Viscoelastic Properties of the Denervated Muscles in Children With Upper Trunk Obstetrical Brachial Plexus Palsy

Birth lesion of the brachial plexus, generally referred as "obstetric brachial plexus palsy (OBPP)", frequently includes traction or tearing of the nerve plexus that supply motor, sensory and autonomic innervation to the arm. The extent of damage can vary depending on severity of the injuries; from single nerve root to total root lesions. Impact of OBPP can be seen as transient functional insufficiencies to lifelong total disability, depending on the injury severity. The incidence of OBPP varies between 1.3 - 1.5 per 1000 births in different countries. The most common risk factor for birth injury is shoulder dystocia. Other risk factors are macrosomia, prolonged labor, multiparity, maternal pelvic anatomy and ethnic background.Denervation after delivery leads changes in the muscle tissue due to incomplete maturation of the muscles. The muscle tissue cannot grow longitudinally and have higher connective tissue content. Additionally, muscle strength gain, and development are impaired in the denervation process due to fibrosis and fat infiltration. Many studies demonstrated alterations in histomorphological features of denervated muscles in OBPP via magnetic resonance, ultrasound imaging and gene analysis. Despite many structural alterations in muscles have been investigated; changes in the viscoelastic properties, including muscle tone (tonus), stiffness and elasticity of the muscles, during denervation and reinnervation processes have not yet been investigated in patients with OBPP. The aim of our study was to observe changes in denervated muscles viscoelastic properties and motor performance of OBPP children. Viscoelastic properties have a significant effect on muscle performance; however have not investigated yet in denervated muscle. Hypothesized that the viscoelastic properties of denervated muscles are different than healthy side muscles and can vary depending on the age groups. 74 patients who have C5-C6 root lesion were enrolled to the study. The patients were grouped according to their age groups: 1-5 months, 6-24 months and 25-36 months. Myoton-3 myotonometric measuring device was used to measure the viscoelastic properties (tone, elasticity and stiffness) of deltoid, biceps brachii. Active Movement Scale were used to evaluate the motor function of the muscles. We found different muscle viscoelastic properties depending on age group. Children aged 0-5 months showed significant difference in deltoid muscle tone (p=0.0001), stiffness (p=0.0001), biceps brachii muscle tone (p=0.0001) and stiffness (p=0.0001), when compared with other groups (denervated side was lower in values).Therefore, it is in our opinion that in follow-up, clinical assessment of viscoelastic properties will be useful for monitoring denervated muscle; also treatment programs and purposes for OBPP should be varying according to the muscle properties.