Anatomy and Functional Biomechanics

The meticulous histological analysis of the radioulnar ligaments by Nakamura and colleagues¹ reveals two predominant attachments to the distal ulna: the fovea and the base of the ulnar styloid process. The foveal attachment—just radial to the base of the ulnar styloid—is over a broad area and gives rise to near-vertical fibers. The styloid base attachment is over a smaller area, and its fibers are orientated horizontally. Both attachments are dense in Sharpey’s fibers. The foveal and styloid base fibers coalesce and then divide to embrace the palmar and dorsal edges of the proximal portion of the articular disc.

Isolated sectioning studies of the ulnar insertions of these structures have shown that each part plays an equal role in stability when no load is applied across the wrist. One of the primary functions of the distal ulna, however, is as a weight-bearing joint (Fig. 28-1); and when these sectioning studies are repeated under load, the foveal attachment of the radioulnar ligament is found to contribute significantly greater stability to the DRUJ than the styloid attachment.² This view would be supported by the proximity of the fovea to the rotation axis of the forearm, making it more likely that this is the critical part of the radioulnar ligament’s bony anchorage under dynamic conditions.

FIGURE 28-1 Force transmission through the DRUJ.

No direct bone/ligament connection has been identified over the styloid process from its midportion to the tip, although fibers do originate from the hyaline cartilage to coalesce with a somewhat lax sleevelike structure that some investigators refer to as the “ulnar collateral ligament.”

Ulnar Head Fractures

Ulnar head fractures are rare, occurring in only 6% of all wrist fractures.³ The frequency of each fracture configuration is shown in Figure 28-2. More recently, distal ulnar fractures have been classified according to the Comprehensive Classification of Fractures with an associated Q modifier (Fig. 28-3).⁴

FIGURE 28-2 Incidence of ulnar head fractures.

FIGURE 28-3 Incidence of distal ulnar fractures.

The risk of disabling complications in this injury is unlikely to be DRUJ instability. The attachments of the triangular fibrocartilage complex (TFCC) usually remain undisturbed. These articular fractures will give rise to the usual risks of this group of injuries. Coexistent fractures of the distal radius and ulna significantly increase the incidence of radial nonunion.⁵ Indeed, this is the most likely circumstance in which the unusual complication of radial nonunion will be seen (Fig. 28-4). In spite of this knowledge, combined distal radius and ulna fractures continue to be managed by treating the radius alone.

FIGURE 28-4 Radial and ulnar nonunion occurring when only one bone is stabilized. A, After K-wire stabilization of the radius fracture. B, Displaced nonunion after K-wire removal.

Indications

Displaced or potentially unstable ulnar head fractures require accurate reduction and stabilization. These injuries should be recognized early and treated, ideally, within 7 days of injury.

Standard radiographs will provide most of the information about the fracture pattern (Fig. 28-5). Computed tomography (CT) may be necessary on occasion to fully evaluate the injury.

FIGURE 28-5 Plain radiograph clearly outlines articular fracture pattern.

The advent of angularly stable small locking plates allows patients of all ages to be considered for internal fixation, irrespective of their bone quality.

Surgical Technique

General or regional anesthesia is required. Contrary to previous reports,⁶ regional anesthesia is a safe and comfortable technique that can allow treatment on an outpatient basis.

The affected arm is placed on an arm table. The tip of the ulnar styloid is easier to expose when the forearm is placed in pronation. For this reason, the surgeon may choose to sit at the cranial edge of the arm table. If a distal radius fracture coexists, the surgeon will most likely choose to sit at the caudal edge of the arm table. It is therefore essential that the operating equipment (including mini-C-arm intensifier) is arranged in such a way that surgeon and assistant can move freely around the arm table during surgery.

An upper arm tourniquet is applied. The limb should be prepared and draped to the level of the tourniquet cuff. Intravenous prophylactic antibiotics are recommended immediately preoperatively.

A straight longitudinal incision along the course of the subcutaneous distal ulna is recommended. The dorsal sensory branch of the ulnar nerve lies immediately underneath the skin at the level of the ulnar neck. Extreme care must be taken to avoid this structure in the initial surgical approach.

The approach is deepened ulnar to the sixth extensor compartment to enable the stabilizing implant to be applied on the surface of the distal ulna between the tendons of the flexor carpi ulnaris and extensor carpi ulnaris. It is unusual to need to visualize the articular fragments directly, but in these rare instances a second approach can be made using the same skin incision but passing through the floor of the fifth extensor compartment. Retraction of the tendon of the extensor digiti minimi will allow direct inspection of any articular fragments.

Reduction of the fracture fragments is best performed indirectly using a small angularly stable implant. If reduction is attempted using pointed reduction forceps, the thin cortical bone of the ulnar head often fragments under load, leading to further comminution and possible failure.

The implant is best placed on the medial border of the ulna directly in line with the ulnar styloid. This acts as a buttress for the distal radius to be reduced onto (Fig. 28-6), in this case utilizing a specially designed implant for treating distal ulnar fractures.

FIGURE 28-6 Use of a specially designed low-profile locking plate for a distal ulnar fracture.

Clinical testing of DRUJ stability will reveal if a coexistent unstable TFCC tear is present.

An above elbow cast or sugar tong splint is applied with the elbow flexed to 90 degrees and the forearm in neutral rotation. Early movement is begun depending on stability of fixation.

The skin overlying the distal ulna is thin. As a result, implants placed here are frequently palpable—and may give rise to discomfort. A low threshold for implant removal, once union is certain, is recommended.

Clinical Examples

Case 1

A 77-year-old woman presented after a fall with a painful and deformed wrist. The initial radiographs reveal a displaced articular fracture of the distal radius and a minimally displaced long oblique extra-articular fracture of the distal ulna (Fig. 28-7A, B). Initial treatment consisted of the application of a bridging external fixator. The surgeon clearly concentrated on the reduction of the distal radius fracture, but—in the absence of an intact ulnar buttress—displacement of the unstable ulnar fracture was inevitable (see Fig. 28-7C, D).

FIGURE 28-7 Case 1. A and B, Fractures of both distal radius and ulna. C and D, After application of a bridging external fixator to the distal radius only. E, After ORIF of both bones with angularly stable implants.

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