Atrophy of the infraspinatus(ISP) is one of the most common findings in rotator cuff tears. The purpose of this study was to investigate the relationship between the thickness of ISP and the location in the rotator cuff tear, and between the shoulder external rotational muscle strength (ERMS) and the location in the rotator cuff tear. We examined the thickness of ISP and ERMS of both shoulders in 30 healthy volunteers. We found out the statistical differences for the thickness of ISP between the non-dominant side and dominant side.30 patients with a rotator cuff tear in the dominant side were enrolled in this study. The patients were grouped according to the location of the tear with MRI. Typel (10 cases) had isolated supraspinatus(SSP) tears. Type2 (13 cases) involved SSP-ISP tears. Type3 (7cases) involved ISP tears. The muscle strength was measured with a hand-held dynamometer(MICRO FET): ISP-test at hanging arm, ER II -test at 90 degrees abduction. The thickness of ISP was measured with an ultrasonographic device at rest and on active. The point of the measurement was medial 1/4and 3cm inferior from the scapula's spine. The rates of affected (dominant) / unaffected in ISP-test were 103.2%: volunteers,88.4%(p<0.05): typel,80.0%(p<0.01): type2 and 63.3%(p<0.01): type3. The rates in ER 11 -test were 101.1%: volunteers,88.1%(N. S): typel,68.9%(p<0.05): type2 and 55.7%(p<0.01): type3. The rates in thickness of ISP were 113.9% at rest; 1112% on active: volunteers,110.5%(N. S) at rest; 101.3%(N. S) on active: typel,98.8%(N. S) at rest; 89.7%( p<0.05) on active: type2,85.7%(p<0.05) at rest; 86.4%(p<0.05) on active: type3. We concluded that the cuff tear became enlarged from the SSP to the ISP, if atrophy of the ISP was found.
