31 Chronic Distal Radioulnar Joint Instability

10.1055/b-0039-169271

31 Chronic Distal Radioulnar Joint Instability

Michael C. K. Mak, Pak-Cheong Ho

Abstract

Chronic distal radioulnar joint instability is caused by disruption of its stabilizers of which the triangular fibrocartilage complex (TFCC) has a key role, and it is the aim of this chapter to illustrate a minimally invasive method to reconstruct the TFCC anatomically by means of an arthroscopic-assisted approach. Any causative skeletal malalignment must be identified and corrected before TFCC reconstruction is considered. The current concept of anatomical reconstruction, first proposed by Adams, aims to restore the volar and dorsal radioulnar ligaments and their radial and foveal insertions with uniform tension. An arthroscopic-assisted method of reconstruction was developed and the technique was illustrated. Open capsulotomies are avoided and scarring is minimized, and accurate placement of the foveal insertion is possible by arthroscopic visualization. Outcomes in 28 consecutive cases performed over a period of 17 years in our center were favorable and showed a potential advantage in preserving the range of motion.

31.1 Introduction

31.1.1 Distal Radioulnar Joint Anatomy and Its Stabilizers

Distal radioulnar joint (DRUJ) straddles between the forearm and the wrist joint. Being the distal articulation of the forearm, its related structures are also important parts of the wrist. Its stability is conferred by its bony configuration and soft tissue stabilizers, of which there are static and dynamic components. The bony articulation consists of a semicylindrical ulnar seat with a mean radius of curvature of 8 mm¹ and a shallower concave sigmoid notch with a radius of 15 mm (▶Fig. 31.1). The centers of the subtended arcs of these curvatures do not meet and thus the intrinsic congruence of the DRUJ is nonconcentric, which also limits the articulation contact area. DRUJ rotation results in a combined roll and slide motion of the radius with respect to a fixed ulna, where supination brings the volar rim of the radius closer in contact with the ulna and pronation the dorsal rim. There is no single isometric point of rotation but rather a centrode of rotation located near the center of the ulnar head. ² This configuration accounts for 20% of the stability in a volar–dorsal direction. ³ Thus, DRUJ stability heavily relies on soft tissue stabilizers, which include capsular, ligamentous, and musculotendinous components. The DRUJ capsule, triangular fibrocartilage complex (TFCC), and interosseous membrane (IOM) provide static stability, while the pronator quadratus and extensor carpi ulnaris (ECU) provide dynamic stability. The TFCC was found to be the most important stabilizer, with the volar radioulnar ligament providing almost 50% of the constraint in preventing dorsal subluxation of the ulnar head in relation to the radius in all positions. ³ Division of the TFCC alone results in DRUJ dislocation in all positions even with intact DRUJ capsule and pronator quadratus. ⁴ The IOM and in particular its distal portion, the distal oblique bundle (DOB), assume a significant stabilizing role if the TFCC is injured. ⁵ However, in the presence of an intact TFCC, sectioning of the distal IOM resulted in minimal change in stability. ⁶ Given its key role in stabilization, restoring normal TFCC integrity is most important in the surgical treatment of DRUJ instability.

**Fig. 31.1** The shallower sigmoid notch has mean radius of curvature of 15 mm while that of the ulnar head is 8 mm. The centers of the two curvatures do not meet.

The TFCC is a blend of ligamentous, fibrous, and fibrocartilaginous components that function to stabilize the DRUJ and bear force in the ulnocarpal joint while allowing smooth motion. It consists of the articular disc, meniscus homolog, volar and dorsal radioulnar ligaments, subsheath of the ECU, ulnar capsule, and ulnolunate and ulnotriquetral ligaments. Of these, the volar and dorsal radioulnar ligaments are the most important stabilizing structures. ¹ ^, ⁶ ^– ⁸ It is now known that different parts of these two ligaments have different stabilizing roles as the forearm rotates. The foveal insertion is contributed by deep fibers of the radioulnar ligaments and the more ulnar and distal styloid insertion is contributed by superficial fibers. Superficial dorsal and deep volar fibers of the radioulnar ligaments tighten and provide stability in pronation, whereas superficial volar and deep dorsal ligaments stabilize in supination. ¹ ^, ⁹ The foveal insertion is recognized as the more important, ¹⁰ acting as the anchor of a hammock-like structure. ¹¹

31.2 Indications

As a sequela of distal radius fractures, chronic DRUJ instability may cause persistent pain, weakness of grip or rotation, or clunking after resolution of the acute injury. Studies showed that 43 to 78% of distal radius fractures are associated with TFCC injuries detected by arthroscopy ¹² ^, ¹³ and 10 to 19% of distal radius fractures are associated with DRUJ instability. ¹⁴ ^, ¹⁵ On physical examination, there may be the prominence of the ulnar head, with a positive piano key sign indicating overt instability. ¹⁶ Local tenderness is an important sign to localize the specific lesion present. The sites that have to be covered include the dorsal TFCC, foveal region, ¹⁷ the soft spot between the ulnar head, triquetrum, flexor carpi ulnaris (FCU), and ECU tendons, the DRUJ dorsal capsule, lunate, triquetrum, lunotriquetral ligament, and the volar TFCC. Passive pronosupination of the forearm may elicit pain. DRUJ ballottement test in neutral, supination, and pronation is performed, with up to 5 mm of dorsovolar translation of the DRUJ present in the normal wrist. Any translation in maximal pronosupination should be regarded as abnormal. Furthermore, in full pronation, pain and instability elicited by the dorsal push of the ulnar head relative to the radius indicate tear of the deep palmar radioulnar ligament; whereas in full supination, positive signs on the volar push of the ulnar head indicate tear of the deep dorsal radioulnar ligament. The ulnocarpal ligament stress test is performed with the forearm in neutral rotation and the wrist in radial deviation, in which the ulnar head is balloted as in the DRUJ ballottement test. Abnormal increase in translation indicates ulnocarpal ligament tear. There may be pain on resisted supination and pronation, which is alleviated by a volar push on the dorsal ulnar head. In addition to plain radiographs, computed tomography may be useful in the analysis of skeletal malalignment, in particular, sigmoid notch configuration. Magnetic resonance arthrography is useful in diagnosing TFCC tears and other ligament injuries, and with wrist traction applied, can accurately detect 98% of TFCC tears. ¹⁸

31.2.1 Correction of Skeletal Deformity

Post-traumatic DRUJ instability results from malunion, leading to bony malalignment or incompetence of soft tissue stabilizers or both (▶Fig. 31.2).

**Fig. 31.2** Causes of distal radioulnar joint (DRUJ) instability.

Skeletal malalignment affecting the DRUJ include intra-articular malunion and incongruity of the sigmoid notch and ulnar head, displaced basilar ulnar styloid fracture, shortening of the radius, dorsal tilting, and coronal shift.

Although a positive correlation between ulnar styloid process fractures and TFCC tears was reported in some studies, ¹² ^, ¹⁹ a recent meta-analysis found no correlation between ulnar styloid fracture and subsequent DRUJ instability or symptoms. ²⁰ Therefore, an ulnar styloid nonunion itself may not be the prime culprit of DRUJ instability; rather, distal radius malunion is a more important factor. An intra-articular malunion that results in flattening of the sigmoid notch may lead to instability despite intact radioulnar ligaments, for which a sigmoid notch osteotomy can be performed to increase its concavity. ²¹ Extra-articular malalignment in each of the three planes, past a certain extent, causes DRUJ instability. Dorsal tilt of more than 10° was shown in a biomechanical study to cause DRUJ diastasis, changes in the IOM, and limitation of pronosupination. ²² A 2-mm radial translation of the distal radius, in the presence of an ulnar styloid fracture, is associated with an increased dorsal volar DRUJ displacement due to the loss of tension of the DOB. ²³ Finally, shortening of the distal radius was found to be correlated with DRUJ subluxation and limitation of pronation due to stretching and incompetence of the TFCC. ²⁴ A three-dimensional realignment is thus necessary if deformity correction is to be undertaken.

31.2.2 Triangular Fibrocartilage Complex Reconstruction

If there is no significant bony malalignment or if instability is not completely restored after corrective osteotomy, restoring a functional TFCC is the key to regaining stability.

Arthroscopy is the gold standard in the assessment of the TFCC and to provide information on the extent of injury, reparability, and cartilage condition. TFCC reconstruction with tendon graft is indicated in irreparable TFCC with symptomatic DRUJ instability, which may happen with a neglected chronic injury, a massive tear with tension on apposition, or suboptimal healing after conservative treatment or surgical repair. In these situations, the remaining TFCC substance may be too thinned and friable for robust healing.

With the current understanding of the functional anatomy of the TFCC, anatomical reconstruction of the volar and dorsal radioulnar ligaments, first described by Adams, ²⁵ is now widely adopted. ²⁶ ^, ²⁷ This method aims to restore normal DRUJ kinematics by using a single tendon graft with uniform tension, which is passed through the edges of the sigmoid notch and through the ulna at the foveal insertion site (▶Fig. 31.3, ▶Fig. 31.6a). Based on this method of anatomical reconstruction, since 2000, we have developed and utilized an arthroscopic-assisted technique. ²⁸ ^, ²⁹ In this minimally invasive technique, open capsulotomy and capsular dissection were not necessary, minimizing soft tissue scarring, fibrosis, and stiffness and allowing earlier rehabilitation. Under arthroscopic control, the fovea is clearly located, allowing accurate placement of the graft at the isometric point. Contraindications include significant symptomatic DRUJ arthritis and forearm rotational instability due to insufficiency of the IOM. A diagnostic arthroscopy could be performed before or at the same time as the definitive reconstruction to establish reparability of the TFCC.

**Fig. 31.3** Anatomical reconstruction of volar and dorsal radioulnar ligaments and their insertions into the fovea.

31.3 Surgical Technique

31.3.1 Setup and Instruments

The patient is positioned supine with longitudinal wrist traction of 10 to 15 lb. A tourniquet is applied over the arm. Instruments employed include:

A 1.9-mm or 2.7-mm arthroscope.
Motorized full-radius shaver (2.0/2.9 mm) and radiofrequency probe.
Powered instruments, including cannulated drills.
The 2-mm arthroscopic graspers and suction punch.
Fluoroscopic image intensifier.

Step 1: Wrist Arthroscopy and Triangular Fibrocartilage Complex Central Opening Preparation

The assessment of the radiocarpal joint with standard 3/4 viewing and 4/5 working portals is done to look for any associated chondral or ligamentous injuries. The integrity of the TFCC is assessed by probing of the volar and dorsal periphery, the trampoline test, and the hook test. TFCC reconstruction is indicated when the foveal detachment is beyond repair. As direct access to the foveal insertion is essential for passage of the graft, a central TFCC perforation is required. If the central part of the TFCC is intact, a central perforation is created with an arthroscopic knife or radiofrequency ablation. Any pre-existing central perforation is enlarged to 5 to 6 mm (▶Fig. 31.4), the ulnar head is exposed, and the edge is smoothened to ensure easy passage of the graft.

**Fig. 31.4** Enlarging a triangular fibrocartilage complex (TFCC) central perforation with radiofrequency ablation.

Step 2: Harvesting of Tendon Graft

A 2-cm volar longitudinal incision is made midway between palmaris longus (PL) tendon and radial border of FCU tendon at the level of the proximal wrist crease (▶Fig. 31.5b). The PL tendon is harvested in full length with a tendon harvesting stripper.

**Fig. 31.5** **(a–c)** Volar and dorsal incisions.

The flexor tendons and median nerve are retracted radially, and the FCU, ulnar nerve, and artery are retracted ulnarly to expose the distal radius. The distal border of the pronator quadratus marks the approximate level of the radial tunnel.

Step 3: Radial Tunnel Preparation with Passage of Tendon Graft

A 2-cm dorsal longitudinal incision is extended proximally from the 4/5 portal (▶Fig. 31.5a). A window is made in the extensor retinaculum over the fourth extensor compartment. The extensor tendons were retracted to the radial side to expose the edge of the sigmoid notch. A 1.1-mm guide pin is inserted on the dorsal surface of distal radius radial to the sigmoid notch, 5 mm proximal to the articular surface of lunate fossa, and 5 mm radial to the sigmoid fossa with a volar tilt of 10 to 15° parallel to the surface of the lunate fossa (▶Fig. 31.6b). Tendons and neurovascular structures on the volar side are gently retracted by an assistant, while the guide pin is advanced with direct visualization of the tip (▶Fig. 31.7). After guide pin position is confirmed by fluoroscopy, the tunnel is enlarged to 2.2 to 2.5 mm, depending on the caliber of the tendon graft using cannulated drill bits and soft tissue protection by drill sleeves at both entry and exit sites.