Correlation between semitendinosus and gracilis tendon cross-sectional area determined using ultrasound, magnetic resonance imaging and intraoperative tendon measurements.

The purpose of this study was to examine the correlation in semitendinosus (ST) and gracilis (GT) tendon cross-sectional area (CSA) evaluated directly during anterior cruciate ligament (ACL) surgery and pre-operatively using ultrasound (US) and magnetic resonance imaging (MRI). A total of 14 patients undergoing ACL reconstruction with a quadruple ST-GT graft by the same orthopaedic surgeon participated in this study. Pre-operative evaluation included determination of ST and GT CSA area using US and MRI. Intraoperative measurement of the diameters of the ST, GT and the final ACL graft using a closed-hole sizing block with 0.5-mm increments was made and this diameter was used to estimate tendon CSA. The correlation between graft diameter and CSA were 0.563 (GT) and 0.807 (ST) for MRI and 0.498 (GT) and 0.612 (ST) for US. The final ACL graft diameter displayed a correlation coefficient of 0.813 with MRI CSA and 0.518 with US CSA. No differences in CSA were observed between intraoperative, MRI and US methods (p>0.05). The intraclass correlation coefficients between the US, MRI and intraoperative graft methods for the ST and GT data ranged from 0.502 to 0.903 with an estimation error ranging from 1.41% to 2.26%. These results indicate that in clinical situations where MRI is contra-indicated or not accessible, US can provide measurable values which could predict sufficient diameter of the ACL graft. In addition, determination of tendon CSA using US displays errors less than 2% which is similar to that observed using MRI. This suggests that the application of US can be applied to in vivo examination of the ST and GT CSA.