Purpose of the study: Spasticity of the rectus femoris (RF) in cerebral palsy patients is considered to be the main cause of stiff knee gait. The kinematics of this muscle, variations in length and speed of lengthening, are altered. Research is however lacking on changes in this parameter after surgery. Our objective was to study its effect on the quality of gait and on the kinematics of the RF in order to identify kinetic behaviour with diagnostic value.

Material and methods: Twenty-six transfers were performed during multiple level interventions. A uniform technique was applied: wide separation of the RF from the vastus muscles and supra-patellar tenotomy, suture of the RF tendon to the gracilis tendon tunnelled through the medial intermuscular partition. Intramuscular lengthening of the hamstrings (n=20) was associated with patella lowering procedures (n=4). The Gait-Deviation-Index (GDI) and the Goldberg score were determined pre- and postoperatively to quantify gait quality and search for stiff knee. A musculoskeletal model (virtual RF) was developed to simulate the trajectory of the RF during gait.

Results: The quality of gait improved (+18±12 GDI) with a negative interaction between the preoperative GDI and its improvement. For the Goldberg score, surgery yielded 88% improvement. Surgery had a significant effect on normalising the timing of RF lengthening and the maximal lengthening speed. Improvement in stiff knee was correlated with a normalisation of the timing of maximal length.

Discussion: Improvement in gait quality was greater when the preoperative quality is low; there is a risk of no improvement if the GDI is > 75. Normalisation of the timing of the maximal length of the RF is correlated with improvement in knee oscillation. Early timing signals a postoperative improvement in stiff knee. Early peak in the speed of lengthening of the RF can be explained by early triggering of spasticity during weight bearing which would limit the lengthening of the RF.

Conclusion: Global improvement of gait quality and stiff knee has been demonstrated. Certain muscular kinematic parameters are normalised, demonstrating the effect of transfer during oscillation but also during weight-bearing. Early peak in RF lengthening is a prognostic factor of successful surgery.