Introduction

Arthroscopy of the distal radioulnar joint (DRUJ) is a natural extension of radiocarpal and midcarpal arthroscopy. It provides a minimally invasive means of evaluating the DRUJ, including visualization of the articular cartilage, synovium, and triangular fibrocartilage complex (TFCC). This chapter discusses the relevant anatomy and biomechanics of the DRUJ, indications for DRUJ arthroscopy, and the surgical technique. In addition, open distal radioulnar ligament reconstruction is described for patients with DRUJ instability found to have an irreparable TFCC.

Anatomy and Biomechanics

The DRUJ is a trochoid diarthrodial articulation that allows both rotation and translation during normal forearm motion. The overall dimensions of the sigmoid notch average 15 mm in the transverse plane and 10 mm in the coronal plane. Its dorsal bony rim is typically acutely angled, whereas the volar rim is more rounded and is frequently augmented by a cartilaginous lip. The shape of the notch varies considerably in both planes, which plays a role in both joint stability and ease of arthroscopic access.¹ Due to its relatively shallow and incongruent articulation, the DRUJ relies strongly on the soft tissues for stability. The structures that contribute to DRUJ stability are the pronator quadratus, extensor carpi ulnaris (ECU), interosseous membrane (IOM), DRUJ capsule, and components of the triangular fibrocartilage complex (TFCC).²

The TFCC is generally accepted as the major static soft-tissue stabilizer. The palmar and dorsal radioulnar ligaments are the prime components of the TFCC that stabilize the DRUJ. These ligaments appear as thickenings at the junctures of the triangular fibrocartilage, DRUJ capsule, and ulnocarpal capsule. As each ligament extends from its respective distal margins of the sigmoid notch, it divides in the coronal plane into two limbs. The deep (proximal) limb attaches at the fovea, and the superficial (distal) limb attaches to the base and mid-portion of the ulnar styloid. The palmar ligament provides origins for the ulnolunate and ulnotriquetral ligaments, whereas the dorsal ligament is confluent with the ECU sheath.

During forearm rotation, DRUJ translation occurs because the sigmoid notch is shallow (with a radius of curvature 50% greater than that of the ulnar head). At the extremes of pronation and supination, the ulnar head slides palmarly and dorsally in the sigmoid notch (respectively)—resulting in only 2 to 3 mm of articular contact area at the rims.³ Although DRUJ motion has a substantial translational component (with a changing axis of rotation), its instant axis generally passes near the center of the ulnar head—moving dorsally with pronation and palmarly with supination. The ulnar head serves as the seat for the sigmoid notch, around which the radius rotates.³ The amount of articular cartilage that covers the head varies from a 50-degree to a 130-degree arc.

The ulnar styloid is a continuation of the subcutaneous ridge of the ulna, providing increased area for soft-tissue attachments. At the base of the styloid lies a shallow concavity termed the fovea, which is replete with vascular foramina and is an attachment site for ligaments. Identification of this site is essential for anatomical repair and reconstructive procedures because the axis of forearm motion passes through it.

Indications

The DRUJ is susceptible to trauma, post-traumatic degenerative changes, and inflammatory conditions. Arthroscopy allows for inspection of the articular surfaces of both the sigmoid notch and the ulnar head. Chondromalacia, cartilage defects, and articular shear injuries may be visualized. Systemic inflammatory conditions (including gout and rheumatoid arthritis) are sources of DRUJ synovitis that can be evaluated and treated arthroscopically. PVNS leading to synovial hypertrophy, loose bodies from fracture, or osteophytes can be removed. Undersurface partial- or full-thickness tears of the TFCC can be seen and debrided. Occasionally, the competency of the volar ulnocarpal ligaments may be evaluated.

Contraindications

There are no absolute contraindications to DRUJ arthroscopy. However, the joint is very small and access is limited. Thus, relative contraindications include surgical proficiency and a tight joint that does not allow passage of the scope or instruments without undo joint damage. Radiographic evidence of degenerative changes is a sign that navigating the joint arthroscopically could be very difficult, especially if the joint is stiff.

Surgical Technique

A regional or general anesthetic is administered. The patient is positioned supine on the operating table. An upper-arm tourniquet is applied over cotton padding. The elbow is flexed to 90 degrees and the upper extremity is mounted in a traction tower using finger traps applied to the long and ring fingers. Placing the wrist in full supination facilitates access to the DRUJ, unless the joint becomes excessively tight in this position. In neutral rotation the opposing surfaces of the sigmoid notch and the ulnar head are congruent, whereas in full supination the opposing surfaces have only a marginal contact area of 2 to 3 mm.⁴