Superiority of bridging techniques with medial fixation on initial strength.

PURPOSE: The purpose of our study was to evaluate the initial fixation strength of bridging techniques compared to other suture techniques for rotator cuff repair using a biomechanical animal model, which incorporated pretesting of intact tendons. METHODS: Seventy-six fresh bovine shoulders were used for testing seven suture configurations including simple suture (SS), mattress suture (MS), Mason-Allen (MA), modified double row (mDR), SpeedBridge (SpB), SpeedBridge with medial fixation (mSpB), and double-mattress SutureBridge (dmSuB) techniques. Cyclic loading was performed with all intact bone-tendon complex before (pretest) and after repair of the tendon (main test) at the level of 10 and 180 N at 100 Hz with displacement-controlled ramps of ± 33 mm/s. The pretest was stopped after 200 cycles. For the main test, the loading scheme was continued for a maximum of 500 cycles or until failure. RESULTS: The mean elongation of all 76 intact tendons measured at the pretest was 3.8 ± 0.6 mm (2.4-5.4 mm). No differences of gap formations at the 1st cycle were detected between SS, MS, MA, and mDR. SpB showed significant higher gap formations compared to all other suture techniques (p = 0.001). No significant differences were detected between mSpB and dmSuB, whereas both techniques were significant different when compared to the other groups (p < 0.05). CONCLUSIONS: In this study, results showed that bridging techniques with medial fixations have superior initial repair strength compared to other suture techniques. Knowledge of initial fixation strength of rotator cuff repair techniques may be of informative value to the surgeon.

Early-Age Evolution of Strength, Stiffness, and Non-Aging Creep of Concretes: Experimental Characterization and Correlation Analysis.

Six different concretes are characterized during material ages between 1 and 28 days. Standard tests regarding strength and stiffness are performed 1, 3, 7, 14, and 28 days after production. Innovative three-minute-long creep tests are repeated hourly during material ages between one and seven days. The results from the standard tests are used to assess and to improve formulas of the fib Model Code 2010: the correlation formula between the 28-day values of the strength and the stiffness, and the evolution formulas describing the early-age evolution of the strength and the stiffness during the first four weeks after production. The results from the innovative tests are used to develop a correlation formula between the 28-day values of Young's modulus and the creep modulus, and an evolution formula describing the early-age evolution of the creep modulus during the first four weeks after production. Particularly, the analyzed CEM I concretes develop stiffness and strength significantly faster than described by the formulas of the Model Code. The creep modulus of the investigated concretes evolves significantly slower than their strength and stiffness. Thus, concrete loaded at early ages is surprisingly creep active, even if the material appears to be quite mature in terms of its strength and stiffness.

In-vitro comparison of biomechanical efficiency of three cannulated screws for arthrodesis of the hindfoot.

BACKGROUND: Sufficient inter-fragmentary compression is helpful to achieve successful bony fusion in hindfoot arthrodesis using internal fixation by screws. Beside bone quality, the design of a screw influences inter-fragmentary compression. Compressive force is achievable for any kind of screw system; however, the primary deformation of the bone is different for the different screw systems. The work necessary to achieve compressive force for primary stability was measured for different screw systems and compared to an AO screw with washer. MATERIALS AND METHODS: The compressive force was determined as a function of screw advancement for 3 different cannulated screw types (7.3-mm AO screw with and without washer, the 6.5-mm Herbert screw and the 6.5-mm Ideal Compression Screw (I.CO.S) using different synthetic bone density (0.16, 0.24, 0.48 g/ccm). Compressive force was measured indirectly, via screw tension measurement with strain gauges. RESULTS: We calculated the work to reach a limit of 60 N and the corresponding ratios to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO screw without washer (116%). CONCLUSION: All screw systems yielded acceptable results but the ICOS did produce greater compression. The essential differences were the primary deformation of the bone before reaching the sufficient compressive force for primary stability.

Biomechanical analysis of fracture healing in guinea-pigs.

To validate the hypothesis that healing of fractures can be accelerated by oral administered L-arginine a guinea-pig model was chosen. A diaphyseal defect fracture was established in the right femur of each of the 32 small animals and stabilized. According to randomization groups the oral administration was realized (2 or 4 weeks medication / solvent). The following biomechanical variables were measured after 4 weeeks in 32 right femora and the corresponding uninjured left femora. The measurement for the healed femur was individually compared with that of the uninjured femur in each animal; bending, force (necessary for refracture) and energy (necessary for refracture). To apply the bending moment in a measurable and reproducible way each end of the femur was secured using a special device. For each femur a strain/momentum graph of the measurements and the essential parameters were drawn (stiffness, end of the linear range, and failure-point). The bending moment was always applied with the same loading rate. The following three variables were used for the biomechanical evaluation; bending stiffness, force until failure and energy necessary for refracture. The bending stiffness reached 73% by the control group and 88% by the 4-week treatment group. The force necessary for refracture was 52% in the control compared with 65% in the 4-week treatment group. The energy necessary for refracture was 36% in the control compared with 73% in the group treated for 4 weeks. The 2 week treatment group showed no statistical significant differences to the control, but the femora from the 4 week treatment group required statistically significant higher energy for refracture than the femora from the control.

The influence of oral L-arginine on fracture healing: an animal study.

BACKGROUND: The known biological activities of nitric oxide suggest a role in bone healing. We hypothesized that L-arginine, a source of nitric oxide, expedites the healing process of stabilized diaphyseal defects. TYPE OF STUDY: Prospective blinded animal study. METHODS: Using a guinea-pig model, a 7 mm diaphyseal and periosteal defect was produced in the right femur and splinted intramedullary with a 1.4 mm K-wire. The guinea pigs (n = 44) were treated orally in three parallel groups: two treatment groups received high doses of L-arginine (one group for 2 weeks and the other for 4 weeks) and a control group received vehicle only. After four weeks, all animals were killed and both femora explanted. Radiological, histological, histomorphometric and mechanical evaluation was performed blinded. RESULTS: Radiographs showed significantly more healing in the treatment groups (2 weeks, 10/15; 4 weeks, 11/15) than in the control group (3/14). The mechanical energy necessary for femur failure was significantly higher in the 4-week treatment group than in the control group (P < 0.05). Histology and histomorphometry showed significantly increased coverage of nonvascularized bone fragments with newly formed bone in the treatment groups (P < or = 0.05). The contralateral uninjured femora did not show significant differences between groups. CONCLUSIONS: Oral L-arginine expedites healing in stabilized diaphyseal defects in guinea pigs without detrimentally affecting uninjured counterparts.

Consistent quasistatic and acoustic elasticity determination of poly-L-lactide-based rapid-prototyped tissue engineering scaffolds.

This paper is concerned with reliable and physically sound elasticity determination of rapid-prototyped tissue engineering scaffolds made of poly-L-lactide (PLLA), with and without small portions of tricalcium phosphate (TCP) inclusions. At the level of overall scaffolds, that is, that of several millimeters, multiple uniaxial loading-unloading (quasistatic) tests were performed, giving access to the scaffolds' Young's moduli, through stress-strain characteristics during unloading. In addition, acoustic tests with 0.05 MHz frequency delivered an independent access to elastic properties, in terms of the normal components of the scaffolds' stiffness tensors. The latter strongly correlate, in a linear fashion, with the Young's moduli from the unloading tests, revealing porosity independence of Poisson's ratio. The magnitude of the latter is in full agreement with literature data on polymers. Both of these facts underline that both ultrasound tests and quasistatic unloading tests reliably provide the elastic properties of tissue engineering scaffolds.

Biomechanical criterion for selecting cancellous bone screws: arthrodesis in the hindfoot.

The aim of the paper was to compare primary biomechanical stability of different arthrodesis screws (7.3 mm AO screw with and without washer, 6.5 mm Herbert screw and 6.5 mm Ideal Compression Screw (I.CO.S)). The work necessary to achieve an adequate compressive force with them was compared to the measurement with the AO screw with washer, because this method is for the time being the most commonly used one and is called the golden standard. Compressive force was measured indirectly, via screw tension measurement, with strain gauges method. From the measurements we calculated the work to reach a limit of 60 N and the ratios corresponding to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO-screw without washer (116%). The I.CO.S showed superior results. Only in the case of extremely poor bone quality, a clear advantage of I.CO.S could be expected in practice.