Bridging External Fixation with Pin Augmentation

Published on 16/03/2015 by admin

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Last modified 16/03/2015

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CHAPTER 6 Bridging External Fixation with Pin Augmentation

Scott Wolfe, MD, Lana Kang, MD

External fixation is fundamental to the principles of orthopaedic trauma. It provides a rapid, simple, and effective surgical treatment for osseous, articular, and soft tissue injuries. Patients with fractures and injuries of the distal radius have and continue to achieve good results after immediate and definitive treatment with external fixation.1–4

The term “bridging” refers to the design of the frame in which the radiocarpal joint is spanned, and fracture stability is achieved via distraction and ligamentotaxis, which refers to the support provided by soft tissue tension to align and hold the reduction.5 Additional fixation is supplemented by Kirschner wire (K-wire) pins, which are percutaneously or internally placed into the distal radius. This is the concept referred to collectively as “bridging external fixation with pin fixation” or “augmented external fixation.”6 “Nonbridging external fixation” refers to a frame design that fixes the metaphyseal/articular fragments to the proximal diaphysis without spanning the wrist joint, sparing the capsule and the ligaments from the potentially damaging effects of traction.7–11

Although the specific roles of external and internal methods of fixation in the treatment of distal radius fractures continue to evolve, restoration of articular congruity, radial length, radial height, and dorsal tilt remains a common tenet to all modes of treatment.12 After Vidal and colleagues5 introduced the concept of ligamentotaxis as a means to align bony fragments using soft tissue tension, the use of the external fixator soared. A decade later after widespread adoption of the technique internationally, an increased awareness of its limitations and attendant complications, such as loss of reduction, digital and wrist stiffness, and complex regional pain syndrome, unfolded.13,14

As we have developed an improved and more sophisticated understanding of fracture healing and wrist biomechanics, we have been better able to refine the application of external fixation for distal radius fractures. Its combined use with limited internal,15 arthroscopic,16–20 and percutaneous fracture reduction techniques,21 and supplemental bone graft or bone graft substitutes has enhanced the stability of the fixation construct,22–30 and simultaneously minimized the dependency on traction for maintenance of reduction.

Despite its effectiveness, and similar to other forms of treatment, external fixation has its problems and concerns. These include poor patient tolerance or acceptance, pin tract infection, iatrogenic injury to the small branches of the superficial radial nerve, loss of fixation, settling, radioulnar joint dysfunction, radiocarpal arthrofibrosis, and, as stated previously, hand and digital stiffness.13,31–34 In addition, external fixation without supplementation inherently lacks the capacity to fix rigidly impacted or comminuted articular “die-punch” fragments and, by itself, has been associated with loss of articular reduction and articular incongruency.35 In the last few years, the ease of application and increased fixation strength of volar locking plates have led to an unprecedented increase in the popularity of internal fixation and a concomitant shift away from external fixation of distal radius fractures.

Although correct principles of application of augmented external fixation are in danger of becoming a lost art among orthopaedic surgical training programs, the technique continues to be the only viable treatment option in certain situations. In addition, more recent randomized clinical studies attest not only to its clinical utility, but also to improved functional and satisfaction outcomes compared with internal fixation.1–3 It is imperative that hand and upper extremity surgeons who routinely provide care for fractures and injuries of the distal radius be well versed in techniques of external fixation and prepared to use this form of treatment when applicable.

Basic Science

The basic biomechanical principles of external fixation apply to the distal radius. Strength and stability are indirect, and reduction is attained by distraction and ligamentotaxis. Stability of the fixation construct is improved with the following:

• Direct contact of the fracture ends
• Larger diameter pins
• Decreased rod-bone distance
• Increased spacing of pins relative to the fracture (near-near and far-far)
• Pins in different planes
• Increased number of bars (stacking)36

In contrast to nonbridging applications of external fixation to long bones, such as the tibia, femur, or humerus, peculiar to the distal radius is the need to span the neighboring radiocarpal and intercarpal joints, and the associated deleterious effect of distraction on the intrinsic and extrinsic carpal ligaments. Although it is important to gain reduction of fracture fragments, it is crucial that the principle of ligamentotaxis not compromise soft tissue viability or tendon gliding by prolonged maintenance of traction. Lengthy or excessive traction predictably results in digital stiffness and joint contractures,37 and the resultant dysfunction of the hand and wrist negates any of the goals of fracture healing with external fixation.

Principles of Augmented External Fixation

Augmentation with percutaneous or open pin fixation or bone graft or both is needed to provide increased stability to the external fixator construct and reduce the need for applied distraction.27,38 Although application of an external fixator can acutely restore radial height and correct angular rotation alignment, there is a tendency for the fracture fragments to settle over time because of the stress-relaxation of the surrounding collagenous soft tissue envelope.38 This settling of fracture fragments especially occurs when there is metaphyseal comminution and bone loss, which precludes firm bony contact, diminishing construct stability. In addition, traction alone does not restore articular congruency when there is impaction and displacement of intra-articular fragments, in which case a limited open incision is required to attain reduction.27,29

Biomechanical studies have shown that supplemental pin fixation decreases the dependency on ligamentotaxis for maintenance of reduction by minimizing the extremes of positioning and need for distraction.33 A pin placed through the radial styloid neutralizes the deforming force of the brachioradialis38 and the powerful wrist radial deviators of the first dorsal compartment. A single pin placed dorsally (dorsal transfixation wire [DTW]) provides a statistically significant increase in resistance to deformation, by gaining purchase on the stout volar metaphyseal cortex and directly opposing the strong dorsally deforming forces of the wrist and digital extensors. The increased stability gained by the augmentation pins more than offsets the biomechanical differences in the material strength of different external fixation models39; consequently, a fixator should be chosen because of ease of application and use, rather than because of its size or material properties.

Bone Grafting with Augmentation of External Fixation

Several studies have shown that the addition of bone graft or bone graft substitutes supports the articular surface and effectively prevents fragment settling.22,28,40 Leung and colleagues22–24 showed that bone graft application into the metaphyseal void that is created after reduction of dorsally displaced and articular impaction injuries enables earlier removal of the external fixator by expediting healing and providing firm support for the reduced articular surface. Subsequent studies have shown that bone graft substitutes are equally effective in provision of articular support and minimization of fracture fragment settling.25,30

Indications

The indications for external fixation with pin augmentation depend on an array of factors that should be tailored to the individual case. These include patient factors (age, dominance, occupation, comorbidities, other injuries, compliance), the personality of the fracture pattern, availability of equipment, and surgeon skill level and preference.

The patient should be apprised of the different options and expected outcomes and be involved in the decision-making process. The patient may accept the additional risk of open reduction and internal fixation to allow for a shorter period of cast immobilization. The patient should understand that an initial attempt at minimally invasive percutaneous reduction before open reduction is an acceptable treatment algorithm that is well supported by clinical studies.1–3 Kreder and colleagues3 showed that if an optimal and stable reduction is achieved with percutaneous fixation, open reduction is unnecessary, and function is superior.

The ideal candidate for external fixation with pin augmentation is a patient who has an unstable intra-articular fracture of the distal radius (Fig. 6-1). Specific indications for operative management include articular depression (1 mm) after attempted closed reduction, or loss of reduction, defined as a dorsal tilt exceeding 10 degrees, loss of radial length exceeding 5 mm, or articular depression exceeding 1 mm.12,28 The technique of augmented external fixation is useful for a variety of fracture patterns, however, which may include intra-articular and extra-articular fractures that are displaced and unstable. Other indications for external fixation include injuries with soft tissue compromise, grossly contaminated open fractures, and unstable multitrauma patients who are brought to the operating room for other life-threatening injuries. These emergent situations potentially apply to patients of all age groups. Percutaneous techniques for fracture fixation should not be delayed longer than 10 to 14 days because of the early callus and soft tissue scarring that would preclude closed fracture manipulation and the effects of ligamentotaxis.

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FIGURE 6-1 Anteroposterior (A) and lateral (B) plain radiographs of an unstable intra-articular fracture of the distal radius that is amenable to treatment with external fixation with pin augmentation.

Contraindications

There are very few contraindications to augmental external fixation. Absolute contraindications include medical comorbidities that disallow the safety of the manipulation or the required degree of anesthesia, ongoing systemic infection, and local infection at the planned site of external fixator and K-wire pin placement. Relative contraindications include gross comminution that would preclude augmented pin fixation, volar lip fracture patterns that are not amenable to percutaneous fixation, and severely osteoporotic bone that would hold fixation pins poorly and may be more amenable to simple closed reduction or locked plate internal fixation.

Surgical Technique

The patient is positioned supine on the operating room table. Anesthesia can be either regional or general, the choice of which is based on the preference and skill level of the anesthesiologist and the medical conditions of the patient. Complete muscle relaxation of the patient should be achieved. Antibiotic prophylaxis is provided. A tourniquet is placed above the elbow of the involved extremity, which is sterilely prepared over a radiolucent hand board attachment. Intraoperative fluoroscopic imaging is mandatory.

The external fixator generally can be placed without the need for a tourniquet, diminishing reactive postoperative edema, and allowing more time later if a complicated open reduction and grafting is required. A preliminary reduction is performed to align the fracture fragments grossly and ensure that the frame would be appropriately aligned with the fracture. The guiding philosophy is that the fixator is applied exclusively to neutralize muscle forces and maintain overall fracture alignment, and should not be thought of as a tool to gain reduction through application of force, excessive traction, or extremes of positioning.

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