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In Vivo Assessment of the Tensor Vastus Intermedius Cross-sectional Area Using Ultrasonography

LEVEL OF EVIDENCE: 2B SUMMARY Background. There is growing evidence that the quadriceps muscle group includes a fifth head, the tensor of vastus intermedius (TVI). The purpose of this study was to quantify the anatomic cross-sectional area (CSA) of the TVI using ultrasound. Methods. Ultrasonography scans were taken from 21 young males and females at rest, at 0° (= full extension), 45° and at 90° of knee flexion and they were repeated a week after to establish reliability. Measurements of the CSA were obtained from the most proximal and the most distal part of the muscle belly and from three different parts toward the course of the tendon. Results. US evaluation of the CSA displayed high reliability with an intraclass coefficient (ICC3,3) ranging from 0.85 to 0.99 and a standard error of measurement ranging from 0.0019 to 0,2789 mm2. Analysis of variance indicated that the TVI muscle belly was larger proximally than distally and it was smaller at full extension compared with greater flexion angles (p < 0.05). The tendon CSA was greater proximally than middle and distal measurement sites (p <0.05) but it did not differ between various knee flexion angles. Conclusions. Future studies on the quadriceps muscle function and morphology should include examination of the TVI.