How to Improve the Prediction of Quadruple Semitendinosus and Gracilis Autograft Sizes with Magnetic Resonance Imaging and Ultrasonography

BACKGROUND Hamstring tendon grafts may have an unacceptable size for use in anterior cruciate ligament (ACL) reconstruction. Magnetic resonance imaging (MRI) has been proposed to predict the diameters of hamstring tendon grafts. HYPOTHESIS Preoperative ultrasonography (US) might reliably anticipate intraoperative 4-strand semitendinosus and gracilis tendon (4ST-GT) graft sizes similarly to MRI. An MRI evaluation of the hamstring tendons with a higher magnification may improve the accuracy of the method. STUDY DESIGN Cohort study (diagnosis); Level of evidence, 2. METHODS A total of 33 patients undergoing ACL reconstruction with a 4ST-GT graft and MRI performed at our institution were included. The cross-sectional area (CSA) of each semitendinosus tendon (ST) and gracilis tendon (GT) was calculated preoperatively with US and with MRI under 2× and 4× magnification. Intraoperative measurement of the final diameter of the 4ST-GT using a closed-hole sizing block with 0.5-mm increments was made. Pearson correlation coefficients were calculated to determine the relationship between the final intraoperative graft diameter of the 4ST-GT and the CSA of the ST and GT measured with US and MRI with 2× and 4× magnification. Simple linear regression was also calculated to attempt to predict the graft diameter based on given measurements. RESULTS There were statistically significant correlations between the measured CSA with US and both MRI magnifications with the 4ST-GT diameter. However, MRI under 4× magnification showed a much higer correlation (0.86) than MRI under 2× magnification (0.54) or US (0.51). Final graft diameters ≥8 mm were observed in 80.8% of patients with a CSA >14 mm(2), in 76.9% of patients with a CSA >25 mm2, and in 96.2% of patients with a CSA >17 mm2 measured with US, 2× magnification of MRI, and 4× magnification of MRI, respectively. CONCLUSION Preoperative calculation of the CSA of the hamstring tendons with MRI and US can help to reliably estimate 4ST-GT grafts. In terms of correlation of the CSA with graft diameter, US was comparable to 2× MRI, but 4× MRI showed a much greater accuracy. Threshold values of the CSA of the ST and GT of 25 mm2, 17 mm2, and 14 mm2 with the 2× MRI, 4× MRI, and US methods, respectively, are needed to reliably predict a 4ST-GT graft with a minimum diameter of 8 mm.