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Updated: Dec 17, 2025
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Published on: September 5, 2025
Quantitative Analysis of Patellar Tendon After Total Knee Arthroplasty Using Echo Intensity: A Nonrandomized
Yusuke Sato1, Alexander Kösters2, Florian Rieder3
1Department of Sport and Exercise Science, Paris Lodron University of Salzburg, Salzburg, Austria; Department of Orthopedic Surgery, Chiba University Hospital, Chiba, Japan.
Background:
Despite the knee extensor weakness, less attention has been paid to the evaluation of patellar tendon after total knee arthroplasty (TKA). We previously observed patellar tendon hypertrophy after TKA. The purpose of this study is to reanalyze these ultrasound data to detect whether brightness mode ultrasound imaging reflects pathological changes of the patellar tendon after TKA.
Methods:
Twenty-eight participants with post unilateral TKA were assigned to an intervention group or control group. The intervention group underwent a 12-week skiing program. Patellar tendon mechanical properties were obtained by combining isometric dynamometry, ultrasound imaging, and electromyography in operated knee and nonoperated knee. Luminosity ratio (LR) was measured using echo intensity in a relaxed and maximally loaded phase.
Results:
Baseline comparisons revealed significant effects of the surgical side (P < .001) and loading phase (P = .017), but no interaction between leg and phase (P < .149). LR of the operated knee was significantly lower than LR of the nonoperated knee in relaxed (P < .001) and maximally loaded phases (P = .003). In addition, there was a significant correlation between LR of maximum phase and isometric knee extension torque (r2 = 0.156, P = .038). However, LR was not related to patellar tendon stiffness, Young's modulus, or strain. There was a significant time effect in knee extension torque, but no time effects on LR and tendon force.
Conclusion:
Patellar tendon LR is decreased along with degenerative change after TKA. Ultrasound imaging provides a promising metric to acquire in vivo patellar tendon pathological assessment after TKA.
