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

Abstract

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.

The Cartilage Wear Index: a new evaluation method to improve patient selection in surgical treatment of recurrent posterior glenohumeral instability

“…Analogous to other studies, we also found an increased incidence of glenoid retroversion in the patients with B2 instability. 5 , 15 , 17 , 19 , 31 The median glenoid version of all patients measured with the vault method was 14.8°. Meanwhile, the glenohumeral index was normal being 52% ( Table II ).…”

Correction of Static Posterior Shoulder Subluxation by Restoring Normal Scapular Anatomy Using Acromion and Glenoid Osteotomies

“…Our case is in agreement with the experimental data and documents that correction of scapular anatomy can restore normal glenohumeral congruity in SPSL in vivo. Given the similarity of scapular pathology in static and dynamic posterior instability 22 , quantitative correction of the anthropometric abnormalities of the scapula may open a new way for the understanding and treatment of posterior shoulder instability. n…”

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

“…Although Walch et al stated that static posterior subluxation of the humeral head preceded posterior glenoid wear, with glenoid retroversion as a risk factor [11,13], there is currently no consensus regarding this chicken-or-egg debate [6,14,15]. To our knowledge and despite the recent study by Beeler et al [10], there are no published data on the correlation between the detailed three-dimensional (3D) acromion shape and glenoid retroversion.…”

“…Furthermore, Meyer et al were able to link a decreased posterior acromion slope and increased glenoid retroversion with static posterior subluxation of the humeral head and posterior glenoid wear [9]. More recently, Beeler et al reported that the scapula of a shoulder with dynamic and static posterior instability was characterized by an increased glenoid retroversion and an acromion that was shorter posterolaterally and higher and more horizontal in the sagittal plane [10].…”