Acromial arch shape: assessment with MR imaging

Automated detection and classification of the rotator cuff tear on plain shoulder radiograph using deep learning

BACKGROUND

The diagnosis of rotator cuff tears (RCTs) using radiographs alone is clinically challenging; thus, the utility of deep learning algorithms based on convolutional neural networks has been remarkable in the field of medical imaging recognition. We aimed to evaluate the diagnostic performance of artificial intelligence (a deep learning algorithm; a convolutional neural network) to detect and classify RCTs using shoulder radiographs, and compare its diagnostic performance with that of orthopedic surgeons.

METHODS

A total of 1169 plain shoulder anteroposterior radiographs (1 image per shoulder) were included in the total dataset and divided into four groups: intact, small, medium, and large to massive tear groups. The sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and area under the receiver operating curve were measured for the detection of RCTs through binary classification. The average accuracy, recall, precision, and F1-score were divided into four groups by cuff tear size for multiclass classification.

RESULTS

The convolutional neural network demonstrated a high performance, with 92% sensitivity, 69% specificity, 86% accuracy, and an area under the receiver operating curve of 0.88 for the detection of RCTs. The average accuracy, recall, precision, and F1-score of the convolutional neural network for classification were 60%, 0.42, 0.49, and 0.45, respectively. The accuracy of the convolutional neural network for the detection and classification of RCTs was significantly better than that of orthopedic surgeons.

CONCLUSION

The convolutional neural network demonstrated the diagnostic ability to detect and classify RCTs using plain shoulder radiographs, and the diagnostic performance exhibited equal to superior accuracy when compared with those of shoulder experts.

Reliability of Bigliani's Classification using Magnetic Resonance Imaging for Determination of Acromial Morphology

Introduction

Bigliani classification is used for determination of acromial morphology, but poor inter-observer reliability has been reported on conventional radiographs. This study aims to assess inter- and intra-observer reliability using magnetic resonance imaging (MRI).

Materials and methods

Forty consecutive patients diagnosed with subacromial impingement syndrome were included to study. All subjects underwent standard shoulder MRI scan and acromial shape was evaluated by nine observers of different level of expertise (three attending surgeons, three senior orthopaedic residents and three radiologists). A second set of evaluation was performed in order to assess intra-observer reproducibility. Kappa (κ) coefficient analyses both for interobserver reliability and intra-observer reproducibility were then performed.

Results

Overall inter-observer agreement among nine observers was fair (κ=0.323). κ values for all 4 individual types ranged from 0.234 to 0.720 with highest agreement for type 4 and lowest agreement for type 3. Second evaluation did not result with an increase of inter-observer agreement (κ=0.338, fair). The κ coefficients for intra-observer reproducibility of nine observers ranged from 0.496 to 0.867. Overall intra-observer reproducibility was substantial. Comparison of inter- and intra-observer reliability among three groups showed no significant difference (p=0.92 and 0.22, respectively).

Conclusion

Results showed that MRI did not show superior reliability compared to conventional radiographs. Moreover, inter- and intra-observer agreement did not differ between observers of different level of expertise. Findings of present study suggest that despite a sophisticated imaging modality like MRI, Bigliani's classification apparently lacks accuracy and additional criteria, or different assessment methods are required to assess acromial morphology for clinical guidance.

To explore the reasonable selection of clavicular hook plate to reduce the occurrence of subacromial impingement syndrome after operation

Background

Acromioclavicular joint dislocation is a shoulder joint injury common in the clinical setting and is generally surgically treated with clavicular hook plate technique with confirmed curative effect. However, symptoms such as shoulder abduction limitation, shoulder discomfort and joint pain postoperatively may occur in some patients. Therefore, this study aimed to explore whether the existing clavicular hook plate can be reasonably selected to reduce the incidence of subacromial impingement syndrome (SIS) and provide a reference for clinical diagnosis and treatment.

Materials and methods

Patients with SIS admitted from March 2018 to June 2020 were selected as the experimental group and asymptomatic patients postoperatively, as the control group. The hook end depth and acromial height of the hook plate used in patients were recorded, and the difference between them was calculated.

Results

The difference between the hook plate depth and acromial height was 7.500±1.912 mm and 6.563±1.537 mm in the experimental and control groups, respectively, with statistically significant difference (t=3.021, P=0.006). A difference of >0.6 mm as a grouping index is required to perform a single factor analysis, with statistically significant difference (t=3.908, P=0.048).

Conclusions

The occurrence of SIS after placing the clavicular hook plate may be related to the difference between its depth and the acromial height. A difference of >6 mm may be a factor affecting the occurrence of SIS. Pre-imaging measurement of the acromial height can provide suggestions for selecting the type of hook plate intraoperatively.

Relationship of the Shape of Subacromial Spur and Rotator Cuff Partial Thickness Tear

Background

The present study was undertaken to evaluate the relationship between location of the rotator cuff tear and shape of the subacromial spur.

Methods

Totally, 80 consecutive patients who underwent arthroscopic repair for partial thickness rotator cuff tear were enrolled for the study. Bigliani’s type of the acromion, type of subacromial spur, and location of partial thickness tear of the rotator cuff were evaluated using plain X-ray and magnetic resonance imaging. We then compared the groups of no spur with spur, and heel with traction spur.

Results

Of the 80 cases, 25 cases comprised the no spur group, and 55 cases comprised the spur group. There was a significant difference in type of tear (p=0.0004) between these two groups. Bursal side tears were significantly greater (odds ratio=6.000, p=0.0007) in the spur group. Subjects belonging to the spur group were further divided into heel (38 cases) and traction spur (17 cases). Comparing these two groups revealed significant differences only in the type of tear (p=0.0001). Furthermore, the heel spur had significantly greater bursal side tear (odds ratio=29.521, p=0.0005) as compared to traction spur.

Conclusions

The heel spur is more associated to bursal side tear than the traction spur, whereas the traction spur associates greater to the articular side tear.

Shoulder measurements on MRI: Statistical analysis of patients without and with rotator cuff tears and predictive modeling

This study aims to determine significant differences between various measurements of shoulder structures and relationships in patients with and without rotator cuff tears and identify a subset of these measurements that may merit further investigation. Shoulder MRIs of 120 patients with rotator cuff tears (RCT group) and 80 patients with normal examinations (No RCT group) were retrospectively identified. Numerous measurements of shoulder anatomy and relationships and pathology characterization were performed for each study. The mean and ranges of measurements for each group were identified, and P-values were calculated to assess differences between the two groups. Classification and Regression Tree (CART) identified prediction models for separating the two groups based on these shoulder MRI measurements. Statistically significant differences were observed for 9 of 18 of the shoulder measurements between the two groups (P < 0.05). Using long head of biceps tendon tear, tendinosis, and subacromial-subdeltoid bursal fluid, the prediction model from CART demonstrated 99.5% accuracy in separating the two groups. Subacromial distance, subacromial spur size, and acromioclavicular osteophyte could also separate the two groups with 97.5% accuracy. Other measures less commonly associated with impingement and rotator cuff tears could also be used to separate the two groups with up to 81.5% accuracy. This study introduces new measures and clarifies ranges for existing measurements on shoulder MRI. Abnormalities of some of these measurements may be associated with subacromial impingement, and combinations of these parameters may be useful for separating patients with or without rotator cuff tears. Clin. Anat. 33:173-186, 2020. © 2019 Wiley Periodicals, Inc.

Artifacts and pitfalls in shoulder magnetic resonance imaging

Magnetic resonance imaging has revolutionized the diagnosis of shoulder lesions, in many cases becoming the method of choice. However, anatomical variations, artifacts and the particularity of the method may be a source of pitfalls, especially for less experienced radiologists. In order to avoid false-positive and false-negative results, the authors carried out a compilation of imaging findings that may simulate injury. It is the authors' intention to provide a useful, consistent and comprehensive reference for both beginner residents and skilled radiologists who work with musculoskeletal magnetic resonance imaging, allowing for them to develop more precise reports and helping them to avoid making mistakes.

Rotator cuff tears: association with acromion angulation on MRI

OBJECTIVE

Using magnetic resonance imaging (MRI), evaluate the correlation of acromion angulation with thickening of the coracoacromial ligament (CAL) and narrowing of the subacromial space resulting in impingement upon the rotator cuff tendons.

MATERIALS AND METHODS

Eighty-nine shoulder MRI studies performed on a 3T scanner were retrospectively analyzed by two blinded independent reviewers. Measurements of the acromion angle (delta angle), CAL thickness and distance between the CAL and humeral head were obtained. The data were categorized into two groups, delta angle less that and greater than 7.5°. The presence or absence of full thickness (FT) or near full thickness (NFT) rotator cuff tears was noted.

RESULTS

In group 1, the acromion angle varied from -6.8 to 6.8° (1.7±3.5°) with a CAL thickness of 0.91±0.20 mm and a subacromial distance of 6.47±0.88 mm. Group 2 acromion angle varied from 7.6° to 46.8° (18.0°±8.1°) with a CAL of 1.77±0.51 mm and a subacromial distance of 4.52±0.82 mm. The difference in CAL thickness and subacromial distance were significantly different between the two groups (P<.001). In Group 1, 3 out of 51 patients had a FT or NFT tear of the rotator cuff compared to 20 out of 38 in Group 2 (P<.001). There was no significant interobserver variability.

CONCLUSION

Steep acromion angulation is associated with CAL thickening and narrowing of the subacromial space. Patients with a steep acromion angle had a statistically increased incidence of rotator cuff tears.

Magnetic resonance imaging of rotator cuff disease and external impingement

Magnetic resonance (MR) imaging plays a major role in helping to identify rotator cuff disease and in demonstrating the pathology associated with external impingement. Many surgeons rely on MR imaging to assist in decision making and presurgical planning for patients with rotator cuff pain. This article reviews the etiology of external impingement and rotator cuff tears, and describes the MR imaging appearance of the normal and the pathologic rotator cuffs. It focuses on the supraspinatus tendon because this is the tendon involved in 95% of rotator cuff tears.

Pictorial essay: pitfalls in magnetic resonance imaging of the shoulder

Numerous imaging pitfalls of normal variants due to imaging technique and artifacts can be seen on routine magnetic resonance imaging of the shoulder. Familiarity with these pitfalls is crucial to avoiding diagnostic errors. Understanding of the common causes of shoulder imaging artifacts will enable the radiologist to make rational changes in imaging technique to eliminate or reduce the effects of artifacts on magnetic resonance images. This pictorial essay highlights possible pitfalls that arise from imaging techniques, imaging artifacts, and normal variations, and how they may be recognized.

Pain related to rotator cuff abnormalities: MRI findings without clinical significance

MRI has become an important diagnostic tool in the evaluation of rotator cuff pathology and the technology continues to evolve. Direct MR arthrography, diagnosis-specific sequencing such as fat suppression, special positioning such as abducted externally rotated (ABER) views and ultra high field magnets allow for an unprecedented level of detail in imaging. In this article, we review MRI findings in patients with rotator cuff abnormalities that are anatomic variants or incidental findings. Although MRI findings may be diagnostic in some cases, we find that clinical correlation with history and physical examination is critical to differentiate between anatomic variants, incidental findings, and true pathology. We conclude that good communication between the orthopedic surgeon and the radiologist is necessary to optimize diagnostic yield.

Shoulder MR imaging normal variants and imaging artifacts

The appearance of osseous, labral, hyaline cartilage, ligament, muscle, and tendon variants and pitfalls are discussed with attention to the keys to distinguishing each of the findings from pathologic lesions of the shoulder.

In vivo glenohumeral analysis using 3D MRI models and a flexible software tool: feasibility and precision

PURPOSE

To implement a PC-based morphometric analysis platform and to evaluate the feasibility and precision of MRI measurements of glenohumeral translation.

MATERIALS AND METHODS

Using a vertically open 0.5T MRI scanner, the shoulders of 10 healthy subjects were scanned in apprehension (AP) and in neutral position (NP), respectively. Surface models of the humeral head (HH) and the glenoid cavity (GC) were created from segmented MR images by three readers. Glenohumeral translation was determined by the projection point of the manually fitted HH center on the GC plane defined by the two main principal axes of the GC model.

RESULTS

Positional precision, given as mean (extreme value at 95% confidence level), was 0.9 (1.8) mm for the HH center and 0.7 (1.6) mm for the GC centroid; angular GC precision was 1.3 degrees (2.3 degrees ) for the normal and about 4 degrees (7 degrees ) for the anterior and superior coordinate axes. The two-dimensional (2D) precision of the HH projection point was 1.1 (2.2) mm. A significant HH translation between AP and NP was found.

CONCLUSION

Despite a limited quality of the underlying model data, our PC-based analysis platform allows a precise morphometric analysis of the glenohumeral joint. The software is easily extendable and may potentially be used for an objective evaluation of therapeutical measures.

Acromial morphology: effects of suboptimal radiographs

Acromial morphology is one of the important factors related to rotator cuff pathology, especially if there is acromial encroachment onto the supraspinatus tendon. This is the rationale for many surgeons performing an acromioplasty, based on preoperative radiographs, in their treatment of rotator cuff disease. However, geometric measurements of the acromion are dependent on the radiographic view, and suboptimal radiographs of the scapula might bias the acromial morphology on the radiographs. Our objective was to study the effect of suboptimal lateral-view radiographs of the scapula on 6 acromial angles, which have been correlated with rotator cuff pathology, by use of a computational method. Anatomic landmarks were digitized on 12 cadaveric scapulae via a spatial linkage system. A coordinate system based on the scapula was then created that allowed projection of the anatomic landmarks on the sagittal plane and simulated the optimal lateral-view radiograph of the scapula. By rotating the coordinate system in the coronal plane (cranial and caudal projections) and axial plane (anterior and posterior projections) with 5 degrees, 10 degrees, 15 degrees, and 20 degrees increments, 16 suboptimal lateral-view radiographs of the scapula were simulated. Significant differences in the 6 acromial angles (P < .01) between the optimal and suboptimal lateral-view radiographs of the scapula were found in almost every cranial and caudal projection. Rotating the projection in the axial plane did not significantly affect the acromial angles (P > .05) up to 20 degrees of rotation in the anterior and posterior direction. Of the 6 different acromial angles, the acromial slope was least affected when the projection was varied. In contrast, the anterior slope of the acromion was highly affected by errors in the projection.

MR imaging of the rotator cuff

MR imaging is the optimal method for evaluating suspected rotator cuff pathology. Current techniques of fast spin-echo imaging without and with fat suppression allow accurate identification and characterization of tendinous and myotendinous abnormalities of the rotator cuff. Impingement disorders, tendon degeneration, instability,and trauma comprise the multifactorial nature of rotator cuff disease. This article addresses the role of MR imaging in evaluating the rotator cuff and the importance of MR imaging in identifying other lesions that may mimic rotator cuff pathology. A rationale for protocol design, including MR arthrography and the use of specialized positioning, such as abduction and external rotation (ABER), are discussed.

Dynamic Sonography Evaluation of Shoulder Impingement Syndrome

OBJECTIVE

Our aim was to characterize shoulder impingement syndrome using dynamic sonography.

CONCLUSION

Dynamic sonography allows direct visualization of the relationships between the acromion, humeral head, and intervening soft tissues during active shoulder motion and can provide useful information regarding potential intrinsic and extrinsic causes of shoulder impingement syndrome.

Shoulder Impingement: Objective 3D Shape Analysis of Acromial Morphologic Features

PURPOSE

To retrospectively and quantitatively analyze the acromial undersurface in three dimensions and to determine its association with impingement syndrome and rotator cuff tears.

MATERIALS AND METHODS

Institutional review board approval was received with exemption of informed consent for this retrospective HIPAA-compliant study. Magnetic resonance images were evaluated in 84 patients (63 males, 21 females; mean age, 42.6 years; age range, 15-74 years). On the basis of surgical results, patients were separated into three groups: those without shoulder impingement or rotator cuff tears (31 patients), those with shoulder impingement (22 patients), and those with rotator cuff tears (31 patients). To quantitate the acromial undersurface, the structure was manually plotted, and a mathematic model was created by using splines. The undersurface was divided into a 20 x 20 grid. For each patient, a shape index (SI) data set and local undersurface angulation (LUA) data set were determined. Regression analyses were used to identify differences between groups, and prediction models were constructed on the basis of correspondent areas.

RESULTS

Analysis of both data sets yielded no apparent progression between groups and demonstrated a lack of similarity between the impingement and rotator cuff tear groups. Discrimination between groups could be demonstrated by dividing the lateral portion of the acromial undersurface into contiguous blocks. The highest overall diagnostic accuracy of our prediction models was 58.3% (49 of 84) by using 10 blocks of the SI data set and 73.8% (62 of 84) by using five blocks of the LUA data set.

CONCLUSION

Three-dimensional modeling yields objective data about the acromial undersurface. On the basis of this method, osseous impingement by the acromion is not a primary cause of shoulder impingement syndrome or rotator cuff tears.

Rotator Cuff Tears: Clinical, Radiographic, and US Findings

Rotator cuff tears are a common cause of shoulder pain. Clinical and radiographic findings can suggest the presence of a rotator cuff tear. The most sensitive clinical findings are impingement and the "arc of pain" sign. Radiographic findings are usually normal in the acute setting, although the "active abduction" view may show decreased acromiohumeral distance. In more chronic cases, an outlet view may show decreased opacity and decreased size of the supraspinatus muscle due to atrophy. In late cases, the humeral head may become subluxated superiorly, and secondary degenerative arthritis of the glenohumeral joint may ensue. Ultrasonography (US), with over 90% sensitivity and specificity, can help confirm the diagnosis in clinically or radiographically equivocal cases. US can also reveal the presence of other abnormalities that may mimic rotator cuff tear at clinical examination, including tendinosis, calcific tendinitis, subacromial subdeltoid bursitis, greater tuberosity fracture, and adhesive capsulitis.

A systematic approach to magnetic resonance imaging interpretation of sports medicine injuries of the shoulder

Magnetic resonance imaging has developed as a useful imaging modality in the evaluation of the athlete with shoulder pain. The multiplanar capabilities of magnetic resonance imaging make it ideal for detecting the anatomical variations of the osseous outlet that may contribute to the clinical syndrome of impingement. Its superb soft tissue contrast and spatial resolution allow for accurate differentiation between tendinopathy, partial-thickness tear, and full-thickness tear of the rotator cuff and also allow for detection of the subtle lesions of the capsule and labrum that are associated with shoulder instability. However, to accurately interpret the numerous images and pulse sequences obtained in a standard magnetic resonance examination of the shoulder, it is helpful to have a systematic approach to ensure that each of the pertinent anatomical structures are evaluated. This article will provide a systematic approach to the interpretation of a magnetic resonance examination of the shoulder. The normal imaging appearance of each anatomical structure will be described, and the most useful pulse sequences and imaging planes for the evaluation of each structure will be discussed. Finally, the signs of injury will be described and illustrated.

Comparison of MRI and Conventional Radiography for Assessment of Acromial Shape

OBJECTIVE

Our aim was to determine the value of different MRI planes independently and in combination for assessment of acromial shape.

MATERIALS AND METHODS

Sixty-one patients with subacromial impingement syndrome who had undergone acromioplasty after failure to respond to conservative treatment were included in the study. Parasagittal T2-weighted MR images and outlet view radiographs of the affected shoulders were acquired preoperatively. Three-dimensional models of all acromions were constructed from the MR images, and the Bigliani type of acromion depicted by these models was determined. Results were compared with the acromial type assessed during acromioplasty. To provide a reliable reference for further processing and correlation, we used only those 56 acromions with agreement on acromial shape between intraoperative findings and 3D models. Then, acromial shape was determined for three MRI slice positions (S-1, lateral acromial edge; S-2, just lateral of acromioclavicular joint; and S-3, lateral portion of acromioclavicular joint), for a combination of S-1 and S-2, and for the radiographs.

RESULTS

Kappa coefficients were 0.36 (36%) for S-1, 0.41 (41%) for S-2, and -0.10 (-10%) for S-3. For the outlet view radiographs, the kappa coefficient was 0.55 (55%), showing better correlation than any single slice position. Best results, however, were achieved with a combination of S-1 and S-2, with a kappa coefficient of 0.66 (66%).

CONCLUSION

For determination of acromial shape, outlet view radiographs are superior to any single MRI slice position, but inferior to a combination of two MRI slices (S-1 and S-2). If a single MRI slice is being used, the slice position just lateral to the acromioclavicular joint is recommended.

[Impingement syndrome of the shoulder]

The impingement syndrome is a clinical entity characterized by shoulder pain due to primary or secondary mechanical irritation of the rotator cuff. The primary factors for the development of impingement are a curved or hook-shaped anterior acromion as well as subacromial osteophytes, which may lead to tearing of the supraspinatus tendon. Secondary impingement is mainly caused by calcific tendinopathy, glenohumeral instability, os acromiale and degenerative changes of the acromioclavicular joint. Conventional radiographs are initially obtained, mainly for evaluation of the bony structures of the shoulder. If available, sonography can be used for detection of lesions and tears of the rotator cuff. Finally, MR-imaging provides detailed information about the relationship of the acromion and the acromioclavicular joint to the rotator cuff itself. In many cases however, no morphologic cause for impingement syndrome can be found. While patients are initially treated conservatively, chronic disease usually requires surgical intervention.

Clinically significant skeletal variations of the shoulder and the wrist: role of MR imaging

Several skeletal variations of the upper extremity may cause painful conditions or precipitate early degenerative changes, either spontaneously or in response to overuse and trauma. Magnetic resonance imaging has proved particularly useful for accurate interpretation of many of these clinically significant skeletal variations; however, the widespread use of MR imaging may have contributed to over-emphasizing their clinical importance, which is still controversial in many cases. We review, illustrate, and discuss clinically significant skeletal variations of the upper extremity as seen on MR images, particularly those involving the shoulder and the wrist. In the shoulder region, we evaluate variations of acromial and coracoid processes as well as variations and minor dysplastic deformities of the glenoid fossa. We also review different skeletal variations of the carpal region, including ulnar variance, ulnar styloid, lunate morphology, carpal coalition, and carpal accessory ossicles. The role of MR imaging in assessing the clinical importance of such conditions, whether potential, controversial, or well established, is emphasized in this review.

Radiographic evaluation of the acromioclavicular and sternoclavicular joints

Plain radiography is useful for the initial assessment of suspected disorders of the sternoclavicular and acromioclavicular joints. Other modalities are often required to further assess more complex pathologies involving these joints, however. Ultrasound has been described as a screening tool to assess possible sternoclavicular joint dislocation; however, it is usually used only if CT and MRI are not readily available. It has also been used to confirm intraoperative relocation. Ultrasound has a limited role in the evaluation of the AC joint, where it is most useful to exclude the presence of joint inflammation. If joint fluid is detected sonographically, it is considered a nonspecific finding, which could represent active inflammation or simply joint effusion due to degenerative arthrosis. CT allows for excellent visualization of the articular surfaces, osseous changes, subtle or complex fractures, and joint malalignment, with a rapid scan time, making it particularly helpful in the work up of trauma patients. With its multiplanar capabilities and superior soft-tissue resolution, MRI is a very effective modality for characterizing soft-tissue injuries, inclusive of ligamentous tears and cartilaginous injuries. In the specific case of posterior sternoclavicular dislocations, both CT and MR angiography can be very helpful in elucidating occult associated vascular injury.

Magnetic resonance imaging of the shoulder: rotator cuff

Magnetic resonance imaging has proven to be useful in the assessment of rotator cuff injuries. Improvements in magnetic resonance techniques, including fast spin-echo imaging and fat saturation, have facilitated demonstration of tendinous abnormalities of the rotator cuff. Rotator cuff disease is multifactorial. Primary impingement within the coracoacromial arch, degeneration of the rotator cuff tendons, trauma, and glenohumeral instability may be contributing factors. Shoulder pain in athletes can be related to acute myotendinous and muscle injuries, which can be easily detected using magnetic resonance imaging.

Relevance of arm position and muscle activity on three-dimensional glenohumeral translation in patients with traumatic and atraumatic shoulder instability

BACKGROUND

No quantitative data on glenohumeral translation exist allowing one to distinguish insufficiency of the active or passive stabilizers in different forms of shoulder instability.

HYPOTHESIS

To determine whether 1) in traumatic or atraumatic shoulder instability an increase of glenohumeral translation can be observed in specific relevant arm positions, 2) muscle activity leads to recentering of the humeral head, and 3) there exist differences between traumatic and atraumatic instability.

STUDY DESIGN

Prospective clinical trial.

METHODS

In 12 patients with traumatic and 10 patients with atraumatic instability, both shoulders were examined in different arm positions-with and without muscle activity-by using open magnetic resonance imaging and a three-dimensional postprocessing technique.

RESULTS

At 90 degrees of abduction and external rotation, translation (anterior-inferior) was significantly higher in patients with traumatic unstable shoulders compared with their contralateral side (3.6 +/- 1.5 versus 0.7 +/- 1.6 mm). In patients with atraumatic instability, significantly increased translation (4.7 +/- 2.0 mm) was observed, with the direction being nonuniform. Muscle activity led to significant recentering in traumatic but not in atraumatic instability.

CONCLUSIONS

In traumatic instability, increased translation was observed only in functionally important arm positions, whereas intact active stabilizers demonstrate sufficient recentering. In atraumatic instability, a decentralized head position was recorded also during muscle activity, suggesting alterations of the active stabilizers.

CLINICAL RELEVANCE

These data are relevant for optimizing diagnostics and therapeutic strategies.

Magnetic resonance imaging of sports-related injuries to the shoulder: impingement and rotator cuff

MR imaging provides clinically useful information in detecting and characterizing sports-related pathology of the rotator cuff and other shoulder disorders in a non-invasive fashion. Complete and partial tears of the rotator cuff, as well as factors contributing to impingement, can be detected and characterized with MR imaging. The size and location of complete tears of the rotator cuff can be accurately determined with MR imaging.

Magnetic resonance imaging of the shoulder in asymptomatic professional baseball pitchers

The purpose of this study was to evaluate the magnetic resonance imaging findings in both shoulders of asymptomatic professional baseball pitchers. Fourteen pitchers who were without significant prior injury underwent a blinded clinical assessment and magnetic resonance imaging of both shoulders. All images were interpreted by two experienced musculoskeletal radiologists. The appearance of the rotator cuff tendons was graded, with additional evaluation of the biceps, labrum, and osseous structures. Ten athletes were found to have stable shoulders and painless full range of motion. Clinically, four athletes had at least a 40 degrees loss in internal rotation as compared with the nonthrowing arm. There were no significant differences in magnetic resonance imaging findings of the supraspinatus and infraspinatus tendons between the throwing and nonthrowing shoulders. The labrum was abnormal in 79% of the 28 shoulders. Enthesopathic changes of the posterior glenoid labrum were identified in the four pitchers who had loss of internal rotation. We conclude that unenhanced magnetic resonance imaging of the shoulder in asymptomatic high performance throwing athletes reveals abnormalities that may encompass a spectrum of "nonclinical" findings. These data can be useful in separating symptomatic pathologic findings from these variants. Enthesopathic changes of the posterior glenoid labrum in the throwing arm may represent an early Bennett-type lesion. The cause may be excessive traction on the posterior capsule during the pitching motion, with subclinical injury to this area.

MR evaluation of factors predicting the development of rotator cuff tears

PURPOSE

The purpose of this work was to assess the incidence of various factors predicting impingement in the shoulder.

METHOD

MR examination was used to assess various anatomic parameters in 46 patients with clinical abnormalities of the shoulder and 40 asymptomatic volunteers. All patients had undergone surgery, showing no rotator cuff tear.

RESULTS

A few of the parameters evaluated were significantly different in the two groups: The acromion was more frequently curved or hook-shaped in patients than in volunteers. The acromiohumeral distances differed (4.87 mm in patients and 6.05 mm in volunteers); so did the coracohumeral distances (7.9 mm in patients and 8.9 mm in volunteers). The shape of the acromioclavicular joint and the anterior covering of the humerus, defined on the coronal view, also differed (1.07 mm in patients and 1.49 mm in volunteers). Only the shapes of the acromioclavicular joint and of the acromion were linked with age.

CONCLUSION

All these factors reflected a decrease in the acromiohumeral space, except for the anterior covering of the acromial arch, which could be due to anterior instability.

Sex-specific differences of subacromial space width during abduction, with and without muscular activity, and correlation with anthropometric variables

The objectives of this study were to determine sex-specific differences of the subacromial space width during active and passive arm abduction and to analyze the correlation of this space with general and regional anthropometric variables. Fourteen healthy subjects (7 men, 7 women) were examined with an open magnetic resonance system at 30 degrees and 90 degrees of abduction (with and without muscle activity). After 3-dimensional reconstruction, the minimal acromiohumeral distance, the glenoid size, and the humeral head radius were determined. At 30 degrees of abduction, a significant difference of the acromiohumeral distance was observed between men (8.18 +/- 1.0 mm) and women (6.98 +/- 0.75 mm) (P < .05), but not at 90 degrees (6.7 +/- 2.0 mm versus 5.9 +/- 1.0 mm) or under muscle activity (4.9 +/- 2.4 mm versus 3.5 +/- 2.1 mm). Significant correlations between the acromiohumeral distance and anthropometric variables were found at 30 degrees of abduction (r = 0.48 to 0.72), but not at 90 degrees, with or without muscle activity (r = 0.21 to 0.55). The results demonstrate that at physical rest, the subacromial space width is dependent on sex, but the interindividual variability increases substantially during abduction and under muscle activity.

Magnetic resonance imaging of the coraco-acromial ligament

The coraco-acromial ligament is important first for the stability of the shoulder joint and second because it can impinge on the rotator cuff. In this study we demonstrate how the coraco-acromial ligament can be shown by magnetic resonance imaging (MRI) in the axial plane as well as in the more conventional coronal and sagittal planes.

Imaging of the painful shoulder

A variety of imaging techniques are available for evaluating shoulder pathology. The common disorders of impingement, rotator cuff tears, biceps tenosynovitis and instability are discussed along with the role of various imaging modalities in establishing their diagnosis. Plain radiographs can provide useful information particularly with a history of trauma but give limited information on the soft tissue structures around the shoulder. Ultrasound is a useful and inexpensive means of assessing the biceps tendon and rotator cuff but has a number of limitations and varying reports on its accuracy. Computed tomography (CT) is most helpful in the evaluation of shoulder trauma but gives limited information on the soft tissues. When performed with intra-articular contrast, CT can be used to evaluate shoulder instability particularly in cases where magnetic resonance imaging (MRI) is not available or contraindicated. MRI with or without intra-articular contrast is the most accurate imaging modality for evaluating shoulder pathology allowing visualization of the soft tissues that are often the source of pain.

A practical approach to imaging of the shoulder with emphasis on MR imaging

Our understanding of shoulder disorders has changed considerably as a result of improved diagnostic tools, such as arthroscopy and multiplanar imaging modalities. The diagnosis of the cause of shoulder pain can be difficult because a spectrum of disorders, including cervical spine disease, acromioclavicular arthritis, and shoulder instability. Impingement and denervation syndromes can present with similar clinical findings. Accurate depiction of anatomic abnormalities is important for treatment planning. The purpose of this article is to report on the application of available imaging modalities, with emphasis on MR imaging. A strategy for the appropriate use of these studies and their variations of technique is also provided.