Experimental wound healing with electrical stimulation.

The effect of alternating current (AC) and direct current (DC) stimulation was studied on experimental pressure ulcer healing in a new monoplegic pig model. The study was conducted in 30 healthy young Hanford minipigs. The rate of wound healing, histology, vascularization, collagen formation, microbiology, perfusion, and the mechanical strength of the healed wounds were studied. Normal pigskin was compared to denervated control and denervated AC and DC stimulated healed skin. Hind limb denervation was by right unilateral extradural rhizotomies from the L2 to S1 nerve roots. Reproducible uniformly controlled Stage III or higher tissue ulcers were created. When compared to the control wounds, both the AC and DC stimulated wounds showed reduced healing time and increased perfusion in the early phases of healing. DC stimulation reduced the wound area more rapidly than AC, but AC stimulation reduced the wound volume more rapidly than DC. The electrical stimulation did not reduce the strength of the healing wounds below those of the nonstimulated controls. The applied current appears to orient new collagen formation even in the absence of neural influences.

Evaluation of collagen ceramic composite graft materials in a spinal fusion model.

Autogenous bone graft is highly effective in inducing a bone healing response in most clinical settings. However, significant morbidity can occur related to the harvest of an autograft. This makes the development of synthetic or purified nontissue bone grafting materials highly desirable. Both purified bovine Type I collagen and calcium phosphate ceramics have been proposed as promising osteoconductive bone graft substitute materials. One collagen ceramic composite, Collagraft, is approved for use in acute long bone fractures. This study evaluated composites of purified bovine Type I fibrillar collagen and a granular biphasic hydroxyapatite/tricalcium phosphate ceramic in the posterior segmental canine spinal fusion model. Materials were compared based on union score and mechanical testing in 3 separate fusion sites (L1-2, L3-4, L5-6). All composites were found to be inferior in union score to an equal volume of autogenous cancellous bone. In addition, the combination of the collagen ceramic composite with autogenous cancellous bone graft reduced the effectiveness of the autogenous bone graft significantly. These data should be a caution to the clinician who may consider use of collagen ceramic composites similar to Collagraft for spinal fusion applications.

Evaluation of a pressure sore model using monoplegic pigs.

This study evaluated a newly developed swine monoplegic pressure sore model by testing the uniformity of the initial wound size. The natural healing also was evaluated. Nine minipigs were used. The hindlimb was denervated by transecting the unilateral nerve roots L1 through S2. At 5 to 14 days, 800 mmHg of pressure was applied to the denervated skin over the trochanteric area with a 3-cm-diameter disk compressing the skin and subcutaneous tissue against the underlying bone for 48 hours. The wound was then debrided of devascularized tissue. Wound surface areas were calculated from photographs. Wound volumes were obtained by measuring the volume of saline needed to fill the wound defect. Full-thickness sores of uniform size developed in all pigs without mortality or complications. Wound surface area and volume increased initially, peaked, and then decreased in an exponential fashion. This model provides a new tool for direct comparison of pressure sore treatment modalities for short- and long-term studies.

[Histological observations on muscle tissue reactions to porous hydroxyapatite sintered bodies in rats].

Blocks of porous hydroxyapatite (dimensions, 2 X 3 X 4 mm3; sintering temperature, 1,150 degrees C; macroporosity, 48%; pore diameter, 50-300 microns) were implanted into the intervening space between the tibial periosteum and the tibialis anterior muscle in 36 male Wistar rats at the age of 5 months. Specimens from the lower leg were obtained 1, 2, 3, 5, 8 and 12 weeks after implantation. The implants were found to adhere firmly to the tibialis anterior in the 5 and 12 week-specimens. No inflammatory reactions were seen around the implants and a layer of fibrous tissue was observed between the implanted apatite block and the muscle in all specimens. The fibrous tissue penetrated deeply into pores of the apatite block. The resistance to pulling of the interface (3 X 4 mm2) between porous hydroxyapatite and the tibialis anterior muscle was measured using a universal testing machine. The mean of the resistance to pulling was 24.7 +/- 5.1 gf/mm2 in 4 specimens of 12 weeks implantation.