This study aimed to determine the alteration in maximum isokinetic torque in patients after intramedullary femoral leg lengthening. Thirty patients with a median leg-length discrepancy of 3.0 cm underwent femoral limb lengthening with an intramedullary motorized device. Maximum isokinetic, concentric torque of the extensors, and flexors of the knee was measured before (n=30) and 2 years after surgery (n=21). Postoperatively, a significant difference remained for the maximum isokinetic torque of the extensors (22%) between the lengthened and the normal leg, which might have been caused by muscle response to the distraction procedure itself in the form of higher stiffness, less immediate displacement, and inconsistent force relaxation properties. However, we provide evidence that physiotherapy after limb lengthening should focus on extensors to prevent loss of strength.