Basic engineering principles dictate that unplugged screw holes serve as sites of the concentration of stress and the initiation and growth of cracks (1,2). The idea of filling the holes were tested previously in the literature showing promising results (3). However there's either adverse results which might be a design mistake (4). The purpose of this study was to determine if the use of specially designed screw hole inserts in empty locking screw holes improves the strength and failure characteristics of locking plates. Forty two 7-hole locking LC/DCP plates were mounted on cylindric UHMW Polyethylene blocks with a 1-cm gap between blocks, simulating a fracture with comminution and bone loss. 21 plates had a screw hole insert placed in the center hole (centered over the simulated fracture), while 21 of the plates remained empty in the center hole. The plate–block constructs were placed in a mechanical testing machine and subjected to a series of loading conditions. The axial, bending and torsional stiffness and displacements needed for failure of each plate-block construct was calculated. The Statistical analysis was performed by Mann Whitney-U test for independent variables. All plates were then loaded to failure. There were significant difference in the axial load to failure (p=0.017), bending load to failure (p<0.01) and bending diplacements (p<0.01) of the test groups favoring the screw hole insert group as a higher mechanical strength. In conclusion the study demonstrates that the addition of the specially designed locking screw hole insert does significantly change the stength of the locking LC/DCP plates and might be suggested in the clinical application

Introduction. Current treatments of rotational deformities of long bones in children are osteotomies and fixations. In recent years, the use of guided growth for correction of rotational deformities has been reported in several pre-clinical and clinical studies. Various techniques have been used, and different adverse effects, like growth retardation and articular deformities, have been reported. We tested a novel plate concept intended for correction of rotational deformities of long bones by guided growth, with sliding screw holes to allow for longitudinal growth, in a porcine model. Method. Twelve, 12-week-old female porcines were included in the study. Surgery was performed on the left femur. The right femur was used as control. Plates were placed distally to induce external rotation, as longitudinal growth occurred. CT-scans of the femurs were processed to 3-D models and used for measuring rotation. Result. The plates rotated as intended in all 12 porcines. One porcine was excluded due to congenital deformity of the proximal part of the femurs. Two porcines had cut-out of the proximal screw on the lateral side, observed at the end of the intervention. These two porcines were included in the results. We observed a Δrotation of 5.7° ± 2° in external direction (CI: 3.7°– 7.7°). ΔFemur length was -0.4 cm [-0.7 cm – 0 cm] equal to 1.5% shortening of the operated femur. No significant difference was observed in coronal or sagittal plane. Conclusion. Significant external rotation was achieved with minimal effect on longitudinal growth. While the use of guided growth for correction of rotational deformities is already being used clinically, it is still to be considered an experimental procedure with sparse evidence. This study shows promising results for the feasibility of the method in a large animal model and is an important first step in validating the technique and detecting possible adverse effects, before future clinical studies

Objectives

This study tests the biomechanical properties of adjacent locked plate constructs in a femur model using Sawbones. Previous studies have described biomechanical behaviour related to inter-device distances. We hypothesise that a smaller lateral inter-plate distance will result in a biomechanically stronger construct, and that addition of an anterior plate will increase the overall strength of the construct.

This review is aimed at clinicians appraising preclinical trauma studies and researchers investigating compromised bone healing or novel treatments for fractures. It categorises the clinical scenarios of poor healing of fractures and attempts to match them with the appropriate animal models in the literature.

We performed an extensive literature search of animal models of long bone fracture repair/nonunion and grouped the resulting studies according to the clinical scenario they were attempting to reflect; we then scrutinised them for their reliability and accuracy in reproducing that clinical scenario.

Models for normal fracture repair (primary and secondary), delayed union, nonunion (atrophic and hypertrophic), segmental defects and fractures at risk of impaired healing were identified. Their accuracy in reflecting the clinical scenario ranged greatly and the reliability of reproducing the scenario ranged from 100% to 40%.

It is vital to know the limitations and success of each model when considering its application.

Different calcaneal plates with locked screws were compared in an experimental model of a calcaneal fracture. Four plate models were tested, three with uniaxially-locked screws (Synthes, Newdeal, Darco), and one with polyaxially-locked screws (90° ± 15°) (Rimbus). Synthetic calcanei were osteotomised to create a fracture model and then fixed with the plates and screws. Seven specimens for each plate model were subjected to cyclic loading (preload 20 N, 1000 cycles at 800 N, 0.75 mm/s), and load to failure (0.75 mm/s).

During cyclic loading, the plate with polyaxially-locked screws (Rimbus) showed significantly lower displacement in the primary loading direction than the plates with uniaxially-locked screws (mean values of maximum displacement during cyclic loading: Rimbus, 3.13 mm (sd 0.68); Synthes, 3.46 mm (sd 1.25); Darco, 4.48 mm (sd 3.17); Newdeal, 5.02 mm (sd 3.79); one-way analysis of variance, p < 0.001).

The increased stability of a plate with polyaxially-locked screws demonstrated during cyclic loading compared with plates with uniaxially-locked screws may be beneficial for clinical use.

We used demineralised bone matrix (DBM) to augment re-attachment of tendon to a metal prosthesis in an in vivo ovine model of reconstruction of the extensor mechanism at the knee. We hypothesised that augmentation of the tendon-implant interface with DBM would enhance the functional and histological outcomes as compared with previously reported control reconstructions without DBM. Function was assessed at six and 12 weeks postoperatively, and histological examination was undertaken at 12 weeks.

A significant increase of 23.5% was observed in functional weight-bearing at six weeks in the DBM-augmented group compared with non-augmented controls (p = 0.004). By 12 weeks augmentation with DBM resulted in regeneration of a more direct-type enthesis, with regions of fibrocartilage, mineralised fibrocartilage and bone. In the controls the interface was predominantly indirect, with the tendon attached to the bone graft-hydroxyapatite base plate by perforating collagen fibres.

The aim of this biomechanical study was to investigate the role of the dorsal vertebral cortex in transpedicular screw fixation. Moss transpedicular screws were introduced into both pedicles of each vertebra in 25 human cadaver vertebrae. The dorsal vertebral cortex and subcortical bone corresponding to the entrance site of the screw were removed on one side and preserved on the other. Biomechanical testing showed that the mean peak pull-out strength for the inserted screws, following removal of the dorsal cortex, was 956.16 N. If the dorsal cortex was preserved, the mean peak pullout strength was 1295.64 N. The mean increase was 339.48 N (26.13%; p = 0.033). The bone mineral density correlated positively with peak pull-out strength.

Preservation of the dorsal vertebral cortex at the site of insertion of the screw offers a significant increase in peak pull-out strength. This may result from engagement by the final screw threads in the denser bone of the dorsal cortex and the underlying subcortical area. Every effort should be made to preserve the dorsal vertebral cortex during insertion of transpedicular screws.

The re-establishment of vascularity is an early event in fracture healing; upregulation of angiogenesis may therefore promote the formation of bone. We have investigated the capacity of vascular endothelial growth factor (VEGF) to stimulate the formation of bone in an experimental atrophic nonunion model.

Three groups of eight rabbits underwent a standard nonunion operation. This was followed by interfragmentary deposition of 100 μg VEGF, carrier alone or autograft.

After seven weeks, torsional failure tests and callus size confirmed that VEGF-treated osteotomies had united whereas the carrier-treated osteotomies failed to unite. The biomechanical properties of the groups treated with VEGF and autograft were identical. There was no difference in bone blood flow.

We considered that VEGF stimulated the formation of competent bone in an environment deprived of its normal vascularisation and osteoprogenitor cell supply. It could be used to enhance the healing of fractures predisposed to nonunion.