The distal radioulnar joint (DRUJ) consists of the concave, cartilage-covered sigmoid notch of the distal radius (DR) and the convex distal ulnar head. The joint has very little inherent stability from the bony architecture, thus the majority of the restraint is from the surrounding soft tissues, in particular the triangular fibrocartilage complex (TFCC). During normal motion, forearm pronation results in dorsal translation of the ulnar head, whereas supination results in volar translation. Given the reliance on soft tissues, DRUJ instability is a relatively common problem. A wide variety of DRUJ injuries and disorders exist (Table 29.1), but this chapter will focus on TFCC tears, DRUJ dislocations, and DRUJ instability.
Mechanism of injury—Injury to the DRUJ is commonly traumatic from a fall on an outstretched hand. Acute, isolated dorsal and volar DRUJ dislocations are because of a fall that results in wrist extension/hyperpronation and supination, respectively. The most common cause of DRUJ instability is from inaccurate reduction of a DR fracture. Other sources of DRUJ instability are unstable ulnar styloid and Galeazzi fractures.
Anatomy—The ulnar head articulates with the sigmoid notch of the radius to form the DRUJ. There is some degree of rotational and sliding motion of the DRUJ given the articular cartilage and radius of curvature mismatch between the ulnar head and sigmoid notch (Figure 29.1).
Given that there is little bony stability of the DRUJ, the TFCC is the key stabilizer of the DRUJ. The TFCC is composed of the palmar and dorsal radioulnar ligaments (RULs), articular disk, meniscal homologue, and extensor carpi ulnaris (ECU) subsheath (Figure 29.2).
The articular disk, made of fibrocartilage, originates from the lunate fossa of the DR and forms two distinct bundles ulnarly, one that
inserts on the ulnar styloid and the other one on the fovea. The insertion sites are separated by a loose vascular connective tissue called ligamentum subcruentum. The peripheral 20% of the disk is well vascularized and therefore is amenable to healing. Furthermore, vascularity decreases as you move from ulnar to radial.
The ulnotriquetral and ulnolunate ligaments are technically not part of the TFCC, but nonetheless function as additional stabilizers of the DRUJ.
TABLE 29.1 Injuries and Disorders of the DRUJ Intra-articular Fractures Without Instability
Presentation—Patient presentation is highly variable, but patients will likely complain of ulnar-sided wrist pain. They may recall a specific traumatic event that coincides with the onset of pain or report increased pain with certain activities, ie, gripping, twisting doorknobs, open lids on jars. Pain is activity related and may be associated with mechanical symptoms, such as clicking or catching. 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, always compare with the contralateral wrist, and include inspection, palpation, ROM, and neurovascular status. Inspection may reveal swelling or deformity. Palpation should include the DR
and ulna, specifically the ulnar styloid and fovea. Foveal tenderness, suggestive of TFCC tears, can be elicited by palpation in the soft spot ulnarly between the ECU and flexor carpi ulnaris (FCU) tendons. The ECU synergy test may help rule out ECU tendinitis and is performed by having the patient fully extend all fingers, the examiner then grasps the
patient’s thumb and middle finger and the patient radially abducts the thumb against resistance. The test is positive if this maneuver recreates the dorsal/ulnar wrist pain. The DRUJ should be assessed for instability, crepitus, and pain. Patients may also show decreased grip strength.
Perform the DRUJ shuck test (Figure 29.3) in neutral and full pronation/supination and compare with contralateral wrist. “Shuck” the joint by translating the ulna volarly and dorsally while stabilizing the DR. This maneuver is crucial to determining DRUJ instability.
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. 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 (Figure 29.4). This view is obtained with the shoulder abducted 90°, the elbow flexed 90°, the forearm in neutral rotation, and the 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.”
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