A new technique for the radiostereometric analysis of soft tissues.

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. 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 20 N and 170 N at 25 Hz for 225,000 cycles. None of 40 marker beads loosened or became detached after 225,000 cycles. Mean micro-motion of the markers was <0.1mm. Analysis of elastic stretch, plastic stretch and stiffness of the graft model was possible. This method of attachment of tantalum markers to soft tissue is simple, reliable and provides immediate stability. Although further work is required to establish its suitability for in vivo use, this technique could potentially be used in all areas where soft tissue RSA is of interest.