Monday, May 19, 2014

Three-dimensional preoperative planning software to position a glenoid guide pin - what is its value?

Three-dimensional preoperative planning software and a novel information transfer technology improve glenoid component positioning.

The authors propose that their proprietary surgical method, in which three-dimensional preoperative planning software is used to create a patient-specific surgical model along with a transfer device, could substantially improve the positioning accuracy of a glenoid guide pin they use in total shoulder arthroplasty.

Their surgeons placed a guide pin in nine plastic bone models from patients with a variety of glenohumeral arthritis severities using (1) standard instrumentation alone, (2) standard instrumentation and their 3-D preoperative surgical planning software, and (3) their reusable transfer device and 3-D preoperative surgical planning. A postoperative 3-D computed tomography scan of the bone model was made and registered to the preoperative plan, and the differences between the actual and planned pin locations and trajectories were measured.

The accuracy of pin positioning increased by 4.5° in version, 3.3° in inclination, and 0.4 mm in location. Use of their transfer device and the 3-D software improved pin positioning by a further 3.7° in version, 8.1° in inclination, and 1.2  mm in location.

Comment: We are not provided with the incremental cost and time necessary for this type of planning and instrumentation nor with evidence on its utility in real patients rather than plastic models. Thus the value of the system remains to be determined. While the authors' implant technique apparently uses a guide pin, many systems do not because of the potential risk of inadvertent pin advancement or breakage. Finally, attempts to 'normalize' the position of the glenoid by eccentric reaming, bone grafting or special augmented glenoid components have yet to be shown to improve the longevity of the glenoid component in total shoulder arthroplasty.

We applaud efforts to improve the technique of shoulder arthroplasty, but need to be sure that incremental cost and time consumption are justified by improved clinical outcomes.


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