To elucidate the relationship between the wrist-bending force and forearm position, the force of the right hand produced by maximal isometric contraction toward extension, extension/adduction, adduction, flexion/adduction, flexion, flexion/abduction, abduction, and extension/abduction directions (45° step) with the prone (P), semiprone (SP), and supine forearm (S) was measured in twenty righthanded normal men. The force of extension/abduction, extension, flexion, and flexion/adduction was large and that of extension/adduction was small with P, that of abduction and extension/abduction was large and that of extension/adduction was small with SP, and that of flexion/adduction and flexion was large and that of extension, extension/adduction, adduction, flexion/abduction, abduction, and extension/abduction was small with S. The force of extension with P was the largest, next was that with SP and smallest that with S. The force of abduction with SP was the largest, next was that with P and smallest that with S. The force of flexion/adduction was large with S and small with SP, that of flexion/abduction was large with SP and small with S, and that of extension/abduction was large with P and SP and small with S. The results suggest that directions for large force are changed by changing the forearm position. The force seems to become larger when its directions are toward the trunk or face.

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Changes of a wrist motion range by changing the forearm position were studied. 2-D trajectories (coronary plane) of the head of the third metacarpal of the right hand during a wrist full circumduction movement in the 90° pronated (prone: P), 0° pronated (neutral or semiprone: SP), and 90° supinated (supine: S) position of the forearm were plotted in twenty healthy right-handed men. Trajectories were ellipsoid in shape in every forearm position. The range of extension and adduction was larger in SP than in P and that of flexion was the largest in P, next was in SP and smallest in S. The area of the ellipse was larger in P and SP than in S. The long axis of the ellipse tended to be longer in SP than in S and the short axis to be in P and SP than in S. Changing the position from P to SP and from SP to S resulted in approximately 20° step counterclockwise rotation of the long axis. These findings suggest that the range is complicatedly changed by changing the forearm position, it becomes smaller in S, and the direction, in which wrist swing motion becomes larger, turns counterclockwise with supinating the forearm.

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Our previous studies proposed new sites for intramuscular injection into the deltoid muscle instead of an injection site three finger breadths below the acromial lateral edge. They were determined as follows: The distance between the midpoint (a point) at the lateral edge of the acromion and the intersection point (b point) where the perpendicular line from the a point crossed the anteroposterior axillary line (b point) was measured using a tape measure along the surface of the deltoid muscle, divided into three and two equal segments (upper 1/3ab, 1/2ab, lower 1/3ab points), and the upper 1/3ab, 1/2ab, and b points were regarded as new sites for intramuscular injection. We invented a new tool like a carpenter's iron square for easy determination of the intramuscular injection sites. In this study, we compared whether the upper 1/3ab, 1/2ab, and lower 1/3ab sites determined using the tape measure were the same as those using the new tool, with 11 male cadavers aged 83.6 ± 9.3 and 8 female cadavers aged 84.3 ± 10.9. In order to discuss the safety of the intramuscular injection sites, gel was injected at the 1/2ab site determined using the tape measure and the relationship between the axillary nerve and the gel was observed. The muscle thicknesses at upper 1/3ab, 1/2ab, and b sites determined using the tape measure were also measured and compared. The upper 1/3ab and 1/2ab sites measured using the new tool were lower by about 5.8 mm in males and about 7.0 mm in females, and about 4.4 mm in males and about 5.3 mm in females, than those using the tape measure, respectively. The lower 1/3ab sites using the tape measure and the new tool were almost the same and the axillary nerve was observed at this site. The 1/2ab site using the tool was higher by about 14.8 mm in males and 13.5 mm in females than the lower 1/3ab site where the axillary nerve was situated. Gel injected into the 1/2ab site spread in an oval shape, and the axillary nerve was not situated in the center of the gel but at the lower edge of gel or quite separate from the lower edge of it. Muscle thicknesses at 1/2ab and b sites were almost the same, and thicker by about 4 mm in males and about 5 mm in females than at the upper 1/3ab site. From these results, the upper 1/3ab site using the tool is suitable for intramuscular injection like that using the tape measure because avoidance of the site of the axillary nerve can be achieved; therefore, the new tool is useful and safe for determining the sites of intramuscular injections into the deltoid muscle. Moreover, since the muscle at b site is thicker than at upper 1/3ab and the distance from b site to the axillary nerve is larger than that at 1/2ab, this site is more appropriate for safe intramuscular injection.

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