises and testing by knee extension through a full range of motion not be done during the first year following ACL injury or reconstruction.(ABSTRACT TRUNCATED AT 250 WORDS)     

外伤性膝关节前外侧韧带损伤的MR影像特征及相关性分析

目的探讨外伤所致膝关节前外侧韧带损伤病人的MR影像特征,并分析其与前交叉韧带撕裂、外侧半月板撕裂及骨挫伤的相关性,为深入研究前外侧韧带对膝关节稳定性的作用提供可靠依据。方法回顾性分析2016年1月—2017年2月间因外伤进行膝关节MRI检查的320例病人(共321膝)的影像资料。采用美国GE公司生产的Signa HDe 1.5 T MR扫描设备,分别行膝关节斜矢状面T1WI、质子密度加权成像(PDWI)和冠状面、横断面PDWI扫描。根据前外侧韧带的完整性和损伤部位对所有病人进行分类统计。采用独立性卡方检验对前外侧韧带撕裂与前交叉韧带撕裂、外侧半月板撕裂及骨挫伤的相关性进行分析。结果全部病人膝关节MR影像均可显示前外侧韧带,显示率为100%。151/321膝(47.0%;95%CI为41.6%~52.5%)存在前外侧韧带损伤,其中累及胫骨部、股骨部及半月板部的分别为97膝、96膝及65膝。前交叉韧带撕裂158膝,外侧半月板撕裂98膝,股骨外侧髁挫伤58膝,外侧胫骨平台挫伤71膝,分别与前外侧韧带撕裂具有相关性(均P0.001)。结论 MRI检查可以很好地显示前外侧韧带解剖及其损伤情况。膝关节前外侧韧带损伤与前交叉韧带撕裂、外侧半月板撕裂及膝外侧骨挫伤具有相关性。     

Objective assessment of the anterior tibial translation in Lachman test position Comparison between three types of measurement

The purpose of this study was to compare three types of objective measurement in Lachman test position and to validate a new measurement procedure. Twenty-three patients were evaluated after anterior cruciate ligament (ACL) reconstruction at 10 years’ mean follow-up. The contralateral knee had a normal ACL. Both knees were compared using Lachman test, arthrometer, radiological drawer, and electromagnetic sensing device (EMS) measurements. The values were obtained by two trained orthopaedic surgeons independently. Arthrometer assessment was done with the Kneelax 3 (Biodex) at 88 and 132 N. Radiological drawer was measured with a load of 10 kg. EMS is composed of an electromagnetic transmitter and two sensors. Displacement of the sensors was measured along the three perpendicular axes of the transmitter. Data after processing give the displacement of the sensors perpendicular to the tibial axis. The load was applied on the calf perpendicular to the tibial axis with a 10-kg counterweight. Metallic objects must be avoided around the set-up. No significant difference between examiners was observed in clinical (P = 0.45) or objective (P > 0.3) measurements. The best correlation was obtained between arthrometer and EMS measurements (R = 0.94). Arthrometric and radiological drawer were poorly correlated (R = 0.65). The values of the medial radiological drawer were quantitatively similar to the 132 N arthrometric values. The sensitivity of EMS to skin movements was tested. The correlation between the EMS drawer and the other movements was not significant (R≤ 0.37). Quantitative correspondence with Lachman grades was only 36% of the arthrometer and EMS values and 37% of the radiological measurements. The effectiveness of EMS to evaluate anterior tibial displacement in Lachman test position after ACL reconstruction is demonstrated in this study. This method is non-invasive and comfortable for the patient, but needs a careful set-up. This method can potentially be used to assess rotational laxities. Received: 15 November 1996 Accepted: 2 December 1997     

Tears of the anterior cruciate ligament and menisci of the knee: MR imaging evaluation

In 242 of 3,000 patients who underwent magnetic resonance (MR) imaging of the knee between September 1986 and August 1987, original MR imaging reports were compared with subsequent arthroscopic reports to determine the value of MR imaging in the evaluation of suspected meniscal and complete tears of the anterior cruciate ligament. The overall accuracy for the menisci was 93% (sensitivity, 95%; specificity, 91%) with a false-negative rate of 4.8%. For the anterior cruciate ligament the overall accuracy was 95%. T2-weighted sequences were associated with greater sensitivity, specificity, and accuracy than were T1 sequences; the false-negative rate was 0% in the T2-weighted group. MR imaging of the knee is an extremely accurate means for noninvasive assessment of the integrity of the menisci and anterior cruciate ligament, and the accuracy exceeds that usually reported for arthrography.     

Quantitative knee cartilage measurement at MR imaging of patients with anterior cruciate ligament tear

In previous studies, numerous approaches were proposed that assess knee cartilage volume quantitatively using 3D magnetic resonance (MR) imaging. However, the clinical use of these approaches is limited because 3D MR is prone to metal artifacts in postoperative cases. Our purpose in this study was to validate a method for knee cartilage volume quantification using conventional MR imaging in patients who underwent anterior cruciate ligament (ACL) reconstruction surgery. The study included 16 patients who underwent MR imaging before and 1 year after ACL reconstruction surgery. Knee cartilage volumes were measured by our computer-based method with the use of T1-weighted sagittal images. We classified the cartilage into eight regions and made comparisons between preoperative and postoperative cartilage volumes in each region. There was a significant difference between preoperative and postoperative cartilage volumes with regard to medial posterior weight-bearing, medial posterior, lateral posterior weight-bearing, and lateral posterior portions (p = 0.006, 0.023, 0.017 and 0.002, respectively). These results were consistent with the previous studies showing that knee cartilage loss occurs frequently in these portions due to an anterior subluxation of the tibia accompanied by ACL tear. With our method, knee cartilage volumes could be measured quantitatively with conventional MR imaging in patients who underwent ACL reconstruction surgery.     

MR imaging,MR arthrography,and specimen correlation of the posterolateral corner of the knee: an anatomic study

OBJECTIVE: We sought to evaluate the anatomy of the posterolateral aspect of the knee with anatomic dissection, MR imaging, MR arthrography, and sectional anatomy. MATERIALS AND METHODS: We assessed the posterolateral corner of the knee during dissection of one gross anatomic specimen. MR imaging and MR arthrography were performed in seven additional knee specimens. T1-weighted spin-echo MR images were obtained in the standard imaging planes as well as in the coronal oblique plane. The specimens underwent T1-weighted spin-echo MR imaging after administration of intraarticular contrast material and were sectioned into planes corresponding to those of the MR images. RESULTS: At anatomic dissection, the following posterolateral structures were identified: the arcuate ligament (medial and lateral limbs), fabellofibular ligament, popliteofibular ligament, popliteus tendon and its two posterior attachments to the lateral meniscus, fibular collateral ligament, direct and anterior arms of the tendon of the long head of the biceps femoris muscle, and direct and anterior arms of the tendon of the short head of the biceps femoris muscle. Correlation of MR imaging and anatomic findings showed that the popliteofibular ligament and oblique popliteal ligament were found in 57% and 100% of specimens, respectively. At least one of the two limbs of the arcuate ligament was identified in 71% of specimens. The fabellofibular ligament was not identified on MR images in any of the specimens. The anteroinferior and posterosuperior popliteomeniscal fascicles were identified in all specimens. CONCLUSION: The posterolateral corner of the knee comprises complex and variable anatomic structures. Recognition of these variations is important in the assessment of MR images of the knee.