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Intervertebral disc degeneration is a highly prevalent disorder with connections to low back pain. Among the early changes in degeneration is a reduction in glycosaminoglycan content in the nucleus pulposus of the disc. How this biochemical change alters disc health and function is not well defined, though such knowledge is needed to develop therapeutics to halt or reverse degeneration. The overall objective of this work was to model reduced nucleus glycosaminoglycan, as in early degeneration, in a rat lumbar disc to better understand the impact of this change on disc structure, mechanics, and biochemistry and on the progression of disc degeneration. To determine the impact of reduced nucleus glycosaminoglycan on disc mechanics, an in vitro model of this biochemical change was created. Nucleus glycosaminoglycan levels correlated with disc mechanics with loss leading to a state of hypermobility. Dynamic viscoelastic testing demonstrated a similar relationship at low compressive loads across a spectrum of frequencies and showed an increase in phase angle with glycosaminoglycan loss. Thus, reduced glycosaminoglycan can directly alter disc mechanics and may contribute to degeneration progression through mechanical means. Reduced glycosaminoglycan was modeled in a rat lumbar disc in an in vivo environment with temporal changes in disc properties evaluated up to 24 weeks post reduction. Initial changes in mechanics, biochemistry, and height consistent with early human degeneration were noted; however, a response more akin to regeneration than degeneration was observed as properties recovered towards control levels by 24 weeks. No association between the altered nucleus biochemistry and degeneration-like changes in cellularity or disc morphology were observed. Analysis of aggrecan fragmentation revealed an apparent decrease in catabolism in this model, which may be responsible in part for the recovery of disc properties. In summary, in vitro and in vivo models of reduced n

The campaign and Battle of Chickamauga, August-September 1863, is an excellent vehicle for a Staff Ride. Because of the size of the forces involved and the difficulty of the terrain encountered, it represents an opportunity to raise many challenging teaching points relevant to today's officer. Second, the nation has wisely preserved most of the primary battle area in the Chickamauga and Chattanooga National Military Park and has marked most unit positions for detailed study by visitors. The "Staff Ride Handbook for the Battle of Chickamauga, 18-20 September 1863," provides a systematic approach to the analysis of this great Civil War battle. Part I describes the organization of the Federal and Confederate Armies, detailing their weapons, tactics, and logistical, engineer, communications, and medical support. In part II, the Chickamauga campaign is discussed, placing the battle in historical perspective and illustrating how the battle fits into the overall context of the Chickamauga campaign. Part III furnishes a suggested route to follow to get a firsthand, concrete view of how the battle developed. By following this route, various phases of the battle can be discussed and significant points made concerning the evolving battle. Also in part III are various vignettes by participants in the battle that describe the fight and offer insights into the emotional disposition of the combatants. Part IV furnishes current information on the Chickamauga site, sources of assistance, and logistical data for conducting a Staff Ride. In addition, appendixes give order of battle information for the two armies, meteorological data, and a list of Medal of Honor recipients in the battle. A bibliography also is provided