Fixation Burst Strength of Ventral Hernia Repairs:
Using the PermaSorb™ Disposable Fixation Device Compared to Repairs Using Permanent Fixation In an Animal Study G. Kevin Gillian, M.D., F.A.C.S.,a I.D McRury PhD,b J.R Scott PhD,b W. Shiow-jyi PhD,c V. Roy, PE d a c
Virginia Hospital Center, Arlington, VA; b Davol Inc., Subsidiary of C. R. Bard, Inc., Warwick, RI; DaVinci Biomedical Research Products, Inc., S. Lancaster, MA; d Altran Solutions, Inc., Boston, MA
Fixation Burst Strength of Ventral Hernia Repairs: Using the PermaSorb™ Disposable Fixation Device Compared to Repairs Using Permanent Fixation In an Animal Study G. Kevin Gillian, M.D., F.A.C.S.,a I.D McRury PhD,b J.R Scott PhD,b W. Shiow-jyi PhD,c V. Roy, PE d a c
Virginia Hospital Center, Arlington, VA; b Davol Inc., Subsidiary of C. R. Bard, Inc., Warwick, RI; DaVinci Biomedical Research Products, Inc., S. Lancaster, MA; d Altran Solutions, Inc., Boston, MA
INTRODUCTION The utilization of absorbable fixation as an alternative for permanent fixation in hernia repair
Figure 1
is a growing trend in the market, based on the theory that absorbable materials should lead to more natural wound healing and less long-term material retention. Such materials are suitable for use with mesh where rapid tissue in-growth is achieved, such as polypropylene. The PermaSorb™ Disposable Fixation Device [BP] is a general surgery device that is used for fixation of mesh and the re-approximation of soft tissue. The fasteners are made from Poly (D, L) – Lactide (PDLLA) material that is naturally broken down in the body over a period of approximately 16 months, with significant absorption seen in the first 9 months. This study
PermaSorb™ Fixation Device (not shown to scale – actual length is 6.4 mm)
compares the fixation strength of a ventral hernia repair fixated with BP fasteners to that of a repair fixated with permanent fasteners [PF].
STUDY METHODS Twenty-four female Yorkshire pigs were anesthetized with inhalational isoflurane, and the ventral abdomen was prepared for aseptic survival surgery using standard means. A 12 inch (30 cm) midline incision was made into the peritoneal space and individual 1 inch (2.5 cm) surgical defects were created with the use of a 1 inch (2.5 cm) circular die rotated to create a full thickness muscular defect, with no penetration through the outer abdominal adipose tissue and skin layers. A 3.5 inch (8.9 cm) circular Composix™ LP Mesh was fixated with 16 BP fasteners around the circumference of the prosthetic, spaced approximately 0.8 inches (2 cm) apart. This repair was repeated with 16 similarly placed PF fasteners on an alternate location in
each pig. Following placement of the test devices, the abdomen was closed using standard technique. At specified post-implantation observation intervals (T0, 2 days, 1 week, 2 weeks, 4 weeks and 8 weeks) the pigs were sacrificed and the entire abdominal wall was explanted and prepared for mechanical testing. A modified ASTM standard burst test was performed on each repair within 24 hours of explantation at an independent biomaterial consulting firm. The burst pressure (psi) is the peak force (lbs-f) divided by the area of the 1 inch diameter defect (0.79 in2).
RESULTS
DISCUSSION
Two burst pressure measurements were attained from each of 24 pigs, one each from a BP and PF repair. One of the 1 month abdominal wall meshes was damaged during transit to the test facility and the entire pig was removed from the study. Both BP and PF repairs burst at pressures that were significantly greater than the clinical requirement of 4.25 psi.† The BP fixation holds approximately 15 psi less than PF during the initial time points (T0 and 2 days), however, the median burst pressure is still seven times the 4.25 psi clinical requirement. The failure mode during the burst tests at the T0 and 2 day time points was the fasteners pulling from the tissue in 75% of the BP repairs and 25% of the PF repairs. In the remainder of the tests, the fixation held so strongly into the tissue that the failure mode was the mesh tearing. At 7 days and beyond, the failure mode for every test was the mesh tearing. This indicates that just 1 week of tissue in-growth into Composix™ LP Mesh has increased the repair strength beyond the strength of the mesh itself.
There is supposition in the surgical community that converting from permanent to absorbable fixation will reduce adhesions and post-operative pain, and will result in a more natural long term repair. However, the fixation element being used must meet the minimal fixation requirements for the acute repair and must retain enough fixation strength to maintain the repair throughout the healing period. This study showed that in a porcine ventral hernia model, there is rapid tissue in-growth into Composix™ LP Mesh, increasing repair strength in as limited a time period as 2-7 days. The examples shown below illustrate rapid tissue in-growth both around and through the open cannulation in the PermaSorb™ Fastener.
Figure 3
Figure 2
Median Burst Pressure (psi)
PermaSorb™ Disposable Fixation Device
Permanent
70 60 50 40
Acute repair, time 0: Note that there are no exposed points or sharp edges.
Week 2: Extensive tissue incorporation into the mesh and tissue incorporation through the center of the BP fastener.
Week 4: Full reperitonealization of the mesh and BP fasteners are almost complete.
Week 8: The tissue is completely incorporated into the mesh with full revascularization of both the mesh and BP fasteners.
30 20 10 4.25 psi clinical requirement for burst pressure
0 Time 0
2 days
1 week
2 weeks
1 month
2 months
Implantation Time • Bars represent Median data points. • Red zone is clinical requirement of repair ranges. Bar illustrates 4.25 clinical requirement for burst pressure. Note that the burst pressure for the PermaSorb™ Device is always greater than 7x this requirement.
CONCLUSION Two different fixation devices, the PermaSorb™ Device and a permanent fixation device, were used to repair 1 inch diameter ventral abdominal defect models in pigs. Acutely, the holding strength of the PermaSorb™ Fasteners is on average greater than seven times above the physiological requirement. After one week of implantation the repair strength of both devices equaled the strength of the prosthetic itself, causing the mesh to tear before the fixation failed. Given that this is a conservatively derived repair model, the results of this study support the conclusion that the PermaSorb™ Device is well suited for use as a fixation device in hernia repairs.
ACKNOWLEDGEMENTS The study was conducted for C. R. Bard at DaVinci Biomedical Research Products, Inc., South Lancaster, MA. This study was also reviewed and evaluated by the internal Institutional Animal Care and Use Committee (IACUC) of DaVinci Biomedical Research Products, Inc., and was conducted in compliance with all regulations regarding the humane treatment of laboratory animals set forth by IACUC.
DISCLAIMER This study represents a preclinical evaluation of the PermaSorb™ Fixation Device following in vivo implantation in an animal model. The data presented herein is not intended to imply clinical product performance and/or circumvent sound clinical judgment.
References †
ata supporting this specification is on file at Davol in RPT3796573. The majority of clinical evidence is from Twardowski ZJ et al “Intraabdominal Pressures D during Natural Activities in Patients Treated with Continuous Ambulatory Peritoneal Dialysis” Nephron 44:129-135 1986.
Bard, Composix, Davol and PermaSorb are trademarks and/or registered trademarks of C. R. Bard, Inc. or an affiliate. All other trademarks are the property of their respective owners. Please consult product labels and inserts for any indications, contraindications, hazards, warnings, precautions and instructions for use. © Copyright 2009, C. R. Bard, Inc. All Rights Reserved. WP125
Davol Inc. • Subsidiary of C. R. Bard, Inc. 100 Crossings Boulevard • Warwick, RI 02886 1.800.556.6275 • www.davol.com