Poster 273: Vascularity Assessment of Quadriceps Tendon Donor Site After Anterior Cruciate Ligament Reconstruction Using Ultrasound with Superb Microvascular Imaging (SMI)

OBJECTIVES: Quadriceps tendon (QT) is an increasingly popular graft choice for anterior cruciate ligament reconstruction (ACL-R) (1). Evaluation of vascularity using ultrasound has been performed to assess the healing response of tendons (2). Ultrasound with Superb Microvascular Imaging (SMI) is a novel microvascular imaging technology capable of visualizing a slower and smaller blood flow relative to conventional doppler modalities and has been applied to evaluate the vascularity of tendons. Therefore, vascularity assessment using ultrasound with SMI would be helpful to understand the healing response of QT donor site after ACL-R. The objectives of this study were 1) to compare the vascularity of the QT donor site with the contralateral, nonoperative site, 2) to assess whether different areas of the QT donor site healed relatively faster than others, and 3) to assess changes in vascularity of the QT donor site following ACL-R at various pre- and postoperative timepoints. METHODS: Patients who were pre- and post ACL-R using QT autograft were included in this study. Those who had contralateral ACL-R using QT autograft and had additional surgery for meniscal pathology or manipulation under anesthesia following primary ACL-R, were excluded. Ultrasound examination was performed before ACL-R, and 2, 4, 6, 9, and 12 months after ACL-R using a 18-5 MHz linear ultrasound transducer (Aplio i800, Canon medical systems, Japan) by a single sports medicine expert with 11 years’ experience. Participants were positioned supine with the knee at 20˚ of knee flexion. The transducer was placed on the anterior aspect of the knee perpendicular to the longitudinal axis of the QT to obtain the short axis of QT. Short axis images were acquired at 0, 15, 30, and 45 mm proximal to the superior pole of the patella. QT vascularity was assessed using ultrasound with SMI (Figure 1). A three-second video at each location was used to capture the moment of greatest vascularity. To quantify the amount of the vascularity signal within the QT, the area ratio of the vascular signal was evaluated with respect to the total area of QT using Image J software (3). QT vascularity ratio between donor and contralateral sites was compared using Wilcoxon signed-rank test. Vascularity ratio among each timepoint or each assessment location was compared using a Friedman test followed by Bonferroni correction for post-hoc analysis. Statistical significance was set at p < 0.05. RESULTS: All tendons showed healing and no defects were observed at any timepoints. In total, 62 pre- and postoperative timepoints of 40 individuals (22 male, 18 female, 18 right, 22 left) with a mean age of 25.2 ±7.8 years were included for analysis. With regard to the contralateral site, there was no vascularity signal in greater than 85% of cases at any timepoints. No significant difference between donor and contralateral sides was seen preoperatively. After ACL-R, significantly greater vascularity within the donor site was observed compared to contralateral, nonoperative QT at 2 months (all assessment locations), 4 months (all assessment locations), 6 months (0, 15, and 30 mm proximal to the superior pole of the patella), 9 months (0 mm), and 12 months (0 and 15 mm) following ACL-R (Table 1). Vascularity ratio 6 to 12 months after ACL-R was greater at 0 or 15 mm than at 30 and/or 45 mm proximal to the superior pole of the patella (Figure 2). In addition, vascularity ratios 4 months after ACL- R were significantly greater than other timepoints (Figure 3). CONCLUSIONS: The most important finding of this study was demonstration of increased vascularity 4 months after ACL-R. According to literature on patellar tendon donor site, vascularity 2 months after ACL-R was greater than other timepoints by Doppler ultrasound (2). QT donor site healing speed was similar to that of patellar tendon donor site. In this study, vascularity was seen at all observed postoperative timepoints. Surgeons may consider careful closure of the donor site defect especially near the proximal pole of the patellar where healing was observed even until 12 months as demonstrated by high vascularity. Based on this study, QT is an excellent graft choice for patients with ACL tears. Further studies are warranted to investigate the timing of distal QT harvest site healing.