Optimizing compression: Comparing eccentric plate holes and external tensioning devices

Finite element modeling of fracture compression by compression plates

Dynamic compression plating is a common type of fracture fixation used to compress between bone fragments. The quality of compression across the fracture is important for postoperative stability and primary bone healing. Compression quality may be affected by surgical variations in plate prebend, screw location, screw torque, fracture gap, and implant material. Computational modeling provides a tool for systematically examining these factors, and for visualizing the mechanisms involved. The purpose of this study was to develop a finite element model of dynamic compression plating that includes screw insertion under torque control, establish model credibility through sensitivity analyses and experimental validation, and use the model to examine the effects of surgical variables on fracture compression and postoperative stability. Model-predicted compressive pressures had good agreement with corresponding synthetic bones experiments under a variety of conditions. Models demonstrated that introducing a 1.5 or 3 mm plate prebend (using a 4.5 mm narrow LCP plate) eliminated gapping at the far cortex, which is consistent with clinical recommendations. However, models also revealed that plate prebend led to sharp decreases in fracture compressive force, exceeding 80% in some cases. A 1.5 mm plate prebend resulted in the most uniform pressures across the fracture. Testing of a simplified model form used in previous computational modeling studies showed large inaccuracies for constructs with plate prebend. This study provides the first experimentally validated computational models of dynamic compression plate fracture fixation, and reveals important effects of plate prebend and fracture gap on fracture compression quality.

Mechanics of dynamic compression plate application in fracture fixation

BACKGROUND

Dynamic compression plating is a fundamental type of bone fracture fixation used to generate interfragmentary compression. The goal of this study was to investigate the mechanics of the surgical application of these plates, specifically how plate prebend, screw location, fracture gap, and applied torque influence the resulting compressive pressures.

METHODS

Synthetic bones with transverse fractures were fixed with locking compression plates. One side of the fracture was fixed with locking screws. On the other side of the fracture, a nonlocking screw was inserted eccentrically to induce interfragmentary compression. A pressure mapping sensor within the fracture gap was used to record the resulting pressure distribution. Plate prebends of 0 mm, 1.5 mm, and 3 mm were tested. Three locations of the eccentric screw, four levels of screw torque, and two initial fracture gap conditions also were tested.

FINDINGS

With increasing plate prebend, fracture compression pressures shifted significantly toward the far cortex; however, compression force decreased (P < 0.05). The 1.5 mm prebend plate resulted in the greatest contact area. Increasing screw torque generally resulted in greater fracture compression force. The introduction of a 1 mm fracture gap at the far cortex prior to dynamic compression resulted in little or no fracture compression.

INTERPRETATION

The model showed that increasing plate prebend results in an increasing shift of fracture compression pressures toward the far cortex; however, this is accompanied by decreases in compressive force. Initial fracture gaps at the far cortex can result in little or no compression.

Adjustable bone plate: state of art

Background/aim

The success of treatment of bone fracture and defects are based on a proper contact and compression between the bone fracture fragments. Intraoperative manipulations such as bone compression or distractions are generally done in order to achieve this. However, none of the bone plates currently in routine use allow these manipulations after fixation to the bone, requiring refixation and repeated drilling, and screwing operations. Based on this shortcoming, we designed a novel adjustable bone plate (ABP) system which allows bone shortening and lengthening even after fixation to the bone surface. The aim of the paper is to clarify the unique properties of the novel bone plate.

Materials and methods

In this paper, the new generation adjustable bone plate applicability, design, indication, and new characteristics in addition to conventional bone plates with review of the literature were discussed and surgical technique was demonstrated in a saw bone model.

Results

This novel design allows for compression and distraction at the fracture ends post fixation as well as bone segment transfers.

Conclusions

The potential of the new generation ABP plate for use in bone compression, distraction, and the segmental bone transfer is a promising invention for clinical applications in the future.

Effect of the screw tightening sequence on the stress distribution of a dynamic compression plate: A pilot finite element study

OBJECTIVE

Although the optimal screw tightening sequence is a common question orthopaedists encounter during fractures fixation with a dynamic compression plate (DCP), the effect of the screw tightening sequence on the stability of the plate has never been explored. This study explores the effect of the screw tightening sequence on the stress distribution of a DCP using a finite element method.

METHODS

Idealized finite element analysis models of the femoral diaphysis with six-hole or eight-hole DCPs were constructed. The screw tightening preload was simulated using 'bolt load' in ABAQUS. Two screw tightening sequences were studied for the six-hole plate and six sequences were studied for the eight-hole plate. U magnitude and Von Mises stress were used to evaluate the deformation and stress distribution of the plate, respectively. Deformation and stress distribution plots from different sequences were compared.

RESULTS

The different screw tightening sequences showed different deformation processes, while all had the same final deformation after all the screws were tightened. Each screw tightening step of different tightening sequences showed different stress distributions in the plate, while all had the same stress distribution after all the screws were tightened.

CONCLUSION

Using different screw tightening sequences to fix the same DCP can produce the same stability, which means in terms of fixation stability, after the two screws nearest to the fracture line are tightened, surgeons do not need to hesitate about the order in which the rest screws should be inserted during the surgery.