Experimental wound healing: increased breaking strength and collagen synthetic activity in abdominal fascial wounds healing with secondary closure of the skin

Biomechanical Influences on Mesh-Related Complications in Incisional Hernia Repair

Aim: Hernia repair strengthens the abdominal wall with a textile mesh. Recurrence and pain indicate weak bonds between mesh and tissue. It remains a question which biomechanical factors strengthen the mesh-tissue interface, and whether surgeons can enhance the bond between mesh and tissue. Material and Methods: This study assessed the strength of the mesh-tissue interface by dynamic loads. A self-built bench test delivered dynamic impacts. The test simulated coughing. Porcine and bovine tissue were used for the bench test. Tissue quality, mesh adhesiveness, and fixation intensity influenced the retention power. The influences were condensed in a formula to assess the durability of the repair. The formula was applied to clinical work. The relative strength of reconstruction was related to the individual human abdominal wall. From computerized tomography at rest and during Valsalva's Maneuver, the tissue quality of the individual patient was determined before surgery. Results: The results showed that biomechanical parameters observed in porcine, bovine, and human tissue were in the same range. Tissues failed in distinct patterns. Sutures slackened or burst at vulnerable points. Both the load duration and the peak load increased destruction. Stress concentrations elevated failure rates. Regional areas of force contortions increased stress concentrations. Hernia repair improved strain levels. Measures for improvement included the closure of the defect, use of higher dynamic intermittent strain (DIS) class meshes, increased mesh overlap, and additional fixation. Surgeons chose the safety margin of the reconstruction as desired. Conclusion: The tissue quality has now been introduced into the concept of a critical and a gained resistance toward pressure-related impacts. A durable hernia repair could be designed from available coefficients. Using biomechanical principles, surgeons could minimize pain levels. Mesh-related complications such as hernia recurrence can potentially be avoided in incisional hernia repair.

Morphine enhances tissue content of collagen and increases wound tensile strength

PURPOSE

Morphine is a commonly prescribed analgesic for wound pain. Previous studies have shown that morphine enhances accumulation of collagen in cultured fibroblasts. Because fibroblasts are important for the remodeling of connective tissue in incisional wound, this study investigates the biological effects of morphine on cutaneous collagen content and wound tensile strength.

METHODS

A full-thickness incisional wound (2 cm in length) was created on the dorsum of mice followed by treatment with placebo or morphine (5 and 20 mg/kg/day, i.p.). Fourteen days later, tensile strength of the healed incisional wound was measured using a tensiometer. Protein expression of transforming growth factor (TGF)-beta1 and matrix metalloproteinases (MMP)-2 in the incisional wound tissue was analyzed. Degree of tissue remodeling and levels of collagen were determined by histological examination and a dye-binding collagen assay, respectively.

RESULTS

Morphine enhanced the breaking strength of incisional wound 14 days after treatment (92 +/- 10, 102 +/- 10 and 134 +/- 12 mg for control, morphine 5 mg/kg/day and morphine 20 mg/kg/day, respectively; P = 0.03, n = 6-7). Protein expression of TGF-beta1 and MMP-2 was significantly enhanced in mice treated with morphine. Histological examination of the wound tissue showed evidence of increased thickness of the cutaneous fibrous layer and deposition of collagen in the high-dose morphine treatment group. Collagen assays also demonstrated that tissue concentrations of collagen were significantly increased in the wound tissue of morphine-treated animals on day 2 of drug treatment.

CONCLUSION

The present study demonstrates that systemic administration of morphine enhances tissue collagen deposition in the cutaneous tissue, thereby increasing the tensile strength of the incisional wound.

Efeitos do Tenoxicam sobre a cicatrização da parede abdominal: estudo experimental em ratos

OBJETIVO: Analisar os efeitos do tenoxicam, um antiinflamatório não hormonal, na cicatrização da parede abdominal de ratos. MÉTODOS: Foram utilizados 40 ratos adultos, submetidos à laparotomia mediana e distribuídos, aleatoriamente, em um grupo controle (C), constituído de 20 animais que receberam solução de NaCl a 0,9 %; e um grupo tratado (T), constituído de 20 animais que receberam o tenoxicam. Os animais de cada grupo foram divididos, conforme a data de sacrifício, em subgrupos de 10 animais, denominados C7, C14, T7 e T14. As inscrições 7 e 14 determinaram o sacrifício dos animais no sétimo e décimo quarto dia pós-operatório, respectivamente. As soluções de tenoxicam (1mg/ml) e de NaCl a 0,9% foram administradas no pós-operatório imediato e nos quatro dias seguintes, por via intramuscular, na dose volume de 0,6 ml/kg/dia. No dia do sacrifício, realizou-se a ressecção de dois fragmentos da parede abdominal (1cm x 3cm), que foram utilizados para determinação da concentração de hidroxiprolina e avaliação da força de ruptura. RESULTADOS: Não foram observadas complicações da ferida operatória, incluindo infecção ou deiscência, nos quatro subgrupos de animais. Na análise comparativa dos quatro subgrupos de animais, não foi evidenciada diferença estatisticamente significante no estudo da força de ruptura (p=0,262) e na concentração de hidroxiprolina (p=0,392). CONCLUSÃO: A administração de tenoxicam, por via intramuscular, não interfere na cicatrização da parede abdominal de ratos.

The temporal sequence of periosteal attachment after elevation

This study investigated the adherence of periosteum to bone after elevation to document the temporal sequence of healing at the periosteal/bone interface. There has been a lack of consensus among surgeons as to the time required for healing at this interface; some believe that the healing achieves significant strength in a few days, whereas others believe that the periosteum does not adhere to the bone for many weeks. The aim of this study was to document the time course for healing, completeness of the reattachment, and structural characteristics of the union of bone and periosteum. To test the hypothesis, scalp flaps were elevated in a subperiosteal plane and were reattached in 40 adult guinea pigs and controls. The individual groups were studied at 3, 6, 12, 30, and 90 days postoperatively. Postmortem study consisted of analysis of the mechanical and histologic findings. Strength of adherence was documented by measuring the force required for reverse avulsion of the flaps with an Instron Mini 44 tensiometer. The specimens were also submitted for electron microscopic examination. The mean tension recorded in the plateau phase of avulsion of the flaps was as follows: controls, 78 g; experimental at 3 and 6 days, not applicable (weak adherence not permitting exposure for reverse avulsion); 12 days, 39 g (p = 0.0001); 30 days, 58 g (p = 0.0012), and 90 days, 63 g (p = 0.0229). There was a significant difference between all groups and the controls. Electron microscopic study showed collagen deposition at the bone periosteal interface, which became progressively more organized in the groups studied at 30 and 90 days, with decreasing amounts of inflammation and inflammatory cells. This study demonstrated that healing at the bone/periosteal interface progresses at a rate consistent with healing of most other wounds, dispelling many widespread beliefs that the adherence at this interface was accelerated. The temporal sequence of healing at the periosteal bone interface should be considered in the various procedures in which periosteal flaps are elevated. For example, there is clinical relevance in subperiosteal brow lift procedures, in which the periosteum should be reattached by a fixation technique that will remain stable for a minimum of 30 days to allow adequate adherence between the bone and periosteum at the postoperative elevated brow position.

The sympathomimetic agent, 6-hydroxydopamine, accelerates cutaneous wound healing

Using pharmacological stimulation of sympathetic terminals, the present study examines the role of sympathetic post-ganglionic neurons in cutaneous wound healing. Effects of local stimulation of sympathetic post-ganglionic neurons with 0.2 mg/kg 6-hydroxydopamine were studied on the healing of full-thickness skin incisions in rats. Epidermal wound healing was measured by a novel non-invasive quantitative method based on the increasing electrical resistance of healing skin. Dermal healing was determined by measuring wound breaking strength using an Instron Universal Testing device. We report a 35% increase in the rate of epidermal wound healing (P < 0.05. n(e) = 21, n(c) = 18) and a 43% increase in dermal strength (P < 0.05, n(e) = 13, n(c) = 10) after 6-hydroxydopamine treatment. Thus, our results show that pharmacological stimulation of sympathetic post-ganglionic neurons markedly accelerates skin wound healing at both the epidermal and dermal levels. This is the first study to show that peripheral nerve stimulation and specifically sympathetic stimulation accelerates cutaneous wound healing. We discuss these results in relation to neurogenic inflammation.

Pyridinoline in relation to ultimate stress of the patellar tendon during healing: an animal study

The ultimate stress of the central one-third of the patellar tendon was studied in a gap wound-healing model in the rat. The specimens were also analyzed for collagen and nonreducible crosslinks, as measured by hydroxyproline and pyridinoline content, respectively. Thirty days after injury, the ultimate stress of the healing patellar tendon was restored to an average of 71% of the control value and remained constant over time. The pyridinoline content of the healing tendon was twice the control value by 30 days after injury and reached a plateau; however, the hydroxyproline content did not change significantly over time. Stepwise regression analysis demonstrated that pyridinoline was a better biochemical marker for ultimate stress than was hydroxyproline. The current study provides insights into the functional behaviour of the healing patellar tendon by establishing the relationship between the two biochemical components and the ultimate stress of the healing patellar tendon. This study also suggests the possibility of using pyridinoline content as an indirect marker of the ultimate stress because in vivo assessment is impossible.

Imbrication versus excision for fascial healing

BACKGROUND

The purpose of this study was to determine whether imbrication of native fascia versus excision and closure of new raw fascia forms a stronger union.

METHODS

We utilized the anterior rectus sheath fascia of Sprague-Dawley rats as the model. Sixty rats underwent fascial tightening procedures. Each rat had the anterior rectus sheath shortened by 1 cm, 30 by imbrication and 30 by excision and closure. Ten of each group were harvested at 7 days' healing, 10 at 14 days, and 10 of each group at 28 days' healing. The anterior rectus sheath was removed, a "dumbbell" shape constructed, and the cross sectional area at the point of interest determined. The fascia was placed on an Instron tensiometer to determine the breaking strength. Tensile strength was calculated and the data analyzed by ANOVA and the Kruskall-Wallis test. Tissue samples of the closures were histologically analyzed for fibroblast counts, degree of inflammation, and presence of dense fibrous connective tissue. Tissue samples were also analyzed for enzymatic collagen crosslinking.

RESULTS

There was a statistically significant difference in tensile strength between the two groups at 7, 14, and 28 days. Results show that at 7 days the mean tensile strength of excision was 0.133 kg/mm2 +/- 0.056 and the mean tensile strength of imbrication was 0.083 kg/mm2 +/- .048 (P < 0.05); at 14 days the mean tensile strength of excision was 0.105 kg/mm2 +/- 0.033 and the mean tensile strength of imbrication was 0.057 kg/mm2 +/- 0.014 (P < 0.002), and at 28 days the mean tensile strength of excision was 0.279 kg/mm2 +/- 0.143 and the mean tensile strength of imbrication was 0.145 kg/mm2 +/- 0.061 (P < 0.03). Histologic findings showed no statistical significance between the two closure methods when comparing degree of inflammation or the number of fibroblasts present. However, at 7 and 14 days there is a significantly greater presence of dense fibrous connective tissue in the excision group (P < 0.03 at 7 days and P < 0.044 at 14 days by ANOVA). Collagen crosslink analysis showed that by day 28 there is a significantly greater amount (P < 0.05 by ANOVA) of the difunctional crosslink dihydroxylysinonorleucine (DHLNL) and a greater ratio between DHLNL and the difunctional crosslink hydroxylysinonorleucine (HLNL) in the excision and closure group.

CONCLUSION

We conclude that at 7, 14, and 28 days healing, excision provides a significantly stronger closure than imbrication. According to the crosslinking analysis, it is likely that this strength advantage may continue to increase over time. These findings suggest that excision and closure may be the preferred method for fascial tightening procedures.

Rabbit medial collateral ligament scar weakness is associated with decreased collagen pyridinoline crosslink density

This study was carried out to quantify the potential associations between material strength and both collagen concentration and pyridinoline collagen crosslink density in the healing medial collateral ligament of the rabbit and to compare these parameters with those of normal ligaments. The right hindlimbs of 24 skeletally mature (12-month-old) New Zealand White rabbits were subjected to a standardized 4 mm midsubstance "gap" injury to the medial collateral ligament. The animals were killed in groups of six at postoperative intervals of 3, 6, 14, or 40 weeks, and the femur-medial collateral ligament-tibia complexes were mechanically tested in tension to failure. Subsequent to mechanical testing, the failure sites of the ligaments were assessed for concentrations of hydroxyproline and hydroxylysyl pyridinoline. Nine additional rabbits served as age-matched normal controls. In healing ligaments, normal collagen concentrations were reached in less than 14 weeks, but the hydroxylysyl pyridinoline crosslink densities remained low and were only 45% of the control values after 40 weeks of healing. Similarly, mechanical values remained much less than the controls. Linear regression analysis of data on scar tissue alone showed a moderately strong positive correlation between hydroxyproline concentration and material strength (r2 = 0.51, p = 0.0001) but no correlation between crosslink density and strength of scar tissue. A similar pattern of correlation was obtained between the elastic modulus of the scar tissue and the biochemical variables, but the r2 values were lower.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical, biomechanical, and physical changes in the skin in an experimental animal model of therapeutic tissue expansion

Biochemical, biomechanical, and physical changes occurring in the skin during tissue expansion have been studied using an animal model in which a Silastic expander was inserted into the peritoneal cavity. Forty-eight Sprague-Dawley rats were divided into four groups to be studied at 4, 8, 16 and 32 days after expansion. In the experimental animals (6 per group) the expander was inflated by a single injection of 120 ml of saline. Sixteen hours prior to sacrifice each animal received a single injection of tritiated proline. Sixteen days after expansion both the specific activity and the total content of hydroxyproline in the skin were significantly elevated in experimental animals. Intrinsic skin tension increased dramatically at the time of inflation but fell almost to control values at the end of 32 days. Skin thickness, initially decreased, returned to normal by the end of the experiment. There were no significant differences in breaking strengths between skin from experimental and control animals. Skin surface area, initially increased by stretching at the time of inflation, increased further between Days 0 and 8, possibly as a result of stress relaxation combined with enhanced remodelling of connective tissue macromolecules, and again from Days 24 to 32. We conclude that, during tissue expansion, there is a net accumulation of collagen in the skin and that this allows the local cellular environment to return to normal with respect to pressure and/or tension.