Knee dislocations: a magnetic resonance imaging study correlated with clinical and operative findings

OBJECTIVES: Our objectives were to determine retrospectively the prevalence, patients' demographics, mechanism of injury, combination of torn ligaments, associated intra-articular and extra-articular injuries, fractures, bone bruises, femoral-tibial alignment and neurovascular complications of knee dislocations as evaluated by magnetic resonance (MR) imaging. MATERIALS AND METHODS: From 17,698 consecutive knee examinations by magnetic resonance imaging (MRI) over a 6-year period, 20 patients with knee dislocations were identified. The medical records of these patients were subsequently reviewed for relevant clinical history, management and operative findings. RESULTS: The prevalence of knee dislocations was 0.11% [95% confidence interval (95% CI) 0.06-0.16)]. There were 16 male patients and four female patients, with ages ranging from 15 years to 76 years (mean 31 years). Fifteen patients had low-velocity injuries (75%), of which 11 were amateur sports related and four were from falls. Four patients (20%) had suffered high-velocity trauma (motor vehicle accidents). One patient had no history available. Anatomic alignment was present at imaging in 16 patients (80%). Eighteen patients had three-ligament tears, two had four-ligament tears. The four-ligament tears occurred with low-velocity injuries. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were torn in every patient; the lateral collateral ligament (LCL) was torn in 50%, and the medial collateral ligament (MCL) in 60%. Intra-articular injuries included meniscal tears (five in four patients), fractures (eight in seven patients), bone bruises (15 patients), and patellar retinaculum tears (eight partial, two complete). The most common extra-articular injury was a complete biceps femoris tendon tear (five, 25%). There were two popliteal tendon tears and one iliotibial band tear. One patient had received a vascular injury following a motor vehicle accident (MVA) and had been treated prior to undergoing MRI. Bone bruises (unrelated to fractures), four-ligament tears, biceps femoris tears, and popliteus tendon tears were encountered only in the low-velocity knee dislocations. Twelve were treated surgically, five conservatively, and three had been lost to follow-up. The biceps femoris tendon was repaired in every patient who was treated surgically. CONCLUSIONS: Knee dislocations occurred more commonly in low-velocity injuries than in high-velocity injuries, predominantly affecting amateur athletes. Biceps femoris tendon tears were the most common extra-articular injury requiring surgery. Neurovascular injury (5%) was uncommon. At imaging, femoral-tibial alignment was anatomic in the majority of patients.     

The knee: surface-coil MR imaging at 1.5 T1

Seven normal knees (in five volunteers) and seven injured knees (in seven patients) were examined by high-resolution magnetic resonance (MR) imaging at 1.5 T with a surface coil. Seven medial meniscal tears, three anterior cruciate ligament tears, one posterior cruciate ligament avulsion, an old osteochondral fracture, femoral condylar chondromalacia, and one case of semimembranous tendon reinsertion were identified. MR images correlated well with recent double-contrast arthrograms or results of surgery. All tears were identified in both the sagittal and coronal planes. Because of its ability to demonstrate small meniscal lesions and ligamentous injuries readily, MR imaging with a surface coil may eventually replace the more invasive arthrography.     

MR imaging of patellar retinacular ligament injuries

Seventeen patients with patellar retinacular ligament injuries were evaluated with magnetic resonance (MR) imaging. MR findings were correlated with clinical, surgical, and arthroscopic findings. The injuries involved the medial retinacular ligament in 16 of 17 patients and the medial and lateral retinacular ligament in one patient. Nine of 17 patients showed MR evidence of a patellar dislocation. In these patients, a triad of findings that included focal impaction injuries involving the lateral femoral condyle, osteochondral injuries of the medial patellar facet, and injuries of the medial retinacular ligament were seen. Seven of the nine patients with patellar dislocation injuries had frank osteochondral injuries. The injured retinaculum had an indistinct, irregular appearance associated with edema and hemorrhage. The patellar dislocations were clinically unsuspected in the initial evaluation of eight of these nine patients. In eight of 17 patients, the mechanism of injury was a patellar tendon tear (n = 1) or valgus hyperextension (n = 7). In the seven patients with hyperextension injuries, three had associated meniscal and cruciate ligament tears. MR imaging can help define patellar retinacular and associated osteochondral injuries, which may be clinically useful information.     

Acute knee injuries

Skeletally immature athletes do get major knee injuries. Hemarthrosis is associated with peripheral meniscal tears, anterior cruciate ligament ruptures, tibial tubercle avulsion injuries, and patellar/femoral osteochondral fractures and cannot be ignored. The primary diagnostic tool for patients with a knee injury is a clinical examination by a physician well trained in knee evaluation. MR imaging has significant limitations in this age group. The algorithm for anterior cruciate ligament injury treatment must take into account the patient's physiologic maturity, not chronological age.     

MR imaging of the knee in the sagittal projection: comparison of three-dimensional gradient-echo and spin-echo sequences

Fifty patients with suspected internal derangement of the knee had arthroscopic examinations after MR imaging with both a standard T1-weighted spin-echo (SE) sequence and a three-dimensional (3-D) gradient-echo sequence. This series permitted correlative evaluation of 100 menisci and 50 anterior cruciate ligaments. Meniscal tears were diagnosed when intrameniscal signal communicated with the meniscal surface. Criteria for diagnosing anterior cruciate ligament disruption included absence or discontinuity of the ligament, ligamentous laxity, and hyperflexion of the posterior cruciate ligament. Arthroscopic surgery confirmed the presence of 39 meniscal tears and 11 anterior cruciate ligament tears in this population. The sensitivity and specificity of the SE sequence for the diagnosis of meniscal tears were 77% and 98%, respectively. The 3-D gradient-echo sequence had a sensitivity of 87% and a specificity of 88%. For disruption of the ligament, the SE technique had a sensitivity of 82% and a specificity of 95% and the 3-D technique had a sensitivity of 64% and a specificity of 100%. Although these differences in sensitivity and specificity are not statistically significant at the p less than .05 level, probably because of the small sample size, the results show the relative strengths and weaknesses of the two imaging sequences. These data suggest that because of the complementary results of the two MR techniques, both the SE and the 3-D gradient-echo sequences have a role in the diagnosis of knee injuries.     

Magnetic resonance diagnosis of meniscal tears in patients with acute anterior cruciate ligament tears

OBJECTIVE: To evaluate the accuracy of magnetic resonance imaging in the diagnosis of meniscal tear in patients with acute anterior cruciate ligament tears. METHODS: Magnetic resonance images obtained from 41 patients imaged within 6 weeks of injury who had acute anterior cruciate ligament tears identified at arthroscopy were retrospectively reviewed for meniscal tear. RESULTS: With MR imaging the sensitivity, specificity and accuracy for diagnosing meniscal tears in the presence of acute anterior cruciate ligament tears were 71%, 93%, and 88%; for the lateral meniscal tears were 57%, 100% and 85%; and for the medial meniscal tears were 100%, 88%, 90%. All false negative cases (n = 6) involved the posterior horn of the lateral meniscus. CONCLUSION: In the presence of acute anterior cruciate ligament tears, MRI imaging has relatively low sensitivity for detecting meniscal tears due to missed tears in the lateral meniscus.     

Knee injuries: high-resolution MR imaging

Recent technologic advances have made high-resolution magnetic resonance (MR) imaging of the knee a clinical reality. Ten healthy volunteers and 30 patients with suspected knee injuries were imaged using receive-only surface coils and two-dimensional multisection or three-dimensional selective acquisition techniques. Arthroscopic and/or surgical correlation was available in 15 patients. Tears of the cruciate ligament, medial collateral ligament, and meniscus are illustrated. Nonorthogonal views of the anterior cruciate ligament are useful for demonstrating both femoral and tibial attachments in the same section. The posterior cruciate ligament is usually well seen on sagittal views. T2-weighted images are helpful for demonstrating collateral ligament tears and meniscal tears when joint effusion is present. Thin sections (1-5 mm) are necessary to define many meniscal and cruciate tears. High-resolution, thin-section MR imaging can be used to diagnose soft-tissue injuries of the knee and has the potential to become a major imaging method in the evaluation of knee injuries.     

Recent advances in magnetic resonance imaging of the knee

The examination of the knee has rapidly become the most important non-neurologic application of MR imaging. The widespread availability of high signal-to-noise knee coils has made routine imaging with T2-weighted sequences in both coronal and sagittal planes possible in 30 minutes. The spin-echo sequence remains the most important imaging technique, although many newer sequences have also been applied to the knee, with varying degrees of success. Important pitfalls in diagnosis, such as high signal intensity in the posterior horn of the medial meniscus and the transverse meniscal ligament, displaced buckethandle meniscal tears, and discoid menisci, can be recognized with experience. Common clinical problems that are encountered include meniscal cysts, osteonecrosis, and bone bruises. Detection of subtle injuries of the medial collateral ligament, patellar tendon, and anterior cruciate ligament requires careful observation. Intra-articular loose bodies can be reliably detected with MR imaging, and it should be recognized that localized pigmented villonodular synovitis can sometimes simulate the appearance of a loose body. MR imaging is a valuable noninvasive procedure that is complementary to arthroscopy in the evaluation of diseases of the knee.     

Tears of cruciate ligaments and menisci: evaluation with cine MR imaging

A cine magnetic resonance (MR) imaging technique, involving the acquisition of kinematic sagittal images during knee movement, was used to evaluate 52 symptomatic knee joints. Results were compared with those obtained by means of static three-dimensional (3D) MR imaging. Twenty-seven of the 28 anterior cruciate ligament (ACL) tears and 22 of 24 normal ligaments were correctly identified at cine MR imaging for a sensitivity of 96% and a specificity of 92%. Static 3D MR imaging yielded a sensitivity of 71% and a specificity of 88%. All four posterior cruciate ligament tears were identified at cine and 3D MR imaging. For meniscal tears, cine MR imaging yielded a sensitivity of 48% and a specificity of 96%; the sensitivity and specificity for 3D MR imaging were 71% and 96%, respectively. Cine MR imaging proved to be more useful than static MR imaging in assessing the tightness of cruciate ligaments, especially of those that were partially torn, and in assessing the movement of meniscal-free fragments. The increased information obtained with cine MR imaging may warrant continued investigation and clinical application.     

Posteromedial tibial plateau injury including avulsion fracture of the semimembranous tendon insertion site: ancillary sign of anterior cruciate ligament tear at MR imaging.

PURPOSE: To evaluate posteromedial tibial plateau injuries of or about the semimembranous tendon insertion site and their association with anterior cruciate ligament (ACL) tears on magnetic resonance (MR) images. MATERIALS AND METHODS: A retrospective study of MR images and conventional radiographs was performed in 10 patients with posteromedial tibial plateau injuries, including avulsion fractures of the semimembranous tendon insertion site. Associated abnormalities were analyzed, including ACL tears, medial meniscal tears, and other lateral femorotibial compartment injuries. Findings from the clinical history and physical examination were correlated with radiographic and MR imaging findings. Nine patients had arthroscopically or surgically documented ACL tears. RESULTS: All 10 patients had ACL tears at MR imaging. Five patients had posteromedial tibial plateau fractures: Four had avulsion fractures of the tendon insertion site, and one had a fracture lateral to the site. Five patients had posteromedial tibial plateau bruises: Two had bruises at the tendon insertion site. Five patients had tears of the posterior horn of the medial meniscus. Two patients had posterior meniscocapsular separations. Three patients showed evidence of the O'Donoghue triad. Six patients had bruises of the lateral tibial plateau and of the lateral femoral condyle. CONCLUSION: There appears to be an association between posteromedial tibial plateau injuries and ACL tears. Posteromedial tibial plateau injuries may be predictive of ACL status.     

Anterior cruciate ligament tears: MR imaging-based diagnosis in a pediatric population

PURPOSE: To evaluate the diagnostic accuracy of primary and secondary magnetic resonance (MR) imaging findings of anterior cruciate ligament (ACL) tears in young patients with immature skeletal systems. MATERIALS AND METHODS: MR images obtained in 43 patients aged 5-16 years who underwent arthroscopy were retrospectively reviewed. Two reviewers evaluated primary findings (abnormal signal intensity, abnormal course as defined by Blumensaat angle, and discontinuity), secondary findings (bone bruise in lateral compartment, anterior tibial displacement, uncovering of posterior horn of lateral meniscus, posterior cruciate ligament line, and posterior cruciate angle), and meniscal and other ligamentous injuries. RESULTS: There were 19 ACL tears and 24 intact ACLs. Overall sensitivity and specificity of MR imaging in detecting ACL tears were 95% and 88%, respectively. Sensitivities of the primary findings were 94% for abnormal Blumensaat angle; 79%, abnormal signal intensity; and 21% discontinuity. The specificity of all primary findings was 88% or greater. The sensitivity and specificity of the secondary findings, respectively, were 68% and 88% for bone bruise; 63% and 92%, anterior tibial displacement; 42% and 96%, uncovered posterior horn of lateral meniscus; 68% and 92%, positive posterior cruciate line; and 74% and 71%, abnormal posterior cruciate angle. Fifteen (79%) patients had meniscal tears, and five (26%) had collateral ligament injuries. CONCLUSION: Primary and secondary findings of ACL tears in young patients have high specificity and are useful for diagnosis.     

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.     

膝关节半月板损伤的MRI与关节镜对照研究

目的评价MRI在膝关节半月板撕裂诊断和评级中的价值。方法参照Mesgarzadeh标准对76位患者78个撕裂半月板的MR影像作回顾性分析,3位MRI主治医师在不知道关节镜检查结果的情况下独自阅片,按Mesgarzadeh的分级标准确定半月板撕裂的类型并记录评定结果,包括联合的前交叉韧带撕裂。结果MRI诊断半月板撕裂的敏感性和特异性分别为92%和87%,Ⅵ型是半月板撕裂中最常见的类型,尤其在发生移位的半月板撕裂中最常见。结论MRI是半月板撕裂伤和交叉韧带损伤的可靠诊断工具。     

The deep lateral femoral notch: an indirect sign of a torn anterior cruciate ligament.

Magnetic resonance (MR) imaging has shown that tears of the anterior cruciate ligament (ACL) are frequently accompanied by meniscal and osseous injuries. Abnormalities of the cartilage overlying the lateral femoral condylopatellar sulcus (notch) also have been noted during arthrotomy of ACL-deficient knees. In this study, the appearance of this sulcus on MR images and the depth of the sulcus on conventional radiographs are compared in patients with normal and torn ACLs to determine whether a deep sulcus is a useful indirect sign of a torn ACL. In 62 patients with clinically and/or arthroscopically confirmed normal ACLs, the mean depth of the lateral femoral sulcus was 0.45 mm (range, 0.0-1.2 mm) compared with 0.89 mm (range, 0.0-5.0 mm) in 41 patients with clinically and/or arthroscopically confirmed ACL tears (significant at the 5% level). No patient with a normal ACL had a sulcus greater than 1.2 mm in depth. A sulcus deeper than 1.5 mm is equivalent to 3 standard deviations above the mean and was a reliable indirect sign of a torn ACL.     

MR imaging of posterior cruciate ligament injuries

Posterior cruciate ligament(PCL) injuries are less frequent than anterior cruciate ligament(ACL) injuries, but are presumably more common than once thought. Thirty-nine patients with PCL injuries identified on MR images were studied. The criteria for PCL injury were complete tear, partial tear, and avulsion fracture. The approximate site of a partial tear was categorized as proximal, midsubstance, distal, or combination. Fourteen patients(35.9%) had complete tears of the PCL, 21 patients(53.8%) had partial tears, and four patients(10.3%) had avulsion fractures. A total of 12 patients (30.7%) had isolated PCL injuries, while the remaining 27 patients demonstrated evidence of other coexistent knee injuries, such as meniscal tears and ligamentous injuries. Of coexistent knee injuries, meniscal tears(18 patients, 46.2%) were most often seen.     

Diagnostic efficacy in knee MRI comparing conventional technique and multiplanar reconstruction with one-millimeter FSE PDW images

Background: Magnetic resonance (MR) imaging has proved to be an excellent tool in diagnosing injuries of the cruciate ligaments and menisci. However, multiple planes and sometimes optimal oblique or double-oblique scan planes are needed due to the variability in the positioning of important structures, which means there is a lower throughput and longer scanning time.

Purpose: To compare the performance of a 1-mm-thickness fast spin-echo (FSE) proton-density-weighted (PDW) MR imaging technique with multiplanar reconstruction (MPR) in diagnosing tears of the menisci and cruciate ligaments with that of conventional MR imaging.

Material and Methods: Twenty-five consecutive patients underwent preoperative conventional and 1-mm-thickness FSE PDW MR imaging with subsequent knee arthroscopic surgery. Two musculoskeletal radiologists evaluated the status of the cruciate ligaments and menisci using two sets of MR images (method A: conventional images including seven sequences, taking 26 min; method B: 1-mm-thickness FSE PDW images with MPR, taking 7 min 20 s). The diagnostic efficacies of both methods for tears of the cruciate ligament and menisci were calculated and compared.

Results: Arthroscopic surgery revealed 10 anterior cruciate ligament (ACL) tears, one posterior cruciate ligament (PCL) tear, and 26 meniscal tears. The diagnostic values of both methods were 100% for a cruciate ligament tear. The diagnostic values (sensitivity, specificity, accuracy, positive predictive value, and negative predictive value) for meniscal tears were 90%, 100%, 96%, 100%, and 94% for method A, and 95%, 100%, 98%, 100%, and 97% for method B, respectively. There were no significant differences in the diagnostic values between methods A and B.

Conclusion: 1-mm-slice-thickness FSE PDW imaging with MPR showed comparable performance in diagnosing tears of the cruciate ligaments and menisci to conventional sequences but the scan time was much shorter. Therefore, this technique (method B) might improve the throughput of a 3T MR imaging system.     

Healing potential of meniscal tears without repair in knees with anterior cruciate ligament reconstruction

BACKGROUND: Few previous studies have documented the healing potential of meniscal tears that are left to heal without repair. PURPOSE: To determine the healing rates of meniscal tears left without repair in knees with anterior cruciate ligament reconstruction. STUDY DESIGN: Prospective cohort study. METHODS: One hundred and ninety-two knees were evaluated at the time of anterior cruciate ligament reconstruction and repeat arthroscopy. The healing rates of 41 medial and 42 lateral torn menisci without repair were evaluated by the same 2 surgeons in an identical fashion. RESULTS: Of 41 medial torn menisci left without repair, 22 (56%) were considered completely healed, 3 (7%) were incompletely healed, 11 (24%) were unhealed, and 5 (10%) had expanded unhealed lesions. Of 42 lateral torn menisci, 31 (74%) were considered completely healed, 2 (5%) were incompletely healed, 6 (14%) were unhealed, and 3 (7%) had expanded unhealed lesions. The healing rate of a medial meniscal tear was length dependent and not related to reconstructed ligament stability. CONCLUSIONS: Stable meniscal tears at the time of anterior cruciate ligament reconstruction possibly could be left in situ. However, longer medial meniscal tears are thought to require additional stabilizing procedures.     

Diagnosis of popliteus injuries with MR imaging

Objective. Popliteal muscle and tendon injuries are thought to be unusual. This report describes the magnetic resonance (MR) appearances of popliteus muscle and tendon injuries. Design and patients. The study included 24 patients where the diagnoses of popliteal injuries were prospectively made based on MR appearances. The study group was taken from 2412 consecutive knee MRIs. The injuries were characterized as to involving the muscular or tendinous portions of the popliteus apparatus. Results. In 95.8% (23/24) of patients, the tears of the popliteus involved the muscular portion. The injuries were either partial and interstitial or complete. Three patients had tears of both the muscular and tendinous portions or the tendon alone. The anterior and posterior cruciate ligaments were torn in 16.7% (4/24) and 29.2% (7/24) of patients, respectively. There were medial and lateral meniscal tears in 45.8% (11/24) and 25% (6/24) of patients, respectively. There were injuries of the medial and lateral collateral ligaments in 8.3% (2/24) and 4.2% (1/24) of patients, respectively. Bone bruises and/or fractures were seen in 33.3% (8/24) patients. In 8.3% (2/24) of patients, the popliteus injury was an isolated finding. Conclusion. Popliteus muscle and tendon injuries are not uncommon. They usually occur in conjunction with other significant injuries of the knee and can be characterized with MR imaging.Presented at RSNA, Chicago, Illinois, December 1992     

膝关节韧带损伤的MRI诊断

目的:探讨膝关节韧带损伤的MRI表现及诊断价值。方法:36例临床怀疑膝关节损伤的患者于关节镜及手术前行MRI检查,以关节镜结果作为金标准,前瞻性分析膝关节韧带损伤的MRI表现及诊断价值。结果:关节镜证实前交叉韧带损伤21例,其中完全撕裂15例,部分撕裂6例,后交叉韧带损伤12例,正常患者15例。MRI诊断前交叉韧带损伤的敏感度为95.2%,特异度为80%,准确度为88.9%;诊断后交叉韧带损伤的敏感度为100%,特异度为95.8%,准确度为97.2%。结论:MR1是诊断膝关节韧带损伤的理想检查方法,具有较高的临床应用价值。     

Accuracy of magnetic resonance (0.5 T) in traumatic lesions of the knee. Controlled 87 cases]

In this study the authors investigated the diagnostic accuracy of Magnetic Resonance (MR) imaging as a method to recognise traumatic disorders of the knee; in particular its capability to identify meniscal and cruciate ligaments tears was examined. The results have been compared with those from arthroscopy and/or surgery, which were considered the gold standard of the study. Eighty-seven consecutive patients with suspected traumatic injury of the knee were prospectively studied. All patients underwent MR examination (0.5 Tesla magnet, gradient echo sequences, slices thickness = 5 mm) and, within 15 days/1 month, arthroscopy or surgery. The high diagnostic accuracy (internal meniscus = 87.5%; external meniscus = 88.5%; anterior cruciate ligament = 93.1%; posterior cruciate ligament = 96.5%) has confirmed the good diagnostic capabilities of MR in assessing traumatic lesions of the knee.