N. Khouri

Description and classification of the effect of hamstrings lengthening in cerebral palsy children multi-site surgery.

The purpose of multi-site surgery is to improve the cerebral palsy children’s gait by associating multiple surgeries on the same therapeutic time. It is therefore complex to isolate the effect of these actions in this multifocal context. To address this problem we chose to specifically identify the effect of hamstrings lengthening (Chang 2004) in cerebral palsy children with crouch gait. The purposes of this study were as follows:

Simulation of muscle retraction in cerebral palsy. Validation of a decision support system for surgical lengthening of contractured muscles

Musculoskeletal modelling associated with gait analysis permits modelling of the muscle lengths during walking. This helps to exclude indication of a hamstrings lengthening by the objectification of a non-functional impact on a supposed muscular contracture (Arnold et al. 2006). It does not allow the establishment of a positive diagnosis of the indication of hamstrings lengthening. That iswhywedeveloped a customisablemusculoskeletalmodel able to analyse the muscles kinematics during walking and to simulate the maximum muscle length from clinical goniometric measurements (simulation of muscle retraction in cerebral palsy, SiMusCP). This connection introduces a new diagnostic approach, theoretically exhaustive, of the possible causality of muscle contracture on CP children gait impairments. The purpose of this study was to evaluate the real contribution of the SiMusCP procedure in the therapeutic decision.

Does patella lowering improve crouch gait in cerebral palsy? Comparative retrospective study

BACKGROUND Patella lowering aims to improve quadriceps function as a means of correcting crouch gait in patients with cerebral palsy. Few studies have assessed the effects of patella lowering as a component of multilevel surgery. HYPOTHESIS Including patella lowering into the components of multilevel surgery is beneficial in patients with crouch gait and patella alta. MATERIAL AND METHODS In 12 lower limbs with patella alta (Caton-Deschamps index>1.4) in 41 children with cerebral palsy, patella lowering was performed, without distal femoral extension osteotomy or hamstring release. Among limbs with similar surgical procedures (e.g., hamstring lengthening, rectus femoris transfer) except for patella lowering, controls were selected retrospectively by matching on a propensity score for patella lowering. The propensity score was computed based on preoperative knee flexion contracture, knee extension lag, and minimum knee flexion at mid-stance. Clinical and 3D kinematic data were compared between the two groups. RESULTS The improvement in minimum knee flexion at mid-stance was significantly greater in the group with patellar lowering (-24°±12°vs. -12°±7°). The Gait Deviation Index improved similarly in the two groups. Knee flexion contracture improved only in the group with patellar lowering. Extension lag did not improve in either group. Peak knee flexion during the swing phase remained unchanged in both groups. DISCUSSION Patellar lowering is effective in diminishing minimum knee flexion at mid-stance in patients with patella alta and crouch gait due to cerebral palsy. Patellar lowering has not adverse effects on gait. These findings cannot be assumed to apply to patients with normal patellar height. LEVEL OF EVIDENCE IV (retrospective study).

Estimation of Postoperative Knee Flexion at Initial Contact of Cerebral Palsy Children using Neural Networks

Cerebral Palsy affects walking and often produces excessive knee flexion at initial contact (KFIC). Hamstring lengthening surgery (HL) is applied to decrease KFIC. The objective of this work is to design a simulator of the effect of HL on KFIC that could be used as a decision-making tool. The postoperative KFIC is estimated given the preoperative gait, physical examination and the type of surgery. Nonlinear data fitting is performed by feedforward neural networks. The mean regression error on test is 9.25 degrees and 63.21% of subjects are estimated within an error range of 10 degrees. The simulator is able to give good estimations independently of the preoperative gait parameters and the type of surgery. This system predicts the outcomes of orthopaedic surgery on CP children with real gait parameters, and not with qualitative characteristics.

The convex wrapping algorithm

Muscle-tendon lengths, their lengthening rates as well as their moment arms are the parameters of great utility for clinical interpretation purposes. These parameters depend on the paths that the muscles follow. It is, thus, necessary to determine accurate muscular paths during movement. The position of the muscles being inaccessible to direct measurement, various methods were proposed to evaluate their possible paths during the movement studied. They can be split into two categories: the wired models and the finite elements models. Taking into account the ‘wrapping surface’ algorithms (Van der Helm et al. 1992; Delp and Loan 2000; Garner and Pandy 2000), the ‘dynamic via-points’ algorithm (Carman and Milburn 2005) and Marai’s algorithm (Marai et al. 2004) that uses skeleton mesh, the present authors thus developed the ‘convex wrapping algorithm’ to determine the muscular paths, with the following objective: ‘Find the shortest path between the insertion and the origin of a muscle wrapping over the skeleton bone mesh while respecting possible non-sliding constraints’. This algorithm directly employs exact bone geometry, not simple geometrical forms, as the object of envelopment. Thus, this algorithm is detailed. It is then compared with the ‘straight line’ method and ‘wrapping surface’ algorithm by measuring the length and moment arm of the semitendinosus muscle during asymptomatic gait.

Muscle–tendon surgery: effect on length and lengthening velocity of rectus femoris in cerebral palsy children gait

In cerebral palsy (CP), spasticity often induces troubles in muscle–tendon growth. One of the surgery purposes is to correct muscle–tendon length and the consequences of the spasticity. To improve the surgery decisions and results, the use of musculoskeletal model is already proposed (Delp et al. 1996; Arnold et al. 2006). The rectus femoris spasticity is considered as one of the causes of stiff knee gait. Rectus femoris geometric parameters have been studied in stiff knee gait, identifying altered patterns in length and its variations (Jonkers et al. 2006). Nevertheless no results have been published about the effect of rectus femoris surgery on its length and lengthening velocity during gait. We therefore developed a musculoskeletal model to compute those geometrical parameters and to study the effect of rectus femoris transfer on those parameters.