Intervertebral disc pressures during traction.

Pressures in the third lumbar discs were measured in vivo during active and passive traction. During active traction an increase in pressure was always recorded, with larger increases corresponding to larger traction forces. During passive traction the pressure remained close to the resting pressure; sometimes slight increases were recorded, sometimes slight decreases. It is concluded that when traction is applied so that the back muscles contract, then disc pressures will increase.