Which kinds of fractures are best treated with locked plating? How does an orthopaedist select the right implant for a patient? In “Locked Plating: Pitfalls and Complications,”
a session presented by the Orthopaedic Trauma Association during the 2007 Specialty Day at the AAOS Annual Meeting in San Diego, J. Tracy Watson, MD, William M. Ricci, MD, Sean E. Nork, MD, and Philip J. Kregor, MD, addressed these and other questions on the use of locking plates in fracture care.
Advantages and costs of locked plating
According to Dr. Watson, minimally invasive locked plating has both biologic and mechanical advantages over earlier techniques of fracture fixation. Biologic advantages include minimized disruptions from fracture hematomas and vascular pedicles. Mechanical advantages include decreased varus and improved fixation in marginal bone. Costs for locking plates, however, are significantly higher than for traditional devices, and outcome data about whether the costs are justified are currently very limited.
Biomechanics of locked plates and surgical techniques
Dr. Ricci explained that while traditional screws compress plate to bone, locked plates do not depend on the force between plate and bone to achieve stability. Instead, the heads of the screws engage the plate, resulting in less damage to the endosteal blood supply. When osteoporosis or repetitive stress causes traditional screws to fail, they do so sequentially, one at a time. Locked screws, on the other hand, are more resistant to failure because failure of the screws can only occur simultaneously.
When hybrid plating is used, meaning that locked and unlocked screws are used in the same construct, the unlocked screws can act as a reduction tool while the traditional screws provide fixed-angle support and improved fixation in osteoporotic bone. In surgery, unlocked screws should be inserted before the locked screws if the goal is to pull the plate closer to the bone or change the fracture position.
Current plate designs and indications for their use
One of the many variations in locked plating designs, said Dr. Nork, is the different screw configurations designed for certain angles. Locked plates also have varying screw hole designs, some of which allow for placement of either locked screws or traditional screws. Surgeons should consider a plate’s metallurgy (whether titanium or stainless steel), instrumentation, and percutaneous guides when choosing a system. In addition, they should ask the following questions:
- Does the plate use unicortical or bicortical screws?
- Will it require cannulated or solid screws?
- Is there a self-tapping thread?
- What is the relative size and strength of the screws?
The use of locked plating should be considered for osteoporotic bone, said Dr. Nork, adding that hybrid fixations may be optimal in this type of case. Another opportunity to use locked plating is with open fractures, which often require a long healing time and may be highly unstable.
On the other hand, locked plating—and its associated costs—may not be advisable in patients who have good bone quality. Conventional plates are sufficient in patients with humeral shaft fractures, both-bone forearm fractures, and routine fibular fractures. Dr. Nork said that routine plates can most likely be used for any fracture that depends on osseous compression for most of the construct’s stability.
Why locked plates can fail
Dr. Kregor divided the reasons locked plating can fail into two categories: biomechanical and biologic. Biologic reasons damage to the soft-tissue environment of the fracture and situations in which there is significant bone loss without a biologic stimulus, such as with a bone graft. Another major cause of biologic failure is infection. Biomechanical problems that can result in failure of locked plating include the use of fixators that are too short, inappropriate screw placement, and selection of the wrong fracture type.
For more information on the use of locked plates in fracture care, visit the trauma section of the AAOS physician education Web site, Orthopaedic Knowledge Online (www.aaos.org/oko).