Arthroscopic treatment of distal radius fractures

Anatomy

The articular surface of the radius is triangular, with the apex of the triangle at the radial styloid. It slopes in a volar and ulnar direction with a radial inclination of 23 degrees (range, 13–30 deg), a radial length of 12 mm (range, 8–18 mm), and an average volar tilt of 12 degrees (range, 1– 21 deg). The dorsal surface of the distal radius is convex and irregular, and it is covered by the 6 dorsal extensor compartments. The dorsal cortex is thin, which often results in comminution that can lead to an abnormal dorsal tilt. Lister tubercle acts as a fulcrum for the extensor pollicis longus (EPL) tendon, which lies in a groove on the ulnar side of the tubercle. The volar side of the distal radius, which is covered by the pronator quadratus, is flat and makes a smooth curve that is concave from the proximal to distal direction. A cartilaginous anteroposterior ridge divides the distal articular surface of the radius into a scaphoid facet and a lunate facet. The scaphoid fossa is triangular, whereas the lunate fossa is more quadrangular in shape. The triangular fibrocartilage complex (TFCC) originates on the ulnar rim of the lunate fossa and extends ulnarly to insert into the base of the ulnar styloid. The articulation of the ulnar head to the radius is not congruent, with the radius of curvature of the shallow sigmoid notch being slightly greater than that of the convexity of the ulna head. Only the brachioradialis tendon inserts onto the distal radius. The other wrist flexor and extensor tendons pass across the distal radius to insert on the carpal bones or the base of the metacarpals.

The dorsum of the radius is cloaked by the arborizations of the superficial radial nerve (SRN) and the dorsal cutaneous branch of the ulnar nerve (DCBUN). The SRN exits from under the brachioradialis approximately 5 cm proximal to the radial styloid and bifurcates into a major volar and a major dorsal branch at a mean distance of 4.2 cm proximal to the radial styloid. Either partial or complete overlap of the lateral antebrachial cutaneous nerve (LABCN) with the SRN occurs up to 75% of the time. The DCBUN arises from the ulnar nerve 6 cm proximal to the ulnar head and becomes subcutaneous 5 cm proximal to the pisiform. It crosses the ulnar snuffbox and gives off 3 to 9 branches that supply the dorsoulnar aspect of the carpus, small finger, and ulnar side of the ring finger.

Mechanism of injury

Falling onto an outstretched hand is the most commonly cited mechanism of injury in DRFs. The mechanism typically involves a combination of axial loading, a bending moment, and either supination or pronation. The degree, direction, and extent of the applied load may cause further coronal or sagittal splits within the lunate or scaphoid facets. Increasing wrist extension at the time of impact could result in more dorsal comminution. Arthroscopic studies have revealed a high incidence of associated soft tissue injuries, which can impact the prognosis. A recent CT study of 100 DRFs revealed that the fracture lines were significantly more likely to occur at the intervals between the ligament attachments than at the ligament attachments. Common sites of fractures were the center of the sigmoid notch, between the short radiolunate ligament (SRL) and long radiolunate ligament (LRL), and the central and dorsal ulnar aspects of the scaphoid fossa. The authors postulated that the ligament attachment sites might either be strengthened by the ligamentous insertions or that the ligaments might insert in regions of higher bone quality. These findings might explain why ligamentotaxis can be successful in reducing those articular rim fragments with a preserved ligament attachment. Central articular die punch fragments are not reduced because of the lack of ligamentous attachments.

Diagnosis

The patient typically presents with a history of a fall onto an outstretched wrist. High-energy trauma results in a greater degree of swelling. There may be swelling over the radiocarpal joint from fracture hematoma and a garden fork deformity if there is significant dorsal angulation. Finger edema and stiffness are often present and must be treated aggressively. Acute carpal tunnel syndrome may also be present. The definitive diagnosis, however, is made radiographically.

The initial radiographs should include a standard posteroanterior (PA) view, a lateral view, and an oblique view. Traction views can help distinguish an intraarticular from an extraarticular fracture. The PA view should be taken with the elbow and shoulder at 90 degrees and the forearm in neutral rotation, which standardizes the assessment of the ulnar variance. A true lateral radiograph is taken with the forearm in neutral rotation and with the volar aspects of the pisiform and distal pole of the scaphoid overlapped. A 10- to 20-degree laterally inclined view where the beam is directed from the distal-radial to proximal-ulnar direction provides a true lateral view of the ulnar two-thirds of the articular surface, which is normally at an inclination of about 10 degrees. This is especially important following volar plating, to assess whether the ulnar-most subchondral screws penetrate the joint surface. A 45-degree pronated oblique view can be used to assess the distal radioulnar joint (DRUJ) congruency because it profiles the dorsal ulnar cortex that supports the dorsal lunate articular facet and forms the dorsal margin of the sigmoid notch.

Medoff outlined some useful radiographic relationships. He described the teardrop, which is a dense, U -shaped outline seen at the distal end of the radius on the lateral view. It is formed from the confluent outlines of the distal shaft and distal radial ridge and terminates in the volar rim of the lunate facet. The thickness of the cortical bone that forms the base of the teardrop is noted to be significantly greater than the thickness of the dorsal cortical bone and reflects the greater loading forces that normally occur along the volar surface of the radius. The teardrop angle is determined by measuring the angle between a line extended along the longitudinal axis of the radial shaft and a line that is drawn down the center of the teardrop. The normal angle is 70 degrees. Depression of the teardrop angle below 45 degrees is indicative of a sagittal split of the articular surface. The volar ulnar fragment arises because of impaction of the lunate into the lunate facet, which is then driven by the carpus into dorsiflexion. Medoff also observed that with a wrist in neutral on the 10-degree lateral radiograph, a line extended from the volar cortex of the radial shaft should be nearly collinear with the center axis of rotation of the proximal pole of the capitate. Fractures with volar or dorsal displacement result in translation of the carpus with the capitate migrating in a volar or dorsal direction to this line. The AP distance is the point-to-point distance between the corner of the dorsal rim and the corner of the volar rim on the lateral view. In a series of 20 patients with DRFs treated in Hawaii, an increase in the AP distance of more than 21 mm in men and 19 mm in women were correlated with a sagittal split with a separate dorsal-ulnar and volar-ulnar fragment.

The variations in the height of the Lister tubercle and in the depth of the EPL groove are considerable. The triangular shape of the dorsal cortex can obscure the determination of screw protrusion through the dorsal cortex, which can potentially lead to EPL rupture. A CT study of 30 cadaver forearms revealed that the size of Lister tubercle varied from 1.4 to 6.6 mm (average 3.3 mm) in height radial to the tubercle, and the depth of the EPL groove varied from 0.6 to 3.2 mm (average 1.6 mm). Joseph and Harvey described a dorsal tangential view (horizon view) in which the wrist is hyperflexed and the beam is directed along the long axis of the radius to detect dorsal screw protrusion.

CT with sagittal and coronal reconstructions is valuable for operative decision making in intraarticular fracture patterns. CT is particularly helpful in die-punch fractures (fractures with a central depression of the articular surface), volar lip fractures, and fractures involving the scaphoid facet. The axial view is useful to assess the congruency of the sigmoid notch.

Classification

A number of different classification systems for DRFs have been described but are no longer in widespread use. The Frykman classification system focused on the intraarticular extension of the fracture and involvement of the DRUJ and the ulnar styloid. The Mayo classification emphasized the extent of articular involvement whereas the Melone classification highlighted the die-punch lunate facet fracture. Trumble et al. recommended identifying the following clinical/radiographic features: 1) Displacement: dorsal versus volar; 2) Comminution: <50% or only involving one cortex versus >50% or involving two or more cortices; 3) Articular involvement: intraarticular versus extraarticular; 4) Ulna involvement: styloid, head, neck, DRUJ dislocation or radial head injury; and 5) Associated soft-tissue injuries: intercarpal ligament injuries, including scapholunate (SL) and lunotriquetral (LT) ligament tears, or injuries  to the TFCC ( Video 11-1 ).

The AO classification, with its 27 categories, is primarily useful for broad anatomic categorization of large numbers of fractures for trauma registries and research purposes. A-type fractures are extraarticular fractures that spare the articular surface. B-type partial intraarticular fractures spare a portion of the articular surface that remains in continuity with the metaphysis and can result in volar lip, dorsal lip, radial styloid, and medial corner fractures, whereas impaction injuries can cause die-punch fractures. C-type fractures are comprised of complex articular fractures where none of the articular surface remains in continuity with the metaphysis. The fractures can be divided into those with a dorsal or volar pattern or a direct impaction fracture with or without comminution. The fracture pattern can be a T or Y split of the articular surface or both. Metaphyseal comminution may involve greater than 50% of the diameter of the metaphysis on any radiographic view and involve two or more of the cortices. Rikli and Regazzoni introduced the three-column concept in which the distal radius is divided into medial, intermediate, and lateral columns. This theory emphasizes that the lateral, or radial, column is an osseous buttress for the carpus and is an attachment point for the intracapsular ligaments; the primary function of the intermediate column is load transmission; and the medial, or ulnar, column serves as an axis for forearm and wrist rotation as well as a post for secondary load transmission. This classification is the basis for the fragment-specific fixation technique. Medoff expanded on this concept and described five basic fracture components: the radial column, ulnar corner, dorsal wall, free intraarticular, and volar rim.

Treatment of distal radius fractures

External fixation

Ligamentotaxis

External fixation of DRFs may be used in a bridging or nonbridging manner. Bridging external fixation of DRFs typically relies on ligamentotaxis to both obtain and maintain a reduction of the fracture fragments. As longitudinal traction is applied to the carpus, the tension is transmitted mostly through the radioscaphocapitate (RSC) and LRL to restore the radial length. In a similar vein, pronation of the carpus can indirectly correct the supination deformity of the distal fragment. Ligamentotaxis has a number of shortcomings when applied to the treatment of displaced intraarticular fractures. Because ligaments exhibit viscoelastic behavior there is a gradual loss of the initial distraction force applied to the fracture site through stress relaxation. The immediate improvement in radial height, inclination, and volar tilt are significantly decreased by the time of fixator removal ( Fig. 11.1 A–B). In a series of 70 cases, Dicpinigaitis et al. observed a loss of reduction of volar tilt for up to 6 months after external fixation in 34 of the 70 patients, despite the use of adjuvant pinning. The initial deformity, patient age, use of bone graft, and duration of external fixation were not predictors of loss of reduction.

Traction does not correct the dorsal tilt of the distal fracture fragment. This is because the stout volar radiocarpal ligaments are shorter and they pull out to length before the thinner dorsal radiocarpal ligaments exert any traction. Excessive traction may actually increase the dorsal tilt. A dorsally directed vector is still necessary to restore the normal volar angulation. This is usually accomplished by applying manual thumb pressure over the dorsum of the distal fragment. With intraarticular fractures, ligamentotaxis reduces the radial styloid fragment but for the previously stated reasons it does not reduce a depressed lunate fragment. When there is a sagittal split of the medial fragment, traction causes the volar medial fragment to rotate, which often necessitates an open reduction ( Fig. 11.2 A–B). External fixation cannot control radial translation and cannot be used with an unstable DRUJ.

Biomechanical considerations for external fixation

Increasing the rigidity of the fixator does not appreciably increase the rigidity of fixation of the individual fracture fragments. A number of ways exist, however, in which to augment the stability of the construct. After restoration of radial length and alignment by the external fixator, percutaneous pin fixation can lock in the radial styloid buttress and support the lunate fossa fragment. A fifth radial styloid pin attached to the frame of a spanning AO (Synthes, Paoli, PA, USA) external fixator prevents a loss of radial length through settling. The addition of a dorsal pin attached to a sidebar easily corrects the dorsal tilt found in many DRFs. K-wire fixation enhances the stability of external fixation. Supplemental K-wire fixation is more critical to the fracture fixation than the mechanical rigidity of the external fixator itself. Stabilizing a fracture fragment with a nontransfixing K-wire that is attached to an outrigger is just as effective as a K-wire that transfixes the fracture fragments.