16 Radiocarpal Dislocation

10.1055/b-0039-169256

16 Radiocarpal Dislocation

Mark Henry

Abstract

Radiocarpal fracture-dislocations are far more common than pure dislocations; both are easily reduced but may then be underappreciated by a subsequent provider. Complete dislocation between the carpus and the radius requires intrasubstance rupture or bony avulsion of all the extrinsic ligaments of the wrist, both volar and dorsal. Incongruent radiocarpal subluxation may occur with subtotal failure of the extrinsic ligaments. Radiocarpal incongruity with extrinsic ligament failure may occur in combination with intrinsic ligament rupture or distal radius fracture. Key elements of the initial assessment include the mechanism of injury, localization of trauma signs on examination, and plain radiographs demonstrating subtle radiocarpal incongruity or small marginal fracture fragments. When appropriate, further assessment may include CT scan (with or without arthrogram) to reveal incongruity, small marginal fragments, or sites of intrasubstance ligament rupture. The most complete and accurate means of assessing wrist trauma is arthroscopy, but in the setting of complete extrinsic rupture, axial distraction force must be minimized. Because the extrinsic ligaments will heal well as long as all skeletal relationships are accurately maintained, most radiocarpal dislocations can be treated entirely arthroscopically. When a bone fragment carrying a critical ligament attachment will not reduce arthroscopically, a limited open approach for direct fixation is appropriate. Fixation consists of radiocarpal pinning combined with pinning or screw fixation of marginal fragments. The radiocarpal pin may be removed by 4 weeks, with 6 weeks total splint or cast immobilization prior to initiating wrist range of motion therapy. Strengthening exercises progress gradually from 8 weeks onward.

16.1 Introduction

Pure radiocarpal dislocations are extremely rare, requiring intrasubstance failure of all wrist extrinsic ligaments, volar and dorsal. Dorsal dislocations are far more common than volar. ¹ ^, ² ^, ³ ^, ⁴ More common are radiocarpal fracture-dislocations where some of the ligament failures occur through their bony origin on the radius combined with the other extrinsic ligaments experiencing intrasubstance rupture (▶Fig. 16.1). ⁵ ^, ⁶ ^, ⁷ ^, ⁸ ^, ⁹ The volar extrinsic ligaments are the most important stabilizers resisting translation both dorsally (61% of total restraint) and volarly (48% of total). The dorsal extrinsic ligaments contribute very little to restraining translation both dorsally (2% of total) and volarly (6% of total). ¹⁰ These are high-energy traumas typically associated with high falls, violent sports impact, or vehicular accidents. ⁶ ^, ¹¹ The wrist specialist is usually not the first medical provider to encounter the patient, and the emergency responder will have often reduced the dislocation on site or soon thereafter. ⁴ ^, ¹² Consequently, it is possible to underappreciate the gravity of the injury and fail to recognize the major ligament disruption that has actually occurred (▶Fig. 16.2). ¹³ The greatest risk of missing the extrinsic ligament failure is when it accompanies a more obvious distal radius fracture, carpal fracture (lunate mostcommon), or intercarpal dislocation (▶Fig. 16.3). ⁵ ^, ¹⁴ ^, ¹⁵ ^, ¹⁶ ^, ¹⁷ Treatment of the more obvious injury without stabilizing the radiocarpal exact positional relationships may then lead to chronic subluxation, instability, and eventually posttraumatic arthritis (▶Fig. 16.4). ¹⁸ The long-term direction of instability and subluxation is typically ulnar translocation for pure ligamentous injuries or combined with volar when associated with unhealed volar marginal fragments (▶Fig. 16.5). ² ^, ¹⁴ ^, ¹⁹ ^, ²⁰ All wrist traumas must be thoroughly assessed, proactively seeking evidence of any ligament injury patterns to ensure that the appropriate treatment is rendered.

**Fig. 16.1** Radiocarpal fracture-dislocations can occur with a larger radial styloid fragment controlling the origins of the radioscaphocapitate (RSC) and long radiolunate (LRL) ligaments with midsubstance rupture of the remaining volar extrinsics: short radiolunate (SRL), ulnolunate (UL), ulnocapitate (UC), and ulnotriquetral (UT).

**Fig. 16.2** Plain radiographs must be examined carefully to check all congruent relationships. Radiologist read this film as normal, but the proximal scaphoid (*arrow*) can easily be seen displaced over the dorsal rim of the radius in this combined radiocarpal and perilunate dislocation.

**Fig. 16.3** Although the most frequently recognized location for small volar fragment displacement leading to carpal subluxation is the volar lip of the lunate fossa, isolated scaphoid subluxation (*arrow*) despite a congruent lunate is also possible.

**Fig. 16.4** Late sequelae of radiocarpal dislocation without distal radius fracture includes **(a)** volar and ulnar subluxation of the lunate and **(b)** hyaline cartilage loss throughout the radiocarpal interface with preservation of the midcarpal joint in distinct contrast to the pattern seen with scapholunate advanced collapse.

**Fig. 16.5** Late avascular necrosis of key volar marginal fragments that appear **(a)** healed at 6 weeks postoperatively can ultimately lead to **(b)** late carpal subluxation when other intrasubstance ruptures of extrinsic ligaments fail to heal well.

16.2 Indications

Radiocarpal dislocations and fracture-dislocations are fundamentally surgical problems; casting alone is insufficient. ²¹ The indication to act surgically is simply ample evidence from the preoperative assessment that demonstrates the injury pattern. ¹¹ Apart from taking the full history including mechanism of injury and conducting a full examination focusing on local signs of wrist trauma, the surgeon should carefully scrutinize the plain radiographs. In the rare event of a set of films obtained while the wrist is still dislocated, the pathology is clear. Most of the time, the surgeon is viewing postreduction radiographs. ⁴ ^, ¹³ The specific indications being sought are subtle degrees of incongruence in the radiocarpal relationship and small marginal fragments around the rim of the distal radius (▶Fig. 16.6). ¹⁴ In a pure dislocation with no fracture fragments, the radiocarpal relationship may appear perfectly congruent. In this event, further investigation is warranted. Local anesthetic injection into the wrist joint can reduce posttraumatic pain, allowing the examiner to perform manual ligament stress testing. Computed tomography (CT) scanning can reveal subtle incongruity or marginal fractures not appreciated on two-dimensional films. Arthrogram contrast may be added to demonstrate sites of complete ligament rupture. The ultimate assessment tool for defining the pattern and extent of wrist trauma is arthroscopy (▶Fig. 16.7). ²² ^, ²³