Assessment of effectiveness of muscle lengthening surgery in cerebral palsy using musculoskeletal modeling

Abstract

Cerebral Palsy is a permanent movement disorder that manifests itself at early childhood, as poor coordination, and gait difficulty due to muscle spasticity and/or con tracture. Excessive knee flexion during gait e.g., crouch gait is a common impairment and often corrected by hamstring lengthening surgery. Such crouch gait is presumed to originate from shortness (i.e., contracture) and/or slowness in lengthening (i.e., spastic ity) of affected muscles and remedial surgery is considered to improve gait by increasing muscle length or its velocity. However, a third group of patients who neither has short nor slow hamstrings pre-operatively can still undergo surgery. The aim of the thesis is to investigate whether the gait of those patients improved after the surgery by testing the hypotheses: post-operatively, (i) the knee joint movement is improved (ii), the hip joint movement is deteriorated (iii), the gait deviation index (GDI) is increased (iv), muscle unit length do not change, and (v) pre-operative psoas muscle lengths were shorter. Findings showed that mean knee angle decreased significantly at the initial contact (0-3%), terminal stance (28-43%), and the terminal swing phases (95-100%) (p< 0.05). No significant effects were detected in the hip angle or the GDI. Additionally, no significant changes in the hamstring muscle lengths were found. Only half of the patients had shorter psoas muscle lengths pre-operatively. In conclusion, the excessive knee flexion of the patients was decreased without negatively affecting hip movement or gait overall. The improvement in the knee angle was achieved without any change in the muscle length of the hamstrings, suggesting that an isometric position shift of the target muscle occurs, which may be ascribed to post-surgical alterations in the epimuscular connections. NOTE Keywords : Hamstring lengthening surgery, Remedial surgery, Spasticity, Contrac ture, OpenSim, Musculoskeletal modeling, Psoas, Lengthening velocity, Muscle short ness, Cerebral Palsy.