Reliability of a Two-Scan Ultrasonography Method for Evaluating Patellar Tendon Stiffness

Studies have suggested that the unwanted movement of the tibia during isometric knee extension tasks caused substantial errors in evaluating patellar tendon stiffness with in vivo ultrasonographic methods. Methods have been used to adjust for the displacement at the tibial end of the patellar tendon, including a longer probe approach that can cover both ends of the patellar tendon during maximal muscle contraction of quadriceps. However, due to the limited accessibility of such a probe, a more accessible method would be useful. Therefore, we proposed a two-scan method with a standard ultrasound transducer to replace the conventional ultrasound method. The purpose of this study is to compare the reliability of the conventional ultrasound measurement method, which measures only the displacement of patellar insertion of the tendon, to a two-scan method that adjusts for tibial movement. Patellar tendon stiffness of thirteen healthy subjects was examined twice at different days with two methods. Tendon stiffness was compared between the methods as was between-day reliability of each method. Our results showed that the conventional ultrasound method tends to overestimate the stiffness of the tendon. The two-scan method has similar results of the long probe approach and higher between-day reliability than the conventional method.