Malleolar Screw Size: A Vital Consideration In Surgery

Malleolar screws are used to treat medial malleolar fractures, which are among the most common injuries treated by orthopedic surgeons. The size of a malleolar screw is determined by its outer diameter, with options ranging from 3.5mm to 4.5mm. The screw length varies from 25mm to 100mm, with the ideal length depending on the patient's anatomy and the specific fracture being treated. The choice of screw length is crucial for effective fracture compression and to prevent injury to surrounding tissues.

Characteristics and Values of Malleolar Screws

Safe zone for medial malleolar screw placement

The placement of medial malleolar screws requires careful consideration of the safe zone to avoid injury or abutment to soft-tissue structures, particularly the posterior tibial tendon. Here is a detailed overview of the safe zone for medial malleolar screw placement:

Understanding the Safe Zone

The medial malleolus is divided into three zones based on anatomical landmarks: Zone 1, Zone 2, and Zone 3. Zone 1 is the anterior colliculus, Zone 2 is the intercollicular groove, and Zone 3 is the posterior colliculus. The safe zone for screw placement is primarily Zone 1 and, to some extent, Zone 2.

Studies on Safe Zone Placement

A study by Femino et al. used ten unmatched cadaveric limbs and placed three Kirschner wires through the tip of the medial malleolus, with the first wire in the center of the anterior colliculus (Zone 1) and the other two wires posterior to it at 5-mm intervals. They then inserted 4.0-mm screws and found that screws placed in Zone 1 did not contact the posterior tibial tendon in any specimens. Screws in Zone 2 were, on average, 2 mm from the tendon, while screws in Zone 3 resulted in tendon abutment and injury in multiple specimens.

Another study by Belangero et al. also investigated the safe zone for medial malleolar screw placement. They performed a computed tomography analysis of the ankle in 215 patients and measured various parameters related to the medial malleolus. Their findings suggested that there is adequate space for two 4.0-mm screws in some larger cases, but in smaller cases, the second screw may be close to the posterior tibial tendon.

Recommendations for Screw Placement

Based on the studies and anatomical considerations, it is recommended to place medial malleolar screws in Zone 1 or the anterior colliculus to avoid injury or irritation to the posterior tibial tendon. Zone 2 or the intercollicular groove can be used cautiously, as screws placed here may come close to the tendon. Zone 3 or the posterior colliculus should be avoided as screw placement in this area has been associated with a high risk of tendon abutment and injury.

Screw fixation of medial malleolar fractures

Medial malleolar fractures are a common injury treated by orthopedic surgeons. The standard treatment method for medial malleolar fractures is lag screw fixation using partially threaded screws. However, there is a lack of consensus on the ideal screw length, with the choice often being left to the surgeon's discretion. This article will provide an overview of screw fixation techniques for medial malleolar fractures, including the selection of screw length and the benefits of different screw types.

Screw Fixation Techniques

When fixing a medial malleolar fracture with screws, it is essential to use the correct technique to ensure optimal outcomes. One technique is to use two parallel interfragmentary screws, which are most effective when perpendicular to the fracture surface. This technique can be challenging, but it ensures the stable fixation of the fracture fragments. Another technique is to use a single screw fixation, although this is less common as it may not provide sufficient stability.

Screw Length

The ideal screw length for medial malleolar fracture fixation has been the subject of several studies. One study by Labronici et al. (2016) found that the average distance between the medial malleolus tip and the start of the medullary canal was 55 mm, with a standard deviation of 10 mm. Based on this finding, the authors recommended a screw length of no more than 45 mm to optimize screw thread placement in the cancellous bone and achieve effective fracture compression.

Screw Type

The type of screw used for medial malleolar fracture fixation is also important. Partially threaded screws are the most common type used, but fully threaded screws have been proposed as an alternative to achieve better compression. A study by Parker et al. (2013) compared the compression achieved by 30 mm partially threaded screws, 45 mm partially threaded screws, and 45 mm fully threaded screws. The results showed that the median compression at the fracture site was significantly higher for the 30 mm partially threaded screws and 45 mm fully threaded screws compared to the longer partially threaded screws. Therefore, the authors recommended the use of 30 mm partially threaded or 45 mm fully threaded screws for medial malleolar fracture fixation.

Screw length for optimal cancellous bone compression

The ideal screw length for medial malleolar fracture fixation is 45mm. This is based on an anatomic study of the distal tibia metaphyseal bone. The study found that the average distance between the medial malleolus tip and the start of the medullary canal was 55mm, with a standard deviation of 10mm. This means that a screw longer than 55mm will likely bypass the metaphyseal area, resulting in poor fracture compression.

The use of a partially threaded screw of roughly 16mm in thread length is recommended. This is because the threads of a fully threaded screw may not completely bypass the fracture site, leading to inefficient compression.

The cancellous bone screw is designed for fracture fixation of small fragments. It has a smooth shaft and is partially threaded. The cancellous bone screw typically has a diameter of 4.5mm and lengths ranging from 25mm to 100mm. The screw threads should be placed in the optimal cancellous bone to generate effective fracture site compression.

Contraindications and adverse effects

The 4.5mm malleolar screw is contraindicated for patients:

• With any active or suspected infection or local inflammation in the affected area.
• With compromised vascularity that would inhibit an adequate blood supply to the fracture or the operative site.
• With bone stock compromised by disease, infection, or prior implantation that cannot provide adequate support and/or fixation of the devices.
• With a documented or suspected material sensitivity.
• Who are overweight or obese, as this can lead to failure of the fixation of the device.
• With inadequate tissue coverage over the operative site.
• For whom implant utilisation would interfere with anatomical structures or physiological performance.
• With any mental or neuromuscular disorder which would create an unacceptable risk of fixation failure or complications in postoperative care.
• With other medical or surgical conditions which would preclude the potential benefit of surgery.

Possible adverse effects resulting from the implantation of a 4.5mm malleolar screw include:

• Loosening of the screw due to cyclic loading of the fixation site and/or tissue reaction of the implant.
• Early and late infection.
• Further bone fracture resulting from unusual stress or weakened bone substance.
• Temporary or chronic neural damage resulting from pressure or hematomas.
• Wound hematomas and delayed wound healing.
• Vascular disease including venal thrombosis, pulmonary embolism and cardiac arrest.
• Heterotopic ossification.
• Pain and discomfort due to the presence of the 4.5mm malleolar screw.
• Mechanical failure of the implant, including bending, loosening or breakage.
• Migration of the implant resulting in injury.

Additionally, when using an anterior-posterior (AP) screw for posterior malleolar fracture fixation, there is a risk of damaging nearby anatomic structures.

Preoperative planning

Additionally, advanced imaging techniques, such as X-rays and CT scans, play a vital role in preoperative planning. These imaging studies provide valuable information about the patient's bony anatomy, including the location of the epiphyseal scar and the distal-most portion of the tibia, which is crucial for determining the optimal screw length and placement.

In the case of medial malleolar fractures, which are common injuries treated by orthopedic surgeons, the goal is to achieve stable and effective fracture fixation. This can be achieved by selecting the appropriate screw length and type, such as partially threaded or fully threaded screws, to optimize compression and fracture healing.

The choice of screw length is critical. Excessively long screws can bypass the dense metaphyseal area, resulting in inefficient compression, while screws that are too short may compromise fracture compression. Therefore, surgeons must carefully consider the patient's anatomy and bone quality when selecting the appropriate screw length.

Moreover, the surgical team should be well-prepared with the required instrumentation and a complete range of screw sizes to ensure a successful procedure. It is also essential to discuss the potential risks, benefits, and complications of the procedure with the patient to obtain informed consent.

Frequently asked questions