Reliability of the glenoid plane

Three-dimensional glenohumeral relationship in cuff tear arthropathy and its correlation with the type of cuff tear

Objective

The main purpose of this study is to evaluate 1) the three-dimensional (3D) glenohumeral relationship in cuff tear arthropathy (CTA) and 2) the correlation between different types of rotator cuff tears (RCTs) and the 3D glenohumeral relationship.

Method

A total of 124 patients with CTA and 60 control patients were included in this study. 3D models of computed tomography images of the shoulder were reconstructed to evaluate the position of the humerus in relation to the scapula using a Cartesian coordinate system. The glenohumeral relationship of the CTA group is compared to the control group (group N). Next, the CTA group is divided into three subgroups depending on the (im)balance of the transverse force couple (TFC): a balanced RCT group (group B, n = 50), a group with an imbalance of the TFC to anterior (group A, n = 30), and a group with an imbalance of the TFC to posterior (group P, n = 44). The glenohumeral relationship of the RCT group is compared to a control group of 60 patients without RCT (group N).

Results

The CTA group (96° ± 1°) was significant (P < .05) and more superiorly subluxated than the control group (88° ± 1°). There was no significant difference in the superior subluxation between the three subgroups: group A (98° ± 3°), group P (96° ± 3°), and group B (97° ± 2°). Group A (88° ± 2°) showed significantly more anterior subluxation compared to group P (92° ± 1°).

Conclusion

All patients with CTA have a significantly superior position of the humerus compared to the control group. If the TFC is unbalanced, a significantly more anterior or posterior translation of the humerus is observed depending on the direction of the imbalance.

Gender-specific factors influencing the glenoid version and reference values for it

BACKGROUND

Glenoid version is an important factor in the evaluation of shoulder stability and shoulder pathologies. However, there are neither established reference values nor known factors that influence the glenoid version, even though valid reference values are needed for diagnostic and orthopaedic surgery like corrective osteotomy and total or reverse shoulder arthroplasty (TSA/RSA). The aim of our population-based study was to identify factors influencing the glenoid version and to establish reference values from a large-scale population cohort.

RESULTS

Our study explored the glenoid versions in a large sample representing the general adult population. We investigated 3004 participants in the population-based Study of Health in Pomerania (SHIP). Glenoid version was measured for both shoulders via magnetic resonance imaging (MRI). Associations with the glenoid version were calculated for sex, age, body height, body weight and BMI. The reference values for glenoid version in the central European population range between -9° and 7.5°, while multiple factors are associated with the glenoid version.

CONCLUSION

To achieve a reliable interpretation prior to orthopaedic surgery, sex- and age-adjusted reference values are proposed.

Minimal but potentially clinically relevant anteroinferior position of the humeral head following traumatic anterior shoulder dislocations: A 3D-CT analysis

In unstable shoulders, excessive anteroinferior position of the humeral head relative to the glenoid can lead to a dislocation. Measuring humeral head position could therefore be valuable in quantifying shoulder laxity. The aim of this study was to measure (1) position of the humeral head relative to the glenoid and (2) joint space thickness during passive motion in unstable shoulders caused by traumatic anterior dislocations and in contralateral uninjured shoulders. A prospective cross-sectional CT-study was performed in patients with unilateral anterior shoulder instability. Patients underwent CT scanning of both injured and uninjured side in supine position (0° abduction and 0° external rotation) and in 60°, 90°, and 120° of abduction with 90° of external rotation without an external load. Subsequently, 3D virtual models were created of the humerus and the scapula to create a glenoid coordinate system to identify poster-anterior, inferior-superior, and lateral-medial position of the humeral head relative to the glenoid. Joint space thickness was defined as the average distance between the subchondral bone surfaces of the humeral head and glenoid. Fifteen consecutive patients were included. In supine position, the humeral head was positioned more anteriorly (p = 0.004), inferiorly (p = 0.019), and laterally (p = 0.021) in the injured compared to the uninjured shoulder. No differences were observed in any of the other positions. A joint-space thickness map, showing the bone-to-bone distances, identified the Hill-Sachs lesion footprint on the glenoid surface in external rotation and abduction, but no differences on average joint space thickness were observed in any position.

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.

Reverse total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study

BACKGROUND

Optimal implant placement in reverse total shoulder arthroplasty (rTSA) remains controversial. Specifically, the optimal glenoid inclination is unknown. Therefore, a cadaveric shoulder simulator with 3-dimentional human motion specific to rTSA was used to study joint contact and muscle forces as a function of glenoid component inclination.

METHODS

Eight human cadaver shoulders were tested before and after rTSA implantation. Scapular plane abduction kinematics from control subjects and those with rTSA drove a cadaveric shoulder simulator with 3-dimentional scapulothoracic and glenohumeral motion. Glenoid inclination varied from -20° to +20°. Outputs included compression, superior-inferior (S/I) shear, and anterior-posterior shear forces from a 6° of freedom load cell in the joint, and deltoid and rotator cuff muscle forces. Data were evaluated with statistical parametric mapping and t-tests.

RESULTS

Inferior glenoid inclination (-) reduced S/I shear by up to 125% relative to superior inclination, with similar compression to the neutral condition (0°). Superior inclinations (+) increased the S/I shear force by approximately the same magnitude, yet decreased compression by 25% in the most superior inclination (+20°). There were few differences in deltoid or rotator cuff forces due to inclination. Only the middle deltoid decreased by approximately 7% for the most inferior inclination (-20°). Compared with native shoulders, the neutral (0°) rTSA inclination showed reduced forces of 30%-75% in the anterior deltoid and a trend toward decreased forces in the middle deltoid. Force demands on the rotator cuff varied as a function of elevation, with a trend toward increased forces in rTSA at peak glenohumeral elevation.

CONCLUSIONS

Inferior inclination reduces superior shear forces, without influencing compression. Superior inclination increased S/I shear, while decreasing compression, which may be a source of component loosening and joint instability after rTSA. Inferior inclination of the rTSA glenoid may reduce the likelihood of glenoid loosening by reducing the magnitude of cyclic shear and compressive loading during arm elevation activities, although this may be altered by specific-subject body habitus and motion. These factors are especially important in revision rTSA or glenoid bone grafting where there is already a 3-fold increase in glenoid baseplate loosening vs. primary rTSA.

Anatomic total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study

BACKGROUND

Although typically favorable in outcome, anatomic total shoulder arthroplasty (aTSA) can require long-term revision. The most common cause for revision is glenoid loosening, which may result from eccentric cyclic forces and joint translations. "Rocking" of the glenoid component may be exacerbated by the joint geometry, such as glenoid inclination and version. Restoration of premorbid glenoid inclination may be preferable, although laboratory and computational models indicate that both superior inclination and inferior inclination have benefits. This discrepancy may arise because previous studies were limited by a lack of physiological conditions to test inclination. Therefore, a cadaveric shoulder simulator with 3-dimensional human motion was used to study joint contact and muscle forces with isolated changes in glenoid inclination.

METHODS

Eight human cadaveric shoulders were tested before and after aTSA. Scapular-plane abduction kinematics from human subjects were used to drive a cadaveric shoulder simulator with 3-dimensional scapulothoracic and glenohumeral motion. Glenoid inclination was varied from -10° to +20°, whereas compressive, superior-inferior shear, and anterior-posterior shear forces were collected with a 6-df load cell during motion. Outputs also included muscle forces of the deltoid and rotator cuff. Data were evaluated with statistical parametric mapping repeated-measures analysis of variance and t tests.

RESULTS

Inferior glenoid inclination (-10°) reduced both compressive and superior-inferior shear forces vs. neutral 0° inclination by up to 40%, and even more when compared with superior inclination (P < .001). Superior inclinations (+10° and +20°) tended to increase deltoid and rotator cuff forces vs. neutral 0° inclination or inferior inclination, on the order of 20%-40% (P ≤ .045). All force metrics except anterior-posterior shear were lowest for inferior inclination. Most aTSA muscle forces for neutral 0° inclination were not significantly different from native shoulders and decreased 45% and 15% in the posterior deltoid and supraspinatus, respectively (P ≤ .003). Joint translations were similar to prior reports in aTSA patients and did not differ between any inclinations or compared with native shoulders. Joint reaction forces were similar to those observed in human subjects with instrumented aTSA implants, providing confidence in the relative magnitude of our results.

CONCLUSIONS

Inferior inclination reduces overall forces in the shoulder. Superior inclinations increase the muscle effort required for the shoulder to achieve similar motion, thus increasing the forces exerted on the glenoid component. These results suggest that a preference toward aTSA glenoid components in inferior inclination may reduce the likelihood of glenoid loosening by reducing excessive muscle and joint contact forces.

Anatomical plane and transverse axis of the scapula: Reliability of manual positioning of the anatomical landmarks

Background

The aim of our study was to evaluate the accuracy of manual determination of the three key points defining the anatomical plane of the scapula, which conditions the reliability of planning software programs based on manual method.

Method

We included 82 scapula computed tomography scans (56 pathologic and 26 normal glenoid), excluding truncation and major three-dimensional artifact. Four observers independently picked the three key points for each case. Inter- and intra-observer agreement was calculated for each point, using the intraclass correlation method. The mean error (mm) between the observers was calculated as the diameter of the smallest sphere including the four chosen positions.

Results

Lower inter-observer agreement was found for the trigonum superoinferior position and for the glenoid center anteroposterior position. The mean positioning error between the four observers was 6.9 mm for the trigonum point, and error greater than 10 mm was recorded in 25% of the cases. The mean positioning error was 3.5 mm for the glenoid center in altered glenoid, compared to 1.8 mm for normal glenoid.

Discussion

Manual determination of an anatomical plane of the scapula suffers from inaccuracy especially due to the variability in trigonum picking, and in a lesser extent, to the variability of glenoid center picking in altered glenoid.

In Vitro Simulation of Shoulder Motion Driven by Three-Dimensional Scapular and Humeral Kinematics

In vitro simulation of three-dimensional (3D) shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein, we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: (1) robotically simulate seven healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in six cadavers, (2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics, and (3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5 deg were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3 deg mean absolute error (MAE) was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over five repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform for future laboratory studies to investigate shoulder biomechanics and consider the impacts of variable input kinematics from populations of interest, as they can significantly impact study outputs and resultant conclusions.

The Evolution of Reverse Total Shoulder Arthroplasty-From the First Steps to Novel Implant Designs and Surgical Techniques

PURPOSE OF REVIEW

The purpose of this review is to summarize recent literature regarding the latest design modifications and biomechanical evolutions of reverse total shoulder arthroplasty and their impact on postoperative outcomes.

RECENT FINDINGS

Over the past decade, worldwide implantation rates of reverse total shoulder arthroplasty have drastically increased for various shoulder pathologies. While Paul Grammont's design principles first published in 1985 for reverse total shoulder arthroplasty remained unchanged, several adjustments were made to address postoperative clinical and biomechanical challenges such as implant glenoid loosening, scapular notching, or limited range of motion in order to maximize functional outcomes and increase the longevity of reverse total shoulder arthroplasty. However, the adequate and stable fixation of prosthetic components can be challenging, especially in massive osteoarthritis with concomitant bone loss. To overcome such issues, surgical navigation and patient-specific instruments may be a viable tool to improve accurate prosthetic component positioning. Nevertheless, larger clinical series on the accuracy and possible complications of this novel technique are still missing.

Benchmarking off-the-shelf statistical shape modeling tools in clinical applications

Statistical shape modeling (SSM) is widely used in biology and medicine as a new generation of morphometric approaches for the quantitative analysis of anatomical shapes. Technological advancements of in vivo imaging have led to the development of open-source computational tools that automate the modeling of anatomical shapes and their population-level variability. However, little work has been done on the evaluation and validation of such tools in clinical applications that rely on morphometric quantifications(e.g., implant design and lesion screening). Here, we systematically assess the outcome of widely used, state-of-the-art SSM tools, namely ShapeWorks, Deformetrica, and SPHARM-PDM. We use both quantitative and qualitative metrics to evaluate shape models from different tools. We propose validation frameworks for anatomical landmark/measurement inference and lesion screening. We also present a lesion screening method to objectively characterize subtle abnormal shape changes with respect to learned population-level statistics of controls. Results demonstrate that SSM tools display different levels of consistencies, where ShapeWorks and Deformetrica models are more consistent compared to models from SPHARM-PDM due to the groupwise approach of estimating surface correspondences. Furthermore, ShapeWorks and Deformetrica shape models are found to capture clinically relevant population-level variability compared to SPHARM-PDM models.

Biomechanics of anatomic and reverse shoulder arthroplasty

The biomechanics of the shoulder relies on careful balancing between stability and mobility. A thorough understanding of normal and degenerative shoulder anatomy is necessary, as the goal of anatomic total shoulder arthroplasty is to reproduce premorbid shoulder kinematics.With reported joint reaction forces up to 2.4 times bodyweight, failure to restore anatomy and therefore provide a stable fulcrum will result in early implant failure secondary to glenoid loosening.The high variability of proximal humeral anatomy can be addressed with modular stems or stemless humeral components. The development of three-dimensional planning has led to a better understanding of the complex nature of glenoid bone deformity in eccentric osteoarthritis.The treatment of cuff tear arthropathy patients was revolutionized by the arrival of Grammont's reverse shoulder arthroplasty. The initial design medialized the centre of rotation and distalized the humerus, allowing up to a 42% increase in the deltoid moment arm.More modern reverse designs have maintained the element of restored stability but sought a more anatomic postoperative position to minimize complications and maximize rotational range of motion. Cite this article: EFORT Open Rev 2021;6:918-931. DOI: 10.1302/2058-5241.6.210014.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Acromial and glenoid morphology in glenohumeral osteoarthritis: a three-dimensional analysis

Background

The purpose of this study was to determine the association between glenohumeral osteoarthritis (GHOA) and three-dimensional acromial and glenoid morphology.

Methods

In this retrospective study, we compared computed tomographic studies of three groups of scapulae: normal healthy, mild GHOA (Samilson-Prieto grade 1), and severe GHOA (Samilson-Prieto grade 3). All scans were segmented to create three-dimensional reconstructions. From these models, critical shoulder angle and acromial offset were measured, as normalized to scapular height. The coronal plane inclination of the glenoid was measured using a glenoid sphere-fit method. Reliability was confirmed via intraclass correlation coefficients > 0.75.

Results

Eighty scapulae were included: 30 normal, 20 mild GHOA, and 30 severe GHOA. There were no differences in acromial offset between the normal group and either the mild-GHOA group or the severe-GHOA group. The severe-GHOA group had a smaller critical shoulder angle than either the normal (30 ± 5° vs. 34 ± 4°, P = .003) or mild-GHOA groups (34 ± 4°, P = .020), but the normal and mild-GHOA groups did not differ (P = .965). The severe-GHOA group had more inferiorly inclined glenoids than either the normal (7 ± 6° vs. 12 ± 5°, P = .002) or mild-GHOA groups (14 ± 5°, P ≤ .001), but the normal and mild-GHOA groups did not differ (P = .281).

Conclusion

Normal and severe-GHOA shoulders differ in critical shoulder angle and glenoid inclination but not acromial offset. The lack of a difference in critical shoulder angle or inferior inclination between mild-GHOA and normal groups calls into question whether inclination and critical shoulder angle differences predate severe GHOA.

Humeral head subluxation in Walch type B shoulders varies across imaging modalities

Background

The Walch type B pattern of glenohumeral osteoarthritis is characterized by posterior humeral head subluxation (PHHS). At present, it is unknown whether the percentage of subluxation measured on axillary radiographs is consistent with measurements on 2-dimensional (2D) axial or 3-dimensional (3D) volumetric computed tomography (CT). The purpose of this study was to evaluate PHHS across imaging modalities (radiographs, 2D CT, and 3D CT).

Methods

A cohort of 30 patients with Walch type B shoulders underwent radiography and standardized CT scans. The cohort comprised 10 type B1, 10 type B2, and 10 type B3 glenoids. PHHS was measured using the scapulohumeral subluxation method on axillary radiographs and 2D CT. On 3D CT, PHHS was measured volumetrically. PHHS was statistically compared between imaging modalities, with P ≤ .05 considered significant.

Results

The mean PHHS value for the entire group was 69% ± 24% on radiographs, 65% ± 23% with 2D CT, and 74% ± 24% with 3D volumetric CT. PHHS as measured on complete axillary radiographs was not significantly different than that measured on 2D CT (P = .941). Additionally, PHHS on 3D volumetric CT was 9.5% greater than that on 2D CT (P < .001). There were no significant differences in PHHS between the type B1, B2, and B3 groups with 2D or 3D CT measurement techniques (P > .102).

Conclusion

Significant differences in PHHS were found between measurement techniques (P < .035). A 9.5% difference in PHHS between 2D and 3D CT can be mostly accounted for by the linear (2D) vs. volumetric (3D) measurement techniques (a linear 80% PHHS value is mathematically equivalent to a volumetric PHHS value of 89.6%). Surgeons should be aware that subluxation values and therefore thresholds vary across different imaging modalities and measurement techniques.

Age-related differences in humerothoracic, scapulothoracic, and glenohumeral kinematics during elevation and rotation motions

Age affects gross shoulder range of motion (ROM), but biomechanical changes over a lifetime are typically only characterized for the humerothoracic joint. Suitable age-related baselines for the scapulothoracic and glenohumeral contributions to humerothoracic motion are needed to advance understanding of shoulder injuries and pathology. Notably, biomechanical comparisons between younger or older populations may obscure detected differences in underlying shoulder motion. Herein, biplane fluoroscopy and skin-marker motion analysis quantified humerothoracic, scapulothoracic, and glenohumeral motion during 3 static poses (resting neutral, internal rotation to L4-L5, and internal rotation to maximum reach) and 2 dynamic activities (scapular plane abduction and external rotation in adduction). Orientations during static poses and rotations during active ROM were compared between subjects <35 years and >45 years of age (N=10 subjects per group). Numerous age-related kinematic differences were measured, ranging 5–25°, where variations in scapular orientation and motion were consistently observed. These disparities are on par with or exceed mean clinically important differences and standard error of measurement of clinical ROM, which indicates that high resolution techniques and appropriately matched controls are required to avoid confounding results of studies that investigate shoulder kinematics. Understanding these dissimilarities will help clinicians manage expectations and treatment protocols where indications and prevalence between age groups tend to differ. Where possible, it is advised to select age-matched control cohorts when studying the kinematics of shoulder injury, pathology, or surgical/physical therapy interventions to ensure clinically important differences are not overlooked.

The glenoid and humeral head in shoulder osteoarthritis: A comprehensive review

The key management of glenohumeral osteoarthritis is shoulder arthroplasty which aims to reduce pain and restore full shoulder function: it has increased in recent years. A detailed understanding of the anatomy of the glenoid and humeral head, as well as morphological changes of the glenoid in osteoarthritis, are important factors to consider when deciding on replacement components. This review begins with a brief introduction of the glenohumeral joint itself, and then considers the detailed anatomy of the glenoid fossa and humeral head, both of which are reported to have variable morphology. Several studies have been undertaken to assess various parameters, especially of the glenoid fossa including its shape, height, width, and articular surface area, version and inclination, in an attempt to define a standard classification that can be applied to surgical intervention. Nevertheless, no definitive consensus concerning the classification of these morphologies has been forthcoming, hence the need for this review. Following a consideration of these morphologies, the current state of knowledge regarding glenoid deformity in osteoarthritis, as well as its surgical management, is considered.

Reliable interpretation of scapular kinematics depends on coordinate system definition

BACKGROUND

Interpretation of shoulder motion across studies has been complicated due to the use of numerous scapular coordinate systems in the literature. Currently, there are no simple means by which to compare scapular kinematics between coordinate system definitions when data from only one coordinate system is known.

RESEARCH QUESTION

How do scapular kinematics vary based on the choice of coordinate system and can average rotation matrices be used to accurately convert kinematics between scapular local coordinate systems?

METHODS

Average rotation matrices derived from anatomic landmarks of 51 cadaver scapulae (29 M/22 F; 59 ± 13 yrs; 26R/25 L; 171 ± 11 cm; 70 ± 19 kg; 23.7 ± 5.5 kg/m²) were generated between three common scapular coordinate systems. Absolute angle of rotation was used to determine if anatomical variability within the cadaver population influenced the matrices. To quantify the predictive capability to convert kinematics between the three coordinate systems, the average rotation matrices were applied to scapulothoracic motion data collected from 19 human subjects (10 M/9 F; 43 ± 17 yrs; 19R; 173 ± 9 cm; 71 ± 16 kg; 23.6 ± 4.5 kg/m²) using biplane fluoroscopy. Root mean squared error (RMSE) was used to compare kinematics from an original coordinate system to the kinematics expressed in each alternative coordinate system.

RESULTS

The choice of scapular coordinate system resulted in mean differences in scapulothoracic rotation of up to 23°, with overall different shapes and/or magnitudes of the curves. A single average rotation matrix between any two coordinate systems achieved accurate conversion of scapulothoracic kinematics to within 4° of RMSE of the known solution. The average rotation matrices were independent of sex, side, decomposition sequence, and motion.

SIGNIFICANCE

Scapulothoracic kinematic representations vary in shape and magnitude based solely on the choice of local coordinate system. The results of this study enhance interpretability and reproducibility in expressing scapulothoracic motion data between laboratories by providing a simple means to convert data between common coordinate systems. This is necessitated by the variety of available motion analysis techniques and their respective scapular landmark definitions.

Viewing perspective malrotation influences angular measurements on lateral radiographs of the scapula

BACKGROUND

Accurate and reliable assessment of acromial tilt (ATA) and slope (ASA) angles have been important in the clinical evaluation of degenerative and traumatic rotator cuff tears. This study analyzed the influence of radiographic viewing perspective on the ATA and ASA and developed criteria to identify true lateral (TL) view radiographs.

METHODS

Three-dimensional computed tomographic (CT) reconstructions of 52 scapulae without rotator cuff tears or osteoarthritis were studied. Digitally reconstructed radiographs (DRRs) were aligned to obtain a TL view. In 10 random scapulae, incremental ante- and retroversion and up- and downward rotation views were generated (10° increments, ±30°), and ATA and ASA were measured by 2 observers. Clinically applicable criteria were developed and validated to identify TL views.

RESULTS

The mean ATA and ASA on TL views were 33°±4° (range 23°-42°) and 22°±7° (8°-43°), respectively. Mixed effect models showed that DRRs malpositioned in 20° and 30° anteversion and downward rotation decreased the ATA (P ≤ .030). DRRs malpositioned in anteversion and >10° of up- and downward rotation demonstrated a significantly decreased ASA (P ≤ .047). Intra- and interobserver reliability was excellent for TL views (intraclass correlation coefficient ≥ 0.95) but decreased with increasing viewing angle. Anatomic landmark criteria were capable of identifying TL-view radiographs with sensitivity of 81% and specificity of 82%.

CONCLUSION

Both ATA and ASA were significantly affected by malposition in anteversion and downward rotation of the scapula. Reliable ASA measurement was more susceptible in up- and downward rotation than the ATA. New visual criteria can identify TL-view radiographs and should be used in future studies to ensure consistency in ATA and ASA measurement.

Influence of Radiographic Viewing Perspective on Glenoid Inclination Measurement

Introduction

The purposes of this study were to determine (1) whether glenoid inclination (GI) could be accurately measured on plain radiographs as compared to a gold-standard 3-dimensional (3D) measure and (2) whether GI could be reliably measured on plain radiographs.

Materials and Methods

Digitally reconstructed radiographs (DRRs) were made from 3D computed tomography reconstructions of 68 normal cadaver scapulae. DRRs were made in a variety of viewing angles. Inclination was measured on these DRRs. These measurements were also made using a gold-standard 3D method. Measurements were made by 2 orthopedic surgeons and 1 surgeon twice, to calculate interrater and intrarater intraclass correlation coefficients (ICCs).

Results

The gold-standard 3D β was 83 ± 5° (72°–98°). On neutral plain radiographs, the mean ± standard deviation 2D β angle was 80 ± 6° (range, 66°–99°). With regard to accuracy, the 2D β angle was significantly different from the 3D β angle, with the 2D β underestimating the 3D β by 5° (95% confidence intervals −1 to 12). With regard to reliability, interrater ICCs for 2D β with a neutral viewing angle was 0.79. Two-dimensional β varied widely with viewing angle from 0.24 to 0.88. Interrater ICCs for the 3D method was 0.83 (0.60–0.92). Intrarater ICCs for all 3 techniques were high (>0.91).

Conclusions

Two-dimensional radiographic GI measurement is not accurate, as it underestimates the 3D value by an average of 5° when compared to the gold-standard 3D measurement. GI 2D measurement reliability varies with viewing angle on plain radiographs and thus to accurately and reliably measure inclination 3D imaging is necessary.

A computed tomography analysis of three-dimensional glenoid orientation modified by glenoid torsion

Background

The longitudinal axis of the glenoid is not always parallel to the scapular body, and glenoid torsion could affect the values of glenoid orientation. The purpose of this study was to evaluate 3-dimensional glenoid version and inclination modified by glenoid torsion and to clarify the differences between the values of conventional and of modified glenoid orientations.

Methods

Computed tomography scans of 30 shoulders without shoulder pathology, 30 shoulders with primary osteoarthritis, and 30 shoulders with a massive rotator cuff tear or cuff tear arthropathy were retrospectively evaluated. After determining the glenoid axis and the scapular planes and calculating conventional glenoid version and inclination, modified glenoid version and inclination, and glenoid torsion, the values of conventional glenoid orientation and those of modified glenoid orientation were compared statistically.

Results

All shoulders showed anterior torsion of the glenoid with an average of 16° ± 5°. The values of modified glenoid retroversion were significantly smaller than those of conventional glenoid retroversion in all groups (P < .033), and the values of the modified glenoid inferior inclination were significantly larger than those of conventional glenoid inferior inclination in all groups (P < .001).

Conclusions

The present study showed that the glenoid twists with respect to the scapular body and that modification by glenoid torsion could affect the values of glenoid orientation. These results indicated that glenoid orientation with respect to the glenoid longitudinal axis will help surgeons determine proper placement of the glenoid component during shoulder arthroplasty.

Three-dimensional assessment of the normal Japanese glenoid and comparison with the normal French glenoid

INTRODUCTION

In 2014, reverse total shoulder arthroplasty was approved in Japan. We were concerned that the base plate might be incompatible with Japanese who were generally smaller than Westerners. Therefore, we investigated the dimensions and morphology of the normal Japanese glenoid and compared with the normal French glenoid.

MATERIALS AND METHODS

One hundred Japanese shoulders without glenoid lesions (50 men and 50 women) were investigated and compared with 100 French shoulders (50 men and 50 women). Computed tomography was performed with 3-dimensional image reconstruction and images were analyzed using Glenosys software. Glenoid parameters (width, height, retroversion and inclination) were compared between Japanese and French subjects.

RESULTS

In Japanese subjects, the mean glenoid width was 25.5mm, height was 33.3mm, retroversion was 2.3° and inclination was 11.6° superiorly. In French subjects, the mean glenoid width was 26.7mm, height was 35.4mm, retroversion was 6.0° and inclination was 10.4° superiorly. Glenoid width and height were significantly smaller in Japanese subjects than French subjects (P=0.001 and P<0.001), while retroversion was significantly greater in French subjects (P<0.001). There was no significant difference of inclination.

CONCLUSIONS

These findings will help surgeons to identify suitable patients for RSA and perform the procedure with appropriate preoperative planning.

LEVEL OF EVIDENCE

IV: retrospective or historical series.

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.

Accuracy of patient-specific instrumentation in anatomic and reverse total shoulder arthroplasty

PURPOSE

Glenoid component malposition is associated with poor function and early failure of both anatomic and reverse total shoulder arthroplasty. Glenoid positioning is challenging particularly in the setting of bone loss or deformity. Recently, the use of computer assistance has been shown to reduce implantation error. The aim of this study is to evaluate the accuracy of patient-specific instrumentation in cases of anatomic and reverse shoulder replacement in vivo.

METHODS

Twenty patients underwent total shoulder arthroplasty using a computed tomography (CT)-based patient-specific instrumentation (PSI) system, ten anatomic and ten reverse. Preoperative three-dimensional digital templating of glenoid component position was undertaken and surgery then performed using a custom-made guide. Postoperative CT scans were used to compare final implanted component position to the preoperatively planned position in the same patient.

RESULTS

Final component position and orientation closely reflected the preoperatively templated position. Mean deviation in the glenoid version from planned was 1.8° ±1.9° (range, 0.1°-7.3°). Mean deviation in inclination was 1.3° ±1.0° (range, 0.2°-4.5°). Mean deviation in position on the glenoid face was 0.5 ± 0.3 mm (range, 0.0-1.3 mm) in the anteroposterior plane and 0.8 ± 0.5 mm (range, 0.0-1.9 mm) in the superoinferior plane. Actual achieved version was within 7° of neutral in all cases except for one where it was deliberately planned to be outside of this range.

CONCLUSION

PSI in both anatomic and reverse shoulder arthroplasty is highly accurate in guiding glenoid component implantation in vivo. The system can reliably correct bony deformity.

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.

Three-dimensional anthropometric analysis of the glenohumeral joint in a normal Japanese population

BACKGROUND

An understanding of normal glenohumeral geometry is important for anatomical reconstruction in shoulder arthroplasty. Unfortunately, the details of the glenohumeral joint in Asian populations have not been sufficiently evaluated. The purpose of this study was to evaluate the 3-dimensional geometry of the glenohumeral joint in the normal Japanese population and to clarify its morphologic features.

METHODS

Anthropometric analysis of the glenohumeral joint was performed using computed tomography scans of 160 normal shoulders from healthy Japanese volunteers. The glenohumeral dimensions and orientation were analyzed 3-dimensionally. Sex differences and correlations between sides and among the respective parameters in the glenohumeral dimensions were evaluated.

RESULTS

The normal Japanese humeral head has an average width of 41.4 mm, thickness of 13.2 mm, diameter of 42.9 mm, retroversion of 32°, and inclination of 135°. The glenoid has an average height of 31.5 mm, width of 23.1 mm, diameter of 62.0 mm, retroversion of 0°, and inferior inclination of 2°. The values of the glenohumeral dimensions were uniform in men and women, and the humeral head and glenoid were larger in men than in women. The glenohumeral size was well correlated between the 2 sides, and there were direct correlations among the heights, humeral length, humeral head size, and glenoid size.

CONCLUSIONS

The present study revealed the glenohumeral geometry in the normal Japanese population. The present results would be useful to determine the size of implants and to improve the design of shoulder prostheses that reflect the normal anatomy of the Asian glenohumeral joint.

The effect of glenoid cavity depth on rotator cuff tendinitis

INTRODUCTION

Some of the most important causes of shoulder pain are inflammation and degenerative changes in the rotator cuff (RC). Magnetic resonance imaging (MRI) is a noninvasive and safe imaging modality. MRI can be used for the evaluation of cuff tendinopathy. In this study, we evaluated the relationship between glenoid cavity depth and cuff tendinopathy and we investigated glenoid cavity depth on the pathogenesis of cuff tendinopathy.

MATERIALS AND METHODS

We retrospectively evaluated 215 patients who underwent MRI. Of these, 60 patients showed cuff tendinopathy (group A) and 54 patients showed no pathology (group B). Glenoid cavity depth was calculated in the coronal and transverse planes.

RESULTS

The mean axial depth was 1.7 ± 0.9 and the mean coronal depth 3.8 ± 0.9, for group A. The mean axial depth was 3.5 ± 0.7 and the mean coronal depth 1.5 ± 0.8, for group B. There were significant differences in the axial and coronal depths between the two groups.

CONCLUSION

High coronal and low axial depth of the glenoid cavity can be used to diagnose RC tendinitis.

Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty - A simulation study

BACKGROUND

We studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations.

METHODS

Using a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion.

FINDINGS

Change in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level.

INTERPRETATION

135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.

Can an extracorporeal glenoid aiming device be used to optimize the position of the glenoid component in total shoulder arthroplasty?

PURPOSE

Successful total shoulder arthroplasty (TSA) requires a correct position of the glenoid component. This study compares the accuracy of the positioning with a new developed glenoid aiming device and virtual three-dimensional computed tomography (3D-CT) scan positioning.

MATERIALS AND METHODS

On 39 scapulas from cadavers, a K-wire (KDev) was positioned using the glenoid aiming device. It consists of glenoid components connected to the aiming device, which cover 150° of the inferior glenoid circle, has a fixed version and inclination and is available with several different radii. The aiming device is stabilized at the most medial scapular point. The K-wire is drilled from the center of the glenoid component to this most medial point. All scapulas were also scanned with CT and 3D reconstructed. A virtual K-wire (Kct) was positioned in the center of the glenoid and in the scapular plane. Several parameters were compared. Radius of the chosen glenoid component (rDev) and the virtual radius of the glenoid circle (rCT), spinal scapular length with the device (SSLdev) and virtual (SSLct), version and inclination between KDev and Kct, difference between entry point and exit point ("Matsen"-point).

RESULTS

Mean rDev: 14 mm ± 1.7 mm and mean rCT: 13.5 mm ± 1.6 mm. There was no significant difference between SSLdev (110.6 mm ± 7.5 mm) and SSLct (108 mm ± 7.5 mm). The version of KDev and Kct was -2.53° and -2.17° and the inclination 111.29° and 111.66°, respectively. The distance between the "Matsen-point" device and CT was 1.8 mm.

CONCLUSION

This glenoid aiming device can position the K-wire on the glenoid with great accuracy and can, therefore, be helpful to position the glenoid component in TSA. The level of evidence: II.

Consequences of reaming with flat and convex reamers for bone volume and surface area of the glenoid; a basic science study

Background

The effect of reaming on bone volume and surface area of the glenoid is not precisely known. We hypothesize that (1) convex reamers create a larger surface area than flat reamers, (2) flat reamers cause less bone loss than convex reamers, and (3) the amount of bone loss increases with the amount of version correction.

Methods

Reaming procedures with different types of reamers are performed on similar-sized uniconcave and biconcave glenoids created from Sawbones foam blocks. The loss of bone volume, the size of the remaining surface area, and the reaming depth are measured and evaluated.

Results

Reaming with convex reamers results in a significantly larger surface area than with flat reamers for both uniconcave and biconcave glenoids (p = 0.013 and p = 0.001). Convex reamers cause more bone loss than flat reamers, but the difference is only significant for uniconcave glenoids (p = 0.007).

Conclusions

In biconcave glenoids, convex reamers remove a similar amount of bone as flat reamers, but offer a larger surface area while maximizing the correction of the retroversion. In pathological uniconcave glenoids, convex reamers are preferred because of the conforming shape.

Glenohumeral translations during range-of-motion movements, activities of daily living, and sports activities in healthy participants

BACKGROUND

Glenohumeral translations have been mainly investigated during static poses while shoulder rehabilitation exercises, activities of daily living, and sports activities are dynamic. Our objective was to assess glenohumeral translations during shoulder rehabilitation exercises, activities of daily living, and sports activities to provide a preliminary analysis of glenohumeral arthrokinematics in a broad range of dynamic tasks.

METHODS

Glenohumeral translations were computed from trajectories of markers fitted to intracortical pins inserted into the scapula and the humerus. Two participants (P1 and P2) performed full range-of-motion movements including maximum arm elevations and internal-external rotations rehabilitation exercises, six activities of daily living, and five sports activities.

FINDINGS

During range-of-motion movements, maximum upward translation was 7.5mm (P1) and 4.7mm (P2). Upward translation during elevations was smaller with the arm internally (3.6mm (P1) and 2.9mm (P2)) than neutrally (4.2mm (P1) and 3.7mm (P2)) and externally rotated (4.3mm (P1) and 4.3mm (P2)). For activities of daily living and sports activities, only anterior translation during reach axilla for P1 and upward translation during ball throwing for P2 were larger than the translation measured during range-of-motion movements (108% and 114%, respectively).

INTERPRETATION

While previous electromyography-based studies recommended external rotation during arm elevation to minimize upward translation, measures of glenohumeral translations suggest that internal rotation may be better. Similar amplitude of translation during ROM movement and sports activities suggests that large excursions of the humeral head may be caused not only by fast movements, but also by large amplitude movements.

Patient-specific targeting guides compared with traditional instrumentation for glenoid component placement in shoulder arthroplasty: a multi-surgeon study in 70 arthritic cadaver specimens

HYPOTHESIS AND BACKGROUND

The purpose of this study was to compare the accuracy of patient-specific guides for total shoulder arthroplasty (TSA) with traditional instrumentation in arthritic cadaver shoulders. We hypothesized that the patient-specific guides would place components more accurately than standard instrumentation.

MATERIALS AND METHODS

Seventy cadaver shoulders with radiographically confirmed arthritis were randomized in equal groups to 5 surgeons of varying experience levels who were not involved in development of the patient-specific guidance system. Specimens were then randomized to patient-specific guides based off of computed tomography scanning, standard instrumentation, and anatomic TSA or reverse TSA. Variances in version or inclination of more than 10° and more than 4 mm in starting point were considered indications of significant component malposition.

RESULTS

TSA glenoid components placed with patient-specific guides averaged 5° of deviation from the intended position in version and 3° in inclination; those with standard instrumentation averaged 8° of deviation in version and 7° in inclination. These differences were significant for version (P = .04) and inclination (P = .01). Multivariate analysis of variance to compare the overall accuracy for the entire cohort (TSA and reverse TSA) revealed patient-specific guides to be significantly more accurate (P = .01) for the combined vectors of version and inclination. Patient-specific guides also had fewer instances of significant component malposition than standard instrumentation did.

CONCLUSION

Patient-specific targeting guides were more accurate than traditional instrumentation and had fewer instances of component malposition for glenoid component placement in this multi-surgeon cadaver study of arthritic shoulders. Long-term clinical studies are needed to determine if these improvements produce improved functional outcomes.

The influence of radiographic viewing perspective and demographics on the critical shoulder angle

BACKGROUND

Accurate assessment of the critical shoulder angle (CSA) is important in clinical evaluation of degenerative rotator cuff tears. This study analyzed the influence of radiographic viewing perspective on the CSA, developed a classification system to identify malpositioned radiographs, and assessed the relationship between the CSA and demographic factors.

METHODS

Glenoid height, width, and retroversion were measured on 3-dimensional computed tomography reconstructions of 68 cadaver scapulae. A digitally reconstructed radiograph was aligned perpendicular to the scapular plane, and retroversion was corrected to obtain a true anteroposterior (AP) view. In 10 scapulae, incremental anteversion/retroversion and flexion/extension views were generated. The CSA was measured, and a clinically applicable classification system was developed to detect views with >2° change in CSA vs. true AP view.

RESULTS

The average CSA was 33° ± 4°. Intraobserver and interobserver reliability was high (intraclass correlation coefficient ≥ 0.81) but decreased with increasing viewing angle. Views beyond 5° anteversion, 8° retroversion, 15° flexion, and 26° extension resulted in >2° deviation of the CSA compared with the true AP view. The classification system was capable of detecting aberrant viewing perspectives with sensitivity of 95% and specificity of 53%. Correlations between glenoid size and CSA were small (R ≤ 0.3), and CSA did not vary by gender (P = .426) or side (P = .821).

CONCLUSIONS

The CSA was most susceptible to malposition in anteversion/retroversion. Deviations as little as 5° in anteversion resulted in a CSA >2° from true AP view. A new classification system refines the ability to collect true AP radiographs of the scapula. The CSA was unaffected by demographic factors.

Accuracy of the glenohumeral subluxation index in nonpathologic shoulders

BACKGROUND

Correction of posterior humeral subluxation, measured by the humeral subluxation index (HSI) according to Walch, is necessary in total shoulder arthroplasty to prevent early loosening. The 3-dimensional (3D) measurement of the shoulder is becoming well accepted and common practice as it overcomes positional errors to which 2-dimensional (2D) glenohumeral measurements are prone. The first objective was to describe the HSI in a nonpathologic population with the 2D HSI according to Walch and a newly described 3D HSI method. The second objective was to compare both measuring methods with each other.

METHODS

In 151 nonpathologic shoulders, the 2D HSI was measured on the midaxial computed tomography scan cut of the scapula. The 3D HSI, based on the native glenoid plane, was defined as [formula in text], in which X is the projection of the center of the humeral head to the anteroposterior axis of the glenoid fossa and R is the radius of the humeral head. Both measuring methods were compared with each other. Correlation was determined. Interobserver and intraobserver reliability of the 3D HSI was measured.

RESULTS

The mean 3D HSI (51.5% ± 2.7%) was significantly (P < .001) more posterior than the mean 2D HSI (48.7% ± 5.2%), with a mean difference of 2.9% ± 5.6%. No correlation was found between the 2D and 3D HSI. The interobserver and intraobserver reliability was excellent.

CONCLUSION

The 2D HSI seems to underestimate the humeral subluxation compared with a 3D reliable equivalent.

Posterior shoulder instability: does glenoid retroversion predict recurrence and contralateral instability?

PURPOSE

To determine whether glenoid retroversion is a predictor of posterior shoulder instability, contralateral instability, or recurrent instability in patients with traumatic, contact-related posterior shoulder instability.

METHODS

Patients who underwent shoulder stabilization by 2 senior orthopaedic sport surgeons were identified retrospectively. Patients with a connective tissue disorder, multidirectional instability, or non-trauma-induced pathology were excluded. Patients with a glenoid lesion involving greater than 25% of the glenoid or an engaging humeral lesion were also excluded. Thus patients with a traumatic injury and a magnetic resonance imaging scan available for review were included. Magnetic resonance imaging scans were reviewed, and glenoid version was measured using the glenoid vault method. Charts were reviewed for epidemiologic data, recurrent instability requiring reoperation, evidence of glenoid/humeral bone lesions, and contralateral shoulder instability requiring surgery. Both recurrence and contralateral injury were defined based on having repeat surgery.

RESULTS

We identified 143 patients who met the inclusion criteria. Twenty-eight patients had posterior instability, whereas 115 patients had anterior instability. Patients with posterior instability had significantly more glenoid retroversion than patients with anterior instability (-15.4° ± 5.14° v -12.1° ± 6.9°; P < .016). Patients with retroversion of more than -16° showed a higher incidence of contralateral injuries (P < .036). However, no difference in postsurgical recurrent instability was noted.

CONCLUSIONS

Our data show that patients with posterior instability have a higher incidence of having a retroverted glenoid. Patients with increased retroversion showed increased posterior contralateral instability. Furthermore, patients with posterior instability and no humeral bone lesions may be more likely to incur contralateral injuries than those with humeral lesions. These data suggest that glenoid version and concomitant injury patterns may be used to help physicians counsel patients on their future risks of contralateral injury.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Reverse total shoulder arthroplasty: a biomechanical evaluation of humeral and glenosphere hardware configuration

BACKGROUND

Various reverse total shoulder arthroplasty (rTSA) implant options are available for the humeral and glenosphere components. This study used a cadaveric biomechanical shoulder simulator to evaluate how hardware configurations in 2 common rTSA systems affect (1) abduction/adduction range of motion (ROM), (2) rotational ROM, and (3) forces to elevate the arm.

METHODS

Seven pairs of shoulders were tested on a biomechanical shoulder simulator before and after rTSA implantation. The Aequalis Reverse Shoulder (Tornier, Edina, MN, USA) and the Reverse Shoulder Prosthesis (RSP; DJO Surgical, Austin, TX, USA) were implanted in opposing shoulders. Aequalis implant options included humeral polymer insert thickness and eccentricity and glenosphere tilt. RSP implant options included glenosphere diameter and lateralization, humeral shell offset, and polymer insert depth.

RESULTS

Both the RSP and Aequalis shifted the center of rotation inferior and medially compared with native shoulders (P < .001). Increased Aequalis insert thickness reduced adduction (P < .003) and internal/external (P < .028) passive ROM. The 10° inferiorly tilted glenosphere increased deltoid abduction forces (P < .032). In the RSP, smaller glenosphere diameter (P < .012), a semiconstrained humeral insert (P < .023), and a neutral humeral shell offset (P < .002) all decreased adduction deficit, whereas lateral glenosphere offset increased passive abduction ROM (P < .028). Increased humeral shell offset decreased passive internal/external rotation ROM (P < .050).

DISCUSSION

Hardware configurations in rTSA have different effects on passive ROM and deltoid forces required for abduction. Identifying these changes may guide surgical decision making during rTSA placement.

Three-dimensional planning and use of patient-specific guides improve glenoid component position: an in vitro study

BACKGROUND

Glenoid component positioning is a key factor for success in total shoulder arthroplasty. Three-dimensional (3D) measurements of glenoid retroversion, inclination, and humeral head subluxation are helpful tools for preoperative planning. The purpose of this study was to assess the reliability and precision of a novel surgical method for placing the glenoid component with use of patient-specific templates created by preoperative surgical planning and 3D modeling.

METHODS

A preoperative computed tomography examination of cadaveric scapulae (N = 18) was performed. The glenoid implants were virtually placed, and patient-specific guides were created to direct the guide pin into the desired orientation and position in the glenoid. The 3D orientation and position of the guide pin were evaluated by performing a postoperative computed tomography scan for each scapula. The differences between the preoperative planning and the achieved result were analyzed.

RESULTS

The mean error in 3D orientation of the guide pin was 2.39°, the mean entry point position error was 1.05 mm, and the mean inclination angle error was 1.42°. The average error in the version angle was 1.64°. There were no technical difficulties or complications related to use of patient-specific guides for guide pin placement. Quantitative analysis of guide pin positioning demonstrated a good correlation between preoperative planning and the achieved position of the guide pin.

CONCLUSION

This study demonstrates the reliability and precision of preoperative planning software and patient-specific guides for glenoid component placement in total shoulder arthroplasty.

Morphologic features of humeral head and glenoid version in the normal glenohumeral joint

BACKGROUND

The morphologic features and clinical significance of version of the humeral head and glenoid remain unclear. The purpose of this study was to evaluate the normal values of humeral head version and glenoid version on computed tomography scans and to clarify their features in the normal glenohumeral joint.

METHODS

Images for analysis were computed tomography scans of 410 normal shoulders from healthy volunteers. Values of humeral head and glenoid version were measured. In glenoid version measurement, 3-dimensionally corrected slices were reconstructed to eliminate scapular inclination. Differences in humeral head version and glenoid version were assessed between dominant and nondominant shoulders and between men and women. Correlation analyses were also performed in the values of version between dominant and nondominant shoulders and between humeral head version and glenoid version.

RESULTS

The values of humeral head retroversion were widely distributed from -2° to 60°, with an average of 26° ± 11°. Average glenoid retroversion was 1° ± 3°, ranging from -9° to 13°. Both humeral head retroversion and glenoid retroversion were significantly higher on the dominant side than on the nondominant side and significantly higher in men than in women. Humeral head version and glenoid version values were well correlated with those of the contralateral shoulder. No correlation was found between humeral head version and glenoid version.

CONCLUSIONS

This study found differences in humeral head version and glenoid version by sex and shoulder dominance in a large sample. Both the humeral head and glenoid are thought to be more retroverted in high-demand shoulders.

Coupling between 3D displacements and rotations at the glenohumeral joint during dynamic tasks in healthy participants

BACKGROUND

Glenohumeral displacements assessment would help to design shoulder prostheses with physiological arthrokinematics and to establish more biofidelic musculoskeletal models. Though displacements were documented during static tasks, there is little information on their 3D coupling with glenohumeral angle during dynamic tasks. Our objective was to characterize the 3D glenohumeral displacement-rotation couplings during dynamic arm elevations and rotations.

METHODS

Glenohumeral displacements were measured from trajectories of reflective markers fitted on intracortical pins inserted into the scapula and humerus. Bone geometry was recorded using CT-scan. Only four participants were recruited to the experiment due to its invasiveness. Participants performed dynamic arm abduction, flexion and axial rotations. Linear regressions were performed between glenohumeral displacements and rotations. The pin of the scapula of one participant moved, his data were removed from analysis, and results are based on three participants.

FINDINGS

The measurement error of glenohumeral kinematics was less than 0.15mm and 0.2°. Maximum glenohumeral displacements were measured along the longitudinal direction and reached up to +12.4mm for one participant. Significant couplings were reported especially between longitudinal displacement and rotation in abduction (adjusted R(2) up to 0.94).

INTERPRETATION

The proposed method provides the potential to investigate glenohumeral kinematics during all kinds of movements. A linear increase of upward displacement during dynamic arm elevation was measured, which contrasts with results based on a series of static poses. The systematic investigation of glenohumeral displacements under dynamic condition may help to provide relevant recommendation for the design of shoulder prosthetic components and musculoskeletal models.

Avoiding superior tilt in reverse shoulder arthroplasty: a review of the literature and technical recommendations

Superior tilt of the baseplate component in reverse total shoulder arthroplasty leads to tensile baseplate forces and may be a contributor to early loosening. The risk factors for this implant malposition include inadequate exposure through a superior approach and superior glenoid bone deficiency that obscures the native glenoid tilt. Here we review our preoperative evaluation and surgical management strategies to avoid superior tilt. Adequate exposure with a superior approach can be achieved but requires not just proper surgical technique but also careful patient selection. We propose that the superior approach be considered only for acute proximal humerus fractures or in patients when the following criteria are met: no prior open surgery on the shoulder; more than 30° of passive external rotation at 0° of abduction; no medial humeral osteophytes; and any superior migration must be reducible with a sulcus test during examination under anesthesia. Avoiding superior tilt when there is significant superior glenoid erosion can be accomplished with humeral head autograft, most easily performed through a deltopectoral approach. Preoperative templating is critical to determine proper graft thickness, inclination, reaming depth, and harvest technique.

A glenoid reaming study: how accurate are current reaming techniques?

BACKGROUND

Correct reaming of a degenerative glenoid can be a difficult procedure. We investigated how the quality of the reamed surface is influenced by different reamers, by the surgeon's experience, and by glenoid erosion patterns.

MATERIAL AND METHODS

Three shoulder surgeons performed reaming procedures with different types of reamers (flat, convex, K-wire guided, and nipple guided) on a series of similarly sized uniconcave and biconcave glenoids. The reproducibility of reaming and the effect of different reamers on different-shaped glenoids were measured and evaluated.

RESULTS

The center and direction of reaming were constant for all surgeons in the case of type A glenoids. For type B2 glenoids, the center and direction of reaming differed significantly between surgeons. The congruity of the reamed surface was better after flat reaming than after convex reaming. Whether the reamers were guided by a central K-wire or by a nipple had no significant effect on the reamed surface. The experience of the surgeon had no effect on the congruity of reaming.

CONCLUSIONS

Reaming of a uniconcave glenoid is reproducible, but reaming of a biconcave glenoid seems much more difficult. Erosion and deformity of the glenoid influence the accuracy of reaming the most. Surgical experience plays a less important role. We conclude that there is a need for guidance in reaming of biconcave glenoids.

Measurements of three-dimensional glenoid erosion when planning the prosthetic replacement of osteoarthritic shoulders

The three-dimensional (3D) correction of glenoid erosion is critical to the long-term success of total shoulder replacement (TSR). In order to characterise the 3D morphology of eroded glenoid surfaces, we looked for a set of morphological parameters useful for TSR planning. We defined a scapular coordinates system based on non-eroded bony landmarks. The maximum glenoid version was measured and specified in 3D by its orientation angle. Medialisation was considered relative to the spino-glenoid notch. We analysed regular CT scans of 19 normal (N) and 86 osteoarthritic (OA) scapulae. When the maximum version of OA shoulders was higher than 10°, the orientation was not only posterior, but extended in postero-superior (35%), postero-inferior (6%) and anterior sectors (4%). The medialisation of the glenoid was higher in OA than normal shoulders. The orientation angle of maximum version appeared as a critical parameter to specify the glenoid shape in 3D. It will be very useful in planning the best position for the glenoid in TSR.

Biomechanical comparison of reverse total shoulder arthroplasty systems in soft tissue-constrained shoulders

BACKGROUND

Numerous studies have examined the biomechanics of isolated variables in reverse total shoulder arthroplasty. This study directly compared the composite performance of two reverse total shoulder arthroplasty systems; each system was designed around either a medialized or a lateralized glenohumeral center of rotation.

METHODS

Seven pairs of shoulders were tested on a biomechanical simulator. Center of rotation, position of the humerus, passive and active range of motion, and force to abduct the arm were quantified. Native arms were tested, implanted with a Tornier Aequalis or DJO Surgical Reverse Shoulder Prosthesis (RSP), and then retested. Differences from the native state were then documented.

RESULTS

Both systems shifted the center of rotation medially and inferiorly relative to native. Medial shifts were greater in the Aequalis implant (P < .037). All humeri shifted inferior compared with native but moved medially with the Aequalis (P < .001). Peak passive abduction, internal rotation, and external rotation did not differ between systems (P > .05). Both reverse total shoulder arthroplasty systems exhibited adduction deficits, but the RSP implant deficit was smaller (P = .046 between implants). Both systems reduced forces to abduct the arm compared with native, although the Aequalis required more force to initiate motion from the resting position (P = .022).

CONCLUSION

Given the differences in system designs and configurations, outcome variables were generally comparable. The RSP implant allowed slightly more adduction, had a more lateralized humeral position, and required less force to initiate elevation. These factors may play roles in limiting scapular notching, improving active external rotation by normalizing the residual rotator cuff length, and limiting excessive stress on the deltoid.

Determination of a reference system for the three-dimensional study of the glenohumeral relationship

OBJECTIVE

Knowledge of the normal and pathological three-dimensional glenohumeral relationship is imperative when planning and performing a total shoulder arthroplasty. There is, however, no consensus on which references should be used when studying this relationship. The purpose of the present study was to define the most suitable glenoid plane with normally distributed parameters, narrowest variability, and best reproducibility.

MATERIALS AND METHODS

Three-dimensional reconstruction CT scans were performed on 152 healthy shoulders. Four glenoid planes, each determined by three surgically accessible bony reference points, were determined. Two planes were triangular, with the same base defined by the most anterior and posterior point of the glenoid. The most inferior and the most superior point of the glenoid, respectively, define the top of Saller's inferior plane and the Saller's superior plane. The two other planes are formed by best-fitting circles. The circular max plane is defined by the superior tubercle, and two points at the distal third of the glenoid. The circular inferior plane is defined by three points at the rim of the inferior quadrants of the glenoid.

RESULTS

The parameters of all four planes behave normally. The humeral center of rotation is identically positioned for both the circular max and circular inferior plane (X = 91.71°/X = 91.66° p = 0.907 and Y = 90.83°/Y = 91.7° p = 0.054, respectively) and different for the Saller's inferior and Saller's superior plane (p ≤ 0.001). The circular inferior plane has the lowest variability to the coronal scapular plane (p < 0.001).

CONCLUSIONS

This study provides arguments to use the circular inferior glenoid plane as preferred reference plane of the glenoid.

Operative guidelines for the reconstruction of the native glenoid plane: an anatomic three-dimensional computed tomography-scan reconstruction study

BACKGROUND

Reconstruction of the native plane in biconcave eroded glenoids is difficult. Nevertheless, accurate reconstruction of this plane is imperative for successful total shoulder arthroplasty. This study aims to determine guidelines that can increase the accuracy of glenoid component positioning.

METHODS

Three different circular planes were determined on 3-dimensional computed tomography (CT) scans of 152 healthy shoulders. First, the circular max (CM) plane is formed with the superior tubercle and 2 points, 1 anterior and 1 posterior, at the rim of the inferior third of the glenoid. Second, the circular inferior (CI) plane is formed by 3 points at the inferior 2 quadrants of the glenoid rim. Third, the circular minima (Cm) plane is formed with 3 points situated at the noneroded sector of the anterior glenoid. The angulation of the spinal scapular axis (SSA), the line between the most medial point of the scapular spine and the center of the three different glenoid planes, and the correlation coefficient between the radius of the circle and the length of SSA are calculated.

RESULTS

Angle SSA in the x-axis were 94°, 93°, 93° and in the y-axis were 95°, 111°, and 111° for CM, CI, and Cm, respectively. Correlation coefficient between the radius of the circle and the length of SSA: r = 0.69 for CM, r = 0.75 for CI, and r = 0.75 for Cm.

CONCLUSION

Three points situated at the native anterior glenoid can reconstruct, within 2° accuracy (95% confidence interval, 1.8°-2.3°), the CI plane. A relationship exists between the radii of the 3 glenoid circles and the width of the scapula (SSA length).

Effect of glenoid implant design on glenohumeral stability: an experimental study

BACKGROUND

Though several glenoid implants were developed over the past years, a high rate of glenoid loosening remains. This complication is linked to the glenohumeral stability, defined as humeral head translation. In an intact shoulder, this concept is ensured by all active and passive elements, particularly the labrum. Two features of a glenoid implant can be adjusted to improve the stability, or, in other words, to decrease the translations: the first is the mismatch, defined as the difference of curvature between the prosthetic head and glenoid; the second is the shape of the glenoid component. Therefore, the objective of this study was to compare the performance of 2 glenoid components (Ceraver, Roissy, France): (1) a standard design and (2) a design named "labrum design" with a superior part simulating the anatomic labrum.

METHODS

An experimental device was developed to evaluate forces and kinematics. The device simulated active, dynamic and continuous abduction of an entire arm. It reproduced the Scapulo-Humeral Rhythm. The labrum design was installed first. To evaluate the effect of mismatch on the glenohumeral stability, 3 humeral heads were tested, corresponding to the ones recommended by the company. The experiment was repeated for the standard design.

FINDINGS

The results obtained show a general decrease of the prosthetic head translation with the labrum design compared to the standard design. No noticeable effect of mismatch was found.

INTERPRETATION

A proof of concept of the interest of the artificial labrum was provided since it improved the glenohumeral stability.

Three-dimensional measurement method of arthritic glenoid cavity morphology: feasibility and reproducibility

INTRODUCTION

Glenoid component loosening is the main complication of total shoulder arthroplasty. Better knowledge of the arthritic glenoid cavity anatomy can help in developing new implants and techniques. The goal of this study was to describe and validate the reproducibility of a CT scan-based, 3D measurement method used to describe various parameters characterizing arthritic glenoid cavity morphology.

MATERIALS AND METHODS

Twelve CT scans and 29 CT arthrogram were evaluated. These scans were taken from 41 patients with glenohumeral osteoarthritis who received an anatomical shoulder prosthesis. A 3D reconstruction of the scapula was performed based on the DICOM files. Following the 3D volume acquisition, points on the glenoid articular surface were manually extracted by three observers, each one three times, allowing one week between readings, to determine the inter- and intra-observer reproducibility. The intraclass correlation coefficient (ICC) was calculated on five 3D parameters that were automatically calculated: glenoïd height, glenoid width, height at maximum width glenoid version and radius of the articular surface best-fit sphere.

RESULTS

The intra-observer and inter-observer ICC were 0.91 to 0.99, and 0.95 to 0.99, respectively.

DISCUSSION

This study is the first to report on a reproducible 3D measurement method, based on CT scans, for the arthritic glenoid cavity, which derives the joint radius of curvature among other morphology parameters. These 3D measurements are advantageous because they are free of problems related to patient positioning in the CT scanner and to the choice of slices, which limits the accuracy of measurements made on slices from 2D CT scans. Three-dimensional methodology similar to ours has been validated on healthy glenoids.

CONCLUSION

This study confirms the reliability and good reproducibility of our method, which allows us to extend this method to a larger patient cohort and adapt this automated technology to preoperative planning software.

Effect of lateral offset center of rotation in reverse total shoulder arthroplasty: a biomechanical study

BACKGROUND

Lateral offset center of rotation (COR) reduces the incidence of scapular notching and potentially increases external rotation range of motion (ROM) after reverse total shoulder arthroplasty (rTSA). The purpose of this study was to determine the biomechanical effects of changing COR on abduction and external rotation ROM, deltoid abduction force, and joint stability.

MATERIALS AND METHODS

A biomechanical shoulder simulator tested cadaveric shoulders before and after rTSA. Spacers shifted the COR laterally from baseline rTSA by 5, 10, and 15 mm. Outcome measures of resting abduction and external rotation ROM, and abduction and dislocation (lateral and anterior) forces were recorded.

RESULTS

Resting abduction increased 20° vs native shoulders and was unaffected by COR lateralization. External rotation decreased after rTSA and was unaffected by COR lateralization. The deltoid force required for abduction significantly decreased 25% from native to baseline rTSA. COR lateralization progressively eliminated this mechanical advantage. Lateral dislocation required significantly less force than anterior dislocation after rTSA, and both dislocation forces increased with lateralization of the COR.

CONCLUSION

COR lateralization had no influence on ROM (adduction or external rotation) but significantly increased abduction and dislocation forces. This suggests the lower incidence of scapular notching may not be related to the amount of adduction deficit after lateral offset rTSA but may arise from limited impingement of the humeral component on the lateral scapula due to a change in joint geometry. Lateralization provides the benefit of increased joint stability, but at the cost of increasing deltoid abduction forces.

Effect of deltoid tension and humeral version in reverse total shoulder arthroplasty: a biomechanical study

BACKGROUND

No clear recommendations exist regarding optimal humeral component version and deltoid tension in reverse total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

A biomechanical shoulder simulator tested humeral versions (0°, 10°, 20° retroversion) and implant thicknesses (-3, 0, +3 mm from baseline) after reverse TSA in human cadavers. Abduction and external rotation ranges of motion as well as abduction and dislocation forces were quantified for native arms and arms implanted with 9 combinations of humeral version and implant thickness.

RESULTS

Resting abduction angles increased significantly (up to 30°) after reverse TSA compared with native shoulders. With constant posterior cuff loads, native arms externally rotated 20°, whereas no external rotation occurred in implanted arms (20° net internal rotation). Humeral version did not affect rotational range of motion but did alter resting abduction. Abduction forces decreased 30% vs native shoulders but did not change when version or implant thickness was altered. Humeral center of rotation was shifted 17 mm medially and 12 mm inferiorly after implantation. The force required for lateral dislocation was 60% less than anterior and was not affected by implant thickness or version.

CONCLUSION

Reverse TSA reduced abduction forces compared with native shoulders and resulted in limited external rotation and abduction ranges of motion. Because abduction force was reduced for all implants, the choice of humeral version and implant thickness should focus on range of motion. Lateral dislocation forces were less than anterior forces; thus, levering and inferior/posterior impingement may be a more probable basis for dislocation (laterally) than anteriorly directed forces.