Histological and Morphometric Changes in the Femoral Nerve During Lateral Interbody Fusion of the Lumbar Spine: Experimental Study

Abstract

Background. Neuropathies of the lumbar plexus trunks, in particular those of the femoral nerve, are the most common complications of lateral interbody fusion of the lumbar spine. Modeling of this surgical intervention in normal animals experimentally makes it possible to assess the degree of its trauma to the nervous structures, and to understand what is the reason for the persistence or aggravation of neurological symptoms iatrogenic injuries or the existing pathology progression. Purpose to study histological and morphometric changes in the femoral nerve in the long-term periods after the lateral interbody fusion modeling of the canine lumbar spine. Study design an experimental prospective continuous uncontrolled study. Materials and Methods. Discectomy via lateral approach was performed in 18 mongrel dogs (aged 2-3 years, mass 13.2-17.6 kg) at the level of L4-5 и L5-6, interbody titanium implants were mounted, the lumbar spine was stabilized with a wire device for external fixation within 30 days. Clinical and neurological evaluation was performed, as well as histological investigation of the femoral nerves from the side of surgical approach. Results. In the early postoperative period a temporary decrease in the femoral nerve function was observed, which was manifested by the disorder of the support function and muscle weakness of the pelvic limbs, decrease in the knee reflex, the foot support shift to the metatarsal pad. Later, until the end of the study (18 months), the general condition of all animals was satisfactory, there were no disorders of the limb support function and motor reflexes. After six months, in the femoral nerve there was 4-fold decrease in the proportion of large fast-conducting myelin fibers D10 m and 3-fold increase in that of the small ones. The mean axon diameter and myelin thickness were 62% and 53% of the norm. After 12-18 months, the dimensional characteristics of myelin fibers were restored. During the entire experiment, 4-6% of myelin fibers were reactively and destructively altered. Conclusions. The modeling of the lateral interbody fusion of the lumbar spine in normal animals experimentally demonstrated the absence of neurological symptoms after 6-18 months, which indicated low invasiveness of the surgical intervention. Nevertheless, the subclinical reactive and destructive changes in the myelin fibers of the femoral nerve revealed 6 months after the surgery indicated the need for preventive anti-neurotic therapy.