Reliability and validity of a new method of measuring posterior shoulder tightness

Abstract

Study design: Repeated measures of shoulder flexibility on nonimpaired subjects and intercollegiate baseball pitchers.

Objectives: To present a new objective method of measuring posterior shoulder tightness, define the intratester and intertester reliability of the measurement, and assess its construct validity.

Background: Posterior shoulder tightness has been linked to anterior humeral head translation and decreased internal rotation. The reliability of an objective assessment of posterior shoulder tightness has yet to be established in the literature.

Methods and measures: Five repeat measurements were made using a standardized protocol on 21 nonimpaired subjects to determine intratester reliability. To determine intertester reliability, 2 testers (blinded to their measurement) each performed 1 measurement on 49 shoulders. Twenty-two intercollegiate baseball pitchers were measured once by 1 tester to evaluate the construct validity of the measurement.

Results: Measurements of posterior shoulder tightness performed by the same physical therapist had high reliability (ICC dominant = 0.92, nondominant = 0.95). Intertester measures revealed good reliability (ICC = 0.80). Pitchers had reduced dominant arm internal rotation and increased external rotation ROM compared to their other arm whereas nonimpaired subjects had less reduction in external rotation compared to the nondominant arm (pitchers: dominant, 109.7 degrees +/-2.4 degrees, nondominant, 98.9 degrees +/-1.6 degrees; nonimpaired subjects: dominant, 95.9 degrees +/-1.5 degrees, nondominant, 95.2 degrees +/-1.6 degrees) and internal rotation (pitchers: dominant, 50.0+/-2.0 degrees, nondominant, 69.5+/-2.5 degrees; nonimpaired subjects: dominant, 46.4+/-1.3 degrees, nondominant, 50.2+/-1.4 degrees). Pitchers had significantly greater posterior shoulder tightness compared to nonimpaired subjects (pitchers; dominant, 44.9+/-0.8 cm, nondominant, 37.5+/-0.7 cm, nonimpaired subjects; dominant, 32.9+/-0.8 cm, nondominant, 31.4+/-0.8 cm) and manifested a significant correlation between posterior shoulder tightness and internal rotation (r = -0.61) that was not evident in nonimpaired subjects.

Conclusions: Measurement of posterior shoulder tightness using this technique is objective and reliable when done by the same physical therapist. Validity of this measurement is supported from the observation of athletes thought to have tight posterior structures. Further study is needed to determine the relationship of this measurement to patients diagnosed with shoulder impingement syndrome.