Saturday, September 26, 2015

Reverse total shoulder - is there a need for new humeral stem design?

Effect of humeral stem design on humeral position and range of motion in reverse shoulder arthroplasty.

These authors used a three-dimensional computer model of reverse total shoulders to compare a traditional inlay Grammont stem  to a short curved onlay stem with different inclinations (155°, 145°, 135°) and offset (lateralised vs medialised). 

Altering stem design led to a nearly 7-mm change in humeral offset and 4 mm in the acromiohumeral distance (AHD). Different inclinations of the onlay stems had little influence on humeral offset and larger influence on decreasing the AHD. There was a 10° decrease in abduction and a 5° increase in adduction between an inlay Grammont design and an onlay design with the same inclination. Compared to the 155° model, the 135° model improved adduction by 28°, extension by 24° and external rotation of the elbow at the side by 15°, but led to a decrease in abduction of 9°. When the tray was placed medially, on the 145° model, a 9° loss of abduction was observed.

With varus inclination prostheses (135° and 145°), elevation remained unchanged, abduction slightly decreased, but a dramatic improvement in adduction, extension and external rotation with the elbow at the side was observed in the computer model.

Comment: There is great interest in trying different modifications of the reverse total shoulder. Our preference remains for a prosthesis (in which we have no financial interest) that allows (a) secure glenoid fixation with a large central threaded screw, (b) variability in the offset of the glenosphere from the glenoid bone (to enable East-West tensioning and to prevent contact between the humeral polyethylene and the glenoid ), (c) a straight stem than can be impaction grafted so that stress shielding is avoided, and (d) a 135 degree angle on the humeral component to optimize range of motion.  Here is an example case of a patient with pseudoparalysis after failed fracture and cuff surgery.

His shoulder is now painless with 150 degrees of active elevation. 

We're happy with our current approach (see this link).


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