Ulnar Head and Styloid Fractures

INTRODUCTION

The distal ulna is an important weight-bearing component of the wrist joint and an essential element of the forearm articulation. After injury, significant residual malalignment or deformity of the distal ulna and deficiency of its ligamentous support have a deleterious effect on grip strength and forearm rotation.

Fractures of the distal portion of the ulna occur in isolation as a result of a rotational force applied to the wrist or as a result of a direct blow to the ulnar aspect of the distal forearm (nightstick fracture). Isolated ulnar styloid fractures are mostly benign and are treated by nonoperative means. Isolated fractures of the articular portion of the distal ulna are rare and should be treated operatively only if irreducible articular displacement causes a mechanical block to forearm rotation. Isolated fractures of the distal third of the ulnar shaft can be treated successfully by nonoperative means if not significantly displaced and if rotational malalignment is not present. Fractures with significant displacement or those with rotational malalignment (displaced spiral fracture patterns) are best treated by osteosynthesis and functional rehabilitation in order to prevent loss of forearm rotation.

It is important to note that fractures of the distal portion of the ulna that are associated with ligamentous injuries of the distal radioulnar joint (DRUJ) commonly occur concomitantly with distal radius fractures. These ulnar-side lesions may include fractures of the ulna, the ulnar styloid, or the rim of the sigmoid notch of the radius and/or ligamentous injuries such as a rupture of the triangular fibrocartilage complex (TFCC), tear of the ulnocarpal ligaments and, rarely, tear of the radioulnar interosseous ligament. These injuries may result in significant functional impairment if not addressed properly. Therefore, it is important for the surgeon treating distal radius fractures to recognize the presence of these concomitant lesions, understand their significance, and treat them appropriately.

BASIC SCIENCE

In the context of a distal radius fracture, concomitant injury to the distal ulna and DRUJ is the result of residual traumatic forces that have not dissipated even after the distal radius has fractured; this injury can cause further damage after the radius has fractured. We describe here in stages the most common developmental pattern of the ulnar-side injury that accompanies a distal radius fracture.

Stage One: When a strong impact is absorbed by the hand, as during a fall from a height, the hand transmits the impact energy to the carpal bones. These in turn relay the load to the distal articular surface of the radius. If the amount of energy is sufficient and the distal radius is the weakest link in the upper extremity skeletal chain, which is the most common situation, then it fractures. Any further application of energy then progressively displaces the distal radial fragment(s) until its ligamentous attachments to the still-intact ulna become stressed ( Fig. 15-1 A). Because collagen fibers and therefore ligaments cannot tolerate more than 6% deformation without rupturing, most distal radius fractures that remain in this first stage of ulnar-side injury are minimally displaced.

FIGURE 15-1

Stages in the development of a concomitant distal radioulnar joint (DRUJ) fracture. A, In the first stage of injury, the radius has fractured, and tension is being applied on the ligaments attaching the distal radial fragment to the still intact distal ulna. B, In the second stage, the triangular fibrocartilage complex has ruptured and the extensor carpi ulnaris tendon sheath has avulsed the ulnar styloid process. C, In the third stage, the distal radial fragment has displaced farther, and the distal ulna now absorbs the energy of injury and fractures.
Stage Two: As more energy is delivered to the hand, the ligaments attaching the distal radial fragment(s) to the ulna, the TFCC, and the sheath of the extensor carpi ulnaris (ECU) tendon rupture, allowing the distal radial fragment(s) to displace in an unrestricted manner ( Fig. 15-1 B). If the displacement is severe enough, the ulna even may perforate through the volar skin, creating a compound fracture. The deep fiber of the TFCC inserts mainly into the ulnar fovea. The superficial components of the TFCC attach variably into the base of the ulnar styloid. On the other hand, the ECU tendon sheath invariably originates from the middle and distal aspect of the ulnar styloid. The tendon of the extensor carpi ulnaris is enclosed in an independent fibrous tunnel formed by the supratendinous retinaculum superiorly, the infratendinous retinaculum inferiorly, the sixth septum laterally, and the ulnar insertion of the retinaculum reinforced by longitudinal fibers called the linea jugata medially. The common concomitant avulsion fracture of the ulnar styloid occurs at this stage and is usually the result of tension applied by the extensor carpi ulnaris tendon sheath and only rarely by the TFCC. This interpretation is substantiated by histologic studies of ligament insertion sites as defined by the presence of Sharpey’s fibers (William Sharpey, 1846). In this second stage of the injury process, the only surviving stabilizer of the DRUJ is the distal portion of the interosseous forearm ligament, or distal interosseous ligament (DIOL). This structure is a secondary stabilizer; its anatomy is constant, and it behaves in an isometric manner during forearm rotation. The DIOL inserts on the radius proximal to the sigmoid notch and proximal to the location of the fracture line in most distal radius fractures. It also originates from the ulna at a substantially more proximal level, precisely where the axis of forearm rotation intersects the surface of the ulna. Because the DIOL survives intact in the majority of distal radius fractures and provides enough stability in an intact skeleton to allow stable forearm rotation, it is of great importance in the management of their concomitant ulnar-side injuries.
Stage Three: As more energy is delivered to the hand, the distal ulna becomes the most prominent structure on the volar aspect of the wrist and directly absorbs the energy of injury. If sufficient energy is available, the ulna now fractures ( Fig. 15-1 C). This fracture can occur at its articular, neck, or diaphyseal portions and can also occur distal or, proximal to the ulnar origin of the DIOL. Nonetheless, this last structure commonly remains intact.

Although the pattern just described is the most common injury sequence during a distal radius fracture, other less common variations can result in rupture of the DIOL and therefore in instability of the DRUJ. These alternate injury patterns can occur with or without a concomitant ulnar fracture.

The interosseous membrane remains intact after most distal radius fractures. Anatomic reduction tightens the interosseous membrane and approximates the torn edges of the TFCC and extensor carpi ulnaris. There is no need to fix ulnar styloid fractures, since sufficient stability allows for early forearm rotation.

A retrospective study of 200 surgically treated distal radius fractures in 194 patients was performed. Of these patients, 182 had 6 months’ minimum follow-up in which radiologic assessments of the fracture were made using Sarmiento-Lidstrom’s and Stewart-Gartland and Werley’s scoring systems. Distal radius fractures were classified according to the AO/ASIF classification, and ulnar styloid fractures were classified according to displacement, fragment size, and nonunion. Four subgroups were formed to describe ulnar styloid fractures: (1) no ulnar styloid fracture; (2) ulnar styloid fracture; (3) basilar ulnar styloid fracture; (4) ulnar styloid fracture nonunion. Of the 194 patients, 63% showed a fracture of the styloid or ulna accompanied by a distal radius fracture (54% isolated ulnar styloid fractures, 9% fractured ulna). The remaining 37% did not present an ulnar styloid fracture in the original x-rays, but 15% of these patients showed evidence of ulnar styloid fractures in later x-rays. Of the 63% of patients with a clearly present ulnar styloid fracture, 14% were basilar, and 48% were nonunions.

Functional, radiographic, and subjective information was used in the process, and no arthroscopies were performed. The unpaired t test and the chi-square test were applied for statistical analysis. Range of motion and grip strength were measured in all cases. The range of motion of the patients with an ulnar styloid fracture (63%) showed an average flexion of 82%, extension of 70%, radial deviation of 69%, ulnar deviation of 73%, pronation at 88%, supination at 84%, and grip strength of 85% as compared to the other hand. The 37% of patients who had no original ulnar styloid fractures or none at all showed flexion of 87%, extension of 72%, radial deviation of 67%, ulnar deviation of 76%, pronation at 95%, supination at 89%, and grip strength of 79% compared with the other hand. The majority of patients who sustained an ulnar-side injury lost some flexion and pronation.

Most distal radius fractures treated with an internal fixation present an ulnar-side injury. Nonunion of ulnar styloid fractures is common. No clinically significant DRUJ instability was seen in this series. The precise restoration of radial length may decrease the need for internal fixation of large styloid fragments. Internal fixation of a basilar ulnar styloid fracture is not needed if the DRUJ pivot shift test is negative after anatomic reduction. No positive result from postreduction DRUJ pivot shift test was seen. A positive result of this test is probably caused by either an anatomic defect of the sigmoid notch or a rupture of the distal aspect of the interosseous membrane.

RATIONALE FOR TREATMENT

Because the forearm is one articulation with two condyles—the proximal and the distal radioulnar joints—anatomic and stable osteosynthesis of displaced fractures of the radius and/or ulna is frequently recommended to correct articular malalignment and permit functional rehabilitation. Similarly, significantly displaced unstable fractures of the distal radius with an intact ulna, which are invariably accompanied by DRUJ subluxation, should be treated with anatomic and stable osteosynthesis of the radius. Restoring the radius usually automatically corrects any DRUJ subluxation and restores DRUJ stability ( Fig. 15-2 ). This occurs because the DIOL usually remains intact and the tension that is reestablished in this structure by anatomic reduction of the radius is sufficient to stabilize the DRUJ and to institute immediate forearm rotation ( Fig. 15-3 ).