Importance of a three-dimensional measure of humeral head subluxation in osteoarthritic shoulders

Three-dimensional evaluation of the transverse rotator cuff muscle's resultant force angle in relation to scapulohumeral subluxation and glenoid vault morphology in nonpathological shoulders

BACKGROUND

Static posterior subluxation of the humeral head (SPSH) results in glenohumeral osteoarthritis. Treatment strategies for SPSH with or without resulting osteoarthritis remain challenging. There is growing interest in evaluating the rotator cuff muscle volume, fatty infiltration, or forces in osteoarthritic shoulders with SPSH, mainly due to a possible transverse force imbalance. In nonpathological shoulders, the transverse angle of the rotator cuff muscle's resultant force may be associated with scapulohumeral alignment and glenoid vault morphology, despite an assumed transverse force balance. The purpose of this study was to assess the transverse rotator cuff muscle's resultant force angle (TRFA) and its relationship with the scapulohumeral subluxation index (SHSI) and selected glenoid vault parameters using computer modeling.

METHODS

Computed tomography scans of 55 trauma patients (age 31 ± 13 years, 36 males) with nonpathological shoulders were analyzed and all measurements performed in 3-dimension. We placed landmarks manually to determine the humeral head center and the rotator cuff tendon footprints. The contours of the rotator cuff muscle cross-sectional areas were automatically predicted in a plane perpendicular to the scapula. Each rotator cuff muscle was divided into virtual vector fibers with homogeneous density. The resultant force vector direction for each muscle, corresponding to the rotator cuff action line, was calculated by vectorially summing the normalized fiber vectors for each muscle, weighted by the muscle trophic ratio. The resultant force vector was projected on the axial plane, and its angle with the mediolateral scapular axis was used to determine TRFA. The SHSI according to Walch, glenoid version angle (GVA), glenoid anteroposterior offset angle (GOA), glenoid depth, glenoid width, and glenoid radius were also evaluated.

RESULTS

The mean values for TRFA, SHSI, GVA, GOA, glenoid depth, glenoid width, and glenoid radius were 7.4 ± 4.5°, 54.3 ± 4.8%, -4.1 ± 4.4°, 5.1 ± 10.8°, 3.3 ± 0.6 mm, 20 ± 2 mm, and 33.6 ± 4.6 mm, respectively. The TRFA correlated strongly with SHSI (R = 0.731, P < .001) and GVA (R = 0.716, P < .001) and moderately with GOA (R = 0.663, P < .001). The SHSI was strongly negatively correlated with GVA (R = -0.813, P < .001) and moderately with GOA (R = -0.552, P < .001). The GVA correlated strongly with GOA (R = 0.768, P < .001). In contrast, TRFA, SHSI, GVA, and GOA did not correlate with glenoid depth, width, or radius.

CONCLUSION

Despite an assumed balance in the transverse volume of the rotator cuff muscles in nonpathological shoulders, variations exist regarding the transverse resultant force depending on the SHSI, GVA, and GOA. In healthy/nonosteoarthritic shoulders, an increased glenoid retroversion is associated with a decreased anterior glenoid offset.

Management of irreparable subscapularis tears: Current concepts

Primary repair of acute subscapularis (SSC) tears provides excellent results, but tendon retraction, muscle atrophy, fatty infiltration, and humeral head migration may render a more chronic tear irreparable. These irreparable SSC tears present a diagnostic and treatment challenge for orthopaedic surgeons. Careful physical examination and imaging evaluation can help to distinguish those with reparable versus irreparable tears, but they are still not very reliable due to the methodological limitations of current evidence. Therefore, future research using 3D and quantitative measurement techniques is necessary to better predict the irreparability of the SSC. When conservative treatment of an irreparable SSC tear fails, reversed shoulder arthroplasty has been established as the preferred treatment option for older, low-demand patients with arthropathy, providing reliable improvements in pain and function. In younger patients without significant arthropathy, musculotendinous transfers are the treatment of choice. The pectoralis major transfer is historically the most frequently performed procedure and provides improved range of motion and pain relief, but fails to adequately restore strength and shoulder function. The latissimus dorsi transfer has gained increased interest over the last few years due to its biomechanical superiority, and early clinical studies suggest improved outcomes as well. More recently, anterior capsular reconstruction has been proposed as an alternative to musculotendinous transfers, but clinical data are completely lacking. Future high-quality randomised controlled trials are necessary to reliably compare the different musculotendinous transfers and anterior capsular reconstruction.

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

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

Quantitative SSM-based analysis of humeral head migration in rotator cuff tear arthropathy patients

Rotator cuff tear arthropathy (RCTA) is characterized by massive rotator cuff tearing combined with humeral head migration (HHM). The aim of this study is to investigate the quantitative characteristics of this migration and its association with glenoid erosions and prearthropathy scapular anatomy. We quantified HHM and prearthropathy scapular anatomy of 64 RCTA patients with statistical shape modeling-based techniques. Glenoid erosion was classified according to Sirveaux et al. A cutoff value for confirming HHM was 5 mm based on a control group of 49 patients. Group 1 (RCTA without HHM) consisted of 21 patients, with a mean subluxation distance (SLD) of 3 mm. Group 2 (RCTA with HHM) consisted of 43 patients, with mean SLD of 9 mm, SLD in the anteroposterior plane of -1 mm (SD ± 4 mm), SLD in the superoinferior plane of 7 mm (SD ± 3 mm), and subluxation angle (SLA) of -5° (SD ± 40°). Analysis with Fisher's exact test showed a clear association between HHM and glenoid erosions (p = 0.002). Multivariate regression analysis of Group 2 showed that prearthropathy lateral acromial angle combined with critical shoulder angle (p = 0.004) explained 21% of the observed variability in SLD. The prearthropathy glenoid version explained 23% of the variability in SLA (p = 0.001). HHM in RCTA patients has a wide variation in both magnitude and direction leading to a distorted glenohumeral relationship in the coronal and axial plane. HHM is highly associated with the occurrence of glenoid erosions. There is a correlation between the prearthropathy scapular anatomy and the magnitude and direction of HHM.

Walch B2 glenoids. 2D vs 3D comparison of humeral head subluxation and glenoid retroversion

Background

The posterior subluxation and glenoid version in Walch B2 glenoids are routinely assessed by 2-dimensional (2D) computed tomography (CT). Different methods of calculation are used to analyze these parameters. Alternatively, the rising use of 3-dimensional (3D) planification tools in arthroplasty requires the clarification if the 3D measurements are equivalent to 2D. The aim of this study was to compare B2 glenoids characteristics between 2D CT assessment method and 3D automated software method.

Methods

CT scans from patients who underwent a shoulder arthroplasty were identified. In the 2D method, measurement of glenoid version was determined. Measurement of the humeral head subluxation (HHS) (scapula axis method) was determined by the percentage of the humeral head posterior to the Friedman line (scapula axis). Three-dimensional analysis allowed an automated segmentation of the humerus and scapula, definition of scapular planes, and determination of glenoid version and HHS.

Results

Fifty-one CT scans met inclusion criteria. The intraobserver and interobserver reliability of the 2D retroversion (RV) and 2D HHS intraclass correlation coefficient was excellent (intraclass correlation coefficient>0.9).The median RV was 16° [12-20] in 2D and 19° [16-23] in 3D (P < .0001). The median subluxation was 71% [66-75] in 2D and 81% [78-86] in 3D (P < .0001). Linear regression analysis demonstrated low positive correlation between RV and subluxation in 2D and 3D (R² = 0.31 and R² = 0.23, respectively).

Discussion/Conclusion

The assessment of version and HHS in Walch B2 glenoids between 2D CT and a 3D planification were significantly different. Low correlation between RV and HHS was observed (2D and 3D assessment).

Association of the Posterior Acromion Extension with Glenoid Retroversion: A CT Study in Normal and Osteoarthritic Shoulders

Posterior eccentric glenoid wear is associated with higher complication rates after shoulder arthroplasty. The recently reported association between the acromion shape and glenoid retroversion in both normal and osteoarthritic shoulders remains controversial. The three-dimensional coordinates of the angulus acromialis (AA) and acromioclavicular joint were examined in the scapular coordinate system. Four acromion angles were defined from these two acromion landmarks: the acromion posterior angle (APA), acromion tilt angle (ATA), acromion length angle (ALA), and acromion axial tilt angle (AXA). Shoulder computed tomography scans of 112 normal scapulae and 125 patients with primary glenohumeral osteoarthritis were analyzed with simple and stepwise multiple linear regressions between all morphological acromion parameters and glenoid retroversion. In normal scapulae, the glenoid retroversion angle was most strongly correlated with the posterior extension of the AA (R² = 0.48, p < 0.0001), which can be conveniently characterized by the APA. Combining the APA with the ALA and ATA helped slightly improve the correlation (R² = 0.55, p < 0.0001), but adding the AXA did not. In osteoarthritic scapulae, a critical APA > 15 degrees was found to best identify glenoids with a critical retroversion angle > 8 degrees. The APA is more strongly associated with the glenoid retroversion angle in normal than primary osteoarthritic scapulae.

Computer-Assisted Preoperative Planning and Patient-Specific Instrumentation for Glenoid Implants in Shoulder Arthroplasty

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Glenoid component positioning affects implant survival after total shoulder arthroplasty, and accurate glenoid-component positioning is an important technical aspect.

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The use of virtual planning and patient-specific instrumentation has been shown to produce reliable implant placement in the laboratory and in some clinical studies.

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Currently available preoperative planning software programs employ different techniques to generate 3-dimensional models and produce anatomic measurements potentially affecting clinical decisions.

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There are no published data, to our knowledge, on the effect of preoperative computer planning and patient-specific instrumentation on long-term clinical outcomes.

Subluxation in the Arthritic Shoulder

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The term "subluxation" means partial separation of the joint surfaces. In the arthritic shoulder, "arthritic glenohumeral subluxation" refers to displacement of the humeral head on the surface of the glenoid.

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The degree of arthritic glenohumeral subluxation can be measured using radiography with standardized axillary views or computed tomography (CT).

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Shoulders with a type-B1 or B2 glenoid may show more posterior subluxation on an axillary radiograph that is made with the arm in an elevated position than on a CT scan that is made with the arm at the side.

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The degree of arthritic glenohumeral subluxation is not closely related to glenoid retroversion.

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The position of the humeral head with respect to the plane of the scapula is related to glenoid retroversion and is not a measure of glenohumeral subluxation.

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Studies measuring glenohumeral subluxation before and after arthroplasty should clarify its importance to the clinical outcomes of shoulder reconstruction.

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

BACKGROUND

Static posterior subluxation of the humeral head is a pre-osteoarthritic deformity preceding posterior erosion in young patients. Its etiology remains unknown. The aim of this study was to analyze the differences in scapular morphology between young patients with pre-osteoarthritic static posterior subluxation of the humeral head and healthy controls with a centered humeral head.

METHODS

We performed a retrospective analysis of all patients with pre-osteoarthritic static posterior subluxation of the humeral head who were treated in our institution between January 2018 and November 2019. Fourteen shoulders in 12 patients were included in this study and then matched according their age, sex, and affected side with controls. Computed tomography images of both groups were compared in the standardized axial imaging plane for differences in scapular morphology. The following parameters were measured: glenoid version relative to the Friedman line and scapular blade axis, scapulohumeral and glenohumeral subluxation index, and neck angle, as well as glenoid and humeral offset.

RESULTS

The patients in the subluxation group showed significantly higher scapulohumeral and glenohumeral subluxation indexes than controls (0.76 vs. 0.55 [P < .0001] and 0.58 vs. 0.51 [P = .016], respectively). The mean measurements of glenoid version according to the Friedman line and relative to the scapular blade axis were significantly higher in the subluxation group than in controls (19° vs. 4° [P < .0001]and 14° vs. 2° [P = .0002], respectively). The glenoid vault was significantly more anteriorly positioned with respect to the scapular blade axis in the subluxation group than in controls (neck angle, 166° vs. 173° [P = .0003]; glenoid offset, 9.2 mm vs. 4.6 mm [P = .0005]). The midpoint of the humeral head showed a posterior offset with respect to the scapular blade axis in the subluxation group, whereas controls had an anteriorly placed midpoint of the humeral head (-2 mm vs. 3.1 mm, P = .01). A higher scapulohumeral subluxation index showed significant correlations with an increased anterior offset of the glenoid vault (increased glenoid offset: r = 0.493, P = .008 and decreased neck angle: r = -0.554, P = .002), a posterior humeral offset (r = -0.775, P < .0001), and excessive glenoid retroversion measured by both methods (Friedman line: r = 0.852, P < .0001; scapular blade axis: r = 0.803, P < .0001). A higher glenohumeral subluxation index also correlated significantly with an increased anterior offset of the glenoid vault (increased glenoid offset: r = 0.403, P = .034; decreased neck angle: r = -0.406, P = .032) and posterior humeral offset (r = -0.502, P = .006).

CONCLUSION

Young patients with pre-osteoarthritic static posterior subluxation of the humeral head have significant constitutional differences in scapular morphology in terms of an increased anterior glenoid offset, excessive glenoid retroversion, and increased posterior humeral offset in relation to the scapular blade compared with healthy matched controls.

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.

Restoration of the Posterior Glenoid in Recurrent Posterior Shoulder Instability Using an Arthroscopically Placed Iliac Crest Bone Graft: A Computed Tomography-Based Analysis

Background

Posterior shoulder instability is uncommon, and its treatment is a challenging problem. An arthroscopically assisted technique for posterior iliac crest bone grafting (ICBG) has shown promising short- and long-term clinical results. Changes as shown on imaging scans after posterior ICBG for posterior shoulder instability have not been investigated in the recent literature.

Purpose

To evaluate changes on computed tomography (CT) after arthroscopically assisted posterior ICBG and to assess clinical outcomes.

Study Design

Case series; Level of evidence, 4.

Methods

Patients with preoperative CT scans and at least 2 postoperative CT scans with a minimum follow-up of 2 years were included in the evaluation. Of 49 initial patients, 17 (follow-up rate, 35%) met the inclusion criteria and were available for follow-up. We measured the glenoid version angle and the glenohumeral and scapulohumeral indices on the preoperative CT scans and compared them with measurements on the postoperative CT scans. Postoperatively, graft surface, resorption, and defect coverage were measured and compared with those at early follow-up (within 16 months) and final follow-up (mean ± SD, 6.6 ± 2.8 years).

Results

The mean preoperative glenoid version was -17° ± 13.5°, which was corrected to -9.9° ± 11.9° at final follow-up (P < .001). The humeral head was able to be recentered and reached normal values as indicated by the glenohumeral index (51.8% ± 6%; P = .042) and scapulohumeral index (59.6% ± 10.2%; P < .001) at final follow-up. Graft surface area decreased over the follow-up period, from 24% ± 9% of the glenoid surface at early follow-up to 17% ± 10% at final follow-up (P < .001). All clinical outcome scores had improved significantly. Progression of osteoarthritis was observed in 47% of the shoulders.

Conclusion

Arthroscopically assisted posterior ICBG restored reliable parameters as shown on CT scans, especially glenoid version and the posterior subluxation indices. Graft resorption was common and could be observed in all shoulders. Patient-reported clinical outcome scores were improved. Osteoarthritis progression in almost 50% of patients is concerning for the long-term success of this procedure.

Deep learning for the rapid automatic quantification and characterization of rotator cuff muscle degeneration from shoulder CT datasets

Objectives

This study aimed at developing a convolutional neural network (CNN) able to automatically quantify and characterize the level of degeneration of rotator cuff (RC) muscles from shoulder CT images including muscle atrophy and fatty infiltration.

Methods

One hundred three shoulder CT scans from 95 patients with primary glenohumeral osteoarthritis undergoing anatomical total shoulder arthroplasty were retrospectively retrieved. Three independent radiologists manually segmented the premorbid boundaries of all four RC muscles on standardized sagittal-oblique CT sections. This premorbid muscle segmentation was further automatically predicted using a CNN. Automatically predicted premorbid segmentations were then used to quantify the ratio of muscle atrophy, fatty infiltration, secondary bone formation, and overall muscle degeneration. These muscle parameters were compared with measures obtained manually by human raters.

Results

Average Dice similarity coefficients for muscle segmentations obtained automatically with the CNN (88% ± 9%) and manually by human raters (89% ± 6%) were comparable. No significant differences were observed for the subscapularis, supraspinatus, and teres minor muscles (p > 0.120), whereas Dice coefficients of the automatic segmentation were significantly higher for the infraspinatus (p < 0.012). The automatic approach was able to provide good–very good estimates of muscle atrophy (R² = 0.87), fatty infiltration (R² = 0.91), and overall muscle degeneration (R² = 0.91). However, CNN-derived segmentations showed a higher variability in quantifying secondary bone formation (R² = 0.61) than human raters (R² = 0.87).

Conclusions

Deep learning provides a rapid and reliable automatic quantification of RC muscle atrophy, fatty infiltration, and overall muscle degeneration directly from preoperative shoulder CT scans of osteoarthritic patients, with an accuracy comparable with that of human raters.

Key Points

• Deep learning can not only segment RC muscles currently available in CT images but also learn their pre-existing locations and shapes from invariant anatomical structures visible on CT sections.

• Our automatic method is able to provide a rapid and reliable quantification of RC muscle atrophy and fatty infiltration from conventional shoulder CT scans.

• The accuracy of our automatic quantitative technique is comparable with that of human raters.

Reduction of scapulohumeral subluxation with posterior augmented glenoid implants in anatomic total shoulder arthroplasty: Short-term 3D comparison between pre- and post-operative CT

BACKGROUND

Failure rates in anatomic total shoulder arthroplasty (aTSA) are higher in case of asymmetric glenoid bone loss secondary to posterior wear, and in persistent static posterior subluxation of the humeral head (PSH).

HYPOTHESIS

This study aimed to test the hypothesis that the combined use of posterior augmented glenoid (PAG) implants with three-dimensional (3D) surgical planning and patient-specific instrumentation (PSI) guides helps reduce short-term PSH after aTSA in patients with type B2-B3 glenoids.

PATIENTS AND METHODS

We included nine consecutive patients with primary glenohumeral osteoarthritis and type B2 or B3 glenoids, who underwent aTSA with cemented keeled PAG implants (posterior augments of 15, 25, or 35 degrees). All patients underwent preoperative shoulder computed tomography (CT) scans, with 3D surgical planning coupled to PSI at the time of surgery. Postoperative shoulder CT scans were performed at an average of 14 weeks (range, 10-21 weeks). Scapulohumeral subluxation and glenoid version and inclination were measured in 3D, on both pre- and post-operative CT scans, using the same reliable quantitative method.

RESULTS

There was a significant decrease in scapulohumeral subluxation from 49±12% preoperatively to 22±17% postoperatively (p=0.0039), with a large effect size (Cohen's d=1.89). Preoperative glenoid version was corrected from -17.3±9.4 degrees to -5.2±7.5 degrees postoperatively. The absolute difference between the postoperative and surgically planned version and inclination was 5.4±3.6 degrees and 3.3±2.0 degrees, respectively.

DISCUSSION

The combined use of PAG implants with 3D preoperative planning and PSI results in a significant decrease in short-term PSH and glenoid version in patients with asymmetric posterior glenoid wear. We suggest that such implants should not be limited to posterior augmentation, because glenoid deficiency can also be observed in other glenoid sectors.

LEVEL OF EVIDENCE

IV, Basic science study.

A Robotic Glenohumeral Simulator for Investigating Prosthetic Implant Subluxation

Total shoulder arthroplasty (TSA) is an effective treatment for glenohumeral (GH) osteoarthritis. However, it still suffers from a substantial rate of mechanical failure, which may be related to cyclic off-center loading of the humeral head on the glenoid. In this work, we present the design and evaluation of a GH joint robotic simulator developed to study GH translations. This five-degree-of-freedom robot was designed to replicate the rotations (±40 deg, accuracy 0.5 deg) and three-dimensional (3D) forces (up to 2 kN, with a 1% error settling time of 0.6 s) that the humeral implant exerts on the glenoid implant. We tested the performances of the simulator using force patterns measured in real patients. Moreover, we evaluated the effect of different orientations of the glenoid implant on joint stability. When simulating realistic dynamic forces and implant orientations, the simulator was able to reproduce stable behavior by measuring the translations of the humeral head of less than 24 mm with respect to the glenoid implant. Simulation with quasi-static forces showed dislocation in extreme ranges of implant orientation. The robotic GH simulator presented here was able to reproduce physiological GH forces and may therefore be used to further evaluate the effects of glenoid implant design and orientation on joint stability.

Relationship of Posterior Decentering of the Humeral Head with Tear Size and Fatty Degeneration in Rotator Cuff Tear

Background

Posterior decentering is not an uncommon finding on rotator cuff tear patients’ shoulder magnetic resonance imaging. No previous study has reported on the relationship between posterior decentering and rotator cuff tear.

Methods

We assessed patients’ rotator cuff tear humeral head positions based on humeral–scapular alignment (HSA). Subjects were classified into centering and decentering groups based on a <2 mm or >2 mm HSA value, respectively. Differences in rotator cuff tear size, degree of tear, and fatty degeneration between the two groups were evaluated.

Results

One hundred seventy-five patients (80 males, 95 females; mean age: 59.7 ± 6.5 years old) were selected as subjects (case-control study; level of evidence: 3). Tear size, degree of subscapularis tendon tear, and fatty degeneration of the supraspinatus, infraspinatus, and subscapularis muscles were significantly different between the two groups (p<0.001, p<0.001, p<0.001).

Conclusions

The occurrence of decentering was related to rotator cuff tear size, degree of subscapularis tendon tear, and fatty degeneration of the rotator cuff muscles.

Normal Range of Humeral Head Positioning on the Glenoid on Magnetic Resonance Imaging: Validation through Comparison of Computed Tomography and Magnetic Resonance Imaging

Background

To determine the normal range of humeral head positioning on magnetic resonance imaging (MRI).

Methods

We selected normal subjects (64 patients; group A) to study the normal range of humeral head positioning on the glenoid by MRI measurements. To compare the MRI measurement method with the computed tomography (CT), we selected group B (70 patients) who underwent both MRI and CT. We measured the humeral-scapular alignment (HSA) and the humeral-glenoid alignment (HGA).

Results

The HSA in the control group was 1.47 ± 1.05 mm, and the HGA with and without reconstruction were 1.15 ± 0.65 mm and 1.03 ± 0.59 mm, respectively, on MRI. In the test group, HSA was 2.67 ± 1.47 mm and HGA with and without reconstruction was 1.58 ± 1.16 mm and 1.49 ± 1.08 mm, on MRI. On CT, the HSA was 1.72 ± 1.01 mm, and HGA with and without reconstruction were 1.54 ± 0.96 mm and 1.59 ± 0.93 mm, respectively. HSA was significantly different according to image modality (p=0.0006), but HGA was not significantly different regardless of reconstruction (p=0.8836 and 0.9234).

Conclusions

Although additional CT scans can be taken to measure decentering in patients with rotator cuff tears, reliable measurements can be obtained with MRI alone. When using MRI, it is better to use HGA, which is a more reliable measurement value based on the comparison with CT measurement (study design: Study of Diagnostic Test; Level of evidence II).

Biomechanical comparison of glenoid implants with adaptable and fixed backside curvatures in anatomic total shoulder arthroplasty

BACKGROUND

We evaluated the biomechanical effects and potential advantages of glenoid implants with adaptable backside curvature radii and compared them with standard implants having fixed backside curvatures in anatomic total shoulder arthroplasty (aTSA) for primary glenohumeral osteoarthritis with uniconcave glenoids.

METHODS

A glenoid implant with adaptable backside curvatures (Aequalis PerFORM, Tornier SAS, Montbonnot, France) was compared with its previous model having a fixed curvature radius. Virtual aTSAs were performed in 24 patients from preoperative shoulder computed tomography data sets, using both implants in each patient. For all 48 simulated aTSAs, we first measured the glenoid bone reaming depth, subchondral bone quality after reaming, and implant backside surface and then the predicted cement stress, bone-cement interfacial stress, and bone strain at 60° of arm abduction. These biomechanical quantities were tested for differences between adaptable and fixed implants and for correlations between preoperative measurements and postoperative predictions.

RESULTS

Adaptable glenoid implants induced a significant decrease in cement stress (P = .008), bone-cement interfacial stress (P = .045), and bone strain (P = .039), particularly for glenoids with curvature radii larger than 40 mm. However, these biomechanical effects were not significantly correlated with an increase in subchondral glenoid bone quality.

CONCLUSIONS

Our study confirms the presumed biomechanical advantages of adaptable glenoid implants, even though the effects were not directly due to the adaptation of the backside curvature radius. Benefits were more pronounced for glenoids with large curvature radii. Our initial biomechanical findings should now be corroborated with large-scale clinical studies.

A 3D comparison of humeral head retroversion by sex and measurement technique

BACKGROUND

Accurate humeral head reconstruction during shoulder arthroplasty is partially dependent on correctly estimating and replicating native version. The present study evaluated the effects of sex and measurement technique on three-dimensional (3D) humeral version measurements made using the transepicondylar, forearm and flexion-extension axes.

METHODS

Fifty-two full-arm computed tomography scans were converted to 3D models and geometry extracted to define landmarks and coordinate systems. An anatomic humeral head osteotomy plane was used to measure version relative to the three measurement techniques and compare between sexes.

RESULTS

The measurement technique used had a significant affect (p < 0.001) on the resulting version measurement. The forearm axis technique consistently resulted in higher measured version compared to either the flexion-extension [mean (SD) males 9° (4°), females 13° (5°), p < 0.001] or the transepicondylar axes [mean (SD) males 8° (4°), females 11° (4°), p < 0.001]. Version in males was 7° greater than females when referencing either the flexion-extension [p = 0.029; mean (SD) males 37.7° (11°), females 30.4° (13°)] or transepicondylar axes [p = 0.045; mean (SD) males 39° (11°), females 32° (12°)].

CONCLUSIONS

The choice of measurement technique can affect the humeral version angle. These results are important because measuring version using the epicondyles pre-operatively, and subsequently the forearm intra-operatively, will result in approximately 10° under-retroverted osteotomy. For example, 0° neutral version cut during reverse arthroplasty measured referencing the forearm results in 10° anteverted osteotomy when referencing the distal humerus.

Walch B0 glenoid: pre-osteoarthritic posterior subluxation of the humeral head

The management of primary osteoarthritis of the shoulder has been well investigated. However, the etiology and management of posterior humeral head subluxation in the context of primary glenohumeral osteoarthritis remain controversial. The finding of static posterior subluxation of the humeral head before the development of posterior bone erosion of the glenoid in young men with radiographic findings of primary osteoarthritis has been described as arthrogenic posterior subluxation of the humeral head. It demonstrates the earliest form of the osteoarthritic evolution, and an excessive glenoid retroversion is the only probable cause of this static subluxation, although this is controversial. The clinical relevance of these findings is important in allowing the identification of patients at risk for development of glenohumeral osteoarthritis and in developing an early treatment for the subluxation to try to alter the natural course of this disease. The aim of our summary paper was to review the current literature on this matter in an attempt to better understand the pathophysiologic mechanism of this condition, which we named pre-osteoarthritic posterior subluxation of the humeral head, or Walch B-zero (B0) glenoid. It appears that Walch B0 glenoid is a pathologic condition (initially dynamic, eventually evolving into a static condition) that may lead to posterior erosion of the glenoid, taking place once there is asymmetric increased posterior glenohumeral contact forces and possibly associated with increased glenoid retroversion.

Guidelines for humeral subluxation cutoff values: a comparative study between conventional, reoriented, and three-dimensional computed tomography scans of healthy shoulders

BACKGROUND

The humeral subluxation index (HSI) is frequently assessed on computed tomography (CT) scans in conditions of the shoulder characterized by humeral displacement. An arbitrarily set HSI cutoff value of 45% for anterior subluxation and 55% for posterior subluxation has been widely accepted. We studied whether mean values and thresholds of humeral subluxation, in relation to the glenoid and scapula, were influenced by different imaging modalities.

METHODS

The HSIs referenced to the scapula (SHSI) and glenoid (GHSI) were compared between conventional CT scans, CT scans reoriented into the corresponding reference plane (ie, scapular plane for the SHSI and glenoid center plane for the GHSI), and 3-dimensional (3D) CT reconstructions of 120 healthy shoulders. The 95% normal range determined the cutoff values of humeral subluxation.

RESULTS

The SHSI thresholds for conventional, reoriented, and 3D CT scans were 33%-61%, 44%-68%, and 49%-61%, respectively. A different mean SHSI was found for each imaging modality (conventional, 47%; reoriented, 56%; 3D, 55%; P ≤ .014), with the conventional SHSI showing an underestimation in 89% of the cases. GHSI thresholds for conventional, reoriented, and 3D CT scans were 40%-61%, 44%-56%, and 46%-54%, respectively. The mean GHSI did not differ between each imaging modality (conventional, 51%; reoriented, 50%; 3D, 50%; P = .146).

CONCLUSIONS

The SHSI and GHSI are susceptible to different imaging modalities with consequently different cutoff values. The redefined HSI cutoff values guide physicians in the evaluation of humeral subluxation in conditions characterized by humeral displacement, depending on the available image data.

Anatomic Shoulder Arthroplasty: Technical Considerations

Osteoarthritis of the shoulder is a common condition in the aging population, and it can have profound effects on patients’ quality of life. The anatomic total shoulder arthroplasty is a well-described treatment modality resulting generally excellent outcomes. The objective of this review is to discuss the technical aspects of primary anatomic total shoulder arthroplasty, and to provide a framework to follow to achieve a successful surgical result. The topics covered include preoperative planning, surgical considerations, and approaches, humeral preparation, glenoid bone loss and the emerging concept of using the reverse total shoulder arthroplasty for the type B2 glenoid.

Cement stress predictions after anatomic total shoulder arthroplasty are correlated with preoperative glenoid bone quality

HYPOTHESIS

We hypothesized that biomechanical parameters typically associated with glenoid implant failure after anatomic total shoulder arthroplasty (aTSA) would be correlated with preoperative glenoid bone quality.

METHODS

We developed an objective automated method to quantify preoperative glenoid bone quality in different volumes of interest (VOIs): cortical bone, subchondral cortical plate, subchondral bone after reaming, subchondral trabecular bone, and successive layers of trabecular bone. Average computed tomography (CT) numbers (in Hounsfield units [HU]) were measured in each VOI from preoperative CT scans. In parallel, we built patient-specific finite element models of simulated aTSAs to predict cement stress, bone-cement interfacial stress, and bone strain around the glenoid implant. CT measurements and finite element predictions were obtained for 20 patients undergoing aTSA for primary glenohumeral osteoarthritis. We tested all linear correlations between preoperative patient characteristics (age, sex, height, weight, glenoid bone quality) and biomechanical predictions (cement stress, bone-cement interfacial stress, bone strain).

RESULTS

Average CT numbers gradually decreased from cortical (717 HU) to subchondral and trabecular (362 HU) bone. Peak cement stress (4-10 MPa) was located within the keel hole, above the keel, or behind the glenoid implant backside. Cement stress, bone-cement interfacial stress, and bone strain were strongly negatively correlated with preoperative glenoid bone quality, particularly in VOIs behind the implant backside (subchondral trabecular bone) but also in deeper trabecular VOIs.

CONCLUSION

Our numerical study suggests that preoperative glenoid bone quality is an important parameter to consider in aTSA, which may be associated with aseptic loosening of the glenoid implant. These initial results should now be confronted with clinical and radiologic outcomes.

Interest in the glenoid hull method for analyzing humeral subluxation in primary glenohumeral osteoarthritis

BACKGROUND

Posterior humeral subluxation is the main cause of failure of total shoulder arthroplasty. We aimed to compare humeral head subluxation in various reference planes and to search for a correlation with retroversion, inclination, and glenoid wear.

MATERIALS AND METHODS

We included 109 computed tomography scans of primary glenohumeral osteoarthritis and 97 of shoulder problems unrelated to shoulder osteoarthritis (controls); all computed tomography scans were reconstructed in the anatomic scapular plane and the glenoid hull plane that we defined. In both planes, we measured retroversion, inclination, glenohumeral offset (Walch index), and scapulohumeral offset.

RESULTS

Retroversion in the scapular plane (Friedman method) was lower than that in the glenoid hull plane for controls and for arthritic shoulders. The threshold of scapulohumeral subluxation was 60% and 65% in the scapular plane and glenoid hull plane, respectively. The mean upward inclination was lower in the scapular plane (Churchill method) than in the glenoid hull plane (Maurer method). In the glenoid hull plane, 35% of type A2 glenoids showed glenohumeral offset greater than 75%, with mean retroversion of 25.6° ± 6° as compared with 7.5° ± 7.2° for the "centered" type A2 glenoids (P < .0001) and an upward inclination of -1.4° ± 8° and 6.3° ± 7° (P = .03), respectively. The correlation between retroversion and scapulohumeral offset was r = 0.64 in the glenoid hull plane and r = 0.59 in the scapular plane (P < .05).

CONCLUSION

Measurement in the glenoid hull plane may be more accurate than in the scapular plane. Thus, the glenoid hull method allows for better understanding type B3 of the modified Walch classification.

The three-dimensional glenohumeral subluxation index in primary osteoarthritis of the shoulder

BACKGROUND

Assessment of glenohumeral subluxation is essential in preoperative planning of total shoulder arthroplasty. The purpose of this study was to evaluate a 3-dimensional (3D) glenohumeral subluxation index (GHSI) in shoulders with primary osteoarthritis (OA) and its relationship with morbid glenoid retroversion.

METHODS

The 3D computed tomography reconstructions of 120 healthy shoulders and 110 shoulders with primary glenohumeral arthritis (OA group), classified according to Walch's glenoid morphology, were analyzed. The 3D GHSI was assessed by measuring posterior decentering of the humeral head in relation to the native glenoid in each subject, and its correlation to morbid glenoid version was calculated.

RESULTS

The reproducible 3D GHSI (intraclass correlation coefficients ≥ 0.842) showed a posterior decentering of the humeral head in the OA population and in each type of glenoid morphology (P ≤ .005). A moderate correlation was observed in the OA group (r = -0.542; P < .001), but weak linear relationships were found for different glenoid morphology types (r between 0.041 and -0.307). Type A shoulders (r = -0.375; P = .006) correlated better than type B shoulders (r =  -0.217; P = .104). After shoulders were subcategorized according to a threshold for 3D subluxation, the posteriorly subluxated group increased its correlation (r = -0.438; P < .001), whereas the centered shoulders still exhibited no relationship (r = -0.192; P = .329).

CONCLUSIONS

Posterior humeral head decentering in relation to the native glenoid is present in each glenoid morphology type. Grouping measures according to morphology type and 3D subluxation showed at best moderate correlations between morbid version and 3D GHSI.

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis

BACKGROUND

Rotator cuff muscle degeneration is an important parameter to consider when planning shoulder arthroplasty.

HYPOTHESIS

We hypothesized that rotator cuff muscle degeneration is correlated with scapulohumeral subluxation in patients planned for anatomical total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

We developed a semi-automated quantitative CT method to measure rotator cuff muscle degeneration, and retrospectively analyzed 107 preoperative shoulder CT scans of patients with primary osteoarthritis. On a standardized sagittal-oblique CT slice perpendicular to the scapular axis, two observers measured the cross-sectional areas of residual rotator cuff muscle tissues, normalized by the estimated area of healthy muscles. Muscle degeneration was quantified in a semi-automated manner, and divided into atrophy and fatty infiltration. Scapulohumeral subluxation was determined in 3D as the distance between the humeral head center and the glenoid surface center, projected on the same CT slice, and normalized by the humeral head radius. We tested all potential correlations between muscle degeneration and scapulohumeral subluxation.

RESULTS

Muscle degeneration, primarily due to atrophy, predominated in the supraspinatus; it varied from 0.8% to 88.8%. Scapulohumeral subluxation varied from 2.5% to 72.9%, and was mainly in a posterior and postero-superior orientation. There was a significant but weak correlation between the amount of subluxation and both supraspinatus (R=0.207, P=0.032) and infraspinatus (R=0.225, P=0.020) degeneration. Inter- and intra-observer reproducibility of muscle degeneration measurements were both excellent (ICCs range=0.955-0.987 and 0.971-0.988, respectively).

CONCLUSION

This new semi-automated CT method allows to quantitatively and reproducibly measure rotator cuff muscle degeneration in shoulders with primary osteoarthritis. Muscle degeneration is weakly correlated with scapulohumeral subluxation in patients planned for anatomical TSA.

LEVEL OF EVIDENCE

Level IV.

TYPE OF STUDY

Diagnostic retrospective study.

Management of intraoperative posterior decentering in shoulder arthroplasty using anteriorly eccentric humeral head components

BACKGROUND

Posterior humeral decentering presents a challenge in glenohumeral arthroplasty. Soft tissue releases and osteophyte resection can lead to intraoperative decentering not evident preoperatively. Inferior outcomes result if decentering is not addressed as a part of the arthroplasty. When there is >50% posterior subluxation of the humeral head on passive elevation of the arm at surgery, we have used an anteriorly eccentric humeral head component to improve centering of the humeral articular surface on the glenoid.

METHODS

We reviewed the 2-year outcomes for 33 shoulder arthroplasties in which anteriorly eccentric humeral heads were used to manage posterior decentering identified at surgery. Rotator interval plication was performed in 16 cases as an adjunctive stabilizing procedure. Shoulders were evaluated preoperatively and postoperatively with the Simple Shoulder Test (SST). Radiographic centering was characterized before surgery and at follow-up on standardized axillary radiographs with the arm held in a position of functional elevation.

RESULTS

With the anteriorly eccentric head component, preoperative radiographic humeral decentering was reduced from 10.4% ± 7.9% to 0.9% ± 2.3% postoperatively (P < .001). SST scores improved from 4.8 ± 2.3 to 10.0 ± 2.3 (P < .001). Preoperative posterior humeral head decentering did not correlate with preoperative glenoid version. Glenoid retroversion was 19.8° ± 8.9° preoperatively and 15.5° ± 7.5° postoperatively.

CONCLUSIONS

Posterior decentering identified at surgery when standard trial components are in place can be addressed by replacing the anatomic humeral head with an anteriorly eccentric humeral head component.

Are spinoglenoid ganglion cysts early markers of glenohumeral arthritis?

HYPOTHESIS

The objective of this study was to improve our understanding of the pathogenesis and symptoms of ganglion cysts (GCs) in the spinoglenoid notch. Two hypotheses were tested: (1) the labral tears responsible for these cysts are mainly degenerative and nontraumatic, (2) spinoglenoid cysts are early magnetic resonance image (MRI) markers of eccentric posterior glenoid wear.

MATERIALS AND METHODS

This was a descriptive diagnostic study. Patients were included when a spinoglenoid cyst was discovered after complaints of pain in the posterosuperior aspect of the shoulder. MRI and arthroscopy were used to classify the glenoid GC and characterize the glenohumeral joint. The GCs were classified into 1 of 3 types: GC0 (isolated cyst), GC1 (cyst and associated labral lesion), and GC2 (cyst and associated labral and cartilage lesion).

RESULTS

Twenty patients (average age, 43 years) were included between 2000 and 2014. There were 7 GC0, 8 GC1, and 5 GC2 type cysts. Isolated labral tears (GC1) were always located posteriorly, without anterior extension or glenoid detachment. The humeral subluxation index was above 55% in 75% of shoulders, including all of the type GC2 shoulders. The 5 GC2 shoulders had type B1, B2, or C glenoids.

CONCLUSIONS

The management of paraglenoid labral cysts must go beyond addressing the suprascapular nerve compression related to traumatic labral detachment, and surgeons should look automatically for associated degenerative joint damage. The diagnosis of GCs should be supplemented by humeral subluxation index measurement on computed tomography scan or MRI, and the patient should be informed that joint-related posterior shoulder pain might persist in cases of GC1 and GC2.

LEVEL OF EVIDENCE

Basic Science Study; Anatomy; Imaging and In Vivo.

Glenoid Dysplasia: Pathophysiology, Diagnosis, and Management

➤Subtle forms of glenoid dysplasia may be more common than previously thought and likely predispose some patients to symptomatic posterior shoulder instability. Severe glenoid dysplasia is a rare condition with characteristic radiographic findings involving the posteroinferior aspect of the glenoid that often remains asymptomatic.➤Instability symptoms related to glenoid dysplasia may develop over time with increased activities or trauma. Physical therapy focusing on rotator cuff strengthening and proprioceptive control should be the initial management.➤Magnetic resonance imaging and computed tomographic arthrograms are useful for detecting subtle glenoid dysplasia by revealing the presence of an abnormally thickened or hypertrophic posterior part of the labrum, increased capsular volume, glenoid retroversion, and posteroinferior glenoid deficiency.➤Open and arthroscopic labral repair and capsulorrhaphy procedures have been described for symptomatic posterior shoulder instability. Glenoid retroversion of >10° may be a risk factor for failure following soft-tissue-only procedures for symptomatic glenoid dysplasia.➤Osseous procedures are categorized as either glenoid reorientation (osteotomy) or glenoid augmentation (bone graft), and no predictable results have been demonstrated for any surgical strategy. Glenoid osteotomies have been described for increased retroversion, with successful results, although others have noted substantial complications and poor outcomes.➤In severe glenoid dysplasia, the combination of bone deficiency and retroversion makes glenoid osteotomy extremely challenging. Bone grafts placed in a lateralized position to create a blocking effect may increase the risk of the development of arthritis, while newer techniques that place the graft in a congruent position may decrease this risk.

Planning software and patient-specific instruments in shoulder arthroplasty

Computer planning software and patient-specific instrumentation have been investigated in multiple subspecialties of orthopedics with mixed results. Shoulder arthroplasty has evolved over the last decade with improvements in implant design and surgical instrumentation. Despite these advances, glenoid positioning in shoulder arthroplasty continues to be a difficult problem. Recent advances in three-dimensional imaging techniques and the use of computer planning software may potentially address some of the common difficulties encountered by surgeons. The addition of patient-specific instrumentation and guides provide an option for patients with significant glenoid deformity that may allow improved accuracy of glenoid component implantation compared to using standard instrumentation. Studies have reported improved positioning of the glenoid component in both anatomic and reverse total shoulder arthroplasty with patient-specific instrumentation and guides. More research is needed to determine whether these improvements lead to better patient-reported outcomes or implant survival. In addition, further studies will be needed to address whether this technology is cost effective for large-scale implementation in the orthopedic community.