Fractures of the humerus shaft are common injuries that can result from a variety of traumatic events. These fractures can have significant functional consequences for patients and can be difficult to manage. Biomechanical principles play a critical role in the design of fracture fixation devices, and the biomechanics of plate and screw fixation of humerus shaft fractures is of particular interest to orthopedic surgeons. We will discuss the biomechanics of plate and screw fixation of humerus shaft fractures, including the principles of fracture stability, the mechanics of plate and screw fixation, and the clinical outcomes associated with this technique.
Fracture Stability:
The stability of a fracture fixation construct is critical to successful healing of the fracture. Stability refers to the ability of a fixation device to resist the forces that act on the fracture during normal daily activities, such as lifting, and reaching. Stable fixation allows for early motion and functional rehabilitation, which can improve patient outcomes. In the case of humerus shaft fractures, stable fixation is particularly important because the humerus is a bone that experiences significant forces during daily activities.
The stability of a fixation construct depends on several factors, including the properties of the fixation device, the number and location of screws, the quality of the bone, and the position of the fracture fragments. In the case of plate and screw fixation of humerus shaft fractures, the stability of the construct depends primarily on the properties of the plate and screws and the number and location of screws.
Mechanics of Plate and Screw Fixation:
The mechanics of plate and screw fixation of humerus shaft fractures are complex and depend on several factors, including the properties of the plate and screws, the location and number of screws, the position of the fracture fragments, and the properties of the bone.
The plate used for fixation of humerus shaft fractures is typically a narrow DCP metal plate that is contoured to fit the shape of the bone. The plate is held in place with screws that are inserted through the plate and into the bone. The screws used for humerus shaft fracture fixation are typically cortical screws.
The mechanics of plate and screw fixation depend on the number and location of screws. Generally, a minimum of six or eight screws are used for humerus shaft fracture fixation, with three or four screws placed proximally and three or four screws placed distally to the fracture site. The screws are inserted at an angle to the bone to maximize their holding power.
The position of the fracture fragments also plays a critical role in the mechanics of plate and screw fixation. In general, the fracture fragments should be reduced as closely as possible to their anatomical position to minimize the risk of malunion or nonunion. The plate should be contoured to match the shape of the bone and should be placed in a position that allows for maximum contact between the plate and the bone. This maximizes the surface area for screw fixation and improves the stability of the construct.
Clinical Outcomes:
Plate and screw fixation of humerus shaft fractures has been shown to be an effective treatment option with good clinical outcomes. Several studies have reported high rates of fracture healing, low rates of complications, and good functional outcomes in patients treated with plate and screw fixation.
One study reported a 98% rate of fracture healing in patients treated with plate and screw fixation, with a mean time to union of 15 weeks.