Wednesday, July 10, 2013

Computer guidance for a reverse total shoulder, is it of value?

3D navigated implantation of the glenoid component in reversed shoulder arthroplasty. Feasibility and results in an anatomic study

There is a fascination with the use of "3-D computer-guided navigation" to improve the results of shoulder arthroplasty. This study compared 15 navigated and 12 non-navigated cadaveric insertion of the guidewire for glenoid baseplate implantation in reverse shoulder arthroplasty. A Kirschner wire was placed freehand or with the use of a navigated drill guide. For the navigated procedures, a flat detector 3D C-arm with navigation system was used. The goal was to insert the Kirschner wire 12 mm from the inferior glenoid, with an inferior tilt of 10° and centrally in the axial scapular axis.

For the 3D C-arm navigated procedure, the reference array was positioned onto the scapular spine with two 3.0 mm Schanz screws pointing caudally over two small skin incisions. An optoelectronic camera was positioned at a location that enables tracking of both the flat detector 3D C-arm and reference array. Before performing a 3D scan, two-dimensional fluoroscopic images were obtained to identify the correct positioning of the 3D C-arm. For optimum image quality, a carbon table and 3D C-arm system were recommended.

The authors found the inferior glenoid drilling distance was 14.1 ± 3.4 mm for conventional placement and 15.1 ± 3.4 mm for the navigated procedure and that the inferior tilt was 7.4 ± 5.2° for conventional and 7.7 ± 4.9° for the navigated insertion. The glenoid version in the axial plane showed significantly higher accuracy for the navigated procedure, with a mean deviation of 1.6 ±4.5° for the navigated procedure compared with 11.5 ± 6.5° for the conventional procedure.

The authors do not quantitate the increased time and cost of computer guidance. These tests were not carried out in shoulders with the type of pathology encountered in patients needing reverse total shoulders, which may require special consideration of the ideal glenosphere positioning. They confined their analysis to the positioning of the guide wire and did not examine the effectiveness of navigation in placement of the glenosphere positioning. Insertion of two Schanz screws in the scapular spine is a concern and may predispose the spine to fracture. Finally, the radiation exposure is much higher in the navigation approach.

So, all in all, the case is not compelling for this navigation approach.  Instead, we have been impressed with the need to customize the procedure to the special anatomy of each patient - an approach in which navigation to some pre-conceived orientation is not applicable.

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