Rehabilitation training using a single-joint type hybrid assistive limb for the knee after anterior cruciate ligament reconstruction: an initial case report indicating safety and feasibility

[Purpose] The aim of this report was to describe the safety, feasibility, and efficacy of rehabilitation by knee extension and flexion training using the knee single-joint hybrid assistive limb in a patient after anterior cruciate ligament reconstruction. [Participant and Methods] A 33 year-old male underwent an arthroscopic procedure for anatomic single-bundle anterior cruciate ligament reconstruction with a semitendinosus tendon autograft. Rehabilitation training using the knee single-joint hybrid assistive limb was initiated at postoperative week 18 and repeated weekly for 3 weeks. The patient performed five sets of the knee single-joint hybrid assistive limb-assisted knee-extension-flexion exercises per session at a frequency of 10 exercises/set. [Results] The peak extension torque at all velocities with the limb symmetry index was higher after the hybrid assistive limb intervention (post-intervention) than before using it (pre-intervention). Peak flexion torques at 60°/s and 300°/s of limb symmetry index were higher post-intervention than pre-intervention. The range of motion in extension and flexion improved from −2° (pre-intervention) to −1° (post-intervention) and from 124° to 133°, respectively. The Lysholm score increased from 58 (pre-intervention) to 94 (post-intervention). [Conclusion] The knee single-joint hybrid assistive limb can be used safely for anterior cruciate ligament reconstruction training, without any adverse events. Our results indicate that the knee single-joint hybrid assistive limb training may improve muscle function, effectively overcoming dysfunction.