Fragment-Specific Fixation of Distal Radius Fractures

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CHAPTER 12 Fragment-Specific Fixation of Distal Radius Fractures

Leon S. Benson, MD, Robert J. Medoff, MD

Of the various types of distal radius fractures, those with intra-articular extension have the most to gain from operative intervention. Many of these fractures are inherently unstable and not amenable to conservative methods of reduction and cast immobilization. Treatment that fails to correct residual incongruity of the joint and leaves a significant step-off or gap in the articular surface can result in chronic osteoarthritis and pain.¹^–⁴ Furthermore, unreduced fragments that alter the geometry and normal kinematics of the radiocarpal or distal radioulnar joint can cause painful movement, restricted motion, and joint instability. Ideally, treatment should be directed at stable restoration of normal anatomy of the articular surface.

Although intra-articular fractures of the distal radius do not occur as a single, homogeneous pattern, the majority of these injuries contain a subset of five basic fracture elements: the radial column, ulnar corner, dorsal wall, volar rim, and free intra-articular fragments (Fig. 12-1). Occasionally, these fracture elements themselves may have further comminution. In addition to these cortical elements, these fractures may have other associated pathological processes, such as compressive damage to the metaphyseal bone, fractures of the distal ulna, and soft tissue injuries of the triangular fibrocartilaginous complex (TFCC), distal radioulnar joint (DRUJ), and radioulnar syndesmosis. In more complex fracture patterns, appropriate treatment of distal radius fractures often must be customized to the specific components and mechanism of the particular injury. Although recently there has been a rise in the popularity of fixed-angle volar plates for the treatment of distal radius fractures, this method of treatment can be inadequate for fractures with small distal fragments or injuries with complex, multiarticular patterns.⁵ Treatment starts with careful analysis of the injury and initial postreduction radiographs.⁶ When needed, computed tomography (CT) can supplement standard radiographs to help with the interpretation of the fracture pattern. These topics have been covered in previous chapters.

FIGURE 12-1 Fragment-specific classification. Articular fractures of the distal radius tend to propagate along recurrent pathways, resulting in generation of five basic fracture components: the radial column, ulnar corner, dorsal wall, free intra-articular, and volar rim. In addition to these distal radius fracture elements, impaction of the metaphyseal bone, DRUJ and distal ulna injuries, and intracarpal pathologic processes may affect the natural history of a particular fracture pattern.

Fragment-specific fixation is a treatment approach in which each independent major fracture fragment is stabilized with an implant specifically designed for that particular fracture element (Fig. 12-2).⁷^–¹⁰ One objective of fragment-specific fixation is to restore a stable, anatomical joint surface by direct and independent fixation of each major fracture fragment. As a general rule, fragment-specific fixation is a load-sharing construct in which each fracture element is pieced back together into a unified composite structure. Fragment-specific implants are intentionally designed to be extremely low profile and conform to the local surface topography at the site of application, avoiding the need for bulky plates that can irritate tendons or large distal screw holes that can cause further comminution of small distal fragments. Another goal of treatment is to achieve enough stability to allow motion immediately after surgery.

FIGURE 12-2 Fragment-specific implants. A, Radial pin plate for radial column fixation. B, Volar buttress pin for volar rim fixation. C, Ulnar pin plate for ulnar corner fixation. D, Small fragment clamp for dorsal wall fixation. E, Dorsal buttress pin for dorsal wall and free intra-articular fragment fixation. F, Small fragment clamp/buttress pin for combined dorsal wall and free intra-articular fragment fixation.

In some ways, fragment-specific fixation has certain similarities to simple, multiple Kirschner wires (K-wires). In each technique, individual fragments are reduced and secured to the proximal shaft. In each technique, a goal of treatment is to restore normal anatomy to the articular surface. Furthermore, each technique avoids extensive dissection and wide osseous exposure of the distal surface and eliminates fixation that depends on thread purchase in small distal fragments. Fragment-specific fixation, however, has some significant differences to fixation with multiple K-wires because it achieves a stable, load-sharing construct of the fracture components, allowing immediate motion without a cast postoperatively. In addition, fragment-specific fixation avoids potential problems of pin tract irritation and pin site infection, as well as the need to perform a second procedure to remove K-wires.

Fragment-Specific Implants

The radial border of the distal radius is often involved as a major component of distal radius fractures. In most cases this area breaks as the radial column, a single piece of bone that includes the scaphoid facet, the radial styloid, and the osseous pillar that extends proximally to the distal attachment of the brachioradialis tendon. The radial column is typically a large fragment that includes the orthogonal surfaces of the dorsal, radial, and volar cortices and is often a significant fracture element. Although trans-styloid pinning of the radial column is a simple technique, it usually results in rather tenuous fixation because stability is dependent on the stiffness of the K-wire as well as the purchase by the tip of the wire in the far cortex of the proximal fragment. Bending or small amounts of angulation of the K-wire at the site of purchase in the far cortex can result in significant shortening and displacement of the radial column fragment.

The radial pin plate is a fragment-specific implant designed specifically for stable fixation of the radial column fragment. Mechanically, this implant acts as an outrigger to add a second point of constraint to the pin at its entry site on the surface of the unstable radial column fragment. As a result, proximal drift of the K-wire is prevented because pin failure from bending or angulation at the site of purchase in the far cortex is eliminated. The radial pin plate creates a rigid pin construct that triangulates fixation to both near and far cortices of the proximal fragment. Because this maintains the length of the radial column, the carpus is held out to length, preventing collapse of the proximal carpal row into remaining unstable fragments within the lunate facet.

Although the primary function of the radial pin plate is to provide rigid fixation of the radial column, the radial pin plate has a secondary role that can also help with stabilization of many articular fractures. Although the plate is thin, because it is applied along the plane of the radial border, it is extremely stiff in resisting bending moments caused by flexion and extension movements of the wrist. Moreover, the radial pin plate is slightly overcontoured to the curve of the radial border and flattens like a leaf spring against the bone as it is secured to the proximal fragment. This causes the plate to push the distal fragment toward the ulna, locking intra-articular fragments in place and improving DRUJ stability by seating the ulnar head within the sigmoid notch of the radius. Because this property of the radial pin plate is quite effective in securing intra-articular fragments in whatever position they happen to be, it is generally a good idea to ensure that articular fragments are first fully reduced before securing the radial pin plate to the proximal fragment.

Although radial shear fractures are relatively uncommon, it should be noted that these injuries do not generate a typical radial column fragment. In this fracture pattern, the carpus translates radially, causing a failure in shear across the tip of the radial styloid. Radial shear fractures have a characteristic radiographic image that shows a small triangular fragment that involves only the tip of the styloid; unlike the true radial column fracture, the fracture line does not extend proximally into dorsal, radial, and volar cortical surfaces. These injuries are associated with significant shear damage to the articular surface and often have free chondral fragments present in the joint as well as ligamentous tears within the carpus. In addition, injury to the TFCC and/or ulnar styloid is often observed with this pattern of injury. Although a radial pin plate can effectively stabilize radial shear fractures, in healthy bone satisfactory fixation can often be simply achieved with one or two screws.

The ulnar pin plate is a fragment-specific implant that is designed for dorsal fixation of the ulnar corner fragment. This fragment includes the dorsal portion of the sigmoid notch and is typically the result of axial impaction of the lunate against the dorsal surface of the lunate facet. The ulnar corner fragment displaces proximally and dorsally and can cause problems with DRUJ function. Although sometimes this fragment can be quite small, the fracture line nearly always extends to the radial side of the dorsal insertion of the DRUJ capsule. The ulnar pin plate should be used with an interfragmentary pin that penetrates the ulnar corner fragment and is directed proximally and slightly radially to engage the volar cortex of the shaft proximally. Like any plate placed dorsally along the ulnar border of the radius, a 15-degree torsional bend should be added proximally to the plate to match the twist of the dorsal surface of the radial shaft. In addition, the ulnar pin plate may also be used for fixation along the central or radial aspect of the dorsal wall.

Dorsal wire forms (buttress pin, small fragment clamp, and combined wire forms) are prebent 0.045-inch K-wires designed for stabilization of dorsal and free articular fragments. These implants are easily adapted for variations in the size and location of independent fragments. The buttress pin can be simply inserted like a clip and then used as a joystick to reduce and fix a dorsal fragment. Alternatively, the buttress pin can be easily applied through a dorsal defect behind free articular fragments to sandwich them against the proximal carpal row. Other dorsal wire forms include the small fragment clamp that can grab and stabilize dorsal wall fragments and the combination small fragment clamp/buttress pin that can address combined dorsal wall and free articular fragments. These implants may be supplemented with dorsal bone graft to provide additional support behind the distal articular surface.

The volar buttress pin is an implant that is designed for unstable fragments that involve the volar rim. Fragmentation of the volar rim is usually the result of either a volar shear or axial loading mechanism. If the volar rim fragment is small, plate fixation can be inadequate; flexion or axial loading of the wrist can cause this fragment to displace over the edge of the plate, carrying the carpus with it into the palmar soft tissues. Alternatively, if the volar rim fragment is dorsiflexed with a depressed teardrop angle, plate fixation may further aggravate the angular deformity by pushing up on the volar surface of the fragment. The volar buttress pin is often a simple, effective solution for these complicated problems. Like the dorsal buttress pin, the legs of the volar buttress pin can be driven like a clip into the volar rim fragment and the implant then used as a joystick to manipulate and correct the position and angular deformity of the fragment. Once reduction is achieved, the wire form is simply fixed proximally with two screws and washers or a small wire plate.

Fragment-specific implants can also be used to treat certain types of distal ulna fractures when indicated. The ulnar pin plate can be used to stabilize displaced fractures through the base of the ulnar styloid or ulnar head. Wire forms can also be used when indicated on the ulnar side.

Of course, it is possible to augment standard volar or dorsal plating techniques with fragment-specific implants when needed. For instance, a dorsal wire form can supplement a fixed-angle volar plate by securing an unreduced or unstable dorsal or free articular fragment. As another example, a radial column plate can be used as supplemental fixation to a volar plate to add stability to a radial column fragment or to push the distal fragment radially to close the DRUJ.

Fragment-specific fixation has the flexibility to address many different types of fracture patterns. Initially, this simple ability to mix and match implants to the characteristics of the fracture may seem a bit overwhelming. However, fragment-specific fixation is really nothing more than a complete set of tools that has the capability to address a variety of different fracture patterns. For many patterns, there are standardized algorithms that can be used for treatment and will be discussed in the next sections.

Surgical Approaches

Radial Palmar Exposure

The surgical approach to apply a radial pin plate and volar buttress pin can be called “radial palmar” not only because of the implant locations but also because of the incision (Fig. 12-3). Typically, a 7-cm linear incision is made on the “radial palmar” aspect of the distal forearm, extending proximally from the level of the radial styloid.¹¹ The incision is about halfway between the true midlateral line of the forearm and its palmar surface. Another way to situate the incision is to feel the radial artery pulse and make the incision a little radial to this landmark.

FIGURE 12-3 Radial palmar incision. A, Initial exposure with incision between the radial artery and the first dorsal compartment tendons. The tip of a tenotomy scissors is placed along the superficial surface of the first dorsal compartment sheath proximally and swept distally to elevate a skin flap that includes the sensory nerves along the radial border of the wrist. B, Completion of the radial column exposure by releasing the first dorsal compartment sheath proximally, leaving the distal 1 cm intact and reflecting the insertion of the brachioradialis. APL, abductor pollicis longus; EPB, extensor pollicis brevis; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis. Inset, Surgical photograph with radial pin plate applied through radial palmar incision.

Longitudinal blunt dissection is carried out through the subcutaneous fat, and the numerous branches of the radial sensory nerve and the termination of the lateral antebrachial cutaneous nerve are identified and retracted. Although some patients may have quite a network of large and small sensory branches, these nerves can be retracted safely while still gaining adequate exposure to reduce and stabilize the fracture. Keep in mind that whenever K-wires or drill bits are used, soft tissue guides must be employed to prevent inadvertent damage to these sensory nerves (or other soft tissues structures).

The first extensor compartment is next identified and released to mobilize the abductor pollicis longus and extensor pollicis brevis tendons either dorsally or palmarly for exposure of the fracture segments. The extensor pollicis brevis usually has a separate subsheath that can be released. It is prudent to leave the last centimeter or so of the first extensor compartment sheath intact to reduce the likelihood of tendon subluxation postoperatively. The first compartment extensor tendons can be retracted dorsally, which will allow easy visualization of the brachioradialis tendon as it inserts at the base of the radial styloid in the midlateral plane.

The brachioradialis should be released for two reasons. Its insertion obscures access to the radial column fracture site and it must be released completely to allow mobilization of this segment. Additionally, the brachioradialis produces a deforming force on the radial column fracture and release of this tendon insertion reduces the tendency for subsidence of the fracture. The brachioradialis insertion becomes the floor of the first extensor compart ment, and at the margins of the radial styloid prominence it blends into the first extensor compartment tendon sheath.

Once the brachioradialis has been released, dissection should be directed at the palmar side of the first extensor compartment’s palmar sheath. Dissection should hug the palmar surface of the tendon sheath and stay radial to the radial artery, which is within a centimeter of the sheath, running parallel. The radial artery runs adjacent to the incision’s ulnar margin, although at the distal part of the wound the artery starts to angle toward the base of the thumb metacarpal; and, for this reason, care should be exercised when dissecting in the distal part of the incision, where the artery starts to run across the incision line rather than parallel to it. As dissection proceeds toward the radial styloid’s cortical surface, the artery and the radial insertion of the pronator quadratus can be swept ulnarly. It is possible to use a blunt elevator to expose the radial styloid and the entire palmar surface of the distal radius. A wide blunt retractor is ideal to safely retract the pronator quadratus, the median nerve, and flexor tendons palmarly and ulnarly so that the entire radial and palmar aspect of the distal radius can be visualized directly.

Closure of the wound is accomplished via suturing the subcutaneous layer and skin closure. Care should be taken to protect radial sensory nerve branches from entrapment during closure. The first extensor compartment tendons are allowed to return to their native positions, but repair of the tendon sheath is unnecessary. It should also be noted that repair of the brachioradialis is similarly not warranted.

Dorsal Exposure

Access to the dorsal aspect of the distal radius is required to address dorsal wall and ulnar corner fragments, as well as impacted free articular fragments. A dorsal exposure can also be used to aid in the reduction of particularly impacted radial styloid fragments or help elevate and use bone grafts in depressed articular segments. The dorsal incision is longitudinal and typically 5 cm long, located about 1 cm radial to the ulnar head and ending about 1 cm distal to the radiocarpal joint line (Fig. 12-4). Although there are fewer sensory nerves deep to this incision compared with the radial palmar region, care should be taken to pursue blunt dissection until the extensor retinaculum is encountered. There are usually a few large veins that can be either retracted or cauterized. The retinaculum overlying the fourth extensor compartment is next opened longitudinally, and the common digital extensor (and extensor indicis proprius and extensor digiti quinti) tendons can be retracted ulnarly to expose the dorsal metaphyseal area. The extensor pollicis longus should be mobilized by releasing the retinaculum proximally in a longitudinal fashion; often the retinaculum overlying Lister’s tubercle can be left in place and the extensor pollicis longus can be satisfactorily retracted radially. Occasionally, it can be helpful to fully release the extensor pollicis longus from Lister’s tubercle, thereby allowing it to be retracted farther radially. This is particularly helpful when the dorsal wall fragment extends radially and involves Lister’s tubercle as part of the fracture pattern.

FIGURE 12-4 Dorsal incision. Longitudinal incision is made dorsally and extends about 1 cm beyond the distal border of the radius. Retinaculum is incised over the fourth dorsal compartment. Inset, Dorsal incision showing placement of ulnar pin plate and dorsal buttress pin.

Exposure of the dorsal fracture fragments requires patience and attention to detail. Although this part of the surgery does not need to take more than 10 minutes, two critical issues must be addressed to allow placement of the appropriate hardware. First, the soft tissue around the dorsal fragments must be released enough to enable both good direct visualization as well as adequate mobility of the individual fragments so that they can be reduced. Use of a small elevator is helpful to pry apart any hematoma, incipient fracture callus, and periosteal attachments so that dorsal fracture pieces can be clearly identified. Sometimes it is even necessary to free up the retinacular extensions of the second compartment tendons (wrist extensors) as well as transpose the extensor pollicis longus radially so that the dorsal wall and region around Lister’s tubercle can be more easily treated.

The second critical issue relating to the exposure of dorsal fracture segments relates to identifying the proximal fracture perimeter. Fragment-specific fixation implants depend on a base of fixation that is anchored in the solid cortical bone proximal to the fracture; with the dorsal exposure, the shaft of the radius proximal to all fracture lines must be accessible. This can be facilitated by placing a narrow Hohmann retractor in the radial aspect of the wound, wrapping around the proximal, radial margin of the radial shaft. This maneuver will nicely demonstrate the step-off between the shaft of the radius and dorsal fracture fragments, which are usually buckled into each other and elevated dorsally by hematoma and comminution.

The terminal sensory branch of the posterior interosseous nerve is easily seen running just ulnar along the base of Lister’s tubercle. Many surgeons will choose to intentionally transect this nerve at the most proximal margin of the wound to reduce the likelihood of developing a painful neuroma due to compression from either scar formation or metal implants.

Once fracture reduction and fixation have been accomplished, closure of the dorsal wound is routinely accomplished in two layers, with absorbable sutures for the subcutaneous fat layer followed by skin closure.

Fracture Patterns

Extra-articular Fracture

This is the typical “Colles’” pattern, which is a purely metaphyseal fracture that does not have a radiocarpal fracture extension. Whereas many fractures can be treated with a closed reduction and cast, this fracture type can benefit from internal fixation if there is palmar displacement or if dorsal displacement is significant and cannot be reliably controlled with other methods. Additionally, radial column shortening often occurs in older patients or when the initial injury mechanism includes axial loading; and if radial shortening progresses more than 5 mm, operative correction may be warranted in select cases.

Internal fixation of the metaphyseal fracture segment can be accomplished through a single, radial palmar incision. A secure construct and anatomical reduction can be achieved by using a radial pin plate and a volar buttress pin (Fig. 12-5). The radial pin plate restores radial column length, and the volar buttress pin prevents dorsal or palmar translation. The volar buttress pin also has the effect of anatomically reducing the thick cortical margin on the palmar surface of the radius, which helps resist the tendency for proximal subsidence of the metaphyseal segment. It should also be noted that a key effect of the radial pin plate is application of a medially directed vector on the metaphyseal segment, which not only aids in restoration of radial length but just as importantly reduces the DRUJ and allows the cortical perimeter of the distal radius to be anatomically reduced, adding stability to the whole construct. This fracture can be visualized like the top of a rectangular box that has been sawed off and the box top then slides a little sideways and has one or two sides overhanging the base. Exact realignment of the box top allows all four sides of the top to contact the base edges and provides four sides of support.