Effects of hamstring lengthening surgery on muscle–tendon velocities of patients with cerebral palsy

Cerebral Palsy (CP) is a permanent movement disorder seen in early childhood, consisting of muscle spasticity and/or contracture, and difficulty in walking due to poor selective control. In CP patients, crouch gait with excessive knee flexion is usually corrected by hamstring lengthening surgery, which is believed to improve gait, by increasing the length or velocity of the spastic muscle. However, hamstring muscles that may not be not short and slow before the surgery can also be operated on. The thesis aims to assess whether the gait of CP patients improved after the surgery by testing the following hypotheses: (i) knee joint movement does not improve postsurgery, (ii) the hip joint movement was impaired pre-surgery, (iii) the gait deviation index (GDI) increases post-surgery, (iv) the muscle lenghtening velocity remains unchanged in postsurgery, and (v) the pre-surgery psoas lenghtening velocity is slower than post-surgery. 8 limbs of 4 CP patients who had undergone hamstring lengthening surgery were included in the study. Pre-and post-surgery muscle lengthening velocity changes of patients were compared with reference to age-matched TD children (14 limbs of 7 participants) based on gait analysis data and using musculoskeletal modeling (OpenSim). Our results showed that post-surgery, mean knee angular velocity did not change significantly. No significant effect of surgery was shown in hip angular velocity or GDI. Moreover, no significant changes were shown in hamstring muscle lenghtening velocities. Only two of the preoperative patients had slow psoas muscle lenghtening velocity. As a result, post-surgery improvement in knee movement was achieved without a significant change in hamstring muscle lenghtening velocity. Keywords: Muscle Shortness, Cerebral Palsy, Contracture, OpenSim, Hamstring Lengthening Surgery, Spasticity, Psoas, Lengthening Velocity