Here are some recent topics and articles of interest regarding the reverse total shoulder.
*The fixation of single piece (non-modular, monobloc) reverse total shoulder humeral components is more stable than that of modular components when the proximal humeral bone is deficient.
The authors of Torsional stability of modular and non-modular reverse shoulder humeral components in a proximal humeral bone loss model tested the torsional stability of three reverse humeral stem designs (two modular and one monobloc) in Sawbones humeri prepared to simulate intact and proximal humeral bone loss. All fixation failures, whether in intact or bone loss humeri, were in modular implants. In the bone loss model, all of the modular humeral components failed at the connection between the humeral socket and the humeral stem. None of the single piece (non-modular, monobloc) (shown below) humeral components failed in either the intact or bone loss humeri.
*Who gets acromial/spine fractures and in what part of the scapula do they occur?
From Predictive factors of acromial fractures following reverse total shoulder arthroplasty: a subgroup analysis of 860 shoulders, from Acromion Fractures after Reverse Shoulder Arthroplasty Occur in Predictable Clusters and from Predictors of acromial and scapular stress fracture after reverse shoulder arthroplasty: a study by the ASES Complications of RSA Multicenter Research Group we see that the great majority (80%) of the patients with acromial fractures complicating reverse total shoulder had their RSA performed for rotator cuff deficiency. This observation suggests that the deltoid origin on the acromion/scapular spine is at increased risk of fatigue fracture following RSA if the stabilizing and supporting function of the rotator cuff is absent.
CT analysis showed the fracture locations were evenly distributed among four locations on the scapula (Acromion Fractures after Reverse Shoulder Arthroplasty Occur in Predictable Clusters)
Outcomes of conservative treatment of acromial and scapular spine stress fracture post reverse shoulder arthroplasty – a systematic review with meta-analysis noted that non-operative treatment of Type 3 fractures tended to have worse clinical outcomes than non-operative treatment for the other types of fractures.
Since instability is an important risk after reverse total shoulder arthroplasty, one might think that a deeper humeral socket (i.e. a "constrained" liner) would improve the stability of the articulation.
However, the range of glenohumeral motion after a reverse total shoulder relies on freedom from unwanted contact (impingement) between the humeral and scapular elements. In contrast to the hip, which is stabilized by a deep socket, the reverse glenohumeral joint has a shallow socket and is stabilized by concavity compression; see Understanding the dislocating reverse total shoulder: concavity compression. Impingement can not only restrict the range of motion, but can also cause instability as the articular surfaces are levered apart when the humeral cup contacts the scapula.
The authors of Impact of constrained humeral liner on impingement-free range of motion and impingement type in reverse shoulder arthroplasty using a computer simulation aimed to determine the influence of humeral liner constraint (depth) on impingement-free ROM utilizing a computer simulation model. They found that impingement-free ROM was reduced during abduction, external rotation, and internal rotation with the combination of a standard glenosphere and constrained humeral liner. Abduction was limited by contact between the constrained liner and the superior glenoid neck (see figure below). This effect was less with a lateralized glenosphere.
Retentive (constrained) liners can also risk unwanted liner-glenoid contact inferiorly, posteriorly and anteriorly.
*Are we asking the right question?
The authors of Reverse shoulder arthroplasty for primary glenohumeral osteoarthritis: significantly different characteristics and outcomes in shoulders with intact versus torn rotator cuff found that at 2 years following reverse total shoulder arthroplasty, Constant scores were significantly better for primary osteoarthritis (OA) with intact rotator cuff, compared to either primary OA with rotator cuff tears or cuff tear arthropathy (OA secondary to cuff tears).
Notably, one in ten patients having OA with intact rotator cuff experienced a complication (intraoperative humeral fracture, intraoperative glenoid fracture, glenoid loosening, perioperative fracture, neurologic injury).
The point is that we can't change a patient's diagnosis, so this study is unlikely to change treatment. The question that needs to be answered is, "in matched patients with primary osteoarthritis and an intact rotator cuff, how do the results compare between anatomic and reverse total shoulders?" How likely is it that an anatomic total shoulder is complicated by humeral fracture, glenoid fracture, neurologic injury, acromial fracture, or dislocation?
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
