3D morphometric analysis of 43 scapulae

The Use of Linear Formulas to Estimate Glenoid Bone Loss in the Lebanese Population: A 3-Dimensional Computed Tomography Study

Background

Glenoid bone loss (GBL) is common in patients with shoulder instability and plays a major role in surgical decision-making. While a plethora of GBL estimation methods exist, all of which present specific challenges, recent studies have developed simple linear formulas estimating GBL based on glenoid height.

Purpose

To assess the correlation between glenoid height and width, and to develop specific formulas based on age and sex to calculate the native glenoid width in the Lebanese population.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Computed tomography scans for 202 normal shoulders were extracted from our database. The glenoids were reconstructed in 3 dimensions and their width and height were measured. Glenoid width and height were compared between male and female groups. Correlation analysis was also performed on the width, height, age, and body mass index. Formulas estimating glenoid width were developed using regression analysis including all variables significantly influencing the model. Results were then compared with the values calculated using previously published formulas to determine the external validity when using linear formulas to estimate GBL.

Results

Significant differences were found between men and women. Regression analysis found that glenoid height and width strongly influenced the model, and that age showed a weak but significant correlation; therefore, the following 2 sex-specific formulas were developed: width (mm) = 6.1 + 0.51 ×height+ 0.03 ×age, and width (mm) = 4.55 + 0.51 ×height+ 0.03 ×age, in men and women, respectively. The values yielded from the formulas developed in this study and the true width significantly differed from those calculated from previous reports.

Conclusion

A strong correlation was found between glenoid height and width in a the Lebanese population and demonstrated that glenoid width can be accurately calculated based on the glenoid height and patient's age and sex using the following simplified formulas: width (mm) = 6 + 0.5 ×height+ 0.03 ×age, and width (mm) = 4.5 + 0.5 ×height+ 0.03 ×age, in men and women, respectively.

Regarding a human costoscapular joint by Prof. Dr. H. von Luschka (1870): A translation

Knowledge of variant anatomy was important during the time of Dr. Hubert von Luschka (1820-1875) and continues to be of relevance in current practice to prevent medical and surgical errors and to improve patient outcomes. Dr. H. von Luschka described an anatomical variant observed in the left scapula of a 40-year-old male: a connection between the medial superior angle of the scapula, piercing through the serratus posterior muscle to connect via a synovial capsule to the articular surface of the thoracic wall. The clinical relevance of this so-called "Luschka's tubercle" of the shoulder continues to be discussed. This translation is intended to broaden access to this hallmark manuscript to a wide audience of English readers. The introduction places the manuscript in the context of historical and current discussions. Three authors, all proficient in the German and English languages and educated in the anatomy of the shoulder, conducted the translation. The skeletal process that is part of the described joint structure appears similar to what is now called Luschka's tubercle. The full structure, including its connecting parts, are not currently included in anatomical nomenclature. In conclusion, Luschka's text and named tubercle continue to contribute to the discussion of scapulothoracic joint disorders.

3D reconstruction of the scapula from biplanar X-rays for pose estimation and morphological analysis

BACKGROUND

Patient-specific scapular shape in functional posture can be highly relevant to clinical research. Biplanar radiography is a relevant modality for that purpose with already two existing assessment methods. However, they are either time-consuming or lack accuracy. The aim of this study was to propose a new, more user-friendly and accurate method to determine scapular shape.

METHODS

The proposed method relied on simplified manual inputs and an upgraded version of the first 3D estimate based on statistical inferences and Moving-Least Square (MLS) deformation of a template. Then, manual adjustments, with real-time MLS algorithm and contour matching adjustments with an adapted minimal path method, were added to improve the match between the projected 3D model and the radiographic contours. The accuracy and reproducibility of the method were assessed (with 6 and 12 subjects, respectively).

FINDINGS

The shape accuracy was in average under 2 mm (1.3 mm in the glenoid region). The reproducibility study on the clinical parameters found intra-observer 95% confidence intervals under 3 mm or 3° for all parameters, except for glenoid inclination and Critical Shoulder Angle, ranging between 3° and 6°.

INTERPRETATION

This method is a first step towards an accurate reconstruction of the scapula to assess clinical parameters in a functional posture. This can already be used in clinical research on non-pathologic bones to investigate the scapulothoracic joint in functional position.

A predictive model for the critical shoulder angle based on a three-dimensional analysis of scapular angular and linear morphometrics

BACKGROUND

The purpose of this study was to define the features of scapular morphology that are associated with changes in the critical shoulder angle (CSA) by developing the best predictive model for the CSA based on multiple potential explanatory variables, using a completely 3D assessment.

METHODS

3D meshes were created from CT DICOMs using InVesalius (Vers 3.1.1, RTI [Renato Archer Information Technology Centre], Brazil) and Meshmixer (3.4.35, Autodesk Inc., San Rafael, CA). The analysis included 17 potential angular, weighted linear and area measurements. The correlation of the explanatory variables with the CSA was investigated with the Pearson's correlation coefficient. Using multivariable linear regression, the approach for predictive model-building was leave-one-out cross-validation and best subset selection.

RESULTS

Fifty-three meshes were analysed. Glenoid inclination (GI) and coronal plane angulation of the acromion (CPAA) [Pearson's r: 0.535; -0.502] correlated best with CSA. The best model (adjusted R-squared value 0.67) for CSA prediction contained 10 explanatory variables including glenoid, scapular spine and acromial factors. CPAA and GI were the most important based on their distribution, estimate of coefficients and loss in predictive power if removed.

CONCLUSIONS

The relationship between scapular morphology and CSA is more complex than the concept of it being dictated solely by GI and acromial horizontal offset and includes glenoid, scapular spine and acromial factors of which CPAA and GI are most important. A further investigation in a closely defined cohort with rotator cuff tears is required before drawing any clinical conclusions about the role of surgical modification of scapular morphology.

LEVEL OF EVIDENCE

Level 4 retrospective observational cohort study with no comparison group.

Morphological evaluation of the scapula by three-dimensional computed tomography to elucidate shoulder joint function

INTRODUCTION

There are many variations of scapula morphology. Evaluation of scapula morphology is necessary to elucidate shoulder joint movement. We aimed to analyze the bone morphology of various parts constituting the scapula to identify certain conserved features among them.

MATERIALS AND METHODS

Thirty-one healthy individuals were the subjects. We created a scapular three-dimensional (3D) model using computed tomography (CT). X and Y axes were set on a glenoid surface. We measured the approximate plane of the upper and lower scapular bodies and scapular spine and the central axis of the coracoid and acromion. The anatomical position of the scapular spine, upper and lower bodies, coracoid, and acromion was measured. The positional relationship between the upper and lower bodies and scapular spine and the coracoid and acromion was evaluated. The average angle of the upper and lower scapular bodies and the scapular spine with respect to the XZ plane was calculated. The average angle of the coracoid and acromion with the X-axis on the XY plane and Z-axis on the YZ plane was calculated.

RESULTS

On the XY plane, approximate planes of the upper and lower part of the body and the scapular spine were significantly correlated to each inclination. On the XY plane, inclinations of the central axes of the coracoid and acromion were significantly correlated.

CONCLUSIONS

The findings revealed for the first time the correlation between the inclinations of the scapular body and scapular spine and the inclination angle between the coracoid and acromion.

A new geometric model to quantify the area of glenoid bone defect and medialisation of the native joint line in glenohumeral arthritis

PURPOSE

To propose a geometric model to quantify the bone defect and the glenoid medialisation (in millimetres) compared to the native joint line. We also evaluated the reliability of this geometric model.

METHODS

Using two-dimensional CT imaging, we built a hypothetical triangle on the axial scan consisting of the following: side A, length (millimetres) of the glenoid bone; side B, average length (millimetres) of the glenoid in a healthy population; side C, the missing side; and angle α, the retroversion angle calculated using the Friedman method. The resulting triangle represents the bone defect, and its height represents the medialisation of the native joint line. To estimate inter-operator reliability, two physicians (operator 1 and operator 2) took the following measurements: angle α, side A, side C, semi-perimeter, area defect and height.

RESULTS

Forty participants (mean age ± SD 45 ± 10 years, range 26-43 years)-22 women and 18 men-participated in the study. We applied the cosine theorem (Carnot theorem) to calculate side C. After obtaining the three sides, the area of the triangle can be determined. Once the area is known, it is possible to extrapolate the height of the triangle, which corresponds to the loss of vault depth due to the bone defect. With respect to inter-operator reliability, the ICCs for all measurements were > 0.99, exhibiting a very high correlation.

CONCLUSIONS

The proposed geometric model can be used to quantify the glenoid bone deficit and the glenoid medialisation compared to the native joint line, which can be used to improve surgical treatment.

The critical size of a defect in the glenoid causing anterior instability of the shoulder after a Bankart repair, under physiological joint loading

Aims

Patients with recurrent anterior dislocation of the shoulder commonly have an anterior osseous defect of the glenoid. Once the defect reaches a critical size, stability may be restored by bone grafting. The critical size of this defect under non-physiological loading conditions has previously been identified as 20% of the length of the glenoid. As the stability of the shoulder is load-dependent, with higher joint forces leading to a loss of stability, the aim of this study was to determine the critical size of an osseous defect that leads to further anterior instability of the shoulder under physiological loading despite a Bankart repair.

Patients and Methods

Two finite element (FE) models were used to determine the risk of dislocation of the shoulder during 30 activities of daily living (ADLs) for the intact glenoid and after creating anterior osseous defects of increasing magnitudes. A Bankart repair was simulated for each size of defect, and the shoulder was tested under loading conditions that replicate in vivo forces during these ADLs. The critical size of a defect was defined as the smallest osseous defect that leads to dislocation.

Results

The FE models showed a high risk of dislocation during ADLs after a Bankart repair for anterior defects corresponding to 16% of the length of the glenoid.

Conclusion

This computational study suggests that bone grafting should be undertaken for an anterior osseous defect in the glenoid of more than 16% of its length rather than a solely soft-tissue procedure, in order to optimize stability by restoring the concavity of the glenoid.

Radiographic characterization of the B2 glenoid: the effect of computed tomographic axis orientation

BACKGROUND

Glenoid retroversion may accelerate glenoid loosening after total shoulder arthroplasty. Accurate measurement of preoperative glenoid deformity is critical for decision-making and prognostication. The purpose of this study was to determine whether glenoid version, inclination, and depth and humeral subluxation measurements on computed tomography (CT) scan slices oriented in the plane of the body differ from those oriented in the scapular plane and those obtained by automated 3-dimensional reconstruction software in the setting of a biconcave B2-type glenoid.

METHODS

Thirty-one preoperative CT scans in patients undergoing total shoulder arthroplasty with Walch B2-type glenoids underwent a standardized measurement protocol by 3 observers. Glenoid version, inclination, and depth and humeral subluxation were measured on 2-dimensional CT images in the plane of the body, on 2-dimensional images in the plane of the scapula, and by a validated, automated 3-dimensional software program.

RESULTS

Correction of CT slice axis into the plane of the scapula decreased measured retroversion by 2.4° to 4.7° (P < .004) and inclination by 21° (P < .001). Whereas uncorrected version measurements do not differ from automated software measurements, corrected measurements do (P < .001). Whereas corrected inclination measurements do not differ from automated measurements, uncorrected measurements do (P < .001). Automated measurements differed from both corrected and uncorrected subluxation (P < .001 in both cases).

CONCLUSION

If CT images are not reoriented into the plane of the scapula, version and inclination will be significantly overestimated. In the setting of a retroverted, deformed glenoid, automated software may produce similar inclination measurements to corrected 2-dimensional CT, but it produces significantly altered measurements of version and subluxation.

Computerized 3D morphological analysis of glenoid orientation

An accurate preoperative measurement of glenoid orientation is crucial for evaluating pathologies and successful total shoulder arthroplasty. Existing methods may be labor-intensive, observer-dependent, and sensitive to the misalignment between the scapula plane and CT scanning direction. In this study, we proposed a computation framework and performed an automated analysis of the glenoid orientation based on 3D surface data. Three-dimensional models of 12 scapulae were analyzed. The glenoid cavity and external anatomical features were automatically extracted from these 3D models. Glenoid version was calculated using the scapula plane and the fulcrum axis alternatively. Glenoid inclination was measured both relative to transverse axis of the scapula and the medial pole-inferior tip axis. The mean (±SD) of the fulcrum-based glenoid version was -0.55° (±4.17°), while the scapular-plane-based glenoid version was -5.05° (±3.50°). The mean (±SD) of glenoid inclinations based on the medial pole and inferior tip was 12.75° (±5.03°) while the mean (±SD) of the glenoid inclination based on the medial pole and glenoid center was 4.63° (±4.86°). Our computational framework was able to extract the reproducible morphological measures free of inter- and intra- observer variability. For the first time in 3D, we showed that the fulcrum axis was practically perpendicular to the glenoid plane normal (radial line), and thus extended the fulcrum-based glenoid version for quantifying 3D glenoid orientation.

Estimating Glenoid Width for Instability-Related Bone Loss: A CT Evaluation of an MRI Formula

BACKGROUND

Determining the magnitude of glenoid bone loss in cases of shoulder instability is an important step in selecting the optimal reconstructive procedure. Recently, a formula has been proposed that estimates native glenoid width based on magnetic resonance imaging (MRI) measurements of height (1/3 × glenoid height + 15 mm). This technique, however, has not been validated for use with computed tomography (CT), which is often the preferred imaging modality to assess bone deficiencies.

PURPOSE

The purpose of this project was 2-fold: (1) to determine if the MRI-based formula that predicts glenoid width from height is valid with CT and (2) to determine if a more accurate regression can be resolved for use specifically with CT data.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Ninety normal shoulder CT scans with preserved osseous anatomy were drawn from an existing database and analyzed. Measurements of glenoid height and width were performed by 2 observers on reconstructed 3-dimensional models. After assessment of reliability, the data were correlated, and regression models were created for male and female shoulders. The accuracy of the MRI-based model's predictions was then compared with that of the CT-based models.

RESULTS

Intra- and interrater reliabilities were good to excellent for height and width, with intraclass correlation coefficients of 0.765 to 0.992. The height and width values had a strong correlation of 0.900 (P < .001). Regression analyses for male and female shoulders produced CT-specific formulas: for men, glenoid width = 2/3 × glenoid height + 5 mm; for women, glenoid width = 2/3 × glenoid height + 3 mm. Comparison of predictions from the MRI- and CT-specific formulas demonstrated good agreement (intraclass correlation coefficient = 0.818). The CT-specific formulas produced a root mean squared error of 1.2 mm, whereas application of the MRI-specific formula to CT images resulted in a root mean squared error of 1.5 mm.

CONCLUSION

Use of the MRI-based formula on CT scans to predict glenoid width produced estimates that were nearly as accurate as the CT-specific formulas. The CT-specific formulas, however, are more accurate at predicting native glenoid width when applied to CT data.

CLINICAL RELEVANCE

Imaging-specific (CT and MRI) formulas have been developed to estimate glenoid bone loss in patients with instability. The CT-specific formula can accurately predict native glenoid width, having an error of only 2.2% of average glenoid width.

The scapular glenopolar angle: standard values and side differences

OBJECTIVE

The aim of this study is to determine normal glenopolar angle (GPA) values on bone specimens of the scapula and compare them with various radiological views and CT examination.

MATERIALS AND METHODS

GPA values were measured on 100 mature, dry, non-paired scapulae, 20 pairs of dry scapulae, 50 AP radiographs of the shoulder, 50 Neer I views, 50 AP chest radiographs and 20 3D CT reconstructions of the scapula.

RESULTS

Measurements made on bone specimens of the scapula showed an average GPA value of 42.3°; the mean absolute side-to-side difference was on average 1.6°. The average GPA measured on 50 AP shoulder radiographs was 35.9°, on Neer I views 40.6° and AP chest radiographs 37.1°, with the mean absolute side-to-side difference on average 4.9°; on 3D CT the average GPA was 43.0° and the mean absolute side-to-side difference on average 1.4°.

CONCLUSION

GPA values depend on the method of measurement used. Measurements made on 3D CT reconstructions and Neer I views showed almost the same values as those measured on bone specimens. The values measured on AP shoulder views and AP chest radiographs were statistically significantly lower. Side-to-side variability (right and left) measured on 3D CT reconstructions was insignificant, and the obtained values corresponded to the values from bone specimens. Therefore, the best method to measure the GPA is a 3D CT reconstruction and an exact Neer I projection.