Dynamic spasticity determines hamstring length and knee flexion angle during gait in children with spastic cerebral palsy

Background: Previous researchers reported that popliteal angle did not correlate well with knee angle during gait in individuals with spastic cerebral palsy (CP). Research question: To determine if hamstring spasticity, as measured by Modified Tardieu Scale (MTS) M rest, is associated with knee flexion angle at initial contact and midstance during gait. Methods: Thirty ambulatory children (mean age 8.7 +/- 2.4 years) diagnosed with spastic CP participated. The hamstrings' spasticity was assessed in the supine position with the MTS, measuring R1 (muscle reaction to passive fast stretch), R2 (passive range of motion), and R2-R1 (dynamic component of spasticity). We conducted 3-dimensional computerized gait analysis and calculated semimembranosus muscle-tendon length and lengthening velocity during gait using musculoskeletal modeling and inverse kinematic analysis by OpenSim. Pearson correlation coefficients were calculated to estimate the association of MTS with biomechanical parameters during gait. Results: Knee flexion angle at initial contact and maximal knee extension angle during stance phase significantly positively correlated with both R1 and vertical bar R2 - R1 vertical bar of MTS, but not with R2 angle. The length of semimembranosus at initial contact, end of swing, and minimal length during stance phase were strongly negatively associated with R1, rather than R2 or vertical bar R2 - R1 vertical bar angles. Significance: The R1 angle of MTS (muscle reaction to passive fast stretch) is more relevant correlate of knee flexion angle during gait than the R2 (passive range of motion).