Abstract
Aims
Interest in soft tissue Radiostereometric Analysis (RSA) is rising. Previous authors have tried, with varying levels of success, to use this technique to analyse the intra-substance portion of anterior cruciate ligament (ACL) graft constructs. 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 made RSA an attractive tool in the first place. We describe a modification of tantalum marker balls that allows for a new method of secure fixation to soft tissue in order to accurately analyse stretch, displacement and, potentially, dynamic movement using RSA.
Methods
1.5 mm tantalum tendon markers were predrilled with 0.3 mm holes, allowing them to be sutured directly to soft tissue. Using a previously described ACL graft model, the amount of marker ball migration was then analysed using RSA after cyclical loading between 20 N and 170 N at 25 Hz for 225,000 cycles.
Results
None of 40 balls loosened or became detached from the tendon grafts after 225,000 cycles. Mean migration of the tendon attached marker balls was < 0.1 mm. The maximum imprecision in determining the distance between two markers as assessed by intra- and inter-observer variability was 0.082 mm. Analysis of elastic stretch, plastic stretch, stiffness and localisation of stretch within the graft model was possible due to the low migration levels.
Conclusions
This method of attachment of marker beads to soft tissue is simple, reliable and mechanically sound. This technique could potentially be used not only for the post-operative assessment of ACL reconstruction, but in all areas where soft tissue RSA is of interest.
