Scapular Ring Preservation

Abstract

Background: Scapular fractures following reverse total shoulder arthroplasty (RSA) are devastating complications with substantial functional implications. The role of the coracoacromial ligament (CAL), which is often transected during surgical exposure for RSA, is not fully known. We hypothesized that the CAL contributes to the structural integrity of the “scapular ring” and that the transection of this ligament during RSA alters the scapular strain patterns. Methods: RSA was performed on 8 cadaveric specimens without evidence of a prior surgical procedure in the shoulder. Strain rosettes were fixed onto the acromial body (at the location of Levy type-II fractures) and the scapular spine (Levy type III). With use of a shoulder simulator, strains were recorded at 0°, 30°, and 60° glenohumeral abductions before and after CAL transection. The deltoid and glenohumeral joints were functionally loaded (middle deltoid = 150 N, posterior deltoid = 75 N, and joint compression = 300 N). Maximum principal strains were calculated from each rosette at each abduction angle. A repeated-measures analysis of variance with post hoc analysis was performed to compare the maximum principal strain at each abduction angle. Results: With the CAL intact, there was no significant difference between strain experienced by the acromion and scapular spine at 0°, 30°, and 60° of glenohumeral abduction. CAL transection generated significantly increased strain in the scapular spine at all abduction angles compared with an intact CAL. The maximum scapular spine strain observed was increased 19.7% at 0° of abduction following CAL transection (1,216 ± 300.0 microstrain; p = 0.011). Following CAL transection, acromial strains paradoxically decreased at all abduction angles (p < 0.05 for all). The smallest strains were observed at 60° of glenohumeral abduction at the acromion following CAL transection (296 ± 121.3 microstrain; p = 0.048). Conclusions: The CAL is an important structure that completes the “scapular ring” and therefore serves to help distribute strain in a more normalized fashion. Transection of the CAL substantially alters strain patterns, resulting in increased strain at the scapular spine following RSA. Clinical Relevance: CAL preservation is a modifiable risk factor that may reduce the risk of bone microdamage and thus the occurrence of fatigue/stress fractures in the scapular spine following RSA.

Botulinum toxin as adjunct therapy in surgical management of a periprosthetic scapular spine fracture: a case report

“…abduction [7,9]. Additionally, the coracoacromial ligament has been shown to be an important stabilizing structure of the scapular ring -its transection results in increased scapular spine strain after RSA [9].…”

“…abduction [7,9]. Additionally, the coracoacromial ligament has been shown to be an important stabilizing structure of the scapular ring -its transection results in increased scapular spine strain after RSA [9]. For these biomechanical reasons, scapular spine fractures in the setting of RSA have proven difficult to heal, both after non-operative and surgical management.…”

Development of a framework to assess the biomechanical impact of reverse shoulder arthroplasty placement modifications

“…Prominent examples include limited range of motion due to intra-and extra-articular impingement, 9,10 instability and dislocation of the joint due to insufficient deltoid tension, 11 and fractures of the acromion or scapular spine due to excessive deltoid tension. 12,13 To address these complications, several modifications to the RSA design have been studied. Examples of design modifications include lateralization of the glenosphere, 14,15 changes to glenosphere diameter, 16 humeral tray type (inlay vs. onlay), humeral stem neck-shaft angle, 17 and humeral cup depth.…”

“…Examples of glenoid and humeral component placement modifications include lateralization of the glenosphere using bone grafts, 18 glenosphere inferior translation, 9,10,[19][20][21] glenosphere inclination, 19,21 and humeral tray translation. 22,23 These studies used varied methodologies (from retrospective reviews [10][11][12] to cadaveric experiments 9,13,14,16,20 to computational methods 15,[17][18][19][21][22][23] ) to evaluate how prosthesis modifications can affect the biomechanics of RSA. Furthermore, these studies used differing independent variables (such as different prosthesis designs), assessed different motions, and evaluated different outcomes (e.g., range of motion, muscle and joint loading, or joint stability) to determine the biomechanical outcomes for a given modification.…”

“…Despite commercial growth, concerns remain regarding RSA complications. Prominent examples include limited range of motion due to intra‐ and extra‐articular impingement, 9,10 instability and dislocation of the joint due to insufficient deltoid tension, 11 and fractures of the acromion or scapular spine due to excessive deltoid tension 12,13 . To address these complications, several modifications to the RSA design have been studied.…”