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:

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.

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.

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.

A 2.5-cm longitudinal incision is made at the level of the mid radial shaft about 10 cm proximal to the radial styloid and a minimum of 3 cm from the most proximal fracture line. We prefer this mini-incision approach over percutaneous placement of the external fixator pins because of the unpredictable proximity of the superficial branch of the radial nerve (SBRN) and the lateral antebrachial cutaneous nerve.²⁹ The preferred interval is between the extensor common radialis brevis and longus muscles,⁴¹ such that the fixator lies in an oblique plane midway between the coronal and sagittal planes of the forearm. A deep muscular interval between the brachioradialis and extensor radialis longus³⁸ also is acceptable, although there is an increased risk of neurapraxic injury or irritation of the radial sensory nerve (Fig. 6-2). Soft tissue is reflected sharply off the bone without stripping periosteum to allow for secure positioning of the pin guide.

FIGURE 6-2 Diagrammatic illustration of the deep muscular interval between the brachioradialis and extensor radialis longus for placement of the proximal external fixator pins.

Two 4-mm-diameter pins are drilled across two cortices of the shaft. Whether the pins are placed in parallel or convergent depends on the particular fixator design, and there is some suggestion that the obliquity of convergent pin placement increases bone purchase. Although various pin sizes are available, 4-mm pins have been shown to have the best pullout strength and resistance to bending without increasing risk of pin site fracture.⁴² Pin placement is confirmed with fluoroscopy.

A 2-cm longitudinal incision is made in the oblique plane over the index metacarpal distal to the flare of the metacarpal base. The extensor tendon and first dorsal interosseous muscle are sharply reflected to allow exposure to the bone (see Fig. 6-2). Care is taken to avoid injury to the small branches of the SBRN. With the index metacarpophalangeal joint flexed to tension the intrinsics properly, two 3-mm pins are drilled across two cortices in a similar fashion as was done for the radius. Bicortical purchase is again confirmed with fluoroscopy.

The surgical wounds are irrigated, and small bleeding points are coagulated. Skin closure is done with 4-0 or 5-0 nylon sutures, before application of the fixator frame. We have found that closure of the skin at this stage of the procedure is much easier than at the end of the case because of the difficulty of suturing around the fixator frame after it has already been secured and tightened.

The external fixator frame is applied (Fig. 6-3). Most systems comprise a single radiolucent bar that is secured with metal clamps to the stainless steel pins. Subtle variations exist, and technical guidelines should be studied and learned before use.

FIGURE 6-3 Clinical photograph of the external fixator frame after application.

The frame is first loosely applied to the pins, and the final reduction is guided by intraoperative fluoroscopy. A surgical assistant is helpful during the manipulation to provide a gentle countertraction force on the proximal forearm; the assistant also may be asked to secure and tighten the bar to the distal pins while the fracture reduction is held. An alternative method that may be useful when an assistant is unavailable is to suspend the hand with sterile finger traps and apply 5 to 10 lb of countertraction.²¹

Fracture reduction is achieved by a combination of longitudinal traction, ulnar deviation, and dorsal or volar translation of the carpus relative to the shaft of the radius.^43,44 Manual pressure placed directly on the tip of the radial styloid by the surgeon’s thumb helps to restore radial length and inclination. When the fracture is displaced dorsally, a palmarly directed translation force on the carpus is helpful at this time to optimize reduction. When the fracture is displaced volarly, a dorsally directed translation force combined with slight wrist extension and supination is performed. The external fixator is then provisionally locked in position.

A closed reduction alone is usually attainable with fractures that have a simple intra-articular component.²⁹ Additional reduction maneuvers are then required, however, to fix individual fracture fragments directly and obviate the need for maintenance of distraction or extremes of positioning. K-wire placement into the major fracture fragments can be used as joysticks to help guide reduction.

Because of the indirect nature of the external fixator, the frame alone is insufficient to reduce impacted articular fragments. After the larger fragments are aligned or provisionally fixed with K-wires, we perform percutaneous, limited open reduction as described by Fernandez and Geissler.^21,45 Reduction of these fragments is achieved with a 2- to 3-cm longitudinal dorsal mini-incision that is based slightly ulnar to Lister’s tubercle. The interval between the third and fourth dorsal compartments is dissected, and the extensor pollicus longus tendon is transposed radially. The fracture lines in the metaphysis are identified and exposed, and lifting a single large dorsal cortical fragment (trapdoor) exposes the entire metaphysis and the impacted articular pieces. A Freer elevator or dental pick is used to elevate the impacted articular fragments (Fig. 6-4). The displaced fragment is reduced against the lunate; it is important at this phase of the procedure that traction is reduced to allow the lunate and scaphoid to act as a guide to a congruent reduction.

FIGURE 6-4 Intraoperative fluoroscopic image showing use of a Freer elevator to elevate the impacted articular fragments.

Bone graft or bone graft substitute is packed behind the reconstituted subchondral bone (Fig. 6-5). The articular surface is supported with a subchondral 0.045- or 0.062-cm K-wire placed transversely from the radial styloid directed toward the dorsal radial cortex of the sigmoid notch, taking care not to penetrate the radioulnar joint.^21,45 Restoration of radiocarpal articular congruency is guided and confirmed with fluoroscopy. In addition, congruency of the distal radioulnar joint should be ensured at this stage.

FIGURE 6-5 Intraoperative fluoroscopic image after application of bone graft or bone graft substitute.

One (or two) additional K-wires are inserted through the tip of the radial styloid just dorsal to the crossing of the first dorsal compartment and positioned at a relatively acute angle to the radial shaft to cross the fracture and gain purchase in the strong diaphyseal ulnar cortex of the radial shaft. A 14-gauge or 16-gauge angiocatheter is important as a drill guide to prevent injury to the nearby branches of the radial sensory nerve. (If using more than one wire through the styloid, we prefer a parallel configuration.) A DTW is placed in a 45-degree angle to the sagittal plane of the radial shaft through the dorsal rim of the distal radius between the fourth and fifth dorsal compartments. This wire is positioned to cross the fracture site and capture the stout volar cortex of the radial shaft. The placement of this DTW in combination with the pin placed through the radial styloid (Fig. 6-6) has been shown to provide maximal stability to the external fixation construct.³⁸

FIGURE 6-6 Anteroposterior (A) and lateral (B) plain radiographs after placement of the dorsal transfixation wire and radial styloid pins.

Lastly, the distal radioulnar joint should be assessed for stability after radiocarpal fixation. If grossly unstable, numerous techniques can be used to effect stability. Casting in the position of maximal stability (usually partial or complete supination) for 3 to 4 weeks is effective for restoration of stability.^26,46,47 Alternatively, an ulnar styloid pin or two cross pins can be placed through radial and ulnar cortical shafts approximately 5 to 6 cm proximal to the joint and left proud to facilitate removal in the event of fatigue failure. Large basi-styloid fragments can be fixed with K-wires, tension bands, or a small cannulated screw as needed to reattach the disrupted dorsal and volar radioulnar ligaments, which insert at its fovea.

At this point, distraction of the carpus and radiocarpal joint should be checked, and traction is diminished to ensure that the carpus is not overdistracted. Fluoroscopic imaging in the anteroposterior plane should show no more than 1 mm of distraction of the radiocarpal joint beyond that of the midcarpal joint. In addition, passive digital motion should be supple with metacarpophalangeal flexion to 90 degrees.

The skin around the external fixator and K-wire pins is assessed to ensure that there is no undue tension with the final frame configuration. Relaxing incisions should be made as deemed necessary. All pin sites are covered with povidone-iodine (Betadine)–soaked or xeroform dressings. The K-wire pins are either left out of the skin and cut short or cut just below skin level and buried. The patient is immobilized in a sugar tong cast in full supination for the initial few days postoperatively because pain may otherwise initiate a protective posture of wrist flexion and forearm pronation that may be difficult to reverse later.

Technical Pearls and Pitfalls

Postoperative Course and Rehabilitation

The wrist and hand should be elevated for the first 48 to 72 hours. Digital motion exercises are begun immediately after surgery. The skin sutures and postoperative dressing are maintained for 10 to 14 days, and then twice daily pin site care is begun with diluted hydrogen peroxide. If the distal radioulnar joint is determined to be stable at surgery, forearm supination and pronation exercises are begun at the first postoperative visit. Patients are encouraged to use their hand for light activities, such as eating, writing, dressing, and light typing. Lifting, squeezing, and gripping are prohibited until all hardware has been removed. Patients may shower with the frame in place, provided that all wounds are healed and dry, but should avoid immersion in standing water. Fracture healing and maintenance of fracture reduction are checked with plain radiographs every 2 to 3 weeks. Hand therapy is generally instituted early in the postoperative course, especially if stiffness or edema develops. Peroxide pin tract care is supplemented by a short course of oral antibiotics if pin erythema develops; frank pin tract infection requiring premature removal is rare.

The external fixator frame is removed in the office after 4 to 6 weeks, and the K-wire pins are generally removed 2 to 3 weeks later. The exact timing may vary depending on pin site integrity, pin purchase or loosening, bone graft incorporation, degree of articular and metaphyseal comminution, and radiographic evidence of healing. The pin sites are cleaned and covered with a dry sterile dressing. A volar wrist splint is applied, and hand therapy is continued immediately on removal of the external fixator.

Complications

As stated previously, complications include pin tract irritation or infection, injury to the SBRN, radiocarpal arthrofibrosis, and digital stiffness. Injury to the SBRN is more difficult to treat and is best avoided by meticulous open pin placement. Radiocarpal or digital stiffness is treated by intense and early hand therapy. Complex regional pain syndrome must be recognized early and treated with a multifaceted approach involving therapy, pain management, and frequent office visits. This syndrome is almost always associated with nerve injury, excessive or prolonged traction, or both, and these causes must be ruled out and treated before irreparable injury ensues. Patients should be reassured that motion gains continue to be made in radiocarpal and radioulnar joints for the first year after surgery, as is the case with patients after open reduction and internal fixation.

Results

Although biomechanical studies suggest superior fixation strength with internal fixation compared with augmented external fixation,^38,48 clinical studies show little significant difference in functional outcome between dorsal plating, augmented external fixation, or closed reduction and casting.^1,4,49 With augmental external fixation, we have achieved excellent radiographic healing (Fig. 6-7) and restoration of functional wrist motion (Fig. 6-8). In a retrospective cohort of 21 patients consecutively treated with augmented external fixation and bone graft, wrist motion averaged 90% of the uninjured wrist, and grip strength measured 75% of the uninjured side. Of cases, 94% had good or excellent radiographic results by the modified Lidstrom radiographic scoring system and were rated as good or excellent by the criteria of Gartland and Werley. The average DASH functional/symptom score was 90.3 (maximum 100). Radiographic parameters were restored to an average of 12 mm radial length, 4 degrees volar tilt, 23 degrees radial inclination, and 0.6 mm ulnar-positive variance. Articular reduction was maintained in all patients.²⁸

FIGURE 6-7 Anteroposterior (A) and lateral (B) plain radiographs confirming fracture healing after external fixation with pin augmentation.

FIGURE 6-8 Clinical photographs of bilateral wrist flexion (A) and extension (B) showing restoration of functional motion after external fixation with pin augmentation.

There are few level I studies that effectively compare internal fixation and external fixation; the studies that exist support percutaneous fixation over the added surgical dissection and risk of internal fixation, provided that articular congruence and stability can be achieved.^1,3 Although a few more recent studies suggest superiority of locked volar plate fixation,^50,51 no randomized trials have been reported to date. More data are needed to compare sufficiently various fixation techniques that are stratified to patient demographics and specific fracture patterns. Under many circumstances, external fixation with pin augmentation continues to be an ideal method of treatment, supported by decades of clinical and basic research. With proper planning and surgical technique, excellent results can be achieved in a wide variety of fracture patterns.