Roentgen stereophotogrammetric analysis.

Soon after Roentgen's discovery, the 'new' rays were used to produce stereoscopic images or used for spatial reconstruction of positions of foreign bodies. However, no systematic use of roentgen stereo measurements seems to have occurred until the 1970's, although many attempts have been made before. Since 1972, a system for roentgen stereophotogrammetry has been in use at the University Hospital in Lund. The system has been named RSA, roentgen stereophotogrammetric analysis. It is a complete system, including instrumentation for implanting tantalum landmarks, devices for calibration of the stereo roentgen set-up, and comprehensive software. Using different calibration set-ups, any part of the body can be investigated under different conditions using standard roentgen equipment. The computer programs make it possible to calculate spatial landmark coordinates from measured film coordinates, and further to calculate growth, and volume changes or kinematic variables in well-defined and generally used terms. After the basic principles have been established, a survey of applications grouped according to anatomic regions follows. Special emphasis is laid on total hip and knee replacement, which besides complex craniofacial and spinal disorders, are the most rewarding fields of study.