Saturday, February 6, 2016

Preoperative CT scan measurements - are they worth the trouble?

The effect of sagittal rotation of the glenoid on axial glenoid width and glenoid version in computed tomography scan imaging.

These authors point out that computed tomography (CT) scans of the shoulder are often not well aligned to the axis of the scapula and glenoid and that these malalignments can affect axial measurements of anterior-posterior (AP) glenoid width and glenoid version.

They studied 30 CT scans of the shoulder that were reformatted using OsiriX software multiplanar reconstruction. The uncorrected (UNCORR) and corrected (CORR) CT scans were compared for measurements of both (1) axial AP glenoid width and (2) glenoid version at 5 standardized axial cuts.

They found the mean difference in glenoid version was 2.6% (2° ± 0.1°; P = .0222) and the mean difference in AP glenoid width was 5.2% (1.2 ± 0.42 mm; P = .0026) in comparing the CORR and UNCORR scans. The mean angle of correction required to align the sagittal plane was 20.1° of rotation (range, 9°-39°; standard error of mean, 1.2°).

They concluded that uncorrected CT scans of the glenohumeral joint do not correct for the sagittal rotation of the glenoid, and this affects the characteristics of the axial images. Failure to align the sagittal image to the 12-o'clock to 6-o'clock axis results in measurement error in both glenoid version and AP glenoid width. Use of UNCORR CT images may have notable implications for decision-making and surgical treatment.

Comment: While there is no question that measurements of pre and postoperative glenoid orientation are of interest, we find that it is uncommon to need CT scans for 'decision-making and surgical treatment.'

The cost of using corrected scans to change the measurement of version by two degrees or the width by 1.2 mm is not provided.

We find that the necessary and sufficient information for the planning and conduct of shoulder arthroplasty can be gained from the economical standardized AP view in the plane of the scapula

and the standardized axillary view taken with the arm elevated 90 degrees in the plane of the scapula (position of function).


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