Oblique Resonance Research Articles

Comparison of the morphology of the rotator cuff muscles across age groups

We aimed at investigating the morphological difference of the rotator cuff (RC) muscles among age groups from elementary school students to college students. The subjects included 10 college (22.6 ± 1.8 years), 10 high school (16.8 ± 0.6 years), 10 junior high school (13.9 ± 0.6 years), and 10 elementary school (10.4 ± 0.5 years) students. Consecutive oblique sagittal magnetic resonance T1 -weighted images of the dominant shoulder were acquired for each participant. Muscle length, maximal anatomical cross-sectional area (ACSA), the position of the maximal ACSA at full muscle length, muscle volume, and the individual-to-total RC muscle volume ratio for the supraspinatus, external rotators (infraspinatus and teres minor), and subscapularis were evaluated. The muscle length, maximal ACSA, and muscle volume in the RC muscles significantly increased with increasing age (P < 0.01), but there was no significant difference between college and high school students except in regard to the volume of the external rotators. There was no difference in the position of the maximal ACSA or the individual-to-total RC muscle volume ratio among the groups. The findings of this study show that the size of each RC muscle increases with increasing age, but the position of maximal ACSA and the proportion of each muscle to the total RC muscle volume are similar among age groups from elementary school students to college students.

Oblique coronal and oblique sagittal MRI for diagnosis of anterior cruciate ligament tears and evaluation of anterior cruciate ligament remnant tissue

BackgroundThe purpose of this study was to investigate the efficacy of additional oblique magnetic resonance imaging (MRI) for the diagnosis of anterior cruciate ligament (ACL) tear and evaluation of ACL remnant tissue. MethodsWe retrospectively reviewed the records of 54 knees. Three independent readers evaluated the MR images by the use of three methods: orthogonal sagittal images only (method A); orthogonal sagittal and additional oblique sagittal images (method B); and orthogonal sagittal and oblique coronal images (method C). The sensitivity, specificity, and accuracy for the diagnosis of an ACL tear and the detection of the condition of the ACL remnant tissue by the use of each method were calculated in comparison with arthroscopic findings as the reference standard. ResultsThe arthroscopic records revealed 27 knees with intact ACLs and 27 with torn ACLs. Among the 27 knees with torn ACLs, 9 did not have continuous remnant tissue and 18 had certain remnant tissue attached to the femur or the posterior cruciate ligament. The specificities and accuracies of methods B and C for diagnosing an ACL tear were higher than those for method A. The sensitivity, specificity, and accuracy of method C for the detection of ACL remnant tissue were higher than those for method A and B. ConclusionsAdditional use of oblique MRI improved the accuracy of diagnosis of ACL tear and showed a reasonable level of efficacy in detecting ACL remnant tissue. Level of evidenceLevel IV (case series).

Preoperative Prediction for Length of Patellar Tendon in Anterior Cruciate Ligament Reconstruction Using Bone-Patellar Tendon-Bone Autograft

Preoperative prediction of patellar tendon length is important during anterior cruciate ligament (ACL) reconstruction using bone-patellar tendon-bone (BPTB) autograft. Three methods of imaging analysis to predict patellar tendon length were compared in this study. One hundred and twenty-three patients who underwent ACL reconstruction using BPTB autograft by single surgeon during October 2002 through April 2011 were included. We measured the patellar tendon length from true and oblique lateral simple radiographs (classified according to degree of rotation) and magnetic resonance image (MRI). These values were compared with actual length measured during operation and assessed accuracy by calculating the coefficient of determination. The mean length of patellar tendon measured during operation and by true lateral and oblique lateral radiographs and MRI were 42.4±0.45 mm (range, 32.0–54.0 mm), 41.7±0.61 mm (range, 24.2–55.3 mm), 40.7±0.57 mm (range, 24.8–51.5 mm), and 41.7±0.52 mm (range, 28.7– 56.0 mm), respectively. The correlation of patellar tendon length was the most strong between actual length and value from true lateral radiograph (coefficient of determination, r=0.660) according to simple linear regression analysis. R values were 0.361 and 0.332 for oblique lateral radiograph and MRI compared to actual value, respectively. In conclusion, Patellar tendon length measured on true lateral radiograph was the best method to coincide with actual patellar tendon length among various preoperative prediction methods.

Value of thin-section oblique axial T2-weighted magnetic resonance images to assess uterosacral ligament endometriosis

Thin-section oblique axial magnetic resonance imaging (MRI) is useful in staging endometrial and cervical carcinomas but there are no data on its contribution to assessing deep endometriosis. We evaluated the contribution of this MRI technique to diagnosis of uterosacral ligament (USL) endometriosis. In this retrospective study, two radiologists, who were blinded to the surgical and histological results, compared the results from conventional sagittal and axial MRI with those from conventional plus thin-section (3 mm) oblique axial MRI in 100 symptomatic patients. Descriptive statistical analyses including sensitivity, specificity, positive and negative predictive values, accuracy and positive and negative likelihood ratios were performed. Kappa for inter-observer agreement was calculated. Conventional MR images for the diagnosis of left/right USL endometriosis revealed accuracies of 69/76 and 59/75%, sensitivities of 66/71 and 52/71% and specificities of 76/86 and 76/82% for senior and junior readers, respectively. The combination of conventional and thin-section oblique axial MR images revealed accuracies of 82/87 and 74/81%, sensitivities of 89/93 and 73/81% and specificities of 61/72 and 76/79%, for senior and junior readers, respectively. When conventional MRI combined with oblique axial T2-weighted MRI was compared with conventional MRI use only, significant differences in diagnostic accuracies were observed for right (P = 0.04) and left (P = 0.01) USL endometriosis. Thin-section oblique axial T2-weighted imaging can improve the success of conventional MRI for assessment of USL endometriosis. Further prospective studies are required before this new MR protocol is performed routinely for suspected pelvic endometriosis.

Evaluation of Fatty Degeneration of the Supraspinatus Muscle Using a New Measuring Tool and Its Correlation Between Multidetector Computed Tomography and Magnetic Resonance Imaging

Background: The assessment of fatty degeneration of rotator cuff muscles with a reliable grading system is very important. However, there is no generally accepted tool to measure it quantitatively. Purpose: This work was undertaken to introduce a new method to evaluate fatty degeneration by calculating the occupation ratio of the supraspinatus, to determine the correlation between this occupation ratio and the degree of Goutallier’s fatty degeneration or tear size of rotator cuff muscles and to assess the correlation between multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) using this new measuring tool. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Sixty-one patients with full-thickness rotator cuff tears who had undergone arthroscopic rotator cuff repair were included. The occupation ratio was measured using the magic selection tool in Photoshop on MDCT and both T1- and T2-weighted oblique sagittal magnetic resonance images of Y-view. One-way analysis of variance was used to determine the association between this occupation ratio and the degree of fatty degeneration as assessed by Goutallier’s method. The correlation between the occupation ratio and tear size, and the correlation of the occupation ratio between MDCT and MRI, were evaluated using the Pearson correlation coefficient. In addition, the interobserver and intraobserver reliabilities of this measuring tool were assessed on each image by 2 orthopaedic surgeons and analyzed using interclass correlation coefficients. Results: Comparison of the occupation ratio measured by this new method with the Goutallier grade of fatty degeneration on MDCT and MRI revealed a highly significant correlation, with all P values < .001. Also, comparison of this new occupation ratio and cuff tear size showed a reverse correlation on MDCT, T1-weighted magnetic resonance images, and T2-weighted images, with Pearson correlation coefficients of −.61, −.56, and −.50 (all P < .001) by rater 1, and −.57, −.53, and −.43 (all P < .001) by rater 2. Comparison of the occupation ratio between MDCT and MRI demonstrated significant correlation, with Pearson correlation coefficients of .78 and .87 between MDCT and T1-weighted magnetic resonance images and .73 and .82 between MDCT and T2-weighted images. The interobserver and intraobserver reliabilities of this new measuring tool on MDCT and both T1- and T2-weighted magnetic resonance images were excellent in all images, with interobserver correlation of .89, .92, and .91 and intraobserver correlation of .89 and .96, .90 and .98, and .85 and .97, respectively. Conclusion: This new quantitative measuring tool to evaluate the fatty degeneration of rotator cuff muscles was reliable and correlated well with both the preexisting grade of fatty degeneration and cuff tear size. Also, there was a significant correlation between oblique sagittal images of MDCT and MRI using this method; therefore, MDCT can be another option for imaging modality, comparable with MRI, for the evaluation of fatty degeneration of rotator cuff muscles.

Conductivity Image Reconstruction of Oblique Slice With C-Shaped Open Permanent Magnet MRI Systems

This work provides an improved image reconstruction technique, oblique slice magnetic resonance electrical impedance tomography (OS-MREIT), which can provide any cross-sectional conductivity distribution images with any type of MRI scanner. The OS-MREIT method can obtain conductivity distribution images using one component of magnetic field induced by injected currents with rotating subject once, and in the two-dimensional case, the conductivity distribution image can be reconstructed without rotating subject. The results of OS-MREIT studies performed with homemade C-shaped open permanent magnet MRI scanner are also presented in this work.

The Influence of the Acromioclavicular Joint Degeneration on Supraspinatus Outlet Impingement and the Acromion Shape

To assess the anatomic association of acromioclavicular joint degeneration to supraspinatus outlet impingement and the acromion shape. Sagittal oblique magnetic resonance images of 49 shoulders in 49 patients were reviewed. 29 of them (mean age, 59 years) underwent surgery for impingement with or without rotator cuff tear (group 1), whereas the 20 controls (mean age, 27 years) were treated for shoulder instability without rotator cuff disease or acromioclavicular joint derangement (group 2). The supraspinatus outlet and the acromion shape of the 2 groups were compared. The difference in the mean supraspinatus outlet between groups 1 and 2 was 11% (514 vs 577 mm[2], p=0.095) and between the subgroup (of group 1) with full thickness rotator cuff tears and group 2 was 17% (481 vs 577 mm[2], p=0.036). Six of the acromions in group 1 were type III (hooked) compared to none in group 2. In severe acromioclavicular degeneration, distal clavicular excision is recommended, even in cases with an asymptomatic acromioclavicular joint, so as to prevent further osteophyte formation.

Simple Oblique Lumbar Magnetic Resonance Imaging Technique and its Diagnostic Value for Extraforaminal Disc Herniation

Prospective study evaluating the oblique lumbar magnetic resonance imaging (MRI). To present the technique of oblique lumbar MRI and assess the clinical efficacy of this technique for diagnosis of extraforaminal disc herniation. Herniated lumbar discs are traditionally diagnosed using conventional lumbar axial and sagittal MRI. However, conventional lumbar MRI might not reveal nerve root compression in the extraforaminal area. Oblique lumbar MRI can provide clear visualization of the dorsal root ganglion and lumbar nerve root in the foraminal and extraforaminal areas. Ten patients diagnosed with extraforaminal disc herniations underwent bilateral oblique lumbar MRIs before surgery (turbo spin-echo T2-weighted sequence). We compared the side with symptomatic extraforaminal disc herniation to the asymptomatic contralateral side. Oblique lumbar MRI succeeded in depicting pedicles, dorsal root ganglions, and lumbar nerve roots of the foraminal and extraforaminal areas. In 9 of 10 patients (90.0%), nerve root compression by the herniated disc in the extraforaminal area was clearly demonstrated when compared with the asymptomatic contralateral side (P < 0.05). In 1 patient with scoliosis and spinal stenosis, oblique MRI could not clearly display foraminal or extraforaminal anatomy due to spinal deformity. In light of this data, we suggest that oblique lumbar MRI can precisely demonstrate nerve roots in foraminal and extraforaminal areas. This technique is a simple and useful diagnostic tool for extraforaminal lumbar disc herniations.

Which oblique plane is more helpful in diagnosing an anterior cruciate ligament tear?

To evaluate the diagnostic role of additional oblique coronal and oblique sagittal magnetic resonance imaging (MRI) for an anterior cruciate ligament (ACL) tear. A total of 101 patients who had undergone preoperative knee MRI examinations with orthogonal and two sets of oblique images were enrolled in the study. Two radiologists evaluated the MRI images by the use of four methods: orthogonal images only (method A); orthogonal and additional oblique coronal images (method B); orthogonal and oblique sagittal images (method C); and orthogonal images with oblique coronal and sagittal images (method D). The status of the ACL (normal or tear) was determined by consensus. The sensitivity, specificity, and accuracy for an ACL tear with the use of each method were calculated in comparison with arthroscopy as the reference standard, and values were statistically analysed using the McNemar test. The diagnostic accuracies were compared using receiver operating characteristic (ROC) analysis. Arthroscopy identified 10 partial ACL tears and 30 complete ACL tears. The specificities and accuracies for methods B, C, and D were significantly higher than the specificities and accuracies for method A (p<0.05). There was no significant difference in the sensitivity, specificity, and accuracy for methods B, C, and D. Diagnostic ability was not significantly different for each method, as determined by ROC analysis (p>0.05). Additional oblique imaging for an ACL tear improved the specificity. Either of the oblique imaging methods is sufficient, and no further improvement in the diagnostic efficacy was achieved by simultaneous use.

Magnetic Resonance Imaging Appearance of a Repaired Capsulolabral Complex after Arthroscopic Bankart Repair

Background Revision Bankart operations frequently show capsulolabral buttress loss and recurrent soft tissue Bankart lesion. Capsulolabral augmentation is designed to increase glenohumeral stability by 2 separate mechanisms: deepening the glenoid concavity and reducing capsular laxity. This is accomplished by shifting the capsule to buttress the glenoid labrum. Hypothesis A retained capsulolabral buttress may show loss of height and slope at a certain period after surgery, regardless of stability. Thus, the authors wanted to confirm the importance of an intraoperative establishment of capsulolabral buttress in terms of stability. Study Design Case-control study; Level of evidence, 3. Methods Arthroscopically repaired Bankart lesions in 21 consecutive shoulders that showed no frank dislocation were evaluated using axial and oblique coronal T2-weighted magnetic resonance imaging at 3 timepoints (preoperative period, average postoperative week 6 and a nearly full range of motion recovery, and postoperative month 6 with a return to daily activity). The authors measured 2 parameters (height and slope) on axial (mainly capsulolabral containment) and oblique coronal images (mainly inferior glenohumeral ligament) at the anteroinferior portion of the glenoid (5 mm above the most inferior anchor). In addition, they compared the above-mentioned parameters at postoperative month 6 by magnetic resonance imaging in 21 controls and in 21 patients whose instability recurred after surgery (not included in the prospective study). Results There was a significant increase between the preoperative period and postoperative week 6 in all 4 parameters (P < .0001). There was also a significant increase between the preoperative period and postoperative month 6 in all 4 parameters (P < .0001). However, no statistically significant difference was observed between postoperative week 6 and postoperative month 6 in all 4 parameters (P > .1). Furthermore, significant differences were observed between normal controls and patients with recurrent instability (P < .001) and between the authors’ cases and patients with recurrent instability not in the study (P < .001). However, no difference was observed between their cases and normal shoulders (P > .1). Conclusion After suture anchor Bankart repair, initial capsulolabral buttress property was maintained at 6 months postoperatively. Furthermore, the buttress was more prominent in stable and normal shoulders than in recurrent instability shoulders. Therefore, the authors believe that the establishment of a capsulolabral buttress is meaningful during Bankart repair.

Streamlining the Evaluation of Low Back Pain in Children

The workup of low back pain in children often results in overimaging so as not to miss organic back pain. The primary goal of this study was to identify which combination of imaging modalities provides the most sensitive and specific screening protocol for children with low back pain. Medical records from 100 consecutive patients between 2 and 18 years of age presenting with low back pain, without night pain or constitutional symptoms, were evaluated. A hyperextension test combined with a radiograph showed a negative predictive value of 0.81 and sensitivity of 0.90. The addition of a bone scan was highly effective in achieving good negative predictive value and sensitivity. Bone scans had perfect negative predictive value and sensitivity when symptom duration was less than 6 weeks. We identified a set of factors that is highly predictive for distinguishing organic back pain from mechanical back pain. Painless hyperextension combined with negative anteroposterior, lateral, and oblique lumbar radiographs and magnetic resonance images predicts mechanical back pain. For patients with nonneurologic back pain of less than 6 weeks duration, bone scan is the most useful screening test because it is accurate, accessible, inexpensive, and unlikely to require sedation. Level III, diagnostic study.

How are wear-related problems diagnosed and what forms of surveillance are necessary?

Prospective, randomized clinical wear studies have shown significant wear reduction when highly cross-linked, e-beamed, melted polyethylene was compared with conventional polyethylene sterilized by gamma irradiation in air. More complete assessment of wear-induced osteolysis in the general total hip arthroplasty patient population must rely on registries with follow-up of large populations of patients through radiographic evaluation of wear-related factors, such as suboptimal placement of the implant components, osteolytic defects, and aseptic loosening. Follow-up radiographs should be obtained in the early postoperative period and at 1, 5, and 10 years postoperatively, and then every 1 to 5 years, thereafter depending on radiographic findings of osteolysis and its progression. When pathologic findings are present, further examinations, such as oblique Judet views and magnetic resonance imaging (MRI) with artifact minimization should be considered to provide a better determination of the extent of the osteolysis. Because conventional radiographs underestimate the prevalence and extent of osteolysis in many instances, diagnosis and surveillance should be performed with radiographic edge detection, spiral computed tomography (CT), MRI, radiostereometric analysis, and quantitation of wear and osteolysis, including bone and soft-tissue lesions. Helical CT has demonstrated excellent specificity in identifying and quantifying the extent of osteolysis. MRI can more accurately localize both osseous and soft-tissue particulate disease, and detect granuloma and compression on adjacent nerves and vessels.

Magnetic Resonance Imaging of the Long Head of the Biceps Tendon

To evaluate coplanar imaging of the long head of the biceps tendon. We retrospectively compared coronal oblique magnetic resonance images aligned with the principal supraspinatus tendon and with the intra-articular biceps tendon in 21 patients. Magnetic resonance images were analyzed for lesions depicted, including superior labral anteroposterior (SLAP) tears. Arthroscopic findings were reviewed. Coronal oblique images aligned with intra-articular biceps tendon depicted 18 (86%) of 21 coplanar intra-articular biceps tendons. Coplanar images identified 6 cases of tendinosis, 1 tear, 3 intra-articular ruptures, and 20 (95.2%) of 21 exact origins of the tendon. Arthroscopy revealed 18 SLAP tears. The detection of SLAP lesions between both coronal oblique magnetic resonance images was significantly different (P = 0.007). Advantages included imaging of the intra-articular biceps tendon with least partial-volume effects, definition of SLAP lesions and the tendinous origin at the supraglenoid tubercle, depiction of intra-articular bicipital ruptures, and increased sensitivity and specificity for intra-articular lesions.

Use of oblique supine magnetic resonance imaging in breast-conserving surgery following neoadjuvant chemotherapy

11064 Background: The success of breast-conserving surgery (BCS) after neoadjuvant chemotherapy (NAC) is dependent on accurate assessment of the extent of surgical excision of the original tumor bed (OTB). However the difficulty in locating microscopic residual disease often leads to a high re-excision rate (RER) and large excision specimen area (ESA). Methods: Magnetic resonance imaging (MRI) scans in the oblique supine position are performed with the patient in the same posture as that adopted during surgery. Maximum intensity projection (MIP) images of MR coronary section images of OTB are generated and used for surgery. OTB images are copied onto transparent sheets overlaid on the MIP images. These images are projected onto the breast before surgery, and used to determine the lines for surgical excision. In the conventional method (CM), OTB is determined by ultrasonography (US) and CT images. The oblique supine MRI method (SMM) has been used at our hospital since 2005. In this study, 14 patients treated prospectively with SMM (12/05- 12/06) were compared with a series of 19 consecutive patients treated with CM (04/03–11/05). ESA and RER were analyzed. Re-excision was performed in cases with a calcified lesion or tumor within 1 cm of the excised margin by X-ray or US during surgery, or invasive cancer was detected within 1 mm by pathological examination. ESA was analyzed using NIH Image. All patients received anthracycline/taxane-based chemotherapy. Results: There were no significant differences in characteristics of patients in the initial stages (T1, 2) or pathological chemotherapy responses between SMM and CM groups. There were four T3.4 cases in the SMM group, but none in the CM group. Clinical responses in CM and SMM were as follows (cases): CR 6, 7; PR 12, 7; SD 1, 0, respectively. RER was significantly greater in CM (36.8%, n=7) than in SMM (7.1%, n=1) (P&lt;0.05). Average ESA in SMM were 19.0 cm2 (n=2) in T1, 33.6 cm2 (7) in T2, and 59.3 cm2 (5) in T3.4, while corresponding values in CM were 49.4 cm2 (4) and 65.5 cm2 (15), respectively; ESA was significantly improved in SMM. Conclusions: SMM, which has the benefits of decreased ESA and RER with superior cosmetic results, is a reliable technique for BCS following NAC. No significant financial relationships to disclose.

Ferromagnetic resonance in the proximity of the unstable perpendicular equilibrium: A study in Permalloy thin films and nanoscale dots

We are investigating the magnetization dynamics of a ferromagnetic system in the proximity of the unstable perpendicular equilibrium. The test system utilized is Permalloy in thin film and dot arrays with the applied field along a small angle off the film normal. Frequency∕field dispersion curves (up to 15GHz) obtained at different small angles (θH) reveal significant deviations from the perpendicular linear dispersion at low frequencies, and they form almost frequency independent flat plateau with a local minimum near the demagnetization field. The existence of the local minimum results in three resonances in a constant frequency∕swept field scans. Such behavior is modeled successfully, in particular, in the film case, by using an approach for oblique angle resonance [P. E. Tannenwald, Phys. Rev. 105, 377 (1957)]. For the dots, additional influence from either induced in-plane anisotropy or vortex formation is discussed.

Magnetic Resonance Imaging Appearance of a Double Anterior Cruciate Ligament Associated With a Displaced Tear of the Lateral Meniscus

The aim of this study is to report a novel description of a displaced tear of the lateral meniscus as a curvilinear low signal intensity band parallel and posteroinferior to the anterior cruciate ligament (ACL) on midline oblique sagittal magnetic resonance (MR) images, resulting in the appearance of a "double ACL." The appearance of a double ACL may potentially be a specific indicator for a lateral meniscal displaced tear. Increased awareness of this characteristic MR finding may increase accuracy in the diagnosis of displaced tears of the lateral meniscus.

Transmission of waves near the lower oblique resonance using dipoles in the ionosphere

The observations in the OEDIPUS‐C experiment of bistatic propagation along the lower oblique resonance cone between a separated transmitter and receiver in the ionosphere are explained through detailed calculations of the radiated field of the V‐dipole antenna used in the experiment and by a novel theory of the receiving antenna under resonance conditions. Unexpectedly high values of 25 kHz signal observed at the resonance and its structure agree well with calculations of the transmission between the exciter and receiver, when antenna layout and dispersive properties of the plasma at resonance are taken into account.

Electromagnetic whistler‐mode radiation from a dipole in the ionosphere

Dipole‐antenna radiation theory has been tested for electromagnetic whistler‐mode waves in the frequency range 0.1–1.3 MHz using data from the two‐point rocket experiment Observations of Electric‐field Distributions in the Ionospheric Plasma; a Unique Strategy (OEDIPUS) C. Waves were emitted from a double‐V dipole on a transmitting subpayload and received at a distance of about 1200 m on a similar dipole connected to a synchronized receiver. The magnitudes of transmitted signals predicted by a theory for short dipoles have been found to be in good agreement with observations. The agreement is very good in the top two thirds of the frequency range where the dispersion relation and the geometry provide only one saddle‐point solution with the required group direction. In this part of the parameter space studied, the transmitter‐receiver separation is at least 10 wavelengths. This is not always true at the lowest frequencies, where the expected effects of interference of multiple saddle‐point rays and of the oblique resonance cone are observed.

Medial condyle fractures of the humerus in children.

A retrospective study of 21 medial condylar fractures revealed that the complication rate for these rare fractures was 33%. Most of the minimally displaced fractures healed uneventfully with immobilization; however, one patient developed avascular necrosis of the trochlea, and one patient developed a nonunion. Operative treatment was performed if there was >2 mm of displacement at the fracture site. Two of three fracture-dislocations lost reduction in the early postoperative period, requiring revision with more stable fixation. Medial condylar fractures may be difficult to diagnose in younger children and should be considered when there is a history of trauma and medial-sided elbow pain. Oblique views, arthrography, or magnetic resonance imaging can be helpful in confirming the diagnosis. Management of this rare fracture must include adequate stabilization of the fracture and immobilization until there is radiographic evidence of healing.

Temporomandibular joint disk displacement: comparison in asymptomatic volunteers and patients.

To compare the prevalence and type of temporomandibular joint (TMJ) disk displacement in asymptomatic volunteers with those in patients. Bilateral oblique sagittal and oblique coronal intermediate-weighted magnetic resonance (MR) images of the TMJs in 58 patients with pain and dysfunction were analyzed and compared with corresponding MR images of 62 asymptomatic volunteers. Forty-five (78%) of 58 patients had disk displacement compared with 22 (35%) of 62 asymptomatic volunteers. Complete disk displacement was found in 46 (40%) of 115 joints in patients compared with three (2.4%) of 124 joints in asymptomatic volunteers, whereas partial disk displacement occurred in 26 (22.6%) and 27 (21.8%) joints, respectively. Two types of complete disk displacement, anterolateral and anterior, occurred frequently in patients, seldom in volunteers. Only minor differences were found between other types of disk displacement when prevalence in patients was compared with that of volunteers. The disk reduced to a normal position on open-mouth images in all joints in the volunteers compared with 76% of the joints in patients. TMJ disk displacement was less prevalent and was of a different type in asymptomatic volunteers compared with patients with pain and dysfunction.