Posttraumatic arthritis is one of the most frequent causes of disability following joint trauma. The objective of this study was to develop a model of a closed articular fracture in the mouse knee joint to quantify the temporal sequence of joint degeneration in a model of posttraumatic arthritis. Closed intraarticular fractures were created in the tibial plateau of adult mice (C57BL/6) using a computer-controlled materials testing system and a custom-built indenter tip. Tibial plateau fractures were classified and imaged over time using high-resolution digital radiography. Animals were sacrificed at 2, 4, 8, and 50 weeks following fracture, and the experimental and contralateral control limbs were harvested for histology and micro-computed tomography (microCT) analysis. By radiographic analysis, tibial plateau fractures closely resembled clinical fractures. More complex and comminuted fractures correlated to significantly higher fracture energies. Histologic analysis demonstrated progressive joint degeneration as measured by a modified Mankin scale, with fibrillation and loss of proteoglycan in the articular cartilage. Subchondral bone thickening was also observed in experimental joints. The induction of a closed intraarticular fracture of the mouse tibial plateau generated a reproducible and clinically relevant joint injury that progressed to osteoarthritis-like changes by histologic and microCT evaluations. The ability to induce joint degeneration without an osteotomy or open arthrotomy provides a valuable new model for studying the natural sequelae of posttraumatic arthritis. Notably, the use of a murine model will facilitate the use of genetically modified animals for the investigation of specific genes implicated in the pathology of posttraumatic arthritis. ß

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In an attempt to improve the function of the straight ileoanal anastomosis, an experimental study was performed using the swine model. The terminal ileum was altered by completely removing two longitudinal strips of muscle prior to performing a straight ileoanal anastomosis. The intent of the study was to determine whether muscle stripping was technically possible and whether bowel thus treated would remain viable to passively form a pelvic reservoir. The length of time required for formation of the reservoir was noted. All animals survived the procedure to allow evaluation. The muscle stripping was not difficult to perform. Viability was not a problem since the myectomy animals thrived well and demonstrated continence, weight gain, and reservoir formation. The results are encouraging. It appears that strips of muscularis propria can be removed from the terminal ileum without jeopardizing its viability. This seems to disrupt sufficiently the tonus of the bowel to allow better function of the straight ileoanal anastomosis through formation of a passive pelvic reservoir within a month's time in the swine model, and it may have application in the human.

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