Scapular Morphology Research Articles

Scapular morphology of great apes and humans: A three-dimensional computed tomography-based comparative study.

The primate scapula has been studied widely since its shape has been shown to correlate with how the forelimb is used in daily activities. In this study, we expand on the existing literature and use an image-based methodology that was originally developed for orthopaedic practice to quantify and compare the three-dimensional (3D) morphology of the scapula across humans and great apes. We expect that this image-based approach will allow us to identify differences between great apes and humans that can be related to differences in mobility and loading regime of the shoulder. We hypothesize that gorillas and chimpanzees will have a similar scapular morphology, geared towards stability and weight-bearing in knuckle-walking, whilst the scapular morphology of orangutans is expected to be more similar to that of humans given their high glenohumeral mobility associated with their suspensory lifestyle. We made 3D reconstructions of computed tomography scans of 69 scapulae from four hominid genera (Pongo, Gorilla, Pan and Homo). On these 3D bone meshes, the inferior glenoid plane was determined, and subsequently, a set of bony landmarks on the scapular body, coracoid, and acromion were defined. These landmarks allowed us to measure a set of functionally relevant angles which represent acromial overhang, subacromial space and coracoacromial space. The angles that were measured are: the delto-fulcral triangle (DFT), comprising the alpha, beta, and delta angle, the acromion-glenoid angle (AGA), the coracoid-glenoid centre-posterior acromial angle (CGA), the anterior tilt (TA CGA) and the posterior tilt of the CGA (PT CGA). Three observers placed the landmarks on the 3D bone meshes, allowing us to calculate the inter-observer error. The main differences in the DFT were found between humans and the great apes, with small differences between the great apes. The DFT of humans was significantly lower compared to that of the great apes, with the smallest alpha (32.7°), smallest delta (45.7°) and highest beta angle (101.6°) of all genera. The DFT of chimpanzees was significantly higher compared to that of humans (p < 0.01), with a larger alpha (37.6°) and delta angle (54.5°) and smaller beta angle (87.9°). The mean AGA of humans (59.1°) was significantly smaller (p < 0.001) than that of gorillas (68.8°). The mean CGA of humans (110.1°) was significantly higher (p < 0.001) than in orangutans (92.9°). Humans and gorillas showed mainly a posterior tilt of their coracoacromial complex whilst chimpanzees showed mainly an anterior tilt. The coracoacromial complex of the orangutans was not tilted anteriorly or posteriorly. With our image-based method, we were able to identify morphological features of the scapula that differed significantly between hominid genera. However, we did not find an overall dichotomy in scapular morphology geared towards high stability (Pan/Gorilla) or high mobility (Homo/Pongo). Further research is needed to investigate the functional implications of these differences in scapular morphology.

The role of scapular morphology in traumatic rotator cuff tears and greater tuberosity fractures: A retrospective study

BackgroundTraumatic postero-superior Rotator Cuff Tears (RCT) and isolated Greater Tuberosity fractures (GTF) are equivalent injuries resulting in significant shoulder dysfunction if left retracted or displaced. The difference in morphometric aetiology is unclear. A raised critical shoulder angle (CSA) has been associated with rotator cuff degeneration. We hypothesised that traumatic RCT is associated with a raised CSA when compared to GTF. MethodsA retrospective study was conducted across the two trauma units in our institution. All patients between the period of 2010 and 2020 with Traumatic GTF or RCT assessed on cross-sectional imaging (CT or MRI) were identified. Patients were case-matched by age, gender, mechanism and laterality of injury. The primary outcome measurement was the Critical Shoulder Angle (CSA). Other radiographic features of subacromial degenerative change, mechanism of injury, association with shoulder dislocation and delay to diagnosis were also compared. ResultsEighty patients met the inclusion criteria(40 traumatic RCT and 40 GTF). The mean age was 61.8 years with 58(72.5%) left-sided injuries. Thirty-four (43%) were female.The mean CSA was 3.96° higher in the RCT group (95% CI 2.5 to 5.41, p < 0.05). A CSA of 33.73 gave a sensitivity of 0.68 and a specificity of 0.8 to differentiate between RCT and GTF. Patients with RCT were far more likely to display subacromial degenerate changes and experience a significant delay in diagnosis, whereas those with GTF were more likely to have suffered a shoulder dislocation. ConclusionsPatients with traumatic RCT have radiographic features and scapular morphology associated with degenerative rotator cuff disease compared to those with GTF. This supports the theory that tears occur on the background of pre-existing tendon degeneration. Careful assessment of these parameters, combined with clinical assessment, may help guide the provision of appropriate diagnostic imaging. Level of evidenceIII.

Quantitative statistical shape model-based analysis of humeral head migration, Part 2: Shoulder osteoarthritis.

We wanted to investigate the quantitative characteristics of humeral head migration (HHM) in shoulder osteoarthritis (OA) and their possible associations with scapular morphology. We quantified CT-scan-based-HHM in 122 patients with a combination of automated 3D scapulohumeral migration (=HHM with respect to the scapula) and glenohumeral migration (=HHM with respect to the glenoid) measurements. We divided OA patients in Group 1 (without HHM), Group 2a (anterior HHM) and Group 2b (posterior HHM). We reconstructed and measured the prearthropathy scapular anatomy with a statistical shape model technique. HHM primarily occurs in the axial plane in shoulder OA. We found "not-perfect" correlation between subluxation distance AP and scapulohumeral migration values (rs = 0.8, p < 0.001). Group 2b patients had a more expressed prearthropathy glenoid retroversion (13° vs. 7°, p < 0.001) and posterior glenoid translation (4 mm vs. 6 mm, p = 0.003) in comparison to Group 1. Binary logistic regression analysis indicated prearthropathy glenoid version as a significant predictor of HHM (χ² = 27, p < 0.001). Multivariate regression analysis showed that the pathologic version could explain 56% of subluxation distance-AP variance and 75% of the scapulohumeral migration variance (all p < 0.001). Herewith, every degree increase in pathologic glenoid retroversion was associated with an increase of 1% subluxation distance-AP, and scapulohumeral migration. The occurrence of posterior HHM is associated with prearthropathy glenoid retroversion and more posterior glenoid translation. The reported regression values of HHM in the function of the pathologic glenoid version could form a basis towarda more patient-specific correction of HHM.

Comparing scapular morphology of Amblyomma sculptum and Amblyomma dubitatum nymphs allows a fast and practical differential diagnosis of ticks in highly infested areas with dominance of these two species.

Rickettsia rickettsii infection causes the highest human fatality rate among all Rickettsia species of the world and is endemic in Southeast Brazil. In this part of the country most human spotted fever cases are related to unnaturally high populations of ticks, usually a mix of two species, Amblyomma dubitatum Neumann and Amblyomma sculptum Berlese and their local host, capybara (Hydrochoerus hydrochaeris). At the same time, an increase in the number of SF notifications as well as its urbanization was observed, and a better characterization of disease epidemiology is mandatory for control measures and to halt its expansion. It was recently noticed in southeast Brazil that SF endemic areas were characterized by overgrowth populations of A. sculptum and decreased populations of A. dubitatum. Hence, characterization of areas with potential to endemicity, eco-epidemiological studies and control measures may rely on the evaluation of A. sculptum/A. dubitatum rate. However, in potentially endemic scenarios, discriminating the two tick species, particularly the nymphs considered the main vector stage, is a challenge in face of several hundreds to thousands of ticks that should be examined for quantitative studies. We herein present additional morphological features to an existing identification key for Amblyomma nymphs that considerably diminishes the labor to distinguish nymphs of these two tick species. Specifically, the oval-shaped scutum of A. dubitatum and a conspicuous scapula of A. sculptum are prominent discriminating features.

Sub-acromion impingement syndrome: Scapular morphometric analysis: A study on dry bones among Eastern Indian population

Introduction: Among various factors responsible for the development of chronic shoulder pain worldwide, the role of scapula, as a bony factor, is very important. This study focuses on evaluating the scapular shape and contour as a determinant of sub-acromion impingement syndrome. This was a cross-sectional observational study conducted on dry bones. Material and Methods: Dry scapulae (42 right sided and 38 left sided) were studied by taking digital photographs in different views and analyzing various parameters (critical shoulder angle (CSA), glenoid inclination, shape of acromion process, etc.) using ImageJ analyzer. Results were analyzed using measures of central tendency, and statistical significance was analyzed by measuring P values with the help of SPSS software (v25). Results: There were 40% Type I, 38.75% Type II, and 21.25% Type III scapulae, respectively. The Type I and III scapulae showed significant variations on the basis of various acromion overhangs (anterior overhang was 9.03 mm and 11.08 mm in Types I and III, respectively, while for the lateral overhang, the values were 9.73 mm and 6.25 mm in Types I and III, respectively) and angles (lateral acromion angle was 79.5° and 71.9° for Types I and III, respectively, whereas the coraco-acromion angle was 37° and 30.8° in Types I and III, respectively). The glenoid inclination and CSA were also significantly variable between all three types of scapulae. Discussion and Conclusion: The scapular morphology plays a pivotal role which can be extrapolated on a radiological basis in pertinent patients to determine the chances of developing pathological shoulders in future.

COMPARISON OF SCAPULAR MORPHOLOGY IN DEGENERATIVE AND TRAUMATIC ROTATOR CUFF TEARS

Background: Degenerative cuff tears have impingement pathophysiology due to altered scapular morphology as measured by increased critical shoulder angle (CSA), decreased lateral acromial angle (LAA) and increased acromion index (AI). But scapular morphology in traumatic tears has neither been studied nor compared with degenerative tears. Aim: To compare scapular morphology with CSA, LAA, AI between traumatic and degenerative tears and determine their reliability. Methods: This observational study includes 100 patients (50 with traumatic and degenerative tears). We analyzed MRI and standardized AP shoulder radiograph of these patients. Parameters, such as CSA, LAA, AI, were measured on AP radiographs by two separate observers in a blinded manner. The 1st observer repeated measurements after four weeks. We compared age, gender, degree of cuff tear, and CSA values, LAA, and AI between the two groups. Results: On comparison using chi-square test, degenerative group had significantly higher age, higher CSA (mean 37.55, SD 0.88 versus traumatic group mean 36.6, SD 0.95, [Formula: see text]-[Formula: see text], highly significant), higher AI (mean 0.73, SD 0.02 versus traumatic mean 0.69, SD 0.04 [Formula: see text]-[Formula: see text], highly significant), and lower LAA (77.14, SD 2.03 versus traumatic mean 78.36, SD 2.73, [Formula: see text]-value 0.013, significant). Interobserver and intraobserver reliability of parameters using the intraclass correlation coefficient (ICC) revealed excellent (CSA, LAA) and good (AI) agreement. ROC curve analysis calculated sensitivity (0.7) and specificity (0.66) to diagnose degenerative tear for CSA above 37.05[Formula: see text]. Conclusion: Scapular morphology in traumatic tears differs from degenerative. CSA, LAA, AI can be reliably measured on standardized shoulder AP radiographs.

A lower critical coracoid process angle is associated with type-B osteoarthritis: a radiological study of normal and diseased shoulders.

BackgroundDegenerative rotator cuff tears and osteoarthritis (OA) are associated with differences in coronal plane scapular morphology, with particular focus on the effect of the critical shoulder angle (CSA) on shoulder biomechanics. The effect, if any, of axial plane scapular morphology is less well established. We have noticed wide disparity of axial coracoid tip position in relation to the face of the glenoid and sought to investigate the significance of this through measurement of the critical coracoid process angle (CCPA), which incorporates coracoid tip position and glenoid version.MethodsCCPA, CSA, and glenoid retroversion were measured by three independent reviewers from the cross-sectional two-dimensional computed tomography (CT) and magnetic resonance imaging of 160 patients in four equal and matched case-control groups: (1) a control group of patients with a radiologically normal shoulder and no history of shoulder symptoms who had a CT thorax for another reason, (2) patients with primary OA with Walch type-A glenoid wear pattern on CT scan, (3) patients with type-B glenoid primary OA, and (4) patients with magnetic resonance imaging–proven atraumatic tears of the posterosuperior rotator cuff.ResultsInterobserver agreement was excellent for all measured parameters. The median CCPA was significantly lower in the type-B OA group (9.3˚) than that in controls (18.7˚), but not significantly different in the other study groups. There was a trend toward greater glenoid retroversion in the type-B OA group, but receiver operating characteristic curve analysis demonstrated the CCPA to be by far the most powerful discriminator for type-B OA. The optimal cutoff value was calculated for the CCPA at 14.3˚ with a sensitivity of 93% and specificity of 90% for type-B OA. Compared with controls, the CSA was significantly higher in the rotator cuff tear group and lower in both OA groups, but did not differentiate between type-A and type-B OA.ConclusionCombined with a lower CSA, a lower CCPA (<14.3˚) is strongly predictive of type-B glenoid OA. The authors propose a simple model of pectoralis major biomechanics to explain the effect of this axial plane anatomical variation, which requires further investigation.

702 The Role of Scapular Morphology in Traumatic Rotator Cuff Tears and Greater Tuberosity Fractures: A Retrospective Study

Abstract Aim Traumatic Rotator Cuff Tears(RCT) and Greater Tuberosity fractures(GT) are associated with high morbidity and reduced quality of life. Diagnostic and treatment pathways for both RCT and GT fractures are different. In this study we look at whether scapular morphology features can aid in our understanding of these traumatic injuries and influence patient pathways. Method A retrospective study was conducted at 2 hospitals. All patients between the period of 2010 and 2020 with Traumatic GT fractures or RCT were identified. Patients were case matched by age and laterality of injury. Primary outcome measurement was the Critical Shoulder Angle(CSA) and timing to further imaging. Statistical analysis was conducted using STATA™. Results Eighty patients met the inclusion criteria(40 traumatic RCT and 40 GT). Mean age was 61.8 years with 58(72.5%) left sided injuries. The difference between RCT and GT was 3.96 degrees(95% CI 2.5 to 5.41, p &amp;lt; 0.05). An CSA of 33.73 gave a sensitivity of 0.68 and a specificity of 0.8 to differentiate between RCT and GT fractures. The Area under the Curve(AUC) was 0.8 indicating high reliability. The overall difference in presentation to further scan between the 2 groups was 78. 3 days( P &amp;lt; 0.05, 95% CI 48.7 – 108). Conclusions Patients with a traumatic RCT and GT fractures have different scapular morphology and radiographic features which predisposes them to have these injuries. Patients presenting with a traumatic RCT are more likely to have a higher CSA and have a greater delay to further scan.

Supraspinatus-to-Glenoid Contact Occurs During Standardized Overhead Reaching Motion.

Background:Rotator cuff tears may result from repeated mechanical deformation of the cuff tendons, and internal impingement of the supraspinatus tendon against the glenoid is one such proposed mechanism of deformation.Purpose:To (1) describe the changing proximity of the supraspinatus tendon to the glenoid during a simulated overhead reaching task and (2) determine the relationship between scapular morphology and this proximity. Additionally, the patterns of supraspinatus-to-glenoid proximity were compared with previously described patterns of supraspinatus-to-coracoacromial arch proximity.Study Design:Descriptive laboratory study.Methods:Shoulder models were created from magnetic resonance images of 20 participants. Standardized kinematics were imposed on the models to simulate functional reaching, and the minimum distances between the supraspinatus tendon and the glenoid and the supraspinatus footprint and the glenoid were calculated every 5° between 0° and 150° of humerothoracic elevation. The angle at which contact between the supraspinatus and the glenoid occurred was documented. Additionally, the relationship between glenoid morphology (version and inclination) and the contact angle was evaluated. Descriptive statistics were calculated for the minimum distances, and glenoid morphology was assessed using Pearson correlation coefficients and simple linear regressions.Results:The minimum distances between the tendon and the glenoid and between the footprint and the glenoid decreased as elevation increased. Contact between the tendon and the glenoid occurred in all participant models at a mean elevation of 123° ± 10°. Contact between the footprint and the glenoid occurred in 13 of 20 models at a mean of 139° ± 10°. Less glenoid retroversion was associated with lower tendon-to-glenoid contact angles (r = –0.76; R 2 = 0.58; P < .01).Conclusion:This study found that the supraspinatus tendon progressively approximated the glenoid during simulated overhead reaching. Additionally, all participant models eventually made contact with the glenoid by 150° of humerothoracic elevation, although anatomic factors influenced the precise angle at which contact occurred.Clinical Relevance:Contact between the supraspinatus and the glenoid may occur frequently within the range of elevation required for overhead activities. Therefore, internal impingement may be a prevalent mechanism for rotator cuff deformation that could contribute to cuff pathology.

Usefulness Of Lateral Scapular View In Initial Evaluation Of Patients With Nontraumatic Shoulder Pain

Traditional evaluation of non-traumatic shoulder pain (NTSP) involves four radiographic views of the joint: AP, Grashey (G), axillary (AX), and lateral scapular (LS). The LS view has historically been useful in diagnosing various glenohumeral injuries. However, some studies have questioned the clinical utility of the LS view. PURPOSE: To determine if including the LS view makes meaningful contribution to accurate diagnosis and treatment plan for NTSP. METHODS: Two sets of fifty clinical vignettes were developed based on patients who presented with NTSP. Each set included identical patient history and physical exam findings, but different radiographs. The first set included AP, G, and AX views. The second set included AP, G, AX, and LS views. Four independent raters initially evaluated the first set of vignettes and provided diagnoses, need for further imaging, and treatment recommendations. Each rater repeated the evaluation one month later with the second set of vignettes. Cohen’s kappa was used to assess intra-observer reliability across both sets of vignettes. A survey was also created and distributed to members of American Shoulder and Elbow Surgeons (ASES) to evaluate how often surgeons utilize the LS view, and for what reason. RESULTS: Cohen’s kappa demonstrated substantial intra-rater reliability between the two sets of vignettes for diagnosis (0.702), x-ray findings (0.645) and further studies (0.620). Percent agreement was calculated and showed that raters maintained the same diagnosis in 77.5% of cases across both sets of vignettes. Furthermore, none of the raters recommended further x-rays when evaluating the first set of vignettes, suggesting they did not feel a need for the LS view prior to developing a diagnosis and treatment plan. Of surgeons who responded to the ASES survey, 82.6% routinely order a LS radiograph to evaluate patients with NTSP. Indications included: better characterization of acromion morphology (75.4%), better appreciation of humeral head relative to glenoid (38.2%), and better evaluation of scapular morphology (28.1%). CONCLUSION: Most surgeons who responded to the ASES survey report routinely ordering a LS radiograph in the initial evaluation of NTSP. However, responses to clinical vignettes suggest that a LS view may not provide a meaningful contribution to diagnosis.

Acromial Index in Indian Population and it’s Significance on Rotator Cuff Tears

Background: The etiopathogenesis of rotator cuff tears remains debatable. Among the many causes, abnormal scapular morphology has been found to accelerate the degenerative process of rotator cuff tears. The morphology and lateral extension of the acromion process were assessed indetail by Nyffeler et al. and the Acromion Index (AI) was introduced, which measures the lateral extension of the acromion. It was theorized that a large lateral extension of the acromion increased the chances of the supraspinatus tendon to degenerate because of impingement between the acromion and the deltoid muscle. The AI was compared between patients with rotator cuff tears and patients with an intact rotator cuff. Methods: 21 Indian patients presenting to the orthopaedics OPD, Yenepoya Medical College, with rotator cuff tears were taken up for this study between August 2020 and February 2021. Another 21 patients with intact rotator cuff and other shoulder diseases such as frozen shoulder were included in this study. Patients with rotator cuff tears were included in group A, and patients with intact rotator cuff were included in group B. Both groups had the AI measured on radiographs, and their values were compared. Results: The mean Acromial Index (AI) in the rotator cuff tear group was 0.74 and in the intact rotator cuff group it was 0.59, which was statistically significant. There was no statistical difference in AI between male and female patients. The mean age of the patients in the rotator cuff group was 50.8 years, and in non rotator cuff tear group, it was 50.2 years. Conclusion: Acromial Index is a useful predictive tool for detecting rotator cuff tears in the Indian population. Further studies are required to assess its usefulness in predicting the progression of a rotator cuff tear. Keywords: Rotator cuff tear; Acromial Index; Shoulder.

CORR Insights®: Imbalance in Axial-plane Rotator Cuff Fatty Infiltration in Posteriorly Worn Glenoids in Primary Glenohumeral Osteoarthritis: An MRI-based Study.

CORR Insights®: Imbalance in Axial-plane Rotator Cuff Fatty Infiltration in Posteriorly Worn Glenoids in Primary Glenohumeral Osteoarthritis: An MRI-based Study.

Similar scapular morphology in patients with dynamic and static posterior shoulder instability.

BackgroundThere is evidence that specific variants of scapular morphology are associated with dynamic and static posterior shoulder instability. To this date, observations regarding glenoid and/or acromial variants were analyzed independently, with two-dimensional imaging or without comparison with a healthy control group. Therefore, the purpose of this study was to analyze and describe the three-dimensional (3D) shape of the scapula in healthy and in shoulders with static or dynamic posterior instability using 3D surface models and 3D measurement methods.MethodsIn this study, 30 patients with unidirectional posterior instability and 20 patients with static posterior humeral head subluxation (static posterior instability, Walch B1) were analyzed. Both cohorts were compared with a control group of 40 patients with stable, centered shoulders and without any clinical symptoms. 3D surface models were obtained through segmentation of computed tomography images and 3D measurements were performed for glenoid (version and inclination) and acromion (tilt, coverage, height).ResultsOverall, the scapulae of patients with dynamic and static instability differed only marginally among themselves. Compared with the control group, the glenoid was 2.5° (P = .032), respectively, 5.7° (P = .001) more retroverted and 2.9° (P = .025), respectively, 3.7° (P = .014) more downward tilted in dynamic, respectively, static instability. The acromial roof of dynamic instability was significantly higher and on average 6.2° (P = .007) less posterior covering with an increased posterior acromial height of +4.8mm (P = .001). The acromial roof of static instability was on average 4.8° (P = .041) more externally rotated (axial tilt), 7.3° (P = .004) flatter (sagittal tilt), 8.3° (P = .001) less posterior covered with an increased posterior acromial height of +5.8 mm (0.001).ConclusionThe scapula of shoulders with dynamic and static posterior instability is characterized by an increased glenoid retroversion and an acromion that is shorter posterolaterally, higher, and more horizontal in the sagittal plane. All these deviations from the normal scapula values were more pronounced in static posterior instability.

Three-dimensional evaluation of scapular morphology in primary glenohumeral arthritis, rotator cuff arthropathy, and asymptomatic shoulders.

Recently, the 3-dimensional (3D) morphology of the coracoacromial complex in nonpathologic shoulders has been described. The aim of this study was to evaluate and compare the coracoacromial complex in pathologic shoulders (glenohumeral osteoarthritis [GHOA] and cuff tear arthropathy [CTA]) and nonpathologic shoulders. A 3D computed tomography reconstruction of 205 scapulae was performed (49 with GHOA, 48 with CTA, and 108 in normal shoulders [NL]). Subsequently, the center of the glenoid circle and several points at the coracoid, acromion, and glenoid were determined. The distances between these points and the rotation of the coracoacromial complex were calculated, and the acromion-glenoid angle was measured. The acromial overhang was significantly different between the NL (37 mm) and CTA (35 mm) groups (P = .045), as well as between the CTA and GHOA groups (33 mm) (P = .010). The acromion-glenoid angle showed a significant difference between the NL (mean, 50°) and GHOA (mean, 42°) groups (P < .001) and between the CTA (mean, 50°) and GHOA groups (P < .001). Furthermore, a significant difference was found in the acromial height, which was larger in the GHOA group (36 mm) than in the CTA group (30 mm) (P < .001) or NL group (30 mm) (P < .001). This 3D morphologic study showed that the acromial part of the complex was turned more posteriorly in both pathologic groups. Furthermore, we found the coracoacromial complex to be more cranial to the glenoid center in the GHOA group. Finally, a significant difference in the lateral overhang of the coracoacromial complex was observed between the 3 groups. The NL group had a larger overhang than the CTA group, and the CTA group in turn had a larger overhang than the GHOA group.

Are any radiologic parameters independently associated with degenerative postero-superior rotator cuff tears?

Several radiologic parameters representing scapular morphology have been proposed as risk factors for degenerative posterosuperior rotator cuff tear (PSRCT). The causes of PSRCT are multifactorial; many reported risk factors are compound entities. However, no determination, made after adjustment with previously reported risk factors, of which radiologic parameters are independent risk factors for degenerative PSRCT, has been reported. Therefore, this study's purpose was to determine which radiologic parameters representing scapular morphology are independent risk factors for degenerative PSRCT in a general population after adjustment with previously suggested risk factors. This study involved 629 subjects (629 shoulders) drawn from a cohort of rural residents. PSRCT diagnoses were based on magnetic resonance imaging findings. Logistic regression analysis was used to determine the odds ratios and 95% confidence intervals for the following variables: sex, age, height, weight, waist circumference, dominant-side involvement, smoking, alcohol consumption, manual labor, diabetes, hypertension, metabolic syndrome, thyroid dysfunction, serum lipid profile, high-sensitivity C-reactive protein, and radiologic parameters. The evaluated radiologic parameters were the superior displacement of the humeral head (SDHH) and those representing the scapular morphology. The radiologic parameters representing the scapular morphology were lateral acromial angle, acromial slope, acromial tilt, acromial index, and critical shoulder angle (CSA). Univariate logistic regression analyses for all variables, as well as multivariable logistic regression analyses for variables with significant associations and clinical effect sizes in the univariate logistic regression analyses, were performed. In order to determine the cutoff value for significant radiologic parameters, each pair of candidate cutoff values was obtained as follows: 1 candidate, as the lowest significant ordinal value in a univariate analysis, and the other candidate, according to a receiver operating characteristic curve analysis. Then, the cutoff values were determined by selecting the value in each candidate pair that had the larger area under the receiver operating characteristic curve, using the DeLong test. In the multivariable analyses, CSA was significantly associated with degenerative PSRCT after controlling for the following factors: age, waist circumference, dominant-side involvement, manual labor, diabetes, metabolic syndrome, hypo-high-density lipoproteinemia, and SDHH (P ≤ .033). CSA (odds ratio, 1.58 [95% confidence interval, 1.45-1.72]; P < .001) was the only significantly associated radiologic parameter among the studied radiologic parameters representing scapular morphology. CSA (≥35°) is an independent associated factor for degenerative PSRCT after adjustment for the following suggested risk factors: age, waist circumference, dominant-side involvement, manual labor, diabetes, metabolic syndrome, hypo-high-density lipoproteinemia, and SDHH.

The critical shoulder angle does not change over time: a radiographic study.

The anatomy of the scapula may predispose individuals to develop shoulder pathologies. The purpose of this study was to determine if the scapular anatomy, in particular the critical shoulder angle (CSA), changes over a long-term follow-up, or if it is a stable parameter. We hypothesized that increasing age would not influence the scapular morphology. We analyzed shoulder radiographs in our database from 2002 to 2019 to extract radiographs at an interval of at least 10 years. Radiographic analysis included measuring the CSA and assessing the acromion type according to Bigliani and Morrison, the posterior acromial height and the posterior acromial tilt. A total of 41 patients (47 shoulders) with a mean age of 53 years (range, 15-76; standard deviation [SD], ±14) fulfilled the inclusion criteria. The mean interval between the 2 sets of radiographs was 12 years (range, 10-16; SD ±2).The mean CSA did not change significantly with 34° (range, 20-41; SD ±4) at the first and 34° (range, 19-44; SD ±5) (P = .597) at the second assessment. On the initial lateral radiographs ("Neer view"), there were 11 type 1 (24%), 32 type 2 (70%), and 3 type 3 (6%) acromia according to Bigliani and Morrison. At the second assessment, there were 16 type 1 (34%), 28 type 2 (60%), and 3 type 3 (7%). Between both sets of radiographs, 11 were different (23%), without a trend in the type of change being discernible. The posterior acromial height was stable with 19 mm (range, 2-36; SD ±8) at the first and 18 mm (range, 5-38; SD ±8) at the second assessment (P = .186). The posterior acromion tilt changed from 59° (range, 34-81; SD ±10) to 62° (range, 30-81; SD ±10) (P < .001). Among 6 cases with rotator cuff tears (RCTs) already at the first assessment, the CSA did not change significantly at 10 years' follow-up (P = .414). Among the 10 cases with new RCTs at the second assessment, the CSA did not change significantly at 10 years' follow-up from 34° (range, 25-41; SD ±5) to 35° (range, 24-44; SD ±6) (P = .510). In the group of 31 shoulders without RCT, the mean CSA at the first assessment of 34° (range, 28-41; SD ±3) stayed also stable with 34° (range, 28-40; SD ±3) (P = .796). The CSA is an anatomical parameter of the scapula that does not change in size after closure of the physes.

Glenoid vault and humeral head alignment in relation to the scapular blade axis in young patients with pre-osteoarthritic static posterior subluxation of the humeral head

Static posterior subluxation of the humeral head is a pre-osteoarthritic deformity preceding posterior erosion in young patients. Its etiology remains unknown. The aim of this study was to analyze the differences in scapular morphology between young patients with pre-osteoarthritic static posterior subluxation of the humeral head and healthy controls with a centered humeral head. We performed a retrospective analysis of all patients with pre-osteoarthritic static posterior subluxation of the humeral head who were treated in our institution between January 2018 and November 2019. Fourteen shoulders in 12 patients were included in this study and then matched according their age, sex, and affected side with controls. Computed tomography images of both groups were compared in the standardized axial imaging plane for differences in scapular morphology. The following parameters were measured: glenoid version relative to the Friedman line and scapular blade axis, scapulohumeral and glenohumeral subluxation index, and neck angle, as well as glenoidand humeral offset. The patients in the subluxation group showed significantly higher scapulohumeral and glenohumeral subluxation indexes than controls (0.76 vs. 0.55 [P < .0001] and 0.58 vs. 0.51 [P = .016], respectively). The mean measurements of glenoid version according to the Friedman line and relative to the scapular blade axis were significantly higher in the subluxation group than in controls (19° vs. 4° [P < .0001]and 14° vs. 2° [P = .0002], respectively). The glenoid vault was significantly more anteriorly positioned with respect to the scapular blade axis in the subluxation group than in controls (neck angle, 166° vs. 173° [P = .0003]; glenoid offset, 9.2 mm vs. 4.6 mm [P = .0005]). The midpoint of the humeral head showed a posterior offset with respect to the scapular blade axis in the subluxation group, whereas controls had an anteriorly placed midpoint of the humeral head (-2 mm vs. 3.1 mm, P = .01). A higher scapulohumeral subluxation index showed significant correlations with an increased anterior offset of the glenoid vault (increased glenoid offset: r = 0.493, P = .008 and decreased neck angle: r = -0.554, P = .002), a posterior humeral offset (r = -0.775, P < .0001), and excessive glenoid retroversion measured by both methods (Friedman line: r = 0.852, P < .0001; scapular blade axis: r = 0.803, P < .0001). A higher glenohumeral subluxation index also correlated significantly with an increased anterior offset of the glenoid vault (increased glenoid offset: r = 0.403, P = .034; decreased neck angle: r = -0.406, P = .032) and posterior humeral offset (r = -0.502, P = .006). Young patients with pre-osteoarthritic static posterior subluxation of the humeral head have significant constitutional differences in scapular morphology in terms of an increased anterior glenoid offset, excessive glenoid retroversion, and increased posterior humeral offset in relation to the scapular blade compared with healthy matched controls.

Three-dimensional scapular morphology is associated with rotator cuff tears and alters the abduction moment arm of the supraspinatus

BackgroundNumerous studies have reported an association between rotator cuff injury and two-dimensional measures of scapular morphology. However, the mechanical underpinnings explaining how these shape features affect glenohumeral joint function and lead to injury are poorly understood. We hypothesized that three-dimensional features of scapular morphology differentiate asymptomatic shoulders from those with rotator cuff tears, and that these features would alter the mechanical advantage of the supraspinatus. MethodsTwenty-four individuals with supraspinatus tears and twenty-seven age-matched controls were recruited. A statistical shape analysis identified scapular features distinguishing symptomatic patients from asymptomatic controls. We examined the effect of injury-associated morphology on mechanics by developing a morphable model driven by six degree-of-freedom biplanar videoradiography data. We used the model to simulate abduction for a range of shapes and computed the supraspinatus moment arm. FindingsRotator cuff injury was associated with a cranial orientation of the glenoid and scapular spine (P = .011, d = 0.75) and/or decreased subacromial space (P = .001, d = 0.94). The shape analysis also identified previously undocumented features associated with superior inclination and subacromial narrowing. In our computational model, warping the scapula from a cranial to a lateral orientation increased the supraspinatus moment arm at 20° of abduction and decreased the moment arm at 160° of abduction. InterpretationsThree-dimensional analysis of scapular morphology indicates a stronger relationship between morphology and cuff tears than two-dimensional measures. Insight into how morphological features affect rotator cuff mechanics may improve patient-specific strategies for prevention and treatment of cuff tears.

Odd-nosed monkey scapular morphology converges on that of arm-swinging apes

Odd-nosed monkeys ‘arm-swing’ more frequently than other colobines. They are therefore somewhat behaviorally analogous to atelines and apes. Scapular morphology regularly reflects locomotor mode, with both arm-swinging and climbing anthropoids showing similar characteristics, especially a mediolaterally narrow blade and cranially angled spine and glenoid. However, these traits are not expressed uniformly among anthropoids. Therefore, behavioral convergences in the odd-nosed taxa of Nasalis, Pygathrix, and Rhinopithecus with hominoids may not have resulted in similar structural convergences. We therefore used a broad sample of anthropoids to test how closely odd-nosed monkey scapulae resemble those of other arm-swinging primates. We used principal component analyses on size-corrected linear metrics and angles that reflect scapular size and shape in a broad sample of anthropoids. As in previous studies, our first component separated terrestrial and above-branch quadrupeds from clambering and arm-swinging taxa. On this axis, odd-nosed monkeys were closer than other colobines to modern apes and Ateles. All three odd-nosed genera retain glenoid orientations that are more typical of other colobines, but Pygathrix and Rhinopithecus are closer to hominoids than to other Asian colobines in mediolateral blade breadth, spine angle, and glenoid position. This suggests that scapular morphology of Pygathrix may reflect a significant reliance on arm-swinging and that the morphology of Rhinopithecus may reflect more reliance on general climbing. As ‘arm-swinging’ features are also found in taxa that only rarely arm-swing, we hypothesize that these features are also adaptive for scrambling and bridging in larger bodied anthropoids that use the fine-branch component of their arboreal niches.

Is the scapula a good indicator of taxonomy?: A geometric morphometric analysis using macaque monkeys

In primates, scapular shape is often thought to correlate to locomotor patterns with distinct morphologies observed in arboreal versus terrestrial species. However, the extent to which intra‐generic morphological differences might be related to taxonomic differences as opposed to convergent locomotor behaviors remains to be tested. Thus, we tested the hypothesis that closely related, but behaviorally distinct, species may exhibit variation in their scapular morphology that match known phylogenetic relationships among the specious macaque monkey. Our sample (n=230) represented nine species; M. fascicularis, M. mulatta, M. fuscata, M. arctoides, M. radiata, M. nigra, M. nemestrina, and M. sylvanus and a Colobine outgroup (Trachypithecus cristatus). 3D scans of the left scapula were taken using an HDI structured light scanner and 5 landmarks and 61 sliding semilandmarks were applied to the scans to capture overall form. Following Procrustes superimposition, Canonical Variates Analysis (CVA) was performed and Procrustes coordinates were extracted and used for a Discriminant Function Analysis (DFA). The results of the CVA showed clear differences between Trachypithecus and macaques, as well as between M. fuscata and M. radiata and all other macaques. In the cross‐validated DFA, only 34.1% of individuals were correctly classified. The outgroup Trachypithecus showed a correct classification rate of 70%, as did M. nigra consistent with relatively distinct morphology in this taxon. Overall, patterns of morphological variation observed in the CVA do not match phylogenetic history, therefore suggesting environmental factors might influence the pattern of morphological variation among macaque species in novel ways, though this remains to be tested.Support or Funding InformationThis research is supported by a National Science Foundation Grant (NSF BCS‐1830745), Field Museum Visiting Researcher Fellowship, Primate Research Institute Cooperative Research Grant, University at Buffalo Asian Studies Grant, and the Mark Diamond Research Fund (SP‐18‐13).