Anatomical and Clinical Concepts in Distal Radius Volar Ulnar Corner fractures

Abstract

Background Volar ulnar corner fractures are a subset of distal radius fractures that can have disastrous complications if not appreciated, recognized, and appropriately managed. The volar ulnar corner of the distal radius is the "critical corner" between the radial calcar, distal ulna, and carpus and is responsible for maintaining stability while transferring force from the carpus. Description Force transmitted from the carpus to the radial diaphysis is via the radial calcar. A breach in this area of thickened cortex may result in the collapse of the critical corner. The watershed ridge (line) is clinically important in these injuries and must be appreciated during planning and fixation. Fractures distal to the watershed ridge create an added level of complexity and associated injuries must be managed. An osteoligamentous unit comprises bone-ligament-bone construct. Volar ulnar corner fractures represent a spectrum of osteoligamentous injuries each with their own associated injuries and management techniques. The force from the initial volar ulnar corner fracture can propagate along the volar rim resulting in an occult volar ligament injury, which is a larger zone of injury than appreciated on radiographs and computerized tomography scan. These lesions are often underestimated at the time of fixation, and for this reason, we refer to them as sleeper lesions. Unfortunately, they may become unmasked once the wrist is mobilized or loaded. Conclusions Management requires careful planning due to a relatively high rate of complications after fixation. A systematic approach to plate positioning, utilizing several fixation techniques beyond the standard volar rim plate, and utilizing fluoroscopy and/or arthroscopy is the key strategy to assist with management. In this article, we take a different view of the volar ulnar corner anatomy, applied anatomy of the region, associated injuries, and management options.

Keywords: carpal instability; distal radius fracture; lunate facet; osteoligamentous unit; volar rim; volar ulnar corner; watershed line; watershed ridge.

Fig. 1

Anatomy of the distal radius. ( A ) Cadaveric wrist with an oblique osteotomy through the radiocarpal joint. The osteotomy was performed obliquely from the volar ulnar corner across the scaphoid and lunate fossa. The volar cortex is a thick concave calcar that transmits the load to the diaphysis. C, capitate; L, lunate; S, scaphoid. The arrows show the transmission of load. ( B ) An oblique micro-CT image of a cadaveric distal radius demonstrating the thickened trabecular columns that transmit load to the thick volar cortex ( blue dotted arrow ). CT, computerized tomography. Image copyright: Gregory I. Bain.

Fig. 2

The radial and ulnar calcar. Cadaveric dissection illustrating the calcar (C) of the distal radius. The radial calcar is comprised of both the curved volar cortex and the internal thickened trabeculae. The yellow arrow illustrates the interosseous membrane between the radius and ulna. The dotted line along the distal radius and ulna is “Shenton's line.” This arch is parabolic in shape ( dotted lines ), similar to that of a Gothic arch, which mechanically minimizes tensile stresses. Image copyright: Amit Gupta.

Fig. 3

A “sleeper lesion” is a significant injury to a stabilizing structure that can be unmasked following loading or mobilization. By their nature, they are often missed due to the occult radiological changes. The ligamentous injuries can lead to carpal instability including ulnar translocation. The illustration shows the injury zone of the volar ulnar corner fracture, long radiolunate ligament ( black arrow ) and the distal radioulnar joint ( gray arrow ) with minimal bony involvement ( dotted lines ). DRUL, dorsal radioulnar ligament; LRLL, long radiolunate ligament; RSCL, radioscaphocapitate ligament; SRLL, short radiolunate ligament; VRUL, volar radioulnar ligament. Image copyright: Gregory I. Bain.

Fig. 4

The watershed ridge. ( A ) Cadaveric sagittal section highlighting the watershed ridge. Akin to the geographical definition of “watershed” describing a topographic ridge that divides two rainfall catchment areas, rain proximal to the ridge drains into the pronator fossa and the rain distal to the ridge drains toward the wrist joint. The watershed ridge is the most volar aspect of the distal radius ( black arrow ). The blue dotted arrows represent the water and water catchment separated by the ridge. White star = volar ligaments. L, lunate; PQ, pronator quadratus. (Image copyright: Gregory I. Bain). ( B ) Cadaveric anatomical specimen. The watershed ridge is the most volar aspect of the distal radius. The watershed ridge is identified by the dotted line. The thick volar capsule and volar carpal ligaments can make it difficult to palpate the osseous ridge during surgery. LRLL, long radiolunate ligament; RSCL, radioscaphocapitate ligament; SRLL, short radiolunate ligament; PQ, pronator quadratus fossa (Image courtesy: Amit Gupta).

Fig. 5

Coronal T2 MRI of a 17-year-old female 3 weeks following a distal radius fracture. The causes of the posttraumatic high-signal changes surrounding the fracture include osseous edema, hyperemia, and regional osteopenia. The result is soft metaphyseal bone, which is prone to secondary collapse in the first few weeks. MRI, magnetic resonance imaging. Image copyright: Gregory I. Bain.

Fig. 6

Fracture characteristics. With forced wrist extension the ligaments become taut, creating a compressive force. ( A ) Axial forces ( red arrows ) can result in the lunate impacting against the volar ulnar corner (Image copyright: Crespi for Gregory I. Bain). ( B ) Following the fracture, the SRLL remains intact, leading to the displacement of the osteoligamentous unit and volar subluxation of the carpus. SRLL, short radiolunate ligament (Image copyright: Bain Chiri).

Fig. 7

Pronation of the volar ulnar corner fragment. ( A ) Axial CT image of the wrist at the level of the DRUJ. The volar ulnar corner fragment pronates around the intact volar radioulnar ligament attached to the fovea. The fracture fragment is then superimposed and reduced to calculate the angle of rotation. The yellow lines represent the degree of rotation (14°). ( B ) A three-dimensional CT reconstruction showing rotation of the fragment. The arrow shows the pronation of the fragment. Note the volarly subluxated scaphoid (S) and lunate (L). ( C ) Axial CT image with the radius and carpus superimposed and two sagittal CT slices through the lunate fossa and scaphoid fossa. The lunate and scaphoid both subluxate volarly with the fragment. The scaphoid is not contained; therefore, the radioscaphocapitate ligament must be disrupted. L, lunate; S, scaphoid, F, fragment. CT, computerized tomography; DRUJ, distal radioulnar joint. Image copyright: Gregory I. Bain.

Fig. 8

Osteoligamentous concept. ( A ) Volar Ulnar Corner osteoligamentous unit involving the short radiolunate ligament (SRLL). The unit includes the volar ulnar corner fragment (bone), short radiolunate ligament (ligament) and the lunate (bone). These units must not be disrupted during surgery as this may result in delayed carpal instability. ( B ) Radial styloid osteoligamentous unit involving the radioscaphocapitate ligament (RSCL). The bone–ligament–bone unit is highlighted and involves the radial styloid (bone), radioscaphocapitate ligament (ligament) and the capitate (bone). Image copyright: Crespi for Gregory I. Bain.

Fig. 9

Scaphoid and lunate orientation for volar ulnar corner (VUC) fractures. Both the scaphoid and lunate translate in a volar ulnar direction, 1.0 and 1.6 mm, respectively. There is pronation of 4.4° and 5.3°, respectively. The SL interval was increased compared with the control wrists. Image modified from Sun et al.

Fig. 10

Ulnar translocation of the carpus. Preoperative three-dimensional CT reconstruction and radiographs of a 42-year-old male patient following fixation (Synthes Volar Rim Plate) of a very distal volar ulnar corner fracture via an extended FCR approach. The white dotted lines mark the ulnar border of the radius to assess ulnar translocation of the lunate. The majority of ulnar translocation of the carpus occurred between day 14 and 30. We believe this maybe caused by either an iatrogenic volar capsular release used to expose the joint surface, prior to application of the plate or due to subtle osseous collapse following fixation. The associated ligamentous injuries predispose to the further collapse which need to be identified and stabilized. CT, computerized tomography; FCR, flexor carpi radialis. Image copyright: Gregory I. Bain.

Fig. 11

Posttraumatic osseous resorption. 63-year-old female with a volar Barton's fracture. Sagittal CT scan images demonstrate: ( A ) At day 0 of the injury, there is a volar distal radius fracture with no obvious dorsal fracture. Volar tilt is 19°. ( B ) At day 14, there is considerable resorption of the underlying metaphyseal bone. Now the distal radius articular surface is only stabilized by the cantilever of the thin dorsal cortex. The loading point of the lunate facet has slipped volarly, down the articular slope (22°), to be volar to the radial shaft ( dotted white line ). There is now sclerosis of the dorsal metaphyseal bone, which could be from impaction or new bone formation. Any greater force or volar translation, and the dorsal radial cortex would fracture, leading to a volar fracture dislocation. ( C ) At day 35, there is minimal further collapse and the radial volar tilt has stabilized at 22°. Image copyright: Gregory I. Bain.

Fig. 12

Volar ulnar approach. ( A ) The skin incision proximally is radial to FCU tendon then passes the wrist crease obliquely. It then passes across the transverse carpal ligament along the line of the ring finger and enters the palm just ulnar to the thenar crease. It is a safe, extensile approach and allows excellent exposure of the volar ulnar corner (Image copyright: Crespi for Gregory I. Bain). ( B ) The interval is between the ulnar neurovascular bundle and the flexor mass. Pronator quadratus is then reflected from the radius subperiosteally (Image copyright: Crespi for Gregory I. Bain). ( C ) With the transverse carpal ligament divided, flexion of the wrist and retraction of the flexor tendons with Hohmann retractors along the radial border allow for excellent exposure of the volar aspect of the carpus, wrist capsule, pronator quadratus and the distal radius (Image copyright: Gregory I. Bain). FCU, flexor carpi ulnaris, FM, flexor tendon mass, PQ, pronator quadratus, UN, ulnar neurovascular bundle; VC, volar capsule.

Fig. 13

Our recommended method for plate positioning for distal radius fracture. ( A ) Buttress plate. Perform an anatomic reduction of the distal radius and provide provisional fixation with K-wires. Insert a hypodermic needle into the Radiocarpal (RC) joint (1) and the DRUJ (2). Identify the point 8 mm proximal to the RC needle and 6 mm radial to the DRUJ needle. Insert a K-wire parallel to the radiocarpal joint surface (3). ( B ) Advance the ulnar corner hole of the plate over the K-wire (4). Center the proximal aspect of the plate on the diaphysis and insert the second K-wire into the most proximal aspect of the plate (5). Bend the K-wires away from each other which will provisionally stabilize the plate to the radius (6). ( C ) Containment plate. A similar method can be performed for the volar rim plate. Note, however, the K-wire requires to be placed further distal. DRUJ, distal radioulnar joint; K-wire, Kirschner wire. Image copyright: Bain Chiri.

Fig. 14

( A ) Fluoroscopic Anterior Posterior (AP) image of a revision volar ulnar corner fracture in a 42-year-old male who initially had surgical fixation acutely and consequently collapsed and developed ulnar translocation. Revision surgery performed at 3 months included a volar ulnar approach, release of the volar ligaments, and distal radius osteotomy to reduce the inclination and to reduce the risk of recurrent ulnar translocation. The osteotomy was stabilized and the capsule and Triangular Fibrocartilage Complex (TFC) repaired. There was still a tendency for ulnar translocation, so this was reduced, and radiocarpal transarticular K-wires were inserted. Due to the complex situation, a neutralization dorsal bridging plate was applied. ( B ) Lateral radiograph of the same patient at 3 months postfixation. The correction of the ulnar translocation has been maintained with the aid of the K-wires, and the dorsal bridge plate has minimized collapse of the revision distal radius fixation. K-wires, Kirschner wire. Image copyright: Gregory I. Bain.

Fig. 15

Fragment escape after surgical fixation of the volar rim. This is often due to the fragment not being adequately contained and/or captured by the fixation. A lateral X-ray of a distal radius fracture internally fixed with a volar distal radius plate. There is fragment escape of the volar ulnar corner fragment ( yellow arrow ) and associated volar translation of the lunate (L) and carpus ( white arrow ). Image copyright: Gregory I. Bain.