The spinal cord showed marked sensibility to acute compression causing complete and irreversible injury. On the contrary, the spinal cord has more ability for adaptation to slow progressive compression mechanisms having the possibility of neural recovery after compression release. The aim of this experimental study was to establish, by means of neurophysiologic monitoring, the degree of compression needed to cause neurologic injury to the spinal cord, and analyze whether these limits are different making fast or slow compression.Summary Statement
Introduction
A new triggered electromyography test for detection of stimulus diffusion to intercostal muscles of the contralateral side during thoracic pedicle screw placement was evaluated. Experimental research was carried out in order to determine if, using this test, neural contact at different aspects of the spinal cord and nerve roots could be discriminated. Nine industrial pigs (60–75 kg) had 108 pedicle screws placed bilaterally in the thoracic spine (T8–T13). Neural structures were stimulated under direct vision at different anatomic locations from T9 to T12. Recording electrodes were placed over the right and left intercostal muscles. Increasing intensity of the stimulus was applied until muscle response was detected at the contralateral side (diffusion phenomenon). After this first experiment, the thoracic spine was instrumented. Screws were placed in the pedicle in two different positions, the anatomic intrapedicular location and with purposeful contact with the neural elements.Introduction
Methods
To determine the limits of spinal displacement before the onset of neurophysiological changes during spinal surgery. Assessing if the type of force applied or the section of the adjacent nerve roots increases the tolerance to displacement. Experimental study in 21 domestic pigs. Three groups were established according to the displacing force applied to the cord: separation (group 1, n=7), root stump pull (group2, n=7) and torque (group3, n=7). Successive records of cord-to-cord motor evoked potential were obtained. The displacing force was removed immediately when neurophysiological changes observed. The experiment was repeated after sectioning the adjacent nerve roots.Objectives
Methods
This work was aimed at study the role of paraspinal muscles on spinal tensegrity. Four different models of spinal tensegrity breakage with and without injury of the posterior spinal muscle were investigated. Fifteen minipigs (mean age 6-week) underwent costotransversectomy (CTT) at 5 consecutive vertebral segments. In 4 animals ribs and transverse processes (T7–T11) were removed through a posterior midline approach with complete desinsertion of paraspinal muscles. In other 3 animals, CTT was performed by a posterolateral approach (T6–T10) without detachment of paraspinal muscles. Other 4 minipigs underwent rib resection (T7-T11) throughout a thoracoscopic approach avoiding damage of posterior spinal muscles. A final group of 4 animals, a complete detachment of the paraspinal muscles was performed from T7 to T11 without removing bony structures and leaving in deep surgical wax attached to the spinous and transverse processes to avoid reinsertion of the muscles after surgery. Anatomic specimens were radiologically and macroscopically studied just at sacrifice 5 months after surgery All 4 animals operated on of CTT by midline posterior approach developed structural spinal deformity with curve convexity at the side of rib removal (mean Cobb angle 34,6°). Animals undergoing CTT by posterolateral approach without paraspinal muscle detachment did not develop any significant spinal deformity. Absence of spinal deformity was also found in those animals in which rib resection was performed by thoracoscopy without injury of the posterior spinal muscles. All 4 animals undergoing detachment of the paraspinal muscles without CTT and application of the surgical wax developed scoliotic curves (mean Cobb angle of 28°). In conclusion, a new insight on the underlying pathogenic mechanisms of scoliotic curves is given by using this spinal tensegrity model. Isolated damage of the posterior muscle-ligamentous structures around the costotransverse joints breaking muscles spine tensegrity seems to be mandatory to induce scoliotic deformity. Rib removal alone appeared to have less scoliotic inductive implication. The finding questions previous knowledge on scoliosis etiopathogeny.
Various studies have demonstrated that menisci heal in the vascular region but do not heal in the avascular area. Experimental studies of the promotion of meniscal healing in the avascular area have involved the application of fibrin clot, fibrin glue to the injured area, as well as the construction of an access chanel to the vascular regiòn, all of them with poor results. The multilineage potential of adult stem cells has been characterized extensively. The adipose tissue has been described as a useful source of adult stem cells. We try to show that the use of stem cells from the adipose tissue may promete meniscal healing in the avascular area. Twelve New Zealand white rabbits with a mean weight of 3 kg were used. The medial meniscus of both knees was aproached, and was performed a longitudinal tear in the avascular area in the anterior horn with a mean length of 0.5 cm. All the tears were sutured with one vertical stitch of nonabsorbable suture. In each rabbit a solution with 1 00 000–1 000 000 stem cells from the fat was introduced in one of the knees, and the other one was used as a control. The rabbits were killed at 12 weeks, and a macro-microscopic study of the meniscus was done, and also a inmunohistochemistry study for the stem cells. The incidence of healing was better in those menisci with the stem cells solution. Three total and three partial healing was obtained in the stem cells group and none in the control group. The inmunohistochemistry showed that the stem cells were in the repair zone. We think that stem cells will be very useful in the treatment of the lesion in the avascular area of the meniscus.
