Characterisation of the patellar tendon reflex in cerebral palsy children using motion analysis.

Abstract

The patellar tendon reflex (PTR) is an important spinal reflex and an important diagnostic tool assessing neurological disturbances. Reflexes are conveniently assessed but quantifying the response can be subjective. Motion analysis is commonly used to assess gait kinematics in a variety of populations. It can be used to objectively assess the PTR with the advantage that standard technique and hammer can be used without the need for bulky apparatus or fixing the subject position. To compare the PTR in 15 cerebral palsy (CP) children with age and height matched controls. EMG reflex latency in the rectus femoris was assessed using a Noraxon 2400T unit. Knee movement latency, knee angular displacement and peak angular velocity were captured using the CODA mpx 30 system. EMG reflex latency was significantly reduced in CP compared to control limbs (13.11 versus 18.11ms; p<0.01) confirming a 'brisk' response in this population. The kinematic data found that while knee angular displacement was significantly reduced in CP (12.82° versus 20.06°; p<0.01) there was no significant difference in movement latency or peak angular velocity compared to controls. Subjective evaluation of the PTR relies mostly on change in knee angle. Using motion analysis we have confirmed a difference in this variable in CP compared to controls. We have also shown reduced reflex latency associated with a brisk reflex. Knee movement latency and peak angular velocity did not differentiate CP from normal. Further examination of the knee angular response of the PTR is warranted in CP.