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.

The Grip Concept of Incisional Hernia Repair-Dynamic Bench Test, CT Abdomen With Valsalva and 1-Year Clinical Results.

Incisional hernia is a frequent consequence of major surgery. Most repairs augment the abdominal wall with artificial meshes fixed to the tissues with sutures, tacks, or glue. Pain and recurrences plague at least 10-20% of the patients after repair of the abdominal defect. How should a repair of incisional hernias be constructed to achieve durability? Incisional hernia repair can be regarded as a compound technique. The biomechanical properties of a compound made of tissue, textile, and linking materials vary to a large extent. Tissues differ in age, exercise levels, and comorbidities. Textiles are currently optimized for tensile strength, but frequently fail to provide tackiness, dynamic stiction, and strain resistance to pulse impacts. Linking strength with and without fixation devices depends on the retention forces between surfaces to sustain stiction under dynamic load. Impacts such a coughing or sharp bending can easily overburden clinically applied composite structures and can lead to a breakdown of incisional hernia repair. Our group developed a bench test with tissues, fixation, and textiles using dynamic intermittent strain (DIS), which resembles coughing. Tissue elasticity, the size of the hernia under pressure, and the area of instability of the abdominal wall of the individual patient was assessed with low-dose computed tomography of the abdomen preoperatively. A surgical concept was developed based on biomechanical considerations. Observations in a clinical registry based on consecutive patients from four hospitals demonstrate low failure rates and low pain levels after 1 year. Here, results from the bench test, the application of CT abdomen with Valsalva's maneuver, considerations of the surgical concept, and the clinical application of our approach are outlined.

Biomechanical analysis of anterior pelvic ring fractures with intact peripelvic soft tissues: a cadaveric study.

PURPOSE: Biomechanical studies of the pelvis are usually performed using dissected pelvic specimens or synthetic bones. Thereby the stabilising effect of the surrounding soft tissues is analysed insufficiently. Biomechanical data for isolated anterior pelvic ring fractures are currently missing. Therefore, the purpose of this study was to develop a novel testing device for biomechanical analyses of the pelvis and to investigate two different anterior pelvic ring fractures in a cadaveric model with intact peripelvic soft tissues. METHODS: A new biomechanical table construction which enables the fixation and testing of complete cadaveric specimens was developed. It was used to investigate the relative motion and stiffness changes due to unilateral osteotomy of the superior and inferior pubic ramus. Five cadavers with a mean age of 55.6 years (± 15.53 years) were included and loaded with a sinusoidal, cyclic (1 Hz), compressive force of up to 365 N over ten cycles for each condition. RESULTS: Biomechanical testing of the pelvis with complete appended soft tissues was feasible. Native stiffness without a pelvic fracture was 64.31 N/mm (± 8.33 N/mm). A standardised unilateral osteotomy of the superior pubic ramus reduced the stiffness under isolated axial load by 2% (63.05 N/mm ± 7.45 N/mm, p = 0.690). Additional osteotomy of the inferior pubic ramus caused a further, statistically not significant, decrease by 5% (59.57 N/mm ± 6.84 N/mm, p = 0.310). CONCLUSIONS: The developed test device was successfully used for biomechanical analyses of the pelvis with intact peripelvic soft tissues. In a first study, isolated unilateral fractures of the anterior pelvic ring showed no relevant biomechanical variation compared to the intact situation under isolated axial load. Only 7% of the measured stiffness was created by both unilateral pubic rami. Therefore, the clinical practice to treat unilateral anterior pelvic ring fractures conservatively is supported by the results of this study.

Primary and Recurrent Repair of Incisional Hernia Based on Biomechanical Considerations to Avoid Mesh-Related Complications.

Aim: Mechanical principles successfully guide the construction of polymer material composites in engineering. Since the abdominal wall is a polymer composite augmented with a textile during incisional hernia repair we ask: can incisional hernia be repaired safely and durably based on biomechanical principles? Material and Methods: Repair materials were assessed on a self-built bench test using pulse loads to elude influences on the reconstruction of the abdominal wall. Tissue elasticity was analyzed preoperatively as needed with computed tomography at rest and during Valsalva's maneuver. Preoperatively, the critical retention force of the reconstruction to pulse loads was calculated and a biomechanically durable repair was designed based on the needs of the individual patient. Intraoperatively, the design was adjusted as needed. Hernia meshes with high grip factors (Progrip®, Dahlhausen® Cicat) were used for the repairs. Mesh sizes, fixation elements and reconstructive details were oriented on the biomechanical design. All patients recieved single-shot antibiosis. Patients were discharged after full ambulation was achieved. Results: A total of 163 patients (82 males and 81 females) were treated for incisional hernia in four hospitals by ten surgeons. Primary hernia was repaired in 119 patients. Recurrent hernia was operated on in 44 cases. Recurrent hernia was significantly larger (median 161 cm2 vs. 78 cm2; u-test: p = 0.00714). Re-do surgery took significantly longer (median 229 min vs. 150 min; p < 0.00001) since recurrent disease required more often transversus abdominis release (70% vs. 47%). GRIP tended to be higher in recurrent repair (p = 0.01828). Complication rates (15%) and hospital stay were the same (6 vs. 6 days; p = 0.28462). After 1 year, no recurrence was detected in either group. Pain levels were equally low in both primary and recurrent hernia repairs (median NAS = 0 in both groups at rest and under load, p = 0.88866). Conclusion: Incisional hernia can safely and durably be repaired based on biomechanical principles both in primary and recurrent disease. The GRIP concept provides a base for the application of biomechanical principles in incisional hernia repair.

Biomechanical comparison of titanium miniplates versus a variety of CAD/CAM plates in mandibular reconstruction.

BACKGROUND: Titanium plate fixation of free flaps in mandibular reconstruction involves complications such as osseous non-union or imaging artefacts. Interosteotomy movement (IOM) is known to affect bone healing. This study aimed to compare IOM and mechanical integrity of four different fixation systems in a mandible reconstruction model. METHODS: Two polyurethane (PU) fibula segments were fixed in right-sided defects of PU mandibles. Laser-melted patient-specific titanium plates were fixed with non-locking-screws (Ti-NL) or locking-screws (Ti-L). The third group consisted of locking-screws for patient-specific polyetheretherketone (PEEK-L) plates. The last group used titanium miniplates and monocortical screw fixation (Ti-MP). All models were loaded unilaterally via cyclic dynamic loading with increasing loads to simulate mastication. IOM was registered using a 3D optical tracking system. FINDINGS: PEEK-L showed highest vertical displacement (p = 0.010), lowest stiffness (p = 0.004) and highest IOM (p = 0.001). All specimen in PEEK-L demonstrated abnormal bending (n = 5) or plate fracture (n = 1). Vertical displacement or stiffness did not differ between any of Ti-MP, Ti-L and Ti-NL. IOM in Ti-MP was higher than in Ti-L and Ti-NL (p = 0.001). INTERPRETATION: Mechanical integrity of all titanium plates complies with established standards. In this model, the screw system did not influence IOM. In the tested composition and shape, PEEK plates do not seem to guarantee sufficient mechanical integrity for a use in mandibular reconstruction. Thus modifications are needed. Future clinical studies are needed to clarify optimal IOM after mandible reconstruction.

Dynamic intermittent strain can rapidly impair ventral hernia repair.

Ventral hernia repair fails frequently despite advanced mesh inserting surgery. A model for dynamic intermittent straining (DIS) of ventral hernia repairs was developed. The influence of phospholipids, position, overlap, fixation and tissue quality of various meshes on the durability of hernia repair was studied. DIS comprises the repetition of submaximal impacts delivered via a hydraulically driven plastic containment. Pig tissues simulate a ventral hernia with a standardized 5cm defect. Commercially available meshes strengthened with tacks, glue and sutures were used to bridge this defect in an underlay (IPOM) or sublay (retromuscular) position starting with a 5cm overlap in all directions. We tested 35 different ways of ventral hernia repair with up to 425 submaximal intermittent dynamic impacts until mesh dislocation occurred 10 times or a maximum of 4000 impacts each were withstood. The likelihood of a failing repair was related to the mesh, the lubricants, the position, the overlap, the fixation and the tissue quality. Most meshes dislocated easily and required fixation. One of the meshes tested was stable without fixation with a 5cm overlap and failed after reducing the overlap. Phospholipids exerted a strong influence on the biomaterial tested. The sublay position was about 10% more durable in comparison to the IPOM position. DIS revealed distinct degrees of stability with primarily stable, intermediate and primarily unstable repairs. Based on the DIS results available, the currently used ventral hernia repair options can be classified. In the future, DIS investigations can improve the durability of hernia repair.

Influence of cooling on curing temperature distribution during cementing of modular cobalt-chromium and monoblock polyethylene acetabular cups.

Total hip replacements for older patients are usually cemented to ensure high postoperative primary stability. Curing temperatures vary with implant material and cement thickness (30°C to 70°C), whereas limits for the initiation of thermal bone damage are reported at 45°C to 55°C. Thus, optimizing surgical treatment and the implant material are possible approaches to lower the temperature. The aim of this study was to investigate the influence of water cooling on the temperature magnitude at the acetabulum cement interface during curing of a modular cobalt-chromium cup and a monoblock polyethylene acetabular cup. The curing temperature was measured for SAWBONE and human acetabuli at the cement-bone interface using thermocouples. Peak temperature for the uncooled condition reached 70°C for both cup materials but was reduced to below 50°C in the cooled condition for the cobalt-chromium cup (P = .027). Cooling is an effective method to reduce curing temperature with metal implants, thereby avoiding the risk of thermal bone damage.