Algorithm and validation of a computer method for quantifying attachment locus of glenohumeral ligament in vivo

The aim of this work is to validate an algorithm that quantifies the locus of glenohumeral ligament (GHL) attachments on glenohumeral joint (GHJ) bones.

A computed tomography scan of a GHJ was segmented to reconstruct the humerus, scapula, anatomical neck (AN) and glenoid rim (GR) into 3D meshes of interconnecting nodal vectors. These were applied to construct a ‘clock face’ coordinate system in which 3 o'clock points anteriorly.

Based on the assigned clock face coordinate frame and the fitted plane, the error between the fitted plane and the actual bony node was quantified through manual data extraction. This was tested on 50 specimens.

Mean algorithm quantification errors for GHL attachments were 4.8 (SD 2.2 mm) and 4.5 mm (1.7 mm) for the humerus and glenoid, respectively. Further studies would apply this to investigate GHL length changes during function and may suggest how these structures should be handled during surgical repairs.     

Specificity of clinical examinations for testing glenohumeral ligament integrity: a computational study

An accurate diagnosis of glenohumeral joint (GHJ) instability is essential for an effective surgical intervention. There is presently no known comprehensive algorithm of clinical tests for the confirmation of the functional integrity of glenohumeral ligaments (GHLs). A validated computational GHL strain analyser was applied to a set of GHJ kinematics data from the literature to simulate 57 different physiological clinical examination manoeuvres. An algorithm that integrates the GHL pre-straining activities at the toe region of the stress–strain curve was developed for the quantification of ligament loading from prevailing strains. This was used to upgrade the strain analyser and applied to produce a matrix of the various GHL loadings and sensitivities during the manoeuvres. The investigation magnified the likely impact of anatomical variations of GHL attachments as possible causes of misdiagnoses during clinical examinations of GHJ dysfunction. This can serve as an assistive guide to ascertain the functional condition of a specific GHL during symptomatic clinical examinations.     

Modeling the stability of the human glenohumeral joint during external rotation

An analytical model of the human glenohumeral joint was developed to predict glenohumeral kinematics and investigate how the glenohumeral capsule and articular contact between the humeral head and the glenoid stabilize the joint. This was performed during a simulation of an apprehension clinical exam or the cocked phase of throwing, when the humerus is susceptible to anterior instability or dislocation. Contact between the joint surfaces was modeled using a deformable articular contact method and the capsule was modeled as five elements with the ability to wrap around the surface of the humeral head. Experimental measurements (Novotny et al., Journal of Shoulder and Elbow surgery, 1998, 7, 629-639) provided geometric data from four in vitro specimens and kinematic results to validate model predictions. Material properties were taken from the literature. An equilibrium approach was used with the forces and moments produced by the ligaments and surface contact balanced against those applied externally to the humerus during external rotation of the abducted and extended humerus. The six equilibrium equations were solved for the position and orientation of the humerus. The center of the humeral head translated posteriorly and superiorly with external rotation. Model predictions for translational and rotational ranges of motion were not significantly different from experimental findings; however, at individual moment increments, the model underestimated the external rotation and overestimated the superior-inferior position of the humerus relative to the glenoid. The anterior band of the inferior glenohumeral ligament increased in tension with external rotation, while the axillary pouch and posterior band decreased in tension. Contact area, stress and force increased with external rotation and the contact area moved posteriorly and inferiorly around the rim of the glenoid. The model results provide information on how the relationship between the ligament element tensions and contact forces may act to avoid glenohumeral instability.     

The position of the rotation center of the glenohumeral joint

To validate the assumption that the center of rotation in the glenohumeral (GH) joint can be described based on the geometry of the joint, two methods for calculation of the GH rotation center were compared. These are a kinematic estimation based on the calculation of instantaneous helical axes, and a geometric estimation based on a spherical fit through the surface of the glenoid. Four fresh cadaver arms were fixed at the scapula and fitted with electromagnetic sensors. Each arm was moved in different directions while at the same time the orientation of the humerus was recorded. Subsequently, each specimen was dissected and its glenoid and humeral head surfaces were digitized. Results indicate no differences between the methods. It is concluded that the method to estimate the GH center of rotation as the center of a sphere through the glenoid surface, with the radius of the humeral head, appears to be valid.     

Contributions of the individual muscles of the shoulder to glenohumeral joint stability during abduction

The aim of this study was to determine the relative contributions of the deltoid and rotator cuff muscles to glenohumeral joint stability during arm abduction. A three-dimensional model of the upper limb was used to calculate the muscle and joint-contact forces at the shoulder for abduction in the scapular plane. The joints of the shoulder girdle-sternoclavicular joint, acromioclavicular joint, and glenohumeral joint-were each represented as an ideal three degree-of-freedom ball-and-socket joint. The articulation between the scapula and thorax was modeled using two kinematic constraints. Eighteen muscle bundles were used to represent the lines of action of 11 muscle groups spanning the glenohumeral joint. The three-dimensional positions of the clavicle, scapula, and humerus during abduction were measured using intracortical bone pins implanted into one subject. The measured bone positions were inputted into the model, and an optimization problem was solved to calculate the forces developed by the shoulder muscles for abduction in the scapular plane. The model calculations showed that the rotator cuff muscles (specifically, supraspinatus, subscapularis, and infraspinatus) by virtue of their lines of action are perfectly positioned to apply compressive load across the glenohumeral joint, and that these muscles contribute most significantly to shoulder joint stability during abduction. The middle deltoid provides most of the compressive force acting between the humeral head and the glenoid, but this muscle also creates most of the shear, and so its contribution to joint stability is less than that of any of the rotator cuff muscles.     

Effect of abducting and adducting muscle activity 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.     

Arm abduction strength and its relationship to shoulder geometry.

This study was conducted to test whether glenohumeral geometry, as measured through MRI scans, is correlated with upper arm strength. The isometric shoulder strength of 12 subjects during one-handed arm abduction in the coronal plane, in a range from 5 degrees to 30 degrees , was correlated with the geometries of their glenoid fossas. Seven parameters describing the glenohumeral joint geometry in the coronal plane were identified as having expected influence on shoulder strength. In addition to these, a new geometric parameter, named the area of glenoid asymmetry (AGA), was considered to reflect the concavity-compression mechanism as well as the inclination of the glenoid surface. As a result of the high correlation between the AGA and mean force and mean moment (0.80, p0.01 and 0.69, p 相似文献   

MRI development and validation of two new predictive methods of glenohumeral joint centre location identification and comparison with established techniques

Identification of the centre of the glenohumeral joint (GHJ) is essential for three-dimensional (3D) upper limb motion analysis. A number of convenient, yet un-validated methods are routinely used to estimate the GHJ location in preference to the International Society of Biomechanics (ISB) recommended methods. The current study developed a new regression model, and simple 3D offset method for GHJ location estimation, employing easy to administer measures, and compared the estimates with the known GHJ location measured with magnetic resonance imaging (MRI). The accuracy and reliability of the new regression and simple 3D offset techniques were compared with six established predictive methods. Twenty subjects wore a 3D motion analysis marker set that was also visible in MRI. Immediately following imaging, they underwent 3D motion analysis acquisition. The GHJ and anatomical landmark positions of 15 participants were used to determine the new regression and simple 3D generic offset methods. These were compared for accuracy with six established methods using 10 subject's data. A cross validation on 5 participants not used for regression model development was also performed. Finally, 10 participants underwent a further two MRI's and subsequent 3D motion analysis analyses for inter-tester and intra-tester reliability quantification. When compared with any of the other established methods, our newly developed regression model found an average GHJ location closer to the actual MRI location, having an GHJ location error of 13±2 mm, and had significantly lower inter-tester reliability error, 6±4 mm (p<0.01).     

In vivo glenohumeral translation under anterior loading in an open-MRI set-up

The evaluation of the glenohumeral joint laxity requires the estimate of displacements of the humeral head centre (HHC) with respect to the glenoid. To the authors? knowledge, several studies have been conducted to estimate HHC translations in vivo but data under anterior loading conditions has not been collected yet. Aim of this study was to develop a non-invasive experimental methodology based on magnetic resonance (MR) imaging for the in vivo evaluation of the HHC translations due to an anteriorly directed force. Fourteen asymptomatic shoulders were acquired using a horizontal open MR scanner with the subjects in the supine position both at 15° and 90° of arm abduction with and without an anterior force of 20 N applied at the HHC level. When no load was applied, from 15° to 90° of arm abduction, the HHC moved, anteriorly (1.5±1.3 mm) and superiorly (1.8±1.3 mm) while smaller displacements were observed medio-laterally (0.4±0.7 mm). Under the application of the anterior force the 3D displacement of the HHC with respect to the glenoid was 1.6±1.2 mm and 1.3 ±0.7 mm, respectively at 15° and 90° of arm abduction. The level of precision associated to the GHJ translation was less than 0.33 mm along all directions i.e. one order of magnitude smaller than the relevant translations. In conclusion, the MRI-based methodology allowed for the analysis of HHC displacements under conditions of anterior loads within an acceptable level of reliability.     

Measuring dynamic in-vivo glenohumeral joint kinematics: technique and preliminary results

Rotator cuff tears are a common injury that affect a significant percentage of the population over age 60. Although it is widely believed that the rotator cuff's primary function is to stabilize the humerus against the glenoid during shoulder motion, accurately measuring the three-dimensional (3D) motion of the shoulder's glenohumeral joint under in-vivo conditions has been a challenging endeavor. In particular, conventional motion measurement techniques have frequently been limited to static or two-dimensional (2D) analyses, and have suffered from limited or unknown in-vivo accuracy. We have recently developed and validated a new model-based tracking technique that is capable of accurately measuring the 3D position and orientation of the scapula and humerus from biplane X-ray images. Herein we demonstrate the in-vivo application of this technique for accurately measuring glenohumeral joint translations during shoulder motion in the repaired and contralateral shoulders of patients following rotator cuff repair. Five male subjects were tested at 3-4 months following arthroscopic rotator cuff repair. Superior-inferior humeral translation was measured during elevation, and anterior-posterior humeral translation was measured during external rotation in both the repaired and contralateral shoulders. The data failed to detect statistically significant differences between the repaired and contralateral shoulders in superior-inferior translation (p=0.74) or anterior-posterior translation (p=0.77). The measurement technique overcomes the limitations of conventional motion measurement techniques by providing accurate, 3D, in-vivo measures of glenohumeral joint motion during dynamic activities. On-going research is using this technique to assess the effects of conservative and surgical treatment of rotator cuff tears.     

A motion-decomposition approach to address gimbal lock in the 3-cylinder open chain mechanism description of a joint coordinate system at the glenohumeral joint

In this study, the standard-sequence properties of a joint coordinate system were implemented for the glenohumeral joint by the use of a set of instantaneous geometrical planes. These are: a plane that is bound by the humeral long axis and an orthogonal axis that is the cross product of the scapular anterior axis and this long axis, and a plane that is bounded by the long axis of the humerus and the cross product of the scapular lateral axis and this long axis. The relevant axes are updated after every decomposition of a motion component of a humeral position. Flexion, abduction and rotation are then implemented upon three of these axes and are applied in a step-wise uncoupling of an acquired humeral motion to extract the joint coordinate system angles. This technique was numerically applied to physiological kinematics data from the literature to convert them to the joint coordinate system and to visually reconstruct the motion on a set of glenohumeral bones for validation.     

A musculoskeletal shoulder simulation of moment arms and joint reaction forces after medialization of the supraspinatus footprint in rotator cuff repair

A non-anatomical reinsertion of the supraspinatus medially to the original footprint to avoid over-tensioning of the tendon in large and retracted tears is one surgical option in rotator cuff (RC) repair. The purpose of the study was to determine the biomechanical effects on the glenohumeral joint with regard to this surgical technique. A modified musculoskeletal computational shoulder model was used to evaluate the change in moment arms and muscle forces of the RC and the co-contracting muscles and the alteration of the joint reaction forces (compressive and shear forces) after reinsertion of the supraspinatus 5?mm, 10?mm, 15?mm and 20?mm medially to the original footprint. A medialization of the supraspinatus reduces its moment arm in glenohumeral abduction. In case of a medialization of the attachment of 15?mm and 20?mm, the supraspinatus restricts glenohumeral abduction at 54° and 68°. In glenohumeral forward flexion and in lower degrees of internal rotation the moment arm of the supraspinatus increases for a medialized tendon attachment and decreases in external rotation in relation to the anatomical condition. A medialization of the supraspinatus insertion point yields in an increase in muscle force for abduction, internal and external rotation. In the present model a medially non-anatomic reinsertion reduces significantly the compressive glenohumeral joint reaction and the glenohumeral stability. Moreover, the results show that a medialization of the supraspinatus leads to a reduction of the supraspinatus moment arm especially in abduction. This leads to an increase of a compensatory supraspinatus load for stabilization the humerus in space, which may potentially cause a postoperative overload of the tendon-bone-complex.     

Methodology and sensitivity studies for finite element modeling of the inferior glenohumeral ligament complex

The objectives of this research were to develop a methodology for three-dimensional finite element (FE) modeling of the inferior glenohumeral ligament complex (IGHL complex) as a continuous structure, to determine optimal mesh density for FE simulations, to examine strains and forces in the IGHL complex in clinically relevant joint positions, and to perform sensitivity studies to assess the effects of assumed material properties. A simple translation test in the anterior direction was performed on a cadaveric shoulder, with the humerus oriented at 60 degrees of glenohumeral abduction and 0 degrees of flexion/extension, at 0 degrees , 30 degrees and 60 degrees of humeral external rotation. The geometries of the relevant structures were extracted from volumetric CT data to create a FE model. Experimentally measured kinematics were applied to the FE model to simulate the simple translation test. First principal strains, insertion site forces and contact forces were analyzed. At maximum anterior humeral translation, strains in the IGHL complex were highly inhomogeneous for all external rotation angles. The motion of the humerus with respect to the glenoid during the simple translation test produced a tangential load at the proximal and distal edges of the IGHL complex. This loading was primarily in the plane of the inferior glenohumeral ligament complex, producing an in-plane shear-loading pattern. There was a significant increase in strain with increasing angle of external rotation. The largest insertion site forces occurred at the axillary pouch insertion to the humerus (36.7N at 60 degrees of external rotation) and the highest contact forces were between the anterior band of the IGHL complex and the humeral cartilage (7.3N at 60 degrees of external rotation). Strain predictions were highly sensitive to changes in the ratio of bulk to shear modulus of the IGHL complex, while predictions were moderately sensitive to changes in elastic modulus of the IGHL complex. Changes to the material properties of the humeral cartilage had little effect on predicted strains. The methodologies developed in this research and the results of the mesh convergence and sensitivity studies provide a basis for the subject-specific modeling of the mechanics of the IGHL complex.     

Validation of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics

Shoulder motion is complex and significant research efforts have focused on measuring glenohumeral joint motion. Unfortunately, conventional motion measurement techniques are unable to measure glenohumeral joint kinematics during dynamic shoulder motion to clinically significant levels of accuracy. The purpose of this study was to validate the accuracy of a new model-based tracking technique for measuring three-dimensional, in vivo glenohumeral joint kinematics. We have developed a model-based tracking technique for accurately measuring in vivo joint motion from biplane radiographic images that tracks the position of bones based on their three-dimensional shape and texture. To validate this technique, we implanted tantalum beads into the humerus and scapula of both shoulders from three cadaver specimens and then recorded biplane radiographic images of the shoulder while manually moving each specimen's arm. The position of the humerus and scapula were measured using the model-based tracking system and with a previously validated dynamic radiostereometric analysis (RSA) technique. Accuracy was reported in terms of measurement bias, measurement precision, and overall dynamic accuracy by comparing the model-based tracking results to the dynamic RSA results. The model-based tracking technique produced results that were in excellent agreement with the RSA technique. Measurement bias ranged from -0.126 to 0.199 mm for the scapula and ranged from -0.022 to 0.079 mm for the humerus. Dynamic measurement precision was better than 0.130 mm for the scapula and 0.095 mm for the humerus. Overall dynamic accuracy indicated that rms errors in any one direction were less than 0.385 mm for the scapula and less than 0.374 mm for the humerus. These errors correspond to rotational inaccuracies of approximately 0.25 deg for the scapula and 0.47 deg for the humerus. This new model-based tracking approach represents a non-invasive technique for accurately measuring dynamic glenohumeral joint motion under in vivo conditions. The model-based technique achieves accuracy levels that far surpass all previously reported non-invasive techniques for measuring in vivo glenohumeral joint motion. This technique is supported by a rigorous validation study that provides a realistic simulation of in vivo conditions and we fully expect to achieve these levels of accuracy with in vivo human testing. Future research will use this technique to analyze shoulder motion under a variety of testing conditions and to investigate the effects of conservative and surgical treatment of rotator cuff tears on dynamic joint stability.     

Glenohumeral joint cartilage contact in the healthy adult during scapular plane elevation depression with external humeral rotation

The shoulder (glenohumeral) joint has the greatest range of motion of all human joints; as a result, it is particularly vulnerable to dislocation and injury. The ability to non-invasively quantify in-vivo articular cartilage contact patterns of joints has been and remains a difficult biomechanics problem. As a result, little is known about normal in-vivo glenohumeral joint contact patterns or the consequences that surgery has on altering them. In addition, the effect of quantifying glenohumeral joint contact patterns by means of proximity mapping, both with and without cartilage data, is unknown. Therefore, the objectives of this study are to (1) describe a technique for quantifying in-vivo glenohumeral joint contact patterns during dynamic shoulder motion, (2) quantify normal glenohumeral joint contact patterns in the young healthy adult during scapular plane elevation depression with external humeral rotation, and (3) compare glenohumeral joint contact patterns determined both with and without articular cartilage data. Our results show that the inclusion of articular cartilage data when quantifying in-vivo glenohumeral joint contact patterns has significant effects on the anterior–posterior contact centroid location, the superior–inferior contact centroid range of travel, and the total contact path length. As a result, our technique offers an advantage over glenohumeral joint contact pattern measurement techniques that neglect articular cartilage data. Likewise, this technique may be more sensitive than traditional 6-Degree-of-Freedom (6-DOF) joint kinematics for the assessment of overall glenohumeral joint health. Lastly, for the shoulder motion tested, we found that glenohumeral joint contact was located on the anterior–inferior glenoid surface.     

Shoulder joint kinematics during elevation measured by ultrasound-based measuring system.

In order to analyze shoulder joint movements, the authors use a ZEBRIS CMS-HS ultrasound-based movement analysis system. In essence, the measurement involves the determination of the spatial position of the 16 anatomical points, which are specified on the basis of the coordinates of ultrasound-based triplets positioned on the upper limb, the scapula, and the thorax; their spatial position is measured in the course of motion. Kinematic characteristics of 74 shoulder joints of 50 healthy persons were identified during elevation in the plane of the scapula. Kinematic characteristics of motion were identified by scapulothoracic, glenohumeral, and humeral elevation angles; range of angles; scapulothoracis and glenohumeral rhythm; scapulothoracic, glenohumeral, and scapuloglenoid ratios; and the relative displacement between the rotation centers of the humerus and the scapula. Motion of the humerus and the scapula relative to each other was characterized by their rotation as well as the relative displacement between the rotation centers of scapula and humerus. The biomechanical model of the shoulder joint during elevation can be described by analyzing the results of the measurements performed.     

MRI vs CT-based 2D-3D auto-registration accuracy for quantifying shoulder motion using biplane video-radiography

Biplane 2D-3D registration approaches have been used for measuring 3D, in vivo glenohumeral (GH) joint kinematics. Computed tomography (CT) has become the gold standard for reconstructing 3D bone models, as it provides high geometric accuracy and similar tissue contrast to video-radiography. Alternatively, magnetic resonance imaging (MRI) would not expose subjects to radiation and provides the ability to add cartilage and other soft tissues to the models. However, the accuracy of MRI-based 2D-3D registration for quantifying glenohumeral kinematics is unknown. We developed an automatic 2D-3D registration program that works with both CT- and MRI-based image volumes for quantifying joint motions. The purpose of this study was to use the proposed 2D-3D auto-registration algorithm to describe the humerus and scapula tracking accuracy of CT- and MRI-based registration relative to radiostereometric analysis (RSA) during dynamic biplanar video-radiography. The GH kinematic accuracy (RMS error) was 0.6–1.0 mm and 0.6–2.2° for the CT-based registration and 1.4–2.2 mm and 1.2–2.6° for MRI-based registration. Higher kinematic accuracy of CT-based registration was expected as MRI provides lower spatial resolution and bone contrast as compared to CT and suffers from spatial distortions. However, the MRI-based registration is within an acceptable accuracy for many clinical research questions.     

Computational analysis of glenohumeral joint growth and morphology following a brachial plexus birth injury

Children affected with brachial plexus birth injury (BPBI) undergo muscle paralysis. About 33% of affected children experience permanent osseous deformities of the glenohumeral joint. Recent evidence suggests that some cases experience restricted muscle longitudinal growth in addition to paralysis and reduced range of motion at the shoulder and elbow. It is unknown whether altered loading due to paralysis, muscle growth restriction and contracture, or static loading due to disuse is the primary driver of joint deformity after BPBI. This study uses a computational framework integrating finite element analysis and musculoskeletal modeling to examine the mechanical factors contributing to changes in bone growth and morphometry following BPBI. Simulations of 8 weeks of glenohumeral growth in a rat model of BPBI predicted that static loading of the joint is primarily responsible for joint deformation consistent with experimental measures of bone morphology, whereas dynamic loads resulted in normal bone growth. Under dynamic loading, glenoid version angle (GVA), glenoid inclination angle (GIA), and glenoid radius of curvature (GRC) (−1.3°, 38.2°, 2.5 mm respectively) were similar to the baseline values (−1.8°, −38°, 2.1 mm respectively). In the static case with unrestricted muscle growth, these measures increased in magnitude (5.2°, −48°, 3.5 mm respectively). More severe joint deformations were observed in GIA and GRC when muscle growth was restricted (GVA: 3.6°, GIA: −55°, GRC: 4.0 mm). Predicted morphology was consistent with literature reports of in vivo glenoid morphology following postganglionic BPBI. This growth model provides a framework for understanding the most influential mechanical factors driving glenohumeral deformity following BPBI.     

Finite element modelling of the glenohumeral capsule can help assess the tested region during a clinical exam

The objective of this research was to examine the efficacy of evaluating the region of the glenohumeral capsule being tested by clinical exams for shoulder instability using finite element (FE) models of the glenohumeral joint. Specifically, the regions of high capsule strain produced by glenohumeral joint positions commonly used during a clinical exam were identified. Kinematics that simulated a simple translation test with an anterior load at three external rotation angles were applied to a validated, subject-specific FE model of the glenohumeral joint at 60° of abduction. Maximum principal strains on the glenoid side of the inferior glenohumeral ligament (IGHL) were significantly higher than the maximum principal strains on the humeral side, for all three regions of the IGHL at 30° and 60° of external rotation. These regions of localised strain indicate that these joint positions might be used to test the glenoid side of the IGHL during this clinical exam, but are not useful for assessing the humeral side of the IGHL. The use of FE models will facilitate the search for additional joint positions that isolate high strains to other IGHL regions, including the humeral side of the IGHL.     

The effect of glenohumeral plane of elevation on supraspinatus subacromial proximity

Shoulder pain is a common clinical problem affecting most individuals in their lifetime. Despite the high prevalence of rotator cuff pathology in these individuals, the pathogenesis of rotator cuff disease remains unclear. Position and motion related mechanisms of rotator cuff disease are often proposed, but poorly understood. The purpose of this study was to determine the impact of systematically altering glenohumeral plane on subacromial proximities across arm elevation as measures of tendon compression risk. Three-dimensional models of the humerus, scapula, coracoacromial ligament, and supraspinatus were reconstructed from MRIs in 20 subjects. Glenohumeral elevation was imposed on the humeral and supraspinatus tendon models for three glenohumeral planes, which were chosen to represent flexion, scapular plane abduction, and abduction based on average values from a previous study of asymptomatic individuals. Subacromial proximity was quantified as the minimum distance between the supraspinatus tendon and coracoacromial arch (acromion and coracoacromial ligament), the surface area of the supraspinatus tendon within 2 mm proximity to the coracoacromial arch, and the volume of intersection between the supraspinatus tendon and coracoacromial arch. The lowest modeled subacromial supraspinatus compression measures occurred during flexion at lower angles of elevation. This finding was consistent across all three measures of subacromial proximity. Knowledge of this range of reduced risk may be useful to inform future studies related to patient education and ergonomic design to prevent the development of shoulder pain and dysfunction.