Clinically, it is considered that spastic muscles of patients with cerebral palsy (CP) are shortened, and produce higher force in shorter muscle lengths. Yet, direct quantification of spastic muscles’ forces is rare. Remarkably, previous intraoperative tests in which muscle forces are measured directly as a function of joint angle showed for spastic gracilis (GRA) that its passive forces are low, and only a small percentage of its maximum active force is measured in flexed knee positions. However, the relationship of force characteristics of spastic GRA with its muscle-tendon unit length (lMTU) is unknown. Combining intraoperative experiments with participants’ musculoskeletal models developed based on their gait analyses, we aimed to test if spastic GRA muscle (1) operates at short lMTU compared to that of typically developing (TD) children, and exerts higher (2) passive and (3) active forces at shorter lengths, within gait-relevant lMTU range. Ten limbs of seven children with CP (GMFCS-II) were tested. Pre-surgery, gait analyses were conducted. Intraoperatively, isometric spastic GRA distal forces were measured in ten hip-knee joint angle combinations, in two conditions: (i) passive state and (ii) maximal activation of the GRA exclusively. In OpenSim, gait_2392 model was used for each limb to calculate lMTU's per each hip and knee angle combination and the gait-relevant lMTU range, and to analyze gait relevant spastic muscle force - lMTU data. lMTU values were normalized for the participants’ thigh lengths. Two-way ANOVA was used to compare the patients’ lMTU to those of the seven age-matched TD children to test the first hypothesis. In order to test the second and the third hypotheses, Spearman's rank correlation coefficient (ρ) was calculated to seek a correlation between the muscle's operational length (represented by mean lMTU within gait cycle) and muscular force characteristics (the percent force at shortest lMTU of peak force, either in passive or in active conditions) within gait-relevant lMTU range.Introduction and Objective
Materials and Methods
Administration of Botulinum toxin type A (BTX-A) in patients with spastic cerebral palsy aims to improve mobility by increasing joint range of motion and decreasing passive resistance. However, our recent animal experiments indicated that BTX-A can decrease muscle”s length range of force exertion (Lrange), and increase its passive forces and extracellular matrix (ECM) collagen content. Moreover, BTX-A injected into the tibialis anterior (TA) was shown to spread into non-injected synergistic muscles in the whole anterior crural compartment. These effects that contradict the treatment aims deserve further investigation. To test in a rat model if: (1) BTX-A injected into the medial and lateral gastrocnemius (GM&GL) muscles spreads into the synergistic soleus (SOL) as well as antagonistic TA and extensor digitorum longus (EDL). (2) The muscles exposed show a wider Lrange, decreased muscle passive force and reduced ECM collagen.Background
Aim
