Locking Screw Bone Fracture Simulations With Solidworks

Locking plates are a novel method of bone fracture fixation that relies on mechanical and biological concepts to promote bone healing. The use of locking screws in conjunction with plates can help press fractured bones together, reducing gaps and promoting quick healing. SOLIDWORKS is a brand within Dassault Systèmes that provides 2D and 3D product development solutions, including modelling and design software. By utilising SOLIDWORKS' tools, engineers and designers can collaborate to create innovative solutions for bone fracture fixation, such as locking screws. This integration of technology and medical expertise can lead to enhanced fracture treatment and improved patient outcomes.

Locking screw insertion methods

The insertion of locking screws for bone fracture treatment requires careful planning and execution to ensure optimal healing and avoid complications. Here are the key methods and considerations for locking screw insertion:

Preoperative Planning

Preoperative planning is crucial to the success of locking plate fixation. Surgeons must determine the appropriate fracture reduction strategy and select suitable implants, including the type of plate, screws, and their positioning.

Surgical Procedure

During the surgical procedure, the bone fragments are first repositioned (reduced) into their normal alignment. This process involves:

• Incision and Exposure: Creating an incision and exposing the fracture site to access the bone fragments.
• Reduction: Manipulating the bone fragments into their correct anatomical position to promote proper healing.
• Implant Placement: Fixing the locking plate to the bone using the appropriate number and configuration of locking screws.

Screw Insertion Techniques

The insertion of locking screws follows specific techniques to ensure optimal stability and avoid complications:

• Torque Control: Surgeons aim to achieve maximal screw tightening (stopping torque) while avoiding overtightening (stripping torque). This balance ensures a secure fixation without damaging the screw-bone interface.
• Screw Type and Size: Selecting the appropriate type and size of locking screws based on the fracture characteristics and bone anatomy is essential. Different screw designs and sizes are available to accommodate varying fracture patterns and bone dimensions.
• Sequence and Positioning: The sequence and positioning of screw insertion are critical. Inappropriate sequencing or incorrect screw placement can result in an overly rigid or flexible construct, compromising fracture healing.
• Bone Quality: The quality of the bone, such as osteoporotic or normal bone, influences the number and spacing of locking screws required for adequate fixation.

Postoperative Care

After the locking screws and plate are inserted, the incision is closed, and postoperative care begins:

• Weight Bearing: The return to weight-bearing activities must be carefully managed based on the type of fracture and the stability of the construct.
• Implant Removal: In some cases, the locking screws and plate may be removed once the fracture has healed, while in other cases, they may be left in place permanently.

In summary, the insertion of locking screws for bone fracture treatment requires a meticulous approach, from preoperative planning to surgical execution and postoperative care. By following established techniques and guidelines, surgeons can achieve successful fracture fixation, promoting proper healing and reducing the risk of complications.

Advantages of locking plates

Locking plates are an effective treatment option for patients with severe osteoporotic fractures. They are metal plates that are inserted into the bone to hold the fracture in place, providing stability and reducing the risk of further injury.

• Locking plates are particularly beneficial for patients with osteoporosis and fractures with multiple segments. They help decrease the gap between the bones at the fracture site and provide rigid fixation.
• Locking plates are designed with screws that thread into the plate, creating a fixed-angle anchorage. This results in greater stability and higher loads to failure compared to traditional plates.
• The screws in locking plates act in concert, gaining purchase in multiple regions of bone rather than individual sites as with traditional screws. This makes locking plates less susceptible to hardware failure.
• Locking plates behave more like external fixators, achieving stability without direct contact with the periosteal surface. This preserves the blood supply to the bone, which is essential for healing.
• Locking plates are less invasive than traditional plates, making them a suitable option for older patients who may be at higher risk for complications from more extensive surgeries.
• Locking plates can be easier to remove than traditional plates if revision surgery is necessary.
• Locking plates allow for more anatomical reduction of the fracture, which can improve patient outcomes.
• Locking plates do not require precise contact with the underlying bone, unlike non-locking systems. This means that tightening the screws will not pull the bone segments towards the plate, reducing the risk of loss of reduction.

Locking plate placement principles

Planning and Preoperative Considerations:

• Preoperative planning is essential to determine the appropriate fracture reduction strategy and select the suitable implants, including the type of plate and screws.
• The placement of locking plates should be guided by the principles of biological fracture repair, prioritizing soft tissue handling and preservation of blood supply to the fracture site.
• Respect for soft tissues and minimally invasive techniques are recommended for greater success.
• The type and position of screws play a significant role in the mechanical properties of the construct and the overall success of the procedure.

Screw Placement and Selection:

• The number, location, and sequence of screw implantation are critical. Inadequate screw placement or selection can lead to an overly rigid or flexible construct, compromising healing and potentially leading to implant failure.
• For epiphyseal fractures, there are risks of screw cut-out and impaction in cancellous bone, which should be carefully considered during screw selection and placement.
• Biomechanical choices during fixation are vital to avoid delayed fractures at the end of the plates.
• In some cases, such as osteoporotic bone, locking plates provide better bone purchase, but "en bloc" pulling out of the implant is still possible.

Plate Selection and Placement:

• The length of the plate is crucial and should be adequately chosen to allow for modulation of fixation stiffness and the interfragmentary movement that enhances fracture healing.
• The working length of the locking plate construct, influenced by both plate length and locking screw placement, is a significant factor in controlling the interfragmentary movement at the fracture gap.
• In distal femur fractures, the use of longer plates with at least 8 holes proximal to the fracture is recommended to improve outcomes and reduce the risk of failure.
• The stability of conventional screw-plate systems depends on bone quality, while locking plates provide multiple points of fixation even in low bone quality.
• The use of locking plates can cause less disruption to soft tissues, osseous blood supply, and periosteum, making them a good option for osteoporotic bone.

Postoperative Care:

• The return to weight-bearing activities after fracture fixation must be carefully managed and adapted to the type of fracture and construct used.
• Regular follow-up and X-ray evaluations are essential to monitor for any healing issues or complications, such as nonunion or hardware failure.

Locking plates for periprosthetic fractures

Locking plates are the most common treatment for periprosthetic fractures. However, the use of cerclage wires with locking plate fixation has been a topic of controversy.

The Problem of Periprosthetic Fractures

Periprosthetic fractures are a serious complication of hip and knee arthroplasty, affecting between 0.1% and 6% of patients. The incidence of these fractures is rising as the number of patients requiring arthroplasty increases. Periprosthetic fractures are the third most common reason for revision surgery, after aseptic loosening and infection.

Locking plates are commonly used to treat fractures around a well-fixed femoral component. Locked plating is considered to provide a more biologic fixation than standard plating techniques. Locking plates have been used with success in clinical studies for type B1 fractures, which account for approximately 29% of periprosthetic femoral fractures.

Locking Plates vs. Locking Plates with Cerclage Wires

A retrospective study of 47 patients with periprosthetic femur fractures found that cerclage wires used with locking plate fixation successfully treated periprosthetic fractures of the femur with faster time to union, fewer complications, and fewer revisions. The time to union in the cerclage wire group was 3.6 ± 1.0 months, significantly less than the plate group (4.8 ± 2.6 months). The group with the cerclage wires had a significantly lower revision rate of 0% compared to 20.8% in the group not receiving cerclage wires.

Optimising Locking Plate Fixation

To optimise locking plate fixation for periprosthetic fractures, it is important to consider plate length, working length, and bone mineral density.

• Plate length: Longer plates are thought to reduce plate loading, thereby avoiding fatigue failure due to cyclic loading. However, a biomechanical study found no advantage of longer plates over shorter plates in terms of fixation survival. Longer plates may also cause hardware prominence or affect the vastus muscles insertion.
• Working length: A longer working length may reduce strain at the level of the fracture site. However, another biomechanical study found no significant association between a longer working length and increased survival.
• Bone mineral density: Lower bone mineral density was found to be a significant predictor of construct failure. Treatment of periprosthetic femur fracture should include optimisation of patient bone quality.

Problems with locking plates

Locking plates are a novel mechanical and biological concept in fracture fixation. They are particularly useful in cases of highly comminuted fractures, unstable metaphyseal segments, and osteoporotic fractures. However, there are several problems associated with their use:

• Inadequate planning: Failure of locking plate fixation often occurs due to incorrect planning, which is exacerbated when minimally invasive surgery is performed. This can lead to an overly rigid or flexible construct, compromising healing.
• Incorrect fracture reduction: If the fracture is not reduced correctly, it can lead to malunion, affecting the healing process.
• Implant length issues: Using an implant of incorrect length can affect the stability of the construct and the healing process.
• Screw-related issues: The type, number, location, and implantation sequence of screws must be appropriate. Incorrect choices can lead to poor healing and implant failure.
• "En bloc" pulling out: While locking plates provide better bone purchase, there is a risk of the implant being pulled out "en bloc".
• Delayed fractures: Fractures at the end of the plates can occur if incorrect biomechanical choices are made during fixation.
• Cut-out and impaction: In epiphyseal fractures, there is a risk of cut-out and impaction of locking screws in cancellous bone due to the fracture pathology.
• Removal difficulties: Locking plates can be challenging to remove, requiring specialized instrumentation.
• Biomechanical differences: Locking plates function as "internal fixators" with multiple anchor points, while conventional plates provide "absolute rigidity". This difference can affect bone healing, especially in highly comminuted or osteoporotic bone.
• Soft-tissue stripping: In conventional plates, soft-tissue stripping can add biological insult to poor bone quality, leading to adverse outcomes.

Frequently asked questions