Aims

The “2 to 10% strain rule” for fracture healing has been widely interpreted to mean that interfragmentary strain greater than 10% predisposes a fracture to nonunion. This interpretation focuses on the gap-closing strain (axial micromotion divided by gap size), ignoring the region around the gap where osteogenesis typically initiates. The aim of this study was to measure gap-closing and 3D interfragmentary strains in plated ovine osteotomies and associate local strain conditions with callus mineralization.

Secondary bone healing is impacted by the extent of interfragmentary motion at the fracture site. It provides mechanical stimulus that is required for the formation of fracture callus. In clinical settings, interfragmentary motion is induced by physiological loading of the broken bone – for example, by weight-bearing. However, there is no consensus about when mechanical stimuli should be applied to achieve fast and robust healing response. Therefore, this study aims to identify the effect of the immediate and delayed application of mechanical stimuli on secondary bone healing. A partial tibial osteotomy was created in twelve Swiss White Alpine sheep and stabilized using an active external fixator that induced well-controlled interfragmentary motion in form of a strain gradient. Animals were randomly assigned into two groups which mimicked early (immediate group) and late (delayed group) weight-bearing. The immediate group received daily stimulation (1000 cycles/day) from the first day post-op and the delayed group from the 22nd day post-op. Healing progression was evaluated by measurements of the stiffness of the repair tissue during mechanical stimulation and by quantifying callus area on weekly radiographs. At the end of the five weeks period, callus volume was measured on the post-mortem high-resolution computer tomography (HRCT) scan. Stiffness of the repair tissue (p<0.05) and callus progression (p<0.01) on weekly radiographs were significantly larger for the immediate group compared to the delayed group. The callus volume measured on the HRCT was nearly 3.2 times larger for the immediate group than for the delayed group (p<0.01). This study demonstrates that the absence of immediate mechanical stimuli delays callus formation, and that mechanical stimulation already applied in the early post-op phase promotes bone healing

Introduction. Non-union is debilitating, costly and affects 2–8% of intramedullary fixed fractures. Clinical data suggest that percutaneous interfragmentary screws offer a less invasive alternative to exchange nailing. This study aimed to assess their efficiency with biomechanical analyses. Materials and Methods. A tibia was prepared for finite element analysis by creating a fracture of AO classification 42A2b, prior to reaming and insertion of an intramedullary nail. A callus was modelled as granulation tissue and gait loads were applied. The model was validated against published data and with sensitivity studies. The effects of weightbearing, fracture gap and angle, percutaneous screws and exchange nailing were compared through quantification of interfragmentary motion and strain, with the latter used to gauge healing performance via mechano-regulation theory. Results. Axial interfragmentary motion increased with increasing weightbearing, however, shear decreased at 25–50% weightbearing, leading to superior healing performance. Fracture gap had minimal effect on axial motion, but larger gaps gave greater shear, compromising healing. Elevated fracture obliquity culminated in more shear and inferior healing. Exchange nailing reduced axial motion by ∼30%, but had little effect on shear. Conversely, percutaneous screws had negligible effect on axial motion, but reduced shear by ∼15%, with three screws having a similar net effect on healing as exchange nailing from 10 to 11mm. Conclusions. This study provides new insight into fracture healing biomechanics and discovered that partial weightbearing, less oblique fractures and percutaneous screws all reduce shear, enhancing healing

In the course of uneventful secondary bone healing, a fracture gap is progressively overgrown by callus which subsequently calcifies and remodels into new bone. It is widely accepted that callus formation is promoted by mechanical stimulation of the tissue in the fracture gap. However, the optimal levels of the interfragmentary motion's amplitude, frequency and timing remain unknown. The aim of this study was to develop an active fixation system capable of installing a well-controlled mechanical environment in the fracture gap with continuous monitoring of the bone healing progression. The experimental model was adapted from Tufekci et al. 2018 and required creation of a critical size defect and an osteotomy in a sheep tibia. They were separated by a mobile bone fragment. The distal and proximal parts of the tibia were fixed with an external fixator, whereas the mobile fragment was connected to the proximal part with an active fixator equipped with a linear actuator to move it axially for mechanical stimulation of the tissue in the fracture gap. This configuration installed well-controlled mechanical conditions in the osteotomy, dependent only on the motion of the active fixator and shielded from the influence of the sheep's functional weightbearing. A load sensor was integrated to measure the force acting in the fracture gap during mechanical stimulation. The motion of the bone fragment was controlled by means of a custom-made controller allowing to program stimulation protocols of various profiles, amplitudes and frequencies of loading events. Following in vitro testing, the system was tested in two Swiss White Alpine Sheep. It was configured to simulate immediate weightbearing for one of the animals and delayed weightbearing for the other. The applied loading protocol consisted of 1000 loading events evenly distributed over 12 hours resulting in in a single loading event every 44 seconds. Bench testing confirmed the ability of the system to operate effectively with frequencies up to 1Hz over a range of stimulation amplitudes from 0.1 to 1.5 mm. Continuous measurements of in vivo callus stiffness revealed progressive fracture consolidation in the course of each experiment. A delayed onset of fracture healing was observed in the sheep with simulated delayed weightbearing. The conducted preclinical experiments demonstrated its robustness and reliability. The system can be applied for further preclinical research and comprehensive in-depth investigation of fracture healing

There are multiple proximal prosthetic geometries available for a surgeon to select when humeral head replacement is indicated for four-part proximal humerus fractures. We compared different proximal prosthetic geometries in stable and unstable fracture patterns, with a standard tuberosity fixation method. Simulated four-part fractures were created with an oscillating saw in six synthetic shoulder models. Three different proximal prosthetic geometries used polymetylmethacrelate (PMMA) – a smooth circular shape (SCS), a diamond shape (DS) and an irregular multiple fin shape (IMFS) prostheses. A standardised fixation method using vertical, and horizontal straps along with a medial based cerclage strap was performed. Passive motion was then carried out using a robotic articulator. Interfragmentary displacement was measured from tuberosity to tuberosity as well as tuberosity to shaft using mercury strain gauges. The least amount of interfragmentary motion occurred when an IMFS was used in a stable fracture pattern. This geometry provided more interfragmentary stability even with the unstable fracture pattern than the DS or SCS. The least stable construct was the SCS prosthesis with an unstable fracture pattern. Prosthetic geometry does affect stability of tuberosity reconstruction in proximal humerus fractures. An irregular shaped prosthesis augments the fixation construct. When using a smooth prosthetic design a stable fracture pattern must be achieved to prevent excessive interfragmentary motion. A smooth prosthetic design for tuberosity reconstruction is not recommended

Aims: There are multiple proximal prosthetic geometries for humeral head replacement for treatment of four-part proximal humerus fractures. We compared four proximal prosthetic geometries in stable and unstable fracture patterns with a standard tuberosity þxation method. Methods: Twelve synthetic shoulders and 4 cadaver shoulders had a simulated four-part fracture created with an oscillating saw. The following proximal prosthetic geometries were used: smooth circular shape (SCS), diamond shape (DS), irregular multiple þn shape (IMFS), and IMFS with deeper þns (IMSDF). A standardized þxation method using vertical sutures, horizontal sutures and medial based cerclage straps was performed. Passive motion from 0–45 degrees was carried out using a robotic articulator at a rate of 10 degrees per second. Interfragmentary displacement was measured from tuberosity to tuberosity as well as tuberosity to the shaft using mercury strain gauges. This was repeated for stable and unstable fracture patterns. Results: When comparing interfragmentary motion between the four different geometries the greatest amount of motion occurred with the SCS in a stable fracture (0.69mm, p< 0.0001) and unstable fracture (0.71 mm, p< 0.0001). The geometry that provided the most stability was the IMFSDF in stable (0.08mm) and unstable (0.09 mm) fracture patterns. Conclusion: The geometry of the prosthetic device does affect the stability of the tuberosity reconstruction. A smooth circular prosthetic design in a stable or unstable fracture pattern does not prevent excessive interfragmentary motion, while an irregular multiple þn shaped prosthesis with deep þns augments the þxation construct even in an unstable fracture pattern

Osteosynthesis of high-energy metaphyseal proximal tibia fractures is still challenging, especially in patients with severe soft tissue injuries and/or short stature. Although the use of external fixators is the traditional treatment of choice for open comminuted fractures, patients' acceptance is low due to the high profile and therefore the physical burden of the devices. Recently, clinical case reports have shown that supercutaneous locked plating used as definite external fixation could be an efficient alternative. Therefore, the aim of this study was to evaluate the effect of implant configuration on stability and interfragmentary motions of unstable proximal tibia fractures fixed by means of externalized locked plating. Based on a right tibia CT scan of a 48 years-old male donor, a finite element model of an unstable proximal tibia fracture was developed to compare the stability of one internal and two different externalized plate fixations. A 2-cm osteotomy gap, located 5 cm distally to the articular surface and replicating an AO/OTA 41-C2.2 fracture, was virtually fixed with a medial stainless steel LISS-DF plate. Three implant configurations (IC) with different plate elevations were modelled and virtually tested biomechanically: IC-1 with 2-mm elevation (internal locked plate fixation), IC-2 with 22-mm elevation (externalized locked plate fixation with thin soft tissue simulation) and IC-3 with 32-mm elevation (externalized locked plate fixation with thick soft tissue simulation). Axial loads of 25 kg (partial weightbearing) and 80 kg (full weightbearing) were applied to the proximal tibia end and distributed at a ratio of 80%/20% on the medial/lateral condyles. A hinge joint was simulated at the distal end of the tibia. Parameters of interest were construct stiffness, as well as interfragmentary motion and longitudinal strain at the most lateral aspect of the fracture. Construct stiffness was 655 N/mm (IC-1), 197 N/mm (IC-2) and 128 N/mm (IC-3). Interfragmentary motions under partial weightbearing were 0.31 mm (IC-1), 1.09 mm (IC-2) and 1.74 mm (IC-3), whereas under full weightbearing they were 0.97 mm (IC-1), 3.50 mm (IC-2) and 5.56 mm (IC-3). The corresponding longitudinal strains at the fracture site under partial weightbearing were 1.55% (IC-1), 5.45% (IC-2) and 8.70% (IC-3). From virtual biomechanics point of view, externalized locked plating of unstable proximal tibia fractures with simulated thin and thick soft tissue environment seems to ensure favorable conditions for callus formation with longitudinal strains at the fracture site not exceeding 10%, thus providing appropriate relative stability for secondary bone healing under partial weightbearing during the early postoperative phase

Secondary fracture healing processes are strongly influenced by interfragmentary motion. Shear movement is assumed to be more critical than axial movement, however experimental results are controversial. Numerical fracture healing models allow to simulate the fracture healing process with variation of single input parameters and under comparable normalized mechanical conditions. Therefore, a direct comparison of different in vivo scenarios is possible. The aim of this study was to simulate fracture healing under several axial and shear movement scenarios and compare their respective time to heal. We hypothesize that shear movement is always more critical than axial loading. For the presented study, we used a corroborated numerical model for fracture healing in sheep. Numerous variations of the movement amplitude, the fracture gap size and the musculoskeletal loads were simulated for comparable axial compressive and shear load cases. In all simulated cases, axial compressive load had less inhibitory influences on the healing process than shear load. Therefore, shear loading is more critical for the fracture healing outcome in general. Thus, our findings suggest osteosynthesis implants to be optimized to limit shear movements under musculoskeletal loading

Introduction: Standard treatment for distal tibia fractures is the fixation with locking compression plates. Locking plate fixation has revolutionized fracture treatment in the last decade and may be ideally suited for a bridging plate osteosynthesis. This technique allows some controlled axial fracture motion, what essential for secondary bone healing is. A disadvantage of the locking plate technique seems to be an unsymmetrical micro motion along the fracture gap. The micromotion at the far cortex side is much larger than at the near cortex side (near the plate). It is supposed to be that the fracture movement on the near cortex is too small. To increase the motion at the near cortex side a new kind of screws has been developed. In this study we examined the micromotion using normal locking head screws versus the new dynamic locking head screws. Materials and Methods: A simplified fracture model was created by connecting 2 plastic cylinders (POM C, EModul: 3.1GPa) with a standard 11-holes Locking Compression Plate (Synthes). The fracturegap (between the two cylinders) amounted 3mm. Three kinds of fracture models were constructed: The model of a transverse fracture, an oblique fracture and a spiral fracture. An axial load from 0N up to 200N was applied with a testing machine (Zwick). The motion of the fracture model was measured in three dimensions using the optical measurement system PONTOS 5M (GOM, Braunschweig, Germany). The accuracy of the optical measurement system was about 5 micrometers. Results: A total of 72 measurements were compared. Using the new screw, axial stiffness was decreased for 16% and micromotion was up to 200 μm higher in comparison to the old screw. Discussion: Using the new dynamic locking head screw it’s possible to increase interfragmentary motion up to 200μm on the near cortex side (plate side)

Aims

In this study, we aimed to explore surgical variations in the Femoral Neck System (FNS) used for stable fixation of Pauwels type III femoral neck fractures.

Aims

Several previously identified patient-, injury-, and treatment-related factors are associated with the development of nonunion in distal femur fractures. However, the predictive value of these factors is not well defined. We aimed to assess the predictive ability of previously identified risk factors in the development of nonunion leading to secondary surgery in distal femur fractures.

Aims

To fully verify the reliability and reproducibility of an experimental method in generating standardized micromotion for the rat femur fracture model.

Objectives

Secondary fracture healing is strongly influenced by the stiffness of the bone-fixator system. Biomechanical tests are extensively used to investigate stiffness and strength of fixation devices. The stiffness values reported in the literature for locked plating, however, vary by three orders of magnitude. The aim of this study was to examine the influence that the method of restraint and load application has on the stiffness produced, the strain distribution within the bone, and the stresses in the implant for locking plate constructs.

Objectives

External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF).