Disadvantages of interfragmentary shear on fracture healing—mechanical insights through numerical simulation

Abstract

The outcome of secondary fracture healing processes is strongly influenced by interfragmentary motion. Shear movement is assumed to be more disadvantageous than axial movement, however, experimental results are contradictory. Numerical fracture healing models allow simulation of the fracture healing process with variation of single input parameters and under comparable, normalized mechanical conditions. Thus, a comparison of the influence of different loading directions on the healing process is possible. In this study we simulated fracture healing under several axial compressive, and translational and torsional shear movement scenarios, and compared their respective healing times. Therefore, we used a calibrated numerical model for fracture healing in sheep. Numerous variations of movement amplitudes and musculoskeletal loads were simulated for the three loading directions. Our results show that isolated axial compression was more beneficial for the fracture healing success than both isolated shearing conditions for load and displacement magnitudes which were identical as well as physiological different, and even for strain-based normalized comparable conditions. Additionally, torsional shear movements had less impeding effects than translational shear movements. Therefore, our findings suggest that osteosynthesis implants can be optimized, in particular, to limit translational interfragmentary shear under musculoskeletal loading. With the use of numerical models, distinct effects of different loading modes on fracture healing can be simulated. [17][18][19] Recently, we developed a numerical fracture healing algorithm, 20-22 which allows us to investigate the influence of single input parameters on the change in IFM and tissue distribution over the healing time. This enables a direct comparison between different mechanical conditions. Thus, according to experimental data, we identified more cartilage formation under axial compression than under shear loading conditions. 22The present study compares healing outcomes of different loading directions (i.e., axial compression, and translational and torsional shear) under normalized mechanical conditions using our calibrated sheep fracture healing algorithm. The aims were to identify adverse conditions and to explain them based on the predicted tissue development over time.From a mechanical point of view, translational shear and axial compressive loading lead to regions of compressive hydrostatic pressure (negative dilatational strain) which stimulate cartilage development, and therefore promote endochondral ossification. 2,[23][24][25] In contrast, torsional shear loading leads only to distortional strains without compressive hydrostatic pressure generation, which suppresses cartilage development.Thus, we hypothesize that differences in healing outcomes are because of differences in cartilage formation resulting from mechanical tissue strain conditions. METHODS Numerical Fracture Healing ModelWe used a numerical fracture healing simulation algorithm that w...

Biomechanical Property of a Newly Designed Assembly Locking Compression Plate: Three-Dimensional Finite Element Analysis

“…In contrast, when stress is less than optimal, bone resorption dominates [16]. As for comminuted fractures, especially in weight-bearing bone, axial stress easily leads to a transversal shift of bone blocks [17]. Some authors [18] found that intraoperative unstable rotation and poor contact between bone blocks during treatment of femoral nonunion using intramedullary nails was alleviated after bone grafting and insertion of a steel plate to increase local stability.…”

“…In summary, the axial stress and tension shear stress in the NALCP skeletal model were significantly lower than those in the LCP model. Thus, NALCP enhances the stability of bone blocks under stimulation of a slow walking load and a torsional load [17], improving the fixation effect, preventing lateral displacement of the bone block, and promoting bone healing.…”

Aseptic Humeral Nonunion: What Went Wrong? What to Do? A Retrospective Analysis of 20 Cases

“…On the other hand, pure translation and shear torsion does not stimulate callus formation for fracture union. (11)(12)(13)(14) Some authors had suggested that intramedullary nail may not fully eliminate torsion(9,15-19) and distraction at the humerus. (9,19) The rotational stiffness of the nail is largely influence by the nail design and number of interlocking screw placed.…”

Evidence of Healing of Partial-thickness Rotator Cuff Tears Following Arthroscopic Augmentation With a Collagen Implant: A 2-year MRI Follow-up

“…Indeed, studies have demonstrated the inhibitory effect of shear forces on wound healing in other collagenous tissues 29,30 . The addition of 2 mm of new, tendon-like tissue over the bursal surface of the supraspinatus tendon has been proposed as a way to reduce the stress within the injured tendon and improve the healing environment for partial-thickness cuff tears 21,22 .…”