Surgery STAT: Tailor your bone fracture repair technique
Implant failures and union problems are preventable. Save your patients from having to endure additional health issues and surgeries by doing it right the first time.
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On the surface, fracture repair using bone plates can appear to be a simple application of a plate and screws to bone fragments. This common misconception can leave a patient with difficulties and complications after surgery if the procedure isn’t performed correctly. Rules of fracture fixation have been developed through several years of research to maximize the chances of successful repair. Most of the rules were developed for people; however, they have been adapted for dogs and cats, which presents unique challenges because treating an animal is different than treating a person.
Incorrect fracture repair can lead to multiple complications, including implant failure, malunion, delayed union and nonunion. Patient activity can also result in severe complications, so it is critical that pet owners understand that postoperative restrictions are not just suggestions but imperative rules that must be followed.
Implant failure
Implant failure occurs when implants are either inappropriately chosen or inappropriately applied to a specific patient or fracture type. For example, an inappropriately chosen implant might be a 2-mm plate placed on the bone of a 50-pound dog, or it could be a properly chosen 3.5-mm plate for the same 50-pound dog that is not sufficiently long enough to span the desired bone and does not allow for placement of the appropriate number of screws, thus not providing sufficient strength for the construct.
Another example is an appropriate sized plate for the patient, but one that is inappropriate for the type of fracture, e.g. a transverse fracture versus a comminuted fracture. The forces acting on these two fracture types are different and have different requirements for appropriate stabilization.
Mistakes can stem from lack of knowledge and understanding of fracture biomechanics, the forces acting on bones and the different processes of bone healing. Any of these mistakes can cause bending or breakage of the plates, pulling out or breakage of the screws or the development of union problems.
Union problems
There are three types of union problems commonly seen: malunion, delayed union and nonunion.
Malunion (Figures 1A and 1B) describes a fracture that has healed but not in the proper anatomic alignment. Malunions can result from improper alignment at the time of surgery, inappropriate fixation that leads to displacement of the bone fragments, or fractures that have healed out of alignment without surgery. They can result in valgus, varus, procurvatum, recurvatum and torsion of the affected bone. This can lead to abnormal force transmission along the bone and the associated joints, which causes abnormal function and possibly the development of osteoarthritis. Not all malunions are clinically important, but when they are, they need to be modified by corrective osteotomy.
Figures 1A and 1B: Craniocaudal and mediolateral views of a malunion tibial fracture. Note the bony connection but poor alignment and overriding of the fragments. (All photos courtesy of Dr. Karl Maritato.)
Delayed union describes a fracture that takes longer to heal than expected. This might be due to the presence of an infection or weak implants that allow too much motion at the fracture site, which prevents efficient fracture healing. Another cause of delayed union can be a too-rigid fixation that overprotects the bone from normal stress. The term stress protection is used to describe this complication and can be caused by implants that are too large or by too many screws being placed both proximal and distal to the fracture site. If this occurs, gradual strategic destabilization of the construct is generally performed.
Nonunions are divided into viable and nonviable nonunions. A viable nonunion is a fracture that has not healed but has the biologic ability to do so if the conditions are improved, such as better stability of the repair. A nonviable nonunion (Figures 2A and 2B) is nonunion in which the fracture ends have gone dormant and healing will not commence without intervention, including reopening of the medullary canals and application of bone grafts.
Figures 2A and 2B: Craniocaudal and mediolateral views of a nonunion femur fracture of six months’ duration. Note the closed ends of the medullary canal with no evidence of activity.
Fracture biomechanics and repair
The patient shown in Figures 3A and 3B sustained a comminuted radius/ulna fracture that was repaired prior to referral. Comminuted fractures are biomechanically unstable. Let’s compare that to a transverse fracture and see how the two differ when approaching repair.
A transverse fracture could be repaired with the plate shown in Figures 3A and 3B because there are only two fragments associated with the fracture, which can be compressed together and secured by the plate. The bone and the plate are then working together. We call this load sharing between the plate and the bone since the bone has been reconstructed.
With a comminuted fracture, rebuilding the integrity of the bone structure is much more difficult. Because of this, the forces acting across the plate are not shared by the bone nearly as well as with a transverse fracture. In this type of repair the plate is used in a buttress fashion. Therefore, if the implants used are not capable of handling that increased stress, failure will ensue.
Figure 3A: Craniocaudal view of a radius/ulna fracture two weeks after the first repair. Note the misalignment of the fragments from screw loosening.
Figure 3B: A mediolateral view of the radius/ulna fracture two weeks after the first repair. Note the proximal screws pulling out of the radius.
As we can see in Figures 3A and 3B, the comminuted fracture allowed for more force across the fracture line than the plate-screw-bone construct could handle, and the screws began to pull out of the proximal portion of the plate. The subsequent repair used a larger, longer plate with increased number of screws (Figures 4A and 4B). This allowed for better distribution of the forces acting across this comminuted fracture, and the plate could better handle those forces.
Figures 4A and 4B: Craniocaudal and mediolateral views of the same radius/ulna fracture immediately after the second repair. Note the increased length of the plate and the increased number of screws for this sized patient.
