Magnetic resonance-based motion analysis of the shoulder during elevation

Practical considerations for determination of scapular internal rotation and its relevance in reverse total shoulder arthroplasty planning

BACKGROUND

Scapulothoracic orientation, especially scapular internal rotation (SIR) may influence range of motion in reverse total shoulder arthroplasty (RTSA) and is subjected to body posture. Clinical measurements of SIR rely on apical bony landmarks, which depend on changes in scapulothoracic orientation, while radiographic measurements are often limited by the restricted field of view (FOV) in CT scans. Therefore, the goal of this study was (1) to determine whether the use of CT scans with a limited FOV to measure SIR is reliable and (2) if a clinical measurement could be a valuable alternative.

METHODS

This anatomical study analyzed the whole-body CT scans of 100 shoulders in 50 patients (32 male and 18 female) with a mean age of 61.2 ± 20.1 years (range 18; 91). (1) CT scans were rendered into 3D models and SIR was determined as previously described. Results were compared to measurements taken in 2D CT scans with a limited FOV. (2) Three apical bony landmarks were defined: (the angulus acromii (AA), the midpoint between the AA and the coracoid process tip (C) and the acromioclavicular (AC) joint. The scapular axis was determined connecting the trigonum scapulae with these landmarks and referenced to the glenoid center. The measurements were repeated with 0°, 10°, 20°, 30° and 40° anterior scapular tilt.

RESULTS

Mean SIR was 44.8° ± 5.9° and 45.6° ± 6.6° in the 3D and 2D model, respectively (p < 0.371). Mean difference between the measurements was 0.8° ± 2.5° with a maximum of 10.5°. Midpoint AA/C showed no significant difference to the scapular axis at 0° (p = 0.203) as did the AC-joint at 10° anterior scapular tilt (p = 0.949). All other points showed a significant difference from the scapular axis at all degrees of tilt.

CONCLUSION

2D CT scans are reliable to determine SIR, even if the spine is not depicted. Clinical measurements using apical superficial scapula landmarks are a possible alternative; however, anterior tilt influenced by posture alters measured SIR.

Anteroinferior bundle of the acromioclavicular ligament plays a substantial role in the joint function during shoulder elevation and horizontal adduction: a finite element model

Background

Postoperative acromioclavicular (AC) ligament deficiency has been identified as a common cause of failure after isolated coracoclavicular reconstruction. The two-bundle arrangement of the acromioclavicular ligament has recently been reported in histological and anatomical research. In addition, a clear structural advantage of the superoposterior bundle (SPB) over the less consistent anteroinferior bundle (AIB) was also found. However, the current understanding of the function of the acromioclavicular ligament in joint stability is based on uniaxial bone loading experiments and sequential ligament sectioning. Consequently, these rigid biomechanics models do not reproduce the coupled physiological kinematics, neither in the normal joint nor in the postoperative condition. Therefore, our goal was to build a quasi-static finite element model to study the function of the acromioclavicular ligament based on its biomechanical performance patterns using the benefits of computational models.

Methods

A three-dimensional bone model is reconstructed using images from a healthy shoulder. The ligament structures were modeled according to the architecture and dimensions of the bone. The kinematics conditions for the shoulder girdle were determined after the osseous axes aligned to simulate the shoulder elevation in the coronal plane and horizontal adduction. Three patterns evaluated ligament function. The peak von Mises stress values were recorded using a clock model that identified the stress distribution. In addition, the variation in length and displacement of the ligament during shoulder motion were compared using a two-tailed hypotheses test. P values < 0.01 were considered statistically significant.

Results

The peak von Mises stress was consistently observed in the AIB at 2:30 in coronal elevation (4.06 MPa) and horizontal adduction (2.32 MPa). Except in the position 2:00, statistically significant higher deformations were identified in the two bundles during shoulder elevation. The highest ligament displacement was observed on the Y- and Z-axes.

Conclusions

The AIB has the primary role in restricting the acromioclavicular joint during shoulder motion, even though the two bundles of the AC ligament have a complementary mode of action. During horizontal adduction, the SPB appears to prevent anterior and superior translation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-02966-0.

Comparison of glenohumeral joint kinematics between manual wheelchair tasks and implications on the subacromial space: A biplane fluoroscopy study

Scapula and humerus motion associated with common manual wheelchair tasks is hypothesized to reduce the subacromial space. However, previous work relied on either marker-based motion capture for kinematic measures, which is prone to skin-motion artifact; or ultrasound imaging for arthrokinematic measures, which are 2D and acquired in statically-held positions. The aim of this study was to use a fluoroscopy-based approach to accurately quantify glenohumeral kinematics during manual wheelchair use, and compare tasks for a subset of parameters theorized to be associated with mechanical impingement. Biplane images of the dominant shoulder were acquired during scapular plane elevation, propulsion, sideways lean, and weight-relief raise in ten manual wheelchair users with spinal cord injury. A computed tomography scan of the shoulder was obtained, and model-based tracking was used to quantify six-degree-of-freedom glenohumeral kinematics. Axial rotation and superior/inferior and anterior/posterior humeral head positions were characterized for full activity cycles and compared between tasks. The change in the subacromial space was also determined for the period of each task defined by maximal change in the aforementioned parameters. Propulsion, sideways lean, and weight-relief raise, but not scapular plane elevation, were marked by mean internal rotation (8.1°, 10.8°, 14.7°, -49.2° respectively). On average, the humeral head was most superiorly positioned during the weight-relief raise (1.6 ± 0.9 mm), but not significantly different from the sideways lean (0.8 ± 1.1 mm) (p = 0.191), and much of the task was characterized by inferior translation. Scaption was the only task without a defined period of superior translation on average. Pairwise comparisons revealed no significant differences between tasks for anterior/posterior position (task means range: 0.1-1.7 mm), but each task exhibited defined periods of anterior translation. There was not a consistent trend across tasks between internal rotation, superior translation, and anterior translation with reductions in the subacromial space. Further research is warranted to determine the likelihood of mechanical impingement during these tasks based on the measured task kinematics and reductions in the subacromial space.

Comparison of In Vivo Three-Dimensional Glenohumeral Positions and Scapular Kinematics between Young and Older Male Groups

Background

Many researchers have questioned whether shoulder kinematics such as the glenohumeral position and scapular kinematics would be different in different age groups. However, studies comparing shoulder kinematics between different age groups have been rare. The aim of this study was to analyze and compare the three-dimensional (3D) glenohumeral position, scapular kinematics, and scapulohumeral rhythm (SHR) during scapular plane arm abduction between a normal young male group and a normal older male group.

Methods

Twenty normal men (10 young and 10 older) were enrolled in this controlled laboratory study. Fluoroscopic images were obtained using a single plane X-ray system. Bilateral computed tomography scans were taken to create a 3D model. A 3D-2D registration technique was used to determine the 3D position and orientation of the bones of the shoulder.

Results

During scapular plane arm abduction, there were significant differences in scapular kinematics between the groups. The older male group showed more upward rotation, posterior tilt, and external rotation than the young male group. On the other hand, the glenohumeral position such as superior inferior translation, anterior posterior translation, and external rotation of the humeral head did not show significant difference between the groups. The mean value of SHR for the overall arm elevation range from start to maximum elevation angle for the older group and young group was 2.298 ± 0.964 and 2.622 ± 0.931, respectively, showing a significant difference between the two groups (p = 0.035).

Conclusions

Scapular kinematics and SHR were significantly different between the older male group and the young male group. Our study could provide reference values of shoulder kinematics for older men aged 55–65 years.

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, multiple ligaments, and approximately 20 muscles. Unfortunately, shoulder pathologies (e.g., rotator cuff tears, joint dislocations, arthritis) are common, resulting in substantial pain, disability, and decreased quality of life. The specific etiology for many of these pathologic conditions is not fully understood, but it is generally accepted that shoulder pathology is often associated with altered joint motion. Unfortunately, measuring shoulder motion with the necessary level of accuracy to investigate motion-based hypotheses is not trivial. However, radiographic-based motion measurement techniques have provided the advancement necessary to investigate motion-based hypotheses and provide a mechanistic understanding of shoulder function. Thus, the purpose of this article is to describe the approaches for measuring shoulder motion using a custom biplanar videoradiography system. The specific objectives of this article are to describe the protocols to acquire biplanar videoradiographic images of the shoulder complex, acquire CT scans, develop 3D bone models, locate anatomical landmarks, track the position and orientation of the humerus, scapula, and torso from the biplanar radiographic images, and calculate the kinematic outcome measures. In addition, the article will describe special considerations unique to the shoulder when measuring joint kinematics using this approach.

Association between acromioclavicular joint pain and capsular bulging in adolescent baseball players

PURPOSE

The purpose of this study was to investigate the association between acromioclavicular (AC) joint pain and superior capsular bulging assessed by ultrasound in adolescent baseball players.

METHODS

One hundred and fifty players (1st-8th graders) were examined. All subjects underwent physical examinations, including assessment of tenderness on the AC joint and provocative tests (the Buchberger's test and the cross-body adduction stress test). Bilateral AC joints with the arm in both the resting and the cross-body positions were examined by ultrasound.

RESULTS

Twelve of 150 players (8 %) had AC symptoms with both positive tenderness and positive provocative tests. Interestingly, their prevalence increased with age-one of the 70 (1.4 %) 1st-3rd graders, six of 46 (13 %) 4th-6th graders and five of 34 (15 %) 7th-8th graders. Ultrasonography of AC joints in the cross-body position showed that the difference in superior capsular bulging between the throwing and non-throwing sides was significantly greater in symptomatic players (1.6 ± 1.2 mm) than in asymptomatic players (0.2 ± 0.8 mm) (p = 0.002).

CONCLUSION

The prevalence of superior capsular bulging was significantly higher in adolescent baseball players with AC joint pain than in those without it. In adolescent baseball players with shoulder pain, AC joint symptoms should be considered amongst potential causes. Careful observation of these patients is suggested in cases of superior capsular bulging of the AC joint as determined by ultrasonography.

LEVEL OF EVIDENCE

III.

Dynamic Three-Dimensional Shoulder Mri during Active Motion for Investigation of Rotator Cuff Diseases

Background

MRI is the standard methodology in diagnosis of rotator cuff diseases. However, many patients continue to have pain despite treatment, and MRI of a static unloaded shoulder seems insufficient for best diagnosis and treatment. This study evaluated if Dynamic MRI provides novel kinematic data that can be used to improve the understanding, diagnosis and best treatment of rotator cuff diseases.

Methods

Dynamic MRI provided real-time 3D image series and was used to measure changes in the width of subacromial space, superior-inferior translation and anterior-posterior translation of the humeral head relative to the glenoid during active abduction. These measures were investigated for consistency with the rotator cuff diseases classifications from standard MRI.

Results

The study included: 4 shoulders with massive rotator cuff tears, 5 shoulders with an isolated full-thickness supraspinatus tear, 5 shoulders with tendinopathy and 6 normal shoulders. A change in the width of subacromial space greater than 4mm differentiated between rotator cuff diseases with tendon tears (massive cuff tears and supraspinatus tear) and without tears (tendinopathy) (p = 0.012). The range of the superior-inferior translation was higher in the massive cuff tears group (6.4mm) than in normals (3.4mm) (p = 0.02). The range of the anterior-posterior translation was higher in the massive cuff tears (9.2 mm) and supraspinatus tear (9.3 mm) shoulders compared to normals (3.5mm) and tendinopathy (4.8mm) shoulders (p = 0.05).

Conclusion

The Dynamic MRI enabled a novel measure; ‘Looseness’, i.e. the translation of the humeral head on the glenoid during an abduction cycle. Looseness was better able at differentiating different forms of rotator cuff disease than a simple static measure of relative glenohumeral position.

Measurement of dynamic scapular kinematics using an acromion marker cluster to minimize skin movement artifact

The measurement of dynamic scapular kinematics is complex due to the sliding nature of the scapula beneath the skin surface. The aim of the study was to clearly describe the acromion marker cluster (AMC) method of determining scapular kinematics when using a passive marker motion capture system, with consideration for the sources of error which could affect the validity and reliability of measurements. The AMC method involves placing a cluster of markers over the posterior acromion, and through calibration of anatomical landmarks with respect to the marker cluster it is possible to obtain valid measurements of scapular kinematics. The reliability of the method was examined between two days in a group of 15 healthy individuals (aged 19-38 years, eight males) as they performed arm elevation, to 120°, and lowering in the frontal, scapular and sagittal planes. Results showed that between-day reliability was good for upward scapular rotation (Coefficient of Multiple Correlation; CMC = 0.92) and posterior tilt (CMC = 0.70) but fair for internal rotation (CMC = 0.53) during the arm elevation phase. The waveform error was lower for upward rotation (2.7° to 4.4°) and posterior tilt (1.3° to 2.8°), compared to internal rotation (5.4° to 7.3°). The reliability during the lowering phase was comparable to results observed during the elevation phase. If the protocol outlined in this study is adhered to, the AMC provides a reliable measurement of upward rotation and posterior tilt during the elevation and lowering phases of arm movement.

Automatic bone segmentation and bone-cartilage interface extraction for the shoulder joint from magnetic resonance images

We present a statistical shape model approach for automated segmentation of the proximal humerus and scapula with subsequent bone-cartilage interface (BCI) extraction from 3D magnetic resonance (MR) images of the shoulder region. Manual and automated bone segmentations from shoulder MR examinations from 25 healthy subjects acquired using steady-state free precession sequences were compared with the Dice similarity coefficient (DSC). The mean DSC scores between the manual and automated segmentations of the humerus and scapula bone volumes surrounding the BCI region were 0.926  ±  0.050 and 0.837  ±  0.059, respectively. The mean DSC values obtained for BCI extraction were 0.806  ±  0.133 for the humerus and 0.795  ±  0.117 for the scapula. The current model-based approach successfully provided automated bone segmentation and BCI extraction from MR images of the shoulder. In future work, this framework appears to provide a promising avenue for automated segmentation and quantitative analysis of cartilage in the glenohumeral joint.

Management of acromioclavicular joint injuries

Although recent advances have been made in the treatment of acromioclavicular (AC) joint injuries, they are still challenging for shoulder surgeons. There is a consensus that type I and II injuries should be treated nonoperatively, whereas acute type IV, V, and VI injuries should be treated surgically. There is no algorithm for correctly diagnosing and treating type III injuries, but the current trend is toward nonoperative treatment except for those with persistent symptoms and functional limitations after a course of conservative management. If surgery is indicated, newer anatomic techniques of reconstructing the coracoclavicular (CC) and AC ligaments are recommended.

Glenohumeral relationships at different angles of abduction

PURPOSE

The objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction.

METHODS

Fifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position.

RESULTS

The average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head.

CONCLUSIONS

The glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.

Accurate semiautomatic assessment of ligament length variations from MRI data

PURPOSE

A semiautomatic method for the assessment of ligament length variations during different joint positions based on MRI data is proposed.

METHODS

Ligament lengths are represented as distances between points marking characteristic locations in the ligament insertion regions on the bones. These points are defined manually for one single reference joint position and for all other joint positions they are automatically mapped with high accuracy to the correct locations using image registration methods. The methodology is validated using data from 16 volunteers depicting the coracoclavicular ligaments in the left shoulder during different arm abductions.

RESULTS

The method yielded a superior reproducibility of the point locations over different joint positions compared to manual point marking. Significant ligament length variations were found for different abductions which was not possible with manual measurements. Acquisition related geometric distortions and inaccuracies during the registration and segmentation process were small.

CONCLUSIONS

The proposed method provides superior accuracy for the in vivo analysis of ligament dynamics compared to manual measurements. This permits a better understanding of the ligament behavior during joint motion and offers new possibilities for presurgical planning which to date has not been possible with manual data analysis.

Biomechanical evaluation of 3 stabilization methods on acromioclavicular joint dislocations

BACKGROUND

Traumatic acromioclavicular (AC) joint dislocations can be addressed with several surgical stabilization techniques. The aim of this in vitro study was to evaluate biomechanical features of the native joint compared with 3 different stabilization methods: locking hook plate (HP), TightRope (TR), and bone anchor system (AS).

HYPOTHESIS

The HP provides higher stiffness than the anatomic reconstruction techniques.

STUDY DESIGN

Controlled laboratory study.

METHODS

A new biomechanical in vitro model of the AC joint was used to analyze joint stability after surgical repair (HP, TR, and AS). Eighteen cadaveric specimens were randomized for bone density and diameter in the midclavicle section. Joint stiffness was measured by applying an axial load and a defined physiological range of motion for internal and external rotations and upward and downward rotations. Data were recorded at 3 stages: for the native joint after dissecting the AC ligaments, directly after repair, and after axial cyclic loading (1000 cycles with 20 and 70 N at 1 Hz). To evaluate which implant mimics physiological joint properties best, axial stiffness of vertical stability was assessed in combination with rotation. Finally, static loading in the superior direction was applied until failure of the joints occurred.

RESULTS

Axial stiffness of the TR and AS groups was 2-fold higher than for the HP group and the native joint (67.1, 66.1, and 22.5 N/mm, respectively; P < .004). Decreased load-to-failure rates were recorded in the HP group compared with the TR and AS groups (248.9 ± 72.7, 832.0 ± 401.4, and 538.0 ± 166.1 N, respectively). The stiffness of the rotations was not significantly different between the treatment methods but was lower in horizontal and downward rotations compared with the native state. Thus, native AC ligaments contributed a significant share to joint stiffness.

CONCLUSION

The TR and AS groups demonstrated higher vertical load capacity. Compared with the TR and AS, the HP demonstrated an axial stiffness closest to the native joint. For restoring physiological properties, reconstruction of the AC ligaments may be necessary.

CLINICAL RELEVANCE

The results show different biomechanical properties of the HP and anatomic reconstructions.

New dynamic three-dimensional MRI technique for shoulder kinematic analysis

PURPOSE

To establish a new imaging technique using dynamic MRI three-dimensional (3D) volumetric acquisition in real-time, on six normal shoulders for the analysis of the 3D shoulder kinematics during continuous motion.

MATERIALS AND METHODS

At first, a standard static acquisition was performed. Then, fast images were obtained with a multi-slice 3D balanced gradient echo sequence to get a real time series during the initial phase of shoulder abduction. Subsequently, the images were reconstructed; registered and the translational patterns of the humeral head relative to the glenoid and the size of the subacromial space were calculated. Additionally, the intraobserver reproducibility was tested.

RESULTS

The maximal abduction was on average 43° (30° to 60°) and the mean width of the subacromial space was 7.7 mm (SD: ±1.2 mm). Difference between extreme values and average values was low, respectively 2.5 mm on X-axis, 2 mm on Y-axis, 1.4 mm for the width of the subacromial space and 1.2° for the measure of the glenohumeral abduction.

CONCLUSION

This study reported a dynamic MRI protocol for the monitoring of shoulder 3D kinematics during continuous movement. The results suggest that there is no superior shift of the humeral head during the first phase of abduction.

Localization of degenerative changes of the acromioclavicular joint: a cadaveric study

PURPOSE

It has not been fully clarified yet how degenerative changes occur within the acromioclavicular (AC) joint, including their localizations. The aim of this study was to clarify the localization of degenerative changes in the AC joint using cadaveric specimens.

METHODS

Thirty-eight cadaveric AC joints with the sections were cut in the coronal plane. For both the acromion and the clavicle, the joint surface was divided into upper and lower halves. Histological features including the mean thickness of cartilage, reduction of proteoglycan staining and the extent of damaged tidemark were evaluated. The shapes of intraarticular discs as well as their histological structures were also assessed, which were compared between the upper and lower halves.

RESULTS

Articular cartilage in the lower half was significantly thinner than that in the upper half for both the acromion and the clavicle (p < 0.01). Similarly, the lower half of cartilage was more degenerated than the upper half. Intraarticular discs were absent in nine joints and the meniscoid-like type in 29, which contained rich fibrocartilaginous tissues in the upper half, whereas it mainly consisted of the fibrous tissues with granulation in the lower half.

CONCLUSION

The lower half of the AC joint demonstrated more advanced degeneration than the upper half, which might reflect the greater repetitive mechanical stress. The present study revealed both the localization and the extent of degenerative changes in AC joint, which might be useful information for surgeons to determine the proper amount of bony resection in the surgical treatment for osteoarthritis of this joint.

Dynamic function of coracoclavicular ligament at different shoulder abduction angles: a study using a 3-dimensional finite element model

PURPOSE

The aim of this study was to determine the acromioclavicular (AC) motion and change in length and tension of the coracoclavicular ligament during different positions of shoulder abduction using a 3-dimensional finite element model based on computed tomography images from normal human shoulders.

METHODS

The right shoulders of 10 living subjects were scanned with a high-resolution computed tomography scanner at 0°, 60°, 120°, and 180° of shoulder abduction. Several modeling programs were used to simulate AC motion. Finite element models of the conoid and trapezoid ligaments were constructed based on each footprint. The tension and length changes of each ligament during shoulder abduction were assessed.

RESULTS

The distal clavicle exhibited internal rotation with respect to the medial acromion at 0°, 60°, 120°, and full abduction (3.2° ± 2.9°, 23.2° ± 10.8°, 20.6° ± 3.7°, and 37.1° ± 3.4°, respectively). With horizontal motion, the clavicle translated posteriorly at 60° of abduction (4.4 ± 3.4 mm) and then translated anteriorly at 120° and full abduction (0.4 ± 1.6 mm and 1.9 ± 0.4 mm, respectively). The lengths of the conoid ligament gradually increased at 60° to 180° of shoulder abduction whereas those of the trapezoid ligament remained relatively consistent at 60° to 120° of abduction compared with 0° of abduction.

CONCLUSIONS

The distal clavicle had a wide range of motion during shoulder abduction, which did not support the concept of synchronous motion with the scapula. The conoid and trapezoid ligaments functioned reciprocally during shoulder abduction. With increasing shoulder abduction, the length of the conoid ligament gradually increased; meanwhile, the trapezoid ligament was relatively consistent and then lax at full abduction. In particular, the conoid ligament may act as a key restraint to prevent excessive retraction of the scapula during shoulder abduction.

CLINICAL RELEVANCE

The data in this study have the potential to suggest that conoid and trapezoid ligaments should be reconstructed separately, and rigid AC fixation in patients with AC separation is not recommended based on the findings of this study.

The accuracy of measuring glenohumeral motion with a surface humeral cuff

Conclusions about normal and pathologic shoulder motion are frequently made from studies using skin surface markers, yet accuracy of such sensors representing humeral motion is not well known. Nineteen subjects were investigated with flock of birds electromagnetic sensors attached to transcortical pins placed into the scapula and humerus, and a thermoplastic cuff secured on the arm. Subjects completed two repetitions of raising and lowering the arm in the sagittal, scapular and coronal planes, as well as shoulder internal and external rotation with the elbow at the side and abducted to 90°. Humeral motion was recorded simultaneously from surface and bone fixed sensors. The average magnitude of error was calculated for the surface and bone fixed measurements throughout the range of motion. ANOVA tested for differences across angles of elevation, raising and lowering, and differences in body mass index. For all five motions tested, the plane of elevation rotation average absolute error ranged from 0-2°, while the humeral elevation rotation average error ranged from 0-4°. The axial rotation average absolute error was much greater, ranging from 5° during elevation motions to approaching 30° at maximum excursion of internal/external rotation motions. Average absolute error was greater in subjects with body mass index greater than 25. Surface sensors are an accurate way of measuring humeral elevation rotations and plane of elevation rotations. Conversely, there is a large amount of average error for axial rotations when using a humeral cuff to measure glenohumeral internal/external rotation as the primary motion.

In vivo analysis of coracoclavicular ligament kinematics during shoulder abduction

BACKGROUND

Anatomic reconstruction of the coracoclavicular ligaments for the treatment of acromioclavicular joint separations provides superior biomechanical stability compared with other procedures. Clavicular and coracoidal footprints of the conoid ligament (CL) and the trapezoid ligament (TL) are well described. So far, little is known about their kinematics and the changes of the coracoclavicular distance during shoulder abduction.

HYPOTHESIS

The coracoclavicular distance along the coracoclavicular ligaments changes significantly with shoulder abduction and weightbearing.

STUDY DESIGN

Descriptive laboratory study.

METHODS

With use of an open magnetic resonance imaging scanner, the shoulders of 13 healthy volunteers were examined in supine and sitting positions. Three-dimensional magnetic resonance images of the shoulders were obtained in 30° increments of abduction (0°-120°). A manual segmentation of the scapula, the clavicle, and the coracoclavicular ligaments was performed. The insertion points of the coracoclavicular ligaments were identified, and automated measures along the ligamentous course were carried out.

RESULTS

During transfer from the lying to sitting position, the coracoclavicular distance showed significant lengthening of 3 mm along the center of the CL, which significantly increased another 3 mm during shoulder abduction to a total lengthening of 6 mm. In the supine position, the coracoclavicular distance along the TL did not elongate significantly. In the sitting position, the distance along the medial portion of the TL shortened significantly, whereas the distance along the center portion did not elongate significantly during shoulder abduction.

CONCLUSION

The distances between the coracoclavicular insertion points depend on both patient and shoulder positioning. To prevent overconstraining of the graft, the CL should be fixated during 90° to 120° of shoulder abduction in a sitting position. Isometric reconstruction of the TL can be achieved if precise fixation of the graft at the centers of the conoidal and clavicular footprints is performed.

Does scapula taping facilitate recovery for shoulder impingement symptoms? A pilot randomized controlled trial

Scapula taping is a commonly used adjunctive treatment for shoulder impingement pathology. However, this intervention has not previously been subject to formal investigation. A pilot single-blind randomized controlled trial was conducted to evaluate facilitatory taping as an adjunct to routine physiotherapy management. Twenty-two subjects with unilateral shoulder impingement symptoms were randomized into a taping with routine physiotherapy or a routine physiotherapy only group. The intervention group had scapula taping applied three times per week for the first two weeks of their treatment. All subjects were assessed at baseline, then at 2 and 6 weeks after the commencement of treatment. Pain and functional ability were assessed using the Shoulder Pain and Disability Index, range of shoulder elevation, and self-reported pain on elevation. At 2 weeks, the taping group demonstrated a strong trend toward reduced pain both on self-reported activity (SPADI pain subscale mean for taping 27.0 versus 41.5 for control) and pain during measured abduction (mean VAS 22.8 for taped, 46.8 for control), statistical power being limited by small sample size. No similar trend was evident in the SPADI disability subscale. The magnitude of the differences was reduced at 6-week follow-up. This study provides preliminary evidence for a short-term role for scapula taping as an adjunct to routine physiotherapy in the management of shoulder impingement symptoms but also highlights the need for consideration on a case basis relating to risk factors for skin reaction.

Scapular positioning and movement in unimpaired shoulders, shoulder impingement syndrome, and glenohumeral instability

The purpose of this manuscript is to review the knowledge of scapular positioning at rest and scapular movement in different anatomic planes in asymptomatic subjects and patients with shoulder impingement syndrome (SIS) and glenohumeral shoulder instability. We reviewed the literature for all biomechanical and kinematic studies using keywords for impingement syndrome, shoulder instability, and scapular movement published in peer reviewed journal. Based on the predefined inclusion and exclusion criteria, 30 articles were selected for inclusion in the review. The literature is inconsistent regarding the scapular resting position. At rest, the scapula is positioned approximately horizontal, 35° of internal rotation and 10° anterior tilt. During shoulder elevation, most researchers agree that the scapula tilts posteriorly and rotates both upward and externally. It appears that during shoulder elevation, patients with SIS demonstrate a decreased upward scapular rotation, a decreased posterior tilt, and a decrease in external rotation. In patients with glenohumeral shoulder instability, a decreased scapular upward rotation and increased internal rotation is seen. This literature overview provides clinicians with insight into scapular kinematics in unimpaired shoulders and shoulders with impingement syndrome and instability.

Biomechanical consequences of humeral component malpositioning after anatomical total shoulder arthroplasty

HYPOTHESIS

We hypothesized that the malpositioning of the humeral component can preclude the long-term success of anatomical total shoulder arthroplasty. The goal of this study was to evaluate the mechanical consequences of superior and inferior malpositioning of the humeral head.

MATERIALS AND METHODS

A numerical musculoskeletal model of the shoulder joint allowing natural humeral head translation was used to simulate a loaded abduction movement controlled by muscular activation. An inferior and superior malpositioning of 5 mm were compared to an optimal positioning. Impingements, articular contact pattern, and cement stress were evaluated.

RESULTS

Inferior malpositioning of the humeral head induced impingement and limited the abduction level, while superior malpositioning increased the subluxation risk. Both inferior and superior malpositioning increased the stress level within the cement mantle.

DISCUSSION

This numerical study highlights the importance of an anatomical reconstruction of the glenohumeral surfaces for the success rate of anatomical total shoulder arthroplasty.

Contribution of the supraspinatus to the external rotator lag sign: kinematic and electromyographic pattern in an in vivo model

HYPOTHESIS

The external rotation lag sign (ERLS) is a test designed to assess the integrity of the supraspinatus (SSP) and infraspinatus tendons. This study intends to determine the electromyographic pattern of shoulder girdle muscles during a series of ERLS tasks conducted at full adduction and 20 degrees of elevation to figure out the better way to perform the test. The second aim is to assess the final contribution of the SSP to the ERLS by measuring the amount of lag after an SSP block induced by botulinum toxin.

MATERIALS AND METHODS

Ten subjects with healthy shoulders were examined by a series of five ERLS trials at full adduction and 20 degrees of elevation in the scapular plane. Surface and intramuscular electromyographic activity of the shoulder girdle muscles was recorded and normalized against either the mean activity of all the muscles or the peak activity. The lag was simultaneously measured by an infrared optoelectronic system before and after the selective block of the SSP muscle.

RESULTS

The SSP contributed 20% of the electrical activities during the ERLS, which was found to be significantly greater than the contributions of the other shoulder girdle muscles, except for the infraspinatus. The selective block of the SSP caused a lag of 4 degrees in all 10 shoulders at 20 degrees but no increase in lag at 0 degrees of elevation.

CONCLUSIONS

The ERLS is potentially able to detect an isolated SSP tear if the test is performed correctly (20 degrees of abduction). The deltoid and biceps muscles are almost silent during the test, limiting confounding factors.

Investigation of the static and dynamic musculotendinous architecture of supraspinatus

To date, the architecture of supraspinatus (SP) and its relation to joint position has not been investigated. The purpose of this study was to quantify the dynamic architecture of the distinct regions of SP using ultrasound (US). Seventeen subjects (8 M/9 F), mean age 36.4 +/- 12.7 years, without tendon pathology were recruited. The SP was scanned in relaxed and contracted states. For the contracted state, SP was scanned with the shoulder actively abducted to 60 degrees and the glenohumeral joint in neutral rotation; 80 degrees external rotation; 80 degrees internal rotation. Fiber bundle length (FBL) and pennation angle (PA) of distinct regions, and muscle thickness were computed. Measurements of the posterior region were limited because of acromion shadowing. Parameters between regions and changes between relaxed and contracted states were analyzed using paired t-tests and repeated measures ANOVA (P < 0.05). On contraction in the anterior region, mean percentage of FBL shortening ranged between 9% and 21%. However, in the posterior region, shortening of approximately 2% only occurred in two of the three positions; lengthening of approximately 2.5% occurred in internal rotation. For the anterior region, the mean PA increased the least in the externally rotated position, and the mean PA of the middle part was smaller than the deep part for all states. Findings suggest changes in the architecture are not uniform throughout the muscle and joint position may play an important role in force production. The US protocol may serve as an outcome measure of adaptive changes of muscle function following surgery, training, and rehabilitation.

Different scapular kinematics in healthy subjects during arm elevation and lowering: glenohumeral and scapulothoracic patterns

HYPOTHESIS

The scapulothoracic (ST) joint affects glenohumeral (GH) joint function. We observed 3-dimensional scapular motions during arm elevation and lowering to identify the scapulohumeral rhythm in healthy subjects and to compare it between the dominant and nondominant arms.

MATERIALS AND METHODS

Twenty-one healthy subjects participated in this study. Participants randomly elevated and lowered the arms in the scapular plane, and data were recorded by a computerized 3-dimensional motion analyzer at each 10 degrees increment.

RESULTS

Of the 42 shoulders, 21 showed a greater ratio of GH motion relative to ST motion whereas the other 21 showed a smaller ratio of GH motion relative to ST motion. The angle of upward rotation of the scapula showed a statistically significant difference between both types. The mean maximum angles of upward rotation, posterior tilting, and internal rotation were 36.2 degrees +/- 7.0 degrees , 38.7 degrees +/- 5.7 degrees , and 36.8 degrees +/- 12.2 degrees , respectively. No significant difference was found in angles of 3 scapular rotations between the dominant and nondominant arms.

DISCUSSION

These results indicate that there are 2 distinctly different scapulohumeral rhythms in healthy subjects but without a significant difference between dominant and nondominant arms. These findings should be referred to when one is interpreting kinematics in a variety of shoulder disorders.

Rotator cuff fatigue and glenohumeral kinematics in participants without shoulder dysfunction

CONTEXT

Researchers have established that superior migration of the humeral head increases after fatigue of the rotator cuff muscles. In these studies, the investigators used imaging techniques to assess migration of the humeral head during statically held shoulder positions. Their results may not represent the amount of superior humeral head migration that occurs during dynamic arm elevation.

OBJECTIVE

To investigate the effect of rotator cuff fatigue on humeral head migration during dynamic concentric arm elevation (arm at the side [approximately 0 degrees ] to 135 degrees ) in healthy individuals and to determine the test-retest reliability of digital fluoroscopic video for assessing glenohumeral migration.

DESIGN

Test-retest cohort study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty men (age = 27.7 +/- 3.6 years, mass = 81.5 +/- 11.8 kg) without shoulder disorders participated in this study.

INTERVENTION(S)

Three digital fluoroscopic videos (2 pre-fatigue and 1 post-fatigue) of arm elevation were collected at 30 Hz. The 2 pre-fatigue arm elevation trials were used to assess test-retest reliability with the arm at the side and at 45 degrees , 90 degrees , and 135 degrees of elevation. The pre-fatigue and post-fatigue digital fluoroscopic videos were used to assess the effects of rotator cuff fatigue on glenohumeral migration. All measurements were taken in the right shoulder.

MAIN OUTCOME MEASURE(S)

The dependent measure was glenohumeral migration (in millimeters). We calculated the intraclass correlation coefficient and standard error of the measurement to assess the test-retest reliability. A 2 x 4 repeated-measures analysis of variance was used to assess the effects of fatigue on arm elevation at the 4 shoulder positions.

RESULTS

The test-retest reliability ranged from good to excellent (.77 to .92). Superior migration of the humeral head increased post-fatigue (P < .001), regardless of angle.

CONCLUSIONS

Digital fluoroscopic video assessment of shoulder kinematics provides a reliable tool for studying kinematics during arm elevation. Furthermore, superior migration of the humeral head during arm elevation increases with rotator cuff fatigue in individuals without shoulder dysfunction.

Shoulder motion description: the ISB and Globe methods are identical

BACKGROUND

Three-dimensional shoulder position may be described by rotation sequences such as the proposed ISB standard. Alternative techniques to describe position (the Globe method) seek to simplify this description by eliminating rotation sequences and substituting unambiguous measurements.

METHODS

Both methods (ISB and Globe) were applied to an analysis of shoulder positions, and an overall comparison was performed.

FINDINGS

The ISB and Globe methods are numerically identical and interchangeable.

INTERPRETATION

While all analytic methods are mathematically equivalent, investigators have sought simpler and more easily-applied ways of describing shoulder position that would be accurate, easily understood by clinicians, and unambiguous. This study demonstrates that the ISB rotation sequence and Globe descriptive method are numerically the same.

Glenohumeral motion: review of measurement techniques

Measurement of upper limb motion is problematic, not least because of the large range of path dependent description of motion of the joints, and the multiple non-cyclical unstandardised motion tasks measured. Furthermore, appreciation of shoulder motion specifically is obscured by overlying soft tissue. In order to satisfy the complexity of a clinically useful model of the movement of the joint, input data must be acquired from a set of pre-determined movements using a non-invasive technique with a high level of accuracy. Descriptive and predictive modeling of the glenohumeral joint requires input of high-fidelity data into a 6 degree of freedom representation, without which, the application of the tool is of limited clinical significance to the advancement of both operative and non-operative management of shoulder pathology. Electromagnetic, linkage and radiographic techniques have previously been used, however, an optimal solution is yet to be described.

Three-dimensional clavicular and acromioclavicular rotations during arm abduction using vertically open MRI

There have been several reports about the clavicular and acromioclavicular motion, but a precise motion has been unknown. The purpose of this study was to analyze the 3D kinematics of the clavicle and acromioclavicular joint during arm abduction, using 3D MR images obtained by a vertically open MRI. Seven subjects participated in this investigation, which included 14 shoulders. From a seated position, we obtained MR images of their shoulder in seven abducted positions of the arm in the coronal plane. We evaluated the 3D movements of each bone in the shoulder using the volume-based registration technique, and analyzed the clavicular positions relative to the lung and the scapular positions relative to the clavicle. During arm abduction, the clavicular motion relative to the lung showed 30.6 degrees retraction, 7.3 degrees elevation, and 33.2 degrees posterior axial rotation. During arm abduction, the scapular motion relative to the clavicle showed 15.6 degrees protraction, 21.5 degrees upward rotation, and 22.2 degrees posterior tilting. This study succeeded in describing the 3D clavicular and acromioclavicular motion including the axial rotation of the clavicle, and it revealed that both motions had large degrees of rotations.

Asymmetrical shoulder kinematics in children with brachial plexus birth palsy

BACKGROUND

Shoulder movement patterns differ between limbs of children with unilateral brachial plexus birth palsy. To better understand the interlimb differences we examined the glenohumeral and scapulothoracic joint contributions to arm elevation.

METHODS

Sixteen children with brachial plexus birth palsy, 4-12 years of age participated. Shoulder 3D kinematic data were collected using a magnetic tracking device during arm elevation with the involved and non-involved limbs for three trials each at a fixed rate. Based on maximum arm elevation in the involved limb the children were divided into two groups: group one <or=75 degrees ; and group two >75 degrees .

FINDINGS

During arm elevation from 15 to 75 degrees the involved limb of group one displayed lower glenohumeral joint excursion than the non-involved and both limbs of group two. Scapular upward rotation was higher in the involved limb of both groups. For group one, the glenohumeral:scapulothoracic ratio for 15-75 degrees arm elevation was lower in the involved (0.6:1) than the non-involved (2.2:1) limb and both limbs of group two: involved (1.7:1); non-involved (1.9:1). During 15-135 degrees arm elevation for group two, the glenohumeral:scapulothoracic ratio was more similar between limbs: involved (1.5:1) and non-involved (2:1).

INTERPRETATION

The scapulothoracic joint made a greater contribution to arm elevation than the glenohumeral joint only in the involved limb of group one, altering the scapulohumeral rhythm. Musculoskeletal and neural factors may account for the group and limb differences. Routine 3D kinematic analysis of shoulder joint rotation may aid treatment planning and better quantify outcomes in this group.

The effect of muscle loading on the kinematics of in vitro glenohumeral abduction

This in vitro study evaluated the effects of four different muscle-loading ratios on active glenohumeral joint abduction. Eight cadaveric shoulders were tested using a shoulder simulator designed to reproduce unconstrained abduction of the humerus via computer-controlled pneumatic actuation. Forces were applied to cables that were sutured to tendons or fixed to bone, to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and anterior, middle, and posterior deltoid muscles. Four sets of muscle-loading ratios were employed, based on: (1) equal loads, (2) average physiological cross-sectional areas (pCSAs), (3) constant values of the product of electromyographic (EMG) data and pCSAs, and (4) variable ratios of the EMG and pCSA data which changed as a function of abduction angle. The investigator generated passive motions with no muscle loads simulated. Repeatability was quantified by five successive trials of the passive and simulated active motions. There was improved repeatability in the simulated active motions versus passive motions, significant for abduction angles less than 40 degrees (p=0.02). No difference was found in the repeatability of the four different muscle-loading ratios for simulated active motions (p0.067 for all angles). The improved repeatability of active over passive motion suggests simulated active motion should be employed for in vitro simulations of shoulder motion.

3D kinematic analysis of the acromioclavicular joint during arm abduction using vertically open MRI

Many researchers have evaluated the motions of the shoulder girdle, especially scapular and humeral motion. However, few reports exist that describe motions of the acromioclavicular joint. The purpose of the present study was to analyze the 3D kinematics of the acromioclavicular joint during arm abduction using 3D MR images obtained by a vertically open MRI. Fourteen shoulders of seven volunteers were examined in seven static positions from 0 degrees to the maximum abduction in a seated position. 3D surface models of the clavicle and scapula were created, and the movements of the acromioclavicular joint from 0 degrees to each position were calculated using the volume-based registration technique. From these calculations, the translations were evaluated and the rotational motions were analyzed using the concept of the screw axis. In the anteroposterior direction, the clavicle translated most posteriorly (-1.9 +/- 1.3 mm) at 90 degrees of abduction and most anteriorly (1.6 +/- 2.7 mm) at maximum abduction. In the superoinferior direction, the clavicle translated slightly superiorly (0.9 +/- 1.9 mm). When analyzing relative motion of the scapula with respect to the clavicle, the scapula generally rotated about a specific screw axis passing through the insertions of both the acromioclavicular and the coracoclavicular ligaments on the coracoid process. The average rotation was 34.9 +/- 8.4 degrees.

Shoulder kinematics in 25 patients with impingement and 12 controls

We used dynamic radiostereometry to study the three-dimensional kinematics of the shoulder joint during active abduction. Twenty-five patients experiencing shoulder symptoms (Neer Stage 2) for more than 18 months, without total rotator cuff tears, participated. Eight men and four women without shoulder symptoms constituted controls. The rotation of the humeral head relative to a fixed scapula and the absolute rotation of the humerus (caused by humeral, scapular, and trunk motion) were measured. The rotations were calculated in the order of abduction/adduction (anteroposterior axis), internal/external rotation (longitudinal axis), and flexion/extension (transverse axis). The absolute abduction of the humerus in our patients did not differ from controls, nor did the abduction in the glenohumeral joint. During abduction, the humeral centre displaced medially, proximally, and anteriorly. In the patient group, slightly more (1-1.5 mm) proximal translation was observed. Presence of impingement syndrome was associated with increased proximal translation of the humeral head center, which occurred in the early phase of the arc of motion.

LEVEL OF EVIDENCE

Diagnostic Level I. See Guidelines for Authors for a complete description of Levels of Evidence.

Reliability and Precision of in Vivo Scapular Kinematic Measurements Using an Electromagnetic Tracking Device

Context:

In vivo scapular kinematics during humeral movements are commonly assessed with electromagnetic tracking devices despite few published data related to reliability and precision of these measurements.

Objective:

To determine the intrasession reliability and precision of assessing scapular kinematics using an electromagnetic tracking device.

Design:

Scapular position and orientation were measured with an electromagnetic tracking device during humeral elevation/depression in several planes. Intrasession reliability and precision were established by comparing 2 trials performed in succession.

Setting:

A human-movement research laboratory.

Participants:

15 healthy individuals.

Main Outcome Measures:

Intrasession intraclass correlation coefficients and standard error of measurement of all scapular variables were established.

Results:

The mean intrasession reliability for all variables was ICC = .97 ± .03. The mean intrasession precision was .99° ± .36°.

Conclusions:

In vivo scapular kinematics can be measured with high reliability and precision during intrasession research designs.

Scapular kinematics during humeral elevation in adults and children

BACKGROUND

Appropriate motion of the scapula is important for dynamic positioning of the glenoid during humeral elevation. A number of studies have described the typical scapular kinematics during humeral elevation in adults. However, children and adults may have differences in scapulothoracic musculature and scapular osteology. To our knowledge, no study has been performed examining scapular kinematics in children with either typical or atypical development. Consequently in children the influence of age and development on scapular motion is currently unknown. The aim of this study was to describe and compare the kinematic patterns of the scapula during humeral elevation in children with typical development and healthy adults.

METHODS

Fifteen adults, 7 females, 25-37 years of age, and 14 children, 8 females, 4-9 years of age, participated in this study. Kinematic data were collected using a magnetic tracking device. Subjects were asked to elevate their arm in the scapular plane (40 degrees anterior to the frontal plane) in a sequence of three trials.

FINDINGS

Significant differences were seen between the two age groups in the dependent variables. During scapular plane rotation from 25 degrees to 125 degrees , children showed greater upward rotation (43.9 degrees SD 6.39 degrees ) than adults (29.1 degrees SD 10.1 degrees ). The mean glenohumeral to scapulothoracic ratio in the scapular plane was 2.4:1 for adults, 1.3:1 for children.

INTERPRETATION

This study demonstrates that there are significant differences in scapular kinematic patterns between children and adults. Children have a greater contribution from the scapulothoracic joint, specifically upward rotation toward humeral elevation. From a clinical perspective, these results can be used to help determine the incorporation of stabilization and mobilization of the scapulothoracic joint during exercises for a child with impairment at the shoulder for improving shoulder function.

Contact forces in the subacromial space: effects of scapular orientation

The purpose of this study was to examine the effects of scapular orientation on clearance in the subacromial space. Eight glenohumeral joints from fresh-frozen human cadavers were secured to an Instron mechanical testing machine via a custom-made translation table. Forces were applied to simulate rotator cuff and deltoid contraction. Superior translation of the glenohumeral joint was simulated, and the distance before the development of significant subacromial contact force was measured. Specimens were tested at varying orientations of scapular posterior tilting, upward rotation, and external rotation. Results demonstrated no significant effect of posterior tilting and external rotation. Subacromial clearance was found to decrease with an increase in upward rotation, which is contrary to what was expected. These results suggest that changes in upward rotation observed in patients with impingement syndrome may serve to open the subacromial space. Future work needs to focus on confirming these results and determining contact location.

Effect of abducting and adducting muscle acitivity on glenohumeral translation, scapular kinematics and subacromial space width in vivo

It is currently unknown in which ways activity of the ab- and adductor shoulder muscles affects shoulder biomechanics (scapular kinematics and glenohumeral translation), and whether these changes are relevant for alterations of the subacromial space width. The objective of this experimental in vivo study was thus to test the hypotheses that potential changes of the subacromial space width (during antagonistic muscle activity) are caused by alterations of scapular kinematics and/or glenohumeral translation. The shoulders of 12 healthy subjects were investigated with an open MRI-system at 30 degrees, 60 degrees, 90 degrees, 120 degrees and 150 degrees of arm elevation. A force of 15N was applied to the distal humerus, once causing isometric contraction of the abductors and once contraction of the adductors. The scapulo-humeral rhythm, scapular tilting and glenohumeral translation were calculated from the MR image data for both abducting and adducting muscle activity. Adducting muscle activity led to significant increase of the subacromial space width in all arm positions. The scapulo-humeral rhythm (2.2-2.5) and scapular tilting (2-4 degrees) remained relatively constant during elevation, no significant difference was found between abducting and adducting muscle activity. The position of the humerus relative to the glenoid was, however, significantly (p < 0.05) different (inferior and anterior) for adducting versus abducting muscle activity in midrange elevation (60-120 degrees). These data show that the subacromial space can be effectively widened by adducting muscle activity, by affecting the position of the humerus relative to the glenoid. This effect may be employed for conservative treatment of the impingement syndrome.

Reliability of diffraction enhanced imaging for assessment of cartilage lesions, ex vivo

OBJECTIVE

The assessment of articular cartilage integrity is of value for the detection of early degenerative joint disease in both the clinical and the research settings. It was the purpose of this study to determine the accuracy and reliability of identifying articular cartilage defects through Diffraction Enhanced Imaging (DEI), a high contrast radiographic imaging technique. DEI provides two new sources of image contrast to radiography: refraction and scatter rejection, besides the absorption of conventional radiography.

DESIGN

Cadaveric tali were DEI imaged in the anterior-posterior position at the National Synchrotron Light Source. Two independent observers provided gross score evaluations (on a five point scale) of the trochlear surfaces. The DEI image of each trochlear surface was then graded (on a five point scale) by two additional independent observers who were blinded with regard to the gross evaluation of the articular surfaces. Inter-observer agreement for DEI grades was assessed with the weighted kappa statistic. Correlation of diffraction enhanced image score to the gross score was assessed with Spearman correlation coefficient.

RESULTS

The defects of articular cartilage of talar trochleae could be visualized through DEI. The Spearman correlation of gross grades with DEI grades on the 165 talar regions for observers 1 and 2 were 0.91 and 0.91, respectively. The overall weighted kappa value for inter-observer agreement was 0.93, thus considered high agreement.

CONCLUSIONS

DEI is accurate and reliable for detection of articular cartilage defects ex vivo. Even early stages of degeneration of cartilage can be visualized with this high contrast technique. Future studies will focus on the application of DEI to the identification of such lesions in vivo.

Patella kinematics and patello-femoral contact areas in patients with genu varum and mild osteoarthritis

BACKGROUND

Patients with genu varum of the knee and moderate to severe osteoarthritis often suffer from additional symptoms of the patello-femoral joint. These patients have a poor prognosis following high tibial osteotomy. It is unclear whether varus knees with only mild femoro-tibial osteoarthritis are also associated with alterations of patella biomechanics, and affect the prognosis of intended high tibial osteotomy.

METHODS

Fifteen patients with genu varum and mild osteoarthritis and 15 healthy volunteers were assessed in an open MRI-scanner. 3D-GRE sequences of the knee were obtained in 0 degrees, 30 degrees and 90 degrees with and without activity of the extensor muscles. After segmentation of patella, femur, tibia and the adjacent cartilage, a patella-based local coordinate system was established. Femoral and tibial reference points allowed definition of the spatial position of the patella. Contact areas were defined by intersection of opposing cartilage volumes.

FINDINGS

No significant differences in patella kinematics and patello-femoral contact areas could be found (P > 0.05) between varus knees with mild osteoarthritis and healthy knees either at different flexion angles or under extending muscle activity.

INTERPRETATION

In knees with genu varum and mild medial osteoarthritis we could detect no alterations in patello-femoral kinematics. Since the alterations of patients with genu varum and mild osteoarthritis are restricted to the medial femoro-tibial joint high tibial osteotomy might be successful.

Effects of glenohumeral rotations and translations on supraspinatus tendon morphology

OBJECTIVE

The purpose of this study was to evaluate the effects of glenohumeral rotations and humeral head translations on supraspinatus tendon morphology.

DESIGN

A convenience sample of cadaver shoulders was used to measure supraspinatus tendon shape and dimensions from MRI images.

BACKGROUND

Epidemiological evidence has indicated that shoulder elevation and external rotation may be risk factors for rotator cuff tendon pathology, but little is known about how these postures affect tendon morphology.

METHODS

Measurements of supraspinatus tendon morphology were made from three-dimensional reconstructions based on T2-weighted fast spin-echo magnetic resonance images. Seven cadaver arms were imaged at neutral, 45 degrees external and 45 degrees internal rotations at 0 degrees, 30 degrees, and 60 degrees of glenohumeral abduction. Measurements of the anterior, middle, and posterior portions of the tendon were made using ANALYZE software.

RESULTS

The supraspinatus tendon was twisted at the muscle-tendon junction of the middle and posterior portions in 45 degrees external and 45 degrees internal axial rotations of the humerus, especially over 30 degrees of abduction. Abduction over 30 degrees shortened the entire supraspinatus tendon. External and internal rotation motions elongated the anterior and posterior portions, respectively.

CONCLUSIONS

Arm posture affects morphology of the supraspinatus tendon.

RELEVANCE

The results support the epidemiologic evidence linking external rotation and abduction to supraspinatus tendon disorders.

Influence of adducting and abducting muscle forces on the subacromial space width

PURPOSE

Strengthening of the shoulder depressors is an important component in the treatment of impingement syndrome. However, the quantitative effect of various muscle forces on the width of the subacromial space has never been demonstrated in vivo. Therefore, the purpose of this study was to analyze the influence of adducting and abducting muscle forces on the subacromial space width in healthy volunteers in various arm positions.

METHODS

The shoulders of 12 healthy volunteers were imaged with an open MR system at 30 degrees, 60 degrees, 90 degrees, 120 degrees, and 150 degrees of arm elevation under both isometric adducting and abducting muscle activity (15 N). After segmentation and three-dimensional reconstruction of anatomically relevant structures, the minimal spatial acromiohumeral and claviculohumeral distances were quantified.

RESULTS

Adducting muscle forces led to a significant increase of the acromiohumeral distance in all arm positions (P < 0.01), varying from 32% (30 degrees ) to 138% (90 degrees ) relative to abducting muscle forces. The claviculohumeral distance showed an increase of 9% (30 degrees ) to 24% (90 degrees ), this increase being also statistically significant at all positions (P < 0.05). During elevation of the arm (30-120 degrees ), the absolute subacromial space width was reduced significantly (P = 0.001) by 30% under isometric contraction of the adductors compared with 53% (P = 0.001) under activation of the abductors.

CONCLUSION

This in vivo study shows for the first time that adducting muscle forces lead to a significant increase of the subacromial space width compared with abducting muscle activity. In the future, this technique and data can be used to objectively quantify the effect of physical therapy protocols focused on increasing the depressor effect of adducting muscles in the postoperative and conservative treatment of impingement syndrome of the shoulder.

Three-dimensional relationship of the glenohumeral joint in the elevated position in shoulders with multidirectional instability

Patients with typical atraumatic multidirectional instability often have symptoms develop, especially when the arm is elevated overhead. To clarify the pathomechanics, we analyzed the glenohumeral relationship with the arm in 135 degrees of elevation in the scapular plane using 3-dimensional reconstructed magnetic resonance imaging. We enrolled 40 normal individuals (23 men and 17 women) and 10 patients with atraumatic multidirectional instability (3 men and 7 women) in this study. The mean ages of the normal volunteers and patients were 23.4 years (range, 14-42 years) and 19.4 years (range, 15-25 years), respectively. The humeral head of normal volunteers was located on the glenoid center. In contrast, the humeral head of patients translated posteriorly from the glenoid center, even though the arm was in more extension in the anteroposterior direction. Three-dimensional computer-generated images of the static position with the arm elevated made the difference obvious between the groups and were useful for evaluating the ability to maintain the head in the glenoid center.

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.

Three-dimensional analysis of shoulder girdle and supraspinatus motion patterns in patients with impingement syndrome

Alterations of the shoulder girdle motion have been suggested to be associated with shoulder disorders. The objective of this study was to perform a three-dimensional (3D) motion analysis of the supraspinatus muscle and shoulder girdle in patients with different stages of impingement syndrome. 20 patients with unilateral impingement and 14 normal controls were investigated at 30 degrees, 90 degrees, and 120 degrees of abduction with and without abducting muscle activity. The spatial relationship between the shoulder girdle elements and the supraspinatus was quantified from open MRI data. No significant alterations in glenoid rotation were observed between the patients and asymptomatic volunteers. However, while in the healthy volunteers the values showed a normal distribution (28.5+/-3.6 degrees at 90 degrees abduction with muscle activity), the patients (30.5 degrees+/-9.7 degrees) contained a subset of five individuals with an obvious increase in glenoid rotation angle (>40 degrees) compared with controls (>2.5 standard deviations higher than the mean) and with the healthy contralateral side. These five patients also displayed alterations in the scapulo-humeral rhythm and supraspinatus motion, but not in clavicular position. The study shows that only a specific subset of patients with impingement syndrome demonstrates complex changes in shoulder girdle and supraspinatus motion patterns, suggesting that this subset may benefit from an alternative type of treatment.

An in vivo technique for determining 3D muscular moment arms in different joint positions and during muscular activation - application to the supraspinatus

OBJECTIVE

To develop a 3D in vivo technique for determining the moment arm and insertion angle of muscles in different joint positions and under muscular activity.

DESIGN

An open magnetic resonance imaging system and 3D processing techniques were used for determining the moment arm and insertion angle of the supraspinatus in healthy volunteers.

BACKGROUND

Muscular moment arms are important parameters for the computation of joint forces, however, so far in vivo measurements have not considered the influence of muscle activity and were restricted to two dimensions.

METHODS

10 healthy shoulders were investigated in 30-150 degrees abduction with and without abducting muscular activity, using an open magnetic resonance imaging. The minimal distance between the midpoint of the humeral head and the line of action of the supraspinatus was determined in 3D. The insertion angle was derived by calculating the angle between the humerus and the supraspinatus.

RESULTS

During elevation a significant (P < 0.001) increase of the supraspinatus moment arm was observed (19.9 mm (SD, 2.3 mm) at 30 degrees; 23.3 mm (SD, 2.5 mm) at 150 degrees ), being significantly larger at 90 degrees and 120 degrees under muscle activity. The insertion angle also increased significantly during elevation (P < 0.001), the values becoming larger under muscle activity at 60 degrees (P < 0.01) and at 90 degrees (P < 0.05).

CONCLUSIONS

This 3D technique permits to determine the moment arm and insertion angle of muscles in vivo not only in various joint positions but also under in vivo muscle activity. For the supraspinatus, we observed a constant increase of both parameters during arm abduction.

RELEVANCE

The technique and these data can be used for improved computation of joint forces in biomechanical model, and for precise diagnostics in patients with altered scapulohumeral motion patterns.

Scapular and clavicular kinematics during humeral elevation: a study with cadavers

A combination of kinematic testing and graphic reconstruction of cadaveric shoulders was used to characterize shoulder kinematics during a simulated passive clinical range-of-motion examination. Cadaveric shoulders were elevated in the coronal, scapular, and sagittal planes while the scapula, clavicle, and humerus were kinematically tracked. Graphic models of each shoulder were created from computed tomography data. The models were animated to display the experimental motions. Shoulder kinematics varied between elevation planes. The scapular and clavicular rotations were relatively small until the humerus reached approximately 90 degrees of elevation. Clavicular and scapular rotations that occurred at low humeral elevation angles for elevation in the coronal plane were significantly larger than for the other two planes. The glenohumeral to scapulothoracic ratio was approximately equal to 2 for the entire range of elevation for each elevation plane, but it was dramatically larger during early elevation than during late elevation.

Dynamic measurements of three-dimensional scapular kinematics: a validation study

The validation of two noninvasive methods for measuring the dynamic three-dimensional kinematics of the human scapula with a magnetic tracking device is presented. One method consists of simply fixing a sensor directly to the acromion and the other consists of mounting a sensor to an adjustable plastic jig that fits over the scapular spine and acromion. The concurrent validity of both methods was assessed separately by comparison with data collected simultaneously from an invasive approach in which pins were drilled directly into the scapula. The differences between bone and skin based measurements represents an estimation of skin motion artifact. The average motion pattern of each surface method was similar to that measured by the invasive technique, especially below 120 degrees of elevation. These results indicate that with careful consideration, both methods may offer reasonably accurate representations of scapular motion that may be used to study shoulder pathologies and help develop computational models.

[A new in vivo technique for 3-dimensional analysis of the translation of femoral condyles and the menisci responding to antagonistic muscle forces]

The aim of our study was to develop a 3-D MR-based technique for the analysis of meniscal and femoral translations during flexion of the knee, and under the influence of antagonistic muscle forces in healthy subjects. In an open MR system, 5 knees were examined at 30 degrees and 90 degrees flexion using a T1-weighted 3-D gradient echo sequence. A force of 30 Newtons, first in the extending and then in the flexing direction, was applied to the distal lower leg. After three-dimensional reconstruction, the minimal distances between the centre of the tibial plateau and the posterior edge of the menisci and femoral condyles were determined. At 30 degrees flexion, the minimum distance for the meniscus was larger medially than laterally (23.2 +/- 1.8 mm vs. 16.2 +/- 3.3 mm), and this also applied to the condyles (25.1 +/- 1.5 vs. 19.0 +/- 3.0 mm). During flexion to 90 degrees, a posterior translation of 0.5 +/- 0.2 mm was observed for the lateral, and of 3.4 +/- 1.2 mm for the medial, meniscus. The condyles demonstrated a different posterior translation (lateral 2.2 +/- 0.56 mm; medial 1.8 +/- 1.9 mm). No obvious differences were found between extension and flexion muscle activity for the different positions of the knee. In the present study, a new 3-D technique is presented for the analysis of the femoral and meniscal translation at various positions of the knee, and under muscle activity. The results suggest different translation for the menisci and condyles.