Tension Decrease during Skin Stretching in Undermined versus Not Undermined Skin: An Experimental Study in Piglets

Refractory Folliculitis Decalvans Treatment Success with a Novel Surgical Excision Approach Using Guarded High-Tension Sutures

Purpose

Folliculitis decalvans (FD) is a difficult-to-treat, localized scarring alopecia characterized by an expanding area of chronically inflamed purulent plaques or masses. Current treatment modalities vary and often result in only temporary remission. There are no reports of surgical therapies for FD. Here, we describe FD treatment using surgical excision and second-intention healing aided by guarded high-tension sutures.

Methods

Five patients (one woman and four men) with histologically confirmed FD were treated by surgical lesion excision. All wounds were allowed to heal via second-intention. Guarded high-tension sutures were employed to minimize tissue tears while aiding and guiding wound contraction.

Results

All wounds healed with a 47-83% spatial contraction of the maximum wound diameters. Three patients healed entirely by second-intention, while two required a minor skin graft to close the wound completely. No disease recurrence was noted at 10-24 months.

Conclusion

Surgical excision with second-intention healing aided by guarded high-tension sutures effectively treated small and extensive FD lesions with no recurrence at long-term follow-up. To our knowledge, this is the first report of successful surgical treatment of FD.

Measuring Forces in Suture Techniques for Wound Closure

BACKGROUND

The use of sutures remains the first choice for wound closure. However, incorrect use of a suture technique can lead to impaired healing. Many techniques are described for high-tension wounds, but not much is known about their mechanical properties. Complications of excessive tension include dehiscence, infection, and ischemic necrosis and could be prevented. This study aimed to compare forces in five techniques (single, horizontal mattress, vertical mattress, pulley, and modified pulley suture) in a standardized wound tension model.

MATERIALS AND METHODS

A standardized neoprene wound model was developed on the ForceTRAP system (MediShield B.V., Delft, The Netherlands) to mimic a 5 Newton (N) wound. Five different suture techniques were each repeated 10 times by a student, resident dermatology, and dermsurgeon. The pulling force of the suture's first throw was measured with the Hook-in-Force sensor (Technical University Delft, The Netherlands). Changes in wound tension were measured by the ForceTRAP system. The ForceTRAP is a platform measuring forces from 0 to 20 N in three dimensions with an accuracy of 0.1 N. The Hook-in-Force is a force sensor measuring 0-15 N with an accuracy of 0.5 N. Maximum and mean forces were calculated for each suture technique and operator.

RESULTS

Mean maximum pulling force: 5.69 N (standard deviation [SD], 0.88) single, 7.25 N (SD, 1.33) vertical mattress, 8.11 N (SD, 1.00) horizontal mattress, 3.46 N (SD, 0.61) pulley, and 4.52 N (SD, 0.67) modified pulley suture. The mean force increase on the skin (substitute) ranged between 0.80 N (pulley) and 0.96 N (vertical mattress).

CONCLUSIONS

The pulley suture requires less pulling force compared with other techniques. The mechanical properties of sutures should be taken in consideration when choosing a technique to close wounds.

Percutaneous Fasciotomies versus Traditional Keystone Flap: Evaluating Tension in Complex Wound Closure

Supplemental Digital Content is available in the text.

The keystone flap is a popular reconstructive option for closure of cutaneous defects. Traditionally, this is a perforator-based fasciocutaneous advancement flap that uses both skin incision and fascial release. We propose a limited skin incision technique that utilizes percutaneous fasciotomies to accomplish wound closure.

Biomechanical Modeling of Wounded Skin

Skin injury is the most common type of injury, which manifests itself in the form of wounds and cuts. A minor wound repairs itself within a short span of time. However, deep wounds require adequate care and sometime clinical interventions such as surgical suturing for their timely closure and healing. In literature, mechanical properties of skin and other tissues are well known. However, the anisotropic behavior of wounded skin has not been studied yet, specifically with respect to localized overstraining and possibilities of rupture. In the current work, the biomechanics of common skin wound geometries were studied with a biofidelic skin phantom, using uniaxial mechanical testing and Digital Image Correlation (DIC). Global and local mechanical properties were investigated, and possibilities of rupture due to localized overstraining were studied across different wound geometries and locations. Based on the experiments, a finite element (FE) model was developed for a common elliptical skin wound geometry. The fidelity of this FE model was evaluated with simulation of uniaxial tension tests. The induced strain distributions and stress-stretch responses of the FE model correlated very well with the experiments (R2 > 0.95). This model would be useful for prediction of the mechanical response of common wound geometries, especially with respect to their chances of rupture due to localized overstraining. This knowledge would be indispensable for pre-surgical planning, and also in robotic surgeries, for selection of appropriate wound closure techniques, which do not overstrain the skin tissue or initiate tearing.

Wound tension and 'closability' with keystone flaps, V-Y flaps and primary closure: a study in fresh-frozen cadavers

BACKGROUND

Previous publications have implied that the keystone flap provides mechanical benefits compared to primary closure. This has not been objectively demonstrated.

METHODS

Elliptical defects were created in 'fresh-frozen' cadaveric specimens. Two approaches were used to investigate the potential mechanical benefits of keystone flaps. Experiment 1 (wound closure): 18 defects were incrementally enlarged until they could not be closed primarily either with a single 'midpoint' suture or with a continuous suture. Attempts were then made to close these wounds with island flaps: 13 keystone flaps (seven 'type IIA' and six 'Sydney Melanoma Unit (SMU) modification') and five V-Y flaps. Experiment 2 (tension reduction): 28 defects were fashioned to be 'closable' under high tension. The 'pre-flap tension' was measured with a single midpoint suture and tensiometer. Fourteen keystone flaps (seven type IIA and seven SMU modifications) and seven V-Y flaps were then developed and mobilized with no flap constructed on the remaining seven 'primary closure' wounds. The secondary defects resulting from flap mobilization were closed leaving the primary defect unsutured. The primary defect 'post-flap tension' was then measured using the same technique.

RESULTS

For Experiment 1, V-Y flaps enabled closure in four of five 'unclosable' defects. Keystone flaps did not enable closure in any of the 13 cases (P < 0.001). For Experiment 2, the V-Y flap (n = 7) was the only group that produced a significant drop in wound tension across the primary defect (mean 'pre-flap' to 'post-flap' tension change: -53%, 95% CI: -67 to -39%, P < 0.001).

CONCLUSION

The data raise questions about the biomechanical benefits of keystone flaps.

A REALISTIC 3D COMPUTATIONAL MODEL OF THE CLOSURE OF SKIN WOUND WITH INTERRUPTED SUTURES

Wounds or cuts are the most common form of skin injuries. While a shallow wound may heal over time, deep wounds often require clinical interventions such as suturing to ensure the wound closure and timely healing. To date, suturing practices are based on a surgeon's experience and there is no benchmark to what is right or wrong. In the literature, there have been few attempts to characterize wound closure and suture mechanics using simple 2D computational models. In our current work, for the first time, a realistic three-dimensional (3D) computational model of the skin with the two layers, namely the epidermis and dermis, have been developed. A 3D diamond shaped wound with a varying cross-section has been modeled, and interrupted sutures have been placed numerically in multiple steps to close the wound. Nonlinear hyperelastic material properties have been adopted for the skin and a skin pre-stress was applied bi-axially. The force requirements for each suture were estimated numerically using a novel suture pulling technique. The suture forces were found to lie in the range of 0–5 N with a maximum value at the center. Also, the center suture was observed to require an approximately four times pull force compared to the first end suture. All these findings provide important guidelines for suturing. Additionally, the suture force can be approximated as a polynomial function of the displacement. Given a wound geometry, wound depth, skin material properties, skin pre-stress, suture wire material and cross-sectional area, using our computational model, such a relationship can be used to estimate and characterize the suture force requirements accurately. To our knowledge, such a 3D computational model of skin wound closure with interrupted sutures have not been developed till date, and would be indispensable for planning robotic surgeries and improving clinical suturing practices in the future.

Absolute polarity determination of teeth cementum by phase sensitive second harmonic generation microscopy

The absolute sign of local polarity in relation to the biological growth direction has been investigated for teeth cementum using phase sensitive second harmonic generation microscopy (PS-SHGM) and a crystal of 2-cyclooctylamino-5-nitropyridine (COANP) as a nonlinear optic (NLO) reference material. A second harmonic generation (SHG) response was found in two directions of cementum: radial (acellular extrinsic fibers that are oriented more or less perpendicular to the root surface) and circumferential (cellular intrinsic fibers that are oriented more or less parallel to the surface). A mono-polar state was demonstrated for acellular extrinsic cementum. However, along the different parts of cementum in circumferential direction, two corresponding domains were observed featuring an opposite sign of polarity indicative for a bi-polar microscopic state of cellular intrinsic cementum. The phase information showed that the orientation of radial collagen fibrils of cementum is regularly organized with the donor (D) groups pointing to the surface. Circumferential collagen molecules feature orientational disorder and are oriented up and down in random manner showing acceptor or donor groups at the surface of cementum. Considering that the cementum continues to grow in thickness throughout life, we can conclude that the cementum is growing circumferentially in two opposite directions and radially in one direction. A Markov chain type model for polarity formation in the direction of growth predicts D-groups preferably appearing at the fiber front.

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.

Skin stretching for primary closure of acute burn wounds

BACKGROUND

In burn care, a well-acknowledged problem is the suboptimal scar outcome from skin grafted burn wounds. With the aim of improving this, we focused on a new technique: excision of the burn wound followed by primary closure, thereby using a skin-stretching device to stretch the adjacent healthy skin. The short- and long-term effect of Skin Stretch was compared to split skin grafting (SSG) in a randomized controlled trial.

METHODS

Patients with burn wounds were randomized for SSG or primary wound closure using Skin Stretch. Follow-up was performed at 3 and 12 months postoperatively. The scar surface area was calculated and the scar quality was assessed, using subjective and objective measurement methods.

RESULTS

No significant differences between the SSG and the Skin Stretch group were found for scar surface area. In the Skin Stretch group, a significant reduction of the surface area from 65.4cm(2) (13.6-129.1) to 13.4cm(2) (3.0-36.6) was found at 3 months (p=0.028) and at 12 months postoperatively (65.4cm(2) (13.6-129.1) to 33.0cm(2) (8.9-63.7), p=0.046, Wilcoxon signed ranks test).

CONCLUSIONS

Skin Stretch for primary closure of acute burn wounds is a suitable technique and can be considered for specific circumscript full-thickness burn wounds. However, future research should be performed to provide additional scientific evidence.

Adaptation of the dermal collagen structure of human skin and scar tissue in response to stretch: an experimental study

Surgeons are often faced with large defects that are difficult to close. Stretching adjacent skin can facilitate wound closure. In clinical practice, intraoperative stretching is performed in a cyclical or continuous fashion. However, exact mechanisms of tissue adaptation to stretch remain unclear. Therefore, we investigated collagen and elastin orientation and morphology of stretched and nonstretched healthy skin and scars. Tissue samples were stretched, fixed in stretched-out position, and processed for histology. Objective methods were used to quantify the collagen orientation index (COI), bundle thickness, and bundle spacing. Also sections were analyzed for elastin orientation and quantity. Significantly more parallel aligned collagen bundles were found after cyclical (COI = 0.57) and continuous stretch (COI = 0.57) compared with nonstretched skin (COI = 0.40). Similarly, more parallel aligned elastin was found after stretch. Also, significantly thicker collagen bundles and more bundle spacing were found after stretch. For stretched scars, significantly more parallel aligned collagen was found (COI = 0.61) compared with nonstretched scars (COI = 0.49). In conclusion, both elastin and collagen realign in a parallel fashion in response to stretch. For healthy skin, thicker bundles and more space between the bundles were found. Rapid changes in extension, alignment, and collagen morphology appear to be the underlying mechanisms of adaptation to stretching.

Closure or reduction of the donor defect of a sural flap with a purse-string suture: long-term results

We aimed to reduce the defect with a purse-string suture to minimise the deformity of the flap donor area and to assess the later efficiency at long-term follow-up. We studied 20 patients who required a sural flap for the reconstruction of defects of the lower extremity. The mean (SD) area of the donor defect was roughly 28.7 (20.3) cm(2). The mean (SD) defect area after closure with a purse-string was 8.2 (5.8) cm(2) (p < 0.001). The measurements made in the third year were 8.4 (5.3) cm(2). The purse-string can be used successfully in the distal lower extremity, the long-term cosmetic outcome is good, and the scar has not expanded since the postoperative period.

The analysis of forces needed for the suturing of elliptical skin wounds

There is a lack of information regarding the forces required for suturing human wounds. The knowledge of suturing forces serves as complementary information for setting up the limiting geometry when using tissue adhesives and it might also be used in robot-assisted surgery. The main purpose of this paper was to evaluate the forces required for suturing selected skin wounds. An elliptical wound was chosen for our study. In this study a numerical analysis and in vivo experiments were performed. Regarding the numerical models, the maximum forces occurred in the middle of the elliptical wound in all cases. In the case of highest pre-stress used in these analyses the maximal force varied from 0.5 N for the smallest wound (30 × 5 mm) to 1.5 N for the largest wound (30 × 15 mm). The maximum peak force for the wound with a size of 46 × 13 mm was 3.2 N. The minimum peak force for the wound with a size of 36 × 5 mm was 1.1 N.

[Optimized negative pressure therapy. Case report]

Our patient showed major abdominal cutaneous necrosis. Detersion removed the entire thickness of half of the right-hand wall of the abdomen. We are going to explain how, by combining well known procedures, we conducted this closure. This deals with a patient aged 53, with a long case history of dermatomyositis and highly debilitating sub-cutaneous calcinosis. This patient has been treated with Imurel and high doses of corticoids since 1997. In the face of the much debilitated terrain of the patient, it was not certain that a local flap or even a pediculated flap could be made to cover this loss of substance with a minimum of risk. A cutaneous extension was then envisaged using a system of Wisebands fillets. To protect the parietal plate, accelerate its growth and reduce the skin tension, we used in combination a system of foam dressing with negative pressure therapy (NPT). The optimized NPT was used for 2 weeks. The Wisebands were installed for 1 month. The treatment lasted for 50 days and required five short sessions of general anaesthesia. The histopathological interpretation revealed an EBV lymphoma. The assessment of the extension and the therapeutic treatment of the lymphoma contributed to the duration of hospitalisation and the number of general anaesthesia sessions. The synergy effect of these two associated procedures have allowed a faster skin closure; 18 months later, no complications have occurred. The wound has closed totally and the abdominal wall is solid in spite of not having resorted to a flap or separation.

Tattoos: surgical removal

Surgical treatment of tattoos remains a useful tool for complete removal despite the availability of laser and other nonsurgical techniques. The procedures are in accordance with standard dermatosurgery used in aesthetic and oncologic therapies. Healing by primary intention or healing by secondary intention has its own indications. Skin defects can be closed by flaps, grafts, tissue extension, or tissue expansion.

Delayed primary closure of fasciotomy wounds with Wisebands, a skin- and soft tissue-stretch device

BACKGROUND

Fasciotomy incisions for limb compartment syndrome usually cannot be closed primarily. The conventional method of wound closure with split-thickness skin grafting is effective, but it results in an insensate and disfiguring wound and is associated with donor site morbidity. We present our experience in delayed primary closure of fasciotomy wounds with Wisebands (WB), a skin- and soft tissue-stretching device.

PATIENTS

Between 2000 and 2003, we treated 16 patients with extremity fasciotomy wounds for which primary closure was not feasible.

RESULTS

The Wisebands devices achieved controlled stretching of the wound edges, including skin and underlying soft tissue, until primary closure was feasible. Fourteen patients (88%) had successful wound closure, two patients (12%) had minor wound complications that did not necessitate the removal of the device, and two patients had local wound complications (infection, intractable pain) and their devices were removed prematurely. Delayed primary closure was achieved at the initial surgery using intraoperative skin stretching in 3 of the 14 cases (21%). After a 2-year follow-up (1.3-4 years), the treated area showed stable scarring with good aesthetic outcome and no functional deficit.

CONCLUSIONS

The Wisebands device facilitates closure of fasciotomy wounds with low complication rates and good functional and aesthetic outcome. Its application is simple and safe and requires a short learning curve. Nevertheless, appropriate patient selection, intraoperative judgment and close postoperative supervision are essential for optimal results.

Long-Term Results of Wounds Closed under a Significant Amount of Tension

BACKGROUND

The authors present the long-term follow-up of scars on various locations up to 7 years postoperatively, after closure of large skin defects with the use of a skin-stretching device.

METHODS

In a prospective, nonrandomized study of 30 patients whose initial wound could not be closed primarily without using a significant amount of tension, a complete follow-up of 24 cases was possible. Patients were observed preoperatively, postoperatively, and at long-term follow-up (mean, 7 years) for wound control and scar evaluation.

RESULTS

In 28 cases (93 percent), successful closure of a large defect was achieved. In the other two cases, a split-thickness skin graft was needed for wound closure. With respect to long-term scar formation after 7 years (24 cases), scarring was observed mainly on the scalp (average, 56 percent), back (average, 52 percent), and shoulder (average, 53 percent). On the extremities, including thigh and groin, there was significantly less scarring (p = 0.0004; average, 10 percent). Three weeks after the operation, 23 percent of the total scar formation had already occurred, whereas 57 percent occurred by 3 months postoperatively and 83 percent occurred by 6 months postoperatively.

CONCLUSION

This study demonstrates the considerable difference in scar formation among scalp, back, and shoulder defects compared with those on the extremities, groin, and thigh.

Our Experience with Wisebands: A New Skin and Soft-Tissue Stretch Device

Complex wounds that involve skin and soft-tissue defects that are unsuitable for primary closure by conventional suturing are common in the field of surgery. Among the many surgical options available to overcome these problems are various mechanical devices that have recently been proposed for delayed primary closure of such wounds. The authors present their experience with a new complex wound closure device, Wisebands, a device uniquely designed for skin and soft-tissue stretching. During the last 2 years, the authors have treated 20 patients with 22 skin and soft-tissue wounds for which primary closure was not feasible. The Wisebands devices were applied to the wounds, stretching the skin and underlying soft tissue, gradually closing the defects until the edges were sufficiently approximated for primary closure. Successful wound closure was achieved in 18 patients (90 percent). The Wisebands devices were removed in two patients (10 percent) because of major wound complications. In two other patients (10 percent), minor wound complications had occurred that did not necessitate removal of the device. At a mean follow-up of 1 year (range, 10 months to 2 years), stable scarring with no functional or significant aesthetic deficit was achieved. The authors conclude that the Wisebands device facilitates closure of complex skin and soft-tissue wounds, with low morbidity and complication rates, and can provide the surgeon with another important tool for closing complex wounds. Nevertheless, appropriate patient selection, intraoperative judgment, and close postoperative care are essential to ensure closure and avoid undue complications.

Oxygenation and Microcirculation during Skin Stretching in Undermined and Nonundermined Skin

The aim of this experimental study was to assess the skin microcirculation of undermined and nonundermined wound edges closed with a skin-stretching device. In eight piglets, 9 x 9-cm wounds were created on both flanks by excision of the skin and the subcutaneous layer down to the muscular fascia, with general anesthesia. On one flank, the surrounding skin was completely undermined. For a period of 30 minutes, wound closure was performed with a stretching device, using the principle of load cycling. The device stretched the skin and moved the opposing wound edges toward each other. During this period, laser Doppler flowmetry and transcutaneous oximetry were simultaneously used to monitor microcirculation and oxygenation in the stretched skin of both flanks. Undermining of the surrounding skin produced a 12 percent decrease in the laser Doppler flowmetry signal and a 21 percent decrease in the transcutaneous oximetry value. Skin stretching resulted in decreases in the laser Doppler flowmetry signals and the transcutaneous oximetry values, whether or not the skin was undermined. Releasing the stretching device resulted in rapid normalization of the laser Doppler flowmetry values in undermined and nonundermined skin and a slow return of the transcutaneous oximetry values to close to baseline levels in nonundermined skin. The transcutaneous oximetry values in undermined skin did not return to baseline levels; each period of skin stretching resulted in an additional decrease in the transcutaneous oximetry values. Stretching of undermined skin for 30 minutes produced a significant (p < 0.0001) decrease in skin oxygenation. As a result, 50 percent of the undermined stretched skin demonstrated skin necrosis at the wound edges, which was still present after 1 week. Wound healing in the nonundermined stretched skin proceeded without problems. It is concluded from these experiments that the viability of undermined skin becomes compromised as a result of significantly decreased oxygen availability in the skin during and after stretching. Consequently, it is recommended that skin stretching be performed on nonundermined skin, rather than undermined skin. In addition, when skin is stretched to close a large defect, it is logical to use cyclic loading, so that recuperation of the skin circulation can occur. Furthermore, laser Doppler flowmetry seemed to produce atypical signals in monitoring of skin viability of wound edges closed with a skin-stretching device.

A quantitative method to determine the orientation of collagen fibers in the dermis

We have developed a quantitative microscopic method to determine changes in the orientation of collagen fibers in the dermis resulting from mechanical stress. The method is based on the use of picrosirius red-stained cryostat sections of piglet skin in which collagen fibers reflect light strongly when epipolarization microscopy is used. Digital images of sections were converted into binary images that were analyzed quantitatively on the basis of the length of the collagen fibers in the plane of the section as a measure for the orientation of the fibers. The length of the fibers was expressed in pixels and the mean length of the 10 longest fibers in the image was taken as the parameter for the orientation of the fibers. To test the procedure in an experimental setting, we used skin after 0 and 30 min of skin stretching. The orientation of the fibers in sections of control skin differed significantly from the orientation of fibers in sections of skin that was stretched mechanically for 30 min [76 +/- 15 (n=5) vs 132 +/- 36 (n=5)]. The method described here is a relatively simple way to determine (changes in) the orientation of individual collagen fibers in connective tissue and can also be applied for analysis of the orientation of any other structural element in tissues so long as a representative binary image can be created.

Rapid alignment of collagen fibers in the dermis of undermined and not undermined skin stretched with a skin-stretching device

A controlled, quantitative histochemical study was performed in five piglets to establish changes in undermined and not undermined stretched skin. The skin was stretched with a stretching device for 30 minutes to close a large skin defect. On each flank of the piglet, at a standard position, 9 x 9-cm wounds were created under general anesthesia. On one flank, the surrounding skin was undermined cranially and caudally over a 10-centimeter area. Sections of skin biopsies obtained during stretching were stained with picrosirius red and studied with routine light microscopy and polarized light microscopy in combination with image analysis. The length of collagen fibers was analyzed as a parameter of changes in the dermis resulting from skin stretching. This newly developed quantitative method appeared to be valid, specific, and reproducible, allowing for objective determination of changes in the length of the fibers in the plain of the sections. Changes in the orientation of collagen fibers in the dermis as a result of skin stretching were thereby determined. Epidermal thickness did not change significantly under the influence of stretching forces in both undermined and not undermined skin. However, the orientation of the collagen fibers changed significantly as a result of skin stretching. In undermined wounds, parallel alignment and elongation of the fibers in the plane of the sections was already observed after 15 minutes of stretching. The fibers became aligned in the direction of the stretching force, perpendicular to the wound margin. After 30 minutes of stretching, the mean major axes of the collagen fibers were longest in the plane of the sections (p < 0.001). This meant that elongation and parallel alignment of the collagen fibers had occurred. Stretching of not undermined skin for 15 minutes resulted in significantly stronger parallel alignment in the plane of the sections as compared with undermined skin. This was less well defined after 30 minutes of stretching in not undermined skin. It is concluded that skin stretching with a skin-stretching device for 30 minutes results in significant histomorphological changes of collagen fibers in the dermis of both undermined and not undermined skin. The fibers realign rapidly as a result of stretching forces and become aligned in the direction of the stretching force, perpendicular to the wound margin. These dynamic changes in collagen fibers explain the significantly decreased wound closing tension resulting from skin stretching and explain how skin stretches beyond its inherent extensibility.