The Ultimate Hardware Screw Lock Compression Guide

Locking plates and screws are an important aspect of fracture fixation, offering improved stability and mechanical performance over non-locking constructs. The locking mechanism provides increased resistance to disassembly, with the screws being locked into the plate through a threaded chamber or an adapted ring. This technology has found particular success in osteoporotic bone and severely comminuted fractures, where it can enhance fracture healing and provide superior bridging. However, the removal of locking screws and plates can present technical challenges, requiring careful techniques and, occasionally, specialised tools.

Locking plates vs non-locking plates

Locking plates and non-locking plates are both used in fracture fixation. While non-locking plates rely on friction between the plate and bone to stabilise the fracture, locking plates use screws that lock into the plate, forming a fixed-angle construct. This means that, unlike non-locking plates, locking plates do not require an exact fit to the bone to be effective.

Advantages of Locking Plates

Locking plates have several advantages over non-locking plates:

• They do not require an exact fit to the bone, making them particularly useful for minimally invasive plating techniques.
• They do not disrupt the underlying cortical bone perfusion as much as non-locking plates, which compress the undersurface of the plate to the cortical bone.
• The screws are unlikely to loosen, even if they are inserted into a fracture gap, which may reduce the incidence of inflammatory complications.
• They provide more stable fixation than non-locking plates.

Disadvantages of Locking Plates

Despite these advantages, locking plates also have some disadvantages:

• They are more expensive than non-locking plates.
• They are thinner than non-locking plates, which may cause discomfort and increase the risk of infection.

Use Cases

Locking plates are particularly useful for:

• Osteoporotic bone, where they can provide improved fixation.
• Highly comminuted fractures.
• Metaphyseal and intra-articular fractures.

Screw stripping

Use a Different Driver

Try using a manual flathead screwdriver to remove a stripped Phillips head screw. Angle the blade into the screw head and force it down hard. Once you've exposed about 1/4-inch of the screw, clamp locking pliers to the sides of the screw head and turn it out the rest of the way. You can also bypass the stripped screw head and grip the screw directly with locking pliers, turning the adjustment screw on the pliers and clamping down from the top or sides.

Use a Manual Screwdriver

Manual screwdrivers offer more torque and control than electric drills, making it easier to apply pressure without risking further stripping. Tap the screwdriver into the screw head with a hammer to seat the tip deeper for a better grip. Turn the screw counter-clockwise to remove it.

Use Common Materials

Common materials like rubber bands, steel wool, or abrasive powder can help you remove a stripped screw. Place a rubber band between the screwdriver tip and the screw head to increase grip and fill in gaps. For screws flush or embedded in wood, groove a couple of shallow indentations next to the screw head for better grip. Steel wool can also be used to improve friction—place a coin-sized piece on top of the screw head, insert the screwdriver tip through it, and press down while turning counter-clockwise.

Use a Screw Extractor

If other methods aren't working, a screw extractor kit is the best option. These kits come with two special drill bits: one with forward threads and another with reverse threads. Use the first drill bit to drill a hole in the screw, then switch to the reverse drill bit to remove it. For stubborn or rusted screws, apply penetrating oil and let it sit for about 30 minutes before removal.

Prevent Screw Stripping

To avoid dealing with stripped screws in the first place, always use the correct screwdriver or bit that is the right size for the screw. Avoid using a screwdriver with a rounded tip and do not bear down too hard when driving the screw. Hold the driver inline (perpendicular) to the screw, and consider using a manual screwdriver for better torque control.

Screw insertion

Understanding Screws

Before delving into the insertion process, let's understand the basic anatomy of a screw. A screw consists of a head, a shaft, threads surrounding the shaft, and a tip. The head of the screw is essential for advancing it into the bone using a screwdriver, while also preventing it from sinking completely. The shaft can be measured by its core diameter or thread diameter, with the latter offering more contact with the bone and better resistance to dislodging. The tip can vary, with some screws being self-tapping or self-drilling, eliminating the need for pre-drilling.

Insertion Process

Now, let's break down the steps of screw insertion:

• Drill Hole: Unless you're using a self-drilling screw, the first step is to create a drill hole in the bone. The diameter of the drill hole depends on whether you're using the screw as a lag screw or not.
• Create Threads: If you're using a non-self-tapping screw, you'll need to create channels for the threads using a device called a tap.
• Insert Screw: With the hole and threads prepared, you can now insert the screw. For self-tapping screws, this step involves cutting the thread channels as the screw advances. Use a screwdriver to advance the screw, ensuring it's secure.
• Achieve Compression: Screws can be used to compress two fragments of bone together, known as the lag screw technique. This can be achieved by having different thread engagements on each side of the fracture, pulling the fragments closer together as the screw is driven in.
• Check Stability: Once the screw is in place, ensure that it provides the required stability. The "pullout strength" of the screw depends on the thread diameter and its contact with the bone.
• Adjust as Needed: If necessary, make adjustments to the screw insertion. This may involve tightening or loosening the screw to achieve the desired compression and stability.

Types of Screws

There are different types of screws used in orthopedic surgery, each with unique characteristics:

• Cortical Screws: These screws are fully threaded with a smaller pitch and smaller threads, making them ideal for anchoring in dense cortical bone.
• Cancellous Screws: Cancellous screws have a larger thread-to-core diameter ratio, allowing them to anchor in soft cancellous bone. They are often partially threaded and self-tapping.
• Cannulated Screws: These screws are hollow, allowing them to be inserted over a K-wire for precise placement. However, this precision comes at the cost of slightly reduced pullout strength.

In conclusion, screw insertion in hardware screw lock compression is a precise and critical process that requires a good understanding of screw types and their applications. By following the steps outlined above and selecting the appropriate screw type, surgeons can effectively fix fractures and promote bone healing.

Screw extraction

Gather the Right Tools:

• Screw extractor: Look for a set with double-ended boring/screw extracting bits, as they are easier to use. Choose a screw extractor with hardened steel bits, as they need to be strong enough to handle the job.
• Drill: It is recommended to use a drill with variable speed settings and the ability to operate in reverse. Avoid using an impact driver, as it may have too much torque and speed for this delicate task.
• Drill bits: If your screw extractor does not have a boring end, you will need separate drill bits. Choose a drill bit with a smaller diameter than the screw you need to remove.
• Safety gear: Always wear safety glasses to protect your eyes from metal shards that may fly during the extraction process. You may also want to wear gloves to protect your hands from metal shavings.
• Thread cutting oil: This will help with the drilling process and make it easier to remove the screw.
• Penetrating oil: If the stripped screw is rusted or affixed to metal, penetrating oil can help loosen its grip.

Prepare the Screw for Extraction:

• Punch it out: Use a centre punch to create a small indentation in the centre of the screw head. This will help guide your drill bit and ensure it stays straight.
• Drill a guide hole: Secure the drill bit to your power drill and apply a small amount of thread cutting oil to the head of the broken screw. Slowly and carefully drill into the screw head, maintaining a straight alignment. Drill to a depth of about 1/8" to 1/4", or as needed to accommodate your screw extractor size.

Perform the Extraction:

• Insert the screw extractor: Place the tip of the screw extractor into the bored hole. Depending on the model, you may need to use a wrench or the drill (in reverse) to turn the extractor counterclockwise.
• Bite and twist: As you turn the screw extractor, its reverse threads will draw it down into the hole until it bites into the screw. Once it has a good grip, continue turning counterclockwise and apply gentle pressure to pull the stripped or broken screw out.
• Troubleshoot: If the screw extractor doesn't bite properly, try drilling a little deeper into the screw head or using the next size up extractor. If the screw is particularly stubborn, consider manually turning the extractor by hand, as using the drill at high speed can break the bit.

By following these steps, you can effectively extract damaged or broken screws and get your project back on track!

Plate extraction

Identifying the Problem:

Before initiating plate extraction, it is crucial to identify the specific issues causing difficulties in removing the locking compression plate. Common problems include screws jamming on the plate, destruction of the recess of the screw head, or cold welding of the screws to the plate. These issues can arise from poor screwing technique, excessive force during screw insertion, or improper use of tools like the torque-controlling screwdriver.

Techniques for Removing Locked Screws:

Technique 1: Drilling and Extraction:

If the screws are jammed or the screw heads are damaged, one technique involves using tungsten drills to destroy the screw heads. Afterward, the screw bodies can be extracted using a trephine drill. This method is invasive and may result in metallic shavings and lengthened operative time.

Technique 2: Conical Left-Turn Screwdriver:

In cases where the screw/plate thread remains intact, a conical left-turn screwdriver can be used to remove the screws, even if the recess of the screw head is destroyed. This approach is less destructive but may not work in all scenarios.

Technique 3: Cutting the Plate:

When multiple screws are stuck and cannot be removed, one option is to cut the plate between the screws using a large bolt cutter. This technique is useful when dealing with low-profile plates or plates with a small gap between the screws. By cutting the plate, each screw and its attached portion of the plate can be unscrewed and removed separately.

Technique 4: Levering the Plate:

In cases where the bone is osteoporotic, and only one or two screws are stuck, the plate can be levered off the bone. However, this method carries a risk of iatrogenic fracture and is not suitable when multiple screws are involved.

Technique 5: Drilling Out the Screw Head:

Another approach involves drilling out the screw head using carbide drill bits or a diamond-tipped burr. Afterward, the remaining screw shanks must be removed with a hollow mill. This technique can generate heat and metallic debris, and it may not be feasible if there is insufficient space between the plate and the bone.

Preventative Measures:

To avoid the challenges associated with plate extraction, it is essential to adhere to rigorous techniques during the initial placement of the plate and screws. This includes the proper use of targeting devices, drilling, and inserting screws, as well as the systematic use of torque-controlling screwdrivers. Additionally, verifying the proper screw position can help prevent issues that may require subsequent plate extraction.

Frequently asked questions