Posterior Acromial Morphology Is Significantly Associated with Posterior Shoulder Instability

Meyer, Dominik C.; Ernstbrunner, Lukas; Boyce, Glenn; Imam, Mohamed A.; Nashar, Rany El; Gerber, Christian

doi:10.2106/jbjs.18.00541

Cited by 40 publications

(65 citation statements)

References 33 publications

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“…Measurements on anteroposterior views included the critical shoulder angle, 22,30,31,34 the acromiohumeral distance, 4 and the osteoarthritis stage according to Hamada. 27 Measurement of the orientation of the acromion in the sagittal plane was conducted as previously described on true lateral radiographs 28 and included the posterior acromial tilt, the anterior and posterior acromial coverages, and the posterior acromial height.…”

Section: Methodsmentioning

confidence: 99%

Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

et al. 2020

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Background: Chronic pseudoparalysis is generally defined as the inability to actively elevate the arm above 90° with free passive range of motion and no neurological deficits. It has been suggested that this arbitrary cutoff needs to be refined. Purpose: To analyze whether there are structural and biomechanical differences in patients with chronic pseudoparalysis and those with chronic pseudoparesis. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective study, 50 patients with chronic massive rotator cuff tears (mRCTs; ≥2 tendons) and free passive and active scapular plane abduction <90° were divided into 2 groups: pseudoparalysis group (n = 24; active scapular plane abduction, <45°) and pseudoparesis group (n = 26; active scapular plane abduction, >45° and <90°). Radiographic measurements included the critical shoulder angle, acromiohumeral distance, posterior acromial tilt, anterior and posterior acromial coverages, and posterior acromial height on outlet views. Measurements on magnetic resonance imaging (MRI) included fatty infiltration of the rotator cuff muscles, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extensions, and global (anterior + posterior) tear extension in the parasagittal plane. A published musculoskeletal model was used to simulate the effect of different mRCTs on the muscle force required for scapular plane abduction. Results: Plain radiographs revealed no differences between patients with chronic pseudoparalysis and those with pseudoparesis. MRI assessment showed significant differences between patients with chronic pseudoparalysis and those with pseudoparesis with respect to fatty infiltration of the subscapularis (2.9 vs 1.6; P < .001) and infraspinatus (3.6 vs 3.0; P < .001) muscles, and anterior (−23° vs 4°; P < .001), posterior (−23° vs −14°; P = .034), and global rotator cuff (225° vs 190°; P < .001) tear extensions. The anterior tear extension in patients with chronic pseudoparalysis always involved more than 50% of the subscapularis, which was associated with an odds ratio of 5 for inability to actively abduct more than 45°. The biomechanical model was unable to find a combination of muscles that could balance the arm in space when the tear extended beyond the supraspinatus and the cranial subscapularis. Conclusion: This study confirms that chronic pseudoparalysis and pseudoparesis are associated with different structural lesions. In the setting of a chronic mRCT, involvement of more than 50% of the subscapularis tendon with fatty infiltration of stage 3 is associated with pseudoparalysis of active scapular plane abduction <45°. The key function of the subscapularis was confirmed in the biomechanical model.

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Section: Methodsmentioning

confidence: 99%

Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

et al. 2020

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“…So far, recurrent posterior shoulder instability and static posterior humeral head subluxation are understood as two distinct pathologic conditions, which become symptomatic in different periods of life. Although the pathogenesis remains multifactorial and—hitherto—poorly understood, there is increasing evidence that the scapular shape could play a relevant role in both conditions 2 , 16 , 17 , 21 , 26 , 28 : Increased glenoid retroversion has been discussed extensively, but on its own is unable to comprehensively explain the observations. 2 , 21 , 26 , 28 More recently a flat acromial roof with less posterior bony support has been observed and described as an anatomical variant which is strongly associated with posterior instability.…”

Section: Introductionmentioning

confidence: 99%

“… 2 , 21 , 26 , 28 More recently a flat acromial roof with less posterior bony support has been observed and described as an anatomical variant which is strongly associated with posterior instability. 2 , 16 , 20 Up to now, these observations were analyzed either independently of each other, two-dimensionally 16 , 17 or without a healthy control group. 2 …”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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

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“…Recently, more attention has been paid to the morphologic characteristics of the posterior acromion in the sagittal plane. 2,3,30 A wider posterior acromial coverage of the humeral head has been described as a risk factor for RCT. 2 We found no significant difference in terms of anterior or posterior acromial coverage between patients with PP and those without PP.…”

Section: Discussionmentioning

confidence: 99%

“…Measurements on anteroposterior views included the CSA, 4,23,31,32,36 the acromiohumeral distance (ACHD), 11 and the assessment of the degree of osteoarthritis according to Hamada et al 29 Measurement of the orientation of the acromion in the sagittal plane was conducted as previously described 30 and included measurement of the posterior acromial tilt, the anterior and posterior acromial coverage (AAC and PAC), and the posterior acromial height (PAH) (Figure 1).…”

Section: Methodsmentioning

confidence: 99%

Scapular Morphologic Characteristics and Rotator Cuff Tear Pattern Are Independently Associated With Chronic Pseudoparalyis: A Matched-Pair Analysis of Patients With Massive Rotator Cuff Tears

et al. 2020

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Background: It is unclear which structural parameters determine the development or the absence of chronic pseudoparalysis (PP) in patients with massive rotator cuff tears (mRCTs). Purpose: To determine whether scapular morphologic characteristics and extent of rotator cuff tearing are independent factors associated with chronic PP. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective case-control study, 50 patients with chronic mRCT (≥2 fully detached tendons) and active scapular plane abduction less than 90° (PP group) were age- and sex-matched with a cohort of 50 patients with chronic mRCT and an active scapular plane abduction greater than 90° (non-PP; NPP group). Analysis of standardized, plain radiographs included measurement of the critical shoulder angle (CSA) and the acromiohumeral distance (ACHD) on anteroposterior views and measurement of posterior acromial tilt, anterior and posterior acromial coverage, and posterior acromial height on standardized outlet views. Measurements on magnetic resonance imaging included fatty muscle infiltration, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extension, and global tear extension (anterior + posterior tear extension) in the parasagittal plane. Results: Overall, no significant difference was found in patients’ demographic characteristics ( P > .05). Univariate analyses confirmed significant differences between the PP and NPP groups in active scapular plane abduction (51°± 22° vs 135°± 29°; P < .001). Multivariate analyses revealed independent factors associated with PP compared with the NPP group: CSA (38.2°± 4.6° vs 35.2°± 3.7°; P = .001); ACHD (4.7 ± 2.2 vs 7.3 ± 2.6 mm; P < .001); posterior acromial height (22 ± 10 vs 17 ± 7 mm; P = .005); and anterior (–9°± 21° vs 25°± 12°; P < .001) and posterior (–18°± 14° vs 2°± 14°; P < .001) tear extension. The NPP group had significantly less involvement and fatty infiltration of the subscapularis (1.4 ± 0.6) compared with the PP group (2.2 ± 0.9) ( P < .001). Conclusion: This study confirms that global RCT extension and the quality of the inferior half of the subscapularis are significantly associated with chronic pseudoparalysis. The study further shows that acromial morphologic characteristics are relevant in the development of pseudoparalysis. Patients with pseudoparalysis have a larger CSA, less ACHD, and a higher positioned acromion in the sagittal plane.

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Posterior Acromial Morphology Is Significantly Associated with Posterior Shoulder Instability

Cited by 40 publications

References 33 publications

Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

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

Scapular Morphologic Characteristics and Rotator Cuff Tear Pattern Are Independently Associated With Chronic Pseudoparalyis: A Matched-Pair Analysis of Patients With Massive Rotator Cuff Tears

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