Fracture fixation technical errors (Proceedings)

Fracture repair results in the creation of a bone-implant composite. Although most of our interventions for fracture repair are successful, at times it seems as though there are an endless number of errors that may prevent the fracture from healing. Fortunately, once the cause of the complication is recognized, the underlying problem can often be corrected and a successful outcome eventually attained.

Failure of a bone-implant composite can occur in one of three ways:

      1. The implant can fail

      2. The attachment of the implant to the bone can fail.

      3. The bone can fail to heal.

Implant failure

Implants rarely fail due to material, manufacturing, or design flaws. Instead the typical cause of implant failure is technical error. Technical error includes poor preoperative assessment/planning, improper implant selection (i.e. the selected implant is inadequate to counteract the forces at the fracture site), and improper application of the implant.

Attachment of the implant to the bone

A set of guiding principles exist for the selection and application of implants. Indeed, one of the major goals of this course is help familiarize the surgeon with these guiding principles. When implants loosen, critical evaluation of the repair often reveals that one or more of these principles was violated. Although there are some underlying common principles, a specific set of guidelines exist for application of pins, wire, plates, screws, and external skeletal fixation.

The bone can fail to heal

In addition to the presence of instability, bone fails to heal when the biologic environment is poor secondary to trauma, or if the biologic environment has been compromised by the method of repair. Examples include open fractures with devascularized tissue secondary to trauma, or fractures with avascular and unstable fragments secondary to iatrogenic trauma. In instances where the biologic environment is insufficient to allow healing, nearly all bone-implant constructs will eventually fail.

In many instances fracture healing can be aided by considering the cause of the injury, the condition of the surrounding soft tissues, the forces acting at the fracture site, and factors inherent to the patient (age, body status, general health) when selecting a repair technique. Techniques to promote fracture healing, such as application of a cancellous bone graft, are often beneficial and are rarely contraindicated.

Common failures

When considering fracture fixation failure, it is generally due to inadequate control of the forces acting at the fracture site. The primary forces acting at the fracture site are rotation, bending, tension or compression, and shear. Knowledge of the ability to counteract each of these forces using various fixation methods is critical for not only appropriately selecting a fracture fixation method, but also for understanding why fracture fixation fails. The most common error leading to fixation failure is a decision making error, where an implant is asked to perform a function that it is incapable of performing. Application errors, where an implant is applied improperly (such as a screw being too short or an implant being placed in the wrong position) also occur, but an implant incapable of performing a function will fail even if applied properly.

Most examples of fracture fixation failure involve the use of pins and wires. This is not because pins and wires are a poor method of fixation. Instead, it is typically due to poor application of pins and wires. Intramedullary pins are generally considered to be excellent for counteracting bending forces, useful for counteracting shear forces if the medullary cavity is filled, and poor at counteracting compression and rotation. If used in conjunction with cerclage wire, bone can be reconstructed to allow load sharing, and rotational, shear, and compressive forces can be counteracted. However, principles of cerclage wire application must be followed. In most instances, failure of pin and cerclage wire fixation involves failure to follow these principles. Examples of pin/wire fixation failure commonly demonstrate wire that is too small, inappropriate numbers of cerclage wires, inappropriate placement of wire, inappropriate pin size, inappropriate placement of pins, and inability/inappropriate fixation to counteract the forces existing at the fracture site.

Failure of plate or screw fixation occurs due to a variety of reasons. Implants may be of an inappropriate size. Implant selection guidelines exist and can be found in the AO manual. Additionally, forces existing at the fracture site based on the initial fracture configuration and applied repair must also be considered. Perhaps the most common cause of plate failure is the lack of a trans cortex, and therefore the plate serves as a buttress plate. When this occurs, the plate is subjected to bending forces. As the plate is subjected to repetitive bending forces, if fatigue damage accumulates and exceeds the yield stress prior to adequate bone healing, disruption of the bone-implant composite may occur. Failure tends to occur through areas that are stress risers, such as screw holes. Knowledge of the relative properties of various types and sizes of plates and screws is necessary to address these issues.

Approach to determining the cause of failure and developing a treatment plan

In order to address fixation failures, an honest assessment of case management is necessary. This includes all aspects of care, not only intraoperative treatment. The following questions must be asked:

      1) Was the initial treatment plan appropriate for the patient's condition?

      2) Were technical problems encountered?

      3) How and why did the fixation fail?

      4) What change in the treatment plan can be made to allow for healing to occur?

It is a technical error to devise revision plans based entirely on mechanical aspects of the repair. Instead, revision plans must consider both biological and mechanical aspects of failure, and address each appropriately. Once this is determined, a decision is made to replace, remove, revise, or augment the current fixation. Augmentation of failed fixation should be performed only if adequate alignment and reduction exist, and there is evidence of bone healing. Replacement, removal, or revision of the original fixation should be performed with appropriate consideration of soft tissues. If the fracture site is approached to improve mechanical stability, appropriate planning should be performed to allow application of bone grafts or techniques to increase the likelihood of healing.