Wednesday, March 1, 2017

Reverse total shoulder - the value of 3D planning

Preoperative Planning for Accurate Glenoid Component Positioning  in Reverse Shoulder Arthroplasty

These authors used a 3D virtual mode to estimate the accuracy of glenoid component positioning when only the glenoid surface is visible compared to when the entire scapula is visible. CT scans of 30 arthritic shoulders were reconstructed in 3D models. Two surgeons then virtually placed a glenosphere component in the model while visualizing only the glenoid surface, in order to simulate typical intraoperative exposure (“blind 3D” surgery). One surgeon then placed the component in an ideal position while visualizing the entire scapula (“visible 3D” surgery).

The implant modeled is shown here

Perforation of the glenoid vault was evaluated visually by assessing whether the central keel could be seen outside the vault on 2D and 3D-CT views as shown below.

Mean version and tilt after "blind 3D" surgery were +1.4° (SD 8.8°) and  +7.6° (SD 6°), respectively; glenoid vault perforation occurred in 17 specimens.
Mean version and tilt after "visible 3D" surgery were +0.3° (SD 0.8°) and +0.1° (SD 0.5°), respectively, with glenoid vault perforation in 6 cases.

The authors concluded that "when the entire scapula is used as reference, accuracy is improved and  glenoid vault perforation is less frequent. This type of visualization is only possible with pre-operative 3D CT planning, and may be augmented by PSI."

Comment: This article brings up several questions:
(1) Does this model reflect the way surgeons implant reverse arthroplasties in patients?
(2) How big a problem is glenoid vault perforation?
(3) Were the differences noted clinically significant?
(4) Are these results relevant to this prosthesis design or are they generalizable to other designs (i.e. those without a keel)?
(5) What is the added cost in dollars and time of pre-operative 3D CT planning and PSI?

By contrast, here is a reverse total shoulder we did yesterday without a preoperative CT scan, 3D planning or PSI. There was no unintended glenoid perforation and the desired component position was achieved.


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