The Evolution of Knee Flexion During Gait in Patients with Cerebral Palsy

Abstract

Walking with flexed knees (knee flexion gait with foot equinus or crouch gait with excessive dorsiflexion) is a common problem in cerebral palsy. Treatment can be difficult and often with unsatisfactory outcome. Descriptive classifications at the moment are of limited help in understanding the pathology as the gait pattern may change over time. The gait disorder gives the impression of being mechanically influenced by spasticity. However, other dimensions such as developmental retardation, body perception, and sensation, which are hard to quantify, may be equally relevant. When considering mechanical and nonmechanical factors, two vicious circles are identified which are mutually dependent; the progressive foot deformity driven by triceps overactivity and inappropriate loading and the knee and hip flexion deformity driven by the hamstrings. The triceps surae is overly activated to provide for more stable knee extension. If knee flexion occurs, even in spite of the triceps activity, control of the center of mass is used to divide up the load between knee and hip extensors in order to avoid collapsing. Both hip and knee joints require extensor activity to maintain upright body posture and support body weight when the hamstrings extend the hip in a flexed knee position, vasti counteractivity is required, which leads to longterm failure of the knee extensors by over stretching. These accommodations lead to a perception of insecurity in body support in stance further increasing the activity of the muscles involved and of increasing muscle tone in general reflected as spasticity. This concept including the psychological reaction of the individual offers a wider insight into the biomechanical causes of the individual pathology, which may provide for better treatment and prophylactic strategies.