Purpose of the study: Intramuscular injection of the botulinum toxin into the psoas can be proposed for permanent hip flexion due to spastic disorders. Several approaches have been described: retrograde subinguinal, anterolateral suprailiac, and posterior. Ultrasound or computed tomography can be used to guide needle position. These approaches are however limited to access to the L4 region, i.e. far from the motor points and with the risk of injury to the ureter. The purpose of this work was to determine the innervations of the psoas muscle that would be best adapted to this type of injection and thus to describe the most effective and reliable approach.

Material and methods: This anatomy study included 20 dissections to: describe vertebral insertions of the psoas major and the psoas minor and to measure their distance from the iliac crest; define the region where the ureter crosses in front of the psoas.

Results: More than 80% of the psoas muscles presented a proximal insertion on the transverse process of T12 and the body of L1; the mean length of the psoas in the adult is 27 cm above the inguinal ligament; the nerve roots collateral to the lumbar plexus are: 33% L2, 25% L3, 19% L1, 9% L4, 3% L5 and 1% T12, the remainder arising directly from the femoral nerve; the L2-L3 region is situated 4.6 cm on average above the iliac crest.

Discussion: The region facing the L2-L3 space enables access to more than 50% of the psoas nerve branches. Injection via a posterior approach situated in adults 4.6 cm above the iliac crest and identified fluoroscopically is the most reliable access. This will avoid injury to the ureter which lies lower.

Conclusion: This anatomy study described a new more effective less dangerous approach for botulinum toxin injections into the psoas muscle.

Purpose: The purpose of this study was to analyse changes in foot dynamics secondary to tibiotalar arthrodesis and examine the adaptation mechanisms induced by wearing shoes.

Material and methods: A 3D gait analysis was performed (Vicon 370) in ten patients with a tibiotalar arthrodesis fixed in a neutral position and in ten matched controls. Recordings were made in three conditions: walking barefooted, walking at a comfortable self-chosen speed wearing shoes, and walking at maximal speed wearing shoes. We measured tibial inclination in the sagittal plane, knee flexion, and the tibia-forefoot angle produced at heel lift-off. The distance of the ground reaction force (GRF) from the heel was measured during the weight-bearing phase and at lift-off. Statistical comparisons were made with the contralateral side and the control group.

Results: Heel lift-off came significantly earlier on the arthrodesis side compared with the contralateral side and with the control group. At heel lift-off, the knee was in complete extension in all three groups. The GRF moved forward more rapidly but remained more posterior on the arthodesis side at heel lift-off in comparison with the contralateral side and the control group. Wearing shoes enabled later heel lift-off on the arthrodesis side and increased tibial inclination at lift-off as well as decreased speed of the anterior displacement of the GRF. The GRF however remained more posterior than in the control group. At maximal walking speed, heelk lift-off came earlier on the arthrodesis side and at the same time a lesser anterior tibial inclination and a more posterior position of the GRF.

Discussion: Early heel lift-off on the arthrodesis side allows anterior inclination of the tibia to continue and to increase stride length. Heel lift-off however occurs when the GRF has not yet advanced to the metatarsophalangeal position, thus increasing stress on the rear and mid foot. Wearing shoes improves the kinematic parameters and decreases stress on the joints below the arthrodesis. Increased walking speed aggravates the perturbed foot dynamics when walking.