ABSTRACT

Paralysis of the hamstrings results in weakness of active knee flexion. However, since the knee can passively flex due to the effect of gravity, both while walking and sitting down, no treatment is required for hamstring paralysis. If the hamstrings are functioning in a child with quadriceps paralysis, a flexion deformity of the knee may develop. Genu recurvatum also may be seen in children with quadriceps paralysis. Of all the consequences of quadriceps paralysis, knee instability is the most disabling. The quadriceps is an antigravity muscle and its function is vital in stabilising the knee while walking. During the single limb stance phase of the gait cycle, when the centre of gravity falls behind the axis of the knee, powerful active contraction of the quadriceps is essential to prevent the knee from buckling. Power of knee extension can be restored by performing a hamstring tendon transfer; however, not all patients with quadriceps paralysis are candidates for this transfer.