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Biomedical subjects

J Massie

Publications and source records attributed to J Massie.

5 recordsLinked to original sources
PubMed1995

Spinal nerve root compression.

The pathophysiology of sciatica is not completely understood, although our understanding of its causes is increasing. Mechanical alterations combined with inflammatory changes lead to pain. Compression alters nerve root conduction and compromises the nutritional support of spinal nerve roots (through intrinsic and extrinsic vascularity and cerebral spinal fluid percolation). Mechanical forces can lead to intraneural damage and functional changes in nerve roots. Chemical and metabolic effects can create an inflammatory response. Varying causes of inflammation coupled with varying degrees of compression can occur anywhere along the cauda equina or spinal nerve root, including the dorsal root ganglia, and contribute to the pain response and neurologic deficits associated with sciatica.

Animals↗
PubMed1992

Strain, stress and stretch of peripheral nerve. Rabbit experiments in vitro and in vivo.

Mechanical stretching is known to cause morphologic and functional changes in peripheral nerve. The points at which these changes occur, however, are not clearly defined and reported data are conflicting. The studies presented in this paper provide a basic understanding of the biomechanical properties, stretch-injury patterns, and changes of conduction properties of peripheral nerves due to stretching. Our studies showed that peripheral nerves exhibited non-linear stress-strain characteristics when placed under tension. Initially, under tension, the nerve had a low modulus that increased gradually with increasing strain until reaching a maximal value. When the nerve failed under tension, the perineurium inside the nerve ruptured, but the exterior of the nerve remained intact. Our results also show that a peripheral nerve in situ was under significant strain, but minimal in situ stress (less than 0.05 MPa). The in situ strain might vary with limb position, but did not appear to exceed the limit beyond which substantial tension or stress would be developed in the nerve. The time-dependent viscoelastic behavior of peripheral nerves were also characterized. The maintenance of small in situ stresses suggests that sustained increases in tension could be adversely affecting the electrophysiologic properties of the nerve. Indeed, marked alteration of conduction properties resulted from even a small stretch of 6 percent beyond the in situ length of the nerve, or stress less than 10 percent of the ultimate strength of the nerve.

Animals↗
PubMed1991

Anatomic consideration for sacral screw placement.

Instrumentation of the lumbosacral spine increasingly involves screw fixation to the sacrum. Recommended locations and techniques for screw placement vary, particularly when bicortical purchase of the sacrum is performed. The purpose of this study was to describe the critical anatomy and potential injuries to neurovascular and visceral structures anterior to the sacrum. Lack of awareness can lead to life-threatening complications. The study included 22 fresh human cadavers with no prior spinal surgery. Specimens were placed in a prone position, and the lumbosacral spine was exposed. Two 6.5-mm screws were inserted using one of two techniques, respectively: Starting just inferior to the S1 facet one screw was angled 25 degrees caudally and 30 degrees laterally; in the second technique, lateral inclination was increased to 45 degrees. In addition, all specimens had screws placed in the S2 pedicles. An anterior dissection was performed to allow evaluation of the neurovascular and visceral structures at risk for injury by, or adjacent to, the screw tips. All significant neurovascular structures in the area of concern were constant in position. The internal iliac vein and the lumbosacral nerve trunk were most at risk for injury by the 30 and 45 degrees laterally directed screws. The sigmoid colon, though close to the S2 screw, was protected by its mesentery. Screws placed in the S1 pedicle were least likely to injure the neurovascular bundle. A lateral and a midline safe zone were identified.

Aged↗
PubMed1990

Radiographic assessment of sacral screw placement.

Sacral screw penetration of the anterior sacral cortex runs the risk of injury to neural, vascular, and visceral structures. This study examined the accuracy of the standard anteroposterior (AP) and lateral roentgenographic views as compared to a modified pelvic inlet (MPI) view in determining sacral screw penetration and angulation. Ten human cadaveric specimens were studied. Screw depth and screw angulation in the transverse plane were best evaluated with the MPI view. Screw penetration was overestimated by 0.4 mm (+/- 2.2 mm) on the MPI view, whereas the lateral view overestimated screw penetration by 2.8 mm (+/- 4.7 mm). Screw angulation in the sagittal plane could only be evaluated by the lateral view. The standard anteroposterior view provided little useful information on sacral screw orientation. To study all parameters of sacral screw placement, the radiographic series should include a modified pelvic inlet view and a lateral sacral view.

Bone Screws↗