Sunday, March 10, 2013

Component position after total shoulder arthroplasty

Development and validation of a new method of 3-dimensional assessment of glenoid and humeral component position after total shoulder arthroplasty

This article assesses the intrarater and inter-rater reliability of 3-dimensional CT measurements of component position and alignment after total shoulder arthroplasty in two patients and one cadaver. The imaging techniques described require utilization of thin-section CT imaging with slice thickness of less than 1 mm and image acquisition of the entire scapula. The accuracy of the described methods is dependent on the  imaging software and the accuracy of virtual placement of the digital implant templates - the user is required to accurately place the virtual implant over the defects in the bone created by the actual implant and align the metal marker within the actual implant. In that the inference of the location of the glenoid component is from the location of the defects in the glenoid bone created by the pegs, the analysis becomes more difficult when there is distortion or radiolucencies around the implant.

The authors found that the precision of the measurements were related to observer experience, with the least experienced observer having the worst results. Of interest is that the anteroposterior position of the humeral head relative to the glenoid was different for the two arm positions studied: arm overhead and arm at the side. The authors conclude that this method can provide very precise and reproducible assessment of component position after shoulder arthroplasty, suggesting that correlation of these measurements with clinical outcome, anatomic factors, prosthetic design, and surgical factors will allow for better understanding of the causes of implant failure.

The authors do not provide data on the time to complete the analysis, the costs associated with the application of the method and the radiation exposure to the patient - factors which would discourage the general use of this method. This is even more the case if, as the authors suggest, the method is to be used for comparison of preoperative and postoperative glenohumeral anatomy or for sequentially following changes in component position.

Thus one must consider whether the benefit of this method is sufficient to justify its cost in time, dollars and radiation.

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