Proper Use Of The Locking Plate!

A locking plate is a fracture fixation device with a threaded hole. When a screw with a threaded head is screwed into the hole, the plate becomes a (screw) angle fixation device. A locking (angle stable) plate can have both locking and non-locking screw holes for different screws to be screwed into (also called a combined plate). Since the concept of locking plates was proposed and applied to fracture treatment, it has been widely used in the fixation of periarticular fractures, comminuted and osteoporotic fractures due to its advantages of providing stable support and fixation of fractures, a higher fracture healing rate, less soft tissue damage and blood supply disruption. Today's morning reading will give you a detailed introduction to locking plates, which is worth learning from!

(A)Basic Overview

1.What is a locking plate?

Any steel plate that can be screwed into angle fixing/angle stabilizing screws or pins is essentially a locking plate.

2. Advantages and disadvantages of locking plates

Advantages

■ Angular stability, resistance to bending and torsion

■Conical shape of screw head improves mechanical distribution

■Provide radial preload, prevent bone resorption and screw loosening

■Anatomically shaped to accommodate localized anatomical patterns

■Matching templates to allow percutaneous fixation in the diaphysis (single cortical, self-drilling, self-tapping locking screws)

■Locking screws provide excellent anchorage for both flexible bridging and absolute stabilization fixation

■No need for close contact with the bone surface, preserving blood supply

■Controlled micromotion, favoring fracture healing

■Generally no bone grafting is required

It is especially effective for osteoporotic fractures or any highly unstable fractures.

Disadvantages

■Locking screws do not have a reduction and compression effect, especially in intra-articular fractures or simple oblique fractures

■The plate cannot be used as a reduction tool to assist in reduction.

■The screws do not feel as good as conventional screws when inserted.

■The direction of screws cannot be adjusted (except for multiaxial locking screws).

■The screws are placed too tightly, which can lead to “cold welding”.

■Angle deviation >5°, strength loss; >10°, locking effect is ineffective

■Possible subcutaneous protrusion if the plate is not contoured

Stiffness issues

Without good cortical contact or compression of the fracture ends, the use of locking splints, especially stainless steel splints, will prevent phase II healing of the fracture due to excessive stiffness and elimination of favorable micromotion at the fracture site;

If intraoperative traction is applied and then locking splint fixation is applied, the fracture break gap will be preserved, resulting in delayed or no fracture healing;

If a simple fracture is not reset and pressurized, the load is transmitted through the plate, resulting in a stress concentration that can easily lead to plate breakage.

3. Major biomechanical differences between locking plates and conventional plates

Conventional plates rely on friction at the bone-plate interface to accomplish plate compression of the bone.

4. Comparative advantages of locking plate and ordinary steel plate

1.The pull-out resistance of locking screws is much higher than that of ordinary screws.

2. The epiphyseal locking screws are angled to each other, which greatly increases the screw's resistance to pullout compared to parallel screws.

(B) Application principles

1. Principles of immobilization:

●Pressurization principle: osteoporotic diaphysis fracture

●Neutralization principle: osteoporotic diaphysis fracture

●Bridging principle: comminuted diaphysis or extra-articular metaphyseal fracture

Principle of union: comminuted intra-articular metaphyseal fracture

2. Bridging principle:

●Typical approach: percutaneous minimally invasive plate fixation (MIPO or MIPPO technique)

●Indirect reduction technique

●For adequate bridging plate fixation, 3-4 screw holes should be left open near the fracture end.

3.Principles of union:

● Combined use of the two biomechanical principles of compression and bridging in a single plate - locking compression plate (LCP)

● Simple fractures in one segment of the fracture and comminuted fractures in the other (e.g., comminuted fractures of the metaphysis, diaphysis)

●The principle of union should only be applied to plates that allow for the placement of both locking head screws as well as common screws.

Locking plates do not rely on friction between the bone-plate interface and rely primarily on the interface between the screw and plate with angular stability to maintain stability.

Because of their stable unity, the extraction force of screws with locking heads is much higher than that of common screws, unless all surrounding screws are extracted or fractured. Typically, it is difficult for a single screw to be extracted or fractured on its own. Locking head screws do not provide inter-fold pressurization. Pressurization can be obtained by using a pressurizing device or by driving regular screws into “mixing holes” (tension screws first, then locking nails).

1.If standard screws have been used to secure the splint (e.g. 1), screwing in the locking screws will be very easy (e.g. 2).

2.If locking screws have been used to secure the splint and bone block (e.g., 1), it is not recommended that standard screws be screwed into the same bone block (e.g., 2) unless the locking screws are loosened and retightened (LHS).

3.Once the metaphyseal fracture block has been secured with a screw with a locking head (LHS), compression fixation between the fracture blocks is achieved by screwing a standard screw into the power compression hole of the Locking Compression Plate LCP combination.

(C) Indications and contraindications

1. Indications

Most surgically treated fractures do not require locking plate fixation. As long as the principles of orthopedic surgery are followed, most fractures can be healed by means of conventional plates or intramedullary nailing.

However, there are specific types of fractures that are susceptible to loss of reduction, plate or screw breakage, and subsequent nonunion, often referred to as “unresolved” or “problematic” fractures, including intra-articular comminuted fractures, periarticular fractures with small bone fragments, and osteoporotic fractures. These types of fractures are often referred to as “unresolved” or “problem” fractures and include intra-articular comminuted fractures, periarticular short tuberosity fractures and osteoporotic fractures. These fractures are all indications for locking plates.

The classic and ideal indications for locking plate fixation of fractures are the bridging principle and the union principle for more comminuted fractures - high-energy fractures in younger patients or osteoporotic fractures in older patients.

2. Contraindications

Although locking plates have been widely used and their indications are broader, we must recognize and avoid several contraindications to locking plates. If locking plates are used indiscriminately, failure of fixation and nonunion of the fracture may occur.

Simple fractures that require interbody compression, such as simple forearm stem fractures treated with locking internal fixation, are prone to non-union.

Similarly, percutaneous placement of locking plates for simple fractures using minimally invasive techniques is also a contraindication.

Indirect reduction and locking plate fixation are also not suitable for displaced intra-articular fractures, which require open anatomical reduction and compression between the fracture fragments and firm fixation.

A relative contraindication to locking plates, due to their high cost, is fractures that can be satisfactorily fixed with conventional plates. For example, fractures of the forearm symphysis have a healing rate of more than 90% when treated with conventional plates.

(D) Installation of locking plate

1. Screw the drill bit into the screw holes of the plate. Deviations of >5° between the screw and the screw hole can lead to failure of screw locking, and it is recommended to use the drill bit to drill the holes preferably.

2. Place the steel plate on the surface of the bone and drill the holes through the drill sleeve.

3. Measure the depth with a depth sounder, taking care that the head of the sounder is inserted into the screw hole.

4. Select the appropriate length of the locking screw.

5. Installation of the pressurized screws is the same as for ordinary steel plates.

6. Finally tighten the locking screws with a torque wrench, when tightened, there will be obvious sliding feeling and snapping sound, to avoid screwing in too tight, resulting in removal difficulties.

(E) Locking plate removal

Clinical locking plate screws are widely used, but easily encountered removal difficulties, mainly manifested in the screw slipping wire and nail cap and plate nail hole threads between the wrong buckle.

1. Screw cap groove damage

Under normal circumstances, the complete screw cap groove and the corresponding screwdriver is compatible. The screwdriver should be aligned with the screw cap groove before screw insertion or removal, otherwise the screw cap groove is likely to be deformed during screwing in or screwing out, resulting in slippage.

In addition, after fracture healing, the screw cap notch is usually wrapped with bone crust or fibrous tissue, which should be cleaned up before removing the screw, but if no attention is paid, the screw cap notch and angular structure may be artificially damaged.

Because the rotation axis of the operator's forearm is not consistent with the screwdriver's long axis, there is often a certain angle, when the operator forcefully screwed out the screw, it is inevitable that the screwdriver wobbles, resulting in damage to the cap groove of the screw due to the uneven force. Therefore, the damage to the screw groove can easily lead to screw slippage.

2. Nail cap or nail hole deformation

In the process of intraoperative application of anatomical locking steel plate, occasionally according to the need for appropriate bending or shaping of the steel plate, Raja et al. believe that if the bending part happens to occur in the locking screw holes, when screwing in the locking screws will be screw cap and nail hole mismatch, which is very likely to occur between the nail cap and the steel plate nail holes threads wrong buckle, or screwed close to the steel plate when the tail of the nail deformation caused by the strong screwing, etc., which may lead to the later removal of the Difficulty.

3. Application of self-tapping cortical locking nails

Because the cortical bone grows inward along the nail hole and thus will hold the screw, leading to difficulties in screw removal, especially the application of self-tapping double cortical bone screws, Suzuki et al. do not recommend the use of self-tapping screws for double cortical fixation. Hou Yunfei et al. suggested that unnecessary bicortical fixation with screws should be avoided for upper extremity fractures, and Maehara et al. also suggested that frequent use of locking screws should be avoided when using locking plates, and that there is a need to establish a universal standard for the selection and application of locking screws.

4. Structure and location of screws

The size, orientation, and location of the locking screw can affect the removal of the screw. Some scholars have found that if the screw is not located in the center of the locking hole, once the nail hole eccentricity of more than 5 ° there may be a loose screw fixation, threads wrong buckle or nail tail deformation stuck and lead to failure of fixation or the second phase of the removal of difficulties.

5.Cold welding

Normal titanium internal fixation surface has a layer of passivated protective layer, in the process of surgical placement of internal fixation, due to the tools of grasping and shaping, or the head of the screw and the friction between the steel plate, etc., may lead to passivated protective layer wear area. 2 metal contact surface between the substantive contact point will be adhered to, that is, the formation of cold welding.

In addition, galvanic coupling between metal ions, inflammatory reactions, etc. can also promote the formation of cold welds. Most manufacturers of internal fixation devices are also aware of this problem, and therefore unused locking steel plates are covered with oxide film technology between the nail holes and screw contact surfaces, which also aims to inhibit ionization and adsorption of proteins in the body and reduce the occurrence of cold welds.

(F) Removal techniques

Removal techniques reported in the national and international literature can be divided into 2 categories, namely, simple and practical and complex, the former characterized by simple accessibility, practicality, low soft tissue damage, low skill and no need for special instruments, and the latter requiring special specialized instrumentation and equipment.

Maehara et al. suggest using torque-limiting screwdrivers with large shanks whenever possible. When confronted with slipped screws, Pattison et al. reported a simple method of removing slipped screws by wrapping the head of the screwdriver with platinum metal and inserting it into the groove of the screw cap. This method is clever to fill the screw cap groove with metal foil and increase the contact area and friction between the screwdriver and the groove, which facilitates the removal of screws with slipped threads. In this method is still difficult to remove the case, if the screw cap and steel plate nail hole threads are still intact, you can try to use the conical reverse tapping screw remover, that is, from the screw cap groove inserted into the reverse tapping and fill the groove, in the process of rotating and pressurizing the screw out.

On the downside, some locking screws are still difficult to be effective using a conical reverse tapping screw extractor, such as Ehlinger et al. and Bae et al. who found that this method was often effective for 3.5 mm screw slippage, but often ineffective for 4.5 mm screw slippage. In this case, not every tier of hospital orthopedics is equipped with specialized metal grinding equipment such as carbide drills, diamond drills, or high-speed grinding wheels.

Gopinathan et al. introduce a method that does not require these specialized equipment by reporting a case of difficult screw removal from a clavicular reconstruction plate, i.e., using a low cutout of the reconstruction plate, a large wire cutter is used to shear the narrower portion of the plate between the plate nail holes, so that the screws and the nail hole portion of the plate form a small unit, and the screws can be easily removed. This technique is only applicable to titanium reconstruction locking plates, forearm locking plates with narrower low notches, and 1/3 tube-type plates, and cannot be used for wider or thicker plates in the lower extremity.

A simple method has also been described in which a slightly larger drill bit is used to drill a hole in the common hole next to the slipped locking screw, and then the plate and screw are tapped in the direction of the newly drilled common hole, and then the plate and screw are removed by using a bone cutter placed underneath the plate and prying it out with the principle of leverage when it is loosened.

Of course, there is potential for bone damage with this method, so postoperative weight-bearing protection is recommended. In addition, it is also necessary to prepare some commonly used professional tools before the internal fixation removal surgery, such as bolt extractor, hole reamer, screw extraction pliers, T-type pressurized socket and so on.

In the face of locking screw slippery wire removal difficulties, some domestic scholars proposed to change the groove method, that is, the use of dental micro-grinding machine steel sand piece to change the screw cap groove hexagonal or quadrangular groove for the “one” or “ten” groove, or deepen the original groove.

Ehlinger et al. reported that in cases where the conical reverse tapping screw extractor still had difficulty in removing the screw, it was suggested that the steel plate could be removed by destroying the head of the screw by tungsten drill grinding and enlarging the nail holes in the steel plate, and then the body of the screw could be removed by using a ring saw.

Georgiadis et al. and Raia et al. proposed in the screw and steel plate combination is too tight and difficult to remove, special equipment (such as pneumatic high-speed cutting drills, carbide drills, diamond wheels, etc.) on the nail hole around the steel plate cutting method, in the steel plate is cut to loosen the screw, the screw is also naturally easy to remove.

Kumar and Dunlopl reported in the distal femur locking steel plate screw system internal fixation removal process, in the use of standard self-limiting torque screwdriver, conical screw extractor are failed, but also introduced a new method, that is, the use of high-speed thin-flake abrasive wheels along the edge of the steel plate to the edge of the screw hole radial incision, and then wedge the bone knife inserted into the incision, don't open the steel plate nail hole in order to relax the cap, so that the effective removal of the Locking screws.

It is important to note that the above methods should be advanced as slowly as possible during the cutting or grinding of the plate using a high-speed cutting disk to avoid cutting into the head of the screw and damaging the bone and soft tissues. In addition, these techniques may generate high temperatures and metal debris, which can result in an increased risk of medically induced re-fracture, tissue thermal necrosis, and infection.

(G) Summary

■ Allow incomplete plate contact with the periosteum

■The plate must be repositioned prior to locking, as the fracture cannot be repositioned after locking.

■Locking plate can not be pressurized, need to use a pressurizer or centrifugal screwing in the union hole into the ordinary screw, first pressurized, then locking

■ Fracture site 3~4 screw holes without screws to spread the stress; ■ Fracture site 3~4 screw holes without screws to spread the stress; and

■ monocortical fixation of the diaphysis or thick bone cortex, and where the quality of the bone is good; and

■Once locked, it cannot be backed out, while ordinary screws can be backed out

■Strong fixation and too many screws can lead to nonunion; the principle is that plates should be long and fewer screws should be used; in the treatment of periarticular fractures, fewer screws should be applied to the stem and more screws should be used for fixation against the articular surface

■ the length of the bridging plate should be twice the length of the fracture area, the screws should be evenly distributed, and the ideal fixation should be through-the-aperture fixation

■ Force is evenly distributed over a long plate, and fixation with fewer screws can stimulate scab formation and promote bone healing.