Overview of Knee Problems in Cerebral Palsy

Abstract

Although the knee is the largest joint in the lower extremity, it creates fewer problems in children with cerebral palsy (CP) than the hip, foot, or ankle. It is not clear exactly why the knee joint is relatively immune to the pathomechanics that affect the hip and foot; however, because the muscles primarily control motion in a single plane, there is less opportunity to create severely mal-directed force vectors. Most of the stability of the knee is due to its inherent ligamentous stability, the strength of which is usually able to overcome the weak abnormal muscle forces in varus, valgus, or torsional malalignment planes. The high stress on the extensor side of the joint may lead to patella alta and stress reactions in the patella. Stiff knee and crouch gait patterns are most defined by the position of the knee; however, much of the etiology of these problems emanates from the foot as much as the knee. The primary focus of crouch gait, which is increased knee flexion in stance phase, is focused upon the knee. Often a major contributor to this position though is due to a foot deformity. The knees are very sensitive to change in muscle length especially hamstrings and knee extensors. Surgical procedures are frequently required to lengthen muscles and correct fixed flexion deformity of the knee. Patella alta and patellar subluxation are also relatively common problems in children with spasticity. This chapter provides an overview of the pathology which affects the knee joint in children with cerebral palsy.