Back pain of working pregnant women: identification of associated occupational factors.

The objective of this study was to identify major occupational factors that were significantly correlated with back pain in pregnant women working in higher education, health care and service areas. A total of 73 working pregnant women were surveyed using questionnaires specifically designed for evaluating correlations between occupational factors and severity of back pain; 37 women were interviewed at both 20 and 34 weeks of pregnancy, 17 at 20 weeks only, and 19 were interviewed at 34 weeks only. "Rest breaks allowed" and "job autonomy" were negatively correlated with severity of back pain at 20 weeks of pregnancy. "Staying in a confined area" and "having restricted space" were positively correlated with severity of back pain at 34 weeks of pregnancy. The study suggests that allowing pregnant women to take more rest breaks and to have more job autonomy may reduce the severity of back pain during early pregnancy, and that allowing movement outside the working area and providing less restricted space may reduce back pain during late pregnancy.

Simulation of Codman's paradox reveals a general law of motion.

Codman's paradox refers to a specific pattern of motion at the shoulder joint. It asked how a mysterious axial rotation about the longitudinal axis of the arm occurred during two or three sequential arm rotations that did not involve rotation about the long-axis. The objective of this paper was to find how the mysterious axial rotation occurred in the Codman's paradox. First, Codman's paradox and Codman's rotation were defined in general situations that involved arm rotations about orthogonal axes starting from the neutral attitude as well as rotations about non-orthogonal axes and starting from non-neutral attitudes. Then a general law of motion was proposed to answer the question of the Codman's paradox, which is stated as when the long-axis of the arm performs a closed-loop motion by three sequential rotations defined as Codman's rotation, it produces an equivalent axial rotation angle about the long-axis. The equivalent axial rotation angle equals the angle of swing-the second rotation in the three sequential long-axis rotations. Validity of the proposed law of motion is demonstrated by computer simulation of various Codman's rotations. Clinical relevance of the proposed law of motion is also discussed in the paper.

Joint rotation between two attitudes in the spherical rotation coordinate system.

Three-dimensional joint rotation between two attitudes rather than starting from neutral position is the most common pattern of human movement. This paper presents a method for determining the joint rotations starting from a non-neutral attitude in the spherical rotation coordinate system based on a two-step rotation method. The method uses three spherical rotation angles that are consistent with clinical description of joint rotations and are mathematically proved to be sequence independent. The method can be easily understood by clinicians and applied in clinical practice. Two numerical examples of humeral rotations are presented to demonstrate the effectiveness of the method in dealing with different patterns of three-dimensional joint rotations between two attitudes.