Distal Radius Fractures: External Fixation

Michael W. Grafe

Paul D. Kim

Melvin P. Rosenwasser

Distal radius fractures are one of the most common injuries in clinical practice. They tend to occur in a bimodal fashion with a peak associated in children and adolescents as well as elderly patients. Nonarticular fractures of the distal radius and most epiphyseal fractures in children are typically treated, with predictable success, by cast immobilization. With increasing age, osteoporosis and falls lead to fragility fractures of the distal radius, particularly in women. These fractures often have significant fracture comminution with instability, making closed treatment less successful. In young patients with normal bone stock, these fractures are often caused by motor vehicle accidents or a fall from a height, and they often result in highly comminuted fracture patterns. While many of these fractures can be reduced by closed means, comminution and instability lead to loss of reduction and malunion.

The inability to maintain fracture alignment by closed reduction and casting defines fracture instability. Many authors have proposed criteria to predict which fracture patterns are inherently unstable and may benefit from surgical treatment. Lafontaine et al (1) proposed five factors that indicated fracture instability: (a) initial dorsal angulation greater than 20 degrees, (b) dorsal comminution, (c) radiocarpal intra-articular involvement, (d) associated ulnar fractures, and (e) age greater than 60 years. In their experience, patients with three or more of these factors had a high incidence of reduction loss with cast treatment. Nesbitt et al (2) used the criteria of Lafontaine et al and determined that age was the only significant risk factor in predicting instability. In patients over the age of 58 years, there was a 50% risk for secondary displacement, while patients over 80 years had a 77% increased risk. In addition to the Lafontaine factors, carpal malalignment and postreduction incongruity (the combination of articular step-off and fracture gap) have been shown to have a negative impact on functional outcome (3,4).

In the past decade, new implants for fixation of unstable distal-radius fractures have become available, especially the use of anatomically designed plates for the volar, radial, and dorsal aspects of the radius. In the past, external fixation had been the workhorse for unstable distal-radius fractures which had been judged to be too unstable for cast treatment. With
advances in internal fixation, external fixation is used more commonly as an adjunctive procedure to other fixation techniques. These techniques include Kirschner (K) wire fixation, Kapandji pin technique, arthroscopically assisted articular-surface reduction (5) and the placement of fragment-specific miniplates. These techniques are frequently augmented with metaphyseal bone fillers such as cancellous allograft chips and hydroxyapatite cement. Thus, external fixation devices that span the fracture can be used to neutralize the forces around the wrist and to protect the fracture reduction obtained by other direct or indirect means.

In some cases a non–joint-spanning external fixator can be used as both the reduction tool and the neutralization device. This is accomplished through the use of dorsally applied half pins which can directly manipulate and reduce displaced fragments. This construct combines the principle of Kapandji, dorsal, and blocking pins with the security of half pins locked to the frame. It also improves restoration of palmar tilt, which is difficult to accomplish with spanning frames (6).

Clinical Evaluation

A careful history and physical examination, including information gathering on hand dominance, occupational requirements, medical co-morbidities, and patient expectations, are important factors in crafting a treatment strategy. The mechanism of injury and a careful examination of the limb allow the surgeon to assess soft-tissue integrity. Any signs or symptoms of increased compartment pressure or evolving neurological deficits mandate that any splints or cast be removed for more precise evaluation and treatment. Furthermore, it is necessary to check the forearm and elbow for instability and the possibility of combined fracture-dislocation patterns such as Galeazzi, Monteggia, or Essex-Lopresti injuries. The carpus should be carefully palpated to determine if any focal sources of pain or deformity can be found in carpal injuries or dislocations. The hand should also be carefully evaluated for signs and symptoms of injuries to the metacarpals and phalanges.

Careful, systematic examination of the hand for sensation and motor integrity should be documented and the results assessed. The encompassing, and often incorrect assumption of “neurovascularly intact,” should not be used when evaluating patients with a distal radius fracture.

Unrelated, but often present, osteoarthritis of the digits, especially the basal joint of the thumb, should be noted. Often joints with preexistent stiffness are adversely affected by the postfracture swelling, pain, and immobilization, and as a result hand function is compromised.

Acute, concomitant tendon injuries are rare following closed distal-radius fractures. However, the surgeon should caution patients about the small risk of late, extensor pollicis longus (EPL) tendon ruptures.

Extrinsic motor function can be simply assessed by asking the patient to grasp, and to confirm anterior interosseous nerve integrity, by paying particular attention to the flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) to the index finger. Abducting and adducting the second ray will confirm ulnar-nerve intrinsic function. Tip pinch will confirm median nerve thenar function.

Imaging

Following falls or injuries to the wrist, anteroposterior (AP) (7), lateral, and oblique radiographs should be obtained. True lateral x-rays of the wrist are more difficult to obtain when the wrist is immobilized in flexion and ulnar deviation. Contralateral films can be helpful in assessing the normal radial and ulnar lengths as well as radial inclination of the wrist.

A critical review of the initial injury films can be useful in predicting the magnitude of the forces involved as well as the displacement and comminution. Traction films obtained in the emergency room or operating room will allow assessment of articular incongruities such as scaphoid or lunate die-punch injuries. Traction films can also reveal subtle, combined, carpal bone and or ligamentous injury (i.e., transradial styloid-perilunate instability).

Ulnar styloid fractures occur in more than one half of all distal-radius fractures. Although most ulnar styloid fractures heal uneventfully with a fibrous union, some ulnar-styloid fractures are associated with distal radioulnar joint (DRUJ) instability. Ulnar styloid fractures that occur through the base and those displaced greater than 2 mm have highest likelihood of associated DRUJ instability (8). However, DRUJ stability is assessed following stabilization of the radial fracture.

Parameters of acceptable reduction are restoration of radial length to within 2 to 3 mm of uninjured wrist. Radial inclination is approximately 21 degrees and radiocarpal congruence is within 1 mm. The lateral view should demonstrate a collinear relationship with the radial shaft and lunocapitate axis: There should be no more than 5 to 10 degrees of articular dorsal tilt and preferably neutral or inclined toward the normal 10-degree palmar tilt.

Carpal alignment will generally follow the gross reduction of the distal radius. Residual angular or rotational instability, such as dorsal, intercalated, segment instability (DISI), is usually a sign of laxity of the extrinsic capsular ligaments, which can occur secondary to a loss of axial length or from rupture. The peri-articular shear fractures, either dorsal or palmar, are essentially ligamentous injuries that require secure repositioning of the fracture to effect stable reduction. Assessment of the break in the carpal arcs, as described by Sarmiento et al (9), should be recognized; these breaks may be unmasked by traction films taken in the emergency or operating room.

Computerized tomography (CT) scans are not routinely necessary for preoperative planning. In fact, standard two dimensional CT scans done prior to reduction may create more confusion in interpreting the position of unstable, unreduced fragments. We prefer a traction film taken in the operating room for its simplicity in preoperative planning.

Treatment Paradigm

Based on a careful history and physical examination, as well as a thorough review of the radiographs, surgical or nonsurgical treatment is recommended. Based on criteria elaborated previously, we attempt to identify stable and unstable fracture patterns. The ultimate treatment plan is based upon the patient’s expectations, functional requirements, and medical conditions; each plays a role in the indication for surgery. With regard to marked loss of radial length, radial inclination, and reversal of palmar tilt, numerous studies have shown measurable deficits in the objective and subjective outcomes following cast treatment. These differences in outcomes are magnified when loss of articular congruence and carpal subluxation are found (3,4). Treatment decisions should be made in the context of the entire person and not on the radiographic findings alone.

Most patients with displaced distal-radius fractures seen in the emergency room undergo a closed reduction and application of a sugar tong splint with application of a Bier block or a fracture hematoma injection. If a hematoma block is used, one must remember to also inject the ulnocarpal joint to achieve complete anesthesia of the injury. The ulnar side of the wrist joint is almost always involved in a distal radius fracture through an ulnar styloid fracture or peripheral triangular, fibrocartilage complex (TFCC) tear.

Nonsurgical treatment can be considered if postreduction radiographs show restoration of radial length, minimal loss of palmar tilt, and most important, good cortical apposition and minimal fracture comminution. The wrist is held in slight flexion, ulnar deviation, and neutral forearm rotation. Weekly follow-up x-rays for the first 3 weeks are necessary to guard against loss of reduction. The palmar extent of the cast must always be contoured to allow for full metacarpal-phalangeal joint flexion. Casting usually continues for 6 weeks followed by transitional splinting with a removal prefabricated splint. If finger motion can be maintained, then little formal occupational therapy is required. If stiffness or swelling in the immediate postreduction period is significant, then supervised occupation therapy is recommended.

If the fracture is deemed unstable by the criteria of Lafontaine (1), then surgical management is indicated in all but the most elderly or infirm. In most cases, it is better to perform primary osteosynthesis rather than late three-dimensional osteotomy and grafting.

Although most unstable distal-radius fractures can be treated with external fixation, few should be treated with a spanning construct alone. The fracture morphology usually will dictate if additional or augmented fixation is necessary (10

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