2004 Volume 10 Issue 1 Pages 90-94
Since the report by Nachemson (1976) concerning pressure on L3 from various positions, it is believed that sitting in a semi-upright position is contraindicatory after lumbar spine surgery. Nachemson's report indicated that there was twice the amount of pressure or more sitting in a semi-upright position than in an upright one. In this paper, a logical investigation on disc load with regards to action and reaction was performed. When W means body weight and α inclination of the body axis, disc pressure is equal to W (sinα+√3 cosα) in a semi-upright position without back rest. This trigonometric function draws a curve whose peak is 2W at 30 degree and W at 90 degree. These results support the report by Nachemson. On the other hand, disc pressure is equal to W sinα in a semi-upright position with back rest, because reaction is caused by the back rest. As a result, sitting in a semi-upright position with back rest after lumbar spine surgery is a reasonable posture to adopt.