Hip Power and "Stiff Knee" Gait: A Tool for Identifying Appropriate Candidates for Rectus Transfer

Rectus femoris transfer (RFT) is performed in children with cerebral palsy to treat stiff-knee gait. However, the results are variable in part because there is no gold standard to identify appropriate candidates. Hip flexion kinematics and kinetics are important factors in the determination of peak knee flexion during gait. This study aimed to evaluate whether a kinetic preoperative analysis of hip power can be a predictor of RFT outcomes and determine its usability for identifying appropriate candidates for the procedure.

Sixteen children with spastic cerebral palsy (20 limbs) GMFCS I/II who underwent RFT for a stiff-knee gait and had preoperative and postoperative 3D gait analyses were retrospectively evaluated. Patient outcomes were classified as "good" or "poor" according to postoperative results. The outcomes were evaluated as a function of (a) 1-parameter criteria-peak hip power (PHP) with a cut-off magnitude≥0.60 W/kg; (b) 2-parameter criteria-PHP (cut-off magnitude≥0.60 W/kg) and the time the PHP occurred during the gait cycle (tPHP), with a cut-off ≤68% of the gait cycle.

When the 1-parameter criterion was used, 13 limbs met the criterion; of them, 11 had good outcomes. Seven limbs did not meet the criterion; of them, 6 had poor results (P=0.0049). When the 2-parameter criterion was used, 11 limbs met the criteria; all had good results. Nine limbs did not meet the criterion; of them, 8 had poor results (P=0.0002). PHP+tPHP had the same sensitivity as PHP alone (91%) but with higher specificity (100%) for predicting outcomes. The positive predictive value of magnitude PHP+tPHP was 100%, whereas the accuracy index was 95%.

Preoperative kinetic evaluation of the hip power characteristics from 3D gait analysis appears to be a very important predictor for RFT outcomes and identifying appropriate candidates for the procedure.

Level III-therapeutic retrospective study.