Experimental magnesium phosphate cement paste increases torque of trochanteric fixation nail advanced™ blades in human femoral heads.

BACKGROUND: The use of polymethylmethacrylate cement for in-situ implant augmentation has considerable disadvantages: it is potentially cytotoxic, exothermic and non-degradable. Therefore, the primary aim of this study was to develop a magnesium phosphate cement which meets the requirements for in-situ implant augmentation as an alternative. Secondly, this experimental cement was compared to commercial bone cements in a biomechanical test set-up using augmented femoral head blades. METHODS: A total of 40 human femoral heads were obtained from patients who underwent total hip arthroplasty. After bone mineral density was quantified, specimens were assigned to four treatment groups. A blade of the Trochanteric Fixation Nail Advanced™ was inserted into each specimen and augmented with either Traumacem™ V+, Paste-CPC, the experimental magnesium phosphate cement or no cement. A rotational load-to-failure-test (0° to 90°) was performed. FINDINGS: A conventional two-component magnesium phosphate cement failed in-situ implant augmentation consistently due to filter pressing. Only a glycerol-based magnesium phosphate paste was suitable for the augmentation of femoral head blades. While the blades augmented with Traumacem™ V+ yielded the highest maximum torque overall (22.1 Nm), the blades augmented with Paste-CPC and the magnesium phosphate paste also showed higher maximum torque values (15.8 and 12.8 Nm) than the control group (10.8 Nm). INTERPRETATION: This study shows for the first time the development of a degradable magnesium phosphate cement paste which fulfills the requirements for in-situ implant augmentation. Simultaneously, a 48% increase in stability is demonstrated for a scenario where implant anchorage is difficult in osteoporotic bone.

Degradation and Bone-Contact Biocompatibility of Two Drillable Magnesium Phosphate Bone Cements in an In Vivo Rabbit Bone Defect Model.

The use of bone-cement-enforced osteosynthesis is a growing topic in trauma surgery. In this context, drillability is a desirable feature for cements that can improve fracture stability, which most of the available cement systems lack. Therefore, in this study, we evaluated a resorbable and drillable magnesium-phosphate (MgP)-based cement paste considering degradation behavior and biocompatibility in vivo. Two different magnesium-phosphate-based cement (MPC) pastes with different amounts of phytic acid (IP 6) as setting retarder (MPC 22.5 and MPC 25) were implanted in an orthotopic defect model of the lateral femoral condyle of New Zealand white rabbits for 6 weeks. After explantation, their resorption behavior and material characteristics were evaluated by means of X-ray diffraction (XRD), porosimetry measurement, histological staining, peripheral quantitative computed tomography (pQCT), cone-beam computed tomography (CBCT) and biomechanical load-to-failure tests. Both cement pastes displayed comparable results in mechanical strength and resorption kinetics. Bone-contact biocompatibility was excellent without any signs of inflammation. Initial resorption and bone remodeling could be observed. MPC pastes with IP 6 as setting retardant have the potential to be a valuable alternative in distinct fracture patterns. Drillability, promising resorption potential and high mechanical strength confirm their suitability for use in clinical routine.

"Mother and baby plate": a strategy to improve stability in proximal fractures of the ulna.

INTRODUCTION: Proximal ulna fractures with a large zone of comminution, such as in the context of Monteggia injuries, require mechanically strong osteosyntheses as they occur in regions with high physiological joint load. Consequently, implant failure and pseudarthrosis are critical and devastating complications, especially with the background of mainly young patients being affected. An effective solution could be provided by adding a small second plate 90° angulated to the standard dorsal plate in the area of non-union. Thus, this study investigates whether, from a biomechanical point of view, the use of such a mini or baby plate is worthwhile. MATERIALS AND METHODS: Comminuted fractures distal to the coronoid process, equivalent to Jupiter type IIb fractures, are generated on artificial Sawbones® of the ulna and stabilized using two different plate osteosyntheses: in the first group, a dorsal locking compression olecranon plate is used (LCP group). In the second group, a small, ulnar 5-hole olecranon plate is added as a baby plate in addition to the mother plate at the level of the fracture zone (MBP group). Dynamic biomechanical loading in degrees of flexion from 0° to 90° is carried out to determine yield load, stiffness, displacement, and changes in fracture gap width as well as bending of the dorsal plate. RESULTS: The "mother-baby-plate" osteosynthesis had a significantly higher yield load (p < 0.01) and stiffness (p = 0.01) than the LCP group. This correlates with the increased movement of the proximal fracture element during cyclic testing for the LCP group compared to the MBP group as measured by an optical metrology system. CONCLUSIONS: Here, we show evidence that the addition of a small plate to the standard plate is highly effective in increasing the biomechanical stability in severe fractures equivalent to Jupiter type IIb. As it hopefully minimizes complications like pseudarthrosis and implant failure and as the additional preparatory effort leading to compromised blood supply is regarded to be negligible, this justifies and highly advises the use of a mother-baby-plate system.

Retroperitoneal arterial bleeding caused by an undisplaced conservatively treated hyperextension injury of the lumbar spine - A case report.

Background: Hyperextension fractures of the thoracolumbar spine are commonly seen in ankylotic disorders due to the rigidity of the spine. The known complications include instability, neurological deficits and posttraumatic deformity but there is no report of a hemodynamic relevant arterial bleeding in undisplaced hyperextension fractures. An arterial bleeding poses a life-threatening complication and may be difficult to recognize in an ambulatory or clinical setting. Case presentation: A 78-year-old male was brought to the emergency department after suffering a domestic fall with incapacitating lower back pain. X-rays and a CT scan revealed an undisplaced L2 hyperextension fracture which was treated conservatively. 9 days after admission, the patient complained about unprecedented abdominal pain with a CT scan disclosing a 12 × 9 × 20 cm retroperitoneal hematoma on grounds of an active arterial bleeding from a branch of the L2 lumbar artery. Subsequently, access via lumbotomy, evacuation of the hematoma and insertion of a hemostatic agent was performed. The therapy concept of the L2 fracture remained conservatively. Conclusions: A secondary, retroperitoneal arterial bleeding after a conservatively treated undisplaced hyperextension fracture of the lumbar spine is a rare and severe complication that has not been described in literature yet and may be difficult to recognize. An early CT scan is recommended in case of a sudden onset of abdominal pain in these fractures to fasten treatment and hence decrease morbidity and mortality. Thus, this case report contributes to the awareness of this complication in a spine fracture type with increasing incidence and clinical relevance.

Impact of a Femoral Fracture on Outcome after Traumatic Brain Injury-A Matched-Pair Analysis of the TraumaRegister DGU®.

Traumatic brain injury (TBI) is the leading cause of death and disability in polytrauma and is often accompanied by concomitant injuries. We conducted a retrospective matched-pair analysis of data from a 10-year period from the multicenter database TraumaRegister DGU® to analyze the impact of a concomitant femoral fracture on the outcome of TBI patients. A total of 4508 patients with moderate to critical TBI were included and matched by severity of TBI, American Society of Anesthesiologists (ASA) risk classification, initial Glasgow Coma Scale (GCS), age, and sex. Patients who suffered combined TBI and femoral fracture showed increased mortality and worse outcome at the time of discharge, a higher chance of multi-organ failure, and a rate of neurosurgical intervention. Especially those with moderate TBI showed enhanced in-hospital mortality when presenting with a concomitant femoral fracture (p = 0.037). The choice of fracture treatment (damage control orthopedics vs. early total care) did not impact mortality. In summary, patients with combined TBI and femoral fracture have higher mortality, more in-hospital complications, an increased need for neurosurgical intervention, and inferior outcome compared to patients with TBI solely. More investigations are needed to decipher the pathophysiological consequences of a long-bone fracture on the outcome after TBI.

Plate osteosynthesis combined with bone cement provides the highest stability for tibial head depression fractures under high loading conditions.

Older patients sustaining tibial head depression fractures often cannot follow the post-operative rehabilitation protocols with partial weight-bearing of the affected limb, leading to osteosynthesis failure, cartilage step-off and arthritis development. Therefore, the aim of this study was to analyse the biomechanical performance of different types of osteosyntheses alone and in combination with bone cement simulating cyclically high loading conditions of tibial head depression fractures. Lateral tibial head depression fractures (AO: 41-B2.2; Schatzker type III) were created in synthetic bones and stabilized using three different osteosyntheses alone and in combination with a commonly used bone cement (chronOS™): 2 screws, 4 screws in the jail technique and a lateral angle-stable buttress plate. After fixation, the lateral tibial plateau was axially loaded in two, from each other independent testing series: In the first test protocol, 5000 cycles with 500 N and in the end load-to-failure tests were performed. In the second test protocol, the cyclic loading was increased to 1000 N. Parameters of interest were the displacement of the articular fracture fragment, the stiffness and the maximum load. The osteosyntheses revealed a higher stiffness in combination with bone cement compared to the same type of osteosynthesis alone (e.g., 500 N level: 2 screws 383 ± 43 N/mm vs. 2 screws + chronOs 520 ± 108 N/mm, increase by 36%, p < 0.01; 4 screws 368 ± 97 N/mm vs. 4 screws + chronOS 516 ± 109 N/mm, increase by 40%, p < 0.01; plate: 509 ± 73 N/mm vs. plate + chronOs 792 ± 150 N/mm, increase by 56%, p < 0.01). Bone cement reduced the displacement of the plate significantly (500 N level: plate: 8.9 ± 2.8 mm vs. plate + chronOs: 3.1 ± 1.4 mm, reduction by 65%, p < 0.01; 1000 N level: 16.9 ± 3.6 mm vs 5.6 ± 1.3 mm, reduction by 67%, p < 0.01). Thus, the highest stiffness and lowest displacement values were found when using the plate with bone cement in both loading conditions (500 N level: 2 screws + chronOs 3.7 ± 1.3 mm, 4 screws + chronOs 6.2 ± 2.4 mm; 1000 N level: 2 screws + chronOs 6.5 ± 1.2 mm, 4 screws + chronOs 5.7 ± 0.8 mm). From a biomechanical perspective, plate osteosynthesis of tibial head depression fractures should always be combined with bone cement, provides higher stability than 2-screw and 4-screw fixation and is a valid treatment option in cases where extraordinary stability is required.

Surgical Fixation of Calcaneal Beak Fractures-Biomechanical Analysis of Different Osteosynthesis Techniques.

The calcaneal beak fracture is a rare avulsion fracture of the tuber calcanei characterized by a solid bony fragment at the Achilles tendon insertion. Treatment usually requires osteosynthesis. However, lack of biomechanical understanding of the ideal fixation technique persists. A beak fracture was simulated in synthetic bones and assigned to five different groups of fixation: A) 6.5-mm partial threaded cannulated screws, B) 4.0-mm partial threaded cannulated screws, C) 5.0-mm headless cannulated compression screws, D) 2.3-mm locking plate, and E) 2.8-mm locking plate. Different traction force levels were applied through an Achilles tendon surrogate in a material-testing machine on all stabilized synthetic bones. Outcome measures were peak-to-peak displacement, total displacement, plastic deformation, stiffness, visual-fracture-line displacement, and mode of implant failure. The 2.3- and 2.8-mm plating groups showed a high drop-out rate at 100 N tension force and failed under higher tension levels of 200 N. The fracture fixation using 4.0-mm partial threaded screws showed a significantly higher repair strength and was able to withhold cyclic loading up to 300 N. The lowest peak-to-peak displacement and the highest load-to-failure and stiffness were provided by fracture fixation using 6.5-mm partial threaded cannulated screws or 5.0-mm headless cannulated compression screws. As anticipated, large 6.5-mm screw diameters provide the best biomechanical fixation. Surprisingly, the 5.0-mm headless cannulated compression screws yield reliable stability despite the absent screw head and washer. When such large screws cannot be applied, 4.0-mm screws also allow reasonable fixation strength. Plate fixation should be implemented with precaution and in combination with a restrictive postoperative motion protocol. Finally, clinical cases about the surgical application and recovery are included.

Augmentation of suture anchors with magnesium phosphate cement - Simple technique with striking effect.

BACKGROUND: Suture anchors have a large field of application in orthopedic trauma surgery like the refixation of patellar, quadriceps and Achilles tendon or the treatment of rotator cuff tears. The fixation of suture anchors in osteoporotic bone is difficult, a problem that becomes increasingly relevant in the elderly. METHODS: Two types of suture anchors: 1.) Titanium CorkScrew Fast Track II with a knotted eyelet and 2.) polyether ether ketone (PEEK) SwiveLock C with a knotless eyelet were chosen for evaluation in open cell bone blocks with densities of 5-20 pcf supplied by Sawbones AB. A pilot hole of 7 mm diameter and 20 mm depth was drilled in the bone blocks and filled with an experimental drillable magnesium phosphate cement (powder: 92.5 wt% Mg3(PO4)2, 7.5 wt% MgO, liquid: 25 wt% phytic acid (C6H18O24P6)). Anchors were then inserted into the cement and allowed to cure for 24 h (37 °C, 100% humidity) before pullout testing was conducted with a material testing machine. Suture anchors inserted in the blocks after predrilling and tapping served as control. RESULTS: Through augmentation with magnesium phosphate cement pullout strength and stiffness of the suture anchors could be significantly increased in all bone blocks up to 22-fold. CorkScrew anchors failed by rupture of the eyelet with higher pullout strengths, whereas no failure of SwiveLock C anchors could be observed when reinforced with additional FibreWire at the tip. CONCLUSIONS: We present a simple technique, whereby pullout strength of suture anchors can be significantly increased in bone with compromised density. The experimental resorbable and drillable magnesium phosphate cement proved to be effective in resisting tensile load, dispersing in the adjacent bone, and thus increasing the bone-anchor contact surface. Therefore, the experimental magnesium phosphate cement is a promising candidate for clinical application in the numerous scenarios mentioned.

Experimental Drillable Magnesium Phosphate Cement Is a Promising Alternative to Conventional Bone Cements.

Clinically used mineral bone cements lack high strength values, absorbability and drillability. Therefore, magnesium phosphate cements have recently received increasing attention as they unify a high mechanical performance with presumed degradation in vivo. To obtain a drillable cement formulation, farringtonite (Mg3(PO4)2) and magnesium oxide (MgO) were modified with the setting retardant phytic acid (C6H18O24P6). In a pre-testing series, 13 different compositions of magnesium phosphate cements were analyzed concentrating on the clinical demands for application. Of these 13 composites, two cement formulations with different phytic acid content (22.5 wt% and 25 wt%) were identified to meet clinical demands. Both formulations were evaluated in terms of setting time, injectability, compressive strength, screw pullout tests and biomechanical tests in a clinically relevant fracture model. The cements were used as bone filler of a metaphyseal bone defect alone, and in combination with screws drilled through the cement. Both formulations achieved a setting time of 5 min 30 s and an injectability of 100%. Compressive strength was shown to be ~12-13 MPa and the overall displacement of the reduced fracture was <2 mm with and without screws. Maximum load until reduced fracture failure was ~2600 N for the cements only and ~3800 N for the combination with screws. Two new compositions of magnesium phosphate cements revealed high strength in clinically relevant biomechanical test set-ups and add clinically desired characteristics to its strength such as injectability and drillability.

Low-profile double plating versus dorsal LCP in stabilization of the olecranon fractures.

INTRODUCTION: Proximal ulna fractures are common in orthopaedic surgery. Comminuted fractures require a high primary stability by the osteosynthesis, to allow an early functional rehabilitation as fast as possible, to reduce long-term limitations of range of motion. Classical dorsal plating is related to wound healing problems due to the prominence of the implant. New low-profile double plates are available addressing the soft tissue problems by positioning the plates at the medial and lateral side. This study analysed whether, under high loading conditions, these new double plates provide an equivalent stability as compared to the rigid olecranon locking compression plate (LCP). MATERIALS AND METHODS: In Sawbones, Mayo Type IIB fractures were simulated and stabilized by plate osteosyntheses: In group one, two low-profile plates were placed. In group two, a single dorsal plate (LCP) was used. The bones was than cyclically loaded simulating flexion grades of 0°, 30°, 60° and 90° of the elbow joint with increasing tension forces (150 , 150 , 300  and 500 N). The displacement and fracture gap movement were recorded. In the end, in load-to-failure tests, load at failure and mode of failure were determined. RESULTS: No significant differences were found for the displacement and fracture gap widening during cyclic loading. Under maximum loading, the double plates revealed a comparable load at failure like the single dorsal plate (LCP). The double plates failed with a proximal screw pull-out of the plate, whereas in the LCP group, in 10 out of 12 specimens the mode of failure was a diaphyseal shaft fracture at the distal plate peak. CONCLUSION: Biomechanically, the double plates are a good alternative to the dorsal LCP providing a high stability under high loading conditions and, at the same, time reducing the soft tissue irritation by a lateral plate position.

Cement-augmented screw fixation for calcaneal fracture treatment: a biomechanical study comparing two injectable bone substitutes.

BACKGROUND: The role of cement-augmented screw fixation for calcaneal fracture treatment remains unclear. Therefore, this study was performed to biomechanically analyze screw osteosynthesis by reinforcement with either a calcium phosphate (CP)-based or polymethylmethacrylate (PMMA)-based injectable bone cement. METHODS: A calcaneal fracture (Sanders type IIA) including a central cancellous bone defect was generated in 27 synthetic bones, and the specimens were assigned to 3 groups. The first group was fixed with four screws (3.5 mm and 6.5 mm), the second group with screws and CP-based cement (Graftys® QuickSet; Graftys, Aix-en-Provence, France), and the third group with screws and PMMA-based cement (Traumacem™ V+; DePuy Synthes, Warsaw, IN, USA). Biomechanical testing was conducted to analyze peak-to-peak displacement, total displacement, and stiffness in following a standardized protocol. RESULTS: The peak-to-peak displacement under a 200-N load was not significantly different among the groups; however, peak-to-peak displacement under a 600- and 1000-N load as well as total displacement exhibited better stability in PMMA-augmented screw osteosynthesis compared to screw fixation without augmentation. The stiffness of the construct was increased by both CP- and PMMA-based cements. CONCLUSION: Addition of an injectable bone cement to screw osteosynthesis is able to increase fixation strength in a biomechanical calcaneal fracture model with synthetic bones. In such cases, PMMA-based cements are more effective than CP-based cements because of their inherently higher compressive strength. However, whether this high strength is required in the clinical setting for early weight-bearing remains controversial, and the non-degradable properties of PMMA might cause difficulties during subsequent interventions in younger patients.

The Anterior Subcutaneous Pelvic Ring Fixator: No Biomechanical Advantages Compared with External Fixation.

BACKGROUND: Subcutaneous fixation of the anterior pelvic ring is an emerging surgical technique for trauma patients. The aim of this study was to biomechanically evaluate 2 internal fixation devices for stabilizing a disrupted pelvic ring and compare them with traditional external fixation. METHODS: Thirty-six synthetic pelvises with a simulated unstable ring fracture (anteroposterior compression type III) were divided into 3 groups. Group A underwent fixation with a supra-acetabular external fixator; group B, with an internal fixator using the USS II polyaxial system; and group C, with an internal fixator using the Click'X polyaxial system. Biomechanical testing included measurement of peak-to-peak displacement at 300, 400, and 500 N; total displacement; plastic deformation; stiffness; and fracture-line displacement. RESULTS: Statistical analysis of all measured parameters revealed no significant differences among the groups. However, vertical displacement of the preshaped connecting rod within the screw heads occurred as a result of inadequate stability of the internal fixation at the rod-screw interface. CONCLUSIONS: Although internal fixator devices are placed close to the bone and should therefore maintain greater stiffness, our data did not support the hypothesis of superior stability. Special attention is required when using a curved connecting rod as the rod is easily displaced, placing relevant anatomical structures at risk. These devices require further refinement to avoid potential patient injury.

Local Autograft and Strong Pulvertaft Fixation Technique for Reconstruction of a Rerupture of the Extensor Hallucis Longus Tendon: A Case Report.

There are different treatment options for extensor hallucis longus injuries. For primary repair, the end-to-end suture is recommended. The treatment of reruptures or tendon defects is challenging, and a wide range of procedures have been used in this regard, including primary and secondary repairs with and without auto- and allografts. To overcome the disadvantages of second-site morbidity and to achieve high primary stability, we demonstrate a technique using a local tendon graft in combination with a strong Pulvertaft suture technique in a case of rerupture of the extensor hallucis longus tendon.

Biomechanical Evaluation of Promising Different Bone Substitutes in a Clinically Relevant Test Set-Up.

(1) Background: Bone substitutes are essential in orthopaedic surgery to fill up large bone defects. Thus, the aim of the study was to compare diverse bone fillers biomechanically to each other in a clinical-relevant test set-up and to detect differences in stability and handling for clinical use. (2) Methods: This study combined compressive strength tests and screw pullout-tests with dynamic tests of bone substitutes in a clinical-relevant biomechanical fracture model. Beyond well-established bone fillers (ChronOSTM Inject and Graftys® Quickset), two newly designed bone substitutes, a magnesium phosphate cement (MPC) and a drillable hydrogel reinforced calcium phosphate cement (CPC), were investigated. (3) Results: The drillable CPC revealed a comparable displacement of the fracture and maximum load to its commercial counterpart (Graftys® Quickset) in the clinically relevant biomechanical model, even though compressive strength and screw pullout force were higher using Graftys®. (4) Conclusions: The in-house-prepared cement allowed unproblematic drilling after replenishment without a negative influence on the stability. A new, promising bone substitute is the MPC, which showed the best overall results of all four cement types in the pure material tests (highest compressive strength and screw pullout force) as well as in the clinically relevant fracture model (lowest displacement and highest maximum load). The low viscosity enabled a very effective interdigitation to the spongiosa and a complete filling up of the defect, resulting in this demonstrated high stability. In conclusion, the two in-house-developed bone fillers revealed overall good results and are budding new developments for clinical use.

Are Variable-Angle Locking Screws Stable Enough to Prevent Calcaneal Articular Surface Collapse? A Biomechanical Study.

PURPOSE: To compare fixed- or variable-angle locking screws in calcaneal fracture plates using a sawbones biomechanical model. METHODS: Intra-articular calcaneal fractures were created in synthetic bones. Reduction and stabilization was performed with 3 different plates. In group A, a fixed-angle locking plate was used with screws fastened perpendicularly to the plate (3.5 LCP, DePuySynthes). In groups B and C (2.7 VA-LCP, DePuySynthes and 3.5 Aptus, Medartis, respectively), fracture fixation was performed using variable-angle locking plates. Biomechanical testing was conducted. Displacement of the subtalar articular surface, stiffness, maximum displacement, change in the angle of Gissane, and mode of failure under cyclic loading at 200 N, 600 N, and 1000 N (500 cycles each) were determined. RESULTS: No statistically significant difference of articular surface dislocation under cyclic loading was detected. The stiffness and maximum displacement did not reveal any disparity as well. The change in the angle of Gissane showed only minor displacement of the articular surface. CONCLUSION: In our study, the resistance of variable-angle locking plates against articular surface displacement was similar to fixed-angle locking screws.

Biomechanical analysis of different osteosyntheses and the combination with bone substitute in tibial head depression fractures.

BACKGROUND: Tibial head depression fractures demand a high level of fracture stabilization to prevent a secondary loss of reduction after surgery. Elderly individuals are at an increased risk of developing these fractures, and biomechanical investigations of the fractures are rare. Therefore, the aim of this study was to systematically analyze different types of osteosyntheses in combination with two commonly used bone substitutes. METHODS: Lateral tibial head depression fractures were created in synthetic bones. After reduction, the fractures were stabilized with eight different treatment options of osteosynthesis alone or in combination with a bone substitute. Two screws, 4 screws and a lateral buttress plate were investigated. As a bone substitute, two common clinically used calcium phosphate cements, Norian® Drillable and ChronOS™ Inject, were applied. Displacement of the articular fracture fragment (mm) during cyclic loading, stiffness (N/mm) and maximum load (N) in Load-to-Failure tests were measured. RESULTS: The three different osteosyntheses (Group 1: 2 screws, group 2: 4 screws, group 3: plate) alone revealed a significantly higher displacement compared to the control group (Group 7: ChronOS™ Inject only) (Group 1, 7 [p < 0.01]; group 2, 7 [p = 0.04]; group 3, 7 [p < 0.01]). However, the osteosyntheses in combination with bone substitute exhibited no differences in displacement compared to the control group. The buttress plate demonstrated a higher normalized maximum load than the 2 and 4 screw osteosynthesis. Comparing the two different bone substitutes to each other, ChronOS™ inject had a significantly higher stiffness and lower displacement than Norian® Drillable. CONCLUSIONS: The highest biomechanical stability under maximal loading was provided by a buttress plate osteosynthesis. A bone substitute, such as the biomechanically favorable ChronOS™ Inject, is essential to reduce the displacement under lower loading.

Does plastic suture deformation induce gapping after tendon repair? A biomechanical comparison of different suture materials.

Plastic deformation of sutures creates an irreversible extension during load. To test our hypothesis that such plastic deformation causes gap formation after tendon repair, we determined the plasticity of five different suture materials commonly used in tendon surgery. Prolene, Polydioxanone (PDS), Ethibond, Vicryl, and FiberWire sutures were biomechanically tested to determine their offset yield strength, initial extension, creep, relaxed elongation, peak-to-peak displacement, stiffness, and maximum tensile strength under static, constant, and cyclic loading. In addition, 35 porcine hindlimb tendons were used to evaluate gap formation and the biomechanical behavior of the suture materials after tendon repair. Prolene had a low offset yield strength and high initial extensions at 30, 60, and 90N combined with relatively large creep, relaxed elongation, and peak-to-peak displacement. Aside from the low maximum tensile strength and stiffness, these parameters indicate an early plastic deformation during loading. The material properties of PDS were generally better for suturing than those of Prolene, but no difference was found in offset yield strength or initial extension. In contrast to the monofilament materials Prolene and PDS, the braided Ethibond, Vicryl, and FiberWire materials showed significantly less plastic deformation. The lowest amount of plastic deformation was found in the FiberWire and the results for Ethibond and Vicryl were equal. Gap formation occurred at the lowest tension force in the Prolene group, but only FiberWire required a significantly larger tension force to produce gapping at the repair site, indicating a higher resistance to gap formation. The results of this study show that plastic deformation occurs at a lower tension force in the monofilament sutures Prolene and PDS than in the braided materials Ethibond, Vicryl, and FiberWire. After tendon repair, FiberWire likely prevents gap formation, whereas Prolene induces gapping through low-tension plastic deformation. Therefore, plastic deformation should be considered when selecting suture materials for tendon repair surgery.

Bunnell or cross-lock Bunnell suture for tendon repair? Defining the biomechanical role of suture pretension.

BACKGROUND: Suture pretension during tendon repair is supposed to increase the resistance to gap formation. However, its effects on the Bunnell suture technique are unknown. The purpose of this study was to determine the biomechanical effects of suture pretension on the Bunnell and cross-lock Bunnell techniques for tendon repair. METHODS: Eighty porcine hindlimb tendons were randomly assigned to four different tendon repair groups: those repaired with or without suture pretension using either a simple Bunnell or cross-lock Bunnell technique. Pretension was applied as a 10 % shortening of the sutured tendon. After measuring the cross-sectional diameter at the repair site, static and cyclic biomechanical tests were conducted to evaluate the initial and 5-mm gap formation forces, elongation during cyclic loading, maximum tensile strength, and mode of failure. The suture failure mechanism was also separately assessed fluoroscopically in two tendons that were repaired with steel wire. RESULTS: Suture pretension was accompanied by a 10 to 15 % increase in the tendon diameter at the repair site. Therefore, suture pretension with the Bunnell and cross-lock Bunnell repair techniques noticeably increased the resistance to initial gap formation and 5-mm gap formation. The tension-free cross-lock Bunnell repair demonstrated more resistance to initial and 5-mm gap formation, less elongation, and higher maximum tensile strength than the tension-free Bunnell repair technique. The only difference between the tensioned cross-lock Bunnell and tensioned Bunnell techniques was a larger resistance to 5-mm gap formation with the cross-lock Bunnell technique. Use of the simple instead of cross-lock suture configuration led to failure by suture cut out, as demonstrated fluoroscopically. CONCLUSION: Based on these results, suture pretension decreases gapping and elongation after tendon repair, and those effects are stronger when using a cross-lock, rather than a regular Bunnell suture. However, pretension causes an unfavorable increase in the tendon diameter at the repair site, which may adversely affect wound healing.

Biomechanical Analysis of the Modified Kessler, Lahey, Adelaide, and Becker Sutures for Flexor Tendon Repair.

PURPOSE: To compare the biomechanical properties of the modified Kessler, Lahey, Adelaide, and Becker repairs, which are marked by either a locking-loop or a cross-lock configuration. METHODS: Ninety-six lacerated porcine flexor tendons were repaired using the respective core suture and an epitendinous repair. Biomechanical testing was conducted under static and cyclic loads. Parameters of interest were 2-mm gap formation force, displacement during different loads, stiffness, maximum force, and mode of failure. RESULTS: The meaningful gap formation occurred in all 4 repairs at similar tension loads without any significant differences. Maximum force was highest in the Becker repair with a considerable difference compared with the modified Kessler and Lahey sutures. The Adelaide repair showed the highest stiffness. Overall, the displacement during cyclic loading demonstrated similar results with an exception between the Lahey and the Adelaide repairs at 10 N load. Failure by suture pull-out occurred in 42% in the modified Kessler, in 38% in the Lahey, and in 4% in the Adelaide repairs. The Becker repair failed only by suture rupture. CONCLUSIONS: The results of our study suggest that the difference between the 4-strand repairs with a cross-lock or a locking-loop configuration is minor in regard to gap formation. A strong epitendinous suture and the application of core suture pretension might prevent differences in gapping. However, the modified Kessler and Lahey repairs had an inferior maximum tensile strength and were prone to early failure caused by the narrow locking loops with their limited locking power. CLINICAL RELEVANCE: We suggest that surgeons should use pre-tension in repaired tendons to improve gap resistance and should avoid narrow locking loop anchoring to the tendon.