IntroductionDuring gait, many children with cerebral palsy have abnormal electromyographic activity of the rectus femoris during swing. This abnormal activity, caused by spasticity of the quadriceps musculature, has been thought to decrease sagittal plane knee motion during swing producing a stiff knee gait pattern. Gage and Perry noted that spastic rectus femoris activity beyond 15-20% of swing phase is detrimental to the child by limiting the knee flexion required for foot clearance. Several surgical procedures, including rectus remoris transfers and releases have been shown to improve knee flexion during swing by relocating the direction of the muscle force. The decision to perform a rectus femoris transfer or release is based on the information gained from computerized gait analysis. Gait analysis has been used to document the abnormal sagittal plane knee motion and swing phase rectus femoris activity. Knee motion has been defined as the difference between maximum knee extension in stance and the maximum knee flexion in swing. Ounpuu, 1993, defined stiff knee gait as a limitation in knee motion of 20%. Stiff knee gait in conjunction with abnormal activity of the rectus femoris during swing often results in the recommendation of rectus femoris transfer. In order to determine which patients would benefit from a rectus femoris procedure various clinical findings and 3-D gait analysis parameters were evaluated to determine their influence on stiff knee gait. The purpose of this study was to determine if a specific rectus femoris pattern could predict stiff knee gait or if other characteristics such as ELY, type of ambulator, onset of swing phase knee flexion, and decreased stride length would be better indicators of stiff knee gait.MethodologyThirty-seven children with cerebral palsy, spastic diplegia (24 males, 13 females), mean age of 6.0 years (range 3+8 - 10+11 years), were evaluated in the gait analysis laboratory. None of the children had had any surgical intervention at the time of the gait analysis. All children were evaluated in the barefoot condition using any assistive devices. Twenty-three children were independent ambulators with the remainder being dependent. A five camera VICON system was used to collect the three dimensional motion. A MA100 EMG unit, sampling at 500 Hz and surface electrodes were used to assess electromyographic activity during gait. Sagittal plane motion and electromyographic activity were normalized to 100% of a cycle. In this study, stiff knee gait was defined as 70% of the normal knee motion. This level was chosen because often children with knee motion of 80% are not addressed surgically. Rather than looking at solely at rectus activity in swing, rectus femoris activity was examined using three patterns which have been commonly seen during routine gait analysis. These patterns were defined as delayed (onset occurring after 10% of the swing phase), prolonged (continuing from 0-30% of the swing phase, but decreasing prior to toe off), or continuous (continuing through the entire swing phase). Timing of peak knee flexion was determined from the sagittal plane knee motion graphs as a percentage of the gait cycle. The presence or absence of an ELY response was based on clinical examination.ResultsAll thirty-seven children had abnormal swing phase rectus femoris activity. Of these children, 100% had a delayed onset of peak knee flexion in swing, regardless of knee kinematics. At seventy percent of normal knee flexion, lacking 18 degrees of motion, 57% of children did not meet the criteria of stiff knee gait despite having abnormal rectus femoris activity in swing. Of the remaining children, none of the other variables were related to the presence of stiff knee gait.A Spearman rho correlation coefficient was used to determine the relationship between variables.DiscussionBased on the results of this study, it was determined that all children with spastic diplegia evaluated in our laboratory, had rectus femoris activity in swing, regardless of the pattern of knee motion. There was no relationship between the presence of stiff knee gait and abnormal rectus femoris activity in swing. Other variables such as type of electromyographic pattern, the presence of a positive ELY, decreased stride length or type of ambulator did not predict the presence of stiff knee gait. Therefore, rectus femoris activity alone should not be used to predict stiff knee gait. All factors in the physical exam and gait analysis assessment are important to determine whether rectus femoris surgery is indicated. In addition, these findings would question the need for electromyographic assessment in the determination of stiff knee gait.