Anterior Knee Pain and Patellar Subluxation in Cerebral Palsy

Abstract

Patella femoral problems in children and adults with cerebral palsy (CP) are relatively common, especially in patients who have significant spasticity and are ambulatory at the Gross Motor Function Classification System (GMFCS) level II-III. Patella alta, which means the patella is riding high or proximal to its normal location and is out of the femoral groove, is common in patients with spastic lower extremities. This position appears to lead to dysplasia of the femoral groove and in some patients contributes to patellar subluxation. Incidence of patellar subluxation and patellar dislocation on the lateral side of the femur occurs at approximately the same incidence as in normal children. Often, the dislocated patella can be easily reduced but then becomes a recurrent problem, causing pain and mechanical instability of the knee. The dislocation in ambulatory children becomes a definite problem requiring surgical reconstruction, as children cannot walk with a dislocated patella. The surgical plan has to consider the child’s level of spasticity and whole limb alignment. It cannot usually be treated with a typical isolated focus as is common in a sports injury. Children who are GMFCS IV-V and spend most of the time sitting will often become uncomfortable from the dislocated patella. A small group of adolescents with spastic gait develop severe anterior knee pain due to severe torsional malalignment with increased femoral anteversion and external tibial torsion. When this torsional malalignment is present with severe anterior knee pain or subluxation, the pain will usually not subside until the torsional malalignment is corrected. Anterior knee pain may also present in adolescents who are growing rapidly and developing a progressive crouch gait. In this situation there may be stress fractures at the distal pole of the patella or the tibial tuberosity. Occasionally, a sudden stress fracture in the mid-substance of the patella completely separates and becomes an acute fracture. This requires treatment of the crouch gait as well as addressing the stress reaction in the patella.