Impact of Sagittal Rotation on Axial Glenoid Width Measurement in the Setting of Glenoid Bone Loss
TAKE-HOME POINTS
- Standard 2-D CT scans of the shoulder are often aligned to the plane of the body as opposed to the plane of the scapula, which may challenge the ability to accurately measure glenoid width and GBL.
- Underestimations of GBL may lead to insufficient treatment of clinically meaningful GBL, thereby increasing the risk of instability recurrence; whereas overestimations of GBL may lead to unnecessary treatment, subjecting patients to increased surgical morbidity.
- AP glenoid width was consistently underestimated in uncorrected axial cut 1, the most caudal cut.
- AP glenoid width was consistently overestimated in uncorrected axial cuts 3 to 5, the more cephalad cuts.
- CORR 2-D CT scans or a 3-D reconstruction can help in accurately defining the anterior GBL in patients with shoulder instability.
GLENOID WIDTH
Similarly, as described by Gross and colleagues,15 the sagittal en face view was divided via 5 cuts, throughout a superimposed best-fit circle that closely represents the glenoid.9,15,20 For both the UNCORR and CORR, glenoid width (AP distance) was measured on the axial image at the widest point from AP cortex across the glenoid face.
PATIENT GROUPS
Utilizing the en face 3-D CT reconstruction view of the glenoid as the gold standard, patients were placed into 1 of 3 groups according to the degree of anterior GBL measured via the surface method.9,20 The groups were as follows:
I. 10% to 14.9% (N = 12)
II. 15% to 19.9% (N = 16)
III. >20% (N = 15)
STATISTICAL METHODS
Paired t-tests were used to compare all measurements between CORR and UNCORR scans for each of the 5 cuts. A P-value of .05 was used as the threshold for statistical significance in 2-tailed comparisons. Mean and standard errors are presented with standard deviations throughout the study. For interobserver reliability, the measurements between the observers, the intraclass correlation coefficient was calculated. All statistics were performed with SPSS (Version 22).
RESULTS
The study cohort was comprised of 19 left shoulders (44%) and 24 right shoulders (56%), including 36 male patients (84%) and 7 female patients (16%). The average age was 27.8 years (range, 21-40 years). The variability in measured difference, with respect to AP width, was 1.05 mm. The UNCORR CT scans required a mean correction for coronal inclination of 7.0° ± 5.8° (range, -8°-6°). The UNCORR CT scans required a mean correction for scapular angle of 30.2° ± 8.0° (range, 15°-49°). The mean angle of sagittal rotation required to align the glenoid face with the 12-o’clock to 6-o’clock axis was 24.2° ± 5.1 ° (range, 13°-30°). These results are summarized in Table 1.
Table 1. Mean Correction Values Required to Correct the Uncorrected Images to the Corrected Images | |||
Anatomic alignment | Mean (degrees) | Range (degrees) | SD (degrees) |
Scapular angle | 30.2 | 15-49 | 8.0 |
Coronal Inclination | 7.0 | -8-6 | 5.8 |
Sagittal rotation | 24.2 | 13-30 | 5.1 |
For all measurements, the intraclass correlation coefficient for independent observers for all cuts within the 3 groups was r >.900 in all cases.
On an optimized CT scan, over 5 standardized cuts across a best-fit circle of the inferior glenoid, there was a statistically significant absolute mean difference of 12.6% in axial AP glenoid width (2.86 mm ± 2.00 mm, P =.016) when compared with the UNCORR scan. This corresponds to a 3% to 21% error in measurement of the AP width of the glenoid.
Continue to: For the entire cohort...
