What are optimum cycles for immediate primary closure of large cutaneous defects?

Abstract

Background:

In the reconstruction of large complex cutaneous wounds, a myriad of mechanical devices has been designed to facilitate primary wound closure. However, there is a dearth of studies elucidating how best to achieve optimum use and efficiency of skin stretching (SS) when using the device for immediate primary closure of defects.

Methods:

Skin defect wounds (7 × 7 cm) were prepared on the back of three Bama miniature pigs. A total of 15 cycles of SS (cycle loading) were subsequently performed on the skin edges of the wound by EASApprox® SS system. Then, the changes in equidistant points were recorded after each cycle. After the SS test, all wounds were sutured under low tension.

Results:

Skin elongation was observed at all equidistant points on the back wounds of three Bama miniature pigs. Up to an additional 1.10 to 3.75 cm of tissue was garnered. The maximum skin elongation was typically achieved within eight cycles of stretching and relaxation. Beyond this range, additional stretching cycles did not result in further skin extension.

Conclusion:

There may be a close link between mobilization range and the times of acute cyclic stretching (cycle loading) during the process of primary wound closure. However, larger studies are required to further evaluate the accuracy and effectiveness.

Introduction

Large cutaneous defects that are not amenable to primary closure are commonly observed in cases of traumatic injury, burns, and following tumor resection. Conventional suturing is typically used for the closure of small skin defects but is not considered optimal for large wounds.^1,2 The most commonly used methods for the closure of large wounds are split-thickness skin grafts, local flaps, and free tissue flaps.^3–5 However, these methods usually require complex surgical techniques and longer operation times. Moreover, these methods can lead to significant donor site damage, extend and can increase treatment costs.

The biomechanical characteristics of skin can be leveraged to provide a practical and reliable method for the repair of large wounds. By exerting a mechanical stretching force on the skin, both edges of the wound can be pulled together gradually, achieving complete wound closure. In recent years, studies have investigated the use of various external skin stretching (SS) devices for the closure of different types of large cutaneous defects with acceptable results.^6–11 These types of mechanical devices are designed to utilize the properties of the skin (such as mechanical creep and stress relaxation)^12–15 to provide extra skin for wound closure. Nevertheless, the clinical application of these devices is greatly limited by complications of SS, such as wound dehiscence, skin necrosis, hypertrophic scar, infection, and delayed healing.

There is a dearth of studies elucidating how best to achieve optimum use and efficiency of SS with these devices for immediate primary closure of large cutaneous wounds. We sought to elucidate the close link between mobilization range and the number of times of acute cyclic stretching (cycle loading) during the process of primary wound closure and conducted preliminary experiments to verify it.

Materials and methods

Skin-stretching device

EASApprox® skin-stretching system [BIOWIM (China), Ltd., Dalian, China], designed by Wilhelm Fleischmann, consists of special hooked needles, stretch components, and a tension indicator. Unlike other devices that grasp the skin edge with Kirschner wires, the special hooked needles are threaded through the dermis of the wound margins on either side of the defect and are connected by the rod of the stretching device. Three markers on the indicator included with the EASApprox® skin-stretching device respectively represent 0.5 kg (5 N), 1.5 kg (15 N), and 3.0 kg (30 N) of stretching tension. The stretching force on the skin margins is spread over a wide area, thus preventing damage to the skin that may be caused by the application of individual hooks to the skin.

Model preparation and skin-stretching test

As the model animal, three Bama miniature pigs (all females; weight 20–25 kg) were housed indoors, allowed to move freely, and provided outdoor access twice daily. On the day of surgery, the pigs underwent endotracheal intubation and were maintained under general anesthesia for the entirety of the experiment. The body temperature, heart rate, and respiratory rate were monitored throughout the procedure. After the anesthesia had taken effect, skin defect wounds (7 × 7 cm) were prepared by excising the skin and subcutaneous tissue on the back of the Bama miniature pigs. Pinch tests were made to manifest high tension, and a push/pull gage was used to measure the tension of each wound margin (19.52–21.05 N) to standardize the wounds. The length and width of the defects, without the wound edges being undermined, were both 7.0 cm. Subsequently, seven equidistant points, each approximately 1 cm apart, were marked from the wound edge to the distal end on the cephalic and caudal side of the skin defect, respectively.

The hook needles of the EASApprox® skin-stretching device were installed 0.5 cm away from the wound edge (Figure 1). A force of 1.0–3.0 kg was loaded for 4 min, followed by a 1-min period of relaxation.^2,16 A total of 15 cycles of SS (cycle loading) were subsequently performed. Then, the changes in equidistant points were recorded after each cycle. The same method was applied to the back of three piglets.

Figure 1.

The skin defect wounds (7 × 7 cm) were closed with the skin-stretching device.

After the SS test, all wounds were sutured with 2/0 sutures under low tension and bandaged with sterile dressings after disinfection. Following surgery, conventional dressing changes were performed every two days until complete healing of the wound. Wound care was conducted carefully and the status of healing was recorded during the process. Sutures were removed after the complete healing of the wound.

Results

Fifteen cycles of stretching and relaxation loading were performed on the three wounds, which were all eventually sutured under low tension. The measurement indicated that:

Skin elongation was observed at all equidistant points from the three wounds, including part G. Up to an additional 1.10 to 3.75 cm of tissue was garnered.

The range of extension at the equidistant points on the cephalic side of the wound was more obvious than those on the caudal side. Additionally, the points with the most significant change were at 7.0 cm from the wound edge on the cephalic side (Figure 1(g)) and 1 cm on the caudal side (Figure 1(a)).

The length of skin extended with the increase in the number of cycles of SS up to a certain threshold, after which the length showed no further increase. In the stretching state, the maximum stretched length of the primary equidistant points (Figure 1(a)–(g)) was usually reached within the range of six–eight cycles of stretching and relaxation (Figure 2(a)–(f)). In the relaxing state, the maximum stretched length of the primary equidistant points (Figure 1(a)–(g)) was usually reached within the range of seven–eight cycles (Figure 2(g)–(l)).

Figure 2.

The stretching state and the relaxing state of three wounds (A, B, C). (a–f) The stretching state; (g–l) the relaxing state; (a, c, e, g, i, k) the cephalic side of the wound; (b, d, f, h, j, i) the caudal side of the wound.

No more than nine cycles are advised because no extra skin extension occurred with a further increase in the number of cycles. Our findings suggest that there is a connection between the number of cycles of stretching and the length of the extended skin. It is counterintuitive that more cycles of stretching did not result in further skin extension. However, our results indicated that skin may reach its maximum capacity for extension after a certain number of cycles; after reaching that threshold, other ways for further reducing the tension of the skin should be tried.

Discussion

Reconstruction of large complex cutaneous wounds poses a challenge to the surgeon. Closure of large cutaneous defects is often not possible by the primary closure due to high wound tension. ¹⁷ Skin graft, local flap, free tissue transfer procedure, or various combinations of the aforementioned options have been used to close large defects.^{5,6,10,11,17–22} In-depth studies of the biomechanical characteristics of the skin have facilitated the development of mechanical devices to enable the closure of large cutaneous defects that cannot be sutured directly. These devices can downgrade the surgical complexity, reduce operating time and shorten the hospital stay. In 1993, Hirschowitz et al. first reported a skin-stretching device that harnesses the viscoelastic and stress relaxation properties of skin to stretch the tissue and close the defect. ¹² Since then, many modifications, such as SureClosure®, Wiseband®, TopClosure, and BHS®, have been presented in the literature.^{6,8–11,15,17} These methods facilitate wound closure by extending skin in close proximity or adjacent to the margins of a wound or the proposed operative area.^10,23–27 However, due to complications of wound dehiscence, hypertrophic scarring, infection, marginal necrosis, and delayed healing, many of these techniques are not used widely in clinical settings. Song et al. introduced EASApprox® skin-stretching system, a novel and user-friendly skin-stretching device, and demonstrated its effectiveness in facilitating the closure of large cutaneous defects. ²⁸ However, the usage of these skin-stretching devices is yet to be optimized.

Collagen, elastin, and ground substances are the main components of the dermis. ²⁹ Among them, collagen is the main structure of the skin. ³⁰ In the relaxed state, collagen fibers are arranged in a haphazard mode. However, in the stretched state, these fibers are aligned parallel to each other. Mechanically, collagen fibers have high tensile strength and lack extensibility. They are the main source of structural support for the skin but do not play a significant role in its recoiling abilities. ³¹ Elastin, accounting for 4% of the fat-free dry weight of skin, is characterized by long-range elastic extensibility. This implies that elastin maintains the ability to return to its original shape even after maximal strain. Elastin has an intimate relationship with collagen and promotes the return of collagen to its wavy posture in the resting state.

The crux of successful stretching is the viscoelastic property of the skin, which has been divided into four separate entities: (a) inherent extensibility, (b) mechanical creep, (c) biologic creep, and (d) cycle loading. The inherent extensibility can be assessed with the pinch test and varies with the anatomic site. Mechanical creep is one of the biomechanical properties that allows for SS beyond the limitations of inherent extensibility under mechanical loading. The skin extends over a period of time. The rapidity of extension is dependent on the force applied and occurs over several minutes. The loading straightens the collagen fibers from their primary random, convoluted pattern and, with more loading, also displaces the tissue fluid. The corollary of mechanical creep is stress relaxation, wherein if the skin is stretched over a constant distance, the tension required to maintain the stretched state will decline gradually. Biologic creep is not a real stretching of the skin but refers to the gradual expansion of the subcutaneous tissue. This phenomenon usually occurs in the gravid uterus, enlarging tumors, and inflatable tissue expanders. Cycle loading (an intermittent stretching force and relaxation cycle) is believed to be one of the most efficient ways of stretching skin. ³² Based on these principles, skin-stretching systems have been designed to exploit the potential for the primary closure of large cutaneous defects within a short time. Kumar et al. adopt the preoperative SS technique for wound closure with staged cycle. The tension relief system was kept in place for a period until sufficient skin laxity was obtained. However, the mean duration of stretch was still more than 2 weeks. ³³

For better accuracy and representativeness of the results, we chose the back of the miniature pig as the experimental site; it has a flat and wide surface from head to tail, is easy to measure, and is not affected by the bending of the limbs.

A mechanical load cycling was performed by applying traction to wound edges using skin hooks of the EASApprox® device at 5-min intervals for a total of 15 cycles. When the skin is stretched using this method over minutes, the elastic fibers do not revert to their original state. The mechanism of lengthening may include the displacement of fluids and ground substance, fragmentation of elastic fibers, alignment of haphazard collagen fibers into a parallel array, and migration of tissue along the direction of force. ³⁴ This allows for adequate mobilization of the extra adjoining skin to overcome the skin shortage. In our study, up to an additional 1.10 to 3.75 cm of tissue was garnered with this approach. The extent of elongation observed at all equidistant points from the three wounds, including part G, suggested that the skin at 7.0 cm from the wound edge still has the potential to be mobilized. The differences in the extension range at equidistant points on both sides of the wound suggested that the skin on the cephalic side is more easily stretched.

Additional cycles did not result in further stretching of the skin. Besides, the strong stretching force can make the small blood vessels taut and constrict their laminae; thus persistent stretching for too long can even lead to cessation of blood flow, potentially resulting in necrosis of the skin margins. ¹²

Operation time is the limiting factor in the stretching of the skin. Long operation time can severely compromise skin viability. Skin pallor, tautness, pain, and perhaps shininess are indicators that can enable the surgeon to assess the extent of stretching force that can be safely applied to wound margins. Up to now, the surgeon's experience seems to be the main factor determining the modalities of this approach. In our study, the maximum stretched length of the skin was usually reached after seven–eight cycles of stretched state and relaxed state. When both skin and subcutaneous tissues are normal, rapid cyclic stretching within a short time span of 30 to 40 min (six–eight cycles) may be the general rule. In conclusion, we found that there might be a link between mobilization range and times of cyclic stretching (cycle loading). The viscoelasticity of human skin is similar to that of pigs. Our results provide preliminary proof of the duration of stretching that can be applied safely and efficiently to primary wound closure.

Nevertheless, skin viscoelasticity differs in different parts of the body. ¹² A limitation of the study was the lack of discussion of wound closure at other sites of the body, especially in areas subjected to bending and angular stress (e.g. skin overlying the limb joints). We only conducted a preliminary experiment on a plane site (back) which is fairly representative of the commonly encountered cases in clinical practice. Additionally, we did not analyze the sample size of the animals. Although the study was limited to larger animals, the sample size in our study was relatively small. Larger studies are required to further validate our findings.

Conclusion

This study suggests that there may be an optimal stretch relaxation cycling of eight total cycles for wound closure with skin-stretching devices or techniques. The hypothesis proposed herein furthers the understanding of skin biomechanical characteristics, improves the efficiency of new devices for closing large cutaneous defects, and reduces potential complications. Currently, there is a paucity of relevant guidelines for clinical settings. Therefore, deciphering the relationship between mobilization range and the frequency of cyclic stretching is of much clinical relevance.