19 Distal Radioulnar Joint Instability Associated with Distal Radius Fractures

10.1055/b-0039-169259

19 Distal Radioulnar Joint Instability Associated with Distal Radius Fractures

Shohei Omokawa, Takamasa Shimizu, Kenji Kawamura, Tadanobu Onishi

Abstract

This chapter describes the pathomechanics, diagnosis, and treatment protocol of distal radioulnar joint (DRUJ) instability associated with distal radius fractures. The pathomechanics consist of: (1) rupture of the deep ligamentous portion of the triangular fibrocartilage complex (TFCC), (2) extra-articular metaphyseal displacement of the distal radius, (3) intra-articular step in the sigmoid notch, and (4) displaced ulnar styloid base fractures. Pre- and intraoperative assessments can be used to diagnose accompanying TFCC tears and DRUJ instability. DRUJ widening (> 4 mm) on prereduction posteroanterior view is an indicator of joint instability, and manual stress testing after distal radius fixation provides a practical screening test to differentiate the degree of DRUJ instability. Incomplete metaphyseal reduction of the distal radius does lead to DRUJ instability. The arthroscopic hook test at the radiocarpal joint can diagnose foveal detachment injury of the TFCC, and DRUJ arthroscopy with a 1.9-mm scope provides direct visualization of the ulnar attachment site for the radioulnar ligaments, which is deep ligamentous portion of the TFCC. DRUJ arthroscopy can also be used to assess the presence of articular step-off at the sigmoid notch. In the case where accompanying complete ligamentous tear of the TFCC is confirmed, we recommend open or arthroscopic repair of the torn ligament. In the case of a displaced ulnar styloid base fracture after accurate reduction of distal radius fractures, we recommend fixation of the fracture by a compression device (K-wire and wiring). Partial ligamentous tear of the TFCC can be treated by postoperative immobilization of upper arm casting for 3 weeks.

19.1 Introduction

A tear in the triangular fibrocartilage complex (TFCC) is the most frequent soft-tissue injury associated with fractures of the distal radius, and rupture of the deep ligamentous portion of the TFCC is considered to contribute to instability of the distal radioulnar joint (DRUJ). ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ ^, ⁶ ^, ⁷ Moreover, displacement of the fracture fragment(s) can affect the stability of the DRUJ. Extra-articular malalignment of the distal radius ⁸ ^, ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² and intra-articular step in the sigmoid notch ¹³ ^, ¹⁴ can change DRUJ kinematics, leading to DRUJ instability.

The purpose of this chapter is to describe the pathomechanics of DRUJ instability associated with distal radius fractures and discuss the strategies for evaluating and treating patients with acute or chronic instability of the DRUJ.

19.2 Pathomechanics of DRUJ Instability

19.2.1 Metaphyseal Fracture Displacement

Extra-articular malalignment of the distal radius can affect DRUJ kinematics and joint loading mechanics. ⁸ ^, ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² In vivo kinematic studies have found that a malunited distal radius with dorsal metaphyseal angulation can decrease the contact area of the DRUJ and result in lengthening of the dorsal radioulnar ligament (RUL). ⁸ ^, ⁹ Previous cadaveric studies investigating the effects of metaphyseal malalignment on DRUJ stability ¹⁰ ^, ¹¹ ^, ¹² found that 3 mm of radial shortening, 10 degrees of dorsal and volar angulation, or 2 mm of radial translation can lead to DRUJ instability. These biomechanical studies indicate that minimal metaphyseal malalignment can affect DRUJ stability, which may result in ulnar-sided wrist problems. Despite a lack of consensus regarding acceptable metaphyseal alignment, accurate anatomic restoration of the distal radius metaphysis is required to prevent residual DRUJ instability in the treatment of athletes and other active individuals.

19.2.2 Disruptions Accompanying TFCC (Radioulnar Ligament) Tears

The DRUJ is inherently unstable because the curvature of the sigmoid notch of the radius (18 mm) is twice as large as that of the ulnar head (8 mm). ¹⁵ ^, ¹⁶ The ligamentous and capsular structures thus play an important role in stabilizing this complex joint. The deep ligamentous portions of the TFCC are the primary stabilizers of the DRUJ. ⁷ ^, ¹⁷ These fibers, which attach to the ulnar fovea and lie on the axis of forearm rotation, are the most isometric and undergo the least length changes during pronosupination. Supplemental stability is provided by superficial fibers of the RUL, which attaches to the base of the ulnar styloid process, and these fibers may have a checkrein effect during forearm rotation. The other ligamentous structures include the ulnocarpal ligament (UCL) complex and the floor of the extensor carpi ulnaris (ECU) tendon sheath (the ulnar collateral ligament). ¹⁸ ^, ¹⁹

In patients with distal radius fracture, when high-energy forces damage the ligamentous structures of the DRUJ and separate the radius from the ulnar head, the deep ligamentous portion of the TFCC usually detaches from the ulnar fovea with or without ulnar styloid fractures. Complete rupture of the ligaments contributes to DRUJ instability. The incidence of TFCC injury is correlated with intra-articular involvement and the severity of fracture displacement. ³ A long-term prospective cohort study revealed no significant adverse subjective outcomes over the natural course of untreated peripheral TFCC tears in distal radius fractures. ²⁰ However, early recognition and treatment of DRUJ instability may lead to better clinical results rather than attempting to manage chronic instability. ³ ^, ²¹ ^, ²²

19.2.3 Ulnar Styloid Fractures

Ulnar styloid fractures accompany 51 to 65% of distal radius fractures, 25% of which result in nonunion. ²³ ^, ²⁴ ^, ²⁵ Because of its close anatomical location with the TFCC, fractures of the ulnar styloid base may also be associated with a tear in the deep portion of the TFCC and result in DRUJ instability. However, previous studies suggest that ulnar styloid fractures are poor prognostic factors for DRUJ instability. ²⁶ ^, ²⁷ ^, ²⁸ ^, ²⁹ ^, ³⁰ ^, ³¹ When the distal radius is treated by rigid plate fixation, most ulnar styloid fractures do not affect functional outcomes. Only displaced ulnar styloid base fractures following accurate reduction and rigid fixation of the distal radius may be associated with an unstable DRUJ, because these fractures are often associated with displacement of a torn TFCC.

19.2.4 Intra-articular Displacement of the Sigmoid Notch

In 55 to 65% of displaced distal radius fractures, the fracture line can extend into the sigmoid notch. Most frequently, this is associated with the dorsoulnar corner fragment of the distal radius that is best seen on oblique pronated radiographic views. Coronal plane fractures that enter into the sigmoid notch are difficult to identify on radiographs. Indeed, Rozental et al ¹³ identified fracture extension into the sigmoid notch in 65% of cases using computed tomography (CT) but it was observed only in 35% cases using radiographs. Nakanishi et al ³² analyzed fracture patterns and the magnitude of displacement in the DRUJ by 3D-CT and reported that 83% of intraarticular distal radius fractures had DRUJ involvement. In their study, 28% of wrists had multiple fragments, and fracture extending into the distal margin of the sigmoid notch was the most common type of longitudinal fracture. The authors suggested that surgical intervention for the DRUJ fragment(s) may be beneficial when there is remarkable intra-articular displacement.

Although previous studies have addressed the issue of intra-articular malunion involving the radiocarpal joint, ³³ ^, ³⁴ less attention has been paid to the residual gap and step in the DRUJ. Evidence is lacking as to how intra-articular malunion of the DRUJ affects clinical outcomes. When a displaced sigmoid notch fragment is left untreated, residual joint instability or incongruity may lead to degenerative arthritis of the DRUJ, resulting in symptomatic problems. ³⁵ ^, ³⁶ Future prospective studies can elucidate how residual malunion of the sigmoid notch would affect functional outcomes.

19.3 Case Presentation

A 27-year-old male sustained a volar rim fracture of the distal radius and underwent open reduction and palmar plating (▶Fig. 19.1). Six months postoperatively, the patient complained of ulnar wrist pain (VAS: 60, DASH 37, PRWE: 65) and restriction in forearm supination. The ulnar fovea and piano key signs of the ulnar head were positive. CT images showed an intra-articular step-off at the sigmoid notch, and we noted dorsal subluxation of the ulna. Magnetic resonance imaging (MRI) revealed a high signal intensity lesion at the ulnar fovea and fluid collection in the DRUJ on fat-suppressed T2-weighted images.

**Fig. 19.1** **(a)** Anteroposterior X-ray of a volar rim fracture of the distal radius in a 27-year-old male (*left*). *Arrow* indicates an articular step-off of volar rim fragment. Postsurgical X-ray after open reduction and internal fixation by palmar plating (*right*). **(b)** Computed tomography (CT) image showing an intra-articular step-off at the sigmoid notch and dorsal subluxation of the ulna (*left*) compared with the contralateral side (*right*). *Arrow* indicates a bony prominence in the intra-articular displacement site. **(c)** Magnetic resonance imaging shows fluid collection in the distal radioulnar joint (distal radioulnar joint [DRUJ]; *left arrow*) and a high signal intensity lesion at the ulnar fovea (*right arrow*) on fat-suppressed T2-weighted images. **(d)** Open triangular fibrocartilage complex (TFCC) repair and resection of the bony prominence in the DRUJ (*left*). *Arrows* in the CT image (*right*) indicate a bony prominence obstructing the ulnar head from moving into the palmar aspect of the sigmoid notch during forearm supination. **(e)** Postoperative X-ray showing reattachment of the TFCC to the ulnar fovea using a suture anchoring system.

DRUJ arthroscopy was undertaken and was followed by open TFCC repair and resection of a bony prominence in the DRUJ. This bony prominence (intraarticular stepoff) obstructed the ulnar head from moving within the palmar aspect of the sigmoid notch and was the cause of limited forearm supination. Marked synovitis and intra-articular scar formation was noted in the DRUJ. The TFCC was reattached to the ulnar fovea using a suture anchoring system. Three years postoperatively, the patient has minimum wrist pain and disability (VAS:7, DASH 10, PRWE: 19) with improvement in forearm supination.

19.4 Diagnosis of Accompanying TFCC Tears and DRUJ Instability

Although it is difficult to accurately diagnose RUL tears, pre- and intraoperative assessments can diagnose accompanying TFCC tears and DRUJ instability. Evidence of preoperative DRUJ widening on prereduction posteroanterior plain radiography can be used to identify DRUJ instability. Manual stress testing after distal radius fixation can provide a practical screening test to differentiate DRUJ instability. However, surgeons should notice that the most important reason of instability is incomplete metaphyseal reduction of the distal radius fractures. Not only residual shortening and dorsal tilt angle, but radial translation of the distal fragment can also lead to DRUJ instability. ³⁷

The arthroscopic hook test at the radiocarpal joint can be used to accurately diagnose foveal detachment injury of the TFCC. Finally, DRUJ arthroscopy can provide direct visualization of the RUL attachment to the ulna. Here, we outline these preoperative and intraoperative assessments in detail.

19.4.1 Preoperative Assessment

Plain X-Ray

Fujitani et al ³⁸ prospectively treated patients with unstable distal radius fractures with the volar locking plating system. Complete RUL tears representing DRUJ instability were present in 11 (6.7%) of 163 distal radius fracture cases. Using a multivariate logistic regression analysis, the authors identified a radiographic finding of normalized DRUJ gap as a significant risk factor, with the relative risk of instability increasing by 50% when the ratio of DRUJ widening increases by 1%. A cutoff value of 15% for the normalized gap showed the highest diagnostic accuracy rate. Because the normalized DRUJ gap was calculated as the fraction of the DRUJ gap distance relative to the radioulnar width of the proximal fracture fragment, the substantial DRUJ gap was equivalent to 3.0 mm in the patient who had 20 mm of the radioulnar width of the proximal fracture fragment (20 × 0.15 = 3.0 mm). The authors found that a 1-mm increase in the DRUJ gap increases the risk of RUL tear by five times (▶Fig. 19.2 and ▶Fig. 19.3).