Anterior Cruciate Ligament Tear: Reliability of MR Imaging to Predict Stability after Conservative Treatment

OBJECTIVE: The aim of this study is to evaluate the reliability of MR imaging to predict the stability of the torn anterior cruciate ligament (ACL) after complete recovery of the ligament's continuity. MATERIALS AND METHODS: Twenty patients with 20 knee injuries (13 males and 7 females; age range, 20-54) were enrolled in the study. The inclusion criteria were a positive history of acute trauma, diagnosis of the ACL tear by both the physical examination and the MR imaging at the initial presentation, conservative treatment, complete recovery of the continuity of the ligament on the follow up (FU) MR images and availability of the KT-2000 measurements. Two radiologists, who worked in consensus, graded the MR findings with using a 3-point system for the signal intensity, sharpness, straightness and the thickness of the healed ligament. The insufficiency of ACL was categorized into three groups according to the KT-2000 measurements. The statistic correlations between the grades of the MR findings and the degrees of ACL insufficiency were analyzed using the Cochran-Mantel-Haenszel test (p < 0.05). RESULTS: The p-values for each category of the MR findings according to the different groups of the KT-2000 measurements were 0.9180 for the MR signal intensity, 1.0000 for sharpness, 0.5038 for straightness and 0.2950 for thickness of the ACL. The MR findings were not significantly different between the different KT-2000 groups. CONCLUSION: MR imaging itself is not a reliable examination to predict stability of the ACL rupture outcome, even when the MR images show an intact appearance of the ACL.

The Role of Popliteal Lymph Nodes in Differentiating Rheumatoid Arthritis from Osteoarthritis by Using CE 3D-FSPGR MR Imaging: Relationship of the Inflamed Synovial Volume

OBJECTIVE: We wanted to assess the role of the popliteal lymph nodes for differentiating rheumatoid arthritis (RA) from osteoarthritis (OA), and we also wanted to investigate the relationship between the popliteal lymph nodes and the inflamed synovial volume (ISV) by using contrast enhanced (CE), fat suppressed, three dimensional-fast spoiled gradient echo (3D-FSPGR) MR imaging. MATERIALS AND METHODS: Contrast enhanced 3D-FSGPR MR imaging of 94 knees (21 with RA and 73 with OA) was analyzed. A lymph node was defined as being 'observed' if it could be seen in at least two planes of the three orthogonal reformatted planes. The number of observed lymph nodes, the mean of the smallest dimension of each lymph node and the existence of central fatty change were recorded. The OA group was graded according to the ISV calculated by a segmentation method: grade I was 40 cm3. Statistical analysis of the number and the mean size of the popliteal lymph nodes among the four groups (the RA group and the grade I-III OA groups) was performed. RESULTS: The prevalence of the observed popliteal lymph nodes was significantly different between all the OA groups or between the grade III OA group and the RA group (p < 0.0001, 0.0001, respectively). The popliteal lymph node was observed in 32 out of 73 OA cases, whereas it was visible in all of the 21 RA cases. The number (mean+/-standard deviation) of lymph nodes in the grade I OA group, the grade II OA group, the grade III OA group and the RA group was 1.2+/-0.4, 1.2+/-0.4, 1.3+/-0.5, and 2.7+/-1.1, respectively. The mean size (mean+/-standard deviation) of the lymph nodes was 3.8+/-1.0 mm, 3.6+/-1.1 mm, 4.1+/-0.8 mm, and 5.4+/-1.3 mm, respectively. The incidence of central fatty changes was significantly lower in the RA group than in all the OA groups and the grade III OA group. When differentiating RA from OA, and when the differentiation was confined to the RA group and grade III OA group, respectively, the criteria of the number of lymph nodes, their size, their central fatty change and a combination of all these three criteria showed statistical significance (Az values for the former were 0.869, 0.847, 0.776, and 0.942; Az values for the latter were 0.855, 0.799, 0.712, and 0.916). The number and mean size of the lymph nodes correlated with the ISVs (r = 0.49, p < 0.001; 0.50, 0.001, respectively). CONCLUSION: The number, size and central fatty changes in the popliteal lymph nodes observed on the MR images might serve as simple and useful markers in differentiating RA disease from OA disease. These markers would be particular helpful in cases of severe synovial enhancement where the ISVs of both RA and OA overlap. The number and mean size of the lymph nodes also correlated well with the ISV.

Kissing Contusion Between the Posterolateral Tibial Plateau and Lateral Femoral Condyle: Associated Ligament and Meniscal Tears

PURPOSE: Kissing contusion between the posterolateral tibial plateau and lateral femoral condyle is frequently found in association with a tear of the anterior cruciate liagment (ACL). The purpose of this study was to determine which ligamentous and meniscal tears are associated with kissing contusion. MATERIALS AND METHODS: We retrospectively reviewed the findings depicted by 323 consecutive MR images of the knee and confirmed at arthroscopy. For the diagnosis of disruption, ligaments, medial menisci (MM) and lateral menisci (LM) were evaluated using accepted criteria. We compared the prevalence and location of meniscal and ligamentous tears between group I (44 knees with kissing contusion) and group II (279 knees without kissing contusion). For statistical analysis the chi-square test was used. RESULTS: ACLs were torn in all 44 knees (100%) with kissing contusion, and 78 (28%) of 279 without kissing contusion. There were ten medial collateral ligament (MCL) tears (23%) in group I, and 17 MCL tears (6%), five lateral collateral ligament (LCL) tears (2%) and ten posterior cruciate ligament (PCL) tears (4%) in group II. In group I, meniscal tears were found in 22 MM (50%) and in 19 LM (43%), while in group II, they occurred in 128 MM (46%) and 128 LM (46%). In group I, 17 (77%) of 22 MM tears and 13 (68%) of 19 LM tears were located in the posterior horn, while in group II, the corresponding figures were 97/128 (76%) and 60 of 128 (47%). The differing prevalence of ACL and MCL tears between the groups was statistically significant (p0.05). CONCLUSION: Although kissing contusion was a highly specific sign of ACL tears, its presence was also significant among MCL tears. There was no signifficant difference in meniscal tears with or without kissing contusion.

MR Imaging Findings of Avulsion Fracture of the Tibial Spine of the Knee, Focusing on Cruciate Ligament Tear

PURPOSE: To determine the presence of cruciate ligament tears following avulsion injuries involving the ACL and PCL, and to correlate the findings with those of surgery. MATERIALS AND METHODS: Between March 1997 and May 2002, avulsion injury involving the ACL or PCL was diagnosed in 19 patients. Ten of these [8 males and 2 females aged 10-51 (avergae, 27.7) years] were included in this study. We assessed the presence of cruciate ligament tears at MR imaging, correlating the findings with those of surgery. Associated intra-articular injuries, treatment methods and follow-up results were also evaluated. RESULTS: Among Seven patients with ACL avulsion injury, this was assessed at MR imaging as complete tear (n=1), partial tear (n=5), or intact (n=1), while all MR images of PCL avulsion injury (n=3) showed that this was partial tear. All imaging findings corresponded with the surgical findings. In four patients there was associated knee injury involving, respectively, tears of the medial meniscus, lateral meniscus, PCL and MCL, and popliteal ligament. CONCLUSION: Our findings showed that with one exception, patients with avulsion injury of the ACL or PCL had suffered either a partial or complete tear. MR imaging may be useful in the diagnosis of tears of the cruciate ligament which have not been noticed at surgery or arthroscopy in avulsion injuries involving the ACL and PCL.

MR Evaluation of Radiation Synovectomy of the Knee by Means of Intra-articular Injection of Holmium-166-Chitosan Complex in Patients with Rheumatoid Arthritis: Results at 4-month Follow-up

OBJECTIVE: To determine whether MRI is able to demonstrate the effect of radiation synovectomy after the intra-articular injection of holmium-166-chitosan complex for the treatment of rheumatoid arthritis of the knee. MATERIALS AND METHODS: Fourteen patients aged 36-59 years were treated with 10-20 mCi of holmium-166-chitosan complex. A criterion for inclusion in this study was the absence of observable improvement after 3- or more months of treatment of the knee with disease-modifying anti-rheumatic drugs. MR images were acquired both prior to and 4-months after treatment. Clinical evaluation included the use of visual analog scales to assess pain, and the circumference of the knee and its range of motion were also determined. MR evaluation included measurement of the volume of synovial enhancement and wall thickness, the amount of joint effusion, and quantifiable scoring of bone erosion, bone edema and lymph nodes. RESULTS: Visual analog scale readings decreased significantly after radiation synovectomy (p < 0.05). MRI showed that joint effusion decreased significantly (p < 0.05), and that the volume of synovial enhancement tended to decrease, but to an insignificant extent (p = 0.107). CONCLUSION: The decreased joint effusion noted at 4-month follow-up resulted from radiation synovectomy of the rheumatoid knee by means of intra-articular injection of holmium-166-chitosan complex.

Experimentally Induced Pyogenic Arthritis of Rabbit Knees: Comparative Study of MR Imaging and Pathology

PURPOSE: To compare the MR imaging findings of experimentally induced pyogenic arthritis of rabbit knees with the corresponding histopathologic findings. MATERIALS AND METHODS: Infection was induced in 20 rabbit knees by direct intra-articular injection of Staphylococcus aureus. The animals were divided into four groups of five rabbits each, and spin-echo sagittal T1-and T2-weighted images were obtained 3 days, 1 week, 2 weeks, and 4 weeks, respectively, after staphylococcal inoculation. MR-pathologic correlation was performed, with emphasis on intra-and extra-articular soft tissue lesion characteristics. Soft tissue lesion signal intensity (SI) was classified as low, iso, or high on the basis of that of muscle, and high SI was further subdivided into three categories. RESULTS: At T2-weighted imaging, all soft tissue lesions showed high SI. Pathologic examination revealed the presence of inflammatory cell infiltration (n=2), abscess (n=1), granulation tissue (n=3), fibrosis (n=11), edema (n=4), congestion (n=9), and joint fluid (n=11). Except for the abscess, these lesions were irregular in shape and had variable SI (grade 1-3) and at T2WI could not, therefore, be differentiated. In nine kness, extraarticular soft-tissue lesions were demonstrated at T2WI and correlated with infectious soft tissue lesions such as inflammatory cell infiltration, abscess, granulation tissues and fibrosis; and non-infectious reactive soft tissue changes such as edema and congestion. CONCLUSION: In pyogenic arthritis, the MR imaging features of soft tissue lesions varied and were nonspecific, depending on the histopathologic abnormalities observed. Our results indicate that in assessing the extent of pyogenic arthritis with MR imaging, caution is required.

MRI Differential Diagnosis of Complete and Partial Tears of the Anterior Cruciate Ligament of the Knee: The Usefulness of Oblique Coronal T2-Weighted Image

PURPOSE: To assess the usefulness of T2-weighted oblique coronal MR imaging (T2OCI) in the differential diagnosis of complete and partial tears of the anterior cruciate ligament (ACL) of the knee. MATERIALS AND METHODS: Thirty-three patients with ACL tear (16 complete and 17 partial tears), comfirmed by arthroscopy, were included in this study. Conventional MR imaging and T2OCI were performed, and the findings were retrospectively reviewed by two radiologists in terms of continuity, shape, axis and internal signal intensity of the ligament. Each finding was tested if there were stastistically significant differences in its prevalence between partial and complete tears. The diagnostic accuracy of T2OCI and conventional MR imaging in the detection of partial and complete tears of the ACL were compared. RESULTS: Conventional MR imaging revealed no statistically significant finding for differential diagnosis of complete and partial ACL tears. The reliable and statistically significant (p<0.001) findings of T2OCI were complete discontinuity of the ligament in cases involving complete ACL tears (14 of 16 complete tears and 2 of 17 partial tears) and the preservation of the band form for partial ACL tears (2 of 16 complete tears and 15 of 17 partial tears). The accuracy of T2OCI and conventional MR imaging was 88% and 70%, respectively. CONCLUSION: When ACL injury is vague on conventional MR images, a modality which is more useful in the differential diagnosis of partial and complete tears of the ACL, and in predicting the site of a tear, is T2-weighted oblique coronal imaging.

MR Imaging Findings of Patellar Tendon after Anterior Cruciate Ligament Reconstruction with Bone-Tendon-Bone Autograft

PURPOSE: To evaluate the postoperative changes occurring in the patellar tendon after reconstruction of the anterior cruciate ligament (ACL) using the central one-third of the patellar tendon together with patellar and tibial bony plugs. MATERIALS AND METHODS: Ten patients with ACL injury underwent sagittal and coronal T1-weighted MR imaging of both postoperative and normal knee joints. In all cases, reconstruction of the ACL was performed using the central one-third of the patellar tendon, together with patellar and tibial bony plugs. During the follow-up period of 6-27 months, patient were clinically stable. We compared the length, signal intensity and contour of both patellar tendons, as seen on MR images. RESULTS: No defects was found in harvested patellar tendons, and MR images showed high signal intensity within harvested tendons in six of the ten patients. In seven of ten, patellar tendons had irregular margins and were poorly delineated from adjacent tissue. The mean length of patellar tendons was 44.2+/-2.9 mm in normal knee and 43.9+/-3.1mm in postoperative knee, while their mean thickness in postoperative knee, measured at mid-portion, averaged 4.3+/-1.2 mm. There were no statistically significant differences (p>0.05). The greatest mean thickness of patellar tendon was 6.9+/-1.2 mm and 4.3+/-0.5mm in normal and postoperative knee, respectively. Thus, on average, postoperative patellar tendon was 161% thicker than normal tendon (p<0.05). CONCLUSION: In clinically stable patients, patellar tendons after graft harvesting had a higher signal intensity, worse-defined margins and a greater thickness than normal. We suggest that these are the normal postoperative findings.

MR Findings of Traumatic Transient Lateral Dislocation of the Patellae

PURPOSE: To determine the magnetic resonance (MR) imaging characteristics of traumatic transient lateral dislocation of the patellae. MATERIALS AND METHODS: In eight patients (6 males, 2 females, mean age: 22.4 years) in whom transient lateral dislocation of the patella was diagnosed, the distinctive MR imaging findings reflecting known injury mechanism were retrospectively analyzed with regard to bone contusion, chondral defect, fracture, loose body, joint effusion, and the associated soft tissue abnormalities. RESULTS: All of eight patients had bone contusions in the lateral femoral condyle and medial facet of the patella, while in five, chondral defects were present in this latter region. In three patients, fractures of the on lateral femoral condyle (n=2) and medial facet of the patella (n=3) were noted, and in three others, loose bodies were noted. Joint effusion [simple effusion (n=4), lipohemarthrosis (n=3)] was observed in seven patients, and associated soft tissue injuries [to the medial patellar retinaculum (n=8), patellar tendon (n=2), and anterior cruciate ligament (n=1)] in eight. Patellar subluxation was found in seven. CONCLUSION: MR imaging is a useful technique for the diagnosis of traumatic lateral dislocation of the patella. The significant MR findings are bone contusion in the lateral femoral condyle and medial facet of the patella, chondral defect, fracture, joint effusion, injury to the medial patellar retinaculum, and patellar subluxation.

Evaluation of Meniscal Tears of the Knee: The Usefulness of Fat-Suppressed Conventional Spin-Echo T1-Weighted MR Imaging

PURPOSE: To determine the usefulness of the fat-suppressed (FS) conventional spin-echo (CSE) sequence for the diagnosis of meniscal tears. MATERIALS AND METHODS: We retrospectively reviewed 323 MR images of the knee, the standard of reference being the findings of arthroscopy. In all knees, fast SE proton density-weighted and T2-weighted sagittal and coronal images and double-echo in steady state (DESS) sagittal images were obtained, and during 202 MR Procedures, FS-CSE T1-weighted sagittal images were also obtained. The results of MR imaging were then correlated with those of arthroscopy, the accuracy with which meniscal tears were diagnosed being compared between two groups: group I (202 knees for which FS-CSE T1-weighted sagittal images were obtained), and group II (121 knees for which these images were not obtained). For statistical analysis the chi-square test was used. RESULTS: In group 1, sensitivity, specificity and accuracy were 94.7%, 92.4% and 93.5%, respectively, for the medial meniscus, and 83.3%, 95.7% and 90.5% for the lateral meniscus. In group II, the corresponding findings were 92.5%, 94% and 93.3%; and 87.3%, 98.2% and 92.5%. The differences between the groups were not statistically significant (p>0.05) CONCLUSION: For meniscal tears of the knee, the addition of FS-CSE T1-weighted MR imaging to the fast SE proton density-weighted, T2-weighted and DESS sequences does not enhance diagnostic accuracy.

Bilateral Simultaneous Quadriceps Tendon Rupture in a Patient with Secondary Hyperparathyroidism: A Case Report

Simultaneous bilateral rupture of the quadriceps tendon without a significant history of trauma may occur in association with chronic metabolic disorders such as chronic renal failure and secondary hyperparathyroidism, though has rarely been reported. We describe a case of spontaneous bilateral quadriceps tendon rupture in a 36-year-old female patient with secondary hyperparathyroidism.

Evaluation of Chondromalacia in the Knee Joint using Three Dimensional Fourier Transformation Constructive Interference in Steady State(CISS)

PURPOSE: To assess the usefulness of three-dimensional Fourier transformation constructive interference in steady state (CISS) for the evaluation of chondromalacia. MATERIALS AND METHODS: In 110 knee joints which underwent both MR imaging and arthroscopy, the findings were retrospectively reviewed. MR imaging sequences included two-dimensional dual-echo turbo spin-echo imaging along the sagittal and coronal planes, two-dimensional fast low-angle shot (FLASH) with magnetization transfer along the axial plane, and three-dimensional CISS along the sagittal plane. After the cartilage surfaces of each joint were divided into eight areas (each medial and lateral area of patellar facets, trochlear surfaces, femoral condyles, and tibial plateaux), a total of 880 areas were assessed. Using both combined two-dimensional (2-D turbo spin-echo and FLASH) and CISS imaging during different sessions, each chondromalacia case was assigned one of five grades. RESULTS: Arthroscopy revealed the presence of chondromalacia in 162 areas. This was first grade in 77 areas, second grade in 38, third grade in 21, and fourth grade in 26. The sensitivity, specificity, and accuracy of 2-D and CISS imaging were 48.1%, 93.7% and 85.3%, and 45.7%, 95.3% and 86.1%, respectively. Agreement between MR and arthroscopic staging occurred in 81.48% of 2-D imaging procedures and 82.16% of CISS procedures. If a difference of one grade was accepted, these proportions rose to 84.32% and 85.22%, respectively, though this increase was statistically insignificant. CONCLUSION: Though CISS imaging was less sensitive than 2-D imaging in the grading of chondromalacia, additional CISS imaging can help improve the accuracy of this grading.

The Anterior Cruciate Ligament: The Value of Thin-section Proton Density Oblique Sagittal MR Imaging

PURPOSE: To evaluate the usefulness of thin-section proton density oblique sagittal MR imaging in the diagnosis of tear involving the anterior cruciate ligament (ACL). MATERIALS AND METHODS: In 61 arthroscopically confirmed cases (29 patients with ACL injury and 32 normal subjects), thin section proton-density images (TSPDI) were obtained and compared with conventional oblique sagittal PDI and T2-weighted images (T2WI). In TSPD imaging, the scan plane was parallel to the course of the ACL, based on a coronal scanogram; the parameters used were TR/TE 2000 msec/20 -33 msec, 2-mm slice thickness, 16 x16 cm FOV, 256 x192 matrix, two excitations, and no intersection gap. We evaluated the sensitivity and specificity of MR images for diagnosing ACL tear, and their quality, on the basis of whether or not they successfully visualised the anterior/posterior margin of the ACL and linear signal intensities within the ACL fascicles. We also investigated the effects of partial volume averaging between the proximal portion of the ACL and the lateral femoral condyle. RESULT: The sensitivity/specificity of TSPD imaging for diagnosing ACL tear were not significantly different from those of conventional oblique sagittal PDI and T2WI. In the ACL injury group, TSPDI was better in detecting increased signal intensity, ACL thickening, and visualization of torn ACL than conventional oblique sagittal PDI and T2WI. In normal subjects, image quality was constantly better on TSPDI than on conventional oblique sagittal PDI and T2WI. TSPDI clearly revealed the anterior margin in 31/32 cases (97%) and linear signal intensities within the ACL fascicles in all 32 (100%), and also markedly reduced the partial volume effect of the proximal ACL and lateral femoral condyle. CONCLUSION: In evaluating the ACL, the use of TSPD imaging is likely to lead to improved image quality. In addition, where routine MR imaging reveals indeterminate ACL injury, TSPDI can provide additional clues to diagnosis.

Evaluation of Meniscal Subluxation of the Knee with MR Imaging

PURPOSE: The purpose of this study was to determine the normal meniscal position and meniscal subluxation by means of MR imaging. MATERIALS AND METHODS: The normal position of the meniscus was determined by measuring the distance between the peripheral meniscal borders and the tibial plateau, as seen on coronal, sagittal and oblique MR images of 40 normal knees. For 33 abnormal knees in which outward subluxation of the meniscus from the tibial plateau was noted, the involved site, the predisposing factor, and the frequency of meniscus tearing were analyzed. RESULTS: In normal knees, the peripheral border of the meniscus extruded 3 mm or less from the peripheral border of the tibial plateau. Among 33 abnormal knees, in which 5 mm or more outward subluxation of the meniscus was seen, 19 menisci were medial and 14 were lateral. Among the 19, the body was involved in 12, the anterior horn in six, and the posterior horn in one. With regard to the 14 lateral subluxations, involvement of the posterior horn occurred in ten, of both the body and posterior horn in two, of the anterior horn in one, and of the body in one. The common predisposing factor in medial meniscus subluxation was osteoarthritis, seen in 89% of such cases, and in lateral subluxation, anterior cruciate ligament tear, which occurred in 79% of cases. Medial meniscus tear was noted in 89% of medial meniscus subluxations and lateral meniscus tear in 43% of lateral subluxations. CONCLUSION: Meniscal subluxation was easily detected by MR imaging of the knee. The common predisposing factor in medial meniscus subluxation was osteoarthritis, and in lateral meniscus subluxation, anterior cruciate ligament tear. A torn meniscus frequently cooccurred.

Absent Bow-Tie Sign in Knee MRI

PURPOSE: 'Absent bow-tie sign'is interpreted as positive when a bow-tie-shaped body segment is seen on only one or no slice of 4- or 5-mm thick sagittal images, and is a well known as a useful sign in diagnosing bucket-handle meniscal tears. In practice, however, we have found that this sign was also positive in certain cases other than bucket-handle tears. We have assumed that if the normal range of meniscal body width, as determined among Westerners, is transferred to the Korean population without verification and modification this might lead to misdiagnosis. The purpose of this study, therefore, is to examine the reliability of the 'absent bow-tie sign'. MATERIALS AND METHODS: Among 454 cases in which knee MRI had been performed, we retrospectively evaluated 862 menisci, the total remaining after cases of discoid meniscus or those involving previous meniscectomy had been excluded. Among the 862 menisci, 614 were normal, 97 showed degeneration, 43 showed buck-et-handle tearing, and 108 showed tears other than bucket-handle tear. In all cases, proton-denwity and T2-weighted images were obtained in both sagittal and coronal planes, with 3mm section thickness and 1mm gap. We recorded the number of sagittal images in which the body segment of each meniscus had a bow-tie appear-ance, and measured the width of each meniscal body, as seen on midcoronal images. RESULTS: In all cases but one of bucket-handle tears (97.7%), the bow-tie sign was absent, as it was in 73.2% ofnon-bucket-handle tears, 35.0% of degenerated menisci and 27.5% of normal menisci. Among the non-tear group, 56.4% of menisci in the female group and 27.1% in the male group had bodies less than 9mm wide. CONCLUSION: In the diagnosis of bucket-handle tears, the 'absent bow-tie sign'is a very sensitive indicator. It is nonspecific, however, and merely suggests some significant deficiency in the meniscus body or small menis-ci,so can be positive in other cases. Thus the interpreter should be aware of the characteristics of this sign especially when used to interpret MRI of the knee of a female Korean patient.

MR Imaging of Growth Plate Injury in Rabbit: Development of Bony Bridge and Pathologic Correlation

PURPOSE: To evaluate the MR findings of a development of bony bridge within tunnels drilled across growth plates after injury in immature rabbits, and to correlate the MR and pathological findings. MATERIALS AND METHODS: In 19 young rabbits, a growth-plate injury model was constructed in the distal femur by longitudinal drilling with a 5-mm drill. Coronal scans with T1-weighted, T2-weighted fast spin-echo, gradient echo, and gadolinium enhanced T1-weighted sequences were obtained immediately, and at 1, 2, 3, and 4 weeks, and 3, 6 months, postoperatively. Each group underwent pathologic examination, and the signal intensity, shape, and enhancement pattern of the drill holes were assessed. All results were correlated with pathologic findings. RESULTS: During the early period, the signal intensity of the defect site varied due to hemorrhage and inflammatory reaction in the lesion, becoming isointense to that of metaphyseal marrow on all sequences during the late period (3 and 6 months). Pathologically, it corresponded to replacement of the osseous bridge with fatty marrow. The new bone formation shown by pathologic examination to be present in the periphery of the defect during the first week corresponded to the vertical dark rim seen on MR images. It appeared during that week and became more distinct, thickening gradually until the fourth week. Enhancement was absent or faint on follow-up immediately after surgery, inhomogenous and seen in half the rabbits at week 1, and maximal and homogenous at weeks 2 and 3. In had decreased by week 4, and was absent at months 3 and 6. These findings corresponded to the changes in transphyseal vascularity across the drill hole revealed by pathologic examination. CONCLUSION: The contrast enhancement demonstrated by defective growth plate may indicate the development of vascularity throughout the plate, a phenomenon which precedes the formation of a bony bridge after trauma.

Complete and Partial-Thickness Tears of the Anterior Cruciate Ligament: Differential Features Seen on MRImaging

PURPOSE: To evaluate the differential features of complete and partial-thickness tears of the anteriorcruciate ligament, as seen on magnetic resonance imaging(MRI). MATERIALS AND METHODS: We retrospectvely reviewedMR images of 36 patients with ACL injuries (complete tear 16, incomplete tear 20). In all cases, the presence ofan ACL tear was determined by arthroscopy or surgery. Primary and secondary signs of ACL injury and associatedinjuries were assessed. RESULTS: Ligamentous discontinuity of the ACL was observed in ten complete tears (63 %),but in only four (10%) of those that were partial (p=0.009). In addition, complete tears were more likely to showa low degree of ACL axis, less than 45 degree(11/16 : 2/20, p=0.001). There was, however, no statistically significantdifference between complete and partial tears with regard to signal intensity of ACL, PCL buckling or angle,anterior dis-placement of the tibia, uncovered meniscus sign, deep notch sign, empty notch sign, and associatedinjuries. CONCLUSION: Ligamentous discontinuity and the ACL axis are features which usefully differentiatebetween complete and partial tears of the ACL.

Diagnostic Value of MR Imaging in Differentiation of Meniscal Tear Patterns

PURPOSE: To evaluate the diagnostic accuracy of magnetic resonance (MR) imaging in the differentiation ofmeniscal tear patterns of the knee. MATERIALS AND METHODS: MR images of 93 patients with meniscal tear wereincluded in this study. On the basis of arthroscopic findings, the configuration of meniscal tears was classifiedas horizontal (n=44), longitudinal (n=34), transverse (n=11), or oblique (n=5). Oblique sagittal and coronal MRimages were obtained and com-pared with the arthroscopic findings. RESULTS: Among 94 cases ofarthroscopically-proven meniscal tears, 35 of 44 horizontal and 27 of 34 longitudi-nal configurations werecorrectly interpreted on MR images. Sensitivity and specificity for horizontal configu-ration were 80 % and 80 %,respectively, while the corresponding values for longitudinal configuration were 79 % and 95 %. On MR images, tworadial configurations were correctly interpreted from 11 confirmed tears and only one oblique configuration fromfive confirmed tears. CONCLUSION: MR imaging was useful for the differentiation of horizontal and longitudinaltears, but inaccurate in cases involving radial or oblique tears.

Usefulness of Fat-Suppressed Turbo SE MR Imaging for the Evaluation of Meniscal Tears

PURPOSE: Suppression of the relatively high signal intensity of fat leads to more efficient use of thedynamic range for display of tissue contrast. In order to evaluate meniscal tears, we compared a fat-suppressedturbo spin-echo(FSTSE) sequence with turbo SE(TSE). MATERIALS AND METHODS: One hundred and seven knees in 103consecutive patients referred for MR study of the knee were imaged using both FSTSE and TSE sequence. The turbo SEsequence provided proton density-weighted and T2-weighted images (dual echo technique) with an effectiveecho-train length of five. For fat-suppression, a frequency-selective chemical presaturation pulse was applied.Forty-two knees (84 menisci) were studied arthroscopically and the findings were taken as the reference standard.FSTSE and TSE images were reviewed retrospectively by two radiologists. Next, for each patient, the quality ofFSTSE and TSE images was compared;the former were scored by each reviewer as either superior to, equal to, orinferior to TSE images. RESULTS: Among the 214 menisci evaluated, the results of FSTSE and TSE imaging were verysimilar (kappa index 0.87). Twenty four tears were found during arthroscopy in 84 menisci. FSTSE imaging was moresensitive than TSE (96% versus 83%), though specificity was equal(98%). Among the 107 cases, FSTSE images wererated by both observers as superior to TSE images for overall quality and visualization of the meniscus itself.CONCLUSION: For the evaluation of meniscal tears, FSTSE sequences were more sensitive than those obtained withTSE, and their image quality was superior. For the study of meniscus tears among a large population, FSTSE istherefore more useful than TSE.

MR Imaging of Articular Cartilage: Comparison of Magnetization Transfer Contrast and Fat - Suppression inMultiplanar and 3D Gradient-Echo, Spin-Echo, Turbo Spin-Echo Techniques

PURPOSE: The purpose of this study was to evaluate the effects of magnetization transfer contrast(MTC) andfat-suppression(FS) in variable spin-echo and gradient-echo sequences for articular cartilage imaging and todetermine the optimal pulse sequences. MATERIALS AND METHODS: Using variable 7-pulse sequences, the knees of 15pigs were imaged Axial images were obtained using proton density and T2-weighted spin-echo (PDWSE and T2WSE),turbo spin-echo (TSE), multiplanar gradient-echo (MPGR), and 3D steady-state gradient-echo (3DGRE) sequences, andthe same pulse sequences were then repeated using MTC. Also T1-weighted spin-echo(T1WSE) and 3D spoiledgradient-echo(3DSPGR) images of knees were also acquired, and the procedure was repeated using FS. For each knee,a total of 14 axial images were acquired, and using a 6-band scoring system, the visibility of and thevisibilities of the the articular cartilage was analyzed. The visual effect of MTC and FS was scored using a4-band scale. For each image, the signal intensities of articular cartilage, subchondral bone, muscles, and salinewere measured, and signal-to-noise ratios(SNR) and contrast-to-noise ratios(CNR) were also calculated. RESULTS: Visibility of the cartilage was best when 3DSPGR and T1WSE sequences were used. MTC imaging increased the negativecontrast between cartilage and saline, but FS imaging provided more positive contrast. CNR between cartilage andsaline was highest when using TSE with FS(-3 5 1 . 1 +/-15.3), though CNR between cartilage and bone then fell to-1 4 . 7 +/-10.8. In MTC imaging using MPGR showed the greatest increase of negative contrast between cartilage andsaline(CNR change=-74.7); the next highest was when 3DGRE was used(CNR change=-34.3). CNR between cartilage andbone was highest with MPGR(161.9 +/-17.7), but with MTC, the greatest CNR decrease(-81.8) was observed. Thegreatest CNR increase between cartilage and bone was noted in T1WSE with FS. In all scans, FS provided acartilage-only positive contrast image, though the absolute value of CNR was lower than that of MTC imaging. CONCLUSION: The most prominent effects of MTC and FS were seen in MPGR and T1WSE, respectively, though forcartilage, optimal high signal intensity and contrast can be achieved using 3DGRE with MTC, and 3DSPGR with FS.