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CHAPTER 8 • Fractures of the Distal Radius and Ulna

and wrist placed on the cassette, with the shoulder abducted 90 degrees, elbow flexed 90 degrees, and forearm in neutral rota- tion (Fig. 8-22). The importance of ulnar variance relates to the force transmission across the wrist with axial loading. Normally, the radiocarpal joint bears approximately 80% of the axial load across the wrist, and the ulnocarpal joint bears 20%. Changes in the length relationship of the radius and ulna alter respective load bearing. Indeed, 2.5 mm of ulnar positive variance has been demonstrated to double the forces borne across the ulnocarpal articulation in adult biomechanical analyses. 105,153 Biomechani- cal and clinical studies have shown that this load distribution is important in fractures, TFCC tears (positive ulnar variance), and Kienbock disease (negative ulnar variance). 4,75 The distal radius normally rotates around the relatively sta- tionary ulna. The two bones of the forearm articulate at the proximal radioulnar joints and DRUJs. In addition, proximally the radius and ulna articulate with the distal humerus and distally with the carpus. These articulations are necessary for forearm pronation and supination. At the DRUJ, the concave sigmoid notch of the radius incompletely matches the convex, asymmetric, semicylindrical shape of the distal ulnar head. 22,153 This allows some translation at the DRUJ with rotatory move- ments. The ligamentous structures are critical in stabilizing the radius as it rotates about the ulna (Fig. 8-23).

V

C

H

S

TQ

L

surface. 100 However, measurement of ulnar variance in chil- dren requires modifications of this technique. Hafner et al. 89 described measuring from the ulnar metaphysis to the radial metaphysis to lessen the measurement inaccuracies related to epiphyseal size and shape, a technique recently validated by Goldfarb et al. (Fig. 8-21). 80 If the ulna and radius are of equal lengths, there is a neutral variance. If the ulna is longer, there is a positive variance. If the ulna is shorter, there is a negative variance. Variance measurement is made in millimeters. Although not dependent on the length of the ulnar styloid, 22 the measurement of ulnar variance is dependent on forearm posi- tion and radiographic technique. 61 Radiographs of the wrist to determine ulnar variance should be standardized with the hand Figure 8-19.  Diagrammatic drawing of the TFCC and the prestyloid recess. The meniscal reflection runs from the dorsoulnar radius to the ulnovolar carpus. The arrow denotes access under the reflection to the tip of the styloid, the so-called prestyloid recess. V, fifth metacarpal; S, scaphoid; C, capitate; H, hamate; L, lunate; TQ, triquetrum. (Redrawn from Bowers WH. Green’s Operative Hand Surgery . New York: Churchill- Livingstone; 1993.)

TREATMENT OPTIONS FOR FRACTURES OF THE DISTAL RADIUS AND ULNA

NONOPERATIVE TREATMENT OF FRACTURES OF THE DISTAL RADIUS AND ULNA

The goal of pediatric distal radius fracture care is to achieve bony union within acceptable radiographic parameters to opti- mize long-term function and avoid late complications. Manage- ment is influenced tremendously by the remodeling potential of the distal radius in growing children (Fig. 8-24). In general, remodeling potential is dependent on the amount of skeletal growth remaining, proximity of the injury to the physis, and relationship of the deformity to plane of adjacent joint motion. Fractures in very young children, close to the distal radial physis, with predominantly sagittal plane angulation have the greatest remodeling capacity. Acceptable sagittal plane angu- lation of acute distal radial metaphyseal fractures has been reported to be from 10 to 35 degrees in patients under 5 years of age. 63,108,114,149,163,171,211 Similarly, in patients under 10 years of

Ulna

Interosseous membrane

Figure 8-20.  The attachment and the fibers of the interosseous membrane are such that there is no attachment to the distal radius. (Redrawn from Kraus B, Horne G. Galeazzi fractures. J Trauma . 1985;25:1094.)

Radius