Analysis of Balance Disorders After Botulinum Toxin Treatment in the Rectus Femoris in Patients With a Stiff Knee Gait

Patients who suffered a stroke, cranial traumatism, medullar lesions or multiple sclerosis can present spastic muscular complications, which is particularly impairing if it concerns muscles of the leg. Muscular spastic complications of the legs can alter significantly the ability to walk because it clinically manifests itself by a stiffness of the leg, thus generating a complication called "Stif Knee Gait" (SKG). It means that the femoro-patello-tibial articulation cannot be mobilized as it should because it stays spastic instead of being mobile.

However, it remains possible to treat this kind of medical condition by using Botulinum toxin injections in the target muscle, in particular the rectus femoris (which is part of the quadriceps).

As a reminder, botulinum toxin, sold under the international common denomination "Botox®", is a neurotoxin of 150 kDa produced by the bacteria "Clostridium Botulinum" and is the most powerful natural poison known to humankind, with its DL50 between 1 and 2 nanogramms / kg in humans. This toxin works by entering the neuro-muscular synaptic junctions and by linking itself to a proteic complex called SNARE. The link between the toxin and the SNARE complex inhibits the fusion of the acetylcholinergic synaptic vesicles with the plasmic membrane of the pre-synaptic axone. The Botox® blocks the exocytosis of the acetycholin (Ach) vesicle in the inter-synaptic space at the neuro-muscular junction and blocks the nervous transmission, thus generating muscular flaccid paralysis. This kind of intoxication is caused directly by an infection by Clostridium Botulinum and is called Botulism. It manifests itself clinically by flaccid paralysis, swelling, diarrhea tiredness, respiratory failure, vomiting etc…

Despite its highly toxic properties, Botox® can be used as a therapeutic tool against number of medical conditions (strabismus, hyperhidrosis, migraines etc…) and even as a cosmetic tool (anti face-wrinkles). It can be used against spastic muscular paralysis, especially like the ones encountered in the patients of this study.

The current Standard Of Care (SOC) against SKG is to inject Botox into the rectus femoris in order to counter its spasticity. It has been shown to upgrade the walking ability of SKG patients by enhancing the leg kinetics. More precisely, it has been shown to improve the fluidity of the movement of the spastic leg in SKG patients, especially the knee flexion. However, the rectus femoris' contractility remains necessary to be able to stand up statically and to stay balanced during the walk and everyday-activity and the myorelaxant properties of Botox® may be problematic and alter the leg biomechanics despite its utility. To this day, no study has been published to compare the static and dynamic balance troubles before and after Botox injections in the rectus femoris.

The medical bibliography does not report any augmentation of the risk of fall in the case of Botox injection in the rectus femoris. However, we consider the hypothesis along which those injections can enhance the risk of fall. Therefore, we decided to conduct a monocentric, prospective observational clinical study to compare the state of the static and dynamic balance before and after Botox injections in the rectus femoris (in SKG patients) by using balance scores.

In order to complete this objective, we compared the following parameters before and after the Botox injection in SKG patients :

• Time Up and Go test(in seconds) : primary evaluation criteria
• Berg Balance Scale (BBS) : secondary evaluation criteria
• Stair climb and descent time test (SCT) : secondary evaluation criteria.
• Number of falls.