Biomechanics of Posterior Dynamic Fusion Systems in the Lumbar Spine: Implications for Stabilization With Improved Arthrodesis.

STUDY DESIGN: A comparative biomechanical human cadaveric spine study of a dynamic fusion rod and a traditional titanium rod. OBJECTIVE: The purpose of this study was to measure and compare the biomechanical metrics associated with a dynamic fusion device, Isobar TTL Evolution, and a rigid rod. SUMMARY OF BACKGROUND DATA: Dynamic fusion rods may enhance arthrodesis compared with a rigid rod. Wolff's law implies that bone remodeling and growth may be enhanced through anterior column loading (AL). This is important for dynamic fusion rods because their purpose is to increase AL. METHODS: Six fresh-frozen lumbar cadaveric specimens were used. Each untreated specimen (Intact) underwent biomechanical testing. Next, each specimen had a unilateral transforaminal lumbar interbody fusion performed at L3-L4 using a cage with an integrated load cell. Pedicle screws were also placed at this time. Subsequently, the Isobar was implanted and tested, and finally, a rigid rod replaced the Isobar in the same pedicle screw arrangement. RESULTS: In terms of range of motion, the Isobar performed comparably to the rigid rod and there was no statistical difference found between Isobar and rigid rod. There was a significant difference between the intact and rigid rod and also between intact and Isobar conditions in flexion extension. For interpedicular displacement, there was a significant increase in flexion extension (P=0.017) for the Isobar compared with the rigid rod. Isobar showed increased AL under axial compression compared with the rigid rod (P=0.024). CONCLUSIONS: Isobar provided comparable stabilization to a rigid rod when using range of motion as the metric, however, AL was increased because of the greater interpedicular displacement of dynamic rod compared with a rigid rod. By increasing interpedicular displacement and AL, it potentially brings clinical benefit to procedures relying on arthrodesis.

Primary biliary B-cell lymphoma of the cystic duct causing obstructive jaundice.

A distinctive case of primary biliary lymphoma occurring in the cystic duct causing extrinsic compression of the porta hepatis in a 48-year-old woman is presented. Imaging studies revealed stricture of the common hepatic duct with a 2.5-cm nonhomogeneous mass at the porta hepatis, mimicking a Klatskin tumor. Exploratory laparotomy revealed a mass in the gallbladder neck with extension into the cystic duct akin to Mirizzi's syndrome. A soft, tan-yellow 1.0-cm mass was removed from the cystic duct, and infiltrating atypical lymphocytic nodules were identified with a final diagnosis of an anaplastic variant of diffuse large B-cell lymphoma.