A new technique for the radiostereometric analysis of soft tissues

BACKGROUND: Interest in soft tissue RadioStereometric Analysis (RSA) is rising. Previous studies have attempted to use this technique to analyse anterior cruciate ligament (ACL) graft constructs, and more recently, the movement of soft tissue as a precursor to RSA follow up of rotator cuff repairs. These methods were either prone to large amounts of marker migration, deemed unsuitable for in vivo use or, where alternative markers such as stainless steel sutures were used, lost the inherent accuracy that makes RSA an attractive tool in the first place. We describe a modification of tantalum marker balls that allows for immediate secure fixation to soft tissue in order to accurately analyse stretch and displacement of soft tissues using RSA. METHODS: 1.5mm tantalum marker balls were converted to marker beads by pre-drilling with 0.3mm holes, allowing them to be sutured directly to soft tissue. Using an established ACL graft model, the amount of marker micro-motion was then analysed by RSA after cyclical loading between 20N and 170N at 25Hz for 225,000 cycles. FINDINGS: None of 40 marker beads loosened or became detached after 225,000 cycles. Mean micro-motion of the markers was