Wednesday, January 25, 2017

Is the 'critical angle' critical?

Does the Critical Shoulder Angle Correlate With Rotator Cuff Tear Progression?

These authors point out that the critical shoulder angle (CSA) has previously been reported to be associated with rotator cuff disease and has been suggested as an etiology for cuff tears.

In this study they asked, "(1) How often can the CSA be reliably measured? (2) Is the CSA associated with rotator cuff disease? (3) Is the CSA correlated with baseline tear size or tear enlargement? (4) Does the CSA change with time?"

In their study they included 313 patients with radiographs, only 179 of which (57%) had radiographs meeting the criteria for inclusion in the analysis. 50 of 119 (42%) control subjects met the criteria.

In total, of the 1552 radiographs evaluated, only 326 (21%) were of sufficient quality to measure the CSA. 

The CSA averaged 2° higher among patients with cuff tears in comparison to control subjects (34° ± 4° versus 32° ± 4°; mean difference, 2.0°; 95% CI, 0.7°–3.2°; p = 0.003). 

The CSA did not correlate with baseline tear length (ρ = 0.22, p = 0.090) or width (ρ = 0.16, p = 0.229). 

The CSA was not different between tears that enlarged and those that were stable (34° ± 3° versus 34° ± 4°; mean difference, 0.2°; 95% CI, −0.9° to −1.4°; p = 0.683). 

The CSA did not change over time (CSA Time 1: mean 33° ± 4° SD; CSA Time 2: mean 33° ± 4° SD; mean difference, −0.2°; 95% CI, −0.6° to 0.1°; p = 0.253).

The authors concluded that most radiographs were of insufficient quality for CSA measurement. Although patients with a history of degenerative cuff disease have higher CSA values than control subjects, the difference is small enough that it could be influenced by measurement error in practice; in any case, a difference of the magnitude we observed is likely to be clinically unimportant. The CSA is not correlated with tear size or tear progression, and does not seem to change with time. These results suggest that the CSA is unlikely to be related to rotator cuff disease.

Comment: As was the case for the different types of acromion seen on the AP view, previous authors have proposed that the CSA plays a role the pathogenesis of cuff tears. As revealed by this large well-characterized patient cohort, the contribution of the 'critical shoulder angle' to our understanding of rotator cuff failure or its role in determining patient management appears limited. 

Interested readers may wish to visit this related post: The 'critical' shoulder angle- cause or effect of shoulder pathology?

Another recent article suggests that a higher CSA is associated with retear after rotator cuff repair. See this link Higher critical shoulder angle increases the risk of retear after rotator cuff repair

They reviewed 76 patients who had undergone rotator cuff repair with postoperative ultrasound examination. Ultrasound findings were graded no retear (NT), partial-thickness (PT) retear, or full-thickness (FT) retear. Preoperative radiographs were used to measure CSA, glenoid inclination, lateral acromion angle, and acromion index.

On ultrasound examination, 57 shoulders (74.0%) had NT, 11 (14.2%) had PT retears, and 8 (10.3%) had FT retears. There was no significant difference in retear rate by age, gender, or tension of repair. 

Average CSA was significantly lower for the NT group at 34.3° ± 2.9° than for the FT group at 38.6° ± 3.5° (P < .01). If CSA was >38°, the odds ratio of having an FT retear was 14.8 (P < .01). In addition, higher CSA inversely correlated with postoperative American Shoulder and Elbow Surgeons scores (P < .03). Average glenoid inclination was significantly lower in the NT group at 12.3° ± 2.7° compared with 17.3° ± 2.6° in the FT group (P < .01). If glenoid inclination was >14, the odds ratio of having a FT retear was 15.0 (P < .01).

While this article concluded that at short-term follow-up, "higher CSA significantly increased the risk of an FT retear after rotator cuff repair," a plot of the data shows that the standard deviations are large in respect to the differences among the groups, so that the utility of the measurement in predicting the outcome for individual case is likely to be limited.


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