Assessing anterior shoulder instability: Reliability of the humeral head centralization test

Background: Motor control impairment of the rotator cuff muscles is reported to compromise the stability of the glenohumeral joint. However, an easily applicable, reliable parameter for quantifying anterior translation of the humeral head during active arm movements is lacking. Therefore, a novel (humeral head centralization) test was developed and evaluated. Study design: Case-control study with reliability analysis (Level III). Methods: This research project examined the shoulders of 25 patients with anterior shoulder instability and 25 asymptomatic controls. A physical therapist assessed humeral head translation in both groups during shoulder external rotation and elbow extension using ultrasound imaging. For test-retest and inter-rater reliability, the ultrasound assessment was repeated by the physical therapist and a radiologist after one week. Patients, the physical therapist, and the radiologist were blinded to the test results. In the evaluation of the difference in translation between the patients and controls, the Wilcoxon rank sum test was employed. The test-retest and inter-rater reliability were estimated using Intraclass correlation coefficients (ICC2,1). Results: In patients, in active elbow extension, a significantly greater anterior translation of the humeral head was observed compared to participants in the asymptomatic group (p < .001). The test-retest reliability of the physical therapist demonstrated poor agreement for the external rotation movement (ICC2,1 0.32 (95% CI -0.08-0.63)) and moderate agreement for the extension movement of the elbow (ICC2,1 0.66 (95% CI 0.36-0.84)). The inter-rater reliability of the physical therapist and radiologist was moderate for both the external rotation (ICC2,1 0.51 (95% CI 0.16-0.75)) and elbow extension movements (ICC2,1 0.62 (95% CI 0.30-0.82)). Conclusion: Although translation of the humeral head during active elbow extension movement was increased in patients compared to controls, this study found difficulties in reliably measuring anterior glenohumeral translation. Therefore, this novel test, in its current form, cannot be recommended for use in clinical practice or research.