Biomechanical Effects of Unidirectional Expansion Using Anisotropic Expanders in Horse Skin Tissue.

The use of a self-inflating tissue expander is a technique to stretch cutaneous tissues for potential use in reconstructive skin surgeries. This study investigates the mechanical properties of horse skin stretched by the subcutaneous implantation of anisotropic tissue expanders at the forehead, right shoulder, and dorsomedial part of the cannon region of the right forelimb in six (n = 6) horses. After 14 days of skin expansion, expanded and normal (control) skin samples were harvested and their mechanical properties of elastic modulus (EM), maximum force (MF), maximum stress (MSs) and maximum strain (MSr) were evaluated using uniaxial tension test. The expanded skin from shoulder area has higher EM, MSs, MSr and MF than the normal skin when compared to the forehead and lower forelimb. Statistically, there was a significant (P= .02) mean difference for MSs between the expanded shoulder and lower forelimb skin, but the pairwise comparison of EM, MSr and MF showed no significant difference between the locations. The overall effect of locations on EM and MSs was statistically significant (P < .05), however, there was no overall effect of horse factor, treatment factor (normal and expanded skin) and location interaction on the EM, MSS, MF and MSr. In conclusion, the expanded skin from the frontal head and the distal limb are less elastic (stiffer) compared to that of the expanded skin of the shoulder, thus anatomical location of the skin has some degree of effect on EM and MSs.

Outcome of reconstruction of cutaneous limb defects in dogs using hygroscopic "self-inflating" tissue expanders.

OBJECTIVES: To describe the placement of self-inflating tissue expanders and clinical outcomes in 12 consecutive cases of reconstruction of distal cutaneous limb defects in dogs. MATERIALS AND METHODS: Cases of distal cutaneous limb defect were divided into three groups based on the location of the placement of the self-inflating tissue expanders: Group A (n=4): on, or proximal to, the elbow and stifle; Group B (n=4): distal to the elbow or stifle and proximal to the carpus or tarsus; and Group C (n=4): distal to the carpus or tarsus. Owner satisfaction and clinical outcome were documented. RESULTS: Thirteen cases were originally included, but one was excluded because of incomplete follow-up. In one case, the self-inflating tissue expanders were removed before expansion started. A mean of five expanders were implanted per dog (range 2 to 9). Devices were removed after a mean of 24 days (range 13 to 42 days). Primary closure was achieved in eight of 11 cases, including all cases from Group A and 75% and 33% of cases from Groups B and C, respectively. All incompletely reconstructed defects or areas of wound dehiscence healed by second intention. Eight of 12 owners were satisfied. CLINICAL SIGNIFICANCE: Self-inflating tissue expanders can be used as an alternative for the reconstruction of limb defects in dogs in which direct primary closure would otherwise not be achievable. Defects below the carpus and tarsus are more challenging to treat with this method.

Comparison of three skin-stretching devices for closing skin defects on the limbs of dogs.

Our objective was to evaluate the effectiveness of skin-stretching devices for closing defects on the extremities of dogs. Antebrachial skin defects were created on the limbs of 24 dogs randomly divided into three groups. Skin stretchers included staples and sutures passing through them (group A), sutures and hypodermic needles (group B), and Pavletic device (group C). Wounds on the left were further undermined in all groups. Tension and blood perfusion were assessed. After removing the stretchers on day 3, the defects were sutured and wound healing was clinically scored. Histological variables evaluated were cellular infiltration, edema, collagen orientation, and thickness of epidermis. Significant differences in tension were found among groups (p 0.0005) and between measurement times for undermined (p = 0.001) or non-undermined (p < 0.0005) wounds. In contrast, blood perfusion values did not differ significantly. Clinical scores for group B seemed to be better than those for groups A and C, but differences were not significant. Primary wound closure using the Pavletic device was not feasible. No significant differences in histological variables were found between groups. Skin stretching with staples or hypodermic needles resulted in successful wound management with minor side effects on skin histology and circulation.

Use of a full-thickness autograft on the tarsus of an ostrich.

Full-thickness, cutaneous autografting was successfully performed on an adult female ostrich to heal a granulomatous wound on the right tarsus. With surgical techniques used in domestic species such as dogs and horses, skin grafting is an alternative in avian species when conventional wound closure is not appropriate.

Rapid tissue expansion for the development of rotational skin flaps in the distal portion of the hindlimb of dogs: an experimental study.

In phase I, tissue expanders were implanted subcutaneously over the lateral crural region of four dogs. The expanders were inflated daily to maintain a constant intraluminal pressure for 7 days. All animals tolerated the pressurized expanders well. Some animal patient discomfort was associated with repeated injections into the subcutaneous filling port. One dog developed a limited area of tissue loss and exposure of the expander. Tissue response to the expanders included epidermal hyperplasia, dermal collagen compression with early fibroplasia, and subcutaneous granulation tissue formation adjacent to the expander pocket. In phase II, a second group of four dogs underwent rapid skin expansion over 7 days. The pressure applied to the expanding skin was determined daily and adjusted to approximate the value reported for capillary pressure in the dog. Tissue discoloration occurred in two dogs, suggestive of impaired circulation. Skin flaps were developed from expanded skin and rotated over the talocrural region. Wound dehiscence occurred along the distal flap margin in three phase II dogs. These wounds healed by second intention. Branches of the caudal saphenous artery were identified, using angiography, as the primary blood supply to the skin flaps.

Controlled tissue expansion in the distal extremities of dogs.

Controlled tissue expansion using a 100 cc rectangular silicone elastomer expander was performed in the mid-antebrachium and mid-crus of eight adult mixed-breed dogs. Two expander inflation schedules were followed. Group 1 dogs (n = 4) underwent expander inflation using 10 cc sterile saline every other day, and group 2 dogs (n = 4) underwent expander inflation using 15 cc sterile saline every other day until the nominal volume (100 cc) was attained. Significant mean postexpansion increases in skin surface area of 94.1 cm2 (35.9%) and 108.9 cm2 (37.3%) were measured in the antebrachium and crus, respectively (p < .05). In a second procedure, the expanders were removed and skin flaps were developed from the redundant tissue generated during the expansion process. Single pedicle advancement flaps and transposition flaps were used to cover surgically created defects measuring 5 x 10 cm in the antebrachium and crus. Single pedicle advancement flaps consistently measured 10 x 10 cm and could be advanced to cover defects involving one third of the mid-antebrachial or mid-crural circumference. Transposition flaps were rotated up to 170 degrees and the donor site defects were easily closed under minimal or no tension. Complications included an abscess in one dog and seroma formation in four dogs. Differences in success or complication rates between group 1 dogs and group 2 dogs were not observed; an accelerated inflation schedule using 15 cc sterile saline every other day was recommended.

Tissue expansion.

Although tissue expansion is unlikely to replace skin grafting and other basic reconstructive procedures in the horse, its continued success in humans will undoubtedly stimulate client interest in its use. Its biggest advantage is the advancement of full-thickness skin over large defects where grafting techniques would not provide the same degree of protection. The resulting cosmetic appearance of the wound is also better.