INTERITY OF THE REPAIRED ROTATOR CUFF: A ROENTGEN STEREOPHOTOGRAMMETRIC ANALYSIS WITH ULTRASOUND COMPARISON

Abstract

There is no non-invasive gold standard for measuring gap formation following rotator cuff repair; re-tears are reported both on MRI and Ultrasound. Roentgen Stereophotogrammetric Analysis (RSA) has previously been used to monitor microscopic migration of markers in rigid bodies. We present a novel RSA technique using a combination of 1mm tantalum beads and metal sutures to allow accurate monitoring of gap formation following rotator cuff repair. The RSA system combines a commercially made calibration cage with software developed at Imperial College. We verified the RSA system by analysing a movable glass phantom and comparing the data with precise physical measurements of the same object: it identified a 2mm distraction of the phantom to within 0.05mm. In vitro work involved cadaveric human shoulders. We placed three 1mm RSA tantalum beads in the greater tuberosity and three metal sutures in supraspinatus tendon. We then created a tear in supraspinatus at its insertion into the greater tuberosity. We were able to show that RSA images taken before and after the tear correlated closely with direct measurements. The processed data demonstrated movement associated with gap formation. We have performed two open rotator cuff repairs using trans-osseous sutures. During surgery RSA markers were inserted into the shoulder to allow post-operative monitoring of the repair (guided by the in vitro work). Direct measurements of the distance between markers each side of the repair were taken intra-operatively (T=O). RSA images were taken immediately post-operatively (T=1 hours), day 3, day 14, and day 84. The RSA data suggests gapping of typically 3mm may have occurred at the repair sites in both patients. Ultrasound imaging was performed at the same intervals by consultant musculoskeletal radiologists blinded to the RSA data. Preliminary results correlating the two modalities suggest that ultrasound can visualise gap formation accurately even immediately post-operatively.