Distal Ulna Fractures
Adam S. Martin
Hisham M. Awan
Fractures of the distal ulna present in two distinct varieties—isolated distal ulna fractures and distal ulna fractures in association with distal radius (DR) fractures.1 Isolated distal ulna fractures are relatively rare and can be categorized as distal diaphyseal, aka nightstick, or styloid fractures, whereas distal ulna fractures associated with DR fractures are very common.
Mechanism of injury—Nightstick fractures are the result of a direct blunt trauma to the ulna. Distal ulna fractures in association with DR fractures occur with similar mechanisms as those with isolated DR fractures, such as low-energy falls from standing, high-energy falls from height, or motor vehicle collisions.
Epidemiology—The incidence of DR fractures in the United States is more than 640 000 per year.2,3 Approximately 50% to 60% of DR fractures have concomitant fractures of the distal ulna. Isolated distal ulna fractures are relatively rare.
Anatomy—The ulnar shaft widens distally to form the ulnar neck.1 Distal to the neck are the two most distinct structures of the distal ulna: the ulnar head and ulnar styloid (Figure 28.1).4
The styloid is distal, dorsal, and medial relative to the ulnar head. A groove, called the fovea, lies between the head and styloid and can be palpated on the ulnar side of the wrist between the flexor carpi ulnaris and extensor carpi ulnaris (ECU) tendons; furthermore, the fovea is an important attachment site for the triangular fibrocartilage complex (TFCC).
Given that there is little inherent stability provided by the bony structure of the distal radioulnar joint (DRUJ), the TFCC is the main stabilizer of the DRUJ. The TFCC is composed of the palmar and dorsal radioulnar ligaments, articular disk, meniscal homologue, and ECU subsheath.
The ulnar head articulates with the sigmoid notch of the radius to form the DRUJ. The DRUJ, specifically the ulnar head, is the distal center of rotation for pronation and supination of the forearm.
Presentation—Patients often present with ulnar-sided wrist pain that localizes to the distal ulna. They may recall a specific traumatic event that coincides with the onset of pain. If patients present early, they may report swelling or ecchymosis around the wrist. If the injury is chronic, then patients may complain of loss of wrist range of motion (ROM) or a sense of instability around the wrist.
Physical examination—On examination, one should have a systematic approach and include inspection, palpation, ROM, and neurovascular status. Inspection may reveal swelling, deformity, and/or ecchymosis. Palpation should include the DR and ulna, specifically the ulnar styloid and fovea. The DRUJ should be assessed for instability via the shuck test.
Perform the DRUJ shuck test (Figure 28.2) in neutral and end ranges of pronation/supination and compare with contralateral wrist.
“Shuck” the joint by translating the ulna volarly and dorsally while stabilizing the DR.
There should be an equivalent amount of motion in neutral to contralateral wrist and firm endpoints at full supination and pronation.
In general, DRUJ is more stable in supination.
Imaging—Radiographic imaging should consist of a neutral rotation posteroanterior (PA) and true lateral views of the wrist (Figure 28.3). An acceptable PA view is evident when the cortical outline of the concavity of the ECU groove is radial to the long axis of the ulnar styloid. This view is obtained with the shoulder abducted 90°, elbow flexed 90°, and forearm and wrist in neutral. Likewise, an acceptable lateral view is obtained when the volar cortex of the pisiform is between the volar cortices of the scaphoid and capitate, also known as the “SPC lateral.”
Several methods exist for measuring ulnar variance (UV); however, the most commonly used is the method of perpendiculars. A transverse line is drawn through the volar sclerotic line of the lunate fossa of the DR perpendicular to its long axis; the distance
the ulnar head projects proximal or distal to this line is the UV (Figure 28.3).
Average UV is approximately 1 mm.
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