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Background: A transverse force couple (TFC) functional imbalance has been demonstrated in osteoarthritic shoulders by recent 3-dimensional (3D) muscle volumetric studies. Altered rotator cuff vectors may be an additional factor contributing to a muscle imbalance and the propagation of glenoid deformity., Methods: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (ISP-Tm) and scapula were manually segmented. The volume masks and scapular landmarks were imported into MATLAB to create a coordinate system, enabling calculation of muscle force vectors. The direction of each muscle force vector was described in the transverse and vertical plane, calculated with respect to the glenoid. Each muscle vector was then resolved into compression and shear force across the glenoid face. The relationship between muscle force vectors, glenoid retroversion or inclination, compression/shear forces on the glenoid, and Walch type was determined using linear regression., Results: In the transverse plane with all rotator cuff muscles combined, increasing retroversion was significantly associated with increasing posterior drag (P < .001). Type B glenoids had significantly more posterior drag than type A (P < .001). In the vertical plane for each individual muscle group and in combination, superior drag increases as superior inclination increases (P < .001). Analysis of individual muscle groups showed that the anterior thrust of ISP-Tm and supraspinatus switched to a posterior drag at 8° and 10° of retroversion respectively. The compression force on the glenoid face by ISP-Tm and supraspinatus did not change with increasing retroversion for type A shoulders (P = .592 and P = .715, respectively), but they did for type B shoulders (P < .001 for both). The glenoid shear force ratio in the transverse plane for the ISP-Tm and supraspinatus moved from anterior to posterior shear with increasing glenoid retroversion, crossing zero at 8° and 10° of retroversion, whereas the subscapularis exerted a posterior shear force for every retroversion angle., Conclusion: Increased glenoid retroversion is associated with increased posterior shear and decreased compression forces on the glenoid face, explaining some of the pathognomonic bone morphometrics that characterize the osteoarthritic shoulder. Although the subscapularis always maintains a posterior thrust, the ISP-Tm and supraspinatus together showed an inflection at 8° and 10° of retroversion, changing from an anterior thrust to a posterior drag. This finding highlights the importance that in anatomic TSA the rotator cuff functional balance might be better restored by correcting glenoid retroversion to less than 8°., (Copyright © 2022 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: The etiology of the Walch type B shoulder remains unclear. We hypothesized that a scapulohumeral muscle imbalance, due to a disturbed transverse force couple (TFC) between the anterior and posterior rotator cuff muscles, may have a role in the pathogenesis of the type B morphology. The purpose of this study was to determine whether there is a TFC imbalance in the Walch type B shoulder using an imaging-based 3-dimensional (3D) volumetric and fatty infiltration assessment of segmented rotator cuff muscles., Methods: Computed tomography images of 33 Walch type A and 60 Walch type B shoulders with the complete scapula and humerus including the distal humeral epicondyles were evaluated. The 3D volumes of the entire subscapularis, supraspinatus, and infraspinatus-teres minor (Infra-Tm) were manually segmented and analyzed. Additionally, anthropometric parameters including glenoid version, glenoid inclination, posterior humeral head subluxation, and humeral torsion were measured. The 3D muscle analysis was then compared with the anthropometric parameters using the Wilcoxon rank sum and Kruskal-Wallis tests., Results: There were no significant differences (P > .200) in muscle volume ratios between the Infra-Tm and the subscapularis in Walch type A (0.93) and type B (0.96) shoulders. The fatty infiltration percentage ratio, however, was significantly greater in type B shoulders (0.94 vs. 0.75, P < .001). The Infra-Tm to subscapularis fatty infiltration percentage ratio was significantly larger in patients with >75% humeral head subluxation than in those with 60%-75% head subluxation (0.97 vs. 0.74, P < .001) and significantly larger in patients with >25° of retroversion than in those with <15° of retroversion (1.10 vs. 0.75, P = .004). The supraspinatus fatty infiltration percentage was significantly lower in Walch type B shoulders than type A shoulders (P = .004). Walch type A shoulders had mean humeral retrotorsion of 22° ± 10° whereas Walch type B shoulders had humeral retrotorsion of only 14° ± 9° relative to the epicondylar axis (P < .001)., Conclusion: The TFC is in balance in the Walch type B shoulder in terms of 3D volumetric rotator cuff muscle analysis; however, the posterior rotator cuff does demonstrate increased fatty infiltration. Posterior humeral head subluxation and glenoid retroversion, which are pathognomonic of the Walch type B shoulder, may lead to a disturbance in the length-tension relationship of the posterior rotator cuff, causing fatty infiltration., (Copyright © 2021 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Continuum-level finite element models (FEMs) of the humerus offer the ability to evaluate joint replacement designs preclinically; however, experimental validation of these models is critical to ensure accuracy. The objective of the current study was to quantify experimental full-field strain magnitudes within osteoarthritic (OA) humeral heads by combining mechanical loading with volumetric microCT imaging and digital volume correlation (DVC). The experimental data was used to evaluate the accuracy of corresponding FEMs. Six OA humeral head osteotomies were harvested from patients being treated with total shoulder arthroplasty and mechanical testing was performed within a microCT scanner. MicroCT images (33.5 µm isotropic voxels) were obtained in a pre- and post-loaded state and BoneDVC was used to quantify full-field experimental strains (≈ 1 mm nodal spacing, accuracy = 351 µstrain, precision = 518 µstrain). Continuum-level FEMs with two types of boundary conditions (BCs) were simulated: DVC-driven and force-driven. Accuracy of the FEMs was found to be sensitive to the BC simulated with better agreement found with the use of DVC-driven BCs (slope = 0.83, r 2 = 0.80) compared to force-driven BCs (slope = 0.22, r 2 = 0.12). This study quantified mechanical strain distributions within OA trabecular bone and demonstrated the importance of BCs to ensure the accuracy of predictions generated by corresponding FEMs.

Glenoid component stability is essential to ensure successful long-term survivability following total shoulder arthroplasty. As such, this computational study assessed the stability of five all-polyethylene glenoid components (Keel, Central-Finned 4-Peg, Peripheral 4-Peg, Cross-Keel, and Inverted-Y), using simulated joint loading in an osteoarthritic patient cohort. Stability was assessed on the basis of component micromotion in the tangential and normal directions. Maximum tangential micromotion occurred in the Cross-Keel (146 ± 46 µm), which was significantly greater (p < .001) than the other components. Maximum normal micromotion occurred in the Inverted-Y (109 ± 43 µm), which was significantly greater (p ≤ .002) than the other four components. In general, the Central-Finned 4-Peg exhibited the least normal and tangential micromotion, while the keeled components shown the highest normal and tangential micromotion. This study suggests that modifications to keeled designs do not improve component stability under the conditions tested, and pegged components show superior computational stability.

Purpose: Glenoid reaming is a technically challenging step during shoulder arthroplasty that could possibly be learned during simulation training. Creation of a realistic simulation using vibration feedback in this context is innovative. Our study focused on the development and internal validation of a novel glenoid reaming simulator for potential use as a training tool., Methods: Vibration and force profiles associated with glenoid reaming were quantified during a cadaveric experiment. Subsequently, a simulator was fabricated utilizing a haptic vibration transducer with high- and low-fidelity amplifiers; system calibration was performed matching vibration peak-peak values for both amplifiers. Eight experts performed simulated reaming trials. The experts were asked to identify isolated layer profiles produced by the simulator. Additionally, experts' efficiency to successfully perform a simulated glenoid ream based solely on vibration feedback was recorded., Results: Cadaveric experimental cartilage reaming produced lower vibrations compared to subchondral and cancellous bones ([Formula: see text]). Gain calibration of a lower-fidelity (3.5 [Formula: see text] and higher-fidelity (3.4 [Formula: see text] amplifier resulted in values similar to the cadaveric experimental benchmark (3.5 [Formula: see text]. When identifying random tissue layer samples, experts were correct [Formula: see text] of the time and success rate varied with tissue type ([Formula: see text]). During simulated reaming, the experts stopped at the targeted subchondral bone with a success rate of [Formula: see text]. The fidelity of the simulation did not have an effect on accuracy, applied force, or reaming time ([Formula: see text]). However, the applied force tended to increase with trial number ([Formula: see text])., Conclusions: Development of the glenoid reaming simulator, coupled with expert evaluation furthered our understanding of the role of haptic vibration feedback during glenoid reaming. This study was the first to (1) propose, develop and examine simulated glenoid reaming, and (2) explore the use of haptic vibration feedback in the realm of shoulder arthroplasty.

Background: The type B3 glenoid is an addition to the Walch classification. A potential etiologic theory is that it is a progression of the B2. It is characterized by uniconcavity, absent paleoglenoid, medialization, retroversion, and subluxation. The purpose of this study was to describe the morphology of B3 glenoids., Methods: Fifty-two patients with B3 glenoids underwent 3-dimensional analysis of computed tomography data. Glenoid measurements (retroversion, inclination, medialization) and humeral head subluxation according to the scapular and glenoid planes were determined. The measured variables were compared between male and female patients., Results: The mean B3 retroversion, inclination, and medialization were 24° ± 7°, 8° ± 6° superior, and 14 ± 4 mm, respectively. The mean posterior subluxation was 80% ± 8% and 54% ± 6% according to the scapular and glenoid planes, respectively. There were no differences in B3 characteristics between sexes (P > .05). A significant correlation existed between glenoid retroversion and humeral head subluxation relative to the scapular plane, with every 1° increase in retroversion translating to a 1% increase in subluxation (P < .001). In contrast, when referencing the glenoid plane, the humeral head remained concentric to the erosion., Conclusions: The B3 is uniconcave and retroverted. As glenoid retroversion increases, posterior humeral head subluxation significantly increases as referenced to the scapular plane; however, when referenced to the glenoid plane, the head remains concentric to the erosion. This appearance of "concentricity" is acquired secondary to the wear pattern, creating a uniconcave glenoid. Therefore, surgeons should be aware that the visualized concentricity is a product of the erosion pattern and thus may conceal a greater amount of subluxation potential., (Copyright © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: Posterior glenoid erosion is thought to be initiated by humeral head subluxation. However, it is unknown whether subluxation is entirely caused by soft-tissue instability and unbalanced muscle activity or whether osseous morphology is a contributing factor. We hypothesized that patients with posterior erosion may exhibit premorbid glenoid morphology that is inherently retroverted and inferiorly inclined compared with age-matched normal glenoids., Methods: This study examined 80 scapulae, evenly distributed between 2 groups: osteoarthritic with type B2 glenoids and age-matched normal glenoids. From 3-dimensional computed tomography reconstructions, version and inclination were measured from the anterior paleoglenoid region of the B2 glenoids, which is representative of the premorbid glenoid, and compared with measurements obtained from similar regions in the normal cohort., Results: The anterior paleoglenoid region of B2 glenoids was significantly (P < .001) more retroverted (-14° ± 6°) compared with similar regions in nonarthritic normal glenoids (-5° ± 5°). There were no significant differences (P = .166) in the glenoid inclination angle between type B2 glenoids (0° ± 6°) and nonarthritic normal glenoids (2° ± 5°). Negative values represent retroverted and inferiorly inclined glenoids., Discussion: Understanding premorbid glenoid morphologic variations may provide insight into the pathoanatomy of humeral head subluxation, osteoarthritis, and posterior glenoid erosion. The results of this study indicate that patients with type B2 osteoarthritic glenoids have significantly greater premorbid glenoid retroversion compared with nonarthritic normal glenoids, suggesting that this premorbid morphologic variation may be one contributing factor to posterior erosion., (Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: The purpose of this study was to evaluate and to compare the size and morphologic patterns among normal and osteoarthritic (OA) humeral heads., Methods: This comparative anatomic imaging study evaluated 150 humeral heads that were separated into 3 cohorts: normal, OA with symmetric glenoid erosion, and OA with asymmetric (type B2) glenoid erosion. Three-dimensional models were created of the humeral head from computed tomography data, and point coordinates were extracted for evaluation. Parameters measured were diameter (sphere fit and circle fit), chord distance (superoinferior and anteroposterior), and humeral head height., Results: The sphere-fit diameter of the humeral head for the entire OA cohort (100 patients; mean diameter, 59 ± 9 mm) was significantly greater (P < .001) than that of the normal cohort (50 patients; mean diameter, 49 ± 5 mm). Similarly, the humeral head circle-fit diameters in the superoinferior and anteroposterior planes were significantly greater (P < .001) in the combined OA cohorts (59 ± 9 mm and 56 ± 10 mm, respectively) compared with the normal cohort (51 ± 5 mm and 47 ± 5 mm, respectively). However, there were no significant differences (P ≥ .099) between the symmetric and asymmetric OA cohorts in sphere-fit or circle-fit diameters. The mean values of humeral head heights were not significantly different (P = .382) between cohorts, 19 ± 2 mm, 18 ± 2 mm, and 18 ± 2 mm for the normal, symmetric, and asymmetric cohorts, respectively., Discussion: Although OA humeral head morphology varies significantly from normal, it does not vary as a function of the Walch classification between symmetric and asymmetric glenoids. Understanding of the morphologic variability of the pathologic humeral head may provide insight into the pathoanatomy of osteoarthritis and the development of various erosion patterns., (Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: The purpose of this computational modeling study was to compare the volume of glenoid bone removal required to implant 3 augmented component designs for management of B2 erosions. In addition, we assessed bone quality of the supporting bone directly beneath the implants by measuring bone density and porosity., Methods: Three augmented component designs—full-wedge, posterior-wedge, and posterior-step—were studied by virtual implantation in a cohort of 16 patients with B2 glenoids. B2 retroversion was corrected to 0° and 10°. The outcome variables were the volume of glenoid bone removal required for implantation and the density and porosity of the bone immediately beneath the implant., Results: Implant design had a significant effect on the volume of bone removal (P < .001). When correcting to 0°, the posterior-wedge implant removed less bone than the posterior-step (P < .001) and the full-wedge (P = .004). At 10° retroversion, the posterior-wedge removed less bone (P = .029) than the posterior-step but was no different than the full-wedge (P = .143). The residual glenoid bone density with the posterior-wedge was significantly greater than with the posterior-step (P = .048), with no other significant differences (P > .05). Residual glenoid bone porosity was not significantly different between implants (P > .262)., Conclusions: Augmented components can provide a bone-preserving option for B2 glenoid management. Substantial variations in the volume of bone removal and the quality of the remaining glenoid bone were found between 3 different designs of augmented implants. Simulations with the posterior-wedge implant resulted in substantially less glenoid bone removal, with the remaining supporting bone being of better quality., (Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: The purpose of this computed tomography-based study was to quantify erosions in B2 glenoids. We hypothesized that erosions do not occur symmetrically and that they have a predictable orientation., Methods: This study evaluated 55 type B2 glenoid cases. Computed tomography data were used to create three-dimensional reconstructions, and point coordinates were extracted from each reconstruction for morphologic analysis of the osteoarthritic glenoid and humerus., Results: There was a significant difference between the mean orientation angle (28° ± 11°) of the posterior glenoid line of erosion and the superoinferior axis (P < .001), which resulted in the average erosion being directed toward the 8-o'clock position. On average, the erosion started 1.6 ± 3.4 mm posterior to the glenoid center point. In 35% of B2 cases, the line of erosion was curved. The mean surface area was 763 ± 296 mm(2) for the neoglenoid and 957 ± 276 mm(2) for the paleoglenoid, indicating that the neoglenoid occupied 44% ± 12% of the total glenoid area. In this cohort, the mean radius of the humeral head neoarticulation was 32 ± 6 mm, the neoglenoid radius was 37 ± 8 mm, and the paleoglenoid radius was 34 ± 7 mm. The radius of the humeral head was significantly less than that of the neoglenoid (P < .001) and the paleoglenoid (P = .009). In addition, the radius of the neoglenoid was significantly greater than the radius of the paleoglenoid (P = .012)., Discussion: Type B2 glenoids have a predictable wear pattern, which is not axisymmetric to the glenoid superoinferior axis. In addition, the identified anatomic characteristics of B2 erosions will aid surgeons in the operative management of bone loss and may assist manufacturers in the design of augmented components., (Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: Accurate characterization of regional variations in bone density in symmetric and asymmetric (B2) glenoid erosion patterns can assist with surgical planning, reaming, and component implantation. The purpose of this study was to characterize regional bone density and porosity in symmetric and asymmetric (B2) osteoarthritic glenoids., Methods: Symmetric (n = 25) and asymmetric (B2) (n = 25) erosion patterns were compared by computed tomography-based imaging software. An orthogonal coordinate system separated each glenoid into quadrants. In addition, a linear best-fit line defined the line-of-erosion between the paleoglenoid and neoglenoid in the asymmetric cohort. All glenoids were further divided into volumes at depths of 0 to 2.5 mm and 2.5 to 5 mm. Average bone density was measured in Hounsfield units. Bone voids or cysts were included to quantify regional porosity as the fraction of void volume to total glenoid volume., Results: For the symmetric cohort, there were no significant differences in bone density between quadrants at either depth (P ≥ .089). For the asymmetric cohort, bone density was significantly higher in the posterior quadrants compared with the anterior quadrants (P < .001), especially posteroinferiorly (P ≤ .007) at both depths. In addition, the neoglenoid had significantly higher density and lower void fraction compared with the paleoglenoid (P < .001). There were also significant differences in void fraction between quadrants for both cohorts, at both depths (P ≤ .004)., Conclusions: This study demonstrates that osteoarthritic glenoids with symmetric erosion have uniform subarticular bone density. However, asymmetric (B2) erosion patterns have potentially important regional variations in bone density and porosity, with the densest bone with the least porosity found posteroinferiorly or in the neoglenoid region., (Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Introduction: Glenohumeral instability with glenoid bone loss is commonly treated with the Latarjet procedure. The procedure involves transfer of the coracoid and conjoint tendon, which is thought to provide a stabilizing sling effect; however, its significance is unknown. This study evaluated the effects of the Latarjet procedure, with and without conjoint tendon loading, on shoulder stability and range of motion (ROM)., Materials and Methods: A custom simulator was used to evaluate anterior shoulder stability and ROM in 8 cadaveric shoulders. Testing conditions included intact, 30% glenoid defect, and Latarjet with and without conjoint loading. Unloaded and 10-N loaded states were tested in adduction and 90° abduction. Outcome variables included dislocation, stiffness (neutral and 60° external rotation), and internal-external rotational ROM., Results: All 30% defects dislocated in abduction external rotation. The loaded Latarjet prevented dislocation in all specimens, whereas the unloaded Latarjet stabilized 6 of 8 specimens. In abduction external rotation, there were no significant differences in stiffness between loaded and unloaded transfers (P = .176). In adduction, there were no significant differences between the intact and the loaded Latarjet (P ≥ .228); however, in neutral rotation, the unloaded Latarjet (P = .015) and the 30% defects (P = .011) were significantly less stiff. Rotational ROM in abduction was significantly reduced with the loaded Latarjet (P = .014) compared with unloaded Latarjet, and no differences were found in adduction., Conclusions: These findings indicate that glenohumeral stability is improved, but not fully restored to intact, with conjoint tendon loading. The results support the existence of the sling effect and its importance in augmenting stability provided by the transferred coracoid., (Copyright © 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.)

Background: The remplissage procedure may be performed as an adjunct to Bankart repair to treat recurrent glenohumeral dislocation associated with an engaging Hill-Sachs humeral head defect. The purpose of this in vitro biomechanical study was to examine the effects of the remplissage procedure on glenohumeral joint motion and stability., Methods: Cadaveric shoulders (n = 8) were mounted on a biomechanical testing apparatus that applies simulated loads to the rotator cuff and the anterior, middle, and posterior heads of the deltoid muscle. Testing was performed with the shoulder intact, after creation of the Bankart lesion, and after repair of the Bankart lesion. In addition, testing was performed after Bankart repair with and without remplissage in shoulders with 15% and 30% Hill-Sachs defects. Shoulder motion and glenohumeral translation were recorded with an optical tracking system. Outcomes measured included stability (joint stiffness and defect engagement) and internal-external glenohumeral rotational motion in adduction and in 90° of composite shoulder abduction., Results: In specimens with a 15% Hill-Sachs defect, Bankart repair combined with remplissage resulted in a significant reduction in internal-external range of motion in adduction (15.1° ± 11.1°, p = 0.039), but not in abduction (7.7° ± 9.9, p = 0.38), compared with the intact condition. In specimens with a 30% Hill-Sachs defect, repair that included remplissage also significantly reduced internal-external range of motion in adduction (14.5° ± 11.3°, p = 0.049) but not in abduction (6.2° ± 9.3°, p = 0.60). In specimens with a 15% Hill-Sachs defect, addition of remplissage significantly increased joint stiffness compared with isolated Bankart repair (p = 0.038), with the stiffness trending toward surpassing the level in the intact condition (p = 0.060). In specimens with a 30% Hill-Sachs defect, addition of remplissage restored joint stiffness to approximately normal (p = 0.41 compared with the intact condition). All of the specimens with a 30% Hill-Sachs defect engaged and dislocated after Bankart repair alone. The addition of remplissage was effective in preventing engagement and dislocation in all specimens. None of the specimens with a 15% Hill-Sachs defect engaged or dislocated after Bankart repair., Conclusions: In this experimental model, addition of remplissage provided little additional benefit to a Bankart repair in specimens with a 15% Hill-Sachs defect, and it also reduced specific shoulder motions. However, Bankart repair alone was ineffective in preventing engagement and recurrent dislocation in specimens with a 30% Hill-Sachs defect. The addition of remplissage to the Bankart repair in these specimens prevented engagement and enhanced stability, although at the expense of some reduction in shoulder motion.

The kinematics and stability of the shoulder during in-vitro simulation are affected by the muscles chosen for simulation and their loads. Existing simulators have commonly actuated the rotator cuff and deltoids; however, the contribution of secondary muscles, such as those which form the conjoined tendon, are not well understood. The conjoined tendon consists of the origins of the short head of the biceps and coracobrachialis (SH&C), and is thought to produce an anterior stabilizing effect. This study investigated the effect of SH&C tension at four loading levels: 0, 5, 10, 15N. Our primary outcome variable was glenohumeral stiffness for anterior loading but internal/external rotation and extension ranges of motion were also measured. Four joint configurations were tested: adduction and 90° combined abduction, each in neutral and maximal external rotation. Increasing SH&C load resulted in a significant trend of increased glenohumeral stiffness across the average of all joint configurations (p=0.008). In abduction, neutral rotation differences were found between the stiffness at 10 and 15N compared to 0N (p=0.038 and 0.043, respectively); however, no differences were found for the three other joint configurations. There was a tendency for a decrease in the range of shoulder extension with increasing SH&C load, but this did not achieve significance (p=0.065). These findings demonstrate that the SH&C provides a stabilizing barrier effect, but only in configurations when it wraps directly anterior to the humeral head. Thus SH&C loading is likely critical to in-vitro simulation due to its effect on joint stability and kinematics., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Glenoid replacement is challenging due to the difficult joint exposure and visualization of anatomical reference landmarks. Improper positioning of the glenoid component or inadequate correction of the retroversion using currently available instrumentation may lead to early failure. The objective of this study was to evaluate a computer-assisted technique to achieve a more accurate placement of the glenoid component compared to traditional techniques., Methods: Sixteen paired cadaveric shoulders were randomized to either traditional or computer-assisted glenoid implantation. Preoperative planning consisting of CT scanning with 3-dimensional image modeling of the shoulder specimens and intraoperative tracking with real-time feedback provided to the surgeon was employed in the computer-assisted group. A validated, previously published, standardized protocol for tracking the orientation of the glenoid in space using 3 glenoid surface landmarks was employed. All phases of glenoid implantation (initial guide pin insertion, reaming, drilling of the peg holes, and final component implantation) were tracked and recorded by the computer. A post-implantation CT scan was performed in both groups to compare how accurately the implants were placed., Results: The computer-assisted technique was more accurate in achieving the correct version during all phases of glenoid implantation and as measured on the post-implantation CT scan (P < .05). The largest errors with traditional glenoid implantation were observed during drilling and, more so, during reaming. The trend was to overly retrovert the glenoid., Conclusions: Computer assisted navigation results in a more accurate glenoid component placement relative to traditional techniques., Level of Evidence: Basic Science Study.

This study was conducted to determine the effect of in vitro passive and active loading on humeral head translation during glenohumeral abduction. A shoulder simulator produced unconstrained active abduction of the humerus in 8 specimens. Loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and anterior, middle, and posterior deltoid muscles was simulated by use of 4 different sets of loading ratios. Significantly greater translations of the humeral head occurred both in 3 dimensions (P < .001) and in the sagittal plane (P < .005) during passive motion when compared with active motion from 30 degrees to 70 degrees of abduction. In the sagittal plane, passive abduction experienced a resultant translation of 3.8 +/- 1.0 mm whereas the active loading ratios averaged 2.3 +/- 1.0 mm. There were no significant differences in the translations that were produced by the 4 sets of muscle-loading ratios used to achieve active motions. This study emphasizes the importance of the musculature in maintaining normal ball-and-socket kinematics of the shoulder.

Objective: Replacement of the diseased shoulder joint with implants is a procedure whose frequency is rapidly increasing. However, glenoid replacement remains challenging due to the difficult joint exposure and visualization of anatomical reference landmarks during the procedure. Improper positioning of the glenoid component can lead to early failure. The objective of this study was to develop and evaluate a Computer Assisted Glenoid Implantation (CAGI) technique to achieve a more accurate and reliable placement of the glenoid component., Materials and Methods: Twenty cadaveric scapulae were imaged with CT. The accuracy of an electromagnetic tracking system and 3D surface modeling for the measurement of glenoid position was compared to that of the standard CT-based method. Custom jigs were then developed to track instruments and to correct for scapular motion during in vitro trials. A standardized protocol for determining, in real time, the glenoid position and placement was developed and validated., Results: The version angles measured by the tracking system, CT, and the 3D modeling software were 0.0 +/- 1.2 degrees , -1.3 +/- 1.0 degrees , and -1.1 +/- 1.1 degrees , respectively. The magnitudes for inclination angles were 0.7 +/- 0.7 degrees , 0.9 +/- 0.8 degrees , and 1.0 +/- 0.7 degrees , respectively. A statistically significant difference was found only between measurements made with the tracking system and with CT (p < 0.05). Testing of the CAGI system in a cadaveric trial resulted in an accuracy of 1.17 degrees of version and 0.60 degrees of inclination. The procedure was readily performed with excellent feedback and guidance for the surgeon., Conclusions: Preoperative planning using CT imaging with 3D modeling and intraoperative tracking were combined to produce improved accuracy and reliability of glenoid implantation in the setting of total shoulder arthroplasty.

A computer-assisted technique was developed for treatment of 4-part proximal humeral fractures via a hemiarthroplasty and tuberosity fixation. This was compared with a standard traditional method in 7 pairs of cadaveric shoulders. The computer-assisted technique used preoperative computed tomography data and computer simulations of anatomic characteristics of the contralateral humerus. This allowed accurate anatomic reconstruction by use of an electromagnetic tracking system and real-time intraoperative feedback. Various anatomic measurements were used to quantify the accuracy of the reconstruction. The differences between the intact and reconstructed values were improved with the computer-assisted technique for 5 of 7 characteristics. However, this was statistically significant only for humeral head offset (P < .05). With further investigation and refinement, this technique should allow for a more anatomic reconstruction of the proximal humerus, potentially resulting in improved patient outcomes. The technique may also prove to be a valuable resource for the laboratory training of inexperienced surgical trainees.

This in vitro study evaluated the effects of four different muscle-loading ratios on active glenohumeral joint abduction. Eight cadaveric shoulders were tested using a shoulder simulator designed to reproduce unconstrained abduction of the humerus via computer-controlled pneumatic actuation. Forces were applied to cables that were sutured to tendons or fixed to bone, to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and anterior, middle, and posterior deltoid muscles. Four sets of muscle-loading ratios were employed, based on: (1) equal loads, (2) average physiological cross-sectional areas (pCSAs), (3) constant values of the product of electromyographic (EMG) data and pCSAs, and (4) variable ratios of the EMG and pCSA data which changed as a function of abduction angle. The investigator generated passive motions with no muscle loads simulated. Repeatability was quantified by five successive trials of the passive and simulated active motions. There was improved repeatability in the simulated active motions versus passive motions, significant for abduction angles less than 40 degrees (p=0.02). No difference was found in the repeatability of the four different muscle-loading ratios for simulated active motions (p0.067 for all angles). The improved repeatability of active over passive motion suggests simulated active motion should be employed for in vitro simulations of shoulder motion.

Background The Walch B3 glenoid is theorized to be a progression of the B2 biconcave pattern. The present study aimed to compare glenoid indices between B2 and B3 patterns. We hypothesized that the B3 pattern would have significantly worse retroversion, inclination and medialization. Methods Computed tomography scans of 50 patients with B2 erosions [mean (SD) age 68 (9) years; 25 male] and 50 patients with B3 erosions [mean (SD) age 72 (8) years; 22 males] were converted into three-dimensional reconstructions. Retroversion, inclination, medialization and humeral head subluxation were compared. Results The data demonstrated no statistically significant differences [mean (SD)] between groups when assessing retroversion: B2 = 21 (8)°, B3 = 24 (7)° (p = 0.602); glenoid inclination: B2 = 9 (6)°, B3 = 8 (6)° (p = 0.967); or medialization: B2 = 12 (4) mm, B3 = 14 (4) mm (p = 0.384). In the B2 group, the mean (SD) humeral head subluxation was 80% (10%) according to the scapular plane and 55% (9%) according to the glenoid plane, which was not statistically different from the B3 group with a mean (SD) humeral head subluxation of 81% (7%) according to the scapular plane (p = 0.680) and 54% (7%) according to the glenoid plane (p = 0.292). Conclusions These results demonstrated no significant differences between the B2 and B3 erosion patterns, with respect to the glenoid indicies measured. The aetiology of the B3 glenoid cannot be completely explained by progression of wear in a B2 glenoid. [ABSTRACT FROM AUTHOR]