Relationship between radiographic patella-alta pathology and walking dysfunction in children with bilateral spastic Cerebral Palsy.

BACKGROUND: Patella-alta is very common in patients with Cerebral Palsy (CP). While several diagnostic x-ray indices have been developed for patella-alta in general, the specific relationship with walking dysfunction in CP is only partly understood.

METHODS: 33 participants with bilateral spastic CP between 4 and 20 years (GMFCS I-II without previous surgery) that underwent 3D gait analysis as well as a radiographic exam within 0.8 (SD 1.2) months were retrospectively included. The Caton-Deschamps, the Insall-Salvati and the Koshino-Index, as well as the moment-arms of the quadriceps, the pattelar-tendon length and patellar tilt angle were analyzed from x-rays. During gait, tempo-spatial parameters, the knee flexion kinematics, the knee moments and the moment impulse were calculated and correlated to x-ray parameters.

RESULTS: Smaller quadriceps moment-arms were related to slower walking speed (r=0.48, P=0.005) and less knee extension during stance (r=0.68 P<0.001). Smaller quadriceps moment arms and longer patellar-tendons were also significantly related to a larger knee flexion moment impulse in the second half of the stance phase (r=-0.36, P=0.045 and r=0.39, P=0.028) and hence to more abnormal knee loads. Yet, none of the traditional indices was related to any parameter of gait.

INTERPRETATION: Traditional radiographic indices for patella-alta possess little to no informative value for walking dysfunction in individuals with CP suspected to have knee pathology. Smaller moment-arms are a key feature of patellofemoral pathology in CP reducing the knee extensor mechanism, an aspect which is not sufficiently picked up by traditional indices.