Scapular Landmarks Research Articles

Restoration of glenoid joint line: a three-dimensional analysis of scapular landmarks

Restoration of the glenoid joint line in shoulder arthroplasty is important for implant positioning and function. Medialization of the glenohumeral joint line due to glenoid bone loss is commonly encountered in primary and revision of shoulder arthroplasty albeit the direction and location of bone loss varies with different pathology. Three-Dimensional (3D) planning software has assisted in preoperative planning of complex glenoid deformities. However, limited literature is available defining a reliable 3D method to evaluate the glenoid joint line preoperatively. The purpose of this study is to identify a set of reliable scapular landmarks to be used as reference points to measure the premorbid glenoid joint line using 3D segmented models of healthy scapulae. Bilateral computed tomography scans from 79 patients eligible for primary stabilization procedures were retrospectively selected from our institutional surgical database (mean age 35±10 years, 58 males and 21 females). 3D models of the contralateral healthy scapulae were created via computed tomography scan segmentation using Mimics 24.0 software (Materialise, Leuven, Belgium). Anatomical landmarks were identified using 3-Matic 16.0 software (Materialise, Leuven, Belgium). The distance between identified landmarks and a sagittal plane created on the deepest point of the glenoid was recorded for each scapula and reliability of each landmark was assessed. Inter- and intra-observer reliabilities were also evaluated using intraclass correlation coefficients (ICCs). Four landmarks showed statistically significant results: the scapular notch (SN), the centroid of the coracoid (CC), a point on the most medial border of the scapula in line with the scapular spine (TS), and the most lateral point of the acromion (AL). The mean (± standard deviation) joint line measured from the SN, CC, TS and AL were 28.36±2.97 mm, 11.66±2.07 mm, 107.52±8.1 mm, and 29.72±4.46 mm, respectively. Inter-observer reliability analysis for SN, TS, and AL showed excellent agreement with ICC values of 0.966, 0.997, and 0.944, respectively, and moderate agreement for CC with ICC of 0.728. The results from this study assist in estimating joint line medialization preoperatively and in planning its subsequent restoration. A set of reliable landmarks can be used as references to estimate the premorbid glenoid joint line preoperatively.

Does the osteoarthritic shoulder have altered rotator cuff vectors with increasing glenoid deformity? An in silico analysis.

A transverse force couple (TFC) functional imbalance has been demonstrated in osteoarthritic shoulders by recent 3-dimensional (3D) muscle volumetric studies. Altered rotator cuff vectors may be an additional factor contributing to a muscle imbalance and the propagation of glenoid deformity. Computed tomography images of 33 Walch type A and 60 Walch type B shoulders were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (ISP-Tm) and scapula were manually segmented. The volume masks and scapular landmarks were imported into MATLAB to create a coordinate system, enabling calculation of muscle force vectors. The direction of each muscle force vector was described in the transverse and vertical plane, calculated with respect to the glenoid. Each muscle vector was then resolved into compression and shear force across the glenoid face. The relationship between muscle force vectors, glenoid retroversion or inclination, compression/shear forces on the glenoid, and Walch type was determined using linear regression. In the transverse plane with all rotator cuff muscles combined, increasing retroversion was significantly associated with increasing posterior drag (P<.001). Type B glenoids had significantly more posterior drag than type A (P<.001). In the vertical plane for each individual muscle group and in combination, superior drag increases as superior inclination increases (P<.001). Analysis of individual muscle groups showed that the anterior thrust of ISP-Tm and supraspinatus switched to a posterior drag at 8° and 10° of retroversion respectively. The compression force on the glenoid face by ISP-Tm and supraspinatus did not change with increasing retroversion for type A shoulders (P=.592 and P=.715, respectively), but they did for type B shoulders (P<.001 for both). The glenoid shear force ratio in the transverse plane for the ISP-Tm and supraspinatus moved from anterior to posterior shear with increasing glenoid retroversion, crossing zero at 8° and 10° of retroversion, whereas the subscapularis exerted a posterior shear force for every retroversion angle. Increased glenoid retroversion is associated with increased posterior shear and decreased compression forces on the glenoid face, explaining some of the pathognomonic bone morphometrics that characterize the osteoarthritic shoulder. Although the subscapularis always maintains a posterior thrust, the ISP-Tm and supraspinatus together showed an inflection at 8° and 10° of retroversion, changing from an anterior thrust to a posterior drag. This finding highlights the importance that in anatomic TSA the rotator cuff functional balance might be better restored by correcting glenoid retroversion to less than 8°.

Variability in total shoulder arthroplasty planning software compared to a control CT-derived 3D printed scapula.

Two techniques exist from which all 3D preoperative planning software for total shoulder arthroplasty are based. One technique is based on measurements constructed on the mid-glenoid and scapular landmarks (Landmark). The second is an automated system using a best-fit sphere technique (Automated). The purpose was to compare glenoid measurements from the two techniques against a control computed tomography-derived 3D printed scapula. Computed tomography scans of osteoarthritic shoulders of 20 patients undergoing primary total shoulder arthroplasty were analyzed with both 3D planning software techniques. Measurements from a 3D printed scapula (Scapula) from the true 3D computed tomography scan served as controls. Glenoid version and inclination measurements from each group were blinded and reviewed. In 65% (Automated) and 45% (Landmark) of cases, either inclination or version varied by 5° or more versus 3D printed scapula. Significant variability in version differences compared to the scapula group existed (p = 0.007). Glenoid version from the Scapula = 13.0° ± 10.6°, Automated = 15.0° ± 13.9°, and Landmark = 12.2° ± 7.8°. Inclination from Scapula = 5.4° ± 7.9°, Automated = 6.1° ± 12.6°, and Landmark = 6.2° ± 9.1°. A high percentage of cases showed discrepancies in glenoid inclination and version values from both techniques. Surgeons should be aware that regardless of software technique, there is variability compared to measurements from a control 3D computed tomography printed scapula.

The utility of the acromion marker cluster (AMC) in a clinical population

IntroductionThe acromion marker cluster (AMC) is a non-invasive scapular motion tracking method. However, it lacks testing in clinical populations, where unique challenges may present. This investigation resolved the utility of the AMC approach in a compromised clinical population. MethodsThe upper body of breast cancer survivors (BCS) and controls were tracked via motion capture and scapular landmarks palpated and recorded using a digitizer at static neutral to maximum elevation postures. The AMC tracked the scapula during dynamic maximum arm abduction. Both single (SC) and double calibration (DC) methods were applied to calculate scapular angles. The influences of calibration method, elevation, and group on mean and absolute error with two-way fixed ANOVAs with interactions (p < 0.05). Root mean square errors (RMSE) were calculated and compared. ResultsDC improved AMC estimation of palpated scapular orientation over SC, especially at higher arm elevations; RMSE averaged 11° higher for SC than DC at maximum elevation, but the methods were only 2.2° different at 90° elevation. DC of the AMC yielded mean error values of ∼5–10°. These approximate errors reported for AMC with young, lean adults. ConclusionsThe AMC with DC is a non-invasive method with acceptable error for measuring scapular motion of BCS and age-matched controls.

Assessing structural adaptation of biceps brachii motor units after stroke

The acromion marker cluster (AMC) is a non-invasive scapular motion tracking method. However, it lacks testing in clinical populations, where unique challenges may present. This investigation resolved the utility of the AMC approach in a compromised clinical population.The upper body of breast cancer survivors (BCS) and controls were tracked via motion capture and scapular landmarks palpated and recorded using a digitizer at static neutral to maximum elevation postures. The AMC tracked the scapula during dynamic maximum arm abduction. Both single (SC) and double calibration (DC) methods were applied to calculate scapular angles. The influences of calibration method, elevation, and group on mean and absolute error with two-way fixed ANOVAs with interactions (p < 0.05). Root mean square errors (RMSE) were calculated and compared.DC improved AMC estimation of palpated scapular orientation over SC, especially at higher arm elevations; RMSE averaged 11° higher for SC than DC at maximum elevation, but the methods were only 2.2° different at 90° elevation. DC of the AMC yielded mean error values of ∼5–10°. These approximate errors reported for AMC with young, lean adults.The AMC with DC is a non-invasive method with acceptable error for measuring scapular motion of BCS and age-matched controls.

The morphometric anatomy of the delto-fulcral triangle: A 3D CT-based reconstruction study

This study introduced the new delto-fulcral triangle (DFT), the first anatomical model of its kind. As seen from the orthopaedician's supraspinatus-outlet view, the antero-superior point of the coracoid process along with the lateral- and posterior-most acromial landmarks form the boundaries of the DFT. Since these osseous scapular landmarks accounted for both dynamic and static stabilisers of the glenohumeral joint, knowledge of the anatomical features of the DFT may prove beneficial to the orthopaedic surgeon. This study thus aimed to investigate the morphometry of the new DFT. The bony surfaces of one-hundred and sixty-nine (n=169) normal and pathological (Omarthrosis and Cuff-Tear Arthropathy) shoulders from the hospital's CT scan database were reconstructed (Mimics®: Materialise, Leuven, Belgium). Statistical significance was observed between all three groups for Side 2 (LACPF: distance between most lateral and most posterior points of the acromion) and angles α (angle between sides 1 and 3) and β (angle between sides 1 and 2) of the DFT. It was postulated that although pathological cases present with a smaller lateral acromial distance (LACPF), their lateral acromion landmark is more posteriorly placed from the scapular plane than that of a normal case. As the aspects of the morphometric anatomy of the DFT presented with levels of statistical significance, it may provide a means to evaluate the anatomy of normal and pathological cases. Additionally, the three osseous scapular landmarks that create the DFT are clearly visualised and palpable, therefore they are easily reproducible from both X-ray images and CT scans.

A comparison of acromion marker cluster calibration methods for estimating scapular kinematics during upper extremity ergometry

Accurate measurement of joint kinematics is required to understand the musculoskeletal effects of a therapeutic intervention such as upper extremity (UE) ergometry. Traditional surface-based motion capture is effective for quantifying humerothoracic motion, but scapular kinematics are challenging to obtain. Methods for estimating scapular kinematics include the widely-reported acromion marker cluster (AMC) which utilizes a static calibration between the scapula and the AMC to estimate the orientation of the scapula during motion. Previous literature demonstrates that including additional calibration positions throughout the motion improves AMC accuracy for single plane motions; however this approach has not been assessed for the non-planar shoulder complex motion occurring during UE ergometry. The purpose of this study was to evaluate the accuracy of single, dual, and multiple AMC calibration methods during UE ergometry. The orientations of the UE segments of 13 healthy subjects were recorded with motion capture. Scapular landmarks were palpated at eight evenly-spaced static positions around the 360° cycle. The single AMC method utilized one static calibration position to estimate scapular kinematics for the entire cycle, while the dual and multiple AMC methods used two and four static calibration positions, respectively. Scapulothoracic angles estimated by the three AMC methods were compared with scapulothoracic angles determined by palpation. The multiple AMC method produced the smallest RMS errors and was not significantly different from palpation about any axis. We recommend the multiple AMC method as a practical and accurate way to estimate scapular kinematics during UE ergometry.

MEASURING SCAPULAR MOVEMENT USING THREE-DIMENSIONAL ACROMIAL PROJECTION.

Background The current jig standard for measuring scapulohumeral movement of the shoulder complex only allows for static measurements of scapular positioning. Methods We compared scapular positioning as determined by a scapular jig with that projected from a marker triad placed on the acromion process of the scapula using an infrared motion capture system. Nine individuals performed abduction and scaption shoulder movements while arm and shoulder positioning were recorded during static and dynamic trials. Virtual scapulae were projected from surface marker triads on participants' acromia and compared with the position of three scapular landmarks identified by placement of a customized plastic jig. Static and dynamic positioning at a series of angles was compared to the jig standard to determine validity of the technique. Results There were no statistically significant differences between the virtual projections and jig standard for scapular external rotation, upward rotation, and anterior-posterior tilt planar measurements. Dynamic positioning correlated well with static projections, but virtual scapular projections generally overestimated upward rotation of the scapulae, as compared to the jig. This could potentially be corrected through the development of a linear correction factor. Conclusion Acromial projection allows for reproducible, non-invasive dynamic video motion capture of the scapula.

Development of a Method for Analyzing Three-Dimensional Scapula Kinematics

Scapula mobility complicates upper extremity kinematics assessment. Existing methods are diverse, providing inconsistent results. The current gold standard (bone pins) is prohibitively invasive. The purposes of the current study are to describe a virtual projection alternative to surface markers for video motion capture (VMC) of the scapula and to compare the results of the projection and surface marker methods to the results of similar existing methods. Ten participants were evaluated using VMC. Surface markers were applied to the trunk and arm in accordance with existing guidelines. Three markers were affixed to plastic base on the skin over the acromion process. Other scapular landmarks were digitized in a neutral position. These landmarks' locations were defined in reference to the acromion cluster and used to generate the projection. Humerothoracic, glenohumeral, and scapulothoracic kinematics were evaluated during shoulder abduction, flexion, and scaption. Joint angles produced by the surface markers and the projection were compared by Bonferroni-adjusted t tests. The results were compared to prior findings in the literature. The projection resulted in greater scapulothoracic upward rotation, internal rotation, and anterior-posterior tilt and less glenohumeral elevation (p < .0055) than did surface markers. The virtual scapula produced greater estimates of scapular mobility than did surface markers, corresponding to pre-existing results from similar methodologies. The result is a noninvasive measurement tool that produces different and superior results than do scapula surface markers. Measuring scapula kinematics via VMC without bone pins will facilitate future investigations into interactions between upper extremity injury, kinematics, and activity performance.

Identification of scapular kinematics using surface mapping: A validation study

The immediate goal of this study was to develop and validate a noninvasive, computational surface mapping approach for measuring scapular kinematics by using available motion capture technology in an innovative manner. The long-term goal is to facilitate clinical determination of the role of the scapula in children with brachial plexus birth palsy (BPBP). The population for this study consisted of fourteen healthy adults with prominent scapulae. Subject-specific scapular templates were created using the coordinates of five scapular landmarks obtained from palpation with subjects seated and arms relaxed in a neutral position. The scapular landmarks were re-palpated and their locations recorded in the six arm positions of the modified Mallet classification. The six Mallet positions were repeated with approximately 300 markers covering the scapula. The markers formed a surface map covering the tissue over the scapula. The scapular template created in the neutral position was iteratively fit to the surface map of each trial, providing an estimate of the orientation of the scapula. These estimates of scapular orientation were compared to the known scapular orientation determined from the scapular landmarks palpated in each Mallet position. The magnitude of the largest mean difference about an anatomical axis between the two measures of scapular orientation was 3.8° with an RMS error of 5.9°. This technique is practical for populations with visibly prominent scapulae (e.g., BPBP patients), for which it is a viable alternative to existing clinical methods with comparable accuracy.

Tracking the scapula using the scapula locator with and without feedback from pressure-sensors: A comparative study

BackgroundThe scapula locator method has associated intra-observer and inter-observer errors caused by the dependency on the observer to locate the scapular landmarks. The potential effect of the pressures applied by the observer on the measured scapular kinematics when this method is used has also been overlooked so far. The aim of this study was to investigate the effect of using feedback on the pressures applied on the scapula using the locator on the intra-observer and inter-observer reliabilities of the method as well as on the kinematics obtained using this method. MethodsThree observers tracked the scapular motion of the dominant shoulder of each subject using the locator with no reference to pressure-feedback for three trials of bilateral elevation in the scapular plane and using the locator with pressure-feedback for three other trials. Variations between the measurements obtained were used to calculate the intra-observer errors and variations between the measurements obtained by the three observers for the same subject were used to calculate inter-observer errors. Repeated-measures ANOVA tests were used to look at differences between the two methods in terms of intra-observer and inter-observer errors and scapular kinematics. FindingsUsing pressure-feedback reduced the intra-observer errors but had no effect on the inter-observer errors. Different scapular kinematics was measured using the two methods. InterpretationsPressure-feedback improves the reliability of the scapula locator method. Differences in the scapular kinematics suggest that unregulated pressures have an effect on the physiological scapular motion.

Mapping of Scapular Fractures with Three-Dimensional Computed Tomography

Fractures of the scapula involve a unique and challenging set of considerations, which must be understood to provide optimal treatment. The primary goal of this study was to create a frequency map of a series of surgically treated scapular fractures that specifically involved the scapular body and/or neck. A prospective database was used in the collection of consecutive radiographic imaging studies of patients undergoing operative treatment of scapular fractures. Scanned three-dimensional computed tomography images were superimposed and oriented to fit a model scapular template. Size dimensions were normalized by aligning specific scapular landmarks. Fracture lines were identified and traced over the combined three-dimensional computed tomography model to create a scapular fracture map. Of ninety fractures that met the criteria for inclusion, 68% involved the inferior aspect of the glenoid neck and 71% involved the superior vertebral border. Seventeen percent of the patterns included articular extension, and 22% of the fractures entered the spinoglenoid notch. Of fractures involving the inferior aspect of the glenoid neck at the lateral scapular border, 84% traversed medially to exit just inferior to the medial extent of the scapular spine, and 59% of these inferior neck fractures also had propagation to the inferior third of the vertebral border. Among the fractures involving the spinoglenoid notch, the most common pattern was demonstrated by coexisting fracture lines; 60% of the fractures of the spinoglenoid notch exited just inferior to the glenoid, 65% extended to the superior-medial vertebral border, and 45% extended to the inferior-medial vertebral border. In contrast, articular fractures did not follow predictable patterns; they demonstrated the greatest variability in trajectory, which was almost random, and there was a wide distribution of exit points along the vertebral border. Surgically treated scapular fractures display very common patterns. The most common pattern is the lateral border fracture immediately inferior to the glenoid, which extends to the superior vertebral border in more than two-thirds of cases. A smaller proportion of scapular fractures enter the spinoglenoid notch or the articular surface. There is great variation in the patterns of fractures involving the articular surface.

MRI VALIDATION OF A NEW REGRESSION MODEL FOR GLENOHUMERAL CENTRE OF ROTATION ESTIMATION

Identifying the centre of the glenohumeral joint (GHJ) is essential for three-dimensional (3D) upper limb motion analysis. The International Society of Biomechanics recommends a predictive method to locate the GHJ based on the identification of scapular landmarks [Meskers, 1998]. However, it is not practical to track these landmarks in dynamic motion analysis using skin based markers [Karduna, 2001]. Consequently, alternate, markerset dependent, unvalidated GHJ estimation methods proliferate. This study aimed to develop and validate a regression model (RM) to locate the GHJ using a practical and applicable marker set.

Scapular position: the validity of skin surface palpation

The assessment of the resting position of the scapula forms part of the examination of upper quadrant posture. The purpose of this study was to determine if surface palpation is a valid indicator of actual scapular position. Twelve embalmed shoulders were examined and the actual location of three bony scapular landmarks and three bony thoracic landmarks were compared with surface palpation of these locations. The results, based on the upper value for a distance (with 95% confidence), suggested that the difference between the surface location of the root of the spine of the scapula, the acromial angle and the inferior angle would be less than 0.67 cm, 0.98 cm and 0.46 cm respectively from the centre of the bony locations. The difference between the twelfth thoracic spinous process (SP), the SP corresponding with the root of the spine of the scapula, and the SP corresponding with the inferior angle and the surface points would be 1.46 cm, 1.09 cm and 1.01 cm respectively. The results of this study suggest that surface palpation of scapular location is a valid method for determining the actual location of the scapula. The findings also suggest that surface palpation can determine the location of thoracic landmarks, which may serve as reference points for scapular position.

The scapulo-humeral rhythm: effects of 2-D roentgen projection

Objective. The objective of this study is to illustrate the low accuracy of two-dimensional (2-D) X-ray projection methods for the quantification of the three-dimensional (3-D) shoulder motions. Background. The traditional method for the quantification of the gleno-humeral motion is by means of 2-D X-ray recording. The motion was characterized by the scapulo-humeral rhythm: the ratio of the nett humeral elevation over nett scapular rotation. The method was based on the quantification of the planar projection of the spatial positions of X-ray dense structures of the scapula. The deformations introduced by the central projection method, a feature of X-ray projection, cannot be compensated for by calibration: the position of the scapula with respect to the camera setting is unknown, and skeletal landmarks of the scapula cannot uniquely be identified. The transformation from 3-D orientations to 2-D angles will, therefore, be inaccurate. Methods. A 2-D X-ray projection of the scapula during a typical arm abduction was simulated. The 3-D motion was obtained by means of palpation and subsequent digitization of skeletal landmarks of the scapula. The 3-D positions of the recorded landmarks were projected on a plane by a simulation based on the parameters of the X-ray equipment. The scapulo-humeral rhythm was calculated for the different scapular landmarks, and for the orientation of the subject with respect to the projection axis. The results were compared with previous published scapulo-humeral rhythms. Results. The scapulo-humeral rhythm depends both on the choice of the skeletal landmarks, used to quantify the scapular rotations, and on the orientation of the subject in the X-ray setting. The full range of results obtained from earlier published experiments could be obtained from a simulation based on a single 3-D arm abduction. Conclusions. The 2-D scapulo-humeral rhythm, obtained from planar X-ray projection, is an inaccurate parameter to define the scapular motions.

An anatomical study of the suprascapular nerve

The course of the suprascapular nerve and its distance from fixed scapular landmarks were measured in 90 cadaveric shoulders. In an additional 15 cadavers, three pins were passed at various angles in a general anteriorposterior direction through the middle of the glenoid neck just inferior and lateral to the base of the coracoid process. The distance between the exit site on the posterior glenoid neck and the suprascapular nerve at the base of the scapular spine was recorded for each pin. Inferiorly directed pins were the furthest from the suprascapular nerve and averaged 16 mm. On the basis of these data, a relative safe zone is described in the posterior glenoid neck. Knowledge of the anatomic course of the suprascapular nerve may aid the physician in the diagnosis and treatment of suprascapular neuropathies. Appreciation of the safe zone may help the shoulder surgeon avoid iatrogenic injury to the suprascapular nerve during arthroscopic Bankart procedures and other open surgical procedures requiring dissection of the posterior glenoid neck.