Dislocation of the distal radioulnar joint is a rare injury pattern. There
is little in the English literature describing this injury and even less to
direct treatment. We present the case of a patient with an irreducible
dislocation of the distal radioulnar joint and discuss the pathoanatomy and
operative treatment. In addition, we describe a novel radiographic and
clinical finding of an ulnar impaction fracture, which we equate to the
Hill-Sachs lesion noted in the humeral head following dislocation of the
shoulder. Our patient was informed that data concerning the case would be
submitted for publication.
Aforty-year-old, right-hand dominant man presented to the emergency
department immediately following a work-related injury. The patient had pain
in the right wrist and lack of forearm rotation. In an attempt to catch a bag
of cement that was thrown down from a truck, he struck the dorsum of the right
wrist, which was supporting the 50-lb bag, against the right knee.
The patient had no medical or surgical history that was relevant to the
injury, nor had he sustained any previous injuries to the right forearm,
wrist, or hand.
On physical examination, the patient was only able to rotate the forearm
between 30° and 80° with the right wrist held in a position of
supination. There was loss of the dorsal prominence of the ulnar head, which
was instead palpable on the volar side. The wrist was moderately swollen,
tender to palpation, and painful with attempted pronation. The patient had no
elbow or forearm pain. The skin and the neurovascular function, specifically
including ulnar nerve function, were intact.
Initial radiographs were made. The posteroanterior radiograph demonstrated
an overlap of the radius and ulna at the distal radioulnar joint
(Fig. 1-A), and a true lateral
radiograph demonstrated volar displacement of the ulna with respect to the
radius (Fig. 1-B) (henceforth
referred to as volar dislocation of the distal radioulnar joint). There were
no associated fractures or abnormalities of the carpus. With the patient under
conscious sedation, a closed reduction was attempted in the emergency
department with use of a commonly accepted maneuver of distraction of the
distal radioulnar joint, direct pressure on the ulnar head, and passive
pronation1. There
was a clear block to reduction; thus, the attempt was abandoned to avoid
causing a fracture, and the wrist was placed in a protective splint until the
dislocation could be reduced operatively.
Further imaging with computed tomography demonstrated a volar dislocation
of the distal radioulnar joint. The distal end of the ulna was impacted on the
volar rim of the sigmoid notch of the radius, and there was the suggestion of
a lucency across the volar rim of the radius in the sagittal plane (Figs.
2-A and 2-B). The patient was
then taken to the operating room where the distal radioulnar joint was exposed
with use of a dorsal approach over the fifth extensor compartment. Open
reduction of the dislocation was then achieved with a Freer elevator.
Distraction was used to disengage the impacted osseous lesion. Reduction
revealed a volar osteochondral lesion involving the radius at the edge of the
distal radioulnar joint, which was consistent with the lucency seen on the
computed tomography scan. Also visible was a tear in the triangular
fibrocartilage complex; the tear was comprised of an avulsion of the deep
fibers of the dorsal radioulnar ligament from their ulnar attachment. These
fibers were reattached with use of a suture anchor (Mitek Mini Anchor; DePuy
Mitek, Raynham, Massachusetts) placed in the fovea of the ulna. Pronation and
supination under an image intensifier showed that, perhaps due to injury to
the dorsal radioulnar ligament, the ulna subluxated dorsally (in the opposite
direction from the dislocation) with respect to the radius when supination
exceeded 70°. The distal radioulnar joint was completely stable throughout
the arc of pronation. The repaired triangular fibrocartilage complex was
protected by the placement of two 0.062-in (0.157-cm) Kirschner wires across
both the radius and the ulna just proximal to the distal radioulnar joint. The
arm was placed in a double sugar-tong splint in 30° of pronation.
At the follow-up visit to the clinic two weeks after the operation, the
double sugar-tong splint was removed and replaced with a Muenster cast, which
was worn for an additional two weeks. Four weeks after surgery, the Kirschner
wires were removed, the wrist was placed in a thermoplastic removable splint,
and motion was initiated under the supervision of a hand therapist. Initially,
full pronation was allowed but supination was limited to 45°. At six
weeks, full pronation and supination were allowed and strengthening exercises
were initiated. At six months postoperatively, there was full, symmetric range
of motion of both forearms, with 80° of active supination and 70° of
active pronation. The patient could actively extend the right wrist to 75°
compared with 85° on the left, and he could actively flex the right wrist
to 80° compared with 90° on the left. Fluoroscopy showed no scissoring
of the radius and ulna on the lateral view and no diastasis on the
posteroanterior view. Plain radiographs showed normal congruity of the distal
radioulnar joint with no residual subluxation (Figs.
3-A and 3-B). The patient had
returned to his job catching 50-lb bags of cement, and he had no subjective
instability in the wrist.
Acute, isolated dislocations of the distal radioulnar joint were first
reported by Desault in
17772. However, in
1992, Bruckner et al. coined the term "complex DRUJ dislocation"
to describe dislocations of the distal radioulnar joint that met the following
criteria: "obvious irreducibility, recurrent subluxation, or `mushy'
reduction caused by soft-tissue or bone
interposition."3
Their case series described eleven patients with dislocations of the distal
radioulnar joint. Of these, four were "complex" dislocations of
the distal radioulnar joint by the above criteria. They concluded that complex
dislocation of the distal radioulnar joint occurs more frequently than
previously reported and that it is an important indication for operative
exploration and open
reduction3.
Cases of persistent or even unrecognized subluxation of the distal
radioulnar joint after reduction of a dislocation have been reported in the
literature over the course of many years, and multiple mechanisms have been
proposed to describe the recurrent incongruity of the distal radioulnar joint
and the block to
reduction4-6.
The first hypothesized mechanism, thought to be the most common, is extensor
carpi ulnaris interposition from a dislocated extensor carpi ulnaris tendon
draped around the radial border of the ulna and protruding into the distal
radioulnar joint7.
The extensor carpi ulnaris can also be wrapped around the ulnar border in
dorsal dislocation of the distal part of the
ulna8. Displacement
of the ulnar styloid has generally been thought to contribute to extensor
carpi ulnaris tendon dislocation and thus, in turn, to the blocking of
reduction of the distal radioulnar
joint3. Other blocks
to reduction include entrapment of the extensor digitorum communis to the ring
and little finger, the extensor digiti minimi, the flexor pollicis longus,
fragments of a torn triangular fibrocartilage complex, or even the median
nerve1,9-11.
In the case of our patient, we describe a novel mechanism of complex
dislocation of the distal radioulnar joint. The block to reduction was due to
an impacted fracture of the distal part of the ulna from the rim of the
sigmoid notch. While this case involved a volar dislocation, the same
mechanism could theoretically occur with a dorsal dislocation as well. The
anatomical axis of forearm rotation is through the fovea of the ulna. Thus, it
is the radius that rotates about the ulna, and therefore the description of a
dislocation of the distal radioulnar joint technically should note the
position of the radius relative to the ulna. However, it is customary in the
literature to note the position of the ulna relative to the
radius. We have followed this convention in this report, and thus
volar dislocation of the distal radioulnar joint refers to the situation in
which the ulna is volar to the radius.
This injury is directly analogous to a much more common orthopaedic entity,
the anterior dislocation of the glenohumeral joint. Both joints are shallow,
with the majority of the stability provided by surrounding soft-tissue
structures. The impacted ulnar fracture is reminiscent of a Hill-Sachs lesion
of the humeral head, while the sigmoid rim fracture corresponds in some ways
to an osseous Bankart injury.
Our review of the literature revealed that the case of our patient was
unlike the previous reports of patients with complex dislocation of the distal
radioulnar joint, which have generally described an associated fracture of the
forearm complex that was visible on plain radiographs. The fractures in those
reports imparted instability or irreducibility through either extensor carpi
ulnaris tendon dislocation (ulnar styloid fracture), malalignment of the
distal radioulnar joint (Galeazzi fracture), acute radioulnar length
discrepancy (fracture of the distal end of the radius with shortening, forearm
fracture including both the radius and the ulna, or an Essex-Lopresti injury),
or intra-articular disruption of the distal radioulnar joint (a displaced
intra-articular fracture of the distal radioulnar
joint)3,9.
Our patient did have a small osteochondral fracture of the rim of the sigmoid
notch; however, it was not visible on plain radiographs, even in retrospect,
and a computed tomography scan was beneficial in delineating it. While this
portion of the injury could have been a result of the initial attempt at
reduction, this seems unlikely because closed reduction was quickly abandoned
when there was a clear block to reduction when an appropriate amount of force
was applied. The absence of a destabilizing fracture involving the forearm
complex may have contributed to the impaction because some of the stabilizing
forces, such as the pronator quadratus, were still in place to provide
compressive forces across the joint, even in its dislocated state.
In conclusion, the case presented here represents a novel mechanism for
irreducibility of a so-called complex dislocation of the distal radioulnar
joint. The ulna can become impacted on the rim of the sigmoid notch. We
recommend acquiring a computed tomography scan of all complex dislocations of
the distal radioulnar joint to search for this impaction injury. ?