Despite the recent introduction of several collagen based soft tissue substitutes, a lack of comparative clinical and histological analysis has complicated long term characterization.  Ideally, such material would be durable, nonimmunogenic, virtually noninfectious, and would maintain consistency for an extended time period.  Although AlloDerm (cadaveric dermal matrix), Enduragen (porcine dermal matrix), and Dermamatrix (cadaveric dermal matrix) reportedly offer these characteristics, comparative analyses of these materials over an extended time period is presently nonexistent.  In the present study, the long-term clinical and histologic response of these three popular collagen-based materials in the in vivo murine model.
Methods:  Adult mice (n=8) received standardized 3mm^X1cm^X1cm AlloDerm, Enduragen, and Dermamatrix implants in individual dorsal subcutaneous pockets at Day=1.  At time periods 3,6,9, and 12 months, n=2 mice were harvested for examination of all implant materials.  Composites of skin, subcutaneous tissue, implant, and underlying muscle were harvested for qualitative study.  Upon clinical analysis, graft materials were evaluated for migration, firmness, and mass maintenance.  Histologically, specimens were analyzed for inflammatory response, encapsulation, and degree of tissue incorporation. 
Results:  Although histological assessment of all three samples demonstrated similar encapsulation, peripheral infiltration, and surrounding inflammation, substantial variation was apparent on macroscopic evaluation.  Enduragen maintained its original shape, and developed a cartilaginous firmness.  Alloderm samples developed a loose, folded spherical shape, and were palpably firm.  Dermamatrix, the second cadaveric dermal implant, both maintained its original shape and consistency.  Despite these deviations in form, the volume and mass of all implants remained unchanged throughout the study period.  Additionally, implant migration or extrusion was not observed. 
Conclusions:  Histologically, all implant materials evaluated in the present study promoted neovascularization, incorporation, volume maintenance, and a high degree of host tolerance.  However, subtle differences in microscopic behavior likely explain significant, long term variations in graft consistency and structure.