Mesh pullout force: comparative study of different deployment techniques in a sheep model

Introduction and hypothesis

Pullout force of mesh from tissue is one of the important mechanical properties of an implanted mesh to repair pelvic organ prolapse (POP). The EndoFast Reliant? system kit allows mesh attachment with soft-tissue fasteners. The aim of this study was to compare the pullout force that developed in mesh that was attached by EndoFast Reliant fasteners to mesh that was attached by trocar-based methods (tunnel, pocket) in a sheep model.

Methods

Six sheep underwent mesh attachment with three methods (EndoFast Reliant, tissue pocket, tissue tunnel), and each method was repeated five times in both thighs of the same sheep. The pullout force was measured at different time intervals from surgery: 0, 3, 7, 15, 30, and 45 days. Statistical analysis was performed by using the appropriate one-way analysis of variance (ANOVA) for each time interval and a general linear model for repeated measures using IBM® SPSS® software version 20.0.0.

Results

During the immediate postoperative period (0–3 days), pullout force was significantly higher with EndoFast Reliant than with tissue pocket or tissue tunnel. At day 7, this trend continues without statistical significance. Pullout force increased progressively until day 15, when the force caused the mesh to tear; it was similar in all three groups. ANOVA showed significant effect of time and study group.

Conclusions

The EndoFast Reliant system provides significantly stronger attachment in the immediate postoperative period (0–3 days) compared with trocar-based techniques, and this difference disappeared at day 15 postsurgery.     

Tissue reactions of 5 sling materials and tissue material detachment strength of 4 synthetic mesh materials in a rabbit model

PURPOSE: We evaluated tissue reactions to 5 sling materials used in tension-free vaginal tape (TVT), intravaginal slingplasty (IVS), polypropylene mesh hernia repair, the suprapubic approach to suburethral polypropylene tape (SPARC) and cadaveric fascia lata procedures. We also compared the mesh-to-tissue attachment strength of 4 sling mesh materials (TVT, IVS, surgical polypropylene mesh and SPARC) at on days 2, 7, 15 and 30 after implantation. MATERIALS AND METHODS: A total of 20 female New Zealand White rabbits were randomized to group 1-2 days, group 2-7 days, group 3-15 days and group 4-30 days. After the rabbits were anesthetized an 8 cm midline incision was made for rectus muscle access, and 0.5 x 1 cm pieces of TVT, IVS, SPARC, surgical polypropylene mesh and cadaveric fascia lata were sewn to the rectus muscle with direct contact. At the same time 4 subfascial tunnels in the medial surface of the upper extremities were prepared, and 1.0 x 0.5 cm strips of TVT, IVS, SPARC and polypropylene mesh were implanted in each tunnel. On days 2, 7, 15 and 30 after implantation mechanical testing was performed to define tissue detachment strength. The strips of 5 sling materials were then harvested with the surrounding tissue. Specimens were studied by light microscopy. RESULTS: Mean detachment strength, that is the minimum weight needed to move the mesh, of the synthetic meshes from days 2 to 30 were 291.6 to 2,390.0 gm for TVT, 178.4 to 2,160.0 gm for SPARC, 188.4 to 1,850.0 gm for hernia mesh and 92.8 to 1,510.0 gm for IVS (at all data points TVT vs IVS p < 0.05). Light microscopy revealed a quite uniform tissue reaction with a sign of marked acute inflammation in and around the mesh fibers on days 2 and 7 after implantation. All meshes showed stable fibrosis and muscle infiltration on day 30. CONCLUSIONS: All 5 synthetic sling materials produce similar tissue reactions beginning soon after implantation. Cadaveric fascia lata persisted in tissue with remarkable perifascial fibrosis at day 30. When comparing the 4 polypropylene mesh materials; the attachment capacity of TVT was superior and that of IVS was the least of the 4. TVT was statistically better than IVS at all data points. SPARC and hernia mesh provided results similar to those of TVT.     

Time-dependent reduction in load to failure of wedge-type polyglyconate suture anchors.

SUMMARY: Thirty-two absorbable (polyglyconate) and 24 nonabsorbable (polyacetal) wedge-type suture anchors (TAG; Acufex, Mansfield, MA) were implanted into sheep tibiae. Load to failure tests were performed on the day of insertion and at weeks 3, 6, and 12, followed by macroscopic examination. Failure type was suture breakage for nonabsorbable anchors in all groups, with average forces of 142.5 +/- 4.8 N on the first day, 138.0 +/- 6.6 N in week 6, and 135.6 +/- 2.9 N in week 12. In the absorbable group, suture breakage occurred on the first day with a mean force of 133.5 +/- 4. 2 N. In weeks 3, 6, and 12, suture cutout occurred with average forces of 33.75 +/- 5.0 N, 23.25 +/- 2.2 N, and 23.25 +/- 5.9 N, respectively. For absorbable anchors, results at weeks 3, 6, and 12 were significantly lower compared with initial results (P <.001). These results show that wedge-type polyglyconate anchors lose 75% of their initial pullout strength within the first 3 weeks and 84% in 6 weeks.     

Long-term tensile properties of tension-free vaginal tape, suprapubic arc sling system and urethral sling in an in vivo rat model

PURPOSE: Slings have gained widespread popularity for stress urinary incontinence. Commonly used sling materials include TVT, SPARC and Stratasis. To our knowledge no long-term comparative in vivo studies assessing the tensile strength of these materials have been reported. We examined tensile properties during a 1-year period after in vivo implantation in a rat model. MATERIALS AND METHODS: A total of 30 Sprague-Dawley rats had 1 x 2 cm strips of TVT, SPARC and Stratasis implanted on the inner abdominal wall. The animals were grouped for sacrifice at 6 weeks, and 3, 6, 9 and 12 months, at which time the tape materials along with their associated fibrotic tissue were removed. Tensile properties were analyzed. RESULTS: The initial control mean break load for TVT, SPARC and Statasis was 0.717, 0.453 and 0.298 kg, respectively (p=0.001). At 6 weeks, and 3, 6, 9 and 12 months TVT had a mean break load of 0.525, 0.678, 0.696, 0.568 and 0.522 kg, respectively. During the same intervals SPARC had a mean break load of 0.516, 0.596, 0.450, 0.514 and 0.496 kg, respectively. Stratasis had a mean break load of 0.147, 0.183, 0.132, 0.062 and 0.070 kg, respectively. CONCLUSIONS: TVT has tensile properties comparable to those of SPARC and each is superior to Stratasis. These differences in tensile properties of the mesh material along with the fibrous reaction may have clinical implications in terms of the success of pubovaginal slings made with such materials.     

Collagen-coated vs noncoated low-weight polypropylene meshes in a sheep model for vaginal surgery. A pilot study

The aims of this study were dual. First, to evaluate the feasibility of a sheep model as an animal model for vaginal surgery with meshes. Second, to compare host response to two low-weight polypropylene (PP) meshes, a noncoated (Soft Prolene™, Gynecare, Ethicon) and a coated mesh with an absorbable hydrophilic film (Ugytex™, Sofradim). Thirty-six 20×20 mm polypropylene meshes (18 coated and 18 noncoated) were surgically implanted by the vaginal route in 12 adult ewes. Meshes were implanted in the anterior (n=12) and the posterior vaginal compartments (n=24). Animals were killed 1 (n=6) and 12 (n=6) weeks after surgery. Postimplantation evaluation included macroscopical examination, histological and immunohistochemical analysis and histomorphometrical measures of the distance between the meshes and the vaginal epithelium. The experimental procedure was feasible in all cases. Vaginal erosions were observed twice as frequently with the noncoated-PP meshes (6/18, 33.3%) as with the coated-PP meshes (3/18, 16.7%), even if that difference was not significant (p=0.4). However, no differences were observed between the two meshes in terms of shrinkage, tissue ingrowth, inflammatory response, and position of the mesh in the vaginal wall. The mechanism involved in the reduction of vaginal erosion could be due to the lesser adhesion of the coated mesh on the vaginal wound during the early postoperative period.     

Strength of tissue attachment to mesh after ventral hernia repair with synthetic composite mesh in a porcine model

Background A prospective animal study involving 12 female swine aimed to measure the strength of tissue attachment to composite mesh at various time points after laparoscopic ventral hernia repair in a porcine model. Methods Each animal had two 10 × 16-cm sheets of polypropylene/expanded polytetrafluoroethylene (ePTFE) composite mesh laparoscopically affixed to the abdominal wall with a helical tacking device. No transfascial sutures were used. The animals were euthanized 2, 4, 6, and 12 weeks after surgery, and abdominal walls were resected en bloc with the patches. Each patch was cut into 2 × 7-cm strips, and each strip was independently analyzed. The strength of the tissue attachment to the mesh was measured using a servohydraulic tensile testing frame. The abdominal wall was peeled from the mesh, and the transverse, or “lap-shear” force was recorded. Data are reported as mean force in pounds. Results The mean lap-shear force was 0.83 ± 0.06 lbs at 2 weeks, 1.06 ± 0.07 lbs at 4 weeks, 0.88 ± 0.08 lbs at 6 weeks, and 1.13 ± 0.07 lbs at 12 weeks. The mean force was higher at 12 weeks than at 2 weeks (p < 0.05). No other periods were significantly different from any other. Conclusions The findings demonstrate that the majority of tissue ingrowth and strength has occurred by 2 weeks after laparoscopic placement of a composite hernia prosthesis. Strength very gradually increases until 12 weeks after surgery. This has clinical implications for human ventral hernia repair. Further study is needed to evaluate the necessity of transfascial sutures for securing polypropylene-based prostheses to the abdominal wall during ventral hernia repair. Presented at the 85th Annual Meeting of the New England Surgical Society, 2 October 2004, Montreal, Quebec, Canada     

Surgical management of vaginal wound healing defects after tension-free vaginal tape placement

The use of tension-free vaginal tape (TVT) made of polypropylene mesh carries the risk of causing vaginal wound healing defects, which are usually detected within 4 weeks of operation. We present three cases of vaginal wound healing defects after TVT procedures. These defects were managed using surgical techniques aimed at preserving the mesh, but all failed. There are many options for dealing with the problems of vaginal wounds following TVT. These include further observation, mesh removal, suturing the wound, or using tissue flaps to cover it. However, the latter two options cannot be recommended as they usually fail.     

Short‐term assessment of a tension‐free vaginal tape for treating female stress urinary incontinence

OBJECTIVE

To evaluate the short‐term surgical complications and results of a tension‐free vaginal tape (TVT) system (TVT‐Secur^TM, Gynecare, Ethicon, Somerville, NJ, USA) in the treatment of female stress urinary incontinence (SUI).

PATIENTS AND METHODS

TVT‐Secur was applied to 107 women with SUI through a vaginal incision and left abutting the urethra. Postoperative pain, complications, de novo lower urinary tract symptoms, incontinence cure rate and the King’s Health Questionnaire (KHQ) score were evaluated.

RESULTS

The operative duration was 12 min; the mean pain score was 2.3 and only one patient had transient voiding difficulties. After a mean follow‐up of 15 months, 71% of the patients were dry and 14% improved. The KHQ scores decreased significantly for most subscores. Urgency appeared de novo in six patients (5.6%), and vaginal erosion required one TVT‐Secur explantation.

CONCLUSION

This study shows that TVT‐Secur is a simple and safe treatment for female SUI, but before recommending this sling as a first choice for treating SUI, TVT‐Secur must pass the test of time and comparative studies with conventional slings.     

Initial vascularization and tissue differentiation are influenced by fixation stability.

Fracture healing requires a certain degree of mechanical stability and an adequate blood supply. The hypothesis of the present study was that increased interfragmentary shear leads to a reduced initial vascularization and prolonged healing. The aim of the study was to quantitatively analyze the histological appearance of vascularization and tissue differentiation with regard to fracture stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, differing in bending stiffness. Interfragmentary movements and ground reaction forces were evaluated in vivo during a 9-week period. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were prepared for analysis of tissue differentiation and vascularization. Larger interfragmentary shear movements in the semirigid fixator group were associated with a reduced initial blood supply. At 6 weeks the semirigid fixator group showed a significantly lower percentage of mineralized bone and a higher amount of fibrous tissue leading to a significantly lower stiffness of the callus than the rigid fixator group. This initial delay in healing was compensated for in the later stages with the production of greater volumes of callus tissue so that both groups showed the same callus stiffness at 9 weeks. However, the rigid fixator group showed signs of the beginning of callus remodeling at the latest time points suggesting a faster bone healing. The results indicate the important role of the initial mechanical stability specifically in the vascularization of an osteosynthesis. Further studies should illustrate the precise role of mechanical conditions on the regulation of angiogenesis during early bone healing.     

The benefit of bone marrow concentrate in addition to a glass‐reinforced hydroxyapatite for bone regeneration: An in vivo ovine study

This study evaluates the ability of a Glass Reinforced Hydroxyapatite Composite (GRHC), in a new microporous pellet formulation with autologous bone marrow concentrate (BMC), to enhance bone regeneration and new bone formation. Ninety non‐critical sized bone defects were created in the femurs of nine Merino breed sheep and randomly left unfilled (group A), filled with GRHC pellets alone (group B) or filled with GRHC pellets combined with BMC (group C). The sheep were sacrificed at 3 weeks (three sheep), 6 weeks (three sheep) and 12 weeks (three sheep) and histological analysis (Light Microscopy‐LM), scanning electron microscopy (SEM) and histomorphometric analysis (HM) were performed. At 3, 6, and 12 weeks, HM revealed an average percentage of new bone of 48, 72, 83%; 25, 73, 80%, and 16, 38, 78% for Groups C, B and A respectively (significantly different only at 3 weeks p < 0.05). LM and SEM evaluation revealed earlier formation of well‐organized mature lamellar bone in Group C. This study demonstrates that the addition of a bone marrow concentrate to a glass reinforced hydroxyapatite composite in a pellet formulation promotes early bone healing. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1176–1182, 2017.

     

Biomechanical and histological analysis after tenotomy of the long head of the biceps in the rabbit shoulder model

Tenotomy of the long head of the biceps tendon (LHBT) is gaining popularity in shoulder surgery. We evaluated biomechanical and histological changes after tenotomy in a rabbit LHBT tenotomy model to confirm that autotenodesis is a phenomenon that occurs after the procedure. Twenty‐three rabbits were included. The right shoulder was harvested from 10 randomly selected rabbits. The shoulders were tested to determine the pullout strength of LHBT at the bicipital groove immediately after being tenotomized. The left shoulder of three of these rabbits also underwent histological analysis. The other 13 rabbits underwent LHBT tenotomy (tenotomy model). Six weeks post‐operatively, 10 were assigned for biomechanical study, and three underwent histological analysis. The pullout strength and histology were compared with the immediate post‐tenotomy data. The pullout strength of the immediate post‐tenotomy (5.53 ± 2.22 N) was significantly (p < 0.001) less than the pullout strength of the 6 weeks post‐tenotomy model (44.07 ± 7.75 N). On histological analysis, marked fibrosis was noted around the LHBT at the bicipital groove in the 6 weeks post‐tenotomy model. Adhesion of the LHBT at the bicipital groove after tenotomy, which is called “autotenodesis,” is a definite phenomenon that could help the tendon resist distal migration of the LHBT after tenotomy. These results support execution of biceps tenotomy in shoulder surgery. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:416–422, 2012     

Rib fracture healing after osteosynthesis with wire mesh titanium and screws: a histological study in sheep

Twenty sheep were placed under general anesthesia and five ribs (6-10) were transected at their lateral angle using a pair of rib shears. The fractures were stabilized by titanium wire mesh plates. After 4, 6, 8, 10 and 12 weeks groups of 4 animals were sacrificed and rib samples were prepared for histological examinations. The study showed that the osteosynthesis stabilized the fractures and that the healing is similar to untreated rib fractures. This osteosynthesis method is a good contribution to severe injured chest treatment.     

Delayed vaginal and urethral mesh exposure: 10 years after TVT surgery

Delayed mesh exposure after tension-free vaginal tape (TVT) procedure is rare. We report a case of mesh exposure into the vagina and urethra that developed 10 years after TVT surgery. A 58-year-old postmenopausal woman presented with mixed urinary incontinence. She was investigated, and her stress urinary incontinence was cured with a TVT procedure 10 years ago. She was then scheduled follow-up annually. Two years postsurgery, a granulation tissue was observed and excised at the vaginal incision site. Vaginal examination 10 years postsurgery showed vaginal mesh erosion 0.5 cm from urethral meatus. Cystoscopy revealed concomitant urethral erosion at the posterior urethral wall. Mesh excision was performed, and urethra and vagina were repaired in layers. Postoperative recovery was uneventful. This finding shows that, although rare, complications can occur even after 10 years of TVT surgery.     

Late erosions of mid-urethral tapes for stress urinary incontinence—need for long-term follow-up?

Tension-free vaginal tape (TVT) procedure has become one of the most common treatments of female urinary stress incontinence. Success rates as high as 81.3% were reported over a follow-up period of 7 years. Erosion of the synthetic mesh is a well-described complication. The mean time for the onset of erosion after sling insertion was 11.2 months. These case reports describe an erosion of a mid-urethral tape after 18 and 28 months, which is uncommon. There is a need for long-term follow-up of patients with TVT.     

The 7‐year outcome of the tension‐free vaginal tape procedure for treating female stress urinary incontinence

OBJECTIVE

To evaluate the long‐term results and predictive risk factors for efficacy after the tension‐free vaginal tape (TVT) procedure for treating female stress urinary incontinence (SUI).

PATIENTS AND METHODS

Inall, 306 women (mean age 50.7 years, sd 8.7) who had a TVT procedure for SUI were selected and followed ≥7 years (mean 92.3 months, range 84–110) after surgery. We analysed the long‐term results, the variables predictive of cure rates, and patient satisfaction.

RESULTS

The overall 7‐year cure rate was 84.6%, with a satisfaction rate of 69.3%. The cure rates were lower in patients with high‐grade SUI (50% in grade III, 82.8% in grade II and 90.7% in grade I; P < 0.001). On multivariate analysis, there were no independent risk factors related to cure rate, and urgency was the only factor independently associated with patient satisfaction (P = 0.008; odds ratio 2.47). Seventy‐one patients (23.2%) had complications at the 1‐month follow‐up after surgery, but only eight (2.6%) had complications at the 7‐year follow‐up, including mesh exposure in six and de novo urgency in two.

CONCLUSION

The absence of long‐term adverse events associated with the TVT procedure, and high subjective and objective 7‐year success rates with no independent predictive factors affecting the long‐term cure rate, make the TVT procedure a recommendable surgical treatment for female SUI.     

How four and twelve weeks of implantation affect the strength and stiffness of a tendon graft securely fixed in a bone tunnel: a study of Evolgate fixation in an extra-articular model ovine model

Healing of a tendon graft to a bone tunnel is slower than the healing of a bone plug. Therefore, the device chosen for hamstring fixation may need to maintain its strength and stiffness longer than the device chosen for bone-tendon-bone fixation. We evaluated, in an extraarticular ovine model, how 4 and 12 weeks of implantation affect the strength of a tendon graft fixed to bone with the Evolgate. The long digital extensor tendon was transplanted and fixed with the Evolgate into a 30-mm long, 8 mm diameter bone tunnel drilled in the tibial metaphysis of both posterior limbs of 15 skeletally mature Suffolk sheep. Immediately after implantation, and 4 and 12 weeks later, biomechanical cyclic load tests in 50 N increments were performed until failure to evaluate the ultimate failure load (UFL). Histological analysis was also performed at 4 and 12 weeks. Biomechanical tests revealed a UFL of 339±120 N at time 0, and increases to 635±19 N (4 weeks) and to 867±80 N (12 weeks). The differences between all 3 groups were significant (p<0.001, paired t test). The histological evaluation showed a layer of cellular, fibrous tissue between the tendon and the bone, along the length of the bone tunnel; this layer progressively matured and reorganized during the healing process. The collagen fibers that attached the tendon to the bone resembled Sharpey’s fibers. The strength of the interface significantly and progressively increased between weeks 4 and 12 after transplantation, and was associated with a degree of bone ingrowth noted histologically. The use of the Evolgate seems not to interfere with the bone ingrowth after implantation, allowing an improvement in strength of the bonetendon- device complex.     

Replacement of the anterior cruciate ligament using a deep-frozen bone-Lca- Bone Allograft. An experimental study

Summary One ACL in each of 17 mature sheep was replaced with a deep-frozen bone – an ACL bone allograft. Allografts were obtained from skeletally mature sheep using a standard aseptic technique and stored deep frozen for at least 6 days (mean 21 days). Macroscopical, biomechanical, and histological changes were evaluated 12, 24, and 52 weeks following implantation. At autopsy all allograft ligaments were present and demonstrated no evidence of infection or immune reaction. We found slight arthrotic changes in 3 knees after 12 weeks, in 4 knees after 24 weeks, and in 3 knees after 52 weeks. Twelve weeks after the operation the maximum load of the allografts was 17.5 % of the contralateral controls and increased to 20.9 % after 24 weeks and to 32 % of controls after 52 weeks. Ligament stiffness in the linear region also increased from 18.9 % of controls (12 weeks) to 32.5 % after 52 weeks, whereas maximum load decreased from 112.2 % of controls (12 weeks) to 98 % of controls (52 weeks). Histologically, the allografts progressively matured with time, becoming nearly identical to normal ligaments at 52 weeks.      

Evaluation of Soft Tissue Attachments to a Novel Intra-abdominal Prosthetic in a Rabbit Model

Background. Laparoscopic ventral hernia repair requires placement of an intraperitoneal prosthetic. Composite mesh types have been developed to address the shortcomings of standard meshes. The authors evaluated the host reaction to intraperitoneal placement of a novel composite material. Materials and Methods. A comparison of an innovative polypropylene/polylactide composite mesh was made to Parietex Composite (PCO), Proceed, and DualMesh. Eighteen meshes per group were implanted on intact peritoneum in New Zealand White rabbits. The main outcome measures included the formation of visceral adhesions, adhesion tenacity, tensiometric measurements, and histological analysis. Evaluations of adhesions were made at 1, 4, and 16 weeks using a 2-mm minilaparoscopy. Results. There were no significant differences in the mean adhesion scores between the composite mesh types at week 1 (P = .15) and week 16 (P = .06). At 4 weeks, PCO had significantly fewer adhesions when compared with the other 3 mesh types (P = .02). Adhesion tenacity was also equivalent within the group at 16 weeks (P = .06). Tensiometry and histological analysis revealed no statistically significant differences between the mesh types. Conclusions. Four different composite mesh types had equivalent intra-abdominal soft tissue attachments in a rabbit model after a 16-week implantation period. PCO demonstrated the lowest mean adhesion score of each mesh type. Each mesh exhibited equivalent stiffness and energy to failure after explantation. The 4 composite mesh types demonstrated the successful formation of a neoperitoneum and comparable host biocompatibility as evidenced by similar degrees of inflammation.     

Evaluation of different methods of securing intravenous catheters: measurement of forces during simulated accidental pullout

The purpose of the study was to compare the relative effectiveness of several combinations of tapes and taping methods with respect to the force required to pull out intravenous catheters. A simulated forearm model consisting of a section of firm PVC pipe was used for the first and second series of experiments. In the third experiment, one method of taping catheters was compared in the PVC model and in volunteers. Pull-out forces were measured with a force transducer and recorded on paper. In the first experiment, catheters secured with Curity tape resisted pullout to a greater extent than those with Transpore tape and provided approximately twice the force advantage (P < 0.05). In the second experiment using Curity tape, minimum forces to dislodge the catheters were (means ± SD) 53 ± 13, 82 ± 13, 113 ± 29, 124 ± 24, 176 ± 29 and 141 ± 46 N, for methods 1–6, respectively. In the third series, the minimum pullout forces were higher for Curity than with Transpore tape for both the human and simulated PVC forearm surfaces (63 ± 11 and 55 ± 12 N vs 52 ± 7 and 44 ± 12 N, P < 0.01), and the pullout forces were higher for the simulated vs the human skin surface for both tape types (P < 0.01). Compared with Curity tape, Transpore tape was more likely to fail by tape fracture in both the simulated and human skin surfaces (P < 0.05). The data suggest that there are important differences in pullout forces and mechanisms of dislodgement depending on taping method and tape type. Curity tape, using method 5 or 6, was superior to Transpore tape and the other taping methods in resisting pullout.